best engine for distance and speed?

[bubbrubb21]

what engine is best for distance and speed? I'm pretty sure HP doesn;t necessarily mean more top-end speed.. not sure differences amongst the Rotax 912,914iS and Lycoming, etc etc. thank you!

[Av8r3400]

My "old" plane was a 912UL (80 hp) and it would cruise all day long at an honest, GPS verified, 120 mph showing 5200 rpm and just under 4 gph.

The plane was a model IV-1050, long wing, 68" Warp Drive taper tip, with the radiator scoop and tail plane ribs of the speedster package, Grove gear and 21x800-6 tires, no pants.

It was a very clean build with an excellent fitting cowl. Empty weight of 650 pounds.

Ol Yeller.jpg

[Esser]

Anything that is turbo should go faster since you can go up higher into thibger Air and still make full power. Sky star said the SS7 with a 914 could do 160mph true at 16,000 feet. Add fuel injection to that and you’re looking at 4-5 gallons an hour.

[aviator79]

what engine is best for distance and speed? I'm pretty sure HP doesn;t necessarily mean more top-end speed.. not sure differences amongst the Rotax 912,914iS and Lycoming, etc etc. thank you!

More HP does mean more speed, but there are competing constraints (weight, cg, etc), and diminishing returns at some point. The 914's cruise advantage isn't so much the marginal HP increase, but the turbocharger that lets you climb into thinner air while still making sea level power. That engine costs 50% more than a 912 uls, which is many dollars per mph. I don't think it is worth it if you just want a few more mph in cruise. You'd be better off spending the extra money for an injected 912is and a constant speed prop. Now if you often operate at high density altitude airports or in and around tall mountains, the calculus changes a bit.

There is also the newly released 915is, which brings a turbo, fuel injection, and 135 HP to the party. I imagine you'd get rocket ship performance from that, but you're also looking at twice the price of a 912 uls, and last I heard they must be mated to a hydraulic CS prop, which is a non-starter for me personally. Also, the turbo engines really want a constant speed prop to squeeze out their cruise performance advantage, and the Airmaster prop is $8k.

[aviator79]

As a data point, I had dinner in Idaho with Paul Leadebrand from Stick and Rudder, and Gary, one of his instructors. I brought up the topic of engine choices. Paul has one plane with a 912iS mated to an Airmaster CS prop, and another with a 914 mated to a FP prop. Both Paul and Gary thought that the 912iS with a CS prop was a better setup, and their opinion carries quite a bit of weight. However, when Paul mentioned a 914 with the CS prop, Gary grinned like an idiot and nodded his head so enthusiastically I thought he might pull a muscle. This is the setup John McBean has on his plane, and what I plan to do on mine. But I also fly out of an airport at at 7200 feet with DA regularly over 10k, with 12-14k peaks nearby.

[av8rps]

I agree with Larry and others here in stating that the Rotax 912 is probably the most efficient engine for the Kitfox. His Kitfox pretty much proves that, along with a bunch of others, mine included. The new fuel injected 912 would probably be the real champion as it is really a fuel mizer, while making as much or more power than other 912's.

I joke with my fellow aviators when they marvel at my low fuel burn, stating "I think my 912 Kitfox might be making gas when I'm flying? " Yeah it really is fuel efficient. Car gas prices makes current fuel costs only $9 an hour. I can't go for a drive in my pick up truck for that. I fly mine on floats and at 95-100 mph my fuel burn is only 3.1 gph. So considering that I have almost 30 gallons of fuel, endurance is pretty hard to beat. But it is good for speed too. Using an IVO inflight prop, even with big draggy floats hanging down there it will top out at 125 mph. So all in all the 912 series is a great engine both for endurance and speed.

However, the larger aircraft engine versions like the 125 hp Continental IO-240 will typically produce the fastest cruise speeds, although that comes at the price of much higher fuel burns. One of the posters on this forum said that he can VNE his IO-240 Model 5 in a moderate climb. I have never seen a 912-914 series capable of that. I suppose the new 135 hp Rotax 915 might be the Rotax that can, but that will be yet to be seen (the McBeans I'm sure will be able to tell us that soon )

In the 90's an aviation magazine did a fly off of a 125 hp IO-240 powered Kitfox 5 against a 115 hp Turbo Rotax 914 Model 4 and in every regard the 914 outperformed the IO-240. Although, it wasn't really an apples to apples test in my opinion, as the Model 5 is a larger and heavier airframe than the Model 4. And while the Model 4 had a 151 mph top cruise, that was at high altitudes that the average Kitfox owner will never fly.

In defense of that original test, in the 2000's Skystar proved twice that the newer Kitfoxes were super efficient with Rotax power. They flew a Turbo 914 tri gear Model 6/7 from Idaho to Sun-N-Fun in Florida and recorded speeds as high as 185 mph, averaging 150 mph. But again that was at high altitudes (as high as 21K). And then there was also the 912ULS powered Model 6/7 tri gear in the Sun-100 air race that averaged 139 mph with 2 guys over the 100 mile course. And that was not flown high, but rather close to sea level.

