1. Product Introduction and Planned Function 1 1.1. Mission Statement 11.2. Product Description 11.3. Stakeholders 21.4. Scope Limitations 21.5. Market Potential 31.6. Market Competitors 31.7. Project Deliverables 4

2. Concept Development 5 2.1. Weather Resistance & Covers 52.2. Ramps 62.3. Boxes 72.4. Fuel Containment 82.5. Trailer Type 92.6. Lift Mechanism 11

2.6.1. Elevated Deck Trailer 112.6.2. Four Bar Linkage Lift Platform 122.6.3. Parallel Lift Platform 122.6.4. Crane 132.6.5. Scissor Lift Platform 132.6.6. Cumulative Concept 14

2.7. Launch Platform & Landing Platform 142.7.1. Flat Deck 152.7.2. Winged Flat Deck 152.7.3. Bilco Door Deck 15

2.8. Tie Down Systems & Attachment Points 162.9. Rotor Blade Vibration & Protection Packaging 162.10. Payload Vibration Isolation 172.11. Helicopter Suspension 182.12. Electrical Sub-System Development 18

3. Feasibility Assessment 24 3.1. Weather Resistance & Covers 263.2. Ramps 263.3. Boxes 273.4. Fuel Containers 283.5. Trailer Type 283.6. Lift Mechanism 283.7. Launch Platform 293.8. Crane 29

I

3.9. Tie Down Systems 303.10. Tie Down Attachment Points 303.11. Power Converter Module 303.12. Battery Charging Module 31

4. Design Objectives and Criteria 32 4.1. Weather Resistance & Covers 324.2. Ramps 324.3. Boxes 334.4. Fuel Containment 344.5. Trailer Type 354.6. Lift Mechanism 364.7. Launch Platform 364.8. Crane 374.9. Tie Down System 384.10. Tie Down Anchor Points 384.11. Rotor Blade Vibration & Protection Packaging 384.12. Payload Vibration Isolation 394.13. Power Supply Adapter 394.14. Power Converter Module 404.15. Battery Charging Module 404.16. Wire Gauge Selection 41

5. Analysis of Problems & Synthesis into the Design 42 5.1. Vibrations Analysis 445.2. Structural Analysis 46

5.2.1. Fuel Containment Structure 465.2.2. Fuel Tank Support Beams 47

6. Preliminary Design 49 6.1. Preliminary Drawing Packages 506.2. Bill of Materials, Supplier Identification, & Pricing 516.3. Electrical Systems Layout 52

6.3.1. Electrical Subsystems Design 52

7. Matlab Vibration Simulation 53

8. Future Plans 55 8.1. Schedule 56

II

9. Appendix 9.1. Feasibility Pugh Charts (Simple and Weighted)

9.1.1. General Project Concerns A19.1.2. Waterproofing A2-A39.1.3. Ramps A4-A59.1.4. Boxes A6-A79.1.5. Fuel Containers A8-A99.1.6. Trailer Type A10-A119.1.7. Lift Mechanism A12-A139.1.8. Launch Platform A14-A159.1.9. Crane A16-A179.1.10. Holding Mechanism A18-A199.1.11. Attachment Points A20-A219.1.12. Electrical Converter A22-A239.1.13. Electrical Charger A24

9.2. Concept Sketches B1-B109.3. Vibrations Output Graphs

9.3.1. Payload Acceleration With Full Fuel Load C19.3.2. Payload Displacement With Full Fuel Load C29.3.3. Payload Acceleration Without Full Fuel Load C39.3.4. Payload Displacement Without Full Fuel Load C4

9.4. Electrical Resistance Tables D19.5. Senior Design II Schedule E1-E29.6. Vendors F1

III

1. Product Introduction and Planned Function

1.1. Mission Statement

The future of warfare will be much different than it is now. Unmanned air and ground

support vehicles are currently in development to assist and possibly lead assaults on enemy

forces. Airborne sensor platforms currently being developed are the future eyes in the sky for

military commanders and will aid in reconnaissance and targeting. Continuous surveillance of

enemy forces will be possible without risking the safety of soldiers and pilots once developing

technology takes flight over the battlefield.

1.2. Product Description

As defined by DARPA (Defense Advanced Research Projects Agency) “the DP-5X

program will provide a flight-ready, tactically transportable, vertical take-off and landing

unmanned air vehicle (VTOL UAV) to integrate with a gimbaled payload for technology

demonstration of the JIGSAW sensor package. The UAV will be employable by a two person

team and deployable in a single high mobility multipurpose wheeled vehicle (HMMWV), also

known as a Humvee. It will provide lift for a 75 lb payload with 6 hours endurance, 100 knots

cruising speed, with nap of the earth agility. Multi-mission capability and modularity will allow

the DP-5X to rapidly integrate additional payloads for sensing, communications, and target

effects”. [1]

The project team will develop a system that will transport this UAV behind the

HMMWV in combat situations and provide all necessary ground support.

1

1.3. Stakeholders

Dragonfly Pictures are the creators of unmanned autonomous vehicles (UAVs) which it

has been developing since the early 1990’s. Currently in development is the DP-5X which is

based around an Advanced Multi-Mission Platform (AMMP) and is funded under DARPA

which is the central research and development organization for the Department of Defense. The

5X has performed several tests flights and is nearing autonomous flight capability, completing

the original design intent of the craft. Dragonfly Pictures Incorporated is only one of the

companies funded under DARPA that are competing to have the most advanced UAV, therefore

careful consideration of time, funding, development, and efficiency are key.

1.4. Scope Limitations

Initially the scope was set to design a carrier kit for the back of an HMMWV and off road

trailer that will load, unload and provide secure transport over rough terrain at 65 mph for the

DP-5X.  Design lift handles and tie downs. Adhere to military specifications on lifting and

carrying, with two soldiers maximum.  Provide electrical interface from HMMWV for charging

and ground support equipment. 

As the project progressed, the scope continued to grow as additional sponsor

requirements were suggested. Dragonfly Pictures is currently seeking to develop a deployment

system for the DP-5X so that it may fill the immediate need of UAVs that do not require a

runway. The proposed system for deployment is a single DP-5X in a trailer which will allow

sustained flight for long periods of time, and contain all necessary equipment for a seventy two

2

our mission hour mission . The trailer must serve several purposes. Primarily it will allow safe

transport and protection from environmental factors such as rain, sand, mud, and snow.

It was determined that the trailer will be in combat for three days. Therefore, the trailer

will also house enough fuel to provide continuous coverage over target for seventy two hours

while located in remote areas. There will be compartment storage for rotor blades, payloads, and

support equipment. The trailer will also utilize a crane to load/unload the UAV, mount,

dismount and maneuver payloads, and aid in field service when required.

1.5. Market Potential

The primary market for the VTOL UAVs is currently the United States Department of

Defense. The ability to launch and recover the UAV without the requirement of a runway is a

great advantage to current UAV currently deployed in the US forces. As the development of

VTOL UAVs is advanced, and proven there is a greater chance of creating a secondary market.

If these systems become cost effective, they could be seen patrolling areas where cameras are not

present in the commercial surveillance industry. The application could be utilized in the media

industry to acquire daily traffic reports, crop dusting, and coastguard search and recovery

missions.

1.6. Market Competitors

The military currently uses small unmanned aircraft for surveillance and reconnaissance.

Some designs require bulky, long, trailers that must be towed along with the convoy to launch

these aircraft for situations in which a runway is not available. This is one of the main

3

advantages of VTOL systems. In order to break into and replace the current applications the DP-

5X must prove to meet all of its expectations.

1.7. Project Deliverables

Project Qualifiers (12/7/2004):

Modified Trailer That DPI Purchases for Project Concept Sketches of Alternatives with Pros & Cons Preliminary Design of Fully Modified Trailer Complete Design Report Stress Analysis of Critical Components Stresses and Loads on Aircraft During Landing and Transport Finite Element Analysis of Critical Components Latch Design Suspension Design Video Animation of Landing, Dismounting, Offloading, Loading, and Landing Operational Plan for Using the Trailer in Accordance to CONOPS (Concept of

Operations) Preliminary Design of HMMWV Modification Modified HMMWV That RIT Gets From National Guard on Loan Production Cost Estimate and Manufacturing Plan Demonstration of Trailer and/or HMMWV at DPI with S/N 101 at 65 MPH Over the

Back 40

Project Winners

The project scope was narrowed to address the main concerns which are:

Concept sketches of alternatives with pros and cons Preliminary design of trailer modification Modified trailer that DPI purchases for RIT project Stress analysis of critical components Stress analysis of aircraft/landing interface Finite element analysis of critical components

4

2.0 Concept Development

Based on the requirements for the deployment system and the limited area of the trailer

deck size, much time and effort was necessarily spent brainstorming different configurations and

concepts. Keeping the overall goal of the system in mind, while adhering to weight and size

constraints proved to be a challenging experience for our team. Each week, new concepts were

developed, replacing or building upon earlier concepts.

