Effect of Wingspan on the Trend of
Download for Winged Helicopters in Hover
High-Wing Configuration

Low-Wing Configuration

Which is more efficientfor hovering ?

Shunsaku ARITA, Noriaki ITOGA
National Defense Academy

Experimental Research

Background
Winged helicopter has long been studied for enhancing maneuverability or high-speed flight.

1950s

http://www.aviastar.org/helicopters_eng/mc
donnell_xv-1.php

2010shttps://vertipedia.vtol.org/air
craft/getAircraft/aircraftID/2
91

https://en.wikipedia.org/wiki/Lo
ckheed_AH-56_Cheyenne

https://en.wikipedia.org/wiki/
Piasecki_X-49_SpeedHawk

https://www.airbus.com/en/who-we-are/our-history/helicoptershistory/x3

Background
There are high and low-wing configurations for winged helicopters
High-Wing Configuration

https://vtol.org/qr/march-2012https://www.airbus.com/en/who-we-are/our-history/helicopters-history/x3

Low-Wing Configuration

https://en.wikipedia.org/wiki/Piasecki_16H_Pathfinder

https://www.popsci.com/technology/bell-360-invictus/

Background
One problem with winged helicopters
DownwashDownload acting on wings

Low-speed flightorHovering

Studies (including for tiltrotors) have been conducted to reduce wing downloads.
These researches are summarized in the paper (Sugawara et al. 2020)

BackgroundThe distance between the rotor andwing affects the hovering performance

High-wing configuration is more efficient for hovering!
Low-wing configuration is more efficient for hovering!

There is no unified view…
It is worthwhile to examine!

Background
High-wing configuration is better(smaller download)

Cassarino, 1970

Kobayashi et al., 2019

Background
High-wing configuration is better(smaller download)
Rotor

Low velocity
Small download
High velocity
Large download

Explanation by momentum theory

BackgroundLow-wing configuration is better(smaller download)

Felker and Light, 1988

Nakashima and Itoga, 2018

BackgroundLow-wing configuration is better(smaller download)

High-wing

Low-wing
Time history of pressure on the wing surface(Makofski and Menkick, 1958)

Explanation by periodic load

BackgroundExperimental conditions of previous studies

High-wing is better
Cassarino,1970

Fuselage
Wingspan(ratio to rotor
diameter)

Kobayashi et al.,2019

Low-wing is better
Felker and Light,1988

exist

Nakashima andItoga, 2018

none0.50

0.61

0.75

0.79

(Relatively short)(Relatively short)(Relatively long)(Relatively long)Objectives of this research• Confirming if the relationship between the download and rotor-wing
distance is reversed by the existence of fuselage or changing wingspan.
• If it is reversed, consider the cause of it.

Experimental Apparatus
Details of Rotor

Main Rotor
Balance Sys.

Rotor Radius

569mm

Blade Chord

60mm

Airfoil

NACA0015

TwistNone

Number of blades

2Hinge offset

17mm

Root cutout

113mm

Fuselage

Details of Fuselage

Wing
Support PillarLength

644mm (1.13R)

Width

189mm (0.33R)
Details of Wing

Span897mm(0.79D), 569mm(0.5D)

Cord242mm (0.43R)
12

Experimental Conditions

z/R=0.2

z/R=0.3

z/R=0.4

z: Distance between rotor and wing
R: Rotor radius
13

Experimental Conditions
Rotor operating torque

𝐶

4.75

10

Corresponding to approximately
5 10𝐶𝐶

8.5

Wingspan0.79R

10Corresponding to approximately
8 10𝐶

0.5R

With or without fuselage

Results
Wingspan 0.5R

0.22

0.11

0.21

0.1
DL/T

WithFuselage

DL/T

Wingspan 0.79R

0.2

0.190.09

0.08
4681040.2

0.08

0.19

0.07

0.18

0.17
468CQ

6810810CQ

DL/T

Without
Fuselage

DL/T

CQ

100.06

0.05
46CQ

z/R

●
●
●

０．２
０．３
０．４

Results
Wingspan 0.5R

0.22

0.11

0.21

0.1

0

DL/T

With
Fuselage

DL/T

Wingspan 0.79R

0.2

0.19
4

Download islarger for thefuselage

6810

CQ

0.2

No change0.08
in the trend 4of the orderof the plots 0.08

6810810

CQ

0.07
DL/T

DL/T

0.19

Without
Fuselage

0.09

0.18

0.17
468CQ

100.060.05
46CQz/R●●●

０．２０．３０．４

Results
Wingspan 0.5R

0.22

0.11

0.21

0.1

0.20.19
4Lowwing isbetter
6DL/T

With
Fuselage

DL/T

Wingspan 0.79R

8CQ

0.2

10The orderof the plots
is inversed

0.08
4High- 8
CQ iswing
better
610

z/R

0.08

0.07
DL/T

Without
Fuselage

DL/T

0.19

0.09

0.18

0.17
468
CQ

100.06

0.05
468CQ

10●
●
●

０．２
０．３
０．４

Verification and Discussion
Details of Wing

Details of Rotor
Rotor Radius

360mm

Span

582mm(0.81D)

Blade Chord60mm

Cord157mm(0.44R)

Airfoil

NACA0015

Twist

None

Number of blades

2Hinge offset

17mm

Root cutout

113mm

𝐶4.75

10Corresponding toApproximately
7 10𝐶● Pressure ports

Verification and Discussion
Average Pressure [pa]

30
25z/R

20

●
●

0.2 (High-wing)
0.5 (Low-wing)

0.2

0.4
r/R [-]

15
105000.6

r: Distance from the rotor center
R: Rotor radius

0.8

Verification and Discussion
Average Pressure [pa]

30
25z/R

20

●
●

0.2 (High-wing)
0.5 (Low-wing)

0.2

0.4
r/R [-]

1510500

Short wingspan0.60.8

Verification and Discussion
Average Pressure [pa]3025z/R

20●●

0.2 (High-wing)
0.5 (Low-wing)

0.2

0.4
r/R [-]

15
105000.6

Long wingspan0.8

Verification and Discussion
Average Pressure [pa]

3060
40

25z/R

20

●
●

0.2 (High-wing)
0.5 (Low-wing)

40
20
015
100120

240

360

0120

240

360

Explanation by periodic load

5020
060

0

Explanation by momentum theory

0.2

0.4
r/R [-]

0.60.8

Conclusion• Download of winged helicopter in hover is experimentally investigated.
• There are both cases where the download becomes larger and smaller as
the rotor-wing distance increases.
• The download trend was inversed by changing wingspan; it can at least
partially be explained by mixing the momentum theory and periodic load.