Very close to ordering a SuperSTOL XL

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Re: Very close to ordering a SuperSTOL XL

Postby av8rps » Tue Jan 05, 2016 9:08 pm

Paul,

I'm surprised to hear your Kitfox is not faster? My 912uls Highlander on 8.50's and open tube gear will easily fly 100 (verified) mph in the mid 5k range. And that is with my prop set favoring climb. Are you sure you have your prop set correctly?
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Re: Very close to ordering a SuperSTOL XL

Postby AV8R Paul » Wed Jan 06, 2016 1:36 am

av8rps wrote:Paul,

I'm surprised to hear your Kitfox is not faster? My 912uls Highlander on 8.50's and open tube gear will easily fly 100 (verified) mph in the mid 5k range. And that is with my prop set favoring climb. Are you sure you have your prop set correctly?


I pitched the prop, to 15.5 degrees. I am getting about 5150 RPM static. I am now seeing 103 to 105 indicated cruise at 5300 rpm. Haven't done a circuit, but I'm happy.
AV8R Paul
SuperSTOL XL - S/N JA498-11-16
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Re: Very close to ordering a SuperSTOL XL

Postby AV8R Paul » Wed Jan 06, 2016 1:42 am

SuperFly wrote:Paul,

I do have the larger tires, 29" Alaskan Bush Wheels. Speed was not much of an issue to me, as I don't typically go very far, and when I do, I will be building time ;). This is my escape from work, so if it takes me longer to get there and home, well, thats kinda the point.

I am progressing very well, I just dont have time to update the website. I plan to do that this winter once the airplane is flying and its to crummy outside to fly. Actually last night I put the life bloods in engine, burped the oil system, and cranked it until I had oil pressure. If its decent out this afternoon, I plan to light the fires for the first time. A handful of punch list items, and its ready for inspection. Watch my website later this winter, as I will get the rest of the build put on there.


Ben,
I am about in the same boat, I only make one or two trips a year, other than that I'm flying a circuit in the flat lads of North Texas. Your video on first run was great, congratulations.

Paul Z.
AV8R Paul
SuperSTOL XL - S/N JA498-11-16
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Re: Very close to ordering a SuperSTOL XL

Postby av8rps » Wed Jan 06, 2016 9:47 pm

Paul,

I'm not familiar enough with your prop / engine combination, but I believe if you could reduce some pitch (get a slightly higher static rpm) you may actually get better cruise speed. I've learned on my 912 powered airplanes that for the best overall performance if I can get about 5600-5800 rpm wide open throttle while straight and level that I will get the highest cruise speed out of the engine and airframe combination. It seems the 912 Rotax does better with higher rpm's than it does lugging around with lower rpms. At least that's been my experience. I've tested that theory again and again on my 912 ul Kitfox amphib as it has an IVO in flight adjustable prop (making testing that really easy - the lazy man's way; no wrenches, I just have to move a switch).

The fastest top speed I can get with wide open throttle straight and level is actually right at 5800 rpm. But since you can only run at that rpm for 5 minutes, if running a ground adjust prop I like to have it set for a max throttle straight and level rpm of 5600-5700 so I can just pull my throttle back slightly to get to 5500 rpm, and can cruise at that speed all day if I choose to do so, or just want to get somewhere fast. That's how my Sensenich 2 blade 70 inch prop on my 912uls Highlander is set, and that setting gives me just a tad under 110 mph at 5500 rpm. And I am totally happy with that for getting places when I need to, and it still climbs great. And if I really want to show off to my friends in their slower airplanes I can firewall it at 5650-5700 for 5 minutes and get 112 mph to 115 mph (depending on the day and how I'm loaded). That is in my opinion pretty dang good for an airplane that can land pretty much anywhere.

Of course, like most people flying Stol type planes, speed is not my primary concern. So I usually fly around at around 5 grand or less. If I am going cross country somewhere I compromise on speed and gallons per hour, cruising around at 5200-5300 at approximately 100 mph, much like you are doing.

My original intent in asking about your prop setting is that I think your Kitfox might be able to go a lot faster than it currently is with some minor prop tweaking. The airfoil you have on yours is the same as my 80 hp 912 Model 4 Kitfox floatplane, and my experience comparing it to my Highlander is that the Kitfox even on floats is quite a bit faster (I once screwed up while chasing some of my buddies Highlander floatplanes around and without realizing it hit 155 mph in a long shallow dive :shock:. Not recommended for sure. But what blew me away is that the airplane was still accelerating. I'm not sure, but I doubt my Highlander going straight down would go that fast? That great old Dean Wilson / Avid undercamber airfoil is marvelous for STOL, but seems to hit a wall when you hit the 120 mph range. I say all that to demonstrate how different the wings between the two planes work, not that I recommend operating that way, or that I do that on a regular basis...)

Please don't take my comments here about your Kitfox as criticism. I'm just offering some of my experience with prop settings in an effort to help you make your Kitfox more efficient, and fun, while also sharing the info with the Highlander / Super Stol guys here.
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