2.1. Weather Resistance & Covers

The method of waterproofing used is heavily contingent on the overall design chosen for

the trailer. Early designs of the trailer called for structural cabinets to extend above the rotor

height of the helicopter. On top of this structural surface, a rigid tonneau cover could be mounted

much like that on the back of a pickup truck. The design currently being used does not have

structural cabinets extending above the height of the rotor because of excessive weight issues,

and thus a choice had to be made: Which method for waterproofing will prove most effective,

while limiting the intrusion into future designs, keeping important factors of time, weight, and

cost in mind? With this considered, there were two main choices.

The first method was that of the concept that originated when the structural cabinets

extended to the height of the helicopter rotor. A steel frame would be built in the place that the

5

cabinets would have sat, and on top of that, the tonneau cover would be mounted. While this

would have allowed for a more simplified method of covering the trailer, it had some major

drawbacks.

Additional weight

Additional construction time

Added cost

The second method was simply using a canvas-type of cover that would be thrown over

the top of the trailer to keep water and other elements off of the sensitive equipment underneath.

The main drawbacks of this method are that it lacked structure to keep it from lying on the

equipment underneath water drainage. A compromise between the two choices proved to be

most effective. A lightweight frame would be built using round tubing as supports. This frame

would support the canvas cover keeping it from lying on the equipment underneath and give it

the necessary structure to shed water. Since this design uses a limited number of parts, it saves

time, cost, and weight, not inhibiting a future platform design. This design facilitates a future

launch/recovery system to easily be added at a latter

2.2. Ramps

A method of loading and unloading the aircraft has been paramount since the beginning

of the design process. Much like waterproofing, this concept is heavily contingent upon the final

design chosen. Earlier designs had considered a possible tailgate or lifted platform that would

double as a ramp for loading and unloading. After the design became finalized, it became

apparent that there was only a single “best” choice for loading and unloading the helicopter. A

fundamental method such as ramps has proven the most effective way to load and unload

6

without having to depend on an external source of energy that may become unusable should

failure occur. The concept of using ramps has been chosen because of both its simplicity and its

versatility. Earlier methods such as that of a folding tailgate or lift platform/ramp have the

following limitations;

Need an external power source for functionality

Limit use to only the trailer (helicopter on hummer or other vehicle would have to be

unloaded by other means)

2.3. Boxes

            There were 3 separate concepts when considering the best box for storing the tools,

blades, and gear, and payload.  Custom boxes were used as the baseline. They were compared to

a pre-built unit that was already being manufactured and also boxes that the team would have to

design and produce from the ground-up.  The winner in this case was Custom Boxes that would

be designed and built by a vendor according to the team’s specifications.  The main reason that

this concept was pointed to was because customization was an important issue, because space

was limited and the boxes needed to be integrated into the fuel compartments, while being able

to support a launch platform in the future.  Lead-time is a large concern and custom boxes do

take slightly longer to get than pre-made boxes, custom boxes were preferred because it is

essential that the boxes conform to the dimensions the group has designed around.  No pre-made

boxes were found to do this, therefore, the group agrees with the chart’s decision.

2.4. Fuel Containment

The transportation system for the DP-5X autonomous aircraft is required to carry fuel for

several hours of operation, in addition to tools, spare parts, and a detachable payload. Due to the

7

large size of the aircraft and the multitude of accessory items, there is very little room in the

loading plan to carry the necessary volume of fuel. To address the issue, a design was created

that incorporated the fuel tanks into two bays on either side of the trailer, which also provide

support for tool and supply boxes. This solution, however, presented another problem of its

own. The spaces where the fuel tanks are destined to be placed are interrupted by the wheel

wells of the trailer. As a result, typical prefabricated containers would be unsuitable for this

application.

The solution for this new found design problem began with a survey of commercially

available products. Knowing a few desired characteristics of the fuel system, anything that

looked like it might be applicable was considered and compared. As the list of options grew, it

became apparent that some ideas were better than others, often due to features that had not been

initially considered as requirements.

As the transportation system is intended for the military, initial search efforts were

focused towards pre-existing military systems. However, as with many military destined

products, specifications and other general information on such items were scarce at best. The

one option that was gleaned from this particular search was the collapsible fuel bladder. The

world of automobile racing, however, provided several promising solutions, which are

specifically designed to be used in punishing and dynamically demanding environments.

Containers designed for racing applications are generally referred to as fuel cells, and come in

rigid and semi-rigid varieties. Additionally, there are baffles to prevent the motion of fuels while

the vehicle is maneuvering which in turn ill prevent foaming. The fuel system design turned out

to be far less mathematical in nature, than it was a matter of fitting simple qualitative objectives,

and the end product was chosen accordingly. The final fuel storage degign configuration

8

consists of four separate bladders mounted in enclosed sheeted frames at the four corners of the

trailer. This configuration keeps the load low and distributed, while provided the required

volume of fuel.

2.5. Trailer Type

Brainstorming for the trailer began with the sponsor’s recommendation of using the

Silver Eagle brand trailer. Silver Eagle is a large supplier that currently has government

contracts to build trailers for the military. The first mode of information was simply finding the

company on the internet. Extensive information was provided that included GVW, surface area,

and different trailer types.

With many different trailers to choose from the group had to figure out which trailer

would suit the goals of the project the best. Silver Eagle offered three light tactical trailers (LTT)

that were the of team’s main consideration – LTT-F, LTT-FE, and LTT-HC. See technical data

package. All trailers were similar in that they are based on the same suspension and therefore can

hold the same weight of cargo. The LTT-F and LTT-FE are both flat-deck trailers, but the LTT-

FE has a deck which is three feet longer than the LTT-F. The LTT-HC is the same length as the

shortest trailer, but is constructed with pre-built sides that contain cargo, and a tailgate. Price

quotations for each trailers were analyzed with a negligible difference in price (<10%). Lead

time, which is between ten-twelve weeks prompted quick decision making.

A load plan was considered that restrained the our team to how many trailers and

Hummers would be provided for a mission of three days. With this given information, a brief

layout was made of all of the items that needed to be stored on the trailer. The load plan

included one UAV with one or two payloads, 1200 pounds of fuel, FCS tool kit and blade

9

storage areas, gear, food, and water storage, a potential for keeping everything water proof,

ramps, electrical components, and a tie down system.

It would be best to choose one of the flat-deck trailers because the existing walls on the

LTT-HC would not efficiently incorporate into a highly modified trailer containing all the

necessary gear. Our plan is to make fuel-tank-combination-walls that will be a means of

containing cargo and providing structure around the UAV.

Coming to the decision of getting the LTT-F or the LTT-FE was next. The whole load

plan consisting of two HMMWVs and two trailers would need to be loaded into a C-130 Aircraft

for transport. After determining the dimensions of the C-130 cargo bay from a military technical

data packet, it was determined that it is impossible to fit the shortest trailers with two HMMWVs

inside of one C-130 Aircraft. The only possible solution is to allow the load plan to be carried by

two separate aircraft; the LTT-FE became favored. The UAV would fit on a LLT-F efficiently,

but with consideration of carrying possibly two payloads and all of the other cargo required, the

team was dimensionally constrained to choose the trailer with the largest surface area, the LTT-

FE.

A contact was developed at Silver Eagle who granted the team access to the complete 3D

CAD model of the trailer, after proper legal precautions were in order. This model would

eventually help to shape design decisions for component and locations. Also Silver Eagle

provided vibration effects data for trailer cargo over rough terrain (see technical data package).

At the first visit to the sponsor, it was determined that the cost of a new trailer was more

than was feasible to spend at the time of prototyping. Alternatives were suggested such as

looking for a used Silver Eagle LTT-FE on the internet, particularly E-Bay, and also looking for

other used military trailers that we could build our prototype off of. The final decision was to

10

base the design on an existing LTT-FE, but to build the prototype trailer using a similar used

military trailer.

2.6. Lift Mechanisms

The idea that began brainstorming for the lift mechanisms is simply safety. Dragonfly

pictures suggested the UAV be launched from an elevated position in order to have the spinning

rotor blades as far away from personnel as possible. The elevated position would raise the rotors

to height above the heads of all personal. Safety will always be the trump card with helicopter

type UAVs.

