B360

OTHER: ~ Aerodynamics - Rotor Disk - Dual Configurations

Configurations:

A rotorcraft with adjacent twin main rotors. The distance between the two rotor centers is greater than the rotor diameter. Examples are; the Focke-Achgelis Fa 61, the V-22.

More: OTHER: Aerodynamic - Rotor Disk - Dual Configuration - Side-by-Side

Interleaving:

A rotorcraft with adjacent twin main rotors. The distance between the two rotor centers is greater than the rotor radius but less then the rotor diameter. Both rotors can be in the same plane, which is like the side-by-side and unlike the intermeshed.

More: OTHER: Aerodynamic - Rotor Disk - Dual Configuration - Interleaving

Tandem:

The two rotors are located for-aft in respect to each other, plus they have stagger and gap.

More: OTHER: Aerodynamic - Rotor Disk - Dual Configuration - Tandem

Intermeshing:

A rotorcraft with adjacent twin main rotors. The distance between the two rotor centers is less than the rotor radius. Examples are; Flettner, Kaman, Kellett, DeGraw's Hummingbird, Ivo's. Designs:- UofM Calvert, SynchroLite, UniCopter

More: OTHER: Aerodynamic - Rotor Disk - Dual Configuration - Intermeshing

Coaxial:

The primary advantage of the coaxial is its compactness. All of Nikolai I. Kamov's helicopter designs, which reached the production stage, except the KA-26, were operated by the Soviet Navy.

More: OTHER: Aerodynamic - Rotor Disk - Dual Configuration - Coaxial

Comparison of Required Power for Various Rotor Configurations, in Hover:

Common Criteria:

Item:	Value:	Item:	Value:
Airfoil:	NACA 0012	Tip speeds:	550 ft/sec.
Disk radii:	10 ft	Taper:	None
Chord:	0.67 ft	Twist:	None
Rotor speed:	525 rpm	Gross weight:	1,232 lb. ⁽¹⁾

1,232 pounds was used since it is the maximum gross weight for the US FAA Sport Plane / Pilot category. The proposed European JAR ~ Very Light Rotorcraft is (600 kg.) 1,320 lbs. The Robinson R-22 Beta II is 1,370 lbs

Calculations by Combined Momentum, Blades Element Theory w/ Empirical Corrections ~ from Prouty

	Twin - Side-by-side:	Single w/ 2 blades	Single w/ 4 blades	*Coaxial w/ 2 2-blades**
Blade area (total):	26.8 sq-ft.	13.4 sq-ft.	26.8 sq-ft.	26.8 sq-ft.
Disk area (total):	2 * 314 = 628 sq-ft.	314 sq-ft.	314 sq-ft.	314 sq-ft.
Disk loading:	1.96 lb / sq-ft.	3.92 lb / sq-ft.	3.92 lb / sq-ft.	3.92 lb / sq-ft.
Blade loading:	46 lb / sq-ft.	92 lb / sq-ft.	46 lb / sq-ft.	46 lb / sq-ft.
Rotor solidity ratio:	0.0427	0.0427	0.0853	0.0853
Collective pitch:	7.3º	12.7º	8.3º	7.23º
Power:	74 * 0.88 = 65 hp ^{(1) (2)}	95 hp	100 hp ⁽³⁾	131 hp ⁽⁴⁾??(5)
Checking of program	2 x 35.5 = 71 hp Pitch = 7.1	95 hp Pitch = 12.7	99 hp Pitch = 8.28	131 hp Pitch = 7.22
For Reference only; Power: by Momentum Theory	65 * 0.88 = 57 hp ⁽¹⁾	92 hp	92 hp	Not done yet

Tail-rotor Adjustment: Power reduced by 12% due to the elimination of the tail-rotor.

Reducing the chord on the Side-by-side in half to 0.333 ft will reduce the power to 73 * 0.88 ⁽¹⁾= 64 hp.

Reducing the chord on the Single w/ 4 blades in half to 0.333 ft will reduce the power to 93 hp.

Tail-rotor Adjustment:

I would have assumed that the power for the coaxial will probably be 100 hp [Single w/ 4 blades] * 0.88 ⁽¹⁾= 88 hp. This power is less than the Single w/ 2 blades [by 7%] and less than Single w/ 4 blades [by 12%].

The above 131 hp is based on the Twin Rotor Factor. This is a note from the coding in the Access twin_rotor_factor function 'May 2000 I think that this function is only good for Momentum Theory'

Power for the tandem, interleaving and the intermeshing will be between 65 hp and 88 hp, depending on the amount of stagger.

5.Re Coaxial ~ The 'interference-induced power factor' K_int does not appear to have been coded in correctly. Perhaps it is adjusting parasitic and profile ??? Forget using this for coaxial until ..........................

More;

For comparative power requirements between configurations see; DESIGN: UniCopter ~ Electrotor ~ Rotor

From PPRuNe; October 12, 2005

By NL;

Dave,
There are some effects that help the power efficiency of a coax, but they are generally cancelled by others that affect power in the wrong direction (swirl effects, extra drag, reduced figure of merit from too much blade area). For the simplistic analysis of disk loading as a hover power determinant, I think things are roughly equal, regardless if there are two disks.

By DJ;

Nick,

I totally agree with the above. There is little difference in the power requirements between two closely spaced 2-blade coaxial rotors, and a 4-blade single rotor; if all the blades are identical in span, chord, rpm etc. etc.

However, there is a large difference in the power requirements between two widely spaced 2-blade rotors and two closely spaced 2-blade rotors. In other words, as the two separated disks approach each other (vertically, horizontally, or diagonally in the case of the Tandem) their slipstreams experience an increasing overlap and the power requirement increases.

The supporting [Blade Element Theory] data for the above sketch is located in the section above.

The power requirements for the Interleaving, the Intermeshing and the Tandem will be somewhere between these extremes.

The Interleaving looks like 77 hp (from the following 'located here'. See the upper sketch and following table and notes, located here, for a better understanding of the Interleaving.

The Intermeshing looks like 94 hp (from the following 'located here'. See the upper sketch and following table and notes, located here, for a better understanding of the Intermeshing.

Last Revised: February 13, 2007