Spinning of large airplanes


Material Information

Spinning of large airplanes
Alternate Title:
NACA wartime reports
Physical Description:
14, 1 p. : ill. ; 28 cm.
Seidman, Oscar
Langley Air Force Base (Va.) -- Langley Aeronautical Laboratory
United States -- National Advisory Committee for Aeronautics
Langley Memorial Aeronautical Laboratory
Place of Publication:
Langley Field, VA
Publication Date:


Subjects / Keywords:
Bombers   ( lcsh )
Transport planes   ( lcsh )
Aerodynamics -- Research   ( lcsh )
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )


Summary: Because large airplanes of the transport and bomber categories have been reported to have spun inadvertently, the available information on the subject has been reviewed. Results of model tests, as well as reports of full-scale-airplane spins, were considered. It is concluded that large airplanes should not be intentionally spun because these aircraft are not designed for the loads and speeds that may be encountered in the spin and recovery. If a large airplane is stalled, wither inadvertently or for familiarization purposes, the pilot should apply sufficient down elevator to relieve the stall at the very first sign of stalling. The throttles should be closed if the airplane has started to roll off into a turn and the nose has dropped appreciably. Even after the airplane has rolled off on a wing, the pilot can regain control by promptly moving the stick forward and then using all three controls to return t level flight.
Includes bibliographic references (p. 14).
Statement of Responsibility:
by Oscar Seidman.
General Note:
"Report no. L-96."
General Note:
"Originally issued October 1944 as Restricted Bulletin L4I07."
General Note:
"Report date October 1944."
General Note:
"NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were previously held under a security status but are now unclassified. Some of these reports were not technically edited. All have been reproduced without change in order to expedite general distribution."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003613597
oclc - 71225427
sobekcm - AA00006300_00001
System ID:

Full Text

RB No. L4I07


October 1944 as
Restricted Bulletin IAI07

By Oscar Seidman

Langley Memorial Aeronautical Laboratory
Langley Field, Va.


NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of
advance research results to an authorized group requiring them for the war effort. They were pre-
viously held under a security status but are now unclassified. Some of these reports were not tech-
nically edited. All have been reproduced without change in order to expedite general distribution.

L 96


IATA &- 7

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Digitized by the Internet Archive
in 2011 with funding from
University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundallon


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NACA RB No. 11107




By Oscar Seid.an


Because large airplanes of the transport and bomber
categories have been reported to have spun inadvertently,
the available information on the subject has been reviewed.
Results of model tests, as vell as reports of full-scale-
airolane spins, vere considered. It is concluded that
large airplanes should not be intentionally soun because
these aircraft are not designed for the loads and speeds
that nay be encountered in the spin ard recovery.

If a large airplane is stalled, either inadvertently
or for familiarization purposes, the pilot should apply
sufficient down elevator to relieve the stall at the very
first sigL. of stalling. The throttles should be closed
if the airplane has started to roll off into a turn and
the nose has dropped apprecisaly. Even after the airplane
has rolled off oin a v.ing, the pilot can regain control by
promptly moving the stick forward and then using all three
controls to return to level fliLht.

For recovery from fully developed inadvertent soins,
the rudder and wheel should be moved against the turn and,
about turn later, the control column should be moved
forward. In a spin while on instrument flight, the ball
bank indicator should not be relied upon to indicate the
proper direction in which to move the wheel or rudder,
but the rate-of-turn indicator should be used to deter-
mine the direction in which to move tha rudder and to
indicate when the rotation has stopped. The pull-out
from the recovery dive should be started promptly to
avoid building up excessive speed, but the pilot must be
careful not to pull out too rapidly as the airplane
might stall again or the structural loads might become
excessive. In a spin the pilot would probably encounter
difficulty in moving the controls and :miht have to make
use of the tabs and other booster devices; however, he
should be careful to avoid overcontrolling after spin

2 NACA 9B No. L4T07


Pilots who fly large airplanes tl-h is, trans'.:orts
and bombers have normally had no experience in spins
of such airplanes although these pilots will have bee3n
"checked out" in stalls. Their spin train;ln has been
obtained on small highly maneuverable air..l-:nc. Lrge
airplfr.es are not intentionally spun, ex:cet on r.ere
occasions, for reasons that will be p-p-Er-ent in the dis-
cussion to follow. Relatively little infor-mction is
generally available, therefore, on spin chrrctLristics
of the large aircraft.