2.6.1. Elevated Deck Trailer

An early attempt to solve this problem was to have the UAV initially start high in the air,

then, it would not need to be lifted. This concept could be applied to either the trailer or a

HMMWV as seen in appendix B1. In the case of the HMMWV, all of the extra cargo and

gasoline needs to be stored underneath the UAV. The sides that shield the UAV from the

elements simply fold down and allow the crew to walk around on them as a platform. The great

part about this concept is that it completely eliminates any need for a complicated lifting

mechanism, saving the weight and cost associated with them. The cons that plague this idea are

immediately related to physics. The UAV would rest nearly six feet in the air. A frame would

need to be built or some type of canopy that shielded the system over the top. These two items

would considerably raise the center of gravity of the entire transport system. The system needs

to have a low center of gravity to overcome the terrain that it will be subjected to, not to mention

that the overall height of the system must allow passage under reasonable sizes tree branches.

11

2.6.2. Four Bar Linkage Lift Platform

Another idea for a lift mechanism was a “four-bar” lift. This type of lift is best illustrated

in appendix B2-B3. This lifting mechanism has an advantage because it is very robust. The four

bar lift accomplishes getting the UAV to a safe height , and also folds up to have a low center of

gravity. Another advantage to this design is that it doubles as a ramp to load and unload the

UAV top the ground. This complicates the design due to the sliding track mechanism that must

be developed which ensures the ramp will meet all the desired pitch angles.

2.6.3. Parallel Lift Platform

A third idea is to have a floating platform. This concept can be seen in appendix B4. The

floating platform allows the UAV to be launched from a safe height, but also allows it to be

lowered to the ground for loading/unloading, maintenance and assembly. This method saves

time because the UAV can easily be accessed. The whole unit could fold up and a low center of

gravity is achieved. An inherent design flaw in this concept is that it requires a very powerful

motor or hydraulic cylinder both of which require a great deal of electricity. There are very large

moments that are imposed on the beams supporting the platform in its cantilever position. A

chain drive, which it may require, would need a great deal of development time and posses a

safety issue as well. Much more time is needed than the amount of time that we have been

allotted to develop this design. Another problem is reliability, if a chain link breaks the system is

rendered useless, and could be very difficult to fix in the field, not to mention the total reliance

on electricity to deploy the UAV.

12

2.6.4. Crane

A crane located on the front of the trailer provides many required aspects of the design

requirement except launching and recovering from a safe height. A cargo crane with a

telescoping boom is able to accomplish the task of loading and unloading the UAV by two

soldiers, lift and maneuver the payload as well as lift heavy components of the UAV for CG

adjustment in the field. It is a simple, bolt on system. Underling issue is that the UAV can not

be launch from an elevated position unless it was set on the ground, assembled, and then raised

back up onto a platform. This launch method is time consuming. To meet launch height the

platform would need to be constructed, therefore, the team favored the other ideas which were

quicker and already incorporated platforms, however, none of the other concepts incorporate

lifting the payloads.

2.6.5 Scissor Lift Platform

A scissor lift based power lift platform is another concept that was considered, shown in

appendix B5. The scissor lift is simple and can be developed using readily available systems. It

accomplishes the task of lifting the UAV to the desired height, and it also collapses to keep the

center of gravity low during transport. The scissor lift requires electricity, but it is at an

advantage because all of the hydraulic components were available integrated into the lift.

Therefore, this system would facilitate simple adaptation to suit our platform lift needs.

2.6.6 Cumulative Concept

Multiple scissor lift manufacturers were researched on the internet as seen in the

technical data package. They were much heavier than anticipated and more expensive. This did

13

not stop research. A feasible, self-contained, scissor lift that fulfilled the capacity and width

stability required. The lift has a considerable weight (400 pounds), but it is still within the GVW

limits of the trailer-cargo combination. Other trailer subsystems were developed around the lift

that incorporated maximum lifting height and the placement of the platform on the structural

storage walls. The concept fulfilled all of the project requirements except that it does not

incorporate lifting the payload in place or adjusting the center of gravity of the UAV in the field.

After discussing our concepts in person on a visit to DPI, the requirement to have the UAV

launch and land on a raised platform was relaxed, stressing the importance of the ability to lift

the payloads. Military personal are not able to lift more than 52 lbs per male solider, and half

that for a female solider. The UAV will now launch from the ground, and the trailer will be

designed with the ability to add a launch platform at a latter date.

2.7. Launch & Landing Platform

When considering intergrading a platform that the UAV could launch from and land on,

the autonomous landing accuracy of two meters determined initial size guidelines. We

determined that developing a platform larger than that of the area of the trailer deck to be

mechanically unfeasible. Any platform design needs to be easily positoned, stored, raised and

supported to be feasible. It also needs to be manufactured of light weight material to keep the

overall weight of the system below the maximum GVW of the trailer.

2.7.1. Flat Deck

The first design concept mentioned is a simple flat launch deck that would be lifted by a

mechanical means (scissor, four-bar, or other levers). The deck could be made of a steel tube

14

frame and have expanded metal grating used to cover it’s floor. The area of the launch platform

is limited to the area of the trailer deck. This limits any landing buffer zone that might be

necessary for inaccuracies of coordinate landing systems. Since the platform is completely flat

and rigid, it sits directly on top of whatever lifts it. This creates wasted space below the

platform. Space in this design is limited and must be optimized if all load criteria are to be met.

2.7.2. Winged Flat Deck

An iteration of this design is a tri-fold platform concept (appendix B7). The tri-fold

platform is a flat deck that has three pieces hinged on either side. This type of deck has an

advantage over the flat deck in that it can be made larger than the area that it is stored in. As the

platform is raised the side pieces unfold and rest on the structural storage containers on either

side of the trailer. This design incorporates excellent storage ability for the amount of platform

area provided, however requires the use of a lifting mechanism under the unit that does not

facilitate payload transition.

2.7.3. Bilco Door Deck

A launch platform could also be combined with a weather resistant door that could also

act as a landing/launch platform. This is the idea behind the “Bilco-Doors”. The Bilco-Doors

provide a flat roof. The doors simply split at the center and open upward providing protection

from weather and if supported, a launch/landing area the size of the trailer deck. The UAV

needs to be lifted out of the trailer and then set on top of the closed Bilco-Doors for launching

and landing. This design relies on the concept of using a crane to raise the UAV to the platform

height. It also requires that the doors be modified from their original state and be reinforced to

15

support landing and launching loads. However, issues arise with the ability to raise the UAV

high enough to operate the doors.

2.8. Tie Down Systems and Attachment Points

Tie downs are necessary to restrain the UAV during transport. There must be a means of

securing the helicopter to the trailer to ensure that it does not get damaged during transport. A

location to secure the tie down straps is also required. These attachment points must be able to

withstand the load of 1000lbs each to ensure secure transport. Recessed anchor points attached

to the deck of the trailer will provide required attachment points. Common ratchet type straps

will securely connect the DP-5X tie down rings to the recessed anchor point on the trailer.

2.9. Rotor Blade Vibration & Protection Packaging

An additional requirement for the load plan is the containment and protection of an eight

rotor blades. Each blade is approximately six feet long, six inches wide, and two inches thick.

Unfortunately, commercially available rotor blade carrying devices are not common or readily

available, so it was necessary to design a custom storage system.

Because of their shape and size, a design that emulated a ski rack was amongst the first

ideas to be offered. Other notions included simple tie-down straps, sandwiching blades between

foam pads, a custom fitted sack, and multiple small compartments. Available space on the trailer

became the primary reason for selection of a long custom box with foam lined walls and blade

dividers.

16

2.10. Payload Vibration Isolation

The nose-mounted payloads for the aircraft are detachable, and must be transported apart

from the main frame of the aircraft. They are very expensive, delicate, and must be insulated

from transportation induced shock. Should the contents of the payload become damaged and

inoperative, the entire aircraft system will be of little or no use to its operators. Options were

generated by a combination of creative brainstorming and research into pre-existing products.

Amongst the first ideas was the concept of suspending a load platform by several springs

and dampers, possibly adapted from a motorcycle, or ATV. Potential components were

examined by looking through catalogues for such vehicles.

Another idea turned to technology employed by tractor-trailer trucks used to carry

sensitive cargo. They are “airbag” suspensions, where the spring is replaced by a durable rubber

bag that can be pressurized to provide different spring constants. These airbags would also need

to use an additional damper.

A third option is the use of foam padding, or other common packaging technique.

Internet tools were used to locate a few options for this system. Egg-crate foam, packaging

peanuts, and special vibration damping materials were all considered. The most drastic approach

was to alter the suspension of the trailer itself. This would require changing the spring and

damper rates of the existing suspension to fit the needs of the delicate payloads. This idea

focused on modifying rather than replacing the existing trailer components.

