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NASA 

Technical 

Paper 

2739 

August 1987 

Evaluation of Installed 
Performance of a 
Wing-Tip-Mounted 
Pusher Turboprop on 
a Semispan Wing 

James C. Patterson, Jr., 
and Glynn R. Bartlett 


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NASA 

Technical 

Paper 

2739 

1987 


Evaluation of Installed 
Performance of a 
Wing-Tip-Mounted 
Pusher Turboprop on 
a Semispan Wing 


James C. Patterson, Jr., 
and Glynn R. Bartlett 

Langley Research Center 
Hampton, Virginia 


NASA 

National Aeronautics 
and Space Administration 


Scientific and Technical 
Information Office 



Summary 

An exploratory investigation has been conducted 
at the Langley Research Center to determine the 
installed performance of a wing-tip-mounted pusher 
turboprop. Tests were conducted on a semispan 
model with an unswept, untapered wing and an 
air-driven motor that powered an SR-2 high-speed 
propeller located on the tip of the wing. All tests 
were conducted at a Mach number of 0.70 over an 
anglo-of-attaek range from approximately —2° to 4° 
at a Reynolds number of 3.82 x 10 f) based on the wing 
reference chord of 13 in. 

The data show that it is possible to improve pro- 
peller performance and simultaneously reduce the 
lift-induced drag of the wing. This improved per- 
formance is a result of locating the propeller behind 
the wing trailing edge at the wing tip in the crossflow 
of the wing-tip vortex. 

Introduction 

High-speed propeller designs have recently been 
developed that may be capable of obtaining the 
same thrust performance as present-day fan-jet en- 
gines while achieving a 15- to 20-percent fuel sav- 
ings. These new propeller designs have generated 
considerable interest because of today's fuel econ- 
omy consciousness. As a result, many research ef- 
forts are under way, in NASA and in industry, to 
optimize the propeller designs, to develop new tur- 
bine engines to drive the propellers, and to determine 
the installation effects of the turboprop on airplane 
performance. Both wind-tunnel and flight tests are 
being conducted. 

As a result of these efforts, a number of turboprop/ 
airframe integration concepts have been proposed. 
(See fig. 1.) The conventional tractor turboprop 
installation has several unfavorable characteristics. 
The propeller swirl and the increased velocities over 
the wing may have detrimental effects on the wing 
aerodynamics. This installation arrangement may 
also produce unfavorable noise effects on the fuse- 
lage and on the passengers. The other installation 
arrangements show n are attempts to overcome vari- 
ous problems associated with the conventional trac- 
tor installation (refs. 1 and 2). Research is being 
conducted on each of these concepts. 

A turboprop installation location which has not 
been considered in any study to date is that of locat- 
ing the turboprop on the wing tip. By locating the 
turboprop in a pusher fashion on the wing tip, such 
that the propeller is immersed in the lift-induced vor- 
tex flow behind the w ing, it may be possible to take 
advantage of energy in the swirling vortex flow r to 
enhance propeller performance as w r ell as to disrupt 


the trailing vortex system by mass injection of the 
propeller wake into the vortex core. The exploratory 
research on this concept was conducted to quantify 
the potential benefits of mounting a pusher turbo- 
prop at the wing tip. However, the engine-out effect 
on the stability and control of the aircraft is a factor 
to be considered, but it is not addressed in this pro- 
gram. The directional control power of the double 
and triple slotted rudders now used on some trans- 
port type aircraft may be sufficient to control this 
effect. 

This investigation was conducted in the Langley 
7- by 10- Foot High-Speed Tunnel using a semispan 
model that had an unswept , untapered wing with 
a symmetrical airfoil section. (See fig. 2.) An air- 
driven turbine motor was used to drive a propeller 
mounted on the wing tip in a pusher position. The 
SR-2 propeller blade design discussed in reference 3 
was used. All tests were conducted at a Mach number 
of 0.70, at angles of attack of approximately —2° to 
4°, and at a Reynolds number of 3.82 x 10 () based 
on the model wing chord of 13 in 

Symbols 

.4 cav cavity cross-sectional area between hub 

and nacelle, in 2 

Cp drag coefficient, ^ ra § 

ACp engine installation drag coefficient, 

C D.W/X ~ C DM 

Ci lift coefficient. 

