This investigation was carried out by the National Advisory Committee at Langley Field for the purpose of determining the adaptability of the camera obscura to the securing of turning characteristics of airships, and also of obtaining some of those characteristics of the C-7 airship. The method consisted in flying the airship in circling flight over a camera obscura and photographing it at known time intervals. The results show that the method used is highly satisfactory and that for the particular maneuver employed the turning diameter is 1,240 feet, corresponding to a turning coefficient of 6.4, and that the position of zero angle of yaw is at the nose of the airship

Crowley, J W , Jr

Freeman, R G

English

NASA Technical Reports Server

NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 
REPORT No. 208 
DETERMINATION OF TURNING CHARACTERISTICS 
OF AN AIRSHIP BY MEANS OF 
A CAMERA OBSCURA 
By J. W. CROWLEY, Jr., and R. G. FREEMAN 
Tij~ ALES OF 
R'l COMMIn:EE FOR AERONAUn~ limO AL X GLEV AE AUTlC~L LAIJ )RATOf\ 
:::GLEY FIELD, ~ ~ON. V'RGINI~ 
ATIOHAL AOVt§(}K( 6mdMIffE€ ron f~BrJ~UfI~ 
J,S12 H STRUT, If, 'II, 
~IHGT,* 21, (1,6, 
WASHINGTON 
GOVERNMENT PRINTING OFFICE 
1925 
https://ntrs.nasa.gov/search.jsp?R=19930091274 2020-06-17T04:44:55+00:00Z
AERONAUTICAL SYMBOLS. 
1. FUNDAMENTAL AND DERIVED UNITS. 
Metric. English. 
Symbol. 1-------------------.-------1----------------,-----------1 
Length .. . 
Time ... .. 
Force ... . 
t 
]i' 
Unit. 
meter ...... . .............. . 
second .................... . 
weight of one kilogram .. ... . 
Symbol. 
m. 
sec. 
kg. 
Unit. Symbol. 
I 
foot (or mile) ........... ft. (or mi.). 
second (or hour) ..... " sec. (or hr.). 
weight of one pound. . .. lb. 
Power... P kg.m/sec .......... .... ................ horsepower .............. IP 
Speed .............. m/sec ...................... m. p. s. mi/hr ................... M. P. H. 
I 
2. GENERAL SYMBOLS, ETC. 
Weight, W=mg. 
Standard acceleration of gravity, 
g= 9.806m/sec.2 = 32.172ft/sec.2 
W Mass m=-
, g 
Density (mass per unit vOlume), P 
Standard density of dry air, 0.1247 (kg.-m.-
sec.) at 15.6°C. and 760 mm. = 0.00237 (1b.-
ft.-sec.) 
Specific weight of "standard" air, 1.223 kg/m.s 
= 0.07635 lb/ft.s 
Moment of inertia, mk2 (indicate axis of the 
radius of gyration, k, by proper subscript). 
Area, S; wing area, Sw, etc. 
Gap,G 
Span, b; chord length, c. 
Aspect ratio = b/c 
Distance from c. g. to elevator hinge,j. 
Coefficien t of viRcosi ty, jJ.. 
3. AERODYNAMICAL SYMBOLS. 
True airspeed, V 
Dynamic (or impact) pressure, q=i p p 
Lift, L; absolute coefficient Q= q~ 
Drag, D; absolute coefficient OD= DS q . 
Cross-wind force, 0; absolute coefficient 
o 
Oc=qS' 
Resultant force, R 
(Note that these coefficients are twice as 
large as the old coefficients Lo, Do.) 
Angle of setting of wings (relative to thrust 
line), iw 
Angle of stabilizer setting with reference to 
thrus t line i. 
Dihedral angle, 'Y 
Reynolds Number = p Vl, where l is a linear di-
M 
mension. 
e. g., for a model airfoil 3 in. chord, 100 mi/hr., 
normal pressure, O°C: 255,000 and at 15.6°C, 
230,000; 
or for a model of 10 cm. chord, 40 m/sec., 
corresponding numbers are 299,000 and 
270,000. 