2.11. Helicopter Suspension

The Silver Eagle trailer, around which the UAV transport system is being designed, has

been specified by the manufacturer to impart an acceleration of no greater than three g’s to the

17

payload when tested on the TACOM Aberdeen Proving Ground courses. The air vehicle being

carried on the trailer is to sustain no greater than five g’s of momentary acceleration, and no

more than three g’s repetitively. Thus the trailer meets these requirements without any

modification.

2.12. Electrical Sub-System Development

The initial electrical requirements were for the system to be able to charge the UAV

batteries and supply power to the UAV controller / base-station. The remainder of the electrical

system design would be largely driven by the trailer/HMMWV system design. The original

system design involved a method to raise the UAV to a position where it could take off safely

and a method to electrically aid loading and unloading the UAV from the trailer/HMMWV, in

addition to the electrical requirements. The final element driving the initial design was the

specifications for a HMMWV. Research indicated that the base HMMWV, the M998 uses a

24V electrical system with a 60A alternator. The HMMWV power could be accessed through a

12 pin connector located somewhere along the HMMWV’s body.

The initial electrical design used the following: A 12 pin plug/adapter which would grant

access to 24V at 60A. From there, this power would serve as input to a power inverter which

would convert a 24V DC input to 120VAC output. Using an inverter would allow the use of

typical ac-outlet battery chargers and ac-adapters for either a laptop or PC based controller/base-

station. This design allows great flexibility since and AC based electrical device such as a lift or

winch can be used with the inverter. Also, some inverters have built in battery chargers; an

option which could be selected when more information on the UAV batteries became available.

18

At this point more of the overall system requirements would play a role in the choices

made for the electrical subsystem design. The entire system should be designed so that the UAV

can be deployed within five minutes. This further requires that everything be easy to use and

quick to setup. A power inverter provides quick plug and play operation. Everything operates

the way people are used to operating devices at home. Just plug the appliance into a wall outlet

and turn it on. Similarly, our original designs were to follow a plug in and push this button

model. Plug in the charger, base station, lift, and/or winch, then go ahead and use the devices. A

battery charging inverter limits the number of components that users (soldiers) would have to

inventory. Further, an inverter can be selected with specific electrical protections such as short

circuit, over temperature, over voltage, and over current. Not only does this provide protection

for any attached, and possibly delicate or very expensive, devices, but also there is very little

contact between the solder and exposed sources of power since the HMMWV’s batteries or

alternator would not need to be directly accessed in order to tap power.

The portion of the system design which would shape how final electrical subsystem

designs would turn out was still undecided. Various designs incorporating an electric scissor lift,

electric lift table, crane, and winch were under consideration. In order to proceed with an

electrical design, the portions of an electrical subsystem that would have to be common to any

chosen design would need to be identified. Concurrently, all possible permutations of using an

electric lift mechanism with a winch or crane for loading/offloading the UAV would be

considered. A quick analysis of the electrical subsystem revealed the following items:

An adapter to supply power from the HMMWV to the:

Power converter module which transforms a 24V DC input to whatever output required

Battery charging module (or ability to plug in a charger) for the UAV

19

Power output for use with computer/controller system (this could be part of #3).

Power output for use with devices such as a winch or electric lift.

Since component that would be exactly the same across any design would be the first

item, an adapter used to connect the HMMWV to the power module, research on buying,

building, and using this item was performed. This work showed that the twelve pin plug initially

found for use with the HMMWV was an outdated item. Only one supplier could be located for

the item and the only datasheet found was a drawing dated to the 1980’s. Also, at this time, a

further definition of the system requirements indicated that the electrical system should all be DC

based. This allowed reducing the possible electrical devices to only those which operated on DC

power. However, initial research into DC based winches and lifts showed that a 12V device

would draw 60+ amperes in order to lift loads that would be in the range of the UAV + its

payloads. This indicates that a 60A alternator would not be sufficient for our system if we

wished to use an electrical means to lift and load the UAV.

Further research revealed that there were army projects underway to produce a hybrid

HMMWV with a much larger power output. Since the HMMWV we might be able to obtain

would probably not be an experimental new one, work would have to be done in terms of

looking into changing the alternator of a HMMWV. A website created by a HMMWV

enthusiast showed that there were HMMWVs with larger (100A) alternators. Websites selling

military grade alternators were also found. However, before pursuing this course further, a better

source of information would be the manufacturers of the HMMWV themselves. Our DPI

meeting answered the following questions critical to our design; What kind of power needs to be

available for the UAV? Would we need to design a charger? If so, for what sized batteries?

20

The results of the meeting as it affected the design of the electrical subsystem were as

follows. First, the use of an electric lift and winch can be combined into a crane. A crane would

allow manipulation of the UAV in terms of loading and unloading it (replacing the use of a

winch), lifting and lowering it to and from a platform (replacing the use of a lift), and provide

further utility which was highly desired by DPI, such as adjusting the CG of the UAV,

mounting/dismounting the payload, and lifting larger UAV parts for replacement or repair. This

additional utility allows greater flexibility for onsite modification of the UAV. The UAV

batteries can be charged and the computer system runs, off a 12VDC electrical system. DPI also

specified the battery charger must support a 12V system. Further, it was advisable to use a

common 12VDC system for all electrical devices since this would reduce the complexity and

different types of power converters and chargers. Finally, the UAV and computer system would

need to be operational simultaneous while on the ground. So, both would need to be able to be

powered at the same time.

About a week and a half prior to this, an additional requirement, that we carry enough

fuel for the UAV to complete a 72 hour mission was clarified. At that point, it was the team’s

assumption that this meant the UAV would complete a certain number of missions with some

downtime during this three day period. This would increase the amount of fuel we would have

to carry and thus reduce the amount of available space. Coupled with the other items that our

system would have to store, soldier rations and personal gear, water, a backup UAV, tools,

blades, and electronics; free space was now at a premium.

A 12VDC crane would be used as the primary system for moving the UAV and payload.

The Venturo CT310KX crane was chosen for this use. It is a 12V crane which draws roughly

110A while in use. In the conversation with an AM General representative, the manufacturers of

21

the HMMWV, regarding upgrading the alternator for use with a crane, new key information was

acquired. First, the HMMWV’s with 60A alternators are the older base system. To upgrade the

alternator would require total overhaul of the engine. Second, the newer base HMMWV system

is based on a 200A alternator. These HMMWVs don’t have a 12pin connector but instead use a

“NATO slave plug”, a two pin connector located under the front passenger seat. With this new

information and resolution of electrical design issues, the five parts of the electrical subsystem

can now be specified as:

A NATO plug with 25 foot cabling to reach from HMMWV front passenger seat to the

trailer.

A 24V to 12V DC to DC converter which is able to provide 120A of output current.

A 12VDC battery charger with ability to charger 2 batteries simultaneously powered by

either a 24V or 12V input.

Cabling and wire connectors to allow connecting the batteries to the charger, computer

station to the converter output, and crane to the converter.

This item is now integrated into the previous.

In order to maintain the simplicity of the electrical system, all electrical power is made

available from one central source located on the trailer. The NATO connector plugs on one end

into the HMMWV and on the other end into a socket on the side of the trailer. That area has

sockets available for connecting cabling to charge batteries and to provide power for the

computer station. There is also a socket for connecting the cranes power input. Since the UAV

battery connector and computer station input connector types are unknown, those cables would

use alligator clamps in order to provide a connector that can be adapted to largest variety of

22

situations. On the inside of the trailer, the aforementioned sockets are connected to the input and

outputs of the DC to DC converter, and outputs of the 12V battery charger.

This redesign significantly reduces the complication of using the electrical system. To setup,

the NATO connector is plugged into the HMMWV and its connector on the trailer. The

charging cables are connected to the batteries and their sockets on the trailer. The computer

station and crane are also similarly connected. Then, the DC-DC converter and battery chargers

are switched on allowing use of all systems. This limitation on user contact with the actual

power conversion and charging devices themselves reduces the number of problems that can

occur due to human error. Also, if a part fails, it would be the only portion that needs

replacement since everything is essentially independent of each other. Also, the decision to use a

charger with 12V input would remove the necessity of splicing the wires carrying the 24V input

from the HMMWV to both the converter and the charger; instead a direct connection can be

made between the battery charger and DC-DC converter.

With a final electrical design completed, the next step is to further specify the components

being used. An analysis of the electrical design indicates that the following items must be

present in a specific form: A NATO plug and cabling for connecting all the devices. The wire

sizes (gauge) for all cabling is determined by calculating the maximum voltage drop that can be

afforded along a wire given its length. Once this is determined, the sizes of required connectors

for the trailer sockets, alligator clamps, and wire terminal connectors can be determined. The

only portion of the electrical design left which has any freedom for further design in terms of

feasibility assessment is the DC-DC converter and battery charger.