L <loc S 

C rn pitching-moment coefficient, referenced 

to wing quarter-chord, l>itchi »S 

c mean geometric chord, in. 

D 1Iia j n drag measured by main balance, lbf 

F\ propeller normal force 

L lift produced by propeller, lbf 

N t nacelle incidence angle, dog 

Pcav cavity pressure between hub and nacelle. 
lbf/in 2 

free-stream static pressure, lbf/in 2 

q x free-stream dynamic pressure, lb/ft 2 

5 exposed semispan wing area, 2.88 ft 2 

Sex t exposed semispan wing area including 

wing extension, 3.89 ft 2 

T thrust of propeller and hub, lbf 



A7’ thrust increase due to vortex How field 
on propeller, lbf 

T| )a | thrust measured by propeller balance, lbf 

\ resultant velocity, ft /sec 

\ x free-stream velocity, ft /sec 

U wing 

H / A wing/ nacelle 

n angle of attack, deg 

■ i geometric pitch angle of propeller blade 

(referenced to propeller rotational plane), 
(](■;> 

flprop angle of relative velocity due to propeller 
rotation, deg 

hvorirx angle of relative velocity due to wing-tip 
vortex, deg 

Design Philosophy 

Propeller Performance Enhancement 

The local velocity relative to a propeller blade is 
normally a combination of the rotational velocity of 
the' propeller and that of tlu* free stream. This is 
shown by a simple schematic in figure 3. The lift 
produced by each propeller blade is perpendicular to 
this local flow and is therefore not directed totally in 
a streamwise direction. A component of this lift in 
tlu 1 flight-path direction is then the thrust produced 
by the propeller. A turboprop configuration installed 
in a pusher fashion at the wing tip experiences a 
change in the magnitude and direction of this relative 
velocity as a result of the addition of the lift-induced 
vortex flow that exists at the wing tip as shown in 
figure 3. 

The increase in the angle between the relative 
velocity and the free stream should result in a more 
streamwise rotation of the propeller blade lift vector. 
Consequently, there is an increase in the propeller 
blade thrust component, (fig. 3(1))). Therefore, a 
small reduction in blade pitch will be needed in 
the case of the full-scale aircraft to obtain a given 
ihrust with the result that less engine power will be 
required. 

Induced Drag Reduction 

There are a number of other favorable effects that 
may result from the wing-tip pusher turboprop which 
tend to reduce the induced drag of the wing. The 
vortex flow shed from a lifting wing increases the 
wing downwash velocity normally produced by the 


wing in 1 he process of developing lift . This downwash 
velocity increase, just behind the wing trailing edge, 
occurs without an additional increase in lift of the 
wing. In effect, this increase downwash velocity 
lowers the effective angle of attack of the wing and 
thus requires a physical increase in wing angle of 
attack to maintain the required lift. This change in 
angle of attack will result in induced drag (vortex 
drag). It was concluded in a study conducted on a 
semispan mode! with a turbofan nacelle located at 
the wing tip (rels. 1 and 5) that directing the high- 
energy mass wake of a jet engine into the vortex, 
which interrupts the core axial flow, dissipates the 
vortex. This interruption of the vortex How resulted 
in a decrease in the downwash angh' and, therefore, 
a significant decrease in the drag due to lift of the 
configuration. The propeller wake of the wing-tip- 
mounted pusher turboprop was expected to have a 
similar effect and produce a significant reduction in 
drag due to lift . 

Apparatus and Experimental Methods 

lest Facility 

This investigation was conducted in the Lang- 
ley 7- by 10- boot High-Speed Wind Tunnel, which 
is a continuous-flow subsonic-transonic atmospheric 
wind tunnel. In t hi* closed-test -sect ion configuration, 
the speed range is from very low to approximately 
Mach 0.91. ending on model size. The test section 
is 6.581 ft high by 0.574 ft wide. The useable length 
of the test section is 10.833 ft with a mean cross- 
sectional me a of 03.052 ft 2 . The tunnel operates at 
ambient temperature and pressure and continuously 
exchange's air with the surrounding atmosphere' for 
cooling. ( See ref. 0. ) 

Model Configuration 

Dr avvings of the semispan model used in this 
investigation are shown in figure 1. Figure 2 is a 
photograph of the model wall mounted in the wind 
tunnel with the w dug- tip-mounted pusher turboprop 
installed. 

