Japan-Korea Joint Workshop on Rotorcraft
February 10, 2023, Online

Advanced Compound Helicopter
Research and Development
Masahiko SUGIURA, Hideaki SUGAWARA, Keita KIMURA,Yasutada TANABE, and Noboru KOBIKI
High-Speed Rotorcraft Technology Team
Aviation Environmental Sustainability Innovation HubAviation Technology Directorate
Japan Aerospace Exploration Agency (JAXA)

Outline• Background and objectives••

History and recent developments of compound helicopters
A conceptual study of high-speed compound helicopter at JAXA

• Technology Issues related to high-speed compound helicopters••••

Optimal rotor design for high advance ratio flight
Rotor/Wing Interaction and Single-rotor Lift-offset
Rotor/Propeller Interaction
Low drag fuselage• Realization of a high-efficiency compound helicopter through applying theadvanced technologies• Spin-off effects• Summary and future works

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Maximum flight speed, kts

Background: the conventional helicopter
performance limitation

Increase pitch angle

Year of development
Conventional helicopter maximum flight speed history

Decrease pitch angle

Inflow to the rotor blade and control of therotor blade pitch angle

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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History of Compound Helicopters

Lockheed AH-56 Cheyenne
Development: 1966-1972, 215kt, mu~0.52

Ref) Harris

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Recent Developments of High-Speed Rotorcraft

Sikorsky X-2
Development: 2008-2010, max 250 kt, mu~0.65

Bell-Boeing V-22 Osprey
Development：1982-1997：
In production: 1997~,max 275 kt, cruise 241 kt

Airbus Helicopters X3Development: 2010-2013, max 255 kt, mu~0.7
Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online4

On-going Developments of Compound Helicopters

Sikorsky S-97 Raider
Vne 240 kt, Cruise 220 kt
In test flight

Airbus Racer
Cruise 217 kt ?
First flight expected in 2022

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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A Concept of Compound Helicopter Proposed by JAXA・Designed for EMS of 4 ton class・Electric driven anti-torquepropellers at wing-tips
・Aft-mounted pusher propeller
・Target max speed: 500km/hr (270kts)
・Max advance ratio, mu=0.8Ref) Tanabe Y, Aoyama T, Kobiki N, Sugiura M, Miyashita R,Sunada S, Kawachi K, and Nagao M, A conceptual study ofhigh speed rotorcraft, 40th European Rotorcraft Forum,Southampton, UK, Sept. 02-05, 2014.
Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

6Additional Design Features

Wing-flaps down
during hovering
flight to reduce
download

Wing-flaps in differential
deflections during forward
flight to generate a rolling
moment countering thesingle-rotor lift-offset

Landing gears up
to reduce thefuselage dragAdvanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Technology issues for high-speed
compound helicopter
Rotor/Wing aerodynamic
interaction

Low aerodynamic dragrotor hubOptimized rotor/wing lift
share at high speed

Thrust propeller toachieve high speed

Electrical driven antitorque propellers
Low aerodynamic
drag fuselage

Advanced rotor blades
optimized for high advance
ratio flight

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online8

Outline• Background and objectives••

History and recent developments of compound helicopters
A conceptual study of high-speed compound helicopter at JAXA

• Technology Issues related to high-speed compound helicopters••••

Optimal rotor design for high advance ratio flight
Rotor/Wing Interaction and Single-rotor Lift-offset
Rotor/Propeller Interaction
Low drag fuselage• Realization of a high-efficiency compound helicopter through applying theadvanced technologies• Spin-off effects• Summary and future works

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

9Optimal Rotor Design for High Advance Ratio Flight

μ=0.4

Reversed flow region at high advance ratio

μ=0.8

μ=0.6

μ=0.9

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online10Large root-cut blade design for high-mu flight

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

11Design variables for chord and twist
S10.5cref

S2S3S4S5S6cref

Δrmin=0.1Rr/R=0.130

Δr=0.1R
Transition

Δrmin=0.1R
Rectangle

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

r/R=1.000

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Optimal rotor for flight at mu=0.7,
effect of swept angle
0.700
UH-60A
0.690

Figure of Merit
FM in Hover

Forward swept

Optimal Baseline
Backward swept

0.680

Forward swept

Optimal Baseline

0.670

Backward swept

0.660
0.650
UH-60A Reference

0.640
0.630
2.50

3.00

3.50

4.00

4.50

5.00

5.50

6.00

6.50

7.00

L/DE lift-share of 30%
L/DE at mu=0.7,Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Wind-tunnel testing of the tip portions
Portion of bladetips (20%) arepicked up
Optimal baseline

Forward swept

Optimal baseline

Backward swept

Forward swept

UH-60A

Backward swept

UH-60A

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Blade-tip models
About 1/2 scale
Optimal Baseline
5 components
balance
Cover

Backward swept

Forward swept

UH-60A

Turn table

r/R = 0.5
r/R = 0.875
r/R = 0.75
End plate

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Aerodynamics of blade tips
M=0.4

M=0.6

Ranking of L/Dmax at M=0.6：
1) Backward2) Baseline3) Forward
4) UH-60A

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Drag divergence Mach number of blade tips
Mdd (exp.)

