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Akron , Ohio
PRU.Il.'.I!IAF.Y REPO!lT
IZA :mr::m OF FO!lC 0 AIRSHIP 0 L DURING PASSAG Ttm01JGH All ARTIFICIAL GUST
The test stand used 11 that described in the report on Item 4&) of this contract.
The force1 were measured by mean• of a epeoial be.lanoe, which tho elonr;a-tion
of the suspension wiree under the loe.din{; by th~ •ir forcee a recorded by
means of diamond points aoratohing on a glaaa cylinder 1). Oil da1hpote were
added to the inatrumont de•oribed in 1) - one near eaoh suspension re - to
damp out vibl'!ltions vmich were caused mainly by the elasticity of the vmirling
arm. The model used in the teats we a l/75 aoalo model of tho USS AKRON and
CON, of espcoially light conetruction.
Teet Rosulta
So far only the lift forces ha Te been measured reliably. Th" drag force
reoords are not aatiafaotory beoauee the vibration• in this direotion haTe not
yot be on properly damped. Figures 3, 4, and 5 giTe typical reoorda , photographed
from the glass cylinder with a linear magnification of 25211.
The "front lift" ia the lift component at a point 9.7" in front of the attaohmont
point, the "rear lift" iB the component 9. 7" behind thie attachment
point. The attachmont point of the model to th~ arm is at 40.3 per cent of
the model' a length from tho front; the front lift ii then t! e lift oompanent
at 40.5 per cent from the front, ahead of the hull'• oontor of' buoyanoy; the
rear lift is tho oomponent at 66.1 per oent from the front, aomewhat behind
the oontor of buoyanoy. The oonter of buoyancy ia assumed at 45.7 per oent,
llS in l!ACA Report No 394.
The aotual f'orcos ar deter::dned from these re eloni;aticm reoorda by "'""
of calibl'!ltion curves. The oalibratione consisted of eta tic lea.din{; of' the
model at wrioue points of its length, and of' dynamio calibration. The dynamio
oalibration ooneiated of' l'!lpidly ohangini; loo.de applied to the model by mos.na
of a "1re oonneoted to a orankehaft.
The normal forces and the pitohiJlb momenta were oomputed from the foroo r eoorda
taken from the glaae oylindera. The foroe and moment coefficients for zero
pitch an;::le during the undisturbed !'light are proocnted hero aa a funotion of
relatiTe aitions of tho "1odel in the artificial gust.
The coefficient• are defined ao
llhore JI • norCBl force
Mp• pitching moment about center of buoyancy at 46.7 per oent
1) See Publication No 3, Guggenheim Airship Institute, p 128.
(. -1
.-,~~~-~~~~-~'"'=F ............... ~~ ......
Akron, Ohio
-2- ? • density of air
v = otraight flight velocity of model (in the tests presented
in this preliminary report, v = 12 ni/sec).
For comparison, there are also indicated "theoretical11 force and moment ooefficients.
These forces !'or the bare hull 11re computed aocordinr; to a generalized
Munk formula*:
where vn = local gust velocity normal to undisturbed flight direction
(in this prelimi=ry report Vn = 4.2 ni/sec)
S =- local cross-sectional area of airship hull
x = longitudinal length coordinate.
Figure 10 gives the distribution of vn and dvx/dx in the artificial gust.
J<'igure 9 shows the distribution of the theor<>tical dN/dx over tho ship's length
for variouE- positions of the bare hull in the gust. The "theoretioo.111 forces
on the hull .vi th fins are defined as the theoretical forces on the bare hull,
plus the dii'ference between moment and force coefficients on AKRON-llACON models
with and vtithout fins, measured in the California Institute of Technology wind
tunnel.
!lo attempt has been made here to e stil:!ate theoretically the fin forces acting
while the fins are in the gust transition zone.
A discussion of these results will be given in the final report, after the
measurements of the force tests at other pitch angles and gust velocities have
been evaluated.
Tho accuro.oy of the tests is estimated to be such that the error in the moment
coefficients is not greater than ten per cent.
6-15-37
TT: li'
* This same formula was used by Dr v. KS.rm.l.n in the theoretical investigation
of airship movement under the influence of gusts, presented in the Durand
report.
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