Preliminary flight research on an all-movable horizontal tail as a longitudinal control for flight at high mach numbers

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Material Information

Title:
Preliminary flight research on an all-movable horizontal tail as a longitudinal control for flight at high mach numbers
Alternate Title:
NACA wartime reports
Physical Description:
8, 7 p. : ill. ; 28 cm.
Language:
English
Creator:
Kleckner, Harold F
Langley Aeronautical Laboratory
United States -- National Advisory Committee for Aeronautics
Publisher:
Langley Memorial Aeronautical Laboratory
Place of Publication:
Langley Field, VA
Publication Date:

Subjects

Subjects / Keywords:
Mach number   ( lcsh )
Compressibility   ( lcsh )
Fighter planes   ( lcsh )
Aerodynamics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: The NACA is conducting flight tests of an all-movable horizontal tail installed on a Curtiss XP-42 airplane because of its possible advantages as a longitudinal control for flight at high Mach numbers. The results are presented for some preliminary tests in the low-speed range for which the tail was very closely balanced aerodynamically and a bobweight was used to obtain stable stick-force variations with speed and acceleration. For these tests, the tail was hinged at 0.24 chord and was tried with two arrangements of servotab control. The elevator control was found to be unsatisfactory with the control arrangements tested. Although there were sufficient variation of stick force with acceleration in steady turns and a stable stick-force variation with speed, the near-zero variation of stick force with stick deflection resulted in an extremely sensitive control that required continuous attention in order to avoid motions of the airplane due to inadvertent movements of the control stick. For subsequent tests, the servotabs are being connected as geared unbalancing tabs in order that more conventional elevator hinge-moment characteristics may be obtained. The expected advantages of the all-movable tail with a control system utilizing tabs would of course be limited to flight at Mach numbers below those for which severe compressibility effects are encountered on the tail itself. For higher Mach numbers, the all-movable tail would require an irreversible power-boost control in order to handle the large hinge-moment increases that are expected.
Bibliography:
Includes bibliographic references (p. 8).
Statement of Responsibility:
Harold F. Kleckner.
General Note:
"Report no. L-89."
General Note:
"Originally issued March 1945 as Advance Restricted Report L5C08."
General Note:
"Report date March 1945."
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 - 003614162
oclc - 71247981
sobekcm - AA00006266_00001
System ID:
AA00006266:00001

Full Text

SNhcAF L-5t


ARR No. L50C08


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WAIRTI'IE IRE PORT
ORIGINALLY ISSUED
March 1945 as
Advance Restricted Report L5C08

PREMWEARY FLIGHT RESEARCH ON AN ALL-MOVABLE HORIZONTAL
TAIL AS A LONGITUDINAL CONTROL FOR FLIGHT AT
HIGH MACH NUMBERS
By Harold F. Kleckner

Langley Memorial Aeronautical Laboratory
Langley Field, Va.







NACA


WASHINGTON
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 89


DOCUMENTS DEPARTMENT


e-






































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


http://www.archive.org/details/preliminaryfligh001ang







NACA AR7 No. L5C0O3

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS


ADVANCE RESTRICTED REPORT


PRELIMINARY FLIGHT RESEARCH ON A:I ALL-MOVABLE HORIZONTAL

TAIL AS A LONGITUDINAL CONTROL FOR FLIGHT .-iT

HIGH MACH NU.IBERS

By Harold F. Kleckner


SUMMER Y


The NACA is conducting flight tests of an all-
movable horizontal tail installed on a Zurtiss XP-42 air-
olane because of its possible advantages as a longitudinal
control for flight at high Mach numbers. The results
are presented for some preliminary tests in the low-speed
range for which the tail was very closely balanced aero-
dynamically and a bobweight was used to obtain stable
stick-force variations with speed and acceleration. For
these tests, the tail was hinged at 0.24 chord and was
tried with two arrangements of servotab control.

The elevator control was found to be unsatisfactory
with the control arrangements tested. Although there
were sufficient variation of stick force with accelera-
tion in steady turns and a stable stick-force variation
with speed, the near-zero variation of stick force with
stick deflection resulted in an extremely sensitive
control that required continuous attention in order to
avoid motions of the airplane due to inadvertent move-
ments of the control stick. For subsequent tests, the
servotabs are being connected as geared unbalancing
tabs in order that more conventional elevator hinre-
moment characteristics may be obtained.

The expected advantages of the all-movable tail
with a control system utilizing tabs would of course be
limited to flight at Mach numbers below those for which
severe compressibility effects are encountered on the
tail itself. For higher Mach numbers, the all-movable
tail would require an irreversible power-boost control
in order to handle the large hinge-moment increases
that are expected.








