Several reports have been written on the performance of the Quiet Short-Haul Research Aircraft, which shows the advantages of upper-surface blowing or the propulsive-lift wing as it applies to lift, maneuverability, and short takeoff and landing. This high lift generation at low speeds results in substantial downwash, especially in the low-aft fuselage tail position. The high T-tail of the Quiet Short-Haul Research Aircraft minimizes the undesirable downwash effects from the propulsive-lift wing. Queries from Department of Defense agencies and industry for quantitative values prompted a series of flight-measured downwash tests at the high T-tail and the low aft fuselage position. The results are presented in a summarized format, showing downwash, Delta epsilon/Delta a, for both locations. As would be expected, downwash increases for increased power and USB flap settings. The downwash is greater in the low aft-fuselage position as compared to the high T-tail area

Eppel, Joseph C.

Riddle, Dennis W.

Stevens, Victor C.

English

NASA Technical Reports Server

NASA Technical Memorandum 101 050 
Flight Measured Downwash 
of the QSRA 
Joseph C. Eppel, Dennis W. Riddle, and Victor C. Stevens 
Ames Research Center, Moffett Field, California 
December 1988 
National Aeronautics and 
Space Administration 
Ames Research Center 
Moff ett Field, California 94035 
https://ntrs.nasa.gov/search.jsp?R=19890008222 2020-03-20T03:28:03+00:00Z
SUMMARY 
Several reports have been written on the performance of the Quiet Short-Haul 
Research Aircraft, which show the advantages of upper-surface blowing or the 
propulsive-lift wing as it applies to lift, maneuverability, and short takeoff and 
landing. This high lift generation at low speeds results in substantial downwash, 
especially in the low-aft fuselage tail position. 
Short-Haul Research Aircraft minimizes the undesirable downwash effects from the 
propulsive-lift wing. Queries from Department of Defense agencies and industry for 
quantitative values prompted a series of flight-measured downwash tests at the high 
T-tail and the low aft-fuselage position. The results are presented in a summarized 
format, showing downwash, AE/Aa, for both locations. As would be expected, downwash 
increases for increased power and USB flap settings. The downwash is greater in the 
low aft-fuselage position as compared to the high T-tail area. 
The high T-tail of the Quiet 
INTRODUCTION 
The Quiet Short-Haul Research Aircraft (QSRA) is one of the many research 
aircraft at NASA Ames Research Center. When the upper-surface blowing (USB) project 
was originally conceived and initiated in 1974, the main objective was the proof-of- 
concept and development of a iow-speed powered-lift data base, i.e. , gathering 
performance and handling qualities data associated with takeoff and landing. 
For this research work, a de Havilland C-8A Buffalo airframe modified with a 
propulsive-lift wing was chosen. 
fan engines (prototype to the ALF-502). The engines were configured over the wing 
to provide upper surface blowing (USB), a technique to develop high levels of lift 
at low noise levels. Figure 1 shows the salient features of the QSRA. A detailed 
description of the aircraft can be found in reference 1. The landing gear of the 
QSRA is fixed down since all the research goals are related to relatively low-speed 
flight. The beneficial effect of USB on takeoff and landing performance as compared 
to conventional takeoff and landing (CTOL) aircraft was thoroughly investigated in a 
series of experiments (refs. 2, 3 ,  and 4). These experiments show that landings and 
takeoffs can be consistently accomplished in 700 and 800 ft, respectively, with no 
headwind . 
The QSRA is powered by four Lycoming YF-102 turbo- 
Because of the high levels of wing powered lift, downwash becomes a major con- 
sideration in the design of tail control surfaces. The objectives of the downwash 
experiments were 1) to satisfy the inquiries from DoD and industry concerning the 
