Best engine for Kitfox Mk2?

[kitfoxSwede]

Well maybe not the best engine for a Kitfox but the best engine from the two choices I got. The engines I got to choose from are either a Rotax 912 80hp or a Rotax 582 grey top. The aircraft does not have an engine at the moment and it would be more or less the same work installing any of them, so that is not much of an issue. I have both engines and most of the firewall forward stuff for both, except for propellers.

I know which one of those that are the “better” engine (the 912), but the question is if that is the best engine for my Kitfox 2? The biggest problem with the 912 is the weight as I see it. After looking around I have also seen that most Kitfox 2 still seems to be equipped with the 582 and there must be some reason for that, I figure.

My Kitfox with a 582 weighted in at 531 lbs (empty), and the maximum legal weight here (empty) is 564 lbs. By the way, the POH for Kitfox 2 states 440 lbs as the empty weight! Mine seems to be a little overweight for some reason. I am a little concern that I will not be able to stay within the 564 lbs limit with a 912 even though I have tried to remove all unnecessary things to lighten it a bit.

Anyway what route do you think I should go, 912 or 582?

[av8rps]

If you can work to stay under that weight limitation you have there in Sweden, I most definitely would install the 912. A nice light Model 2 (even at 564 lbs) would be a real screamer with the 912. Not that it won't fly well with a 582, but it would be a much nicer airplane with a 912. And you will burn less fuel.

You may have to move your battery behind the mixer controls behind the baggage if it is currently on the firewall. And it might be good to install a header tank in the same general area to get the center of gravity rearward. I believe replacing a 582 with a 912 is typically between 50 and 75 lbs of weight increase. But I think the biggest issue is keeping your weight down to that 564 lbs. Although one can buid a model 4 with a 912 pretty light - I have one that when originally built it weighed 608 lbs, and since a model 4 and a Model 2 are quite a bit different structurally, I do believe it you wok hard at it you could keep the weight down to the 564.

Maybe you can get "JimS" to respond to your question through a PM. He converted a Model 4-1050 from a 582 to a 912. And his airplane was light to start with, so he would be an excellent source of information for you. Plus he can tell you how he likes the performance and operation between the 582 and the 912.

Just my two cents.

Paul

[kitfoxSwede]

Thanks for you input!

The battery is already behind the seat and a header tank is also installed in the same area. That was the configuration with the 582. So that is not a problem.

My main concerns is the weight and that all that new weight is in the nose of the ac. If that was not an issue the 912 should be an easy winner in this little contest.

[JimS]

If you were at 534# before with a grayhead, I don't think you will be able to meet the weight limit with a 912 in the nose. As Paul mentioned, the weight gain was 60-70 lbs. when I switched from the 582 to the 912. Also with the battery in the aft location with the grayhead set up, I think you might end up quite nose heavy with the 912 on the front end. I moved my battery from the firewall to behind the seats and am still a bit noseheavy.

[kitfoxSwede]

Thanks for the answers. I have in fact tried to do some calculations on the CG with a Rotax 912 in the nose of my Kitfox MkII. They are built on some guesswork on exactly where the extra weight will have its C of G so they probably are not completely accurate. I have used the actual weight and balance with the 582 as the basis for the calculations.

I have calculated on a weight increase of 15 kg (33 lbs), 20 kg (44 lbs) and 25 kg (55 lbs) as I don’t know exactly how much more the installed weight of the 912 will be compared to the 582. I calculated with me in the pilot seat and 10 kg of fuel (22 lbs) in the tanks (wing tanks).

Maybe the weight increases I have calculated on are a little optimistic, I don’t know. Anyway, it looks like with 15 kg increase in weight the CoG would be on the right side of the max forward CoG. With 20 kg increase it will be on the limit and with 25 kg increase it would be about ½ inch to far forward.

Maybe the 582 isn´t such a bad engine after all? It sure has the weight on its side.

[av8rps]

If it were me, I'd do all I could to try and reduce weight elsewhere on the airplane so I could install the 912. That would be an awesome combination for a Kitfox, as it would be light and powerful.

Not sure how much you want to do to try and lower weight, but there are a lot of areas you could bring it down.

Fabric done with a dope finish is very light.

If it uses the fibreglass seat, replace it with a fabric sling

If it has big fibreglass tanks, eliminate one, install a port to add a portable tank for cross country work when needed, and even contemplate the necessity of a header tank, or at least consider a smaller/lighter one

Go with one of the new super lightweight batteries

Eliminate any heavy radio equipment and instruments. With modern technology you can save a lot of weight over the old stuff. Maybe even consider just using a handheld radio?

Run the lightest tires you can

Replace the turtledeck with a lighter version (many are way too heavy for what they need to be) Light aluminum with no glass.

And if that all doesn't still get you to the number you need, buy yourself some scales that read to your advantage

Fwiw; I have an early Avid Flyer that with a 532 Rotax (much like a 582) weighed empty 396 lbs. So putting a 912 in there would be no issue keeping within the numbers you need. And since a Model 2 Fox is only a bit heavier than the Avid if built comparably, it should be do-able to stuff a 912 in there. But for the record, my old Avid Flyer uses a sling seat, a fuselage 9 gallon tank, no electric, mechanical brakes, small tires and tailwheel, no lights, a handheld radio and no transponder, bare minimum instruments, butyrate dope finish, no trim system, etc, etc. But it is a little rocketship with that 532. Climbs solo 2500 fpm in cool weather, stalls around 20 mph, doesn't even need 100 ft to takeoff, and goes over 110 mph wide open with a fixed pitch 72-37 wood prop. If it had a 912 it would only be better.

I still wonder why people buy those ultra expensive Carbon Cubs when they could just buy an early Avid or Kitfox and 912 or 914 it, and probably outperform the Carbon Cub for about 1/10th the cost. And if you got really bored of beating up the Carbon Cub / Super Cub crowd, you could probably take it to Valdez and give the lil' Cub a run for its money .

Hmmm??? Lets say you do a super light airframe like my old A-model Avid and then you hang a big bore turbocharged 912s Rotax on it that pumps out 130+ hp, and install the new Catto 84 inch prop they just created for the 912 that puts out over 500 lbs of thrust... hmmmm????? Oh, and after you do all that, there's still nitrous...

I think the Valdez guys would be getting a real run for their money and probably wouldn't like seeing you show up regularly.

Oops, got a bit carried away...but it sure is fun to think about what one can all do with our early, light airplanes

[martinbguk]

install a port to add a portable tank for cross country work when needed

I've got a Kitfox 3 in the UK with standard tanks and I'd like to add a portable tank for solo cross country work.
Does someone do one off the shelf?
Martin

[Micro Mong Bldr]

Even if you can make the empty weight requirement with the 912, will it give you the useful load you want? Just something to consider.
Cheers,
L

[Pilot4Life]

martinbguk,

http://www.moellermarine.com/afterma...le_fuel_tanks/

Here's one of the many options for portable fuel tanks. These seem like a sturdy, lightweight product.

[jiott]

Here is another option:
http://www.turtlepac.com/