Rotax 582 RPM's & cruise speed

[Steve Schlager]

Hi Everybody:
Since I got my KF II w/582 in January, I've been wondering: what are normal cruise rpm's and what kind of cruise speed can you expect? And, what kind of fuel burn can I expect?
I took off the stock landing gear and replaced it with the HighwingLLC wide bush gear (and I LOVE it!).
Your comments are appreciated...

[GDN]

Hi Steve,

We have the same configuration, changed my landing gear for the Highwing LLC as you (with the fairing)

Fly at 5900 rpm and burn 15L/h at 70 kts

[akflyer]

5800 RPM on wheels gave me a fuel burn of 5.6 GPH at 80-83 MPH indicated. This was at sea level and temps from 40-75F

[av8rps]

As I recall the Model II Kitfoxes were slower than the 1's or the 3's due to the factory making a few wing and tail incidence changes in an effort to improve inflight visibility over the nose. Now don't ask me how I remembered that, but I do specifically remember when the Avids were a lot faster than the Kitfoxes. But then when the Kitfox 4's came along that changed, and then the Avid was the slow one.

I test flew a friends Kitfox Model IV-1050 with a 582 and a warp 3 blade on 1460 full lotus floats that were rigged with a huge amount of tail low on the water incidence (causing the floats to be quite nose down in normal level flight), and even on those bulbous floats it cruised at 5800 rpm in the mid 80's. It would top out in the lower 90's. And fwiw, it was a really FUN floatplane, that had no trouble flying 2 guys off the water (or snow) 2 stroke 582 Rotax and all!

[akflyer]

I test flew a friends Kitfox Model IV-1050 with a 582 and a warp 3 blade on 1460 full lotus floats that were rigged with a huge amount of tail low on the water incidence (causing the floats to be quite nose down in normal level flight), and even on those bulbous floats it cruised at 5800 rpm in the mid 80's. It would top out in the lower 90's. And fwiw, it was a really FUN floatplane, that had no trouble flying 2 guys off the water (or snow) 2 stroke 582 Rotax and all!

I cruise faster on the 1460 full lotus floats, than I do with ski's on. Just because they dont look like a "conventional" float, every one assumes they are super draggy. I have found that to not be the case on the 5 airplanes I have had them on. The only thing I lost was some climb performance due to the increased weight.

Flying side by side with a buddies MK IV extended speed wing he had 8.50's on I was on 24" good years, RPM for RPM he out cruised me by and easy 10 MPH. On skis we were dead even (within 1-2 MPH) With him on skis and me on the full lotus floats, he cruised at 5900 to keep up with me at 5500 RPM. It had us both scratching our heads as it really made NO sense, but we did those tests side by side many different times.

[av8rps]

I agree that full lotus floats (as long as they aren't amphibs) are not as draggy as they look.

But I find it surprising that your skis are draggier than your floats. I put large wheel skis on my Highlander this winter (look at the pictures below and then think about how much drag they must create?), but after accurately testing my cruise and top speeds I found that my max continuous cruise speed is the same whether on gear or wheel skis (108 IAS mph at 5500 rpm - max continuous for a 912). Of course I was pleasantly surprised to have learned that, and the only thing I can come up with is that the front of the ski blocks out the drag of the large tire, which I'm thinking may possibly make up for all the drag of the ski tubeing and cables, etc.? Of course that is just speculation as I really don't know why I didn't lose top speed when going from land gear to skis?

So my experience wasn't the same as yours. But I suspect our difference could even be so simple as the differences in how we have ski incidence set?

And fwiw, I've found the 912 powered Highlander and Kitfox both lose between 7 and 9 mph when adding floats. When I used to fly Avid Flyers I never noticed any speed loss going to floats, and honestly don't recall a speed loss when I installed my Avid wheel pentration skis.

Maybe that's why they call this "Experimental"

[Av8r3400]

Those kinda look familiar...

No loss of cruise speed for me either.

[av8rps]

Hey man, thanks for helping provide some credibility to my claim. If you tell most people that you lose no speed when adding wheel skis they will say that's impossible. But we have two planes for sure that can prove it .

These really are the near perfect airplane...

[JimS]

Two trips to Sun-N-Fun from Wisconsin with my 582 (model IV). Turning 6000 rpm I burned 5 gph consistently. Cruised 90 mph. After 600 hrs on the 582 upgraded to a 912 (Thanks PaulS,) The next trip to SNF saw 3.5 gph at 100mph.
Also, no speed loss when going to wheel skis.

JimS