The un swept, untapered wing shown in figure 4 
has a chord of 13 in., an NACA 64]A012 airfoil 
section, and an aspect ratio of 6.10 based on the full 
wing span of 79. 20 in. The basic wing, wing plus 
wing-tip-mounted turboprop nacelle, and the wing 
turboprop nacelle plus wing extension configurations 
arc shown in figure 4. The exposed basic wing area 
for the configuration under study was used as the 
reference area for the data obtained for the particular 
configuration (i.e., 2.88 ft 2 for the basic wing and 
3.89 fl“ for the wing with the tip extension). 


2 



High-pressure drive air powered the turboprop 
through a four-stage air turbine motor connected to 
the propeller through a shaft system (fig. 4(b)). The 
air turbine motor was mounted on the wing inside the 
fuselage, so not to affect the main balance forces or 
tin* aerodynamic forces. The power output shaft ex- 
tended along and inside of the wing leading edge from 
the engine location to the wing tip. Power was then 
transferred to t Ik* propeller shaft through a set of 90° 
helical bevel gears. The drive air was exhausted into 
t he inner sect ion of a dual annular exhaust system af- 
ter passing through the air turbine motor. This inner 
annular sect ion carried the expanded cold exhaust, air 
of the turbine motor, which then was exhausted into 
the tunnel plenum chamber. Because of the proxim- 
ity of the exhaust to the model's main force balance, 
Ihe outer annular section carried a low flow rate of 
warm air from the heated drive air supply to insulate 
the model balance from the cold exhaust, as shown in 
figure 4(b). The exhaust flow was aligned with the 
center of the* model main balance in the side-force 
direction. Since the balance does not measure side 
force, the force* term caused by the exhaust How was 
eliminated from the* balance measurements. 

Force Balances 

Measurements of force's and moments were ob- 
tained by an internally mounted, wall-supported, 
five-component, electrical strain-gage balance. The 
model was designed so that the wing attached di- 
rectly to the balance and protruded through a clear- 
ance* opening in the nonmet.ric fuselage. The fuselage 
(actually a balance fairing), attached to the wind- 
tunnel wall but not to the balance, was designed to 
traverse the angle-of-attaek range* without the fuse- 
lage* force's being measured by the* balance. 

The main model balance measures the drag of the 
complete model minus the thrust from the turbo- 
prop. To determine the actual drag of the complete 
model, the thrust of the turboprop must be added 
to the main balance drag measurements. To ob- 
tain these data, a three-component internal electrical 
strain-gage thrust balance capable of measuring pro- 
peller thrust, propeller lift, and pitching moment was 
installed in the aft end of the t urboprop nacelle, (See 
fig. 4(b).) The propeller was attached directly to the 
balance shaft while the ot her end of this balance was 
driven, through a Hex coupling, by the turbine air 
motor. The balance housing was fixed to the nacelle, 
but the balance shaft and bearings held by the bal- 
ance beams were free to move under the influence of 
tin* forces produced by the propeller. The propeller 
balance* allows a direct measurement of the propeller 
performance and thrust to be used in combination 
with the main balance. A detailed description of the 


measured forces and bookkeeping system is given in 
the appendix. 

The thrust component in the lift direction was 
small, even at the highest angle of attack tested, com- 
pared with the lift of the wing. Therefore, the lift- 
coefficient values presented have not been corrected 
for the effect of propeller thrust. 

Drive Air System 

The drive air system consists of a high-pressure 
air supply, an air turbine motor, and an exhaust 
system. The high-pressure drive air was controlled 
by two valves upstream of the motor. One valve 
was used to set the maximum pressure in the system, 
and the other valve controlled the air turbine drive 
pressure. By changing the air turbine drive pressure, 
it was possible to vary the thrust output of the 
propeller. A pop-off valve was located between the 
control valve and the turbine motor to prevent a 
possible overpressure. Upstream of t he control valves 
was a steam heater to control drive air temperature 
to the air turbine motor. 

