B360

OTHER: ~ Aerodynamics - Rotor Disk - Dual Configurations

Configurations:

Side-by-Side:

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

PropRotor:

The primary advantage of the PropRotor is its speed during Cruise.

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

 

Other Information on Configuration Comparisons:

·        DESIGN: Electrotor-SloMo - Rotorhead - Disk - Configuration Comparison ~ Comparison of area requirements.

·        DESIGN: Electrotor-SloMo ~ Rotorhead - Disk - Loading

Thrust to Power Ratios for Hover:

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. 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

 

 

Single w/ 2 blades (for ref.)

Twin - Side-by-side:

Single w/ 4 blades

Coaxial w/ 2 * 2-blades

Interleaving w/ 2-blades

 

Blade area (total):

13.4 sq-ft.

26.8 sq-ft.

26.8 sq-ft.

26.8 sq-ft.

26.8 sq-ft.

 

Disk area (total):

314 sq-ft.

2 * 314 = 628 sq-ft.

314 sq-ft.

314 sq-ft.

531.7 sq-ft.

 

Disk loading:

3.92 lb / sq-ft.

1.96 lb / sq-ft.

3.92 lb / sq-ft.

3.92 lb / sq-ft.

2.36 lb / sq-ft.

 

Blade loading:

92 lb / sq-ft.

46 lb / sq-ft.

46 lb / sq-ft.

46 lb / sq-ft.

46 lb / sq-ft.

 

Rotor solidity ratio:

0.0427

0.0427

0.0853

0.0853

0.051

 

Collective pitch:

12.7º

5.1º

8.3º

7.23º

7.25º

 

Power:

95 hp

44.4 * 2 * 0.9 = 80 hp (1) (2)

100 hp (3)

131 hp (4) ??(5)

129 * 0.9 = 116 hp (1) (4) ??(6)

 

Checking of program

 95 hp

Pitch = 12.7

 2 x 35.5 = 71 hp

Pitch = 7.1

 99 hp

Pitch = 8.28

 131 hp

Pitch = 7.22

The twin rotor factor may not be working properly

 

For Reference only; Power: by Momentum Theory

92 hp

89 * 0.90 = 80 hp (1)

92 hp

Not done yet

 

    1. Tail-rotor Adjustment: Power reduced by 10% due to the elimination of the tail-rotor.
    2. 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.
    3. Reducing the chord on the Single w/ 4 blades in half to 0.333 ft will reduce the power to 93 hp.
    4. Tail-rotor Adjustment:

o   I would have assumed that the power for the coaxial will probably be 100 hp [Single w/ 4 blades] * 0.90 (1) = 90 hp. This power is less than the Single w/ 2 blades [by 7%] and less than Single w/ 4 blades [by 12%].

o   The above 131 hp is based on the Twin Rotor Factor. There 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'

    1. Power for the interleaving and the intermeshing will be between 80 hp and 131 hp, depending on the amount of stagger.

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

6. The twin rotor factor may not be working properly

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.

 


Note that the total power of 65 hp. of the two coaxial rotors above is based on them being an infinite vertical distance apart.

Note that when the side-by-side rotor or the coaxial rotors are combined the total power required jumps from 65 hp. to 100 hp.

 

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.

o   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.

o   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.

Power Evaluation for Coaxial Rotors and for Laterally Displaced Rotors:

 Coaxial Configuration: ~~~~~~~~~~~~~~~~ Laterally Displaced Configurations:

 

Symbol:

Definition:

Pi

Induced power

Pref

Reference power

z

Twin rotor vertical spacing

D

Diameter of rotor

d

Twin rotor lateral spacing

 

 

 

 

The above two graphs are from;  Influence of Lift Offset on Rotorcraft Performance

Notes Related to the Above Graphs:

·        z/D of 0.0 and d/D of 0.0 represent a single rotor with 4 blades (i.e. a combining of the 2 blades from each of the spaced rotors)

·        Of special interest is Side-by-Side +/- Interleaving arraignment when the blade tips of the two rotors are in a close proximity to each other. (i.e. where d/D ≈ 1.0). It can be seen on the diagram and has been shown during actual testing that there is a thrust benefit due to this proximity, which exceeds that of two aerodynamically remote rotors.

·        There have been tests and reports about this lateral advantage. 

·        Perhaps it is related to the reason why old fighter airplanes and geese fly in a V formation. Ref:  http://www.squidoo.com/why-birds-fly-in-v-formation.

o   “All the birds except the first fly in the upwash from the wingtip vortices of the bird ahead. The upwash assists each bird in supporting its own weight in flight, in the same way a glider can climb or maintain height indefinitely in rising air. In a V formation of 25 members, each bird can achieve a reduction of induced drag by up to 65% and as a result increase their range by 71%.[1].” ~ http://arxiv.org/abs/0804.3879

·        This advantage for the Interleaving and Side-by-side is in addition to the 8-12% saving in power due to no tail-rotor.

·        X _______________________________________

·        An intriguing aspect of the laterally displaced rotor-rotor proximity is that of how 4 quad rotors might benefit, particularly since the advantage may take place over a much larger arc of the circumferences.

·        Another intriguing thought is; could this be applicable and beneficial to the gyrocopter, with side-by-side or quad rotors? Might it also allow for multiple pre-rotators of unlimited power due to the mutual cancelation of yaw? 

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Last Revised: November 22, 2012