Backpack Helicopters ~ Increasing Safety through Deconstruction

[Rotor Rooter]

Put on a seperate thread because it is a related but distinct subject.

A backpack helicopter that incorporates; a coaxial configuration, short span blades, collective by rotor rpm, and cyclic by weight shifting is probably the most economical helicopter that can be build and the easiest helicopter to fly.

However, critics are rightly concerned that it may be a very unsafe craft due to the lack of speed stability in forward flight, the inability to autorotate, and the risk of stumbling during a stand-up landing.

The conventional solution to overcome these shortcomings would be to upgrade the wish-list by adding; landing gear, then longer blades, then a collective, then a teetering hinge, and finally a bigger engine and transmission to lift this heavier craft. By this point the craft is much more expensive to build and somewhat more difficult to fly. In addition, all these upgrades add their own reliability concerns.

As an alternative, consider the possibility of taking a very different approach. An approach that might be called 'deconstruction'. Consider the possibility of producing a safer backpack helicopter by reducing its complexities and thereby increasing its reliability:

1. Replacing the dozens of wearing engine and transmission parts with a brushless electric motor whose only wearing parts are it's two bearings.
2. Divide the controller's power circuit, the motor's coils, and the battery packs into two or more totally independent circuits.
3. Incorporate redundancy and polling in the control circuitry.
4. Give the extremely rigid propellers (rotors) a high 5º or 6º precone.
5. Give the propellers a 2-position pitch.
6. Locate the batteries below the torso of the pilot.
7. Releasing the batteries to the ground before landing the pilot and motor-rotor assembly.
8. Provide the pilot with undeniable knowledge of low battery power, plus a controlled reduction in the available power to the motor.

Elaboration on the above numbered points.

2. Should a power circuit fail, the motor will still operate, but at reduced power.
3. In addition, this simple craft requires very few pilot actuated controls.
4. To give speed stability during forward flight.
5. A torque-pitch capability so that the rotor can provide thrust and accommodate autorotation. Disk loading would only be 3-1/5 lb/ft. on a 10 ft dia.
6. The lower location of the batteries will assist with weight shifting and reduce the weight of the motor-rotor assembly
7. A lowering or dropping of the batteries will significantly lighten the remaining weight and significantly assist with a controlled landing. Dropped batteries could have their own small parachute incorporated into the battery pack unit.
8. An ultra-capacitor might be incorporated to provide power during the landing if the battery pack unit has been released.

The objective being; absolute reliability, power for controlled landing, and safe flying.

Thoughts????????


Dave

[brett s]

Having a two position collective that only torque senses & changes automatically isn't a viable option to increase safety the way I see it.

If you're hovering close to the ground the last thing you want to happen if the power goes away is reduce pitch automatically, guaranteed to wad it up.

If you're cruising along & lose power, it automatically reduces pitch - so what happens when you get ready to land?

Very few helicopters can successfully autorotate to the ground without pulling collective, the only ones I can think of where it's possible under some conditions have very low disk loading plus wheels. I'm defining successful as being able to re-use the helicopter...

Don't think the FAA would care for the idea of heavy jettisonable objects, especially ones that can carry a lot of energy. Ever see what a damaged LiPo pack can do?

[quadrirotor]

Today, all the elements you mentioned are actual experimental stuff, again on R&DD!...

The best combination to have a reliable helico, today, could be this one:

http://www.rotaryforum.com/forum/showthread.php?t=18431

But if you want to make today an helicopter whith electric elements, you can make a classical monorotor helico like the Safari, for exemple, with an electric fenestron...Electricity could be drawned from the generator of an hybrid car...

[Rotor Rooter]

Constructive criticism. Thanks Brett and quadrirotor.

The following is not to disparage any remarks but to attempt to overcome perceived and real shortcomings.

Having a two position collective that only torque senses & changes automatically isn't a viable option to increase safety the way I see it.

If you're hovering close to the ground the last thing you want to happen if the power goes away is reduce pitch automatically, guaranteed to wad it up.

If you're cruising along & lose power, it automatically reduces pitch - so what happens when you get ready to land?

The autorotative pitch position is intended to be the action of last resort. A sort of final fall-back position. The following proposed 'objectives' are intended to eliminate all reasons for the use of autorotoation.

A/ The failure rate for the motor will probably be far better than the failure rate of most of the many moving parts on today's certified rotorcraft.

B/ The controller should also have an exceptionally high reliability due to split power circuits and the requirement for a well designed control circuit. One example would triple redundancy and a polled response.

C/ Low battery power will probably represent the greatest danger. The alarms and an intentional automatic rate of power reduction are intended to make the pilot very aware of the impending emergency and to get him down near the ground. Just above the ground he can clear and activate a switch that will assure that the capacitor, perhaps in conjunction with the remaining battery power, gives him a small amount of time to complete a normal flare and landing.

Don't think the FAA would care for the idea of heavy jettisonable objects, especially ones that can carry a lot of energy. Ever see what a damaged LiPo pack can do?

The jetsoning of the battery-pack would also be an activity of last resort.

However, the ability to remove the weight of the battery-pack during the final portion of the landing would be extremely advantageous. What if the pack hangs from the harness and can be deposited on the ground. Then the pilot could use the power in the ultra-capacitor to fly a few feet away from it and land.

Today, all the elements you mentioned are actual experimental stuff, again on R&DD!...

Yes there is experimentation, but that is part of the fun.
A quarter scale prototype of this can probably be built today using stock items, starting with this motor. Double AXi 5330/20


Just ideas.


Dave

[karlbamforth]

Military pilots sit on a survival pack/dinghy that weighs quite a lot.

After ejection and deployment of the parachute, the survival pack can be lowered on a lanyard so that it hangs approx 20ft below the pilots feet.

This means that the pack lands first and the weight is not taken by the pilots body during landing.

Emergency landings will hopefully be quite rare.

But every landing will be a potential for disaster. A slight stumble will very quickly turn into a dynamic roll over. Look at the injuries paraglider pilots sustain just trying to land parachutes, many many broken ankles and legs.

Remember you have a big gyro right above your head and once it is moving you will be unable to resist it from a standing position.

[Rotor Rooter]

Karl,

Thanks for the information

The concern, which you and others have mentioned, is obviously a serious one. The intent of this thread is to try and eliminate these concerns by a means that does not incur addition weight and cost etc., such as skids.



One low cost partial solution might be that of having the motors subject to electrical braking when the pilot fully releases the 'throttle' or when he activates a separate switch. Because the motors are counter-rotating and fixed to a common shaft (stub mast) there should not be any unwanted moments created. This may offer some help.

A powered landing should allow for a controlled and stationary touch-down. This is because the weight-shifting of 'absolutely' rigid rotors and the acceleration/deceleration of the low inertia rotors should be quite responsive. This appears to be born out in the Schoeffman videos.

Another objective is to negate any possibility of unpowered rotors during the flare and touchdown.


Dave