Inasmuch as large airplanes have been insdve.rtntly
spun or have been in various stages of spin encry, pilots
are naturally interested in knowing what tc exncct if
their airpiane should get into a spin. T-e Safet:: '-reeu
of the Civil Aeronautics Board therefore requested trj't
the NACA make such information available and the present
report was prepared as a result of this request. The
information presented herein is considered cof interest
to both civil end military pilots.

The NACA has obtained a fair amount lof s.ts on the
spin characteristics from free-spinning tunr.el tests oi
models of lar--ge airplanes. The tunnel Fpro'ides a verti-
celly rising air stream in which the airp,.irne mdciel sins
entirely unsupported except by the air forces. Afte-
the model has been launched in a fully developed spin,
observations ere made of the effectiveness cf tnc c.T-
trols for recovery when they are operated by a rcrrot -
controlled mechanical pilot. Most of the .iiTssion of
spi.ninf in the present paper is based on results of
tunnel tests of about a dozen models. A llritel ,n-io.int
of actual flight data has been gathered f.:',r: pilots'
reports and from accident investigation.?. Fertinent
data on pilots' spin experiences ?-iv'e beni obtainred from
aircraft manufacturers, airlines, and the Iilitrry

Althou.-h the present report is prie al'i1;, intended
to cover spin characteristics, a brief discussion of
stellirii is also given. The discussion of st-11Ling is
largely based on the experiences of UAC~A to~t pilots.

The entire report has benefited fro:: zcug_-etionz
made by ,r. Melvin N. Gough, Chief T-st Pilot of the
NACA Langley i:'-morrial Aeronautical Labora:orv.'.



The large airplanes referred to are the prascnt-cay
convenitiond'-] monoplane transport, bomber, and multie.i!in.-
attack tyo's weighirng more than the arbitrurill;y elected
limit of 1o,000 pounds. These airplanes -Irc t:.o- or
four-ei i.ie types. As a result of tihe installation of
engines and other i tLr.i in the wings, the iistr.bution
of .na!s of th;-s i.niP-lrnes .s 'a CroiDp, as '. sured oD
the ilrplar,- e m.ment, of tinertia, is riweater alon-i the
wings than plon., th3 fusel-ige. 'h=- Douvl-s D1 is f-'.irlv
represent- tive of the cl-!,sE Elthoufgn it hTJr m're ..ass
alone the fisel.ge than alone t.L- wtin.;s. Pccaujt of their
intended uce, al1 tnrise a"rplsner are less nmrnelverahbl?
than and are not designed fcr as hi-n stru-.tural strmnith
as the smAller type, .

The airplanes for vh'ch 3n'n-tu.nnel-mr,-lel results
were Pnalyved inc]i;Jdedic 13 Ltrw-crin-rn and four-en-le
cesgnrs rj'Pinp in wvJight from 1&,0'0) poui.s to
120,000 poun's. Fev.3rtl of tn? twin-enoinc i rrt'Panes in
the sroup %:ere of the relatively more man-.eu,.'erbboe .eontat
types. All were conventional in appearance althcu-rh
twin-boorr tail arraiigemea-its ve-re included.



