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TECHNICAL HOTES
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,- September 1942 ....,.y....
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NATIONAL AD~ZSORY COMMITTEE FOR A15R-0,N”ktiTICS
--
TECHNICAL NOTE NO, 863 -. T=
. .-
.- .-
— -- - . . _
SUMMARY . ..-.
.
I’or several years the National Advisory Committee for .
Aeronautics has b~en conducting an inve6tigition o.f”the
— —-
landing chara~teristics of re~.resentative azrplanes Wi-tih
-----
particular reference to the problem of landi”ng”-gear desfgn. —.
Results of this investigation, which has included aii--- ‘-
. planes ranging in groes weight from approximately 1000 to
50,000 pounds and in spari from 2R. to 149 feet, a??e pre-
sented. SoIEe blind landings,. and also day” and night sery-
ice landings, were included in the program. The coiidi- -
tions imp-osed upon an airplane during a landing, as-di*er-
mined from experience with the 21 airplanes tested, arid.
the ground reactions produced. as a result of these ‘“Z-a-ri-
.
ding conditions are also outlined and discussed. . . . “%”
. ....+ .. .-
~----
.-.+. -=.
—. The maximum vertical velocities attairie~ by the air-
,-.. planes in conventional landings ranged as ‘nigh as 10 feet
e
.?___
per second “for the lighter airplanes an”d=diminished. as
... . _:.-
the airplane weight increased until a value of about. 5“---
feet per se”cond ;as encountered with the large”st airplanes.
In ll~nd landings, vertical velocities .as high as 13 .f”eet .._-
per second were obtained. On the Basis of the dqta- for ‘-’
all the landings, a vertical velocity of 2 or” 3 feet pOY-” -.. ...... ....
second may be termed a *lnormallt conventional landing v6- ---- ...-.
.——
locity fo,r all the aj.rplanes tested.
... ........ . :-... _l . ,
.
The aerodynamic support of the wings at the instant
of ground contact, which ranged from 0.6 to 1.0 ‘ti.ties”the’ ““-
airplane weight, was subtracted from the total airplane ,
vertical load factor in or~er to obtain the landing-gear -:..
vertical load factor. The Ianding+gear” maximum--v5&t~cal “--- - ‘-’“-
load factors for conventional landinrgs ~-p-p-roacheda v~lu~” - “’-’:-”
of 4 for the lighter airplanes and a value of- 1- ?o~-t”he - - “-
heavier airplane:. For hli.nd landings wit’h two of”the” ““
heaviast airplanes, a iandin&-ge”ar: ve2r2tiaal load factor - ------ ‘--
of about 2.was experience~, Based upon ‘a”cong”ider~tidn ..
of all ~he land~ngs, a l“anding~gear- ‘vertical load factor
of 1 may be termed normal for conventi-on”al la’fi~ings with --
all t’he airplanes tested. .— . . ,-
-::._-..-.- ;~.
=..
.
. . .
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* ,.+ .,-
,...
,
2 NACA Technic~l ‘N”ote No.”863
,,
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As the loads produced due to a landing impact under
any given set of landi,ng conditions depend upon the de-
sign of ,the shock-absorbing equipment, it is suggested .
that landing-gear design” be directeid toward the produc- ●
INTRODUCTION ..... .
.
NACA Technical Note No. 863 “3
.
3ecause the loading of the airplane for a given land-
ing depends considerably u~on.the characteristics of the
●
‘landing gear, it apyears most logical”to %ase landing-gear
w design upon lan~in-g conditions. Landing condition-s ‘were
.—
therefore given as much attention in” the investigation as ..
. loading conditions. : .-- — .
..=_=._. , -+
a
.
NACA Technical No.te,Eo. 863 5
Attitude angle
(deg)
.
VerticatieZOcity. - The maximum vertical Velocity. at
impact recorded fo,r each of the airplanes tieste,dis Plot- .
ted againsi airplane weight in figure 1. The numbers cor- .
respond to the order in which the airplane& are listed in
table II, which also gives the ~umber of landings for
each airplane. For most of the airplanes, attempte were
made to sectire as high vertical velocities ae possible)
the ,pllo,t!s judgment being ac.cepted-aq t? whether the a$r-
p~ane could withstand further shock. Because the test
pilots did attempt to cover a large ran~e Of tYPe5 of
landing and because they were all experienced, the manY ‘/
landings pre~i.ously.made by these pilots serve as a Sta-
tistical background”?or figure 1. Landing records of some
100 day and night service landings .with airplane 132 dur-
ing which the pflots were unaware that they were under ob-
servation, did not produce any data that would affect fig-
ure 1.
.
NAOA “Technical Note No. 863 7
““
8 NACA Technical’ Note Nom 863
.
.
