Electric motor?

[mspohr]

I was wondering if anyone had put an electric motor in a Kitfox?
I was thinking that it could work well in a Kitfox since it would be lighter, require much less maintenance, be less susceptible to mechanical failure and could offer enough range for average use.
I am not a pilot but have been intrigued by the Kitfox as a simple, fun aircraft and this might motivate me to try to build one. In reading this forum, it seems that the major problems with flying the Kitfox are due to the engine. Lots of problems there. Electric motors are very simple and very reliable. Same for the batteries and control systems.
An 80 to 100 HP electric motor would weigh 100 to 150 pounds and batteries are about 50 pounds per 5 kWh storage it seems to me replacing the motor, cooling system fuel tanks and fuel weight with an electric system could result in a lighter aircraft. Electric motors, of course, don't suffer loss of efficiency with altitude. They also have nearly constant torque over their entire speed range.
So, is this idea crazy?

[PapuaPilot]

No, it's not a crazy idea. You are correct in wanting to find a light airframe like the Kitfox to convert to electric. Siemens already has a 120HP electric motor that only weighs 57 pounds, which is being tested on the Sun Flyer 2 all electric aircraft. The biggest challenge for any electric aircraft will be batteries and getting enough energy density to be able to fly for an acceptable amount of time.

[rv9ralph]

It looks good on paper. However... the Pipestrel Electric program for flight training in Fresno, CA is a place to look for practicality. The program manager for this endeavor spoke to an EAA meeting I attended about the program. The details are the issue. 45 to 90 minute flight times with reserves, then need to recharge (must have a charging station at the destination airport to charge for return flight.) The battery unit replacement/spare is $70K. Even though you don't need fuel, as fuel burns off the aircraft gets lighter and performs better... batteries stay the same weight regardless of charge level.

Electric flight is possible eventually, but I don't think it's time is right yet. At least for practical use.

Ralph

[mspohr]

Interesting to hear about the Fresno experience with the Pipistrel.
I looked at the Pipistrel Alpha Electro. It's also a light two seater frame and focused on flight training since the cost to operate is just a couple of dollars an hour for electricity.
They use a 50 kW electric motor (about 65 hp) with 106 kg of Tesla style (18650) batteries which should give them about 25 kWh of power. They state an hour of flight time with 20 min reserve. (They also say they can regenerate up to 13% of the power when descending)
You can buy Tesla battery packs for about $1300/5.3 kWh so about $6500 for 26 kWh batteries. Electric motor would be $3000 to $5000 plus controller.

As far as "range" goes, just like with electric cars, it depends on your use. I believe that most flying in this type of airplane is short distance, short duration. I saw a survey that that found most pilots for these light sport aircraft fly less than an hour at a time. Cross country travel (to Oshkosh!) would require frequent stops for charging. Pipistrel says an hour of charging for an hour of flying... so this would be slow.

[efwd]

Don't forget the reserve.

[mspohr]

I was thinking that most electric motors wouldn't be designed to withstand the large lateral and horizontal push pull forces from having a propeller attached. It probably would be best to have a gear mechanism that was designed for these forces which would have as an input the motor shaft. I've looked at governors which are designed for these forces but seem very complicated and do know that a governor is needed. A front gearbox would be good. Do these exist as a 1:1 gearing? I don't think any speed reduction is necessary.

[Shawshaw]

Don't forget the reserve.

What about the idea of a hybrid? Light weight ~80hp gasoline engine generator, small battery bank as a buffer, used Tesla motor to drive the prop?

[mspohr]

Using the specs from the Pipistrel which has a 65 hp motor and 25 kWh of batteries, you could probably get by with a much smaller generator. If you consider that most of the battery drain and power would be used in gaining altitude, you could probably get by with a 20 hp or so generator (10 to 15 kW). The battery would provide most of the power when climbing and the generator could top off the battery when cruising. Also have the potential to regen the battery when descending.
Also, could probably get by with a 65 hp or so electric motor. Much smaller than a Tesla motor.