23

3. Feasibility

The feasibility assessment discusses the justification for each system that has been

considered for the development of the project. For each system, there are many alternatives

(concepts) that need to be strictly evaluated to best satisfy the needs and goals of the final design.

In order to select the “best” concept, the following steps are utilized. First, in the initial

brainstorming stages, ideas are introduced without negative feedback. After many concepts are

introduced, obvious outliers are thrown away and the remaining items are discussed. Finally, a

more rigorous comparison method of complex weighted charts is developed by comparing the

significant attributes of one alternative to those of another.

For these steps to be effective in comparing alternatives, a list of attributes must be

developed first. To decipher which attributes are more important within the scope of the project,

factors such as resources, economics, scheduling, and technical data must be considered during

this evaluation. There are eight attributes developed that are applied to every concept. These

include price, lead-time, usability, breakdown/setup time, durability, reliability, safety, and

weight. Using the same method of evaluation for each system requires a certain leeway to be

developed for general differences within each system. In order to account for this variance,

specific additional attributes are assigned to some of the systems as needed. In many cases these

additional attributes are some of the most important factors to consider when selecting the “best”

concept.

Once the pertinent attributes have been defined, in order to seek out the “initial best”

alternative, a simple, generic Pugh chart is used to show dominant concepts, and determine a

preliminary best alternative. This is accomplished by simply designating a baseline concept

(which concept was irrelevant) to which other alternatives will be compared. A simple “+”, “-”,

24

or “x” denotes if an alternative is better, worse, or the same, respectively. In some cases it is

evident that some ideas are not as good as others, however it is not very evident that some

concepts ranked much higher than others. A problem with the Pugh Chart method is that all

attributes are weighted evenly. This is not actually the case when choosing the best alternative

because some factors have little or no bearing on the small difference between particular

attributes, while other may have significant influence. One example of this is that of attachment

point weight. The D-rings, recessed D-rings, and clinching cams are all miniscule items. With

all other areas considered, the difference in weights is negligible and therefore has a very small

(5%) bearing on the decision of which to use. Weight is simply not a deciding factor in this

aspect.

A much more effective method of comparing factors is the weighted importance of a

particular attribute. The importance or “relative weight” of each attribute is calculated using a

method of direct comparison of attributes. This is accomplished by comparing each attribute

against each other and deciding which one has more importance in the needs of a particular

system. In most cases, the most important attribute is lead-time, based on the time available for

project completion. This would not be so heavily weighted if time was not such a constraint.

Many times, additional attributes carry the most weight in the final choice of a concept, as is

with the crane. Sixty-five percent of the deciding weight is based on power consumption,

payload capacity, and reach. These factors are critical, because if they are not satisfied, the crane

will not be able to be integrated into the system and meet the specified deliverables.

Project concerns and strengths are laid out in the project feasibility assessment

worksheet. Specific items in resource feasibility, economic feasibility, and schedule feasibility

are also assessed. The confidence level for each item is considered, and from this data, rationale

25

and remedy items are created. This chart illustrates which areas are of high concern and need to

be addressed, and which areas are of low concern, needing less assessment. The chart promotes

action to be taken to solve problems that may not have already been considered. This allows the

group to overcome its weaknesses to be identified and corrected while maintaining advancement.

3.1. Weather Resistance & Covers

Four different concepts have been considered for this system: a canvas top, metal plating

with a structural frame, a custom tonneau cover, and a rigid canopy, much like that of a

snowmobile trailer. As shown by the feasibility assessment, metal plating would not be

sufficient. It scored lower than the alternatives that were already considered deficient by the

Pugh Chart. This is largely due to weight issues. Initially, canvas appeared to be the best option,

with the custom tonneau cover and rigid canopy cover tied as second best. After weighing out

all of the items, it is clear that the canvas best suits the project’s requirements. Lead-time,

weight, and safety would not prove sufficient to match the capabilities of the canvas. The group

agreed that canvas would be the most feasible design for covering and waterproofing the trailer

and its exposed cargo.

3.2. Ramps

When considering how to load and unload the DP-5X from the transport system, four

different ideas were considered. These concepts were individual ramps that may or may not be

folded, a folding tailgate that could swing down and open up, “U-Haul-Style” ramps that would

slide into a storage compartment underneath the trailer, and telescoping ramps were all

considered. Inherent design flaws were seen in the telescoping design but it was still included in

26

the assessment. The score was considerably less than the baseline concept and still a great deal

worse than other concept ideas.

The folding tailgate and U-Haul-Style ramps were very close seconds in the generic Pugh

Chart and close after the weights had been applied. Price had not been a concern at first but it

should be noted that the individual ramps are less expensive than the alternatives. Ultimately,

individual ramps were found to be very accessible and the lead-time an acceptable duration.

Safety was the largest concern when transporting the UAV to and from the trailer and Hummer.

As such, all of the concepts considered provided the same degree of safety in their design.

The group’s decision of choosing individual ramps over the alternatives agrees with the

largest normalized score that was provided by the Weighted Pugh Chart, validating the feasibility

assessment.

3.3. Boxes (Component & Tool Storage)

There are three basic options available when considering a storage container for tools,

blades, and gear, and payload. Custom made boxes are used as the baseline. For this assessment,

they were compared to a pre-built unit already being manufactured as well as boxes that would

require design and assembly by the team. Custom boxes built to specification by a vendor prove

to be sufficient. The ability to customize plays a key role in this decision. Space is limited and

the boxes need to be integrated into the fuel compartments, while being able to support a launch

platform in the future. Lead-time is a major concern and custom boxes do take slightly longer to

obtain than pre-made boxes. Custom boxes are preferred because it is essential that the boxes

conform to the prescribed dimensions. These dimensions are not a stock size that any pre-made

box would be available in. The feasibility assessment is again found to be valid.

27

3.4. Fuel Containment

Custom bladders, pre-made bladders, fuel cans, and a fuel tank of original design were all

concepts considered in this feasibility section. Pre-made bladders and simple fuel cans are

equally adequate concepts, with a custom made fuel tank placing a distant second place. In this

case, a different route than what the Pugh charts show is chosen. It is not realistic to attempt the

design of fuel tanks given the lack of experience and lead-time that would be necessary. Due to

the desired placement of the fuel containers, the custom bladders are the preferred option. They

allow fuel placement in the oddly shaped spaces below the storage boxes.

3.5. Trailer Type

In selecting a trailer from Silver Eagle there are several options. Feasible options include

the LTT-F, which is a 7 foot long flat-deck, the LTT-FE, which is a 10 foot long flat deck, and

the LTT-HC, which is a 7 foot long trailer with sides and tailgate. According to the Pugh Chart,

the LTT-F is the most feasible design. When the weights are applied, both the LTT-F and LTT-

FE appear to be feasible in the final design. As surface area is a significant concern, the LTT-FE

was selected as the appropriate choice.

3.6. Lift Mechanism

The different lift mechanisms considered are the scissor lift, the “four-bar” lift, a crane,

and fold-down-sides. The fold-down-sides alternative was found to be the most feasible

according to both the weighted and simple Pugh Chart. A trip to the sponsor provided further

insight to the value of these ideas. The sponsor was most in favor of using a crane to move the

28

UAV to a launch location which was ranked third by the analysis techniques. However, these

methods of evaluation are not always entirely accurate. The advice of the sponsor was adheared

to and it was found that the crane concept would satisfy all the needs of the project effectively.

3.7. Launch Platform

Originally the group was very concerned with keeping the launch height of the UAV at a

safe distance above the heads of personnel. As time went on, deliverables changed and this was

no longer a top priority. With this known, when the feasibility of Bilco Doors, a flat roof deck, a

tri-fold expanding platform, and the ground was considered, the ground came out as number one.

This is because all the other systems were far more complex because they were based on the idea

that a start-from-elevation system was needed. This caused these other systems to score lower

when compared with the attributes of the ground launch system. This feasibility assessment

agrees with the consensus of the group; the ground is the most ideal launch platform.

3.8. Crane

The crane is now a definite system and the feasibility of a fully manually operated crane

have been compared to the feasibility of the same type of crane that folds, and another which

folds but is fully powered. Power consumption, payload capacity, and reach are major concerns

when determining feasibility. The main drawback of the powered crane is that it requires

additional systems to be created to operate it. The advantage is that it has the desired reach and

payload capacity necessary for the needs of the system. Setup and breakdown speed also

contributed to the designation of this concept as the most feasible. The Pugh chart analysis

confirms that the fully powered and folding crane.