Mdd (CFD)

Swept Back Angle

Baseline

0.82

0.80

0.0°

Backward

0.84

0.83

-30.5 °

Forward

0.82

0.81

25.3°

UH-60A

0.82

0.8020.0°

Mdd：dCd/dM>0.1
Ranking of Mdd：1) Backward2) Forward3) Baseline
4) UH-60A

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

17Outline• Background and objectives••

History and recent developments of compound helicopters
A conceptual study of high-speed compound helicopter at JAXA

• Technology Issues related to high-speed compound helicopters••••

Optimal rotor design for high advance ratio flight
Rotor/Wing Interaction and Single-rotor Lift-offset
Rotor/Propeller Interaction
Low drag fuselage• Realization of a high-efficiency compound helicopter through applying theadvanced technologies• Spin-off effects• Summary and future works

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Rotor/Wing Interaction

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Single-Rotor Lift-Offset System
 Proposed differential flap system• Deflect upward under the advancing side, and deflect downward under the retreating side Generate an imbalance of lift on the left and right wings resulting in a rolling moment• Expected to obtain a large rolling moment by small flap deflections
 Occur rolling moment due to aerodynamic interaction
 The main rotor creates the opposite rolling moment and results in a single-rotor lift-offset state.

𝐿𝑂 =Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

𝐶𝐶20

Lift-Offset by the Differential Flaps
 Obtain the maximum lift-offset values at the differential flap angle of 5 deg Arise the lift-offset due to the aerodynamic interaction even with zero flap deflection
 Cause the effect of aerodynamic interaction on the wing with different type of rotors
0.45

Rotor

0.40

Lift-Offset

0.35
0.30
0.25
0.20
0.15
0.10

Optimized rotor blade

0.05

UH-60A rotor blade

0.00
012
34
Differential flap angle [deg]Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

5621

Effect of Lift-Offset on Rotor Performance
9.0

Rotor

8.0

𝑴𝑹/CC𝑪LR𝑫𝑬DE𝑳 ⁄𝑪

7.0
6.0
5.0
4.0
3.0
2.0

Opt-rotor

1.0

UH-60A rotor

0.0
0

0.1

0.2
0.3
Lift-offset

0.4

0.5

 Opt-rotor• Provide higher aerodynamic performance, approximately two times of the UH-60A rotor• Enhance by approximately 50% at the lift-offset of 0.37 compared with zero flap deflections
 UH-60A• Improves 25% at the lift-offset of 0.40 compared with zero flap deflections
Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Overall Performance
12.0

Overall

10.0⁄𝑪
𝑺𝒚𝒔𝒕𝒆𝒎C𝑪L𝑳/C
DET𝑫𝑬

8.0
6.0
4.0
Opt-rotor

2.0

UH-60A rotor

0.0
00.1

0.2
0.3
Lift-offset

0.4

0.5

 The lift-to-drag ratio increases by 10% compared with zero flap deflections
 The opt-rotor is higher than the UH-60A rotor.
 The combination of improved rotor performance through optimization and lift-offset technology by the differential flap
system can further enhance the overall aerodynamic performance.
Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

23Sectional Lift Distributions on the Wing
1.20

Opt-rotor

1.00

UH-60A

cl0.800.60

UH-60A

0.40
0.20
0.00

Opt-rotor

Ret. side

Adv. side-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8y/R

 Both rotors reduces the sectional lift on the wing under the advancing side.
 UH-60A rotor causes stronger aerodynamic interaction.
 Under the retreating side, the sectional aerodynamic performance of the wing with the opt-rotor reduces partiallythan with the UH-60A.
 The induced velocity distribution from the rotor around the wing is different between the rotors.
Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online24Outline• Background and objectives••

History and recent developments of compound helicopters
A conceptual study of high-speed compound helicopter at JAXA

• Technology Issues related to high-speed compound helicopters••••

Optimal rotor design for high advance ratio flight
Rotor/Wing Interaction and Single-rotor Lift-offset
Rotor/Propeller Interaction
Low drag fuselage• Realization of a high-efficiency compound helicopter through applying theadvanced technologies• Spin-off effects• Summary and future works

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

25Rotor/Propeller Interaction

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Downwash from the main rotor in hover

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Flowfields of Rotor/Propeller Interaction

Isolated propeller

Rotor/Propeller Interaction

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online28Performance of side propeller
SP_iso : isolated side propeller
SP/MR : Main rotor with side propeller

C ,Pitch angle 𝜃=More is better𝑇𝜌𝑛 𝐷

𝐹𝑀 ==𝑣 =[deg]𝑇𝑄

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Side propeller thrust fluctuations
with/without the main rotor