Center of pressure coefficient (ratio of distance 
of C. P. from leading edge to chord length), 
Op. 
Angle of stabilizer setting with reference to 
lower wing. (it-iw) = {3 
Angle of attack, ex 
Angle of downwash, E 
----~---
• 
REPORT No. 208 
DETERMINATION OF TURNING CHARACTERISTICS 
OF AN AIRSHIP BY MEANS OF 
995-25t 
A CAMERA OBSCURA 
By J. W. CROWLEY, Jr., and R. G. FREEMAN 
Langley Memorial Aeronautical Laboratory 
• 
ADDITIONAL COPIES 
OF THIS PUBLICATION MAY BE PROCURED FROM 
THE St:PERINTENDENT OF DOCUM El'TS 
GOVERNM ENT ]'RINTING OFFICE 
WASDJNGTON, D. C. 
AT 
IO C~:NT' PER COpy 
REPORT No. 208 
DETERMINATION OF TURNING CHARACTERISTICS OF AN AIRSHIP 
BY MEANS OF A CAMERA OBSCURA 
By J. \V. CnOWLEY, In., and R. G. FUEEMAN 
SUMMARY 
This investigation was carried out b)T the rational Advisory Committee for Aeronautics 
at Langley Field for the purpo e of determining the a lap tab ili ty of the camera obseura to the 
securing of turning characteri tics of airships, and also of obtaining som of tho e character-
istics of the (' 7 airship. The method con i ted in I1ying the airship in circling flight over a 
camera obscura and photographing it at known time intervals. The results show that the 
method used i hio-hly atisfactory and that for the particular maneuver employed the turning 
diameter is 1,240 feet, corresponding to a turning coefficient of 6.4, and that the position of 
zero angle of yaw is at the nose of the airship. 
INTRODUCTIO 
At the present time there are apparently no data taken in flight of the turning character-
istics of a nonrigid air hip . However, there are data available on rigid air hip but aequi ition 
of the arne wa by method admittedly deficient in accuracy. It wa with the view of estab-
lishing a simple but precise method of obtaining the necessary data that the present investi-
gation was made. . 
REF ERE CES 
ll. & M. No. 537.-A Flight in Rigid Airship R- 26. By J. R. Pl\,nnell. 
ll. & M. o. 66 .- Experiments on Rigid Airship R- 33. By J. ll. Pannell and R. A. 
Frazer. 
ll. & M. ro. 12.- Expcriments on Rigid Airship R-32, Part II: Controllability and Turn-
ing Trial ' . By J. R. Pannell, R. A. Frazer, andH. Bateman. 
R . & M. No. 716.-The Application of the R(\'3ults of Experiments on Model Airship to 
Full- cale Turning. By R. Jones. 
R. & M. o. 675. Experiment on Rigid Airship R 39. By J. R. Pannell and A. H. 
Bell. 
METHODS A D APPARATUS 
The Nn,yy C 7 airship, stationed at the ayal Air tation, Hampton Road, was flown 
to Langley Field fol' the e te ts . 
The apparatus used was a camera obscum "with a special automatic hutter. The camera 
consisted of a light-light upper- to ~"y room with lLn op ning in the ceiling to accommodate a 
4 -inch focal-length lens. An object pa ing oYer the len threw an image on a lable below, 
which was covered with overlapping trips 01 photognLphic fi lm. (Fig. 1.) 