downwash in the aft-fuselage area as it may affect the feasibility and requirements 
of a low-tail design, 2) to compare flight-data results of the downwash in the 
1 
T-tail area with wind-tunnel data, and 3) to provide a downwash data base for two 
tail locations to allow limited interpolation of downwash characteristics for a wide 
variety of horizontal tail locations for future aircraft design. 
SYMBOLS 
i = angle of incidence; angle formed by zero lift chord and the longitudinal 
axis 
aaw 
aTRUE = TRUE angle of attack = 9 - y 
= angle of attack of the wing = a T  + iw 
E = downwash angle; difference between angle of attack at the wing and angle of 
attack at the tail 
= flightpath of aircraft relative to the horizon. Y 
0 = aircraft (gyro) pitch attitude relative to the horizon 
Gamma = arcsin ( h  /1.688VT) T 
= angle as measured from the longitudinal axis of the downwash measurement 
probe to the relative wind OP 
Subscripts 
a = absolute 
P = probe 
t = tail 
T = true 
W wing 
TECHNICAL APPROACH AND PROCEDURES 
The rake, an aerodynamically designed structure mounted to the aircraft aft- 
fuselage which held 6 probes to measure the movement of air, is shown in fig- 
ures 2(a) and 2(b). 
Figures 3(a) and 3(b) show the probes in the T-tail position. 
The first downwash experiment was the aft-fuselage measurements. The downwash 
tests were made at a nominal altitude of 8,000 ft, and a series of 18 alpha (angle- 
of-attack) sweeps were made. 
2 
The second experiment was to measure the downwash characteristics forward of 
the horizontal tail. This second experiment required a minimum of three flights 
because at the time of the second experiment, only three probes were available. The 
other three pressure probes were destroyed in a wind-tunnel mishap. Because of this 
situation, the following test procedure was devised so that the probe at position 
t l ,  inboard, would not be moved and would provide a flight-to-flight correlation of 
the results. 
RESULTS AND DISCUSSION 
The parameters of prime concern of this report are downwash ( E )  and wing alpha 
(aaw). 
addressed in this report. 
Sidewash angles and local dynamic pressures were also measured but are not 
Low Tail/Aft-Fuselage Location 
Figure 4 shows downwash versus wing alpha for constant thrust (89% fan rpm) as 
the USB flap positions are varied. 
the USB flap settings are increased from 0" to 60".  Also, the AE/Aaaw slopes 
increase from 0.75 to 1.04 as USB flap setting is increased from 0" to 60" .  
USB flap setting increases there is a well defined difference in the downwash behind 
the inboard and outboard engines. 
engine is 4-5" more than that behind the outboard engine. 
The results show greater values of downwash as 
As the 
At 60" USB flap, the downwash behind the inboard 
Important information gained during this test includes the slope of AE/Aaaw 
for the various conditions and the variation of slope with varying thrust or USB 
flap settings. Table 1 shows a matrix of conditions arranged with increasing thrust 
horizontally and increasing USB vertically. It can be seen that the greatest 
Ae/Aaaw slope is at maximum thrust (89% fan rpm) and 60" USB flap setting, the 
condition for the highest levels of wing powered lift. At a constant thrust corre- 
sponding to 89% fan rpm, the range of Ae/Aa with increasing USB flap setting is 
from 0.75 (0"  USB flap) to 1.04 (60" USB flap). For a constant 60" USB flap set- 
ting, power increases from 70% to 89% fan rpm cause an increase in AE/Aaaw from 
0.88 to 1.04. The typical QSRA takeoff and landing approach conditions are high- 
lighted in table 1. Table 2 shows the relationship between thrust and percent fan. 
T-Tail 
The T-tail downwash experiment consisted of three separate flights because of 
the availability of only three pressure probes. For this reason, it was important 
to investigate the flight-to-flight correlation of data using a common probe posi- 