[Dorsal]

Interesting to hear about the Fresno experience with the Pipistrel.
I looked at the Pipistrel Alpha Electro. It's also a light two seater frame and focused on flight training since the cost to operate is just a couple of dollars an hour for electricity.
They use a 50 kW electric motor (about 65 hp) with 106 kg of Tesla style (18650) batteries which should give them about 25 kWh of power. They state an hour of flight time with 20 min reserve. (They also say they can regenerate up to 13% of the power when descending)
You can buy Tesla battery packs for about $1300/5.3 kWh so about $6500 for 26 kWh batteries. Electric motor would be $3000 to $5000 plus controller.

As far as "range" goes, just like with electric cars, it depends on your use. I believe that most flying in this type of airplane is short distance, short duration. I saw a survey that that found most pilots for these light sport aircraft fly less than an hour at a time. Cross country travel (to Oshkosh!) would require frequent stops for charging. Pipistrel says an hour of charging for an hour of flying... so this would be slow.

I think it is an issue of range. It is fairly typical to cruise at 75% power (very different than car), not sure how you get more than about 30-45 min flight time from the example above. While it maybe true that many flights are less than an hour I can't imagine owning a plane with that fundamental limitation. As others have stated it is getting closer but not there yet in my opinion. One place this does work is small booster motors for motogliders.

[mspohr]

I was just wondering... what is the range of the Kitfox with a Rotax or similar engine?
Fuel consumption gal or pounds per hour?

[109JB]

I think it is an issue of range. It is fairly typical to cruise at 75% power (very different than car), not sure how you get more than about 30-45 min flight time from the example above. While it maybe true that many flights are less than an hour I can't imagine owning a plane with that fundamental limitation. As others have stated it is getting closer but not there yet in my opinion. One place this does work is small booster motors for motogliders.

I agree with most of this post but I do see a bit more potential.

Since most flights leisure flights are an hour or less, a guy that only wants to do that type of flying could benefit from one. I used to be in a flying club that had 2 airplanes and the less than an hour for a typical flight is absolutely accurate from my experience. I was also one of the flight instructors for the club and the longest flights of the month were generally the flight instruction flights. If our flying club had an electric LSA and a C-172 instead of 2 C-172's, I would guarantee that the electric LSA would have gotten as much use as it could handle. The only potential problem I see is recharge time or I see some systems looking a battery swapping.

A pure flight training type environment might be ideal at this point in time. This use would get benefit from a lot of regenerative capability (TOL's)

From a personally owned airplane perspective, I'd do it as a second airplane if I had that much disposable income to play with. I think it would be an interesting and fun project and could fill the evening flight role with another airplane serving the travel duties.. Due to the range limitations it wouldn't be practical as an only airplane because I do like to make short trips from time to time.

[109JB]

I was just wondering... what is the range of the Kitfox with a Rotax or similar engine?
Fuel consumption gal or pounds per hour?

So I have a Kitfox IV powered by a Rotax 582. Winter hit too soon after I bought it but near as I can figure it should cruise about 90 mph using about 4 gallons per hour. I might be off a little because I haven't had chance to nail down my cruise numbers yet. My particular airplane has two 13 gallon wing tanks which would theoretically give a 6.5 hour endurance at 4 gph and a 585 mile range. Not all kitfoxes are outfitted with tanks this large though.

[Shawshaw]

Using the specs from the Pipistrel which has a 65 hp motor and 25 kWh of batteries, you could probably get by with a much smaller generator. If you consider that most of the battery drain and power would be used in gaining altitude, you could probably get by with a 20 hp or so generator (10 to 15 kW). The battery would provide most of the power when climbing and the generator could top off the battery when cruising. Also have the potential to regen the battery when descending.
Also, could probably get by with a 65 hp or so electric motor. Much smaller than a Tesla motor.

Thanks for the info! You make sense. This is just a fun day dream for me. I’m planning on a Rotax.

[drienkm]

I was thinking that most electric motors wouldn't be designed to withstand the large lateral and horizontal push pull forces from having a propeller attached. It probably would be best to have a gear mechanism that was designed for these forces which would have as an input the motor shaft. I've looked at governors which are designed for these forces but seem very complicated and do know that a governor is needed. A front gearbox would be good. Do these exist as a 1:1 gearing? I don't think any speed reduction is necessary.