The shuLLer (Fig. 2) con istell of a IS-inch d iameter circular wooden frame A wilh a 5-inch 
circular opening B eccentl'icallY' loctLted, two flat metal eli ks, 15-inch diameter, coaxial with A 
(one shown at C), and a cOllslant- p cd moLor D. The ('onstant- ' peed molor, mounted on the 
top 01 th wooden frame, drove, through worm and gearing, the two metal eli k which were 
3 
4 REPORT NATIONAL ADYI 'ORY UOMMIT'l'EE FOR AERO AUTICS 
/1 
/1 
II 
===~~L--,\ __ 
1/ 'Lens Roof 
mounted on the lower side of the frame. A rim on the 
circumference of the frame and proj ecting below it pro-
tected the revolving disks. The upper di k was pro-
vided with a radial lit E, which, traveling across the 
opening B in the frame, gave the requisite shutter action 
and made an exposure of about 0.01 econd duration. 
In order to prevent exce ive overlapping of pictures 
it was neces ary to make an exposure at not more 
than every fourth revolution of the slit. This \Va 
accomplished by mean of the lower disk (not shown 
in Fig. 2), in which a 60° sector was cu t away. 1 t 
was driven in the same direction, but at one-fourth 
the speed of the upper disk, and consequently Lhe 
opening in the two cam together at every fourth rC\'T-
olu tion of the lit. In thi manner exposure of 0.01 
sccond were obtained ev ry 3.64 econds. 
1/ 
1/ /1 
Tobie 
In u e the shutLer wa provided with a liD'hL-
Light fabric attached a shown in Figure 2. It was 
placed flat on the table and the fabric loosely pread 
o a to completely envelop the table top and film. 
The lens wa uncover ed and the shutter moved 0 a 
to catch and keep the image in the circular opeuinD'. 
In accordance wi th prearranged procedure the 
air hip made a preliminary low-speed run acro s th 
camera ob cura for focu ing pUI·pOS~s. This aCC0111-
FIG. I.-A vertical section through the camera obscura ph hed, two duplicate circling £lights were made over 
the camera, from which the data were obtained. The 
camera was approached from up-wind at a con tant barometric altitude of approximately 3,000 
feet with engines turning at 1,000 revolutions p er minute. Ju t before entering the camera 
field the rudder was thrown hard over to starboard and the ship tUI'ned to the right, acro 
wind and over the camera. On each run photographs were made for approximately a 90° turn. 
Before the first run an altitude-velocity chart was obtained by means of pilot balloon 
a.nd a theodolite. A wind velocity of 14.3 miles per hour, northwe t, was indicated at 3,000 
feet. 
FIG. 2.-AulolllOlic shuller for cnlOCfIl Ohscufa 
IlETERMJ 'ATLON OLe TUR 'INU Cf[ARA("I'I~RISTIC,' OF A AlH~IIJP 5 
Feef 
c ~ ~ § 2 ~ ~ 
I , , II I , II ! I I " ! 1 ! II II ! , 1 t I , 1 ! 1 I 
FIG. 5.-(Will(l correl'lion per exposure is 70.iiG ft., corresponding to the wino velocity of 14.3 r. P. IT.) 
~ -
------~- ~ 
Zero position 
Feet 
c ~ g ~ g ~ g 
- .- ~ ~ ~ LU_U_LU! t J I , I I tit' ! I I I I , I I I I , I 
C.B. 
FlO. O.-(\\,in<1 ('Or!' clion per exposure is 76.56 ft., corresponding to tbe wind velocity of 14.3 M . P. H.) 
Wind 
-
6 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 
REDUCTIO OF DATA 
For the purpose of working up the data, the developed film was laid out over a sheet of 
paper, and the trips arranged a in the camera obscura. The no e and tail of each succe -
sive position were located by pin prick and the film removed. As shown in Figure 5 and 6, 
the prick points were connected by a solid line, with an arrowhead indicating the nose of the 
ship in each case. The center of buoyancy of the ship was located on each line and smooth 
curves representing the actual path of the points with r eference to the ground were drawn 
through the center of buoyancy, the nose, and the tail. In order to deduce the path of the 
ship in still air from the above curves it was necessary to correct for the wind componen t. 