tion. Figure 5 shows correlation of downwash for two conditions: USB = Oo, fan at 
60%, and USB = 50°, fan at 89%. 
3 
Figure 6 shows the spanwise T-tail downwash variation at constant 89% fan rpm 
settings with increasing USB flap settings for all 6 probe positions. 
increases with USB flap setting, as in the low-tail position (fig. 4). However, the 
downwash magnitudes and the Ae/Aaaw slopes are less at the T-tail location. Also, 
the distinct inboard/outboard downwash magnitude difference seen at large USB flap 
settings at the low-tail position are not evident at the T-tail. 
The downwash 
Table 3 shows a matrix of AE/Aaaw slopes for the tested conditions arranged 
with increasing thrust settings horizontally and increasing USB flap settings verti- 
cally. The largest AE/Aaaw slope changes are found at 89% fan with increasing USB 
flap setting with Ae/Aaaw varying from 0.45 to 0.78. The corresponding low-tail 
downwash slopes (table 1 )  are approximately 1.5 times greater than those at the 
T-tail (table 3) for 89% fan with varying USB flap setting. 
Figure 7, a three-dimensional (3-D) plot of the downwash data obtained in both 
experiments, depicts a sheet of air as experienced by the T-tail and low-tail probes 
for the QSRA landing approach configuration (50" USB flap, 59" DSF and AEO at 
70% fan rpm). 
characteristics of the downwash fields with all engines operating. 
the downwash is greater at the low-tail position as is the downwash slope, AE/Aaaw, 
0.85 to 0.5. 
The 3-D data plot format shows the relatively consistent spanwise 
The magnitude of 
CONCLUSIONS 
1. The downwash angle increases with increasing USB flap setting and thrust, 
the two predominate wing lift increasers. 
USB flap setting and thrust. 
The largest downwash occurs with maximum 
2. The downwash slopes, Ae/Aaaw, also increase with USB flap setting and 
thrust increases. There is also a tendency for slope increases as wing alpha 
increases. 
3 .  The downwash slope, AE/Aaaw, at the low-tail position is about 1.5 to 2 
times the value of that at the high T-tail position. This means that the low-tail 
position provides less stability than the high T-tail position. This would increase 
the need for a stability augmentation system (SAS) for a low-tail configuration. 
The trim changes would also be higher at the low-tail position increasing the need 
for a variable incidence horizontal stabilizer at the low-tail position. Automatic 
trim may be required as USB flap setting and thrust are increased on a low-tail 
configuration. 
4 
REFERENCES 
1. Eppel, J. C.: Quiet Short-Haul Research Aircraft Familiarization Document, 
Revision 1. NASA TM-81298, 1981. 
2. Riddle, D. W.; Innis, R. C.; Martin, J. L.; and Cochrane, J. A.: Powered-Lift 
Takeoff Performance Characteristics Determined from Flight Test of the Quiet 
Short-Haul Research Aircraft (QSRA). AIAA Paper 81-2409, Nov. 1981. 
3. Cochrane, J. A.; Riddle, D. W.; and Stevens, V. C.: Quiet Short-Haul Research 
Aircraft--The First Three Years of Flight Research. AIAA/NASA Ames VSTOL 
Conference, AIAA Paper 81-2625, Dec. 1981. 
4. Riddle, D. W.; Stevens, V. C.; and Eppel, J. C.: Quiet Short-Haul Research 
Aircraft--A Summary of Flight Research Since 1981. SAE Paper 872315, in the 
proceedings of the International Powered-Lift Conference, SAE P-203, Dec. 
1987. 
5 
, Table 1. Low tall posltlon downwash A c / A a a w  slopes 
5900 
5300 
4500 
3800 
3300 
2700 
2400 
2000 
1700 
~ 
USB.0' 0.71 to 
DSF-0' 0.82 
100 23600 
90 21 200 
76 18000 
64 15200 
56 13200 
46 10800 
40 9600 
34 8000 
29 6800 
Ta krof f I Confla o'68 0.74 No data 0.75 I USB-OO (DSF-5B0 I 0.77 
Approach 
Conflg 
... 0.85 USB-50' DS F-59 ' 
0.77 0.85 0.85 
0.92 1.02 
0.34 0.31 0.42 USB-0' DSF-59' 
0.94 to 1.04 
1 .o 0.88 I IvsB-600 DSF.59' I 
Takeoff 
0.45 
Config 
Table 2. Thrust/mglnr fan fpm relatlonahlp. 
... US 8-50 ' 
DSF-50' 
THRUST, 1 4ENGlNE 
THRUST, Ib FAN,% I THRUST,Ib 1 9c 
Approach 0.51 to 
0.78 0.71 0.5 Config 
- 89 
85 - 80 
75 - 70 
65 - 60 
55 
50 
NOTE: 
' 13engldle 17 50 80 59 0.88 
#4 eng Idle 18 50 80 59 0.916-1.1 
Table 3. T-tail position downwash A c / A a a w  slopes 
160% fan 70% fan 80% fan 89% fan I 
I 0.34 USB-0' DSF-0' 0.4 
0.38 0.54 0.57 I DSF-59' 
#3 eng idle 13 50 80 59 0.42 
#4 eng idle 14 50 80 59 0.61 
6 
DROOP ED/ 
ELEVATOR AILERONS 
USB FLAPS BLOWN 
I 
I \ 
OUTBOARD FLAPS TWO-SEGMENT RUDDER 
Figure 1 . -  QSRA with control surfaces ident i f i ed .  
1 OUTB'D 
t 1 T' 4-1 16.5- 1 
10' 
1 1 
88 
NO. 3 
182- I 
NO. 4 - 
b) ENGINE ENGINE 
Figure 2.- QSRA low-tail downwash rake and probes. a) Aircraft location; 
b) plan view. 
7 
i c 
FWD' A T" 
I 
L' '7 OUTB'D 
10" I 
Figure 3.- QSRA T-tail downwash rake and probes. a) Aircraft location; 
b) plan view. 
4.870 
A-- \HORIZ. 
55 
50 
FLT 238 USB 
COND. 12,14,11 60° ..& 
- 4/ - 
45 
B 
U - 40 
w 
25 
20 
0.754/  
l5 t 
10 ' I 
- 5  0 5 10 15 20 25 30 
WING ALPHA, saw, deg 
Figure 4.- Low-tail downwash variation with wing alpha and USB flap setting at 
89% fan rpm and 59" DSF. 
8 ORlGlNAL PAGE 16 
OF POOR QUALITY 
45 I I I I 1 I 
DSF = 59O 
40- FLIGHT 
0 
COND. 8 - 348 - 9\25/84 349 - 1012l84 
35 - ----351 - 10/4/84 - 
g P  50' USB - ~ B 30 - FLT TO FLT CORRELATION 
W ON PROBE 1 ,' 89% FAN 
I z 2 5 - y  - 
3 
820- .d - 
Oo USB 
15 - A r /  Aaaw = 0.65 60% FAN - 
lo d c / A a a w  = 0 . 3 1 4  COND. 7 
P 
- 
I I I I I I 
5 10 15 20 25 
5 
- 5  0 
Figure 5.- Flight-to-flight data correlation of T-tail downwash probe 1, fan at 
605, USB flap at 0" and fan at 895, USB flap at 50". 
30 
45 
40 
35 
0 8 30 
W 
I $ 25 
f g 20 
15 
10 
I I I I 1 -1 
AE / BaaW = 0.70 FLIGHT 
-348 
349 
351 < 
PROBE 
0 1  ---_ 
0 2  * # , J  
A 3  
0 4  J2. 
v 5  
4 6  
5 
WING ALPHA aaw deg 
Figure 6.- T-tail downwash variation with wing alpha and USB flap setting at 
89% fan rpm and 59" DSF. 
9 
Figure 7.- Spanwise downwash comparison of low and T-tail positions for  the QSRA 
landing configuration: AEO at 70% fan rpm, 50" USB, and 59" DSF. 
10 
Report Documentation Page 
1. Report No. 
NASA TM-101050 
2. Government Accession No. 
12. Sponsoring Agency Name and Address 
17. Key Words (Suggested by Authork)) 
National Aeronautics and Space Administration 
Washington, DC 20546-0001 
15. Supplementary Notes 
18. Distribution Statement 
3. Recipient's Catalog No. 
19. Security Classif. (of this report) 20. Security Classif. (of this page) 
Unclassified Unclassified 
5. Report Date 
December 1988 
6. Performing Organization Code 
21. No. of pages 22. Price 
13 A02 
8. Performing Organization Report No. 
A- 88 307 
IO. Work Unit No. 
505-6 1-7 1 
1 1 .  Contract or Grant No. 
13. Type of Report and Period Covered 
Technical Memorandum 
14. Sponsoring Agency Code 
Point of Contact: Joseph C. Eppel, Ames Research Center, MS 237-3, Moffett Field, CA 94035 
(415) 694-6276 or FTS 464-6276 
16. Abstract 
Several reports have been written on the performance of the Quiet Short-Haul Research Aircraft, 
which show the advantages of upper-surface blowing or the propulsive-lift wing as it applies to lift, 
maneuverability, and short takeoff and landing. This high lift generation at low speeds results in sub- 
stantial downwash, especially in the low-aft fuselage tail position. The high T-tail of the Quiet Short- 
Haul Research Aircraft minimizes the undesirable downwash effects from the propulsive-lift wing. 
Queries from Department of Defense agencies and industry for quantitative values prompted a series of 
flight-measured downwash tests at the high T-tail and the low aft-fuselage position. The results are 
presented in a summarized format, showing downwash, A&/Aa, for both locations. As would be 
expected, downwash increases for increased power and USB flap settings. The downwash is greater 
in the low aft-fuselage position as compared to the high T-tail area. 
Powered lift 
Downwash 
Upper surface blowing 
Unclassified-Unlimited 
Subject Category - 05 


Flight measured downwash of the QSRA

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server