flight vehicle loads(1)
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Flight Vehicle Imposed Loads
All loading conditions imposed on a structure must be known before the
flight vehicle structure can be designed. The load conditions are those
encountered both in flight and on the ground.
Since it is impossible to investigate every loading condition which a flight
vehicle may encounter in its service lifetime, it is normal practice to select
only the critical loading conditions for design.
The critical loading conditions are usually determined from past experience
and are definitely specified by the certification or procuring agency.
Limit loads are associate with normal operation of the flight vehicle.
Ultimate loads are typically defined as 1.5 x Limit Loads.
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Inertia Loads
The maximum loads on any part of the flight vehicle structure occurswhen the vehicle is being accelerated.
The loads produced by landing impact, maneuvering, gusts, boost and
staging operations, launches, and dockings are always greater than
the loads occurring when all the forces on the vehicle are in Equilibrium.
In many of the loading conditions, a flight vehicle may be considered
as being in pure translation or in pure rotation.
Translation:
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Inertia Loads(Continued)
Rotation: Rigid mass rotation about point Owith a constant angular
velocity . x-axis chosen through center of gravity C.
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Inertia Loads(Continued)
Rotation: Rigid mass rotation about point Owith a constant angular
acceleration . x-axis chosen through center of gravity C.
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Inertia Loads(Continued)
Rotation: Rigid mass rotation about point Owith a constant angular
acceleration , angular velocity , and linear acceleration aox-axis chosen through center of gravity C.
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Load Factors for Translational Acceleration
When the vehicle has only translational acceleration, every part ofthe vehicle is acted on by parallel inertia forces which are
proportional to the weight of the part. Load factor is a convenient
way to express the magnitude of inertial forces.
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Load Factors for Translational Acceleration(Continued)
Flight vehicles frequently have horizontal acceleration as well as
vertical acceleration.
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Load Factors for Translational Acceleration(Continued)
When the airplane horizontal thrust line is not horizontal, it is usually
convenient to obtain the components of the forces parallel and
perpendicular to the airplane thrust line
Perpendicular to the thrust line
Parallel to the thrust line
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Load Factors for Translational Acceleration(Continued)
The landing load factors are defined by dividing the landing loads
by the airplane weight.
In general, the load factor nin any axis iis given by:
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Load Factors During Maneuvers
A common airplane maneuver is a motion along a curved path (pullup from a steady flight or pull out from a dive)
If the velocity of the airplane
along the path is constant,
then at= 0 ad Ft= 0.
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Load Factors During Launch
Lumped Mass Model Discrete Mass Model
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Example Problem 1
When landing on a carrier, a 10,000 lb airplane is given a deceleration of 3gby means of an arresting hook as shown in the figure below.
(a) Find the tension in the cable, the wheel reaction, and the distance e from the
center of gravity to the line of action of the cable.
(b) Find the tension in the fuselage at vertical section AA and BB if the portion of
the airplane forward section weighs 3000 lb and the portion aft of section BB
weighs 1000 lb.(c) Find the landing run if the speed is 80 ft/sec
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Example Problem 2
A cargo plane shown below is making a level landing with the nose wheel
slightly off the round. The vertical ground reaction is 300,000 lb. The pitching
moment of inertia of the plane is 40,000,000 lb sec2 in.
(a) Find vertical acceleration at the aircraft c.g.
(b) Find vertical acceleration at the pilot c.g
300,000
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Example Problem 3
An airplane weighs 14,000 lb. It is flying horizontally at a velocity of 500 mph
(733 ft/sec) when the pilot pulls up into a curved path with a radius of curvature
of 2500 ft. Assume engine thrust and drag are equal and colinear with each other.
(a) Find airplane acceleration
(b) Find wing lift (L) and tail (T) forces
(c) Find airplane load factor
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Example Problem 4
A spacecraft payload weighs 600 lbs. It experiences load factors nz= 5g and nx= 0.4gduring the launch sequence. Calculate the reactions forces and moments at
the launch vehicle interface
Launch Vehicle
Interface