FIG. 4.-Dingram showing method oflaying out data 
The scale of the drawing was determined through the r elation of the length of the image to the 
length of the hip. From the wind velocity and the scale of the drawing a vector repre enting 
the wind displacement per exposure was determined. Each po ition of the ship wa then 
corrected for the wind di placement and the curves drawn a before. Thi procedure i illus-
trated in Figure 4. From these latter curves were obtained the in tantaneous radii, the posi-
tion of zero angle of yaw, the angle turn ed through, and, the time between exposures b eing 
known, the velocity of the air hip (Fig::;. 5 and 6) . The e have been plotted in Figure 7. 
The focal length of the lens and the r elation of length of the ship to length of the image 
being known , the geolll eLric alti tude was determined for each run. 
DETERMINATIO ~ OF TURNING CHARACTERI Tl('S OF AN AIRR11IP 7 
25° 
20· 
~ 
~/5° 
.... 
o 
<II 
'&-.10° 
t 
" 
0° 
.... 800 
<II 
~ 
.!; 700 
(/) 
.::> 
~ 
~600 o 
/ 
Run 
oj ~ 
0 0 
~ ~ Q] 
'ti 'ti 
.{J ci) 
'\ V 
.......... 
-/3' 
r 
/1 
/ 
1/ 
- ..!!. 
4 8 
I. 
oj 
0 
~ 
<II 
:t 
'<t 
/ 
7 
--12 
oj 
0 
~ 
<II 
:E 
lI) 
7 
V 
,... 
16 
25° 
20° 
~ 
~/5° 
..... 
o 
t, 10° 
t 
<>:: 
5° 
0° 
Run c. 
!Ii oj ~ 0 0 
Q. ~ ~ l( 
<II Q] Q] 
'ti 'ti :E 
.{J ~ '<t 
-~ V 
/1 ' ""- ? 
V 
!y-' 
/3 / 
/ 
1/ 
V ,...... ~ ./ 
4 8 12 
~ oj 
0 0 
~ ~ 
<II <II 
~ ~ 
lI) <0 
/' 
/ 
r.... 
""- ~ 
7 
........ 
':I... 
I 
16 
v 
~ 
20 
E 
o 
40.}. 
t 
::> 
20 ..... 
(/) 
Q] 
t 
O~ 
Tt"me t"n seconds Time in seconds 
V - Velocify of a poin! on fhe nose /3 '- Angle of yow of the foil J3 - Angle of yow at fhe C.B. 
R - RadIus of furn C - Degrees furn from first position 
FIG. 7 
RESULTS 
The re ults of the two circling flights are contained in Table II and FigUTe 7. It i evident 
that exposure o. 6 in Run 2 (Fig. 7) was obtained when the air hip wa coming out of a turn 
and for that reason the instantaneous radiu of that position wa not used in compu ting the 
R - Insfan!aneous rod/us 
(3 - True angle of yow C - Angle of furn 
/3'- Angle of yow at toil 
FlO. a.-Diagram showing angles measured 
diameter of the turning circle. The turning diameter 
for the first run wa 1,240 feet, corresponding to a 
. . (diameter of circle) turnmg coefficlCnt -1 th f . hi of 6.4, and for 
eng 0 mrs p 
the second run wa 1,275 feet, corre ponding to 6.5. 
Both tUTns were very teady, the ma.'{imum variation 
in radius being 41 feet in Run 2. The steadiness of 
the turn is indicated very well hy the loci of the in-
tantaneous center in FigUTe 5 and 6. 
The outstanding featUTe of the investigation wa 
the determination that the position of zero angle of 
yaw was at the nose of the airship in all ca es; i. e., 
the axi of the air hip was tangent to the path at the 
no e. The di tance between the center of huoyancy 
and the po ition of zero anO"le of yaw i R ine {3 (Fig. 3) 
and for mall values of {3, such as encountered here, i 
R{3. This point coming at the nose in all cases seems to 
indicate that the product R{3 = con tant and agrees in 
this re pect with re ult previously determined.' How-
ever, this may be considered a a check on the pre-
vious work only to a very limited extent, ina much a 
the tUTns inve tigated here were so similar in nature 
that no general conclu ions can be drawn from them. 