Turboprop Turbine Horsepower 

Measurements of the airflow were made to facil- 
itate calculation of power output, of the air turbine 
motor. A critical venturi installed between the two 
control valves measured mass How rate through the 
aii' turbine motor. Both pressure and temperature 
were measured upstream and downstream of the air 
turbine motor to determine the pressure drop and 
change in temperature. A magnetic pickup measured 
the revolutions per minute of the air turbine motor. 
The horsepower output of the air turbine motor was 
calibrated dependent on mass flow, inlet pressure, 
and rpm. These calibration curves were then used 
to determine the power output of the turbine for the 
different test conditions. 

Tests 

All tests were conducted at a Mach number of 
0.70 over an angle-of-attack range from —2° to 4° 
at a tunnel total pressure of 2120 lb/ ft ^ and a total 
temperat ure of 120°F. These conditions resulted in a 
Reynolds number of 3.82 x 10 () based on the mean 
wing chord. 

Boundary-layer transition strips, 0.125 in. wide, 
consisting of No. 120 carborundum grains, were in- 
stalled on the upper and lower surfaces of the wing 
0.7 in. behind the wing leading edge. The location of 
fully turbulent flow was thus established. 

The wing fuselage was tested as a baseline con- 
figuration with a symmetrical fairing on the wing tip 
(wing-tip cap). The wing-tip-mounted pusher tur- 
boprop was tested at a constant-thrust output level 


3 



from the propeller throughout the angle-of-attack 
range at two nacelle incidence angles of 0° and —3°. 
This was followed by tests conducted with a 9-in. 
wing extension attached to the outer surface of the 
wing-t i p-mounted nacelle. (See fig. 4(a).) 

Results 

Propeller Performance 

The interaction of the lift -induced vortex with 
the wing-t ip-mounted pusher turboprop resulted in 
a thrust enhancement that may be seen in figure 5. 
The power required for cruise conditions at C l = 0, 
where no vortex exists, has been nondimensionali/ed 
and is presented against lift coefficient. As the lift 
coefficient of the wing was increased, a vortex flow 
was created which changed the incoming flow angle 
to the propeller. As a result, at a lift coefficient 
of 0.T the power required to maintain the same 
zero-lift thrust value was reduced by approximately 
lfl percent. This result is probably caused bv an 
increase in propeller effective pitch angle caused by 
the vortex cross flow. In the case of the full-scale 
aircraft, the propeller-blade pitch angle is variable, 
which allows the pitch to be reduced; therefore, the 
rpm may be held constant, which results in a lower 
fuel rate to the engines. 

To simulate the pusher turboprop located other 
than at the wing tip, tests were conducted with a 9- 
in. wing extension attached to the outboard surface 
of the nacelle. There was approximately a 10-percent 
increase in power required at C\ = 0 compared with 
that of the wing-tip-mounted, turboprop configura- 
tion. This may be the result of the propeller being 
located totally behind the wing where the wing wake 
effects, including the interference associated with two 
wing nacelle junctures, red net 1 the propeller perfor- 
mance. There was a negligible reduction in power 
required for constant thrust with increasing lift co- 
efficient. This would indicate a lack of vortex thrust 
enhancement such as that obtained by the pusher 
turboprop located at the wing tip. With the tip 
extension installed, the wing-tip vortex was trans- 
ferred from the propeller location to the new wing 
tip. and the favorable thrust effect resulting from the 
vortex/propeller interaction no longer existed. 

Drag-Coefficient Characteristics 

The aerodynamic effect on drag resulting from 
mounting a high-performance pusher turboprop/ 
nacelle on the wing tip of the basic wing is presented 
in figure G. Adding the unpowered nacelle to the wing 
results in the expected drag increase 1 at zero lift. This 
increment is primarily the result of the added skin- 
friction drag of the nacelle (estimated to be about 


0.00 lb). As the* lift coefficient increases, the drag in- 
crement caused by the nacelle also increases. This 
added drag is probably caused by the interference 
in the juncture between the nacelle and wing under 
lifting condit ions and by the increase in nacelle form 
drag. 

Adding power at either blade rotation angle re- 
sults in a significant decrease in drag due to lift in 
the normal operating range. At a lift coefficient of 
approximately 0.40. the power effect causes a reduc- 
tion in drag equal to the addition of the nacelle. This 
effect is discussed in more detail in the section 'in- 
duced Drag Characteristics.” 