NACA ARR No. L5C1"


INTRiODUT TIC0


The possible advantages of an all-movable horizontal
tail for longitudinal control have been considered for
som" time. This type of tail recently has been suggested
for flight at high ach numbers since it offers a means
of eliminating the pitching moments that result from the
downwash changes which accomoany compressibility effects
on the wing when conventional fixed stabilizers are used.
As a consequence, an all-movable horizontal tail was
designed for the Curtiss XP-12 airplane (a modified
P-56 airplane), and flight tests were made of the air-
plane with this tail installed. The XP-42 airplane can-
not be flown at Mach numbers at which control difficulties
ordinarily arise; however, snee.ds and accelerations that
needed to be covered in a preliminary research program
could be obtained.

With the all-movable horizontal tail installed on
the XP-42 airplane, a series of ground handling tests
and two flights have been rade. In the two flights,
the maneuvers were limited to low-acceleration turns
and the speed was limited to 200 miles per hour. The
present report summarizes the data obtained.


TAIL CHARACTERISTICS


The all-movable horizontal tail that was designed
for the XP-42 airplane incorporates three distinguishing
features:

(1) An all-movable tail plane (elevator) hinged at
its aerodynamic center

(2) Servotab control

(3) A bobweight in the control system
A tail arrangement incorporating these features
offers several advantages. .Vhen the tail plane is
hinged at its aerodynamic center, the variations of
hinge-moment coefficient with elevator angle Ch6 and
with anile of attack of the tail Ch are vwry near
zero. The stick force required to produce a speed or
acceleration change then depends only on the bobwelght








:-.A A ; ,, L'o. L5 08 5


effect; is indenondent of the tail load and the flow
-e-rection at the tail; and is therefore indeoenrd?-.t of
airplane center-of-grav-'tv position, nower and flap
effects (except for changes in dyna,,ic pressure at the
tail), altitude, and downwash charges that accomnoany
:[ach nuLrber elf-cts on t?e win_.. In addition, an all-
'.o'.Table 'orizontal tail rrov,.des a gr-ater down load in
the landing attitude than a conventional stabilizer and
elevator. This characteristic oer.its an airplane to
meet landing requirements for a -.reater center-of-gravity
range or, 'cr the same range, oer-its a reduction in
tail area 11 more-forward center-of'-.ravity positions
are used.

It was realized that compro.'.ises would probably be
required as the tests nrogressed. Fro. the beginning it
was apparent that longitudinal oscillations right exist
and that the pilot might move the tail to a position at
which the tail load might be excessive before the airplane
acceleration, and therefore the force frcm the bobweight,
would he experienced.

Pertinent characteristics of the tail and its
installation are shown in figures 1 to 5. The tail area
was not reduced in comnarison with the original tail area
because moving the center of gravity of the airplane
forward was not feasible. The aspect ratio was increased
in corm.arison with the original tail to comnensate for the
shorter tail 1 length that was required for installation
rurnoses. The elevator was mass-balanced about its hinge
line, and the servotabs were mass-overbalanced about their
hbnge lines to give d-ynamic balance ."or rotation of the
elevator. The bobweig -t in the control system, which was
located 7.0 feet behind the center of gravity, gave a
force of 6 pounds at the oilot'3 grip.

Two arrangements of the ser'votab control system
have been ussd to date. Schematic drawings of these
systems are given in figure 4. In arrangement 1, a
spring was incornorated on the servotabs to keep them
from banging against their stops in ground handling
tests. The spring did not alter essentially the condi-
tion of Cha = 0 and Ch6 = 0 for this arrangement
when the aerodynamic center was at the hinge line.
After a few tests, the control system was chan-;d to
arrangement 2. In this arrangement, the point at which








;IACA ARR No. L5C08


the additional link was attached was so chosen that the
tabs would deflect in the same direction as the elevator
(unbalancing) in a ratio of tab angle to elevator angle
6t
- = 1 (no spring deflection). This arrangement made
6e
Ch6 negative but permitt d Ch6 to approach zero as
the seed increased, since the action of the spring
reduces 6- with increase in speed. This arrangement
6e
did not alter Cha and retained the servotab action of
a-r.nqrement 1. In arrangement 2 the trim tabs were locked
'n the neutral position; trim changes were made by
changing the servotab position. Arrangement 2, with
spring added, is the geared unbalancing tab arrangement
used to obtain a stable variation of rudder force with
rudder deflection on two all-liovable vertical tails
previously tested at the Langley Laboratory (references 1
and 2).