It's actually quite common to make electric motors with integral thrust bearings. Including a thrust bearing is very easy with no significant added complexity, cost, or weight. Use of a gearbox for an electric propulsion system might only be necessary and justified if you needed to use an off the shelf motor, or turn a extremely low RPM prop.
When the motor design itself is still a variable, cons of including any gearbox in an electric propeller drive design include:
1) Added weight
2) A lubrication system where none was required before
3) An unnecessarily compact motor that, because of its conventionally compact layout, may need additional cooling measures like heat sinks or even liquid cooling. (Max rate of cooling is the only limitation on the power of an electric motor if driving voltage is still a variable)
4) With no engine hum to cover it up, a gear drives make a terrible terrible sound. I'd much rather be able to hear the rather pleasant whirring of the prop:)
I can only think of one pro:
1) Reduced gyroscopic reactions during pitch and yaw because the rotating mass is roughly split running in opposite directions.

An electric motor designed to swing, say a 70" propeller would be relatively large diameter (maybe about 12"), would have a high pole count, and would be open in the middle around the shaft. The thrust loads from the prop would probably be well within the axial load rating of typical sealed ball bearings used to support the shaft.

[jiott]

Standard electric motors are used all the time to drive large, high hp cooling fans in industrial applications.

[alexM]

I'm happy to see electric planes moving forward and it seems we are finally where a small enough plane can get 45-60 minutes. I'm not ready to jump in because I make a lot of flights more than double that duration and there is zero infrastructure in place to charge.

I'll preface my statements by saying I grew up around r/c planes when electric was a joke. I was an early adopter when they finally became somewhat practical and carried forth to the point where my default position would be electric all the way. The weight is no longer a penalty, performance is fantastic, the flight durations are crazy (I have small planes that will fly over 30 minutes which is unheard of with glow-fuel power), and there's no need to wipe castor oil off the plane when I'm done for the day. Sort of a bummer for a guy with a YS53, which is a 4 stroke, supercharged and fuel injected engine. And electric planes are certainly less irritating to neighbors.

As it applies to full scale planes?
I think 65hp would be a dog in terms of performance. Double that and get back to me. I agree with another poster that "as a second plane" I might consider one. As a flight school? I don't see it yet. Any flight school around here is literally hot swapping humans from one lesson to the next every hour. If (big if) you could actually charge a plane in 58 minutes then you would need two planes in order to keep up with a 45 year old Cessna.

You cannot charge a plane in one hour using 110V, which is all I have in my hangar. Simple physics. I sat through a presentation on the new electric Porsche and it's possible to charge the car overnight (not one hour mind you) using 240V, but if all you have is 110V it will take 4+ days. Again, a second plane tucked in the corner of my hangar and charging with 110V might be a fun toy. The one hour charge on the Porsche requires 600V (might be 800V, it's been a while since I sat through this and I couldn't afford one anyway).

As an FBO you would need quite the charging set up, and some extra planes. I think for a flight school you would be looking for a way to hot swap battery packs. With my r/c planes I run three battery packs for a given aircraft. One in the plane, one charging and one cooling off after charging. Hot swapping is easy enough with an r/c plane but with larger voltage/current system it has challenges. Witness electric auto racing where they swap the entire car at a pit stop instead of the battery.

Also, how about the cross country requirements for flight training? Your 250NM commercial XC would become an overnight trip.

On the other hand, performance with electric is already there. My r/c planes have spectacular performance. That electric Porsche is a freak that you can launch all day long and it doesn't care. Telsas with "ludicrous power" will pin you in your seat and make you a believer. Head to your local go-kart track where they have electric power and you'll be amazed at the punch those things have. This is why I say for a two seat plane: ditch the 65hp and give me something that puts a smile on my face.

If I wanted to get into Valdez style extreme STOL competition I would look up the company that makes the plane previously known as the Kitfox Lite, order one in Titanium (which they offer), leave off the covering other than wings and tail, slap that 65hp motor with just enough batteries for 10 minutes of run time and go after it.