Making my series 5 into my dream plane

[jmodguy]

Trent
Thanks for the posts. Good to hear someone is doing something a little different!
I picked up a 5 project last year and am making it "my own". Fun and interesting project. Engine parts coming Tuesday...
Looking forward to your next mod/upgrade!

[AirFox]

Very nice write up Trent. I enjoyed the read and all the detailed information.

Scott

[av8rps]

EXCELLENT THREAD! Thanks for taking the time to fill all of us in on all you've done to your Kitfox 5. That is a pretty amazing conversion. Oh, and I loved the pictures flying it in the bush. What a great Kitfox.

[dholly]

Great job Trent, thanks for the update and all the super pics/vids. Right about now I'm guessing 'your' dream plane is looking a whole lot like what many of 'us' dream of too! Will be interested to hear your pirep for the STi wing.

P.S. - My wife thanks you for the new dog walking umbrellas.

[SSFoxBuilder]

Awesome job, Trent!

[PNWJARED]

Trent,

Really Nice write up! Thanks for sharing..

[trentp]

Hey guys, I have been doing a bunch of little tweaks and mods as of lately but wanted to update on the biggest upgrade I had done, the STi Wing!!! And then the other changes I have done since.

***I do plan on doing a review type video on the STi package but for now I figured I should update this thread.

We actually installed the wing a little over 2 months ago but I have been spending most of my time getting used to it and tweaking things to try to get the absolute most out of it, and because of that I havent posted much about it yet. I now have about 50hrs on it and I can say full heartedly that I LOVE it! It truly changes the performance of the airplane into a whole different animal, but it still maintains the Kitfox feel and is still faster than a super cub. It is a little heavier on roll at high speeds but feels just as light when you are below 80mph or so, and that's where this wing shines, it is incredibly stable at lower speeds and it definitely takes off and lands slower/shorter and the climb rate is noticably better.

When we first installed the wing I still had the stock series 5 elevator on my plane, which is a lot smaller than the series 7, so I was having trouble getting the plane to stall. Whenever I would go to stall the plane (or on landing) the tail would stall before the wing and the tail would lift so I couldnt get the wing any slower, it felt as if it was really nose heavy although the scales didnt agree with that idea. Going to the larger elevator helped a lot with getting the tail down and getting to a higher AOA for landing although I still needed to use a bit of power to get it really slow.

The next was VGs. I know that VGs dont do much on the standard kitfox wing but the guys at Kitfox Aircraft said they did get a decent improvement from VGs on the STi wing. I went with STOLspeed VGs, which I like because they are clear and go on with tape so in the event you dont like the placement you can move them or remove them all together without any real headaches. I copied what I saw a lot of my friends doing with their cubs which was placing the VGs very far forward on the wing, the theory being that they are less likely to become blanketed under the separated airflow at stall AOA. Right away I noticed that my climb rate went up and my stalls were a lot less abrupt, just a smooth break with no wing drops. With the VGs the wing is incredibly stable down almost to stall speed.

The latest change, which was the hardest one for me to swallow, was removing my 75in Airmaster proppeller and installing a 80in Prince P Tip. I have been feeling that the airmaster, as amazing of a prop as it is, isn't as well suited for the strictly STOL application as a large 2 blade. Also, since I have added so much drag, I didn't feel like I was taking advantage of the constant speed setup. So I ended up getting a second hand 80x42 prince off of Steve Henry to try out. The prince is about 15lbs lighter than the airmaster, which ended up helping a ton with me getting my elevator authority back, I can now flare to an extremely high AOA and get the plane very slow on landing because of the weight loss (maybe it was nose heavy afterall). I also lost a few MPH in stall speed with the CG shift . I did have to change out the gear ratio in my engine since I still had the 2.27:1 ratio that came with my 80hp 912, so I flew back out to see Hal Stockman, who makes the Zipper Big Bore kit I am running, and he installed the new 2.43:1 ratio gears that come in the 100hp. The gear change got me to the perfect RPM of about 5300 static and now this prop pulls like I have never felt. I did lose a little cruise compared to the airmaster but not a ton which is interesting, again I attribute that to having so much drag that I wasnt going to go much faster than 105mph without adding some serious power to my motor.

I am still doing my testing and getting numbers on the Prince prop but if I keep seeing the performance I have been seeing then I think I may be selling my airmaster and sticking with the prince full time.

The last of the list of changes is the T3 tailwheel shock, I have broken my tailwheel spring in the past as well as the bolts that hold the leaf spring on so I was definitely due for an upgrade in the tailwheel department. The T3 is great! Absorbs bumps really well, feels like it should handle the beating and it protects the airframe from the harsh bumps.

Onto the performance and speeds...

The interesting thing was I didnt seem to lose much cruise speed going with the STi wing, mind you I had already lost most of my cruise when I went with the bush gear and 29s. Overall I lost about 5mph or so in cruise, which put me at about 100-105mph in cruise, although I could get up to 112mph or so if I wanted to put all the power in. Compared to when I had spring gear, the standard wing and 26in tires I lost about 10-15mph all said and done with the whole STi wing and gear package.

Stall speed has been a little confusing, mainly because we changed out my whole pitot tube and hose and I am now indicating completely different speeds than before (actually indicating 10mph faster in cruise than with the old wing even though GPS says otherwise), so my indicated speeds from the old setup seem to have been low across the board including stall. I now indicate 40mph power off and 35mph power on, although when I fly in slow flight next to another plane I always seem to indicate higher than they do even when we are pacing eachother. (for example when a friends plane is indicating 40 I will be indicating 43 or 44 while we are flying at the same speed). So as much as I was hoping to have solid numbers to compare I really dont have very precise ones. What I do have is my seat of the pants feel and landing/take off distances which all say that I am stalling a good bit slower than before.

The standard kitfox wing performs amazingly well which you all know, its only when you are trying to get into the really short stuff or fly at high altitudes or heavy weight that it leaves you wanting more. My goal going into the STi upgrade was to be able to go places in the summer on a hot day that I would have previously only gone on a cold winter day, or be able to take passengers to places that I would only be comfortable solo before. I can say that I have definitely achieved that goal. The larger wing doesnt seem to care nearly as much about high density altitudes, or adding an extra person. It still feels it, but its not nearly as much as the standard wing. The way it handles at all speeds feels more locked in than the standard wing, probably due to being a larger wing, also I have noticed that the STi wing planes out much easier, so transitioning from a climb to level flight the wing just jumps onto step and is off to the races, where the standard wing would sometimes feel like it wouldnt get up on "step". The lift on it is pretty impressive. I am consistently seeing numbers of sub 200ft for take off or landing, even when the density altitude well over 7000ft. Today I did a drag race takeoff with a friend who has a backcountry super cub, which is a 200hp, constant speed equipped, super cub with extended wings and leading edge slats. Basically a $300k super cub with every mod known to man on it. When we went full throttle we both accelerated about the same off the line but I actually ended up pulling away, I took off slightly shorter than he did and then completely out climbed him. It was a good example of why a lighter weight aircraft is often the better performing one, and it definitely made me feel like I had spent my money on the right airplane, especially when I still out cruise him any day of the week while sipping 1/3 the fuel

To sum it up I am in love with the STi wing and landing gear. I have gone places with my plane that I didnt think you could land any plane at, let alone a Kitfox. It truely has turned into my dream plane.

Sorry for such a long write up, heres the fun part; pictures!

For those wondering the difference between the standard wing and the STi wing, here is a photo of a standard rib next to the STi rib. You can see the STi is thicker, longer and it does have a little extra camber to the underside of the airfoil.


Here's a while back during the initial fitting and rigging phase:


Setting the sweep:


Fairing the new struts:


Wings done with paint and fitting the wing tips:


AND... Wings on, ready for first test flight:


Comparison between the series 5 elevator and the 7:



Wings stil fold for anyone wondering:


New empty weight with the airmaster on still:


Prince P Tip prop:


And just some pics of out having fun:





Here's a video of a takeoff and landing at 5000ft with a 5-10mph wind: https://www.youtube.com/watch?v=NUeXpANxUvM

[rv9ralph]

Trent,