TESTS AND RESULTS S


A'th the elevator control system connected as in
f'-ure 4(a), the control felt uncertain to the pilot
in taxi runs and ground flights (take-off, flight along
runway, and landing). In an attempt to isolate the
trouble, the servotabs were locked and taxi runs with
the tail down were made at about 45 miles per hour with
the elevator moved slowly through its deflection range.
The data of figure 5(a) were obtained in a run of this
type. The slone of the curves in figure 5(a) indicates
that the aerodynamic center of the tail was between 3 and
l percent of the mean aerodynamic chord ahead of the hinge
1-ne, an indication that the tail was overbalanced and
that h was positive and not zero. The breaks in the
curves at large down elevator deflections are the result
of stalling of the tail. Since wind-tunnel tests have
shown that strips on the trailing edge of an airfoil
move the aerodynamic center rearward, this convenient
method was used to bring the aerod.rnamlc center to the
elevator k-Inrae line. Strips of different sizes were
tried until the aerodynamic center was moved back to
the hinge line (fig. 5(b)) by 0.28-inch strips attached
outboard of the servotabs. No strips were attached to
the trailing edges of the servotabs because the strips








NACA ARR Ho. L5COS


would make the variation of servotab hinge-moment coef-
ficient with angle of attack of che tail negative; this
effect is similar to moving the aerodynamic center of
the elevator forward.

With Cha and Ch6 zero, the control still felt
uncertain to the oilot and was unsatisfactory in ground
flights. The uncertain feel of the controls probably
resulted from the absence of stick forces associated with
stick movement. The stick forces from accelerations
(dTue to the bobweight) did not give significant feel to
t-e oilot for these ground flights because the normal
accelerations were small and lagged behind the stick
movements too much at these low speeds. It was con-
cluded that, in take-offs and landings in which rather
large and rapid movements of the control stick are made,
variation of stick force with stick deflection must be
provided in order to give the control the feel necessary
for the pilot to fly the airplane with assurance. The
control system was therefore changed to arrangement 2;
and, after satisfactory ground tests, two flights were
made with this arrangement. For these flights, the air-
plane weight was 6100 pounds and the center of gravity
was at 28.1 percent of the mean aerodynamic chord with
wheels up. The longitudinal characteristics of the air-
plane were recorded in abrupt pull-ups, steady turns,
and steady flight through the speed range. Records of
stick-free oscillations were also obtained. The data of
these flights are given in figures 6 to 3 and indicate
that

(1) The airplane exhibited stick-free and stick-
fixed static longitudinal stability

(2) The airplane would trim throughout the speed
range tested

(5) There was a stick-force gradient in steady
turns of about 8 pounds per g

(i.) Stick-free oscillations at 115 and 157 miles
per hour damped satisfactorily

Despite these satisfactory characteristics, the
pilot considered the control sensitive and uncertain
and therefore unsatisfactory. Continuous attention to
the control was necessary in rough air in order to
avoid motions of the airplane due to inadvertent move-
ments of the control stick. In addition, the control








NACA ARR Ho. L5C08


was considered sensitive because in abrupt maneuvers
the reactions of the airplane were not proportional to
the forces exerted by the pilot.

A comparison is made in figure 9 of data obtained
during g abrupt null-uos made with the XP-42 airplane and
a Curtiss P-4O airplane, for which the stick-force
gradient in steady turns was also about 8 pounds oer g.
The curves of figure 9 show that the force required for
the initial deflection of the all-movable horizontal
tail was about 5 or 10 percent of the force required for
the deflection of the P-40 elevator for approxim-tely
the same resultin- normal acceleration. This comparison
indicates that insufficient variation of stick force
with stick deflection is the reason for the pilot's
dissatisfaction with the control.

It is interesting to note here that, since these
tests were made, the NACA pilots have expressed dis-
satisfaction with closely balanced elevators of con-
ventional design on other airplanes because of the
sensitivity of the control. In this connection, a
theoretical investigation referencee 5) has been made
of the effect of various hin-e-moment parameters on
elevator stick forces in rapid maneuvers.


SUTJSEUTNT TFSTS


For subsequent flight tests, the control system is
being modified to incorporate preload in the servotab
string. With this arrangement conventional stick-
force characteristics can be obtained, but the advantages
that accrue from Ch6 = 0 of course cannot be realized.
'"he possibility still exists of making the all-movable
tail a satisfactory longitudinal control with Ch6 = 0.
In this regard, provision has been made to incorporate
a damper on the servotab scoring. The damper would in
effect elimIn:ate the scoring action from abrupt control
deflections. Preload in the servotab spring will not
destroy the expected advantage of the all-movable tail
for flight at high Mach numbers, because the servotab
will come into action when the stick force is sufficient
to overcome the preload in the spring.








'.ACA ARR :'o. L5C03


'The use of an all-movable tail that depends on tab
action is necessarily limited to flight at Mach numbers
below those for which severe com.lores.sibility effects are
encountered on the tail itself. For higher Miach numbers,
the all-movable tail will require an irreversible power-
boost control in order to handle the large hinge-moment
increases that are expected. It appears that the devel-
oo'nent of such a power-boost control warrants
consideration.