CO CLUSIO S 
Thi method i a very accurate and imple means of determining turning characteristics 
of an air hip. The advantage over the method previously used, that of ohtaining the data 
from the hip itself, aro obvious. The data arc all recorded imultaneously with the exception 
1 R. & M. No. 716. 
8 REPOHT NATlONAL ADVISORY COMMITTEE FOR AERONAUTICS 
of the rudder angle and engine revolutions per minute, and reading of the latter, Laken in 
flight, can ea ily be ynchronizecl with the data obtained on the ground. In thi particular 
experiment the rudder position was hown on orne of the photographs, but, due to lighting 
conditions and the fact that there wa no contra t between Lhe color of the envelope and the 
rudder, it was not shown in all ca es. For further work of this nature the lower edge of tbe 
rudder should be painted orne color contra ting with that of the body. If it were de ired to 
maintain a constant rudder angle at all time it could be accomplished by means of a Telauto-
graph instrument, which measur the angle of a control surface and electrically communi-
cates the values to a visible indicating instrument in the cockpit. By manipulating Lhe rudder 
wheel to keep this reading con tant a constant rudder setting would be obtained. 
It would be of great advantage in future te t to have radio communication between the 
ship and the ground in order to direct the operation of the air hip and to synchronize data. A 
narrow-angle len ,,'a u ed in these experiment but one with a wide field would be preferable. 
Thi would enable complete turn to be recorded without flying at exce ive altitudes or requiring 
elaborate piloting of t.he ship over a certain point. 
This method ha proved 0 satisfactory that it i recommended that more work I the 
same nat.ure in th(' form of <1, compl(,l(, invc t.igation of the turning charactNi tic of an ail hip 
be undertaken. With a few slight modifLcations in the shutter the method is adaptable als(1 
to investigating manellv('rabili ty of an airplane. 
TABLE I 
OBSERVED DATA 
Run 1 
Engine revolutions per minutc ____ 
r 
_____ 1,000 __ _______ ________ ________ _________ 1,000. 
Run 2 
Barometric alti tude _____ ___ ____________ _ 2,900 fe~L ___________________________ _ , 3,000 feel. 
Wind velocity ________ _____________ . __ _ 14.3 miles per bOUL ______ ._. ________ __ 14.3 miles pcr hour. 
Focal length of len5 _____________________ 4S inches __ ____ __ _ __________ _________ 48 inches. 
Time between exposures __ ___ ________ ___ 3.64 seconds _________________________ _ 3.64 seconds. 
Lengtb of image __________ ___________ _ 3.25 inches _______ • _________________ __ 3.12 inches. 
Lengtb of airship___ ______ _ _____ ___ ___ 195 feet. _______ . ______ : ____________ . _ 195 feet. 
Location of C. B. from nose ___ _____ _____ 85 feeL _________________ • _______ ____ ___ 85 feet 
COMPUTED DATA 
Run 1 Run 2 
I--
Geometric altitude _________________ _ _ 19~.~5 4 =2, 0 feeL __ ___ ___ • ______ _ 1 9~.?2 4 =3,000 fect. 
Scaleofd isplacem~ntdrawing -- _______ /9151-linch=175feeL __ ___ _ . ________ _ /9~_1 inch=191 fecL 
Wind component (p~r exposu re) __ _ ___ J4.3X~X3.64=76.4 fect. ____________ ___ \ 76.4 fect. 
