Item 1000

DESIGN: UniCopter ~ Rotor - Disk - Autorotation

Under development - For the fun of it - As time allows

What is the aerodynamic interaction between the driver and the driven regions of the two disks?

Outside Helicopter

Brantly:

the new Brantly B2B was flight-tested for Pilot magazine in the UK by Derek Jones in March 1999. He wrote: "Entering autorotation is no problem as you just lower the lever and keep straight with about half right pedal. The throttle correlation split the needles and there was only a small nose-down pitch. Rate of descent stabilised at a reasonable 1,600 fpm at 55 mph, with the rotor rpm at 460. The maximum allowed is 472. Rolling into moderate turns resulted in a slow rise in rpm, without any collective lever correction required to stay within the limit. It is recommended that the engine is maintained at 2,000 rpm during these manoeuvres, to avoid embarrassing silences.
"The rotor inertia on the Brantly is somewhat greater than that of the Robinson R22, and therefore gives a bigger margin for error during engine-off landings. However, you do have to roll off the throttle as the lever is raised for the touchdown, to prevent the engine re-engaging the freewheel. For practises, it is recommended to run onto the ground at 15 – 20 mph on smooth surfaces, following a flare initiated at 50 – 60 feet. The well-sprung undercarriage is forgiving of errors, although the closeness of the blades to the tailcone would concentrate the mind in the event of a tail-down arrival. Powered go-rounds just require raising the collective to join the needles and co-ordinating the throttle slightly to prevent overspeeding, then settling the speed again at 60 mph for the climb. A happy by-product of the fuel injected engine is not having to remember the carb heat at low power settings."

 

UniCopter

FORM: Flight - Autorotation

For this form to be run the following forms must have been previously opened and run.

The following data is preliminary SynchroLite.

 

[Helicopter] ~ Open at desired helicopter.

 

[Momentum} ~ Open & Run

 

[Flight - Hovering] ~ Open.

 

[Test Conditions] ~ Run.

 

[Flight - Hovering] ~ Run.

 

[Element Data] ~ Open & Run.

 

[Rotor - Hub] ~ Open & Run coning angle.

Notes:

The extreme rigidity will result in heavy rotor hubs and tapered blades where most of their weigh will be concentrated at the root end. I am a little concerned if the heavy rotors will in fact have enough rotational inertia for autorotation.

Rotor Speed Decay: [tKE]

The time from power failure to zero RPM.

Possible solution: The blades, bearings and hub are so strong that the rotors can probably be rotated at a RRPM far above 100% , thereby obtaining the required inertia from speed instead of mass. A negative is that at low elevation there will not be sufficient height to develop the high rpm required for the touchdown.

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To eventually, and maybe, provide;

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If the decision is to use the Traversing Root Pitch Axis then, due to the possible limited controllability of the root, consider the feasibility of swapping the driven and the driving regions on the span of the blade.

Concern:

Will the cutout be so large that it will be detrimental to the driving region, which provides the power to the rotor?

A thought:

During autorotation the lift should probably be equal on the advancing side and the retreating side, or very close to it, so that the stall region is not pushed too much to the retreating side. Under normal flight conditions when the collective is up there is the requirement for more lift on the advancing side, to give dihedral. The implication of this is that increasing collective will probably have to also apply outward lateral cyclic to the disks as well.

For a possible improvement see: DESIGN: UniCopter ~ Rotor - Disk - Autorotation w/ Yaw Control by Differential Collective

Stagger to Radius Ratio:

See: 1001.html

Related Pages at This Sites:

DESIGN: UniCopter ~ Rotor - Disk - Autorotation Yaw by Seperate Root and Tip Control

UniCopter ~ Trim, Stability & Control # Pitch Change & Autorotation.

DESIGN: Dragonfly ~ Rotor Disk - Autorotation

DESIGN: SynchroLite ~ Rotor Disk - Autorotation

OTHER: Aerodynamic - General - Autorotation

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Additional Information:

See; Technical Documents on ABC: ~ Forward Flight Performance of a Coaxial Rigid Rotor, page 5

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Last Revised: Sunday, August 10, 2008