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

Simulation and design of propellers for awinged compound helicopter○Keita Kimura, Hideaki Sugawara, Yasutada Tanabe(Japan Aerospace Exploration Agency(JAXA)
2023.2.10

1Topics
1. Introduction
2. Methodologies
3. Results Summary
3-1
Side propeller
3-2 Tail propeller

4. Concluding remark

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2Development of High-speed helicopter

Sikorsky Raider [1][2]Airbus RACER[3]SB-1 DEFIANT [1][2]

JAXA conceptual compound helicopter [4]✓ Compound helicopters with a fixed wing and propellers are promising way to higher speeds[1][2]✓ In 2013, JAXA presented a concept for a compound helicopter that aims for a flight speed of500km/h (fixed wing + side propellers + tail propellers)[4][1][2] "LOCKHEED MARTIN HP,“. [Online].

2023.2.10 [3] Airbus, "Airbus Helicopters reveals Racer high-speed demonstrator," 20 6 2017. [Online].

[4] Y. Tanabe, et al, “A Conceptual Study of High Speed Rotorcraft,” 40th ERF, Southampton, UK, September, 2014.

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Technical Issues
Main rotor blade design suitablefor high advance ratioReduction of hub dragTail propeller for highspeed flight

Aerodynamic
interference between
wings and rotor blades
Low-drag fuselage

Tail propeller for highspeed flight

JAXA conceptual compound helicopter

In this study, focus on Side/Tail propeller design2023.2.10

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Overview for methodologies
Propeller design flow
(1) Conceptual Design Phase
・Set target condition(Flight speed, required thrust, size and so on)・Research about aerodynamic interactions
b/w Main rotor and/or fuselage
・Define design variables (N = 5~6)

Optimization
startPropThrust
Flightspeed

convergence？
Add new point(s)Low/high-fidelity simulations
Calculate objective function𝑓(𝑥)ԦBEM/BEMT

𝑥𝑚,𝑛 : design variables(2) Optimization Phase

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MR wakeNo

Yes

Surrogate model(Kriging + ExpectedImprovement)

CFD

𝑓(𝑥)
Ԧ

Initial sample points𝑥Ԧ
𝑥1,1 𝑥1,2𝑥1,𝑛𝑥2,1 𝑥2,2 ⋯ 𝑥2,𝑛𝑥3,1 𝑥3,2𝑥3,𝑛Solidity?
Tip speed?
Diameter?

Blade molding (1/7scale)

Propeller performancemeasured in wind tunnel

Estimated func.
Approx. error𝑥(3) Evaluation Phase(by wind tunnel test)5

CFD solver : rFlow3DNumerical methodologies in this study

Outer grids

Governingequations
Spatialdiscretization

Three-dimensional compressible NavierStokes equations
Finite volume method
4 stages Runge-Kutta (Background)

Time integration

Dual-time stepping, LU-SGS (Blade,Fuselage）

Viscous terms

2nd order central difference method
Structured grid : FCMT (Fourth-ordercompact MUSCL TVD) [9]Reconstruction
Unstructured grid : MUSCL+Green-Gauss
with Hishida’s limiter
Advection terms

mSLAU (modified SLAU)✓ Moving overlapped grid method provides a direct representation of the rotor blade motion✓ Trim analysis function can reproduce various flight conditions such as analysis with target
thrust maintained

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Side-propeller design note (1/2)
1. Aerodynamic interference with the downwash of the main rotor(especially when hovering)・Hover : having a major impact

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・Cruise : relatively small impact

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Side propeller/ Main rotor interaction

Target

SP_iso(isolated propeller)

SP/MR(propeller/Main rotor interaction)
Flow visualization

Thrust - efficiency✓ CFD analysis under isolated propeller (SP_iso) and interference condition (SP/MR)✓ In hovering, thrust increase due to wake interference > improved performance

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Verification of propeller performance
Propeller stand-alone drive
connected to the sting

TargetRotation~8000 rpm

Advance ratio J = 2.0

Contents before making it into Paper
Balance : obtain
Thrust & Torque*R = 0.125 m
WindPerformance test
@JAXA 2m×2m Low-speed wind tunnel

Propeller efficiency @ J = 2.0✓ Designed propeller made in 1/7 scale (RC helicopter scale)✓ Wind tunnel test to confirm propeller performance𝑇𝑉✓ Obtain Thrust/Torque to get propeller efficiency 𝜂 = 𝑄𝜔⇒ Confirmed significant performance improvement

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Difficulty in tail-propeller design
Points to note :✓ Thrust large enough to balance fuselage drag at high flight speed(assuming 500 km/h)✓ Thrust distribution between side props and tail prop (see figure)✓ Aerodynamic interference with Main rotor/fuselage ?
✓ Sizing to avoid contact with the groundTail80%?

Ret-side10%?

Adv-side10%?

Example of Thrust distribution(different from the actual numbers)

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Some spacing between
propeller and ground10

Aerodynamic Interactions✓ 2 kinds of effects were investigated by using CFD

Z✓ Fuselage/Tail propeller: positive effect on propeller efficiency✓ Main rotor/Tail propeller: small impact・w/Fuselage

・w/Main rotor
Tail propeller
position

Main rotor

Tail propeller
𝑈∞ = 70 m/s

Target𝑈∞ = 30 m/s

Target𝑈∞ = 30 m/s

More is better

Thrust – efficiency (w/&w/o Fuselage)
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𝑈∞ = 70 m/s

More is better

Thrust – efficiency (w/&w/o Main rotor)
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Concluding remarks
An overview of JAXA’s achivements on propeller design for high-speed compoundhelicopters is presented.

 Side propeller✓ CFD analysis confirms trend of increased thrust generated during hover(improved performance)✓ Presented a concept to enhance system performance by applying different
shapes on the Adv-side and Ret-side propellers.
 Tail propeller✓ Confirm the effect of interference between the fuselage and the main rotor(Positive effect by fuselage interaction)✓ Propeller design for Full-scale application. Appropriate solidity and shape wereobtained.

◼ Future works
Flight test with RC helicopter equipped with
opt-propellers to demonstrate performance
improvement
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Adv-opt

Ret-opt

Tail-opt
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Thank you for your kind attention!

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