1354

Item 1354

OTHER: Helicopter - Inside - Single Rotor - Rotor X Wing - Improving Lift During Transformation:

Objective:

To look into means of improving the lift on the retreating blade side of the craft during transformation.

Calculated Lift by the Retreating Blade:

Calculations done in Access using Blade Element portion in Prouty's Hover program.

Criteria for Calculations:

JAR-VLR allowable maximum GW = 1320 lb. Divided by 4 blades = 330 lb per blade.

Ref: UniCopter RRPM in Hover is 550 rpm, Rotor radius is 9'-6", Tip speed is 547 fps and NACA 0012 airfoil requires 94 hp.

Rotor X Wing:

Rotor Radius = 12'.

Root chord = 24".

Taper =1" per foot

Twist = -12º

Airfoil NACA 0012 symmetrical.

Transformation forward velocity is 80 kts = 92 mph = 135 fps. This is also the reverse airflow at the root of the blade.

At the tip of the retreating blade (@ 270º ψ) the air speed is set to the above 135 fps. The RRPM is therefore 215 rpm.

The above will hover with a blade pitch of 24º and 61 HP. (86 hp by momentum theory)

This places the point of zero velocity at 0.5 R.

This retreating blade will now be considered as a 2-blade rotor with a 6' radius and a tip speed of 135 fps at both tips.

The thrust of this '2-blade rotor' is only 73-lb. Increasing the pitch does not help much.

This means that because of lateral symmetry of lift the advancing blade (@ 90º ψ) can only deliver 73-lb of thrust. However, the tip speed ratio of mu = 0.5 and the larger taper may, as a guestimate reduce the mean moment arm from 0.75 R to 0.6 R. Since the moment arm on the retreating blade is at 0.5 R the lift on the advancing blade may have to be less than 73-lb of thrust. Perhaps a very large twist on the advancing blade may bring its moment arm down to 0.5 R, or even a little less.

A moment arm of 0.5 on the advancing and the retreating blade means that the fore and aft blades must each produce ((330 * 2) - 73) = 587 lb of thrust.

For each of these 2 blades to produce 587-lb of thrust, with 12º twist, their root pitches must be a theoretical 34º.

NOT GOOD ENOUGH.

Potential Means to Improve Lift During Transformation:

Roll Moment from the Horizontal Stabilizers:

The craft will be traveling at 70 to 100 kts during transformation. There would appear to be no reason why the port and starboard horizontal stabilizers cannot be given differential pitches that will produce a roll moment. This will give additional lift on the rotor's retreating side and allow (require) the advancing side to provide more of the lift.

Lifting Body:

Consider giving the fuselage a lifting body effect to assist with lift, particularly during the transition in and out of stopped rotors.

Temporary Stub Wing on Retreating Side:

Stub Wings on Both Side:

Very, very short wings located in the area of the root cutout of the blades (just about an extension of a 'Lifting Body'). These stub wings would have pitch control and would impediment opposed pitch during transformation. This is basically the same as the above ' Roll Moment from the Horizontal Stabilizers',

At Faster Velocity:

Consider having the transformation take place at a faster forward velocity, and thus a faster rotor rotational speed.

Propeller Torque:

Have the rotation of the propeller assist with lifting the rotor retreating side. A temporary high propeller pitch would help.

Other:

??? ??? ???

Introduction Page | SynchroLite Home Page | UniCopter Home Page | Nemesis Home Page

Initially displayed: September 21, 2004 ~ Displayed on PPRuNe and on Rotary Wing Forum: April 9, 2006 ~ Last Revision: September 11, 2007

The above invention is openly and publicly disclosed on the Internet to negate an entity from patenting it, to the exclusion of all others whom may wish to use it. ~ Reference patent law 35 U.S.C. 102 A person shall be entitled to a patent unless - (a) the invention was known ... by others in this country, ..., before the invention thereof by the applicant for patent.