The sitject of stall charqcteristlcs is a much
broader subject thsn srinninr.g and has been covered ..-e-
vioisly in aeronauti-cal l'teratule. The st&ll zhara;-
teri.ti cs of large airpla:ies vsrj widely rn;ing different
specific designs as ao those of sr asler airplane?, 1he
st1l precedes the entry into a spin. In the worst c-se,
the stall ray result in a xioleijt rolling motion of w'lic:i
the pilot recet'es no advance warning eni -gainst which
the aileron control is coinplet.lS infffe-tive or even
detri-mentsl. Tn most cases the ailerons should not b"
used. If the control column is not pron-otly moved forward
a sufficient amount to install the wing, the wing-dropping
r.ay lead to a spiral, a spin, or a falling leaf. In most
stalls the aileron effectiveness will be reduced. .in
better stalls the rollin-' motion may be le-s violent and
advance notice may be given the pilot in the forr of rild


buffeting or control shake. For some airplanes no rolling
motion is involved and the airplane simply pitches nose
down after mild buffeting. An airplane that normally
stalls gently may show a violent stall under adverse
icing conditions. For most airplanes, the wing-dropping
will be more violent with power on than with power off.
The stall in the landing condition (gear and flaps down)
is frequently milder than in the clean condition although
the worst case is almost always for the partial-power,
partial-flap, approach condition. If the stall charac-
teristics are good, the experienced pilot can usually
make the airplane recover from the stalled condition
before the spin actually gets started. NACA test pilots
have, in fact,, made slowly approached stalls in all types
of large aircraft and, although various types of stalls
and roll-offs have been encountered, none have been uncon-
trollable or have gone beyond the very first stages of
spin entry.

Spin Entry

Inadvertent spins generally result from stalls that
have been followed by a violent dropping of one wing.
V.hen the wing loses its lift and drops, the nose of the
airplane also drops and the airplane slips in the direc-
tion of the low win,. This slipping motion will lead
to an air force on the vertical tail tending to turn
the airplane off course toward the low wing. This initial
turning motion, which gives a change in heading, does
not constitute a true spin. Inasmuch as the stall and
roll-off is produced solely by the high angle of attack,
which is controlled by the elevator, control can still
be regained by first installing the airplane by use of
the elevator end then usin: rudder and ailerons as
available and required to counteract yawinr and rolling.
If the elevator is moved down more than necessary, the
airplane will pick up too much speed. If, however, the
pilot fails to check the incipient spin by moving the
stick forward promptly, the airplane progressively winds
up into a stable spin. The rudder and ailerons will tend
to blow with the spin (that is, right pedal forward and
wheel to the right in a right spin) and the elevator
will tend to blow upward. The number of turns before
the airplane gets into a fully developed spin varies
with different airplanes; the consensus is that the
number of turns is greater than one but less then five.
The essential point is that recovery becomes increasingly

NACA RB re. L4T07

difficult and requires more turns and altitude loss front
the time of the initial stall until the spin steadies
down. Pecovery should therefore be started as promptly
as possible at the very first indication of the stall.


it has been found that present-day large airplanes
have, as a group, certain common spin characteristics:

(1) The spins generally tend to be steep (airplane
nose down more than h50 from the horizontal). The air-
plane may exhibit some tendency for oscillations or, in
extreme cases, for a whipping motion during which the
attitude varies.

(2) Rates of descent "ill be high, reaching from
115 to 280 miles per hour (10,100 to 24,600 feet per
minute). Inasmuch as the path of descent is almost
vertical, these figures also represent the true airspeed.
At an altitude of 10,000 feet, a true airspeed of
280 miles per hour is equivalent to an indicated airspeed
of 240 miles per hour. Th. rate of rotation will be
relatively low compared with that for small airplanes.
The time for one turn vi11 be abcut 5 seconds for four-
engine airplanes and shout 2 seconds for twin-engine
designs. An aver: ? .:r-e airplane might, for example,
drop 1000 feet al eic tur..

(3) As a result the rotation, the air-jlane wvll
be subjected to an acceleration of 1.5g to gS at the
center of gravity. Occupants near the center of gravity
will be held down by ? force of 1.5 to 3 tires their
weight. The acceleration at the tail might be as much
as og.