CONCLUDING TMARKS


In preliminary flight tests of an XP-42 airplane
with an all-movable horizontal tail chat incorporated
ver- close aerodynamic balance and a bobweight, the
elevator control was found to be unsatisfactory. There
were sufficient variation of stick force with accelera-
tion in steady turns and a stable stick-force variation
with speed, but the control was sensitive and required
continuous attention in order to avoid motions of the
airplane due to inadvertent movements of the control
stick. The unsatisfactory qualities of the control were
attributed to insufficient variation of stick force with
stick deflection, which resulted from the very close
aerodynamic balance.


Langley 7MTemorial Aeronautical Laboratory
National Advisory Co-amittee for Aeronautics
Langley Field, Va.







8 NACA ARR No. L5CO8

REFERENCES

1. Jones, Robert T., and Kleckner, Harold F.: Theory
and Preliminary Flight Tests of an All-Movable
Vertical Tail Surface. NACA ARR, Jan. 1945.

2. Kleckner, Harold F.: Flight Tests of an All-Movable
'vertical Tail on the Fairchild XR2K-1 Airplane.
..ACA ACR No. 3F26, 1945.

3. Jones, Robert T., and Greenberg, Harry: Effect of
Fing 3-7oment Parameters on Elevator Stick Forces
in Rapid Maneuvers. NACA A?i No. LTJ12, 1944.






NACA ARR No. L5C08 Fig. 1












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NACA ARR No. L5C08


Area, sq ft
Movable tail
Fuselage
Total
Servotab
Trim Lab
Aspect ratio
Taper ratio
M.A.C., ft
Thickness
Root
Tip


---- -- NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS
Elliptical airfoil section to 0.75 chord
Max. tnickness at 0.428 cnord


Root section


Straight contour
from 0.75 chord
to T.R.


Figure 3.- Dimensions of all-movable horizontal tail for the
Curtiss XP-42 airplane.


Fig. 3







Fig. 4 NACA ARR No. L5C08








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(a) original trailing edge, no strips.


8 4 0 4 8 /2
Down Elevator angle deg Up
(b) Trailing edge equipped with 0.28-inch
strips outboard of servotabs.
Figure 5.- Variation of stick force with elevator angle for
steady elevator movements in taxi runs, three-point attitude.
Curtiss XP-12 airplane with all-movable horizontal tail.
1
Readings taken every g second; arrows Indicate direction of
elevator motion.


Fig. 5






NACA ARR No. L5C08


/Speed
(mph
0/50
r 0 200


0 / 2 3 4
Normal acceleration, 9
Figure 6.- Variation of stick force with normal acceleration
in steady turns at an altitude of 5000 feet. Curtiss XP-42
airplane with all-movable horizontal tail; 6-pound bobweight
in control system.


- 04
0).

5



(0
tS



Lu


/00 120 4~O 160
Indicated airspeed, mph


Figure 7.- Variation of stick force and elevator angle with
indicated airspeed. Curtiss XP-42 airplane with all-movable
horizontal tail.


-----<5-----.
Power
( in. H ) (rpm7)
o25 2200
o 13 /500
I NATIONAL ADVISOR Y
.^^COM IMEE FC R AERON UTICS
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Figs. 6,7


180


200







NACA ARR No. L5C08 Figs. 8,9




2




/-4-- --- -

S------ Servoto



0 2
SO^ --- --- --- ---- --- --- ------I -- --






0 / 2 0 / 2
7T'/he Jec 7T/1ie sec
(a) Speed, 115 miles per hour. (b) Speed, 157 miles per hour.
Figure 8.- Records of longitudinal oscillations made by abruptly
moving and then releasing the stick. Curtiss XP-,42 airplane
with all-movable horizontal tail; no stick force available.
NATIONAL ADVISORY
IMMITTEE FOR AERONAUTICS


4






l0 L


0 / 0 1
7Tne sec Time sec
(a) P- 0. airplane; speed, (b) XP-42 airplane; speed,
188 miles per hour. 205 miles per hour.
Figure 9.- Comparison of data obtained during abrupt pull-ups of
Curtisa XP-42 airplane with all-movable horizontal tail and
of Curtiss P-t.0 airplane.


SForce
----- Elevyaor
S --- Accelerafion

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UNIVERSITY OF FLORIDA

3 1262 07749 250 1


DIVERSITY OF FLORIDA
"Cutl CENTSS DEPARTMENT
1 '0 ,1MARSTON SCIENCE UBRARY
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L :5'/ILLE, FL 32611-7011 USA










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