A nacelle incidence angle of —3° was employed 
in an attempt to increase the effectiveness of the 
turboprop/vortex interaction by placing the pro- 
peller above the wing chord plane where it could be 
more aligned with the vortex flow. The vortex tends 
to form just above the wing trailing edge before mov- 
ing downward under the influence of the dovvnwash 
of the wing. The resulting drag-coefficient character- 
istics for this configuration are presented in figure 7. 
Adding power to the nacelle at either blade angle 
significant ly reduces the drag due to lift; at lift coef- 
ficients above about 0.1, drag values lower than the 
value for the wing alone are obtained. Evidently, this 
more favorable location of the propeller wake system 
has a more pronounced effect on the vortex and the 
wing dovvnwash system than does the propeller wake 
for the nacelle at zero incidence, which reduces the 
drag approximately 10 percent. (See figs. G and 7.) 

To determine the effect on drag of a pusher tur- 
boprop located other than at the wing tip. a 9-in. 
wing seel ion was added outboard of the nacelle as 
stated previously (see fig. 4), and the results are pre- 
sented in figure 8. The installed drag associated with 
the unpowered nacelle is more than twice that of the 
wing-t ip-mount ed nacelle (figs. 6 and 8); this result 
should he expected with a wing-nacelle juncture on 
both sides of t lit* nacelle. There is a favorable effect 
of propeller thrust on this large interference drag; the 
lowin' propeller pitch angle (/? = 55.1°) is more effec- 
tive. There is probably an entrainment of flow in the 
region of the wing/nacelle juncture that is caused by 
the turboprop high-speed wake. This wake reduces 
or eliminat es some of the adverse flow effects, which 
results in a reduction in the drag. The configuration 
with the nacelle at —.‘4° has a lower drag due to lift 
t han t he configurat ion with the 9-in. wing-tip exten- 
sion. (Compare fig. 8 with the wing configuration of 
fig. 7.) The data indicate that disrupting the wing- 
tip vortex by the wake from the turboprop may be 
a more effective way of reducing the drag due to lift 
than extending the wing tip. 


4 



Lift-Coefficient Characteristics 

The variations in lift coefficient with angle of 
attack for the wing, wing/nacelle, and wing/nacelle/ 
propeller configurations are presented in figure 9. An 
increase in lift at a fixed angle of attack is indicative 
of a reduct ion in the lift-induced drag. This increase 
in lift would result from a reduction in the effect of 
the lift-induced vortex on the wing downvvash field, 
which increases the effective angle of attack of the 
wing. The addition of the unpowered nacelle to the 
wing tip results in an increase in the lift-curve slope 
of the configuration. This increase is probably the 
result of the “’end plate” effect resulting from the 
physical presence of the nacelle at the wing tip, the 
wing now being nonplanar. The data also indicate 
that there* is a further increase in lift-curve slope as 
a result of the addition of power. This increase is 
probably due to the vortex attenuation effect derived 
from the propeller wake/vortex interaction, which 
results in a further increase in effective angle of attack 
of t he wing. 

Changing the nacelle incidence angle by —.3° re- 
sults in a shift in the angle of attack for zero lift with 
essentially no change in the lift-curve slope. (See 
fig. 10.) This result was expected because of the 
size the nacelle that was deflected —3°. The results 
with power are essentially the same as those noted for 
the undeflected nacelle. (See fig. 9.) Therefore, the 
mechanism for the drag reduction and lift changes 
noted should be the same. 

The results of the addition of the wing-tip exten- 
sion on the basic data of the wing/nacelle/propeller 
configuration with a 0° angle of incidence are pre- 
sented in figure 11. With the nacelle installed, other 
than at the wing tip, there is a minimal increase in 
slope of the lift curve. The effect of installing the 
nacelle/propeller inboard of the wing tip, out of the 
vortex flow, greatly reduced its favorable effect on 
the wing. 

Pitching-Moment-Coefficient Characteristics 

The pitching-moment coefficient is presented 
against lift coefficient in figure 12. The installation 
of the unpowered nacelle at the wing tip at 0° nacelle 
incidence (fig. 12(a)) did not change the static margin 
of the wing alone but did shift the zero-lift pitching- 
moment coefficient in a positive direction. Adding 
power to the configuration with either nacelle inci- 
dence (0° or -3°) resulted in a stable shift in the 
static stability level. This stable effect is maintained 
throughout the lift range and is probably a result of 
the changes in loading on the wing, which is caused 
by the propeller wake effects on the wing down wash. 