29

3.9. Tie Down Mechanisms

The four different concepts evaluated for feasibility in securing the UAV to the trailer are

the ratcheting tie-down, self-clinching tie-downs, mechanical latches, and a rotor catch ring with

straps. The rotor catch ring is easily ruled out by its complexity and difficulty of operation.

Ratcheting tie-downs are confirmed by both charts to be the most feasible. This particular

concept excelled in ease of use, safety, and holding strength. The component is fairly simple and

is proven through analysis to be the most feasible.

3.10. Tie Down Attachment Points

The group came up with three ideas to connect the Tie-Downs to the trailer. Those were

a D-Ring Type, a Recessed D-Ring Type, and a Clinching Cam. A simple D-Ring design that is

not recessed was found to be the most feasible in this case. A protruding D-Ring is easy to use,

has a good breakdown/setup time, and is very reliable. However, safety is concern with this

design because it could be a trip hazard. The clinching cam turned out to be the least feasible

due to its complexity and reliability. The group agrees that the simple D-Ring will be the most

feasible attachment point.

3.11. Power Converter Module

This module steps down power from 24V at 200A to 12V with a 120A maximum output.

Factors that must be considered when choosing one are their ease of use, cost, availability,

reliability, safety, ruggedness, ability to be integrated into current design, and lead time. Based

on the modules found when researching potential products, they all have common safety

30

specifications. All of them operate the same way, so ease of use will also be common to all the

devices. A power converter that supplies at least 1440 watts of power at 12VDC seems to be a

very low market item. This reduces the availability of a single converter that meets the projects

requirements. An alternative design calls for using multiple smaller converters in parallel to

boost the output power to desired levels. Smaller converters are readily available. However, the

low demand for these devices results in high total cost compared to a single large converter.

Designing our own converter would result in significant prices savings, however, other attributes

might be compromised, such as safety and ruggedness.

A feasibility analysis of these attributes as shown in appendix A22-A23 shows that lead

time was the most important consideration in our design followed by ruggedness and cost which

tied for second. From team discussions, cost was a more important factor in choosing

components of our design than ruggedness. While this difference between our ranking and that

from the weighted attribute analysis might go towards explaining why converter concept 1 won

out over our final choice, concept 3, a better explanation would be an attribute which could not

be captured on a graph; our team can tradeoff the two or three week time savings in lead time of

concept 1 for the cost savings of concept 3.

3.12. Battery Charging Module

This module provides a charging system for a 12VDC battery. The attributes considered

in the feasibility analysis as shown in appendix A24 for this item are identical to those discussed

for the DC-DC Converter. Again, ease of use, safety, availability, and reliability were

approximately the same for all chargers considered. However, the low cost of these items frees

us from having to consider designing our own charger.

31

4. Design Objectives & Criteria

4.1. Weather Resistance and Covers

The material used to cover the trailer must be lightweight and have the durability of

withstand the rigors or intense use. A material used for car covers became a principle choice.

WeatherShield HD, a fabric produced by Kimberly Clark and sold primarily by CoverCraft

Industries proved to be an exceptional choice. This newly developed fabric had the highest rating

for protection, durability, and ease of use.

4.2 Ramps

Simple ramps that are stored on the trailer and then attached when needed have the

following benefits;

Usable on both the trailer and humvee

Lower weight than that of a bulky folding tailgate

Ease of adaptability to varying ground conditions

Usable for instances not involving helicopter at all; such as needing a ramp for

moving other objects or personnel

With the limited storage space on the trailer a folding design would be most beneficial. A typical

single folding ramp has a width of 12 - 14inchs which is insufficient for this application. The

wheelbase of the helicopter is 38 inches. Therefore, 3 or more of these single ramps would have

to be utilized in order for it to be. The ramps chosen will need to go side by side in order to

account for this issue of width. Aluminum center-folding ramps, manufactured by Better Built

have all of the properties necessary for this application. With an individual load capacity of

32

1500lbs, these ramps will be sufficient in accomplishing the task of loading and unloading the

UAV while compactly storing away.

4.3. Boxes

Tool boxes were designed and sized based on their required loads.  Four main storage

compartments will contain up to two payloads, the main rotor blades, electrical package, FCS

tool kit and any miscellaneous fluids and solider gear. All storage boxes will have latching

handles and water tight seals on their doors.  The storage box configuration will consist of two

top loading payload boxes in the front of the trailer and two long side loading boxes on either

side of the trailer with the UAV in the middle.  The payload boxes are designed to encompass

1900 cubic inches of the payload with an additional three inches of foam protection lining the

interior of the steel box. These payload boxes must be of a unique shape in order to provide

clearance for the rotation of the crane which is mounted immediately adjacent to them.  Thus,

these custom boxes are close to twice the cost of regular square ones. The boxes containing the

blades are required to safely and securely store eight main rotor blades for the UAV. Each blade

is approximately six feet in length, two inches in thickness and four inches in width. The

resultant box design is actually than the blade length requirement which eliminates dead space at

the end of the trailer.  The two door box contains the electrical package, FCS tool kit,

miscellaneous fluids and maintenance equipment for the UAV.  Any additional space may be

taken up by miscellaneous soldier gear.

33

4.4. Fuel Containment

The fuel containers for the UAV trailer were chosen based on the criteria of geometric

flexibility, transportability, and durability. Each trailer is to carry 1200 pounds of JP-8 fuel.

This requirement imposes challenging geometry, as the trailer wheel well intrudes into the area

designated for fuel containment. The odd shaped container needed must also keep the fuel from

sloshing and foaming during travel as well as resist small arms fire.

The effort to specify a type of container narrowed down to either pillow bladders or semi-

rigid containers. These two were chosen because they could be made to fit in the irregular

spaces defined by the trailer layout. Both are commercially available, come in a variety of sizes,

and are already in use by the armed forces.

A pillow bladder is little more than a fuel proof bag, equipped with special fittings and

nozzles. They are collapsible, and could be used to fill the highly irregular shape imposed by the

intrusion of the trailer wheel well. However, these bladders are unsuitable for transporting fuel

on a trailer, since there are no devices in place within the product to prevent sloshing. Erratic

motion of liquid fuel, resulting from rough terrain, could present an unfavorable driving

condition, whereby control of the vehicle would be compromised.

The alternative solution, is the semi-rigid fuel container. These containers are

constructed from nylon reinforced urethane, and retain their shape regardless of the level of fluid

contained. They are partially deformable and allow some measure of flexure when an adequate

shock is imparted. The semi-rigid containers were chosen over the pillow bladders because they

contain baffles, much like most other fuel tanks, to prevent the sloshing of fuel. The only

downside is that they must be custom fabricated to the desired shape, which may create a slight

34

budgeting issue. These unique tanks are available through Fuel Safe, a company that specializes

in custom containers for race cars and aircraft. Fuel Safe bladder features include:

Meeting volume and geometric constraints

Foam baffles to prevent sloshing

Customizable drain and filler

Ballistic tolerance

4.5. Trailer Type

The performance specification of the trailer is that it must be able to support all of the

subsystems that are associated with safely carrying the UAV and cargo over rough terrain at

sixty-five mph. Safely is defined as being weatherproof and not creating shock loads to cargo

greater than four g’s for the UAV and two and a half g’s for the payload. These subsystems

include the following:

Storage boxes Fuel tanks Canopy Ramps UAV lift mechanisms Launching platform Crane Holding mechanisms Attachment points Blade and payload

packaging Additional suspension Electrical components

The design specifications of the LTT-FE are located in the technical data package The main

areas of concern were payload capacity (2970 pounds) and overall length and width, 165 inches

and 86inches respectively. The LTT-FE was evaluated knowing that Silver Eagle would be the

35

base company to supply the trailer. The LTT-FE model was picked over the other models at

Silver Eagle because it had the largest surface area. Starting with a flat deck allowed for a base

that could easily be modified to incorporate the subsystems into the trailer.

4.6. Lift Mechanisms

Initially the objective of the launch mechanism was to launch the UAV from a safe

height. There was a great deal of design concepts that were developed around this. Those

concepts were developed to meet the following design objectives:

Support a platform

Support the UAV

Lifting capacity of at least 1000 pounds.

Easy to operate.

Use minimal time to launch and receive

After the visit to Dragonfly Pictures, launching the UAV from an elevated position was

not the only method to ensure safety from the rotor blades.

4.7. Launch Platform

Using the ground as a launch platform is not the safest idea, but it is the most feasible

concept. This not only saves design time, but also weight on the trailer deck. The only

downside to using the ground as a launch platform is that it is not guaranteed to be a consistent

level surface. Currently Dragonfly Pictures launches the DP-5X from the ground, so using the

ground as a base should have no negative technical effects.

