Rotax 912 vs Great Plains

[GreyHawk]

Just getting information and past experience with the Great Plains VW engines. Pros and Cons.

[TJay]

Pros with VW, there way way cheaper,

[Av8r3400]

Cons:

No factory supported firewall forward components
Historically poor performance on these planes
Need to turn a small diameter prop or have a heavy redrive
Trial and error on fixed pitch wood propellers, expect to buy several
Constant problems with cooling

By the time you factor in buying several propellers, engine mount custom fabrication and all of the R&D needed to get an unsupported package flying, you will have a comparable amount of money and a lot more time invested as if you would have started with a 912.

If you truly enjoy the experimental part of experimental aviation, which some people really do, I would recommend staying with a proven and supported power package.


A friend of mine recently went through all of this trying to get an AeroVee to work in a Just Escapade. Three years and thousands of dollars wasted he cut his losses and is now happily flying behind a used 912.

[Norm]

A member of our club tried (is trying) a VW conversion in his KitFox It has been 4 years since he started his journey and he probably has less than 10hrs on it due to reliabiity concerns. Just when he thinks he has it worked out something else comes up that he has to fix.
In the meantime I replaced the 582 in my Classic IV and put 60hrs on it in the first 60 days.
If you want to fly get a 912, if you want to tinker (some do) then get an auto conversion.

[SoaringVA]

Norm,

Did you replace it with another 582, or upgrade to a 912? We have a very old NIB 582 that we need to make a decision about. Have a full inspection service done, trade for a new/rebuilt one, or upgrade to a 912.

Chris

[Norm]

Sorry I thought I said I upgraded to the 912. As I reread it I see I did not.

If you can afford the upgrade to a 912 that is a great route to go. I found a older, low priced 912 and that made it an easy choice for me. I would not hesitate to fly a 582 on a KitFox as I have about 600hrs behind a 582 in my old plane. That being said I love the 912 for smooth ride and feel. Sorry if I am no help in giving you a direction to go between the 582 and the 912 but I think that is strictly a matter of finances and affordability.
I am happy I went with the 912.

[rogerh12]

You can get a VW conversion to work in a Kitfox, but as mentioned above it better be your 3rd or 4th VW engine install, else you are going to be spending a lot of time working out hot oil & hot head issues and general reliability & Usability issues (fuels system, carb setup), not to mention, the issue of just getting the prop right for your flying exceptions. It is far cheaper to rebuild a VW compared to rebuilding a 912 motor, but that advantage is offset now days as the cost of a new VW conversion engine has gone way up and the cost of used Rotax 912 80HP engines has fallen way down. I mysrelf have switch to the Porsche 914 VW variant, which is all aluminum and offers much better cooling capacity and power. The VW really wants to be installed in a fast plane, like the Sonex or Sonerai, where high pressure cooling air can be developed under the cowling. Slower old Kitfox models need special attention to cooling air routing to keep the VW happy (and running), but it can be done. Oversize Oil coolers are a help too.

VW performance in a Kitfox can be quite good though (for the money, if you can get a used engine cheap and rebuild it), but expect to pay close to 10K to get an new VW that right for the kitfox (Duel ignition, Injector carb with mixture control ect...). Here are the specs from a flying model 4 that was up for sale a few years back (for $25). Provided by the seller, these numbers were verified by another person who ended up test flying the plane:


Weights:
Basic Empty Weight = 700lbs
Max Weight = 1200lbs
Usefull Load = 500lbs

Two 13 gallon wing tanks and one 1 gallon header tank. 27 Gallons topped off.
Burns 4.5 Gallons an hour. 6 hours of endurance.

Performance:
You can have two 180lbs Pilots (360lbs), plus 40lbs of gear and 3 hours of fuel (16.7 gals) and go...
At max weight and standard day you will be off the ground in 300 feet and can land in the same distance.

The aircraft climbs around 700 fpm with two people and around 1000 fpm with one pilot only (Standard day). It currently is setup with a cruise prop on it. If you wanted a better climb you could have the pitch of the prop changed giving you a better climb. It has an Ed Sterbra wood prop (62x32) (Length & Pitch).

Cruise:
You can cruise around all day long at 90 to 95 mph at 1500' or below at around 3.5 gallons an hour.
If you go up to 4500' to 5500' at wide open throttle you will get a get about 115mph TAS (True Airspeed), 4.0 gallons and hour.
Typical cruise is around 110mph TAS at this altitude.


The airplane handles beautifully. It is very responsive in all axises. The aircraft roll is very quick and is very responsive even while in slow flight. Stalls are very mild with the VG’s. No wing drop or hard nose drop. Just a gentle mush with the nose slowing dropping down slightly below the horizon and the airplane starts flying again. It is really a great performing aircraft and is very inexpensive to operate.


Performance:

takeoff distance, ground roll = 300ft
rate of climb = 1000fpm Single Pilot, 700fpm Dual
max speed Vne = 140mph IAS
cruise speed @ 7500 msl = 110mph IAS
fuel consumption @ cruise = 4.5gal/hr
landing distance, ground roll = 300ft
service ceiling =11500 ft
Stall = 37mph IAS

[av8rps]

I'm not bashing here, as I like to see people try different things so we all can have more choices. But, by comparison, my 81 hp Rotax 912ul Kitfox 4-1200 on a set of 230 lb and 14 ft long amphib floats has better performance than what was just described.

And not that Rogers numbers aren't good numbers, as they are well above average when you compare his VW Kitfox to other typical 80-100 hp airplanes of similar design parameters. But the Rotax is still the reighning champ when it comes to the best performance per pound on this airframe.

Again, not bashing. Just trying to offer perspective. And honestly, I have never met a Kitfox I didn't like, regardless of the powerplant. They just all perform and fly a bit different when powered differently.