For the airplanes equippg~ with tricycle-type land-
ing gear, difficu~ties were encountered in making a noOe-
wheel-first landing with the two airplanes tested and .
only one such landing was obtained, but the possibilities
of obtaining this type of landing might have been in-
creased had the pilots been more familiar with tricycle. ●
.
NACA Technicai Note No. 863 -9
*‘*
s Vertical loads, main and nose wheels.- The —ratio
.
the maximum vertical impact force on the landing gear
corded for each of the airplanes tested to the weight
the airplane as flown has been plotted against the verti-
cal velocity at contact in figure 2(a). (Symbols used on
the figures in this paper are defined in the appendix-)
.-
.
.
NACA Technical Dot”e No. 863
I
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NACA Techntcal Note No. 863 11
.
. —
.
.
?h.ack-
,.
‘ ..“)
,-
where ,
.
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“.
NACA Technical Note No. 863 -“13
.
Iw moment of inertia of wheel, slug-feet square
●
—
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14 NACA Technical Note No. 863
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normally withholds application of the brakes pending the
results of the initial shock. The calculated values of
the coefficient of fri~tion ffir various landings indicated ●
CONCLUSIONS
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●
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APPENDIX
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CALCULATION OF GROUND REACTIONS
Syrlb 01 s
b
ax
oomponent of recorded acceleration at center
~ of gravity that is parallel to ground (pOsi-
tive rearward)
—
—
ar resultant acceleration
[(_
ax
~
a+aza~
~ )J . ..- .
. Zero subscripts are employed to indicate the ac-
celerations at the instant of the first ground oontact.
*
. to instant of first ground contact
—-
1 At~ time interval elapsing between first ground con-
tact atid attainment of maximum verti6”aI ac-
celeration (also referred to as !~equivalent
quarter-period” of impact)
f
&tx t’ime interval elapsing between first ground con-
tact a’nd attainment of maximum horizontal ac-
celeration
.-,
1?WIJ$ UT3 and Tnv vertical forces on main wheels,
tail wheel, and nose wheel, respectively
(positive upward). Note that Fwv is sum,
of’ main-wheel forces
18 VACA Technical Note No. 863
F= = (ax - ax )W (2a)
g g go
&
In this
equation it is assumed that the rotational ,
moment of of the tail wheel is so small that the
inertia
horizontal component of the tail-wheel load Is negligible.
The vertioql force on the tail is given by
Yt = Fz - Fwv (5)
P g
Fz Xn- Fx z - Iy,~
F= (6)
Wv Xw + Xn -.
——
F = Ez - rwv (7)
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NACA Technical Note No. 863 21
.
REFERENCE
.
—
%
.
uoteNo.86Z
IAOA ‘Seo3nioal 22
.
,
.
J+ ..
aii g
Is
—
.
Num- Airplane Number Vertl- Eorl Re- Attl- Normal Longl-
b~r cal zmntal corded tude accel- tucllnal
● la%- veloc- veloo- air- of erationaccel-
illgs lty Lty speed thrust eration
☛
axis
Piper Cub J3L-50 15
!
▼
: Tayloror%ftBC-6
3 Aeronoa 65-C ::
4 B%llanoa 14-9
5 Stinson 105 z
6 ~nd Y-1 25
7 Boeing P-26A 16 x
Boeing YP-29A 30 x
: NorthAmerican 20 x
Bt-9A
10 Curtlss 12 x
XF13C-3
11 ConsolMated 18 x
PB-2
12 Chenoe-Vought 11
●
13 1Cu%%%36A
✎ lZ x x x
14 Chanoe-Vought 45
SB2U-2
15 Northrop A-17A 22 x
✎ 16 Douglas Dolphln 18 x
OA-4A
17 Lockheed 14-H 6
✎
18 Douglas DC-3 x
19 Douglas B-18 : x
2Douglas B-18A 111 x
20 ~~:$ :3-:
4: x
✌✌
21 Boeing B-15 14
3Service land-
2B11.ndlanding.
.
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YAOA Toobniod lfOtO MO. 863 rigs. l,a
‘Is
12 +2()
I
f ~ 05 ~;‘%,+ ‘\ 0 Convenfkqo/ Ion ding”
+ Blho’ fmdmg
\
oI
~ %9
.&?
* a6 0/6
r 0/. .7 ,.f9
Hu . ,=
\
I I
#’
t12{
=! 0/2
2 0,7
0 5 /0 15 20 25 90 35 40 exfo~
Airpfom weigh+as flown, lb ----
Figure1.- Muimm vertiod velocities experlenod by airpl=ee during lsmdingtests.
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. NACA Technical Mote Ho. 863 Flga. 3,4
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Ttme,sec “/ .-=:
Figure 3.- Linearacceleration
experienced
In a typicallanding.
t
o Conveniio@ landing
+ Blind.landing
X ToxyIn9
+ 2021
X17
f5 x 20
2{
of7 0 20
—
8 10 20 30 40XD:
hfiasflown,lb