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online30

Outline• Background and objectives••

History and recent developments of compound helicopters
A conceptual study of high-speed compound helicopter at JAXA

• Technology Issues related to high-speed compound helicopters••••

Optimal rotor design for high advance ratio flight
Rotor/Wing Interaction and Single-rotor Lift-offset
Rotor/Propeller Interaction
Low drag fuselage• Realization of a high-efficiency compound helicopter through applying theadvanced technologies• Spin-off effects• Summary and future works

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Low drag fuselage designCD

CD0*Sref

0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00

“Clean”

Fuselage/Wing/Htail/Vtail
Fuselage/Wing
Fuselage/Htail/Vtail
Fuselage/Htail
Fuselage

Target(-20%)
Achieved(-40%)

4-ton EMS Helicopter

CD0=0.1217-12-8-404812162024α

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Realization of a high-efficiency compound helicopter
through applying the advanced technologies
20Comparison of Fule Mileage

1.8

18

1.6

16

1.4

Fuel mileage ratio(HP/kt)14121086

1.2
1.020.2
JCH-2 (+Optimalrotor)

JCH-3 (+Single-rotor
lift-offset)100%-1%-21%

-24%

0.6
0.4

Conventional
JCH-0 (Compound JCH-1 (+Low draghelicopter @ 250 configuration @ 500fuselage)
km/hkm/h)

+64%

0.8

40

Comparison of Fuel Mileage with Conventional Helicopter

0.0Conventional
JCH-0 (Compoundhelicopter @ 250 km/h configuration @ 500km/h)

JCH-1 (+Low dragfuselage)

JCH-2 (+Optimal rotor) JCH-3 (+Single-rotor
lift-offset)

Comparison of fuel mileage with conventional helicopter
Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Spin-off Effects
Numerical Analysis FlowrFlow3D is being widely used for rotor analysis in Japan
HART-II Fan-Plot, PL=1080 [Nm/rad]
13Blade structural properties
Rotating speed
Root constraint conditions

Flow conditions
Rotor blade controls
Trim conditions

12Observer conditions

1110

rMode

rFlow3D /JANUS

rNoiseNatural Frequency / Omega_ref

98765432
1Natural frequencies
Natural mode shapes(represented withpolynomials)

0Surface pressure on
rotating bladesSound pressure time
history at observation
points00.2

0.4

0.60.8

11.2

Rotor Speed / Omega_ref

Fan-plot by rMode

BVI noise carpet by rNoise

Coaxial rotor

Quad-rotor in ground effect by rFlow3D

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

34Summary•

A new concept of compound helicopter proposed by JAXA is illustrated. Technology issues
related to the high-speed compound helicopter are addressed.
– （１）Optimal design of rotor for high advance ratio flight– （２）Single-rotor lift-offset to improve the rotor performance in high-speed flight– （３） Rotor/propeller interaction– （４） Low drag fuselage design•

Through applying of the above advanced technologies, a high-efficiency compound
helicopter can be realized where the flight speed is doubled while the fuel mileage can bekept the same or even less than the conventional helicopters.
• Spin-off effects of this research is introduced. The multi-disciplinary CFD/CSD/Trim/Noise
prediction tool-chain (rFlow3D) developed alongside with this research has been applied towind-turbines, multiple rotors, Mars helicopter and others.

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Future Works
Optimal high-mu rotor design and other related technologies will be applied to alarger rotorcraft.

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online36Thank you for your kindattentions!

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Appendix

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

38Effect on cyclic pitch angle
Pitch angle :𝟏𝒄Lateral cyclic(Retside)
aftfront(adv-side) lateral cyclic is smaller than other shapes ⇒ more efficient AoA available!
Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Sweep angle effect (Front-side)(Ret-side)
Total vel.

Vel. by rotation@Vel. by inflow
inflow

Forwarddynamic pressure@tip : Decreased(Adv-side)

Backward

dynamic pressure@tip : increased

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Sweep angle effect (aft-side)(Ret-side)@Vel. by inflow
Vel. by rotation

inflow

Total velocity

ForwardBackward

dynamic pressure@tip : Increased

dynamic pressure@tip : Decreased

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Forward

front

Lift distribution (CnM2)
Backward

aft

aft
front

 Forward : tend to generate more lift in aft-side Backward : more lift in front-side
Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Forward

front

Wake shadow effect
BackwardaftWind speed : front-halt > aft-half

front

aft

Lift tends to be smaller in aft-side!

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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Total effect

Backward(1)Backward sweep
Thrust(2)Wake effectTotal

Thrustfront

Unbalanced(→large )Out of good
AoA…

Balanced(→small )Keep good
AoA!

aftForward(1)Forward sweep
ThrustfrontThrust(2)Wake effect

Total

aft

Advanced Compound Helicopter Research and Development, Sugiura, JAXA, Japan-Korea Joint Workshop on Rotorcraft, Online

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