So with all that said, if you really want to go fast, get a Kitfox that is as aerodynamically clean as possible and put a high hp aircraft engine in it with a cruise prop and you are going to be pretty effortlessly zipping along at less than max power while low to the surface flying right at the edge of the Kitfox VNE, which probably will be the only thing holding you back from even higher speeds.

But if you want to go almost as fast and burning a lot less fuel, use a higher hp 912 or 914 turbo Rotax with a shorter prop (66 or 68 inch 3 blade - maybe even in flight adjustable for optimum effect) and you will have a pretty efficient cross country cruiser.

That is what I really like about the Kitfox, you can make it do almost anything...

[Av8r3400]

Like all debates, the first question is: What mission are you trying to fulfill?

Personally, if my mission were to be at 160 mph and 16,000 feet, I would not be owning a Kitfox.

[av8rps]

I think having a cross country cruise speed that gets you places reasonably while still having STOL capabilities to go in and out of short strips, haul a reasonable load, be relatively inexpensive to own and operate, and yet be able to be a good ski plane, a float plane, a tri gear or a taildragger, or a fun sport aerobatic plane with wings that fold for storage is a pretty large list of capabilities. I'm not sure there are any other designs that can claim all that.

But I agree, if speed is the major goal a Kitfox is not the airplane. I like the balance of all things listed above. Otherwise I'd be flying a Glasair 3 with 350 hp and twin turbo's to get me where I need to go.

But that wouldn't be half the fun as getting there in the Kitfox

[bubbrubb21]

Like all debates, the first question is: What mission are you trying to fulfill?

Personally, if my mission were to be at 160 mph and 16,000 feet, I would not be owning a Kitfox.

i would need to get to roughly 700mi on a tank and the quicker I can get there in a KitFox the better (work-oriented mission). No big mountain ranges to cross or anything, mostly grasssland with rolling hills, landing elevation at most 3,000ft

[bubbrubb21]

I agree with Larry and others here in stating that the Rotax 912 is probably the most efficient engine for the Kitfox. His Kitfox pretty much proves that, along with a bunch of others, mine included. The new fuel injected 912 would probably be the real champion as it is really a fuel mizer, while making as much or more power than other 912's.

I joke with my fellow aviators when they marvel at my low fuel burn, stating "I think my 912 Kitfox might be making gas when I'm flying? " Yeah it really is fuel efficient. Car gas prices makes current fuel costs only $9 an hour. I can't go for a drive in my pick up truck for that. I fly mine on floats and at 95-100 mph my fuel burn is only 3.1 gph. So considering that I have almost 30 gallons of fuel, endurance is pretty hard to beat. But it is good for speed too. Using an IVO inflight prop, even with big draggy floats hanging down there it will top out at 125 mph. So all in all the 912 series is a great engine both for endurance and speed.

However, the larger aircraft engine versions like the 125 hp Continental IO-240 will typically produce the fastest cruise speeds, although that comes at the price of much higher fuel burns. One of the posters on this forum said that he can VNE his IO-240 Model 5 in a moderate climb. I have never seen a 912-914 series capable of that. I suppose the new 135 hp Rotax 915 might be the Rotax that can, but that will be yet to be seen (the McBeans I'm sure will be able to tell us that soon )

In the 90's an aviation magazine did a fly off of a 125 hp IO-240 powered Kitfox 5 against a 115 hp Turbo Rotax 914 Model 4 and in every regard the 914 outperformed the IO-240. Although, it wasn't really an apples to apples test in my opinion, as the Model 5 is a larger and heavier airframe than the Model 4. And while the Model 4 had a 151 mph top cruise, that was at high altitudes that the average Kitfox owner will never fly.

In defense of that original test, in the 2000's Skystar proved twice that the newer Kitfoxes were super efficient with Rotax power. They flew a Turbo 914 tri gear Model 6/7 from Idaho to Sun-N-Fun in Florida and recorded speeds as high as 185 mph, averaging 150 mph. But again that was at high altitudes (as high as 21K). And then there was also the 912ULS powered Model 6/7 tri gear in the Sun-100 air race that averaged 139 mph with 2 guys over the 100 mile course. And that was not flown high, but rather close to sea level.

So with all that said, if you really want to go fast, get a Kitfox that is as aerodynamically clean as possible and put a high hp aircraft engine in it with a cruise prop and you are going to be pretty effortlessly zipping along at less than max power while low to the surface flying right at the edge of the Kitfox VNE, which probably will be the only thing holding you back from even higher speeds.

But if you want to go almost as fast and burning a lot less fuel, use a higher hp 912 or 914 turbo Rotax with a shorter prop (66 or 68 inch 3 blade - maybe even in flight adjustable for optimum effect) and you will have a pretty efficient cross country cruiser.

That is what I really like about the Kitfox, you can make it do almost anything...

thank you for the feedback!