(4) The flattest spins will be obtained when all
three controls are deflected fully with the spin. The
most rapid recovery will be obtained by reversing all
three controls. Moving the control column forward after
the rudder has been reversed (that is, moved against the
turn) will be very effective for recovery. Moving the
wheel against the spin (that is, to the same side that
the rudder is moved) will also speed up recovery. In
most cases, the turning will have stopped by the time
all three controls have been moved as recommended.

.'ACA RB No. L4107

(5) Spin characteristics for the landing condition
are jgnerally similar to those 'or the clean condition.
If a large airplane spins while coining in for a landing,
the chance of completing recovery in the height available
is slight.

Little consistent information is available con-
cerninri the effects of power (a ,lied symmetrically or
asymmetrically) on solrs, although it is believed that
application of power in a spin i-ay lead to vibration of
the structure. Use of power is therefore not recommended
in attempting recovery from spins, except as a last resort.

For a number of reasons, spins of large airplanes
are dangerous and should not be intentionally entered:

(1) The air loved on the airplane in a spin may
exceed three times the airplane weight, corresponding to
an acceleration of 3g, which is the usual stfe structural
limit for large airplanes Oscillations durinjr the spin
right so increase the lopd that danger of local failures
or deformations in the structure is encountered. (Fighter
airplanes, on the other hand, can safely take an accel-
eration of 8g.)

(2) The effectiveness of the instruments will be
impaired. In a spin the artificial horizon mr- be
inoperative, and the bell bank indicator may not indicate
the r .orer direction in which to move the wheel or ruocer.
The rate-of-turn indicator should still function properly.

(3) After the airplane stops spinrini., it is in a
dive and Zins speed rapidly. The pilot must pull the
airplane out of the dive before the maximum permissible
diving speed is reached. Very skillful piloting is
required to avoid either pulling ; up too rapidly, which
would impose severe structural loads or even stall the
airplane again, or pulling up too slowly and exceeding
the safe diving speed. In any case, a considerable loss
in altitude would be experienced before the airplane
resumed level flight.

(4) All three controls v tll tend to blow with the
spin. Because of the lar-t' surfaces and hi,_,h airspeeds,
the controls will be herd to move. T:e pilot mny tnere-
fore have to make use of trailin-j-c'J.J ts:,s or oth,-.r
booster devices to help in obtnr.rl.g th sired control

NACA RB No. L4107

(5) HI.gh centrifugal force would affect the crew
physiologically and mi.tht imae it dif ficult to :iove the
controls or to reach as.n hatch. aTh '.. effect could
be most pronounced near the tail portion of tne airjlane.
A ball gunner prcbab'.y viould not be -.le to mo-.ve sbout.

The small airplane may sr-in steer or flat. A small
airplane rotate. faster tihi.i a 1r 35 airolaz-he and has
greater ruuder effectiveness for rec.-v;er7. Re0'oery for
small airr-lanes heavily loaded along the fus.els!,;e may be
c-xpe.li.ted by moving t!.e wheel with t];.! srli-. Small
airplar:ea thst are Lheavily loaded along the rings, however,
as by r-iultinle ':ing guns or u.wi'.:. fu..L tanl-;, %.ill have
the sag-e elevator and aileron cfiectiveness as mentioneded
for large air-clanes. Spins of small t'.-in-engine airplanes
will r:-s3,.iable tlOc3s of large ,~.lan.-..-' ':cePt for the
higher rite of rotation of tb-_,j srlnll ..rnlanes.

considerable infcor-.atic.n is valuablee on the spin
characteristics of tne Douglas 1DC-5 noc'el and airplane.
In apoendtx A, a detailed descrir.,ioni of the moiel spin
characterizL:ico is rdses.at d and the effects of different
lopdinr.s are described.. It i3 shown that if a large air-
!laaqe hEpp%.ns to be relativ-;ly hecavil'- loaded along the
fusl.y.gc, the favorable effect of rov.'.ng the w\hecl .alinst
the spi. may be lost.

