2 stroke vs 4 stroke questions

[Aviator]

Im looking to buy a used KF 3 or 4 probably, Im just undecided between the 912 and the 2 strokes that they are powered with, Ive only flown planes with 4 strokes, and never rode in a KF yet (but want to if I can find a way).

Curious on your thoughts? the 4 stroke more reliable? Cheaper to run/maintain?

Thanks!

[Monocock]

If you have a choice of a 4 stroke then it is worth considering. However, don't dismiss the 2 strokes as they are great simple engines that you can have loads of fun with. They're not built for cruising but will look after you if you look after them.

My personal choice would be a 912 though.

[Aviator]

anyone had a 2 stroke fail? Buddy of mine wouldnt touch a plane with a 2 stroke, not sure I would either unless I was over fields all the time, but looking for opinions as they are alot cheaper to aquire.

[Aviator]

hows your takeoff roll in your bird with the 912?

[Av8r_Sed]

I'll take a crack at this:

Economy: 2 strokes cost less to purchase and less to overhaul but require overhauls more often. 4 strokes are more fuel efficient which could save 1 to 2 gal/hr in cruise for a Kitfox.

Reliability: The edge would go to the 4 strokes. Once they're dialed in they can be fairly trouble free. 2 strokes require greater knowledge on the part of the operator to keep them within allowable temperature limits in flight. They also require more adjustments as seasons or operating altitudes change.

Power/Weight: The lightest planes use 2 strokes which can give some advantages on very short fields. 4 strokes generally are heavier but can deliver more overall power than the popular 2 strokes and allow for higher cruise speeds.

Judging from what I see on the list, the majority favor the 4 strokes if they fit the budget. 2 strokes shouldn't be overlooked though, because they can get you in the air at the lowest possible cost.

My choice for now is the 2 stroke because I think I can master the learning curve and I don't want to invest an extra $6 to $8K just to get it in the air.

-- Paul S

[Aviator]

Thank you Paul

[Av8r3400]

Some of the best STOL performing Kitfoxes have the 2-stroke motors in them. They perform the best because they are the LIGHTEST ones.

[Monocock]

Can I suggest that you fly behind a 2 stroke before you buy one.

Be aware that on the Rotax paperwork that comes with a new 2 stroke engine are the words:

"This engine might stop without warning at any time and cause injury or death" !!!!!!! I always chuckle when I see that.

[Dorsal]

Truly an inspired pice of marketing :D actually I thought that legal CYA statement was included with all their engines or at least the non-certidfied versions.

[DesertFox4]

Curious on your thoughts? the 4 stroke more reliable? Cheaper to run/maintain?Yes to all the above. The early models had no choice other than 2 strokes. When the 4 strokes became available and the performance stats were proven then the 2 stroke sales reduced considerably.


The lightest planes use 2 strokes which can give some advantages on very short fields. True- until you put another person in the seat then short field performance reduces considerably.

If you can find one, buy the 4 stroke version.

[szicree]

This is only my own humble opinion, but I like to think of airplane purchases as parking my money rather than spending it. Building is another story, but a well-purchased airplane can be resold for the same price. With this in mind, I'd say try to find the much more marketable 4 stroke.

[cap01]

If the flying is going to be done mostly around western Washington , the 912 would be my best choice , hands down . Lots of water and lots of hills and if the fire goes out you may be at a loss for a place to put down . The cascades can provide some really fun flying , if a person likes that kind of flying , its not for everyone . sadly there are not a lot of airstrips in the hills like idaho . Flying in the Midwest it may be a different story .

[DesertFox6]

I certainly agree with everything already said, having had a Rotax 2-stroke on my Model !V for just about a year before swapping it out for a 912. The "just about" was an unexpected development but typical of why 4-strokes are favored more these days, so I'll interject it here as an OBTW offering.

The "just about" was brought on by a carburetor fire started by a float bowl overflow condition on takeoff (!) that resulted in some quick diving-turn stuff from the downwind to extinguish the resulting cowl fire and maintain an even takeoff-to-landing ratio. Not tidy at all!

