The ElectraFlyer C plug-n-fly electric plane

[Viv]

This is a beautiful conversion of a motor glider to electric power, very impressive peace of work I think.

Viv

Article Summary
August 19, 2008 The ElectraFlyer C is an electric aircraft based around the now defunct 1980s Moni kit plane designed by John Monnett which features in the Smithsonian Air and Space museum no less. The original and unreliable KFM 107 two-stroke air-cooled motor has been replaced with a modified version of ElectraFlyer’s US$8500 5.6 kWh lithium battery and US$4200 propulsion parts kit, will top 90 mph, fly for 90 minutes plus and recharges from a household power outlet in six hours at a cost of, would-you-believe, sixty cents. That’s serious bang-per-buck for an aircraft and bodes well for the coming era of personal flight being based around sustainable energy and as it’s almost totally silent, sustainable hearing without the need for earplugs. Silent aircraft, like silent RVs, are the way to a sustainable future for the sport.

Link
http://www.gizmag.com/the-electraflyer- ... ure/49558/

[hinote]

This is a beautiful conversion of a motor glider to electric power, very impressive peace of work I think.

The modern motorglider is very efficient--and maximizes the limited power available from an electric power package. The primary power consideration for this type is an acceptable climb rate--the actual power consumption at cruise is remarkably low.

BTW I have a "grandfathered" motorglider endorsement and some hundreds of hours in a handful of motorglider types.

IMO the motorglider type of aircraft is going to become more predominant in the future, because of increasing energy issues. As an extreme illustration of the efficiency of a modern sailplane, the total drag of a top performer is less than 20 pounds at its best L/D speed, and increases very slowly with higher speeds.

[larry cottrill]

For pure pleasure flying, where you care nothing at all about ground distance covered per unit time, this would be hard to beat. In this case, the powered flight might be almost as quiet as the sailplaning itself.

L Cottrill

[Viv]

Hi Bill, I think your perfectly correct, my view is that motor gliders just have not been developed enough as the original IC engines did not add sufficiently to the overall combination, the electric conversion makes complete sense to me.

Yes the airframes performance is astounding but he basic power unit was inelegant.

Larry has a good point as well but I would add to it the need in future for light weight and flexible solar cells for in-flight topping off of the battery pack and to reduce its size.

I always fancied doing my gliders pilots license and motor gliders were one of the attractions for me, I may do that in the next year or two as time allows.

Viv

[Viv]

Hi Bill, I think your perfectly correct, my view is that motor gliders just have not been developed enough as the original IC engines did not add sufficiently to the overall combination, the electric conversion makes complete sense to me.

Yes the airframes performance is astounding but the basic power unit was inelegant.

Larry has a good point as well but I would add to it the need in future for light weight and flexible solar cells for in-flight topping off of the battery pack and to reduce its size.

I always fancied doing my gliders pilots license and motor gliders were one of the attractions for me, I may do that in the next year or two as time allows.

Viv

[hinote]

Hi Bill, I think your perfectly correct, my view is that motor gliders just have not been developed enough as the original IC engines did not add sufficiently to the overall combination, the electric conversion makes complete sense to me.
Viv

One of the very real advantages to an electric power package is the ability to streamline the installation much more than an IC. The elimination of cooling drag and the associated "dirty" ductwork is worth more than a few horsepower--even on an installation like this.

Eventually I see an optimized installation with the motor on a pylon, and the batteries in the fuselage. The nose of the aircraft can then be cleaned up and laminar flow can be maintained a long way back, substantially reducing drag. Additionally, a prop with a controllable pitch would allow for much more efficient utilization of the available power; the classic "cruise/climb" prop with its inherent compromise just doesn't have a place in this kind of project.

Motorgliders are really fun; they allow you to go places and try things you would never do in a pure sailplane. Substantial reductions in power consumption are available to a knowledgeable pilot--even on a cross-country trip--when the correct use of soaring techniques are introduced into the equation.

[Mike Everman]

The cooling requirements of this system, both batteries and motor can not be underestimated. There is a great deal of watts being dissipated somewhere, as this is a very inefficient system! I'm betting most folk would find this out later rather than sooner. $.60 a charge seems very low... I wonder what the Cd of this plane is? A simple energy calc with some low efficiency factor put in would tell if this is in the ballpark.

I've always been taken by electric flight. I truly believe that electric personal helicopters are not too fanciful, and could even be put together now, given some serious money. A few years ago, I saw an RC helicopter lifting itself (probably 15 lb) and about 15lb of camera equipment for about 20 min. I immediately thought of two scenarios, one where you had 20 such rotors on a frame, or one where 20 such motors were driving a single large rotor's bull-gear.

I think the stumbling block for most commercial efforts is the perceived need for some long distance capability, but I expect I'd only need 10 minutes under power to get to work from home!

[hinote]

The cooling requirements of this system, both batteries and motor can not be underestimated. There is a great deal of watts being dissipated somewhere, as this is a very inefficient system! I'm betting most folk would find this out later rather than sooner.

That's a Lemco motor, 90% efficiency. The controller is even better than that.

I'd be worried about putting LiPo's in an aircraft, like this effort; they're too prone to overheating with mismanagement. The newer LiFe batteries like the A123 are much safer and easier to handle (hard exterior). A123 has demo'ed the safety thing by driving a nail through an operating battery, without any consequences.

In any case the total heat generated is worlds less than an IC.

[Mike Everman]

Agreed, far less heat than IC. So 90% efficiency gets you 10% of power going out as heat plus I^2*R, which I neglected to mention. So if you know the resistance of the motor windings, and the amperage, you get X watts out as heat.
Faaaascinating.

[Viv]

Agreed, far less heat than IC. So 90% efficiency gets you 10% of power going out as heat plus I^2*R, which I neglected to mention. So if you know the resistance of the motor windings, and the amperage, you get X watts out as heat.
Faaaascinating.

Hi Mike

Plus the loss in the motor control power output stage, a small fraction of the motor winding loss but significant all the same

Viv

[hinote]

Agreed, far less heat than IC. So 90% efficiency gets you 10% of power going out as heat plus I^2*R, which I neglected to mention. So if you know the resistance of the motor windings, and the amperage, you get X watts out as heat.
Faaaascinating.

Hi Mike

Plus the loss in the motor control power output stage, a small fraction of the motor winding loss but significant all the same

Viv

My experience with controllers so far has been very positive, with no excess heat issues. PWM and power switching has entered new levels of efficiency previously unimagined.

On the motor front, the Halbach motor as developed by CSIRO for the Australian Solar Challenge has a quoted efficiency of 98.5%, making heat generation a minor issue.

BTW congrats to our own Axel Borg for his success in building his own motors of this type!

Bill