Item 1121

OTHER: Aerodynamics - Rotor Disk - Dual Configuration - Interleaving

Overview:

Interleaving Craft:

Inside Concepts:

More Inside Concepts:

Outside Helicopters and Outside Concepts:

Outside Technical Reports:

Sketch:

Note: It may be better if the 'masts' are vertical. This is because the cone of both rotors should provide lateral stability, particularly since the outside blades are providing most of the lift (i.e. the greatest pitch). In this arraignment the tips will be above the roots of the other rotor's blades. Perhaps with a 1ºto 2º greater pre-cone.

Overview (cont.):

(1) There are two locations on the span of the retreating blade that will be not be providing thrust. One is a the point where the air speed and the blade segment speed are the same and the other is where there is a 0º angle of attack. These two locations maybe at the same segment at one or two azimuths.

Potential Engine and Power-train:

Ultrahigh-bypass turbofans:

With the F-35 Joint Strike Fighter's shaft driven lift-fans replaced by shaft driven lift-rotors

 

117 page NASA report on SR-7L Prop-Fan;- http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880019544_1988019544.pdf

 

From Ga6riel on Rotary Wing Forum

Pros & Cons versus Other Twin-Rotor Rotorcraft:

Concerns:

Related Pages:

The Detail Information below must be moved to lower-level pages in the future.

Induced Velocity Distribution: Incomplete. Study and develop at some time.

Random Notes:

Disk Area:

Calculation used for obtaining the area of overlap: Angle is in Radians.

A = 1/2 (R2 (θ - sinθ)) = 1/2 (10 * 10 (1.986 - sin(1.986))) = 1/2 (100 (1.986 - 0.915)) = 1/2 (100 *1.071) = 53.55

 

Individual Twin Disk:

Combined Twin Disks:

Single Disk:

Radius:

10

~

14.14

Area:

314.3

628.6

628.6

Area of Overlap (Circular Segment):

53.55

107.1

~

Area Excluding Overlap:

260.75

521.5

521.5

Radius based on Area of Twin Disks with Overlaps Excluded:

~

~

12.88

Total Lateral Span:

~

31.0

25.8

Total Longitudinal Span:

~

20.0

25.8

Rectangular Area

 

620 sq-ft

665.6 sq-ft

The above data and the comments below only consider the main rotors. They do not include the 10-12% tail-rotor power consumption, nor do they include the downwash velocity on the fuselage, which is dependent on its location under the disk(s).

In addition, I must think more about the above. It may be somewhat appropriate for Momentum Theory but not for Blade Element Theory. I do not believe that the last 4 lines are a valid comparison since if all three rotors have 2 blades each then the overlapping area is not showing the advantage of having 4 blades operating in it. In addition, about 33% of the high thrust area (near the tip) is working in the low thrust area (near the root) of the other rotor. Perhaps for the comparable single disk, the single disk's area should be increased by 1/3 of the total overlap area, plus a 10% increase in the single disk's total area to compensate for the tail-rotor, then a reduction because the fuselage will be subjected to a greater downwash velocity under the intermeshing rotors (at least during hover).

The area of the circular segment is 1/6th of the disk's total area. This would suggest that the power should be considered as; 2 * (4/6 * isolated rotor power + 2/6 * co-located rotor power). Using the figures from OTHER: Aerodynamic - Rotor Disk - Dual Configurations, 4/6th * 65 hp + 2/6th * 100 hp = 77 hp. In other words to provide a specific thrust will require 65 hp from the side-by-side configuration, 77 hp from the Interleaving configuration, 94 hp from the Intermeshing configuration, and 100 hp from the coaxial configuration.

____________________________

The following is the above done again with a little more detail.

Calculation for determining the relative size of the rectangles that enclose the total disk area ~ of three rotor configurations:

 

 

Configurations:

 

 

Single:

Side-by-side:

Interleaving:

 

Radius:

5.64 ft.

3.99 ft.

4.36 ft.

 

Diameter:

11.28 ft.

7.98 ft.

8.72 ft.

 

Sides of rectangle:

11.28 ft. * 11.28 ft.

7.98 ft. * 15.96 ft.

(8.72 ft. - (sin(30) * 4.36)) * 2 = 13.08 ft.

 

Area of rectangle:

127 ft2

127 ft2

114 ft2

 

Relative area:

1.00

1.00

0.90

 

Induced Power:

AOV = mA

m = the tandem (& side-by-side?) rotor overlap factor

A = Which area?? Atot, Asin

m = (2/π)(θ - (d/D)sin θ, where θ = cos -1 (d/D)

TP = Thrust on port rotor

TS = Thrust on starboard rotor

 

P1 = ((1-m)T13/2) / (√2ρA))

P2 = ((1-m)T23/2) / (√2ρA))

POV = (m(T1+ T2)3/2) / (√2ρA))

(Pi)tot = P1 + P2 + POV

From [Source ~ PHA p.72]

transfered over Interleaving:

The required power is increased by a factor (K) = 1.46 - (0.253 * (Stagger / R)). Using this equation the value of K is a little too high when there is very little overlap.

Thrust Distribution During Hover: Probably to be move to separate DISK page in future.

The fuselage will be bigger than shown below but concept still applies.

Proposed Interleaving Rotorcraft by Bölkow:

This web page Derschmidt High-speed Rotor shows some proposed helicopters by Bölkow. The Interleaving ones use Derschmidt semi-rigid rotors

Note that the rotors advance on the inside (breaststroke).

Here is a picture of one of them just incase the outside page disappears. It did disappear ~ March 9, 2012

Twin-Rotor Configurations:

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

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Last Revised: March 9, 2012

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