I was really P.O.'d after all the constant TLC fiddling I had to do with that engine and this is how it paid me back?? Our local engine wizard (Rotax calls HIM for the tough rebuild stuff) allowed as that cantankerous 2-stroke issues like mine are why most "experimenters" were switching to the "new" 912 4-strokes (1999-2000) for the reliability and non-fiddle-ability issues. He fixed the engine like new and then bought it from me! :)

Other members of the Desert Fox Squadron immediately (two hours after landing!) lined me up with a 912 donor (Thank you, DesertFox3, wherever you are...) and I never looked back. "Turn-key" flying had finally arrived at my hangar!

Av8r_Sed perfectly nailed all the salient points earlier, and, as a Puyallup, WA native myself, cap01 brings up an issue near and dear to my heart both in western/northern WA as well as over the southwest deserts of AZ: "How close-up do you want to view that gorgeous, rugged terrain beneath you?";)

"E.T."

[Aviator]

Thanks everybody, I can only afford to buy once, so Ill save extra for the 912, there are alot of nice used planes with them on barnstormers for fair prices. Hopefully toward the end of this year I can get into one!

[Monocock]

Good answer!!!

[av8rps]

A 912 powered Kitfox is a match made in heaven. Just an absolutely wonderful combination.

But I've flown hours and hours with 2 strokes before getting a 912 powered Kitfox, and don't regret any part of my 2 stroke hours. The 2 strokes are just a simpler and less expensive way to get into your own Kitfox sooner. But if you can stand to hold out for the 912 powered Fox, by all means do that. The most important part is to get into a Kitfox :) Engines can be changed later if need be...

[Aviator]

Yeah I hear you. Hopefully in the fall or next spring Ill be zipping around the sky in one!

[cap01]

If fall is a target then you should be able to make it to the Arlington flyin and the concrete flyin and kick some tires

[Aviator]

I am there every year! Never rode in a kf yet either. Hoping to find a ride someday too.

[cap01]

Last year was the first concert flyin I made , was fun . Not a bunch of kfs but some interesting airplanes . The highlight was a couple of Paul Allen's planes , a spitire and a b model p-51 made several high speed low passes . A real treat .
Some really pretty country up there .

[av8rps]

One last comment on the subject of 2 stroke vs 4 stroke;

I've had four engine failures in aircraft since I started flying 30+ years ago. Two of them were with 2 strokes, and the other two were with certified 4 stroke aircraft engines. And three of the failures happened on takeoff (:eek:) All but one of the failures was fuel related, which I believe is the biggest reason for any engine failure in an aircraft.

So don't get too mezmerized by 4 stroke reliability.

Here's what I remind people of when I hear people berating 2 strokes for their poor reliability while talking up how reliable 4 strokes are;

"Fly everything like it has a 2 stroke engine in it. Any engine can fail..."

I love my 912 engines, and have never had one fail me. But I still try to fly it as if it is going to quit any minute... :cool:

[Aviator]

. But I still try to fly it as if it is going to quit any minute... :cool:

Thats what they train to prepare us for!

[Dave F]

Im looking to buy a used KF 3 or 4 probably, Im just undecided between the 912 and the 2 strokes that they are powered with, Ive only flown planes with 4 strokes, and never rode in a KF yet (but want to if I can find a way).

Curious on your thoughts? the 4 stroke more reliable? Cheaper to run/maintain?

Thanks!

I don't think either one is more reliable. The operator/maintainer skillset does have a lot to do with it. I find the tinkerers are the one that have the most troubles. 912 ir a 582 does not matter.

I have thousands of 2 stroke hours and in over 30 year I have have one stop running. ( was a Rotax 185 single ignition on a Lazair in hte Very Early 80s Carbon in gap of plug- landed on one engine pulled plug- clenaed and off again)

You can find 2 sroke Kitfoxs up to Model Iv for 12 to 20k
same one with 912 from 23 to 30 k

Or you can pay double that again for a kit and build it.

Kitfox a great plane, safe and fun.

Check my movies 503, 582 912 and 912S Kitfoxes.

It is what you can afford it seems but build them light to perform.
I have seen 912 Kitfox IV @ 600 lbs and also some tanks at 900 lbs......
unreal !!