Pitching-moment results for 0° nacelle incidence 
with wing-tip extension are presented in figure 12(c). 
The nacelle-alone installation causes a slight reduc- 
tion in the static stability level, which is offset by 
the propeller effects and is equal to the wing-alone 
results. 

Induced Drag Characteristics 

A comparison of the change in drag between 
the basic wing and each wing-tip-mounted pusher 
turboprop configuration is presented in figure 13 at 
a lift coefficient of 0.3. 

The installed drag of the nacelle mounted on the 
wing tip of the basic wing, without propeller, is ap- 
proximately eight counts greater than the calculated 
flat-plate skin-friction drag based on the wetted area 
of the nacelle (dashed line in fig. 13). This differ- 
ence includes form drag and possibly some interfer- 
ence drag of the wing/nacelle combination. The in- 
stalled drag increment of the nacelle-turboprop con- 
figuration with a blade pitch angle of 57° is approx- 
imately one-fifth of that of the wing-nacelle configu- 
ration. This drag reduction is probably due mainly 
to an induced drag reduction of the wing associated 
with the turboprop/vortex interaction (refs. 7 and 8). 
The vortex flow may be altered by the interruption 
of the vortex core axial How by the propeller wake. 
This interruption causes the vortex to dissipate and 
thereby reduce its effect on the wing down wash field 
resulting in a reduction in induced drag. 

Although the lower pitched blades have higher 
drag at Cl = 0 (fig. 6), possibly because of the 
greater propeller frontal area, they are more effective 
in reducing induced drag over the lift range above 
Cl = 0.2. At the highest test lift coefficient, the 
drag due to lift of the wing for the lower pitched 
blades is greater than that for the high pitched blades 
due possibly to the degree of propeller/ vortex-flow 
interaction. 

In an attempt to further reduce the drag of the 
wing/nacelle combination, the nacelle was set at —3° 
incidence relative to the wing as stated previously. 
(See fig. 13(a).) When t he wing is set near the cruise 
angle of attack of 3°. the nacelle is near 0° angle 
of attack relative to the flight path, which should 
contribute to the overall reduction in drag due to the 
reduced nacelle frontal area. The turboprop wake 
is nearer the center of the vortex at this incidence 
angle, and its effect on induced drag is shown by 
the bar graph in figure 13(a). The negative nacelle 
incidence resulted in an additional reduction in drag 
at lift coefficients of 0.3, such that the drag is less 
than that of the basic wing. The basic wing results 
do not include any nacelle drag. Again, the lower 


5 



propeller pitch angle is more efficient, as in the case 
of the zero incidence. 

Direction of Propeller Rotation 

The elfect of rotating the turboprop in the same 
direction as the wing-tip vortex (promt at ion, Cp in 
the negative Cj j range shown in figs. 5 and (>) instead 
of in a counterrot at ional direction is presented in 
figure' 1 3(1) ) . There is a drag increase associated 
with the prorotation case, as would be expected. 
This increase is due to a reduction in the relative 
propeller blade pitch angle, which requires a higher 
rpm (ref. 9) and a higher power input to the turbine 
in the negative lift range (fig. 5) to maintain the 
constant thrust level used in this investigation. 

There was no induced drag reduction with the tip 
extension installed (0° incidence) as can be seen in 
the bar chart in figure 13(c). When the tip vortex was 
moved away from the propeller plane, the induced 
drag reduction was lost. 

Increased Lift Coefficient 

A comparison of the change in drag between the 
basic wing and wing-tip-mounted pusher turboprop 
is presented at a lift coefficient of 0.4 in figure 14. 
Trends at C[ — 0.1 are similar to those at C\ J = 0.3, 
and the favorable effect of the interaction of the 
wing-t ip-mounted pusher turboprop and the vortex 
at the higher lift coefficient is probably due to the 
increased strength of the wing-tip vortex associated 
with the higher lift coefficient (fig. 11(a)). An in- 
creased installed drag for the extended wing/nacelle 
at C j j = 0.1 is presented in figure 11(b) compared 


with that at Cf 0.3 in figure 13(c). This increase 
is probably the result of the increase in wing/nacelle 
interference at this greater lift coefficient. 