36

4.8. Crane

Final selection of the crane was based on the envelope in which it could operate. The

capacity of the crane had to be at least 600 pounds so that it could lift the fully assembled and

flight ready UAV. The crane had to have sufficient reach to be able to pick the UAV off the

trailer and also place the UAV far enough away from the trailer so that when lowering it to the

ground it would not hit the trailer in any way. The crane also had to lift the payloads from their

protective transport cases and position them for attachment on the UAV. This meant that the

crane must have the ability to pick from very near its base since that is where the payload

transport boxes are located. This varied envelope of functioning forced us to find a highly

functional crane. The crane we selected is manufactured by Ferrari Articulating Cranes and

distributed in the US by Venturo Cranes. The crane features powered rotation, boom elevation,

and boom extension and has a capacity rating of 6,000 ft*lbs. This supplies us with a lift of 700

pounds at a fully extended boom length of 9’-3” and a minimum reach of 3’, which satisfies all

of our lifting and reach requirements. The crane will also function as a winch as necessary when

the ramps are employed to remove and load the UAV. A simple corded control remote with

toggle switch controls will allow the UAV to be easily loaded and unloaded from the trailer by a

single soldier. The crane is also purpose built for outside use so exposure to harsh elements

should pose no issues to prolonged service life as will be expected of the UAV trailer.

37

4.9. Tie Down System

A clamp-type of latch will be used due to its ease of operation as well as its durability.

The tie-down being used will be a woven 1 inch flat strap. Available in any custom length and

having test strength of 4000lbs, the straps will be more than sufficient for this application.

4.10. Tie Down Anchor Points

A heavy duty recessed anchor ring made by Erickson Mfg. LTD. is the best choice for an

attachment point. It has a maximum load capacity of 5000lbs per hook and being is of the least

expensive anchor points available. It also satisfies safety concerns by being recessed, leaving less

of a possibility of becoming a trip hazard or getting in the way of other applications. This was

rated as second highest in the feasibility section because it was ease of use and setup/breakdown

time was weighted more than its safety attribute. It is felt that the trip hazard associated with

these anchor points was a larger concern than the speed and ease with which it could be used.

4.11. Rotor Blade Vibration and Protection Packaging

In addition to providing a secure place to stow spare rotor blades, the blade packaging

design also needs to be simple, durable, and easy to use. Only one of the original slews of ideas

met all of these criteria.

Sandwiching the rotor blades between sheets of foam in a stack met all of the criteria for

adequacy. This solution is inexpensive, easy to use, contains very few parts, none of which

move. As a bonus, the foam insulates the aircraft components from transportation related

vibration. The last point of note was never a major point of concern, as rotor blades are very

durable by nature. A “regular charcoal foam” available from www.foambymail.com will be

38

employed for this application. This foam has an Indentation Load Deflection of 65-75 lbs and a

density 1.5-1.7 lb/ft^3. Several sheets of 1”x24”x72” foam will be acquired for this application.

4.12. Payload Vibration Isolation

The main requirement for the packaging of the payload is to limit the terrain induced

acceleration to 2.5 g’s. As with all components in this transportation system, cost, complexity,

and ease of operation are of prime importance.

The airbag suspension concept is complex, and possibly unreliable, as a compressed air

source would be required to drive the system. In the arena of military hardware, simple and

elegant is always preferable to complex and sophisticated.

Accordingly, the foam padding idea won out; it contains an absolute minimum number of

parts, is lightweight, inexpensive, and requires zero operational skill. Required material will

once again be purchased from www.foambymail.com. Foam for the payload packaging has an

Indentation Load Deflection of 33-39 lbs and a density 1.0-1.3 lb/ft^3. Several sheets of

3”x24”x72” foam will be acquired for this application.

4.13. Power Supply Adapter

This portion of the electrical design has very little room for compromise or design. The

components were chosen from those available to achieve the functionality required. In order to

connect to the NATO slave terminal in the HMMWV to gain access to power, a NATO slave

plug is required. To achieve quick connect/disconnect and modular capability at the trailer, wire

connectors which could support the largest wires needed, #4 AWG, and at the same time conduct

currents of up to 200A were chosen. The best connectors found are the Anderson Power SB

39

series. Since the connectors used for the UAV batteries and the computer control station are

unknown, alligator clamps were chosen to terminate the charger and computer control station

power lines.

4.14. Power Converter Module

This module steps down voltage from 24V at 200A to 12V with a 120A maximum

output. It must tolerate variations in input voltage up to 2V while maintaining a regulated 12V

output. Since it will be traveling inside of the trailer, the converter should be reasonably able to

withstand some vibration stresses. The Schaefer Power C3822 was chosen due to its lower cost

and shorter lead time when compared to the other DC-DC converters which met the project

requirements. The mechanical strength of the base model can be increased, a feature not present

in the other models considered.

4.15. Battery Charging Module

This module provides a charging system for a 12VDC battery.  In order to be easily

integrated into the electrical subsystem design, the charger must accept a 12V DC input, which

will come from the converter.  A charging voltage of at least 13.6V and charging current of at

least 20A is also required.  The PowerStream PST DU-700 battery charger was chosen for its

low cost and ease of integration into the electrical design. All the other chargers found had 24V

input requirements. 

40

4.16. Wire Gauge Selection

The sole use of wires in this design is to transfer power from either the HMMWV to the

trailer or from the trailer to any of the connected devices. When transmitting DC power, the wire

resistance must be minimized. High resistance wires transfer less current and encounters larger

voltage drops. Wires classified under the American Wire Gauge system have specified

resistance per 1000 feet for each wire diameter. For example, 12AWG (12 gauge) wire has a

resistance of 5.20864 Ohms per 1000 feet and a diameter of 0.0808 inches. A smaller gauge

wire has a corresponding smaller the resistance per 1000 feet but conversely, larger wire

diameter. The wire diameter becomes a problem when attempting to find connectors or wire

terminals which would allow mating of a large wire to standard sized plugs.

From the HMMWV specification, 28VDC is available at the NATO plug. Examining the

DC-DC converter and charger spec sheets, 13.6V is the actual output voltage at the no load

condition. However, in order to maintain proper operation of both the charger and converter,

we’ll design the system so that a minimum of 24V is present at the input of the DC-DC converter

and a minimum of 12V at the final connection point between the devices connecting to the

converter or charger. Using the knowledge of the length of the wires needed, current the wires

will carry, and maximum voltage drop that can be tolerated, the maximum resistance per 1000

feet for wires used in each part of the electrical subsystem can be calculated. Then, the closest

matching AWG gauge can be chosen. This choice is the wire which meets or exceeds the

calculated maximum resistance per 1000 feet.

Calculating the maximum resistance per 1000/feet is as follows:

(Eq 1)

(Eq 2)

41

(Eq 3)

Equation 1 rewrites Ohm’s law to give resistance as a function of voltage and current, quantities

that we can specify in our system. This allows determination of the maximum resistance that a

given wire section can have by using the maximum voltage drop and current the wire must carry.

In order to calculate the total resistance for each section of wires, the resistance must be divided

by the total length of that section, giving a value with units of resistance per foot. To determine

which wire size to use, we require units of resistance per 1000 feet which is done using equation

3.

Table 4.16.1: Minimum Wire Gauge for Each Section

Section Length (ft)

Max Voltage Drop (V)

Current (A)

Resistance/1000 feet (Ω/1000ft)

AWG Actually will Use

B->C->D->E 28 4 200 0.714285714 8 4E->K->C->I 9 1.6 120 1.481481481 11 10G->H->C->J 9 1.6 60 2.962962963 14 14

E->F->G 3 1.6 60 8.888888889 19 14

5.0. Analysis of Problems & Synthesis into the Design

The first part of this design exercise was merely inventing or specifying solutions to the

myriad of problems that were presented by the sponsor. Integration of these subsystem solutions

was the next task. All of the individual pieces must interact harmoniously with each other, as

well as coexist in a very compact and hostile environment. For example, the wheel wells of the

trailer constrain the dimensions of the fuel storage area, which in turn affect the allowable

volume of the storage boxes to which the trailer cover will be mounted. In addition to providing

a simple measure of weatherproofing for on-board electronics, the cover must also be high

enough to clear the rotor head of the UAV, which, alas, places yet another constraint on both the

fuel container and storage boxes. The ever raging battle for real estate was mediated by a

42

combination of hand sketches, CAD layouts, and countless discussions to decide just what could

be squeezed into where.

