1123

Item 1123

OTHER: Aerodynamics - Rotor Disk - Dual Configuration - Tandem

Downwash on Fuselage of Chinook:

Views of Chinook, and of specific interest; the Plan View.

Rotor diameters = 30 ft.

Stagger = 45 ft.

Fuselage length = 51 ft.

Fuselage Width = 12 ft.

Blades = 3 per rotor (considering 4 per rotor)

My thoughts:

It is interesting to note the large amount of fuselage that is located in the downwash from both rotors. In addition, some of the fuselage is subjected to the higher induced velocities coming from the tip end of the blades.

I have always assumed that the main reason that the interleaving configuration was not pursued was due to the large amount of thrust that would be wasted on the fuselage. It now appears that the downwash on the Chinook tandem fuselage and that on the Interleaving fuselage will be fairly equal.

In fact, in forward flight and with the inclusion of the Advancing Blade Concept (ABC), the Interleaving must be significantly better then the tandem. With ABC the retreating blades are providing a very small portion of the thrust and on the Interleaving configuration the fuselage is located under these retreating blades.

No wonder Colonel Crosby said "I don't see the CH-47 even in its growth as meeting that requirement [the Joint Heavy Lift aircraft]"

Comments on Tandem Helicopter from Rotary Wing Forum:

I have a lot of tandem rotor experience - several years playing with CH-47's.

More transmissions plus large driveshafts (much heavier than a tail rotor driveshaft & gearbox) = more expense & weight. The flight control mixing required will also add weight & complexity. Then there's the tandem rotor handling quirks to consider...very poor yaw control authority all the time + negative speed stability at the upper range without countering it electronically.

~ Material not yet developed ~
Area:

(A_OV) [area of overlap) = mA xxx This A is? The rotors are assumed to have no vertical spacing, therefor these calculations are good for interleaving as well.

Induced Power:
P₁ = ((1-m)T₁^3/2) / (√2ρA))

P₂ = ((1-m)T₂^3/2) / (√2ρA))

P_OV = (m(T₁+ T₂)^3/2) / (√2ρA))

(P_i)_tot=P₁ + P₂ + P_OV

From [Source ~ PHA p.72]

moved overTandem:

For hover forget Gap and use the same as Intermeshing.

Dual Rotor Configurations:

Coaxial | Intermeshing | Interleaving | Side-by-Side | Tandem

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Last Revised: February 13, 2007