The cu-rer-.- tl avA-lable iifform'at ion on pilots'
experirunc.cs in spins of a1E-o c-..r.l.-ns3 is SUmSiui'.I'ized
in aopendcix These fligh-t e-:perlenccs are, o.1 the
whole, con i.stent h what Iotul.ri have tbeen expected
from u.odel est results.


Reference 1 .ives in detail general recommendations
for piloting p'ocedur.; for spinning of pursuit airplanes.
Vith a few exceptions, the general princin'ies specified
therein also apply to larIe .-irnlanrs. For inadvertent
zpins of larga airplanes, ;te follo'.;in; re o....ni..tion-
are. m-'-le?

(1) The pilot should apply sufficient, down elevator
to relieve the stall \and incre.? .'e th3 speed) at the
very first ir.dicationi of stalling. Hi- must :e careful
not; to apply so much down elevabtr as to incrcase:- the
airsneedC ex-cesalvely.

NACA RB No. L,107

(2) If the stall has occurred with power on, the
throttles should be closed when marked rollinri hes devel-
oped and the nose has dropped -plieciably. Closing the
throttles while the nose is unusually high may result in
a whip stall.

(3) If the airplane has rolled off but not yet
wound up into a stable spin, the tuii-nrg motion should
be checked by moving the stick forward to unstall the
wing and then using all three controls to regain level

(4) After the spin has become fully developed and
the controls are with the spin, the most effective con-
trol manipulation is to move the rudder against the turn
Pnd move the wheel to the same side as the rudder and,
about turn later, to move the control column forward
as far as appears necessary. These positions of the
controls should be held until recovery is effected. Once
the airplane begins to respond, the forward movement of
the control column should be stopped, inasmuch as this
movement noses the airplane down and makes the recovery
dive steeper so that the subsequent pull-out takes longer.

(5) In a spin while on instrument flight, the ball
bank indicator should not be relied upon to indicate the
proper direction in which to move the wheel or rudder,
but the rate-of-turn indicator should be used to deter-
mine the direction to move the rudder and to indicate
when the rotation has stopped.

(6) The dive pull-out should be started as soon as
the spin rotation has stopped in ordjr to avoid building
up too much speed during the dive. The pilot should not
pull out too rapidly as the airplane right stall cgr in
or the structural loads miri.t become excessive.

(7) The tabs or other booster devices should be
used as much as necessary to obtain the desired movements
of the control surfaces. The pilot should be prepared
to readjust the trbs upon recovery to avoid overcontrolling
in the ensuing dive.

Although spirnninj- of large airplanes has been suc-
cessfully acc-..n:1lished in several instances, the evidence
points strongly '.-i nst this practice. Even though the
spins r:an: resemble those of some smaller airplanes, the


p.Lrmissib]e overloads -rid diving speeds .re icwr and
tha controls are n-uch hi order to mn.'e. Large airplanes
are not designed for a3robtilcs and should not be ir.ten-
tionally spun.

Langley Iemorial Aeronautical Laboratory
National Adviscry Ccmnimittee for Aerorut ics
Lsangley Field, Va.

NACA ItB io. LklO7



Iodel spin characteristics of the _ou-l s DC-3 air-
plane were obtained frcci tests of a 4-foot-span model
in the rA.JA 20-foot free-spin-i'l.- tunnel. The specific
results in terms of equivalent full-scale data are
described in some detail for illustrative purposes.