TABLE II 
RESULTS-RUN 1 
Position 0 
-----
Instantancous mdius ( f~ I) 
--- ----------------
f,2fi l'i2fl 64 1 f,1l f,29 
Angleof yaw at tai l (degrees) : - -
------- ---
- -
17 . .1 17 .. 1 17. 2 17.8 17. ~ 
A ngle of yaw at ('. O. (rlegrc~s) 8 7.8 
Angle of turn (degrees) _ _ ___ _ _ . . _ _ _ 0 I ~7 
Length of arc b~twecn successi,-c positions (degrees) ______ 211. 196 
Velocity (mean), bctweeu successive positions (foot/sec.) ___ _ .18. I 53. 
'J' . . rr' t _mean diameter of turning circ le - 64 f R 1 UI mng coe IClen s - -- lcngth of airsbip . or un . 
RESUL'1' - RUN 2 
o 
Instantaneous radi us (feet) __ _________ ___ __________ _____ 643 
Angle of yaw at tail (degrees) __ _ __ ____ __ __________ _______ 17 
Angle of yaw at C. B. (degrees) __________ ____________ ___ 7.5 
Angle of turn (degrees) ____ ___ ___ _________ _ __________ ___ 0 
Length of arc between su cee ive .p ositio.ns (degrees) __ _____ __ _____ _ _ 
VelOCity (mean) , between successive pOSitIOns (foot/see.) ______ _____ _ 
1 -, 
644 618 
16. 17. 5 
7.45 
19. 5 
20 .5 
57.3 
36.5 
202 
55.7 
612 
17.5 
8 
56 
1 7 
51. 6 
T ' ffi' ts mean diam~tcr of turning circle 65 f R 2 
urnlDg coe Clen = -- length of ai rsbip - . or uu . 
o 
8. 1 7.9 
.1.1 73 
191. 4 1 6 
.12.6 51. 2 
---I 
663 
16.4 
7.4 
72 
I 5 
50.7 
841 
13 
5. 6 
8 
184 
50.5 
" 
620 
17.2 
7. 
01 
IM.6 
51. 2 
12 
5.1 
99 
184 
50.5 
Positive directions of axes and angles (forces and momenta) are shown by arrows. 
Aria. 
Force 
(parallel 
Sym- to axis) Designation. bol. symbol. 
Longitudinal .... X X 
Lateral. ........ Y Y 
Normal. ........ Z Z 
Absolute coefficients of moment 
Diameter, D 
Pitch (a) Aerodynamic pitch, pa 
(b) Effective pitch, pe 
(c) Mean geometric pitch, PK 
(d) Virtual pitch, pv 
(e) Standard pitch, ps 
Pitch ratio, p/D 
Inflow velocity, V' 
Slipstream velocity, V. 
Moment about axis. Angle. Velocities. 
Designa-
tion. 
rollin~ ..... 
pitc~ng ... 
yawmg ..... 
Linear 
Sym- Positive Designa- Sym- (comr,o-direc· Angular. bol. tion. tion. bol. nenta ong 
L 
M 
N 
axis). 
y~Z roll ..... ~ u p 
Z~X pitch .... s v q 
X~Y yaw ..... 'It w r 
Angle of set of control surface (relative to 
neutral position), o. (Indicate surface by 
proper subscript.) 
4. PROPELLER SYMBOLS. 
Thrust, T 
Torque, Q 
Power, P 
(If "coefficients" are introduced all units 
used must be consistent.) 
Efficiency 1] = T VIP 
Revolutions per sec., n; per min., N 
Effective helix angle <1>= tan- l (2:) 
5. NUMERICAL RELATIONS. 
1 IF = 76.04 kg. m/sec. = 550 lb. ft/sec. 
1 kg. m/sec. =0.01315 IP 
1 lb. = 0.45359 kg. 
1 kg. = 2.20462 lb. 
1 mi/hr. = 0.44704 m/sec. 
1m/sec. = 2.23693 mi/hr. 
1 mi. = 1609.35 m. = 5280 ft. 
I m. = 3.28083 ft. 
c 



Determination of Turning Characteristics of an Airship by Means of a Camera Obscura

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