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1
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2
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- Hub drag for Notional CC Transport aircraft examined
- Hub drag is historically large portion of total vehicle drag,
approximately 1/4 to 1/3 of the total drag
- CC Hub drag very low in relation to historical trends
- Is such a low hub drag feasible?
- General factors affecting hub drag are investigated
- CC general hub design investigated and drag build-up performed for
notional CC Transport aircraft
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3
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4
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- Center section
- Shanks
- Hoses and Cables
- Pylon / Hub gap
- Fuselage attitude
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5
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- Unfaired Hub center section has significant drag
- Shank inboard and outboard areas also contribute
- Hub and inboard shanks have increased drag due to pylon interference
- As they turn the air is “stirred up”
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6
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- “Super flow” region exists above the pylon
- Components in super flow area have increased drag
- Hub height to pylon width ratio is a significant factor for interference
- Empirical interference facture used to account for hub drag in super
flow region*
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7
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- Conventional rotorcraft fly in nose down attitude, increasing hub drag
area
- Compound (auxiliary thrust) rotorcraft can take advantage of level
flight at high speeds
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8
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- Conventional hub drag compared to CC hub drag
- Drag calculation method from: NASA CR-152080, Summary of Rotor Hub Drag
Data
- Hub drag calculated for 22,000 lb HH-60G
- Hub drag calculated for 160,000 lb notional CC Transport
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9
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10
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- Faired hub reduces center body drag
- Typically large height/length ellipsoidal hubs have flow separation in
aft of fairing
- Shaft, swash plate, pitch links and shanks typically remain exposed
- Gaps in fairing for blade shanks have leakage drag
- Faired hubs sometimes have greater drag due to fuselage nose-down
attitude
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11
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- Aerodynamically faired hub
- No exposed shanks
- No leakage at rotor root (fairing fits tight at zero collective pitch)
- Only 2 blades
- No exposed pitch links, swash plate, etc.
- Hub remains parallel to free-stream flow
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12
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- Pylon / Hub interference included*
- Pylon / Fuselage interference included**
- Hub conservatively modeled as ellipsoid (actual design trailing edge is
not bluff as ellipsoid), drag coefficient of 0.1
- Total hub and pylon drag is 4.83 ft2
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13
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- CC Heliplane external hub design differs significantly from historical
designs
- These differences seem to explain the lower than normal hub drag for CC
hub (from historical trends) both qualitatively and quantitatively
- Simple calculation for notional CC Transport yields a hub and pylon drag
fe of 4.83 ft2
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14
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Notes