For the fully developed spin with the elevator up,
rudder with the spin, and ailerons neutral, the nose
would be descent at an altitude of 10,000 feeb would be 117 miles
per hour (10,300 feet ,er minute) and the rate of rota-
tion would be 3.L seconds for one turn1. Th.- acceleration
at the center of gravity would be 1.7g. Complete reversal
of the rudder alone would ivo a recovery in 1 turn,
after which the airplane would descend in a steep glide.
FiJ uo 1 shows the airplane motion during the last turn
of the spin and during the recovery. After recovering
from such a spin, the airplane would be in a dive at
1753 miles per hour true airspeed (152 miles per hour
indicated airspeed at 8500 feet). The pilot then would
have the alternative of pulling out sharply with resultant
high accelerations or pulling out ,!r:iuX.ll y with consid-
erable increase in speed and loss of altitude. If he
increased the acceleration to 2g in 2 seconds and held
this value during the rest of the pull-out, the airplane
would drop 2000 feet during the pull-out to level fli,hht
and the speed would have increased to 225 miles per hour
true airsp-,,:,id or 265 miles per hour indicated airspeed.
This value of the speed is close to the maximum per-
missible diving speed for the 0,'-3 airplane. If the
pilot 3-6d wanted to use the elevator for recovery, it is
estimated that he would have had to push 160 pounds on
the control column to start movln it forward. If the
pilot :i .p. to get the control column to neutral before
reversing the rudder, the spin would be a little flatter
and the recover-: dive would be steeper than if the control
column remained back.

For the model tests in the normal loling ccn.ition,
the wheel position did not seriously affect recovery.
For this loading condition, the model did not show the

NACA RE NTo. L4T07 11

usual favorable effect of movingg the wheel against the
spin because, as mentioned earlier, the DC-5 has a rela-
tively heavy load along the fuselage.

Tests of the model in th2 lightly loaded condition,
for which the load distribution wss more nearly like that
of most other lvrge airplanes, showed a very favorable
effect of moving the wheel against the spin vnd of moving
the elevator down. Tests with changes in the center-of-
gravity location showed thst moving the center of gravity
appreciably forward diminished the tendency of the model
to spin.



Little information is available on intentional arnins
of large airplanes. Information available on insav-rtent
spins is of questionable accuracy because of the confu-
sion of pilot and crew, the. lack of prepared instrumen-
tation, and the feet that the pilot is concentrating on
trying to recover from the spin. This uncertsi-ity in the
information should be borne in mind in evaluFtin- the
following specific information on full-scale spin

Douglas DC-5 Pirplsns.- 'The following instances have
been Frpr: '.- cc -.r",tn spin experiences in the _C-5
airplane (t'.in e2:.,'t-e, 25,5,) lb):

(1) A chief pilot for '"L airline cmT.;-".:- p'rf'o.r.d
intentional spins v.ith the 'C-5 airpIon- sv: rI- -c i :S
acc. jt.J following results were ottFinr : Thr~ I sin.
were made with wheels up and one it. ~t e-LJ leL' '.. n. A-l
s ins were entered at an altitude cf -' -' e'et. ror
these tests the airplane weight was 31 ; 2 ',j" ounr.
One spin of 2 turns was made with e.ch enr'.;e op -',ti;i
at I50 horsepower. There was no elf";et of pr;v.er cr of
lancing gear. The lonjetst spin 1ct-:1 5 t.r.. .L t-.e
time the airplane was ::inning, ccrs .i r bi force- 'as
necessary to hold the ailerons in th7 r.tutr--L pos-tion
and tn,_re was a very marked iuff'etir.n e th.. til zsr-
faces. Ii.- nose was well do.-n, net beig' m'rte ti,-r. 1)
'::-. the vertical. No trouble was ex:' rie-,ce.j .n
brin.i-ni;, the ei:'lpne out of the srpinr; it .,s n.ce.sesrT
only to neutralize the controls after 'i.i:h L-e .spin
stopped in less then L turn. T.'e i:.!U.-. in.aic'Led
airspeed noticed durit-g the spin wars l15C .ics per Lur.
On recovery the airplane attained an in!icct.r'd sl; c se
of app:-o:ximArtely .-3 miles no.r hour. I'n .-i.;:irnj txee
turns, the airplane lost apr'-roxi..tl, ?0.1 f''4r-t o!' alti-
tude fr'.m the time that the spin w enlitere: urnil
recovery was compile-e' and the airlsane s, .Z in leveI

(2) Other instances heve been r:-~corted w.he(r diffi-
culty was encountered. In one ins~ t.-c the .pin w.s


enter-ed aucidentelly with -,.heels and flaps down end with
pTErts1-l pov.er. Ti-e fit-ps were retracted .rd the power
reduced. An attempt to stop the spin with the rudder
brought no results. Full power was applied to the
inboerd engine with no effect. The rudder was then
neutralized and the control column pushed forward with
cons-derab1. force at which time tne spin .toppeu.