Conclusions 

An exploratory investigation has been conducted 
at the Langley Research Center to determine the 
installed performance of a wing-tip-mounted pusher 
turboprop. The study utilized a semispan model that 
had an unswept, untapered wing with a symmetrical 
airfoil section and an air-driven motor to power an 
SR-2 high-speed pusher propeller located on the tip 
of the wing. The results of this study indicated the 
following: 

1. The performance of a propeller located just 
behind the wing tip is increased as a result of the 
influence of the wing-tip vortex How. 

2. The effect of the propeller wake on the wing- 
tip vortex resulted in a reduction in the drag due to 
lift of the wing at each nacelle incidence tested. 

3. The propeller performance enhancement and 
the reduction in drag due to lift associated with 
the wing-tip pusher turboprop is forfeited when the 
turboprop is located inboard of the wing tip (wing 
t ip extended). 

4. A — 3 n turboprop nacelle incidence resulted 
in an additional drag reduction of approximately 
10 percent at a lift coefficient of 0.3. 

NASA Langley Research Center 
Hampton, VA 23665-5225 
June 29, 1987 



Appendix 

Measured-Forces Bookkeeping 

Forces 

The force measurements of the balance have been 
reduced to coefficient form using the exposed semi- 
span wing area. 

Thrust 


fuselage, plus the thrust balance measurements, lo- 
cated in the nacelle. The sum of these measurements 
are the total drag of the wing/nacelle configuration 
as follows: 

Drag = D um \ u 4- T 

The model coefficients were then determined by 
dividing the forces by the dynamic pressure and 
exposed wing area as follows: 


The thrust of the propeller and hub was obtained 
from the thrust balance minus the pressure force 
between the hub and nacelle as follows: 


Drag 

to = 




T ~ T bii I - A cav (pcav - Poc ) 


Drag 

The drag of the model was obtained from the mea- 
surements of the main balance, located inside the 


Cr - 


Lift 


C n 


Pitching moment 
% o ST 


7 


References 

1. Abeyounis, William K.; and Patterson, James C., Jr.: 
Effect of Underwing Aft-Mounted Nacelles on the Longitu- 
dinal Aerodynamic Characteristics of a High - Wing Trans- 
port Airplane. NASA TP-2447, 1985. 

2. Lamb, Milton; Abeyounis, William K.; and Patterson, 

James C., Jr.: Nacelle/Pylon/ Wing Integration on a 

Transport Model With a Natural Laminar Flow Nacelle. 
NASA TP-2439, 1985. 

3. Stefko, George L.; and Jeracki, Robert J.: Wind-Tunnel 
Results of Advanced High Speed Propellers in the Take- 
off ’ Climb, and Landing Operation Regimes. NASA 
TM-87054, 1985. (Available as AIAA-85-1259.) 

4. Patterson, James C., Jr.; and Flechner, Stuart G.: 
An Exploratory Wind-Tunnel Investigation of the Wake 
Effect of a Panel Tip-Mounted Fan-Jet Engine on the Lift- 
Induced Vortex. NASA TN D-5729, 1970. 


5. Patterson, James C., Jr.; and Jordan, Frank L., Jr.: 
Thrust- Augmented Vortex Attenuation. Wake Vortex 
Minimization , NASA SP-409, 1977, pp. 251-270. 

6. Fox, Charles 1L, Jr.; and Huffman, Jarrett K.: Calibra- 
tion and Test Capabilities of the Langley 7- by 10- Foot 
High Speed Tunnel. NASA TM X-74027, 1977. 

7. Patterson, James C.. Jr.; and Flechner, Stuart G.: 
Exploratory Wind- Tunnel Investigation of a Wingtip- 
Mounted Vortex Turbine for Vortex Energy Recovery. 
NASA TP-2468, 1985. 

8. Patterson, James C., Jr.: Vortex Attenuation Obtained 
in the Langley Vortex Research Facility. J. Aircr., 
vol. 12, no. 9. Sept. 1975, pp. 745-749. 

9. Patterson, James C., Jr.; and Bartlett, Glynn R.: Ef- 
fect of a Wing-Tip Mounted Pusher Turboprop on 
the Aerodynamic Characteristics of a Semi-Span Wing. 
AIAA-85-1286, July 1985. 


