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NATIONAL ADVISORY COMMI'l'TEE FOR .trnRCELt'I':.CCS

for

Army Air Corps

A FLIGHT DETBRMINATim:r OF TEE MOM1 :"�T:=:, o:? T?::;: YG-lE

TAPERED BLADE ROTOR .ABOUT THE HUB C::1?TJ1:TFIC'l S

By F. J� BAILEY, JR�

FILECbpyTo lie retumed to , . fhe fi� of the Na.tiooal

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A FLIGHT DETERMI1JATION OF THE MOME1JTS OF THE YG-lB

'!:APER.ED BLADE ROTOR ABOUT THE HUB TRUNNIONS

INTRODUCTION

At the request of the Materiel Division$ Wright Field,

the National Advisory Committee for Aeronautics is conduct­

ing a program of flight tests on a Kellett YG-lB autogiro

· equipped w-ith a new _type 0£ rotor bladee The new blades

J ', are tapered in both pl.� f'orm. and th:tckness and are de-

1 , signed to avoid periodic b:tade twist. one phase of the 'l

'investigation, involving determination of the moments of

the resultan�irotor force about the trunnions on which t.be

1hub �s pivoted for control, haa_been comp1eted. The results

. I -; i obtained are _ reported herein� '

APPARATUS AND METHODS

The new blades were tested on a standard YG-lB :rotor

. · lhUbo The lateral and longitudinal trunnions about vihich i }this hub is J)ivot.ed. fo:r> eontrol inte::rsect in a point '?/lo) -

! inch to the le.ft e.nd 1-5/8 izu!hee- ahead o:f the rotor a.xis,I

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and lie in a plane 2-3/ 4 inches below the plane of' the_

£lapping hinge a ..

Ordinarily the moments or the resultant rotor force

1 vector about the trunnions are counteracted by the moments

applied by the pilot through the control system, plus the

1 moments applied to the hub by the bungee spl:'ing.. In the

' present tests the bungee spring was wedged open unt11, �ith

the bungee lever full forward., the bur..gee cable beemne slack

as soon as the stick was moved approximately an inch back II

, 1 f'rom its full t'orward position. Al.1 records were taken with

the bungee lever full f'orward and the stick :more than an inch

aft of its full rorward position,. Hence the moments con-

! t:ributed by�,., the bu."'lgee spring were zero in every case ..

The lateral and longitudinal moments applied to the

1 control system by the pilot were recorded simultaneously on i 1 a.n N .. A .. · C .. A .. stick type control force recorder.. Mu:Lti-t '

.

1plieation of these moment� by the latera1 and 1ongitud1nal' .

:m.echsnlcal advantages of the control system established the 1 moments of the ;r,otor. vector about the trunnion axes o-'

,

In addition to records of control force, records or

cpntrol pos�tion and air speed were obtained during eachl:

·rµn. Pre:$sure altitude and rotor speed were noted by the

Records were taken in steady level flight and i:n steady

glides at iI I

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indicated air speed.a ranging from ze�o to 110 mtl_es

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Tlm :flights were made., In the f'irst !'light the air-speed.

recorder was connected to the same service head to which the

I pilot's meter is attached; in the second it was connected -1 '1

to a swiveling head mounted on a boom extending to a,, point

' .several feet outboard of the service heado Comparison of

recorded air speed with readings of tile pilot's air-speed ·1

meter for the two fJ.ights·indics.ted that the accuracy of

air speeds recorded with the serviee head was satistactoryo

The air-speed recorder installation waa also cheeked

to insure that no appreciable error resulted f'ro:m rates of

change 0£ static pressure comparable to tl'10se encountez,ed 1n

glides1-

The gross weight of the autogiro at take-off was l,960

pounds<>

RESULTS. AND DISCUSSI0bi

, Data. obtained du!' ing each run are tabulated in table L,

The lateral s.nd longitudinal trun11ion moments are plotted

I against one .another in .figure l :tor the level-flight condition

and in :f'i{:i;ure, 2 £or the glide condition,. Average va.l.ues of the

tip-speed ratio corresponding to i,everal valiie� of longitudinal

trunnion moment are indicated on tigurea land 2o These tip=

speed ratios were determined :fro!"- the faired curves ot longi­

tudinal trunnion moment versus tip-speed :rat,io shown 1n figure 3o

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The actual stick force applied by the pil<..-t can be

obtained by dividing the corr·esponding trunnion moment by

the product of the stick length, lo906 feet., and the mechanical

advantage of the control system, 3.86 longitudinally and 5o27

laterally. The figures given for the mechanical advantages

· were obtained from simultaneous 1:neasuren1ents 0£ hub and stick

angles made pre:7iou&ly on an autogiro of the YG-lll t�e ..

The magnitude of the accidental errors ia ind.ies.ted by

the scatter 01.' the experimental points on fi�>ures land 2 ..

In interpreting this scatter it must be remembered toot· a

lateral tr�uinion moment of 20 foot-pounds corresponds to a

1.atera.1 stick foree of only 2 pounds.. Jiost or the test

records stt.ov;ed third harmonic variations of' sticlc. force having

an an:;,lit-;...1.de of several pounds ., and man:y also showed non-

1:,eriodic variations of' stick i'orce probably traceable to custs.

'The :pilot co:i:nrae1."1ted r,:,articularly on tl:i.e difficulty of holding

' the autogiro ,steady· in the lc.w:-speed g:tides ., where the most

seri0us discrepancies occur.

The consistent differences shown between moments in glides

and in level flight on fi6,ire 3 are believed to be indicative

of the effect of the propeller slipstreruu on the rotor ..

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Control positions, expressed in terms of the tilt

an0les of the hub relative to the fuselt;L,ge reference axes

are shov,n in figures 4 and 5o

Lane;ley r.:emorial Aeronautical Laboratory., IJ.ationa.l .Advisory Co.mmittee fo:r Aeronautics,

Lansley Field, Vao, November 15t 19390

/-�J�h. Frederick Jo Bailey, /;.,a

A�sistru.1.t Aeronautical E11t;lneer �

Ay.:proved:

HE

Elton w .. Eiller, r:r·incipal J,�echa.nical l'.;n[;ineere

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