A two helicopter garage ~ one for the wife

[Dave_Jackson]

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Dave

[heli-cal]

This does not inspire confidence! :eek:

[kevin_mayes]

Hey, its water cooled, that must surely be a first for a helicopter..?

[Runway101]

Post a video where you fly that thing.

[Dave_Jackson]

The four pictures were received by e-mail a couple of days ago. There was no text accompanying the pictures.
The name of the sender appears to be Greek.

He may have got the inspiration from seeing these videos of Frans Schoeffman flying his backpack helicopter.

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Dave

[birrddog]

I wonder if the lack of seat belt and shoulder harness is a safety feature ;)

[Graviman]

I'm impressed by that collective pitch mechanism which allows safe entry into autorotation in the event of water coolant leak etc. And that geared flywheel to allow plenty of spare energy for an engine out flare. Also those landing struts look like they absorb all of the engine kinetic energy from a unflared autorotative descent. Combine that with a disk loading which allows the machine to avoid VRS and you have an extremely well thought out flying machine.

And it even comes with it's own stretcher bearer... :ouch:

[Dave_Jackson]

No argument. Backpack helicopters are cute, they are funny and they are extremely dangerous.

The following is a serious look at the Backpack helicopter from an unusual perspective.

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The 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 built and the easiest helicopter to fly.

However, critics are rightly concerned that it will be a very unsafe craft due to; the lack of speed stability (http://www.unicopter.com/B326.html#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.

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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:

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

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Thoughts????????

Dave


The above utility 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.

[Graviman]

Dave,

Why not just use one of the many propeller pitch mechanisms out there to allow autorotation? A blade with freely feathering root bearings and trim tabs to fix Rel_AOA would still be a safer way for rpm control climb/descend. The batteries may go flat at 10'000 so autorotation is a common sense absolute must.

If going for a constant rpm pitch mech then why not just gear in a flywheel to allow enough inertia for a flare from zero forward speed? These outperform the very best batteries and supercapacitors. They also never overheat, short out, leak charge or risk electrical fire. Obviously the design needs to be high rpm burst proof. I'm not against the idea of a supercap for variable rpm machine flaring though - especially if you had no forward speed.

Those struts should be able to absorb the inertia from the engine/batteries, unless the pilot wants these items coming down on his head. For the sake of a little extra framework, and maybe a trailer, skids and an energy absobing cushion give you a little more safety though.

Once The machine can emergency autorotate and flare then why not go the electric route. The machine is only for fun so does not need to have any range. And a multi-electric system will be at least as reliable as a multi engine design. I think that there should be a reserve energy system which exists for flaring from zero forward speed.

[Dave_Jackson]

Why not just use one of the many propeller pitch mechanisms out there to allow autorotation? :ok: Item 5/.
The intention is to let the motor's Electromotive Force automatically set a 2-position pitch.

If going for a constant rpm pitch mech then why not just gear in a flywheel to allow enough inertia for a flare.... Two flywheels would add weight and one flywheel would add gyroscopic precession. The small rotors will have low inertia, which will allow for fast RPM changes in (thrust).
An automatic torque-pitch mechanism may be added to the Version II. :)

I want the craft to be cheap, and simple, but VERY safe and easy to pilot.

I think that there should be a reserve energy system which exists for flaring from zero forward speed. :ok: Item 8/.

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Mart, this little craft really looks doable. If the development continues to look good, it will be build.

It might might result in a viable product for someone, and it could also be the first step to larger electric VTOL craft.

Dave

[Graviman]

Dave,

You could do a lot worse than NiMH Saft batteries - Honda use them:

Saftbatteries.com (http://www.saftbatteries.com/)

What weight limitation/regulation are you aiming at - Ultralight?

If you had detail drawings (planform & section) of the prop i could have a go at some hover power estimates. I just don't have time to implement the calcs for forward flight right now, but it is on the list (along with supersonic flow for tips).

Do you have any details in mind for the battery pack / power supply? I had wondered whether there was an off the shelf unit which gives a controlled output voltage and charge capability. That saves a lot of development.

I am with you in that i believe there is a market for an affordable but inherently safe personal helicopter. The key is to document all of the modes of failure (environment, machine or pilot) in an FMEA so that you can demonstrate beyond doubt that as much considereation as possible has been put into the design. The perfect result would be a thread on Rotorheads with comments like "these guys really have put safety first". ;)

Mart

[Dave_Jackson]

Mart,

Thanks for the battery link.

Here is the developing Stanford project. High-performance lithium battery anodes using silicon nanowires (http://www.nature.com/nnano/journal/v3/n1/pdf/nnano.2007.411.pdf)
And hopefully this is more than hype. EEStor's potentially game-changing ultracapacitor (http://www.popsci.com/scitech/article/2009-07/eestor-almost-ready-lead-technological-revolution)

The world will spend billions of dollars on electrical storage development.

My interest is to work on the rotorcraft aspects, including an extremely reliable motor and controller. The current idea is to develop and build a very bottom-end electric craft (backpack) and then 'grow' it.

Dave

[Graviman]

Dave,

The problem i have with all of these backpack helicopters is that if the pilot was to stumble then the situation could get very nasty. You just cannot operate a flying machine with exposed rotating components the way you would a paragliding canopy. The benefit of a personal helicopter over a canopy is VTOL from any reasonable location. The cost to my mind is just the need to tow a small trailer - no big deal really.

To keep mass down we are not talking about an extensive fuselage. Just enough for the pilot to sit on with a modicum of protection from awkward landings. The design could easilly be built by any experienced bicycle frame manufacturer. Have a look at some of the tubular steel frame gliders designed in the 60's to see what i mean. Very light but can take a bit of a pounding with the pilot able to walk away in shame. I'm not even suggesting a design this complicated, perhaps more like a miniature teetering hang glider.

McDonnell Model 38 / XH-20 "Little Henry" helicopter - development history, photos, technical data (http://www.aviastar.org/helicopters_eng/mcdonnel_henry.php)

[Dave_Jackson]

Mart,

You are correct, however, an electrically driven backpack offers several previously unobtainable advantages.

1/ An assured emergency power during the landing will keep the weight off of the pilot's back until his feet are firmly planted. Then he can reduce the power and squat to place the tripod on the ground.

2/ The blades have a small diameter and are 'absolutely' rigid for fast response.

3/ The counter-rotating rotors are coaxial and have little rotational inertia. Using the motor as a brake would quickly slow their rotation, without a reaction on the tripod or pilot.


The backpack would be a low-cost prototype, which would 'grow' by adding the light-weight fuselage (http://www.unicopter.com/SynchroLite.html) , then a pusher prop (http://www.unicopter.com/Electric_UniCopter.html), then thisVTOL (http://www.unicopter.com/AeroVantage.html). :)

Dave