This note contains photos and descriptions of airplane flight apparatus for use in conjunction with a recording galvanometer. In measuring the angle of attack a variable resistance is used, being controlled by a vane in the airstream. Thus it is only necessary to measure the change of resistance

Reid, H J E

English

NASA Technical Reports Server

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F\LE CQP'1 
NO. l J 
TECHNI CAL NOTSS 
NATION.\L ADVISORY COMMITTEE FOR AERONAUTI CS. 
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No . 156 
THE N.f\..C . A. RECORDING TACHOMETER 
AND ANGLE OF ATTACK RECORDER 
By H. J. E. Reid) 
Langley lvlemorial Aeronautical Lcboratory . 
ru~ 
August , 1923. 
copy 
, be returned / 
~ i1es of the Natl0 
Advisory Committee. 
for Aeronautics I 
Washington, D. ~ 
..... 
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https://ntrs.nasa.gov/search.jsp?R=19930080934 2020-03-17T04:14:21+00:00Z
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS . 
TECHNICAL NOTE NO. 156. 
THE N. A.O.A. REOORDING TAOHOMETER 
AND ANGLE OF ATTAOK REOORDER. 
By H. J. E. Reid. 
This note contains photographs and descriptions of ai rpl ane 
flight apparatus fo r use in conjunction with a recording galva-
nometer employed for obtaining c'ontinuous records of angle of at--
tack and engine speeds. In measuring the angle of attack a var-
iable resi stance is used, being controlled by a vane in the air 
stream. Thus it is only necessary to measu r e the change of re-
sistance . 
In the case of the tachometer , a rotary switch mounted on 
the engine connects a pair of condensers alternately to a bat-
tery and to the recording galvanometer) which is arranged so that 
its deflection is a measure of the rate of discharges through the 
latter. 
Oontroller for Angle of Attack Reco rder. 
Inasmuch as a recording galvanometer* was already in use , it 
was desirable to make use of apparatus electrically operated The 
principle involves a controller consisting of a movable vane fas-
tened to a variable resistance connected through conveni ent cables 
to a Wheatstone bridge in the recorder. The change of resistance 
in the controller thus causes a change in galvanometer deflection 
* N.A . O. A. Technical Note No. 150 - The N.A.O.A. Oontrol Force 
Recorder. 
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~hich is recorded photographically. 
Fig. 1 shows the angle of attack vane and controlling mechan-
ism, while Fi g . 2 Si10VlS t he wiring diagram. 'I'he controller con-
sists of a vane D connected to a rolling contact C on the re-
sistance A. The l at ter fo r ms ~ith the t wo resistances K1 and 
K2 , t wo a rms of the ~heatstone bridge so that any movement of the 
vane changes the r a tio of these a rms and causes a corresponding 
movement of the galvanome ter mirror . The re s istances are so pro-
portioned that the galvanometer deflection varies as the angular 
movement of the vane and thus as the angle of attack of the air-
pl ane. The controller, which may be mounted in various pos i tions 
on the a irpl ane by means of p roper at tachmen ts, is connected elec-
trical ly to the reco rder by a cable which may be p lugged into a 
sp eci a l three contact bayo net socket E. In order to change the 
sensitivity of the apparatus , variable resistances a re provided 
within the recorder and the r ange may be adjusted by means of the 
collar F on the vane. In practice the appa~atu s is calibr ated 
in place with the a id of a level-pro tractor , the angular position 
of the vane with reference to some known line on the airplane being 
a measure of the displaceMent on the record. Thus, if all dis-
placements on the film are referr ed to a base l ine, future records 
may be scaled off and plotted directly . 
Recording Tachometer- Controller. 
In this mechanism a somewhat different principle is employed 
bu t t he same recording galvanometer i s used . Fig . 3 shows the 
- 3 -
commutator, and Fig. 4 its cross-section and t i.1e wiring di agram. 
The operation of the apparatus is quite simple . There are t wo 
condenser s alternately cha rged and discharged by me~ns of a rot-
ary switch or commutator 1Vhich connects each, first -to the bat-
tery and then to the galvanometer whose deflection i s p ropor-
tional to the rate of the discharges . Si~ce the peTiod of the 
galvanometer is such that for a commutator R.P . M. of 100 or mo re , 
the record is a sn;ooth linp, and not affected by the individual 
dischar ges , it is clear that the greater the number of dis-
charges per second the greater tt.e deflection. In uractice, the 
controller is screwed to the t achometer connection on the engine 
and cables run from the bayonet sockets to t he condensers and 
recorder . As ordinarily ~sed the commutator i s driven a t one-
half the engine speed so i t i s only necessary to obtain a labor-
atory calibration, which serves to plot t he true speeds as t aken 
from the records in fli ght. 
At present , both controllers a re used with t wo of the galva-
nometers of the control fo rce recorder . There is be ing built, 
however , an instrument dri ven by an electric i mpulse motor* and 
housing the two galvanometers for these controllers . ~hen the 
recorder is complete, the whole apparatus will be light and con-
venient to install , and will add considerabl y to the information 
obtainable by means of recording instruments. 
* N. A. C.A. Technica l Note No . 157 - An I mpul se iotor for Driving 
Recording Instruments. 
Fi g . 
.. 
1 
Angl o of attack vane 
nil controll ing 
mech nism. 
FiG' 3 
COIJlIliU td. tor 
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Fi g . 2 
firing iagr arn 
Fig. 4 
Cross-sec tion 
or oon;mutator 
and "i ring 
di9.cr a.m. 
11059 IlS 


The N.A.C.A. Recording Tachometer and Angle of Attack Recorder

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