Just making things fit, however, was not quite enough. In addition to interacting with

each other, all of the system’s parts must interface with existing military hardware and personnel.

This challenge was overcome by using pre-existing military parts and specifications wherever

possible.

A brief summary of the design’s current state is as follows:

Trailer – Silver Eagle LTT-FE trailer.

Loading/Unloading – Individual ramps that can be used with the HMMWV or the trailer.

Lifting Mechanism – Electrically operated crane.

Launch Platform – UAV will be removed from the trailer and launched from the ground.

Storage – Custom built boxes will be positioned on the sides of the trailer above the fuel

containers.

Fuel Containers – Semi-rigid, custom made containers located on the sides of the trailer, under

the storage boxes.

Holding Mechanisms – The 300 pound UAV will be tied down during transportation by 6, 4000

pound maximum capacity ratchet straps.

Attachment Points – The ratchet straps will anchor to pocketed D-rings, recessed into the trailer

bed. Load capacity = 5000 pounds each.

Payload Packaging – The payload will reside in a separate box located at the front of the trailer.

The box will be lined with shock absorbing foam.

Blade Packaging – The rotor blades will be stored in a side storage area. The box will be lined

with foam similar to that used for the payload packaging.

43

DC-DC Converter – Schaefer Power C3822 converter will supply 120 amps at a regulated 12V

output.

12 Volt DC Charger – PowerStream PST DU-700 charger accepts an input of 12V DC charges

the battery to capacity, and then shuts off automatically.

5.1. Vibration Analysis

To begin the analysis, a mathematical model of a fully loaded trailer was constructed.

This three degree of freedom system included the trailer wheels and tires, trailer suspension and

shock absorbers, and the payload vibration control system, each depicted as springs, masses, and

dampers. With the aid of a simple free body diagram, a system of three second-order differential

equations was developed:

To analyze this equation by hand would be time

consuming and subject to error, so the Simulink utility of

MATLAB was employed to facilitate the process. Damping coefficients and spring constants for

the trailer were back calculated from static deflection and cyclical shock compression data

44

provided by the manufacturer. Constants for the tires were estimated from published data for

similar products. For the yet to be designed payload vibration isolator, arbitrary place holders

were inserted into the MATLAB code. For an input, a simple sine function of amplitude, ten

inches, and frequency, forty-eight inches, deemed appropriate for the representation of “rough

terrain” at sixty miles per hour was passed through the Simulink structure.

According to the plots generated by MATLAB, only marginal suspension and damping is

required to sufficiently isolate the payload from excessive shock. This was found to be true with

the sine input as well as with the random input. A worthwhile point of note, however, is the

effect of increasing the damping on the payload. With little or no damping, the relatively high

frequency vibration was filtered considerably. The plots of acceleration vs. time depict slow,

regular oscillation when the system is driven by the specified signal. As the damping coefficient

is increased, more of the terrain induced vibration is present, though still diminished in

magnitude. Thus, the results indicate that additional vibration protection possesses low damping

rates, with sufficient travel to accommodate low-g payload motion. A thick, springy foam pad

will be a simple, cost effective solution.

45

5.2. Structural Analysis

5.2.1 Fuel Containment Structure

The fact of whether or not the vertical supports along the sides of the fuel tank would

deflect under the pressure of the fuel became a concern when selecting the material to use for

this application. In an attempt to create the worst case scenario to prove that the beams would in

fact not deflect, the following preliminary analysis was done.

The boxes within which the fuel bladders are contained can be thought of as simple cubes

with an intermediate vertical support along the side. The size of these cubes is 22 H x 33 W x 15

D. These dimensions were all rounded up for ease of calculation and over-speculation of forces.

To maximize the load placed on these supports and ensure that they would not fail, the cubes

were rotated on their side, to account for maximum hydrostatic forces. Then the nominal

pressure on the bottom face (normally the side) was placed in the center of the vertical support as

a point force. This method over estimates the forces acting on the support to apply a loading case

worse than will actually be seen.

The overall volume of this cube is 10,890 in3. Using the nominal density of JP8 fuel of

6.7 lbs/gal and the conversion that one gallon is equal to 231 in3 it is found that an overall

concentrated force of 315.81 lbs will act on the wall, and thus the vertical support.

Applying this force at the weakest spot on the vertical support (the center height), the

deflection will be computed.

Cross sectional area of the beam having outer dimensions of 1 x 1 inch and a wall thickness

of .125 inches:

The moment of inertia for this particular beam is found using the following formula:

46

, where b is equal to the base dimension of the object and h is equal to that of the

height.

.

Using VonMises to calculate the deflection of the beam, it is found that the maximum

deflection of the beam will be 4.55 x 10-3 inches. This deflection will accompany a maximum

stress well under the yield stress of 100,000 lbs/in2

5.2.2 Fuel Tank Support Beams

The stock trailer receivable from Silver Eagle has an incomplete deck for the application

in which it will be used. The trailer has two main support rails along the sides of the deck, but

inside the width of the wheel wells. Our design will utilize the entire width of the trailer,

including that lying to the outer edges of the wheel well. Therefore, beams extending in the

lateral direction along the trailer must be added for the stability of our design. To ensure that

these beams would not have a maximum deflection exceeding the limits of our design, a basic

ANSYS analysis was completed. The weight of the fuel, as well as an additional 1,000lbs was

speculated to be resting on the added reinforced beams at any given time. Also, given that this

trailer must be operational in rough terrain with bumps, the entire load was multiplied by three

times the acceleration due to gravity. This load was then distributed over the beam and the

following output was recorded. As seen below, the beam has a maximum deflection of .01

inches. This deflection is not accounting for the added support of the rest of the structural

cabinets, or the fact that another beam will possibly be sandwiched underneath it for added

47

support. This analysis is strictly preliminary. Once the design is finalized, a more detailed

structural analysis will be performed for design optimization.

Figure 5.2.2.1. Cantilever Fuel Tank Beam Analysis

48

6.0. Preliminary Design

Isometric View

Left Side View Right Side View

Front View Rear View

49

6.1. Preliminary Drawing Package

Prints designed for the custom toolbox vendor are located in the appendix.

50

6.2. Bill of Materials & Supplier Information

51

6.3. Electrical Systems Layout

Overall Design:

BI

J H

DI

K

F

(A) NATO Slave Plug

(C)Side of Trailer with Input and Output

connectors

(E)DC to DC Converter

(G) 12V Battery Charger

(M) UAV Battery

(L) Crane

(N) Computer Station

Figure 6.3.1: Electrical Subsystem Design

The NATO slave plug is the interface between the HMMWV’s 24V 200A electrical system and

our design. The plug connects under the front passenger seat of the HMMWV. As a result,

cable B must run 25 feet from its connection point to the HMMWV to its connection point on the

trailer, C. From there, wires D travel 3 feet to the DC-DC Converter. The converter supplies

power through F to the 12V Charger and via a wire set, K, it connects back to the input/output

attachment point C. The battery charger output is also routed through wires H to C. From C, the

crane, UAV battery, and computer system are connected via wires I and J.

52

7.0. Matlab Vibrations Simulation

To expedite the calculations required for the vibratory analysis of the payload packaging

scheme, a model was created in Simulink. Through the use of summing, gain, and integrator

blocks, in conjunction with a customizable input signal, a useful electronic representation of the

actual system was constructed and set into motion.

53

54

8.0. Future Plan

Though the current design is more or less complete, there is still much work to be done.

As it stands right now, all of the individual pieces that comprise the UAV transportation system

have been designed, or specified for retail purchase. What remains is the detail work required to

put all of the individual pieces together into a functioning unit. Said integration will require

some additional design work as well as some analysis. Design work will focus mainly around

where exactly and how to bolt, rivet or weld components into place. This task will be dictated to

large extent by the analysis required for appropriate fastener sizing. Both tasks will be

performed in concert with the aid of computer tools such as FEA and CAD applications.

Once the hurdle of system integration has been cleared, a protocol for appropriate usage

by the future operators of the product must be drafted. Such a document should detail all

capabilities and limitations of the transportation system. For example, maximum load, approach

and departure angles, maximum allowable speed, and maximum traversable grade without

rollover need to be documented. Additionally, proper procedures for safe and efficient operation

should be covered. The design team needs to determine the best mode of operation to ensure that

the UAV can be launched and recovered within the allowable time, without posing any hazard to

personnel or bystanders.

The last order of business is to build a functioning prototype. The team will need to

communicate with the sponsor about purchasing parts or acquiring the funds necessary to do so

directly. Once all parts and materials have been successfully procured, the product can be

assembled and delivered to the sponsor for evaluation.

55

8.1. Schedule

56