(5) Several pilots have reported going into 2-turn
spins in bad weather or daring triinnr g mr'neuvers. The
pilots indicate that the -ilerons whip toward thc d"rec-
tion of spin as the a.rpliarne enters tie spin. Recovery
was generally succesFfully accomplished by neutralizing
or reversing all the controls. A 5-turn spin has been
reported during which the ncze was 450 down. The loss
in altitude during a 1-turn scin end pull-out from the
ensuing dive has been reported Fs 3J00 fO'-t.

YPFI-1 airplane.- The YF.M-l airplane (twin ernine,
13,150 ib) entered a spin inadvertently from an
asy.~nmetric-power flight condition. The rudder blew with
the spin and the pilot could not push hrrd encuzgh to
move the pedal. The spin vas steep. 'When the cc-pilot
jumped, he. struck and bent the leading edge of the fin
and also struck the rudder. At about this time, the
pilot found that hs ;was able to move the rudder. The
pilot then appl.-ed opposite r.ldder and followed by
moving tne stick forward and giving opposite sileron,
which brought the airplane out cf the spin. This spin
lasted 19 turns.

L-26 airplane.- A service pilot practicing evasive
action stalled a B-26 airplane (twin engine, 26,650 Ib)
and spun very steeply. He applied controls aith the
spin for one turn, then gave full opposite rudder, end
after one more turn moved the stick forward. i.hen this
manipulation had no effect for two turns, he repeated
the entire series of control movements; then after two
more turns the airolene recovered in a vertical dive.
This spin lasted about 7 turns. The co-pilot h1d closed
the throttles after the first turn. The controls were
very difficult to move.

P-70 airplane.- Sever-l P-70 airplanes (twin engine,
21,245 Ib) hPve been lost in spins. Details .re lacking
but it s3 suspected. that high tiick forces mey have been
a contributing factor.

NACA RB No. L4107

B-17 and B-24 airplanes.- Two four-engine designs,
the B-17 (51,)JJ ib) .rnd the 2-21 (50,000 Ib) have been
reported in spins several times. In some instances
serious structural damage and loss of the airplanes
resulted. In one case, control forces were reported to
be high but the combined efforts of the pilot and co-
pilot finally moved the elevator and rudder controls and
effected recovery. The spin was steep. A crew r--mber
near the middle of the fuselas- was able to move about
but the tail gunner was unable to move because of cen-
trifugal force.

Poein- 307 Pirplrne.- It is tho-.uht that the breaking
up of an experimentrl Boeing 507 airplane (four engine,
42,'JO 1;) in flight r"i.ht have occurred during recovery
from a dive subse-ient to a 2- or 3-turn inadvertent

P-58 airplane.- The P-58 airplane (11,500 Ib), which .
is a small twin-engine design and is similar to some of
the large types, has been spun several times. The test
pilot re--crted that on one occasion he was unable to move
any of the three controls from their with-the-spin -csi-
tion after a spin of 3 turns. He regained control after
ei '.t turns by applying power to both ernr.es.

It would be sopreciated if pilots having additional
information on actual spin experiences in large airplanes
would transmit pertinent data to the National Advi.,cry
Committee for Aeronautics at i; shtin.ton, D. C.

1. Soule, H. A., rn.-1 Se.-!r..Cn, COsr: Influence of LcpJing
C?'n',ition on Pilotir!nz --.-.-nique for :in Reco r--:
for Pursuit Airplanes. I;AA -E, June 012.

NACA RB No. L4I07 Fig. 1

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