8 


I 







(b) Change in velocity components due to vortex flow. 
Figure 3. Concluded. 


12 





2.00 spacer 



Q 


(a) Schematic of wing, fuselage, and pusher turboprop, 
figure 4. Drawings of semispan model. Dimensions are in inches unless otherwise noted 




(b) Details of main and turboprop balances and turbine drive system. 

Figure 4. Concluded. 






Figure 6. Vortex/ propeller interaction oil drag coefficient versus lift coefficient for 0° incidence 









17 




L 


Figure 8. Vortcx/propellcr interaction on drag coefficient versus lift coefficient for 0° incidence with wing-tip 
extension. 


18 




O Wing 
A Wing/Nacelle 



a, deg 

Figure 9. Effect of nacelle and propeller installation on lift coefficient versus angle of attack at 0° incidence. 


19 



6 


.5 


.4 


.3 


C 


L 


.2 


.1 


0 



Figure 10. E 


20 









O Wing 
A Wing/Nacelle 


0 

5 

□ Wi 
O Wi 

ng/Nacelley 

ng/Nacelle/ 

'Propeller, f 
Propeller, p 

1-55. 1° — 
1=57. 0° 

4 




B 

3 



■ 

r 

> 



mm 




/ 








^a! 

V 





1 2 3 


a, deg 


Figure 11. Effect of nacelle and 
with wing-tip extension. 


propeller installation on lift coefficient versus angle of attack at 0° incidence 


21 







(b) Comparison of propeller rotation same as and opposite vortex rotation. 


With extension 



(c) Comparison with and without wing-tip extension for propeller rotation opposite vortex rotation 





(a) Basic wing/nacelle/propeller. 

Figure 14. Drag coefficient increment from wing alone at ( /. = 0.4 







NASA 

Mali final Aeronautics and 

SyaueAam.nistrat.on 


Report Documentation Page 


1. Report No. 

NASA TP-2739 


2. Government Accession No. 


4. Title and Subtitle 

t: valuation of Installed Performance of a Wing-Tip-Mounted 
Pusher Turboprop on a Setnispan Wing 


7. Author(s) 

James C\ Patterson. Jr., and (dyiin R. Haitlott 


9. Performing Organization Name and Address 

NASA Langley Research Center 
Hampton. \ A 23665-5225 


3. Recipient’s Catalog No. 


5. Report Date 

August- 1987 


6. Performing Organization Code 


8. Performing Organization Report No. 

L- 19252 


10. Work Unit No. 

535-03-01-01 


12. Sponsoring Agency Name and Address 
National Aeronautics and Space Administration 
Washington, DC 20546-0001 


11. Contract or Grant No. 


13. Type of Report and Period Covered 

Technical Paper 


14. Sponsoring Agency Code 


15. Supplementary Notes 


16. Abstract 


An exploratory investigation has been conducted at the Langley Research Center to determine the 
effect of a wing-tip-mounted pusher turboprop on the aerodynamic characteristics of a semispan 
wing Tests were conducted on a semispan model with an unswept, untapered wing and an air- 
driven motor that powered an SR-2 high-speed propeller located on the tip of the wing as a pusher 
propeller. All tests were conducted at a Mach number of 0.70 over an angle-of-attack range from 
approximately - 2 ° to 4° at a Reynolds number of 3.82 x 10 (> based on the wing reference chord of 
13 in. The data indicate that, as a result of locating the propeller behind the wing trailing edge at 
the wing tip in the crossflow of the wing-tip vortex, it is possible to improve propeller performance 
and simultaneously reduce the lift-induced drag. 


17. Key Words (Suggested by Authors(s)) 

Turboprop Performance 

Propfan Wing 

Wing-tip vortex Propulsion 

Wing-tip pusher propeller Installation 

Vortex energy recovery 
Induced drag 

18. Distribution Statement 

Unclassified Unlimited 

Subject Category 

05 

19. Security Classif.(of this report) 

Unclassified 

, 20. Security Classif.(of this page) 

[ Unclassified 

21. No. of Pages 

1 

22. Price 

A02 


NASA FORM 1626 OCT 86 

For sale by the National Technical Information Service. Springfield, Virginia 22161-2171 


N ASA-Langley, 1987 


I