Champine, R A

Sjoberg, S A

English

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NATIONAL ADVISORY
ONFitMTIAL	 Rcopy ML9H31a 
NACA 
RESEARCH MEMORANDUM 
PRELIMINARY FLIGHT MEASUREMENTS OF THE STATIC 
LONGITUDINAL STABILITY AND STALLING 
CHARACTERISTICS OF THE DOUGLAS D-558-II
RESEARCH AIRPLANE (BUAERO. NO. 37974) 
By S. A. Sjoberg and R. A. Champine 
Langley Aeronautical Laboratory 
Langley Air Force Base, Va.	 S
n 
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COMM I* 
lCP AIPC)NAUTICS I	 I
WASHINGTON 
October 18, 1949 
https://ntrs.nasa.gov/search.jsp?R=19930085989 2020-06-17T16:16:23+00:00Z
NACA P14 L9R31a	 CONFID ENT IAL 
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

RESEARCH MEMORANDUM 
PRELIMINARY FLIGHT MEASUREMEWS OF THE STATIC

LONGITUDINAL STABILITY AND STALLING

CHARACTERISTICS OF THE DOUGLAS D-558--II 
RESEARCH AIRPLANE (BuAO. NO. 37974) 
By S. A. Sjoberg and R. A. Champine
SUMMARY 
• Brief flight measurements were made of the longitudinal stability 
and stalling characteristics of the Douglas D-58-II (BuAero. No. 37974) 
'research airplane. Longitudinal-stability measurements were made with 
stabilizer settings of 1.30 and 3.40 leading edge up. A stable 
variation of elevator position for trim with Mach number was obtained 
throughout the Mach number range tested with either stabilizer setting. 
No abrupt longitudinal trim changes occurred up to the highest Mach 
numbers reached.: 0.76 with the 1.3 0 stabilizer setting and 0.87 with 
the 3.4 stabilizer setting. In the clean condition, the airplane 
tended to nose up near the stall; this nosing up indicated longi- 
tudinal instability. The nosing-up tendency could be controlled with 
the elevator. In the landing condition the airplane was longitudinally 
stable up to the stall. At the stall the data indicate that the airplane 
became longitudinally unstable. This instability was not noticed by the 
pilot probably because of the yawing and rolling motions 'which also 
occurred at the stall.
INTRODUCTION 
The NACA is engaged in a flight-research program utilizing the 
Douglas D-558-II (BuAero. No. 37974) research airplane. The 
D-578-II airplanes were designed for flight research in the transonic 
speed range and were procured for the NACA by the Bureau of Aeronautics 
of the Navy Department. This paper presents some results obtained on 
the static longitudinal stability and stalling characteristics of the 
airplane during the first two NACA flights. Some measurements of the 
CONFIDENTIAL
2	 CONFIDENTIAL	 NACA R14 L91131a 
dynamic lateral stability characteristics of the airplane, also obtained 
during the first two NACA flights, are reported in reference 1. 
AIRPLANE 
The Douglas D-558--II airplanes have sweptback wing and tail surfaces 
and were designed for combination turbojet 'and rocket power. The air
-
plane being used in the present investigation (BuAero. No. 37974) does 
not yet have the rocket engine installed. This airplane Is powered 
solely by a J-314--44E-40 turbojet engine which exhausts out of the bottom 
of the fuselage between the wing and the tail. Two jatos are used to 
provide additional thrust for take—off. Both slats and stall—control 
vanes are Incorporated on the wing of the airplane. The wing slats can 
be locked in the closed position or they can be unlocked. When the 
slats are unlocked, the slat position Is a function of the angle of 
attack of the airplane. The airplane is equipped with an adjustable 
stabilizer. Dive brakes are located on the rear portion of the fuselage. 
No aerodynamic—balance or control—force booster system Is used on any 
of the control surfaces. Hydraulic dampers are installed, on all control 
surfaces to aid in preventing any control—eurfaceflutter. Photographs 
of the airplane are shown in figures 1 and 2 and a three—view drawing 
is shown in figure 3. Pertinent airplane dimensions and characteristics 
are listed in table I.
INSTRUMENTATION 
Standard NACA recording instruments were installed In the airplane 
to measure the following quantities: 
Airspeed 
Altitude 
Elevator and aileron wheel force 
Normal, longitudinal, transverse accelerations 
Rolling, pitching, yawing velocities 
Rudder—pedal force 
Sideslip angle 
Stabilizer, elevator, rudder, right—aileron position 
Strain gages were installed In the airplane to measure wing and 
tail aerodynamic loads and twist and bending deflections of the right 
wing panel. 
Since high Mach numbers were not expected In the early flights, a 
low—speed—type free—swiveling airspeed head was used to measure both 
CONFIDENTIAL
NACA RM L91131a
	
CONFIDENTIAL	 3 
static and impact pressures. This airspeed head was mounted on a boom 
approximately 8 feet forward of the nose of the airplane.' A vane which 
was used to measure sideslip angle was mounted below the same boom 
approximately 6 feet forward of the nose of the airplane. (See fig. 1.) 
TESTS, RESULTS,. AND DISCUSSION 
This paper presents some results obtained on the static longitudinal 
stability and stalling characteristics of the airplane during the first 
two NACA flights. The airspeeds, altitudes, and Mach numbers presented 
in this paper have not been corrected for the position error of the 
airspeed head or any error inherent in the airspeed head itself. 
Figure 4 shows the variation of elevator angle, elevator force, and 
pressure altitude with Mach number during two dives which were made with 
different stabilizer settings. The stabilizer settings given in 
figure -- are measured with respect to the fuselage reference line. For 
the dive with a stabilizer setting of 3.10, leading edge up, the wing 
slats were unlocked. Therefore, the slat position probably varied 
during the dive, with the slat being open a greater amount at low Mach 
numbers than at high Mach numbers. For the dive with a stabilizer 
setting of 1.3°, leading edge up, the slats were locked in the closed 
position. When the stabilizer setting was 3.40 , leading edge up, 
increasing pull forces on the elevator control were required for trim 
as the Mach number was increased.. However, the increase in pull force 
required for trim does not indicate stick—free instability as the 
elevator wheel force was not trimmed to zero at any point in the Mach 
number range covered. With a stab11izr setting of 1.3°, leading edge 
up, a highly stable variation of elevator force with speed was obtained. 
The variation of elevator position with Mach number was highly 'stable 
throughout the Mach number range tested with either stabilizer setting. 
The differences in the slopes of the curves of elevator position 
against Mach number for the different stabilizer settings are probably 
due to the differences in slat position and to the differences in 
distortion of the horizontal stabilizer and. elevator. No abrupt 'longi-
tudinal trim changes occurred with either stabilizer setting up to the 
highest Mach numbers reached.: 0.76 with a 1.3 0 stabilizer setting and 
0.87 with the 3i40
 stabilizer setting. Much of the scatter in the 
elevator force data is due to the friction in the elevator control 
system. The normal acceleration during the dives varied between 0.85g 
and 1.259. 
Figure 5 shows a time history of an approach to a still in the clean 
condition. As shown on the normal-acceleratioh curve, a light buffeting 
first occurred at an indicated airspeed of approximately 165 miles per 
hour. The buffeting increased in intensity as the airspeed decreased. 
CONFIDENTIAL
4	 CON YLDTIAL	 NACA RM L91131a 
The pilot noted a tendency for the airplane to nose up near the stall. 
This nosing—up tendency,. indicating longitudinal instability, is also 
shown in figure 5 between times 17 and 19 seconds where the elevator 
angle is decreasing but the pitching velocity is positive and the 
acceleration is increasing. The maximum.lift of the airplane was 
probably not reached during the run because when the airplane tended to 
nose up the pilot reduced the angle of attack. 
The maximum value of lift coefficient reached was 1.07 at time 
19 seconds. The pilot was required to use the ailerons almost contin-
uously during the run because of a tendency for the airplane to 
oscillate in yaw and roll. The lateral oscillatory characteristics of 
the airplane are discussed In reference 1. 
A time history of a stall in the landing condition is shown in 
figure 6. light buffeting started at about 135 miles per hour and 
increased in intensity somewhat as the stall was approached. The longi
-
tudinal stability of the airplane in the landing condition was positive 
up to the stall. At the stall the data indicate that the airplane 
became longitudinally unstable, as shown in figure 6, between 34 and 
38 seconds. In this time interval the pilot moved the elevator from 200 
up to 100 down, but the normal acceleration remained practically constant 
and the pitching—velocity curve showed a slight nose up. The Instability 
was not noticed by the pilot probably because of the yawing and rolling 
motions which also occurred at the stall. The maximum value of lift 
coefficient reached was 1.43 at time 35 seconds. 
SUMMARY OF RESULTS 
Brief flight measurements were made of the longitudinal stability 
and stalling characteristics of the D-558—II (BuAero. No. 37974) 
research airplane. A stable variation of elevator position for trim 
with Mach number was obtained throughout the Mach number range tested 
with stabilizer settings of either 1.3 leading edge up or 3•4 0
 leading 
edge up. No abrupt longitudinal trim changes occurred up to the highest 
Mach numbers reached: 0.76 with the 1.3 0 stabilizer setting and 
0.87 with the 3.14 0
 stabilizer setting. In the clean condition, the air-
plane tended to nose up near the stall; this nosing up indicated 
longitudinal instability. The nosing—up tendency could be controlled 
with the elevator. In the landing condition the airplane was longi
-
tudinally stable up to the stall. -At the stall the data indicate that 
CONFIDENTIAL
NACA RM L9H31a	 CONFIDENTIAL	 5 
the airplane became longitudinally unstable. This instability was not 
noticed by the pilot probably because of the yawing and rolling motions 
which also occurred at the stall. 
Langley Aeronautical Laboratory 
National Advisory Committee For Aeronautics 
Langley Air Force Base, Va. 
REFERENCE 
1. Sjoberg, Sigurd A.: Preliminary Measurements of the Dynamic Lateral 
Stability Characteristics of the Douglas D-558--II (BuAero. 
No. 37974) Airplane. NACA RM L9G.18,
 1949. 
CONFIDENTIAL
6	 CONFIDENTIAL	 MACA PM L9H31a 
TABLE I 
DIMENSIONS AND CHARACTERISTICS OF THE

DOUGLAS D-578-II AIRPLANE 
Wing: 
Root airfoil section (normal to 0.30 chord) ....... MACA 63-010 
Tip airfoil section (normal to 0.30 chord) 	 ...... NACA 63-012 
Total area,	 sq ft	 ..................... 177.0 
Span,	 ft	 ......................... 25.0 
Mean aerodynamic chord, 	 In.................. 87.301 
Root chord (parallel to plane of symmetry), In...... . 108.508 
Tip chord (parallel to plane of symmetry), in...... . 61.180 
Taper ratio	 ........................ 0.565 
Aspect	 ratio	 ....................... 3.570 
Sweep at 0.30 chord,	 deg	 ................. 35.0 
Incidence at fuselage center line, deg 	 .......... 3.0 
Dihed.ral,d.eg	 ....................... -3.0 
Geometric twist,	 deg	 ................... 0 
Total aileron area (aft of hinge), sq ft
	 ......... 9.8 
Total flap area,	 sq ft	 ................... 12.58
Horizontal tail: 
• Boot airfoil section (normal to 0.30 chord) ..... . NACA 63-010 
Tip airfoil section (normal to 0.30 chord) ..... . MACA 63-010 
Area (Including fuselage), sq ft ............... 39.9 
Span, in . . . . . . . . . . . . ... . . . . . . . . .. . . .	 71.8 
Mean aerodynamic chord, In............... ... ..14.1.75 
Root chord (parallel to plane of symmetry) ....... . 53.6 
Tip chord (parallel to plane of symmetry) ........ . 26.8 
Taper ratio ........................ 0.50 
Aspect ratio. ......................3.59 
Sweep at 0.30 chord line
.
,deg ................	 40.0 
Dihedral, deg ........................ 0 
Elevator area, sq ft	 ....................3.78 
Vertical tail: 
Airfoil section (parallel to fuselage center line) . . NACA 63-010 
Area, sq ft ........................ 36.6 
Height from fuselage center line, in ............. 98.0 
Boot chord (parallel to fuselage center line), in.	 146.o
Tip chord (parallel to fuselage center line), in..... . 14.14.0 
Sweep angle at 0.30 chord, deg .............. 14.9.0 
Budder area (aft of hinge line), sq ft ......... . 6.15 
CONFIDENTIAL 
NCA RM L9H31a	 CONFIDENTIAL	 7 
TABLE I - Concluded 
DIMENSIONS AND CHARACTERISTICS OF THE

DOUGLAS D-558—II AIRPLANE - Concluded 
Fuselage: 
Length, ft .......................... 
Maximum diameter, in ................... 60.0 
Fineness ratio .......................8.1iO 
Speed—retarder area, sq ft .................5.25 
J-34—WE-40Power plant ....................2 jatos for take—off 
Airplane weight (full fuel), lb ................lO,551 
Airplane weight (no fuel),lb'.................8,99li-
Airplane weight (full fuel and 2 jatos), lb ..........10,969 
Center—of—gravity locations: 
Full fuel (gear down), percent moan aerodynamic chord .
	
23.4 
Full fuel (gear up), percent mean aerodynamic chord
	 .	 23.9 
No fuel (gear down), percent mean aerodynamic chord . 24.6 
No fuel (gear up), percent mean aerodynamic chord ......25.2 
Full fuel and 2 jatos (gear down), percent 
moan aerodynamic chord .................26.9 
CONFIDENTIAL
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CONFIDENTIAL 
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CONFIDENTIAL 
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different stabilizer settings. Flaps up; gear up; military power, 
engine of 12,500 rpm; center of gravity at 211.9 percent mean 
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Preliminary flight measurements of the static longitudinal stability and stalling characteristics of the Douglas D-558-II research airplane (BuAero No. 37974)

Preliminary flight measurements of the static longitudinal stability and stalling characteristics of the Douglas D-558-II research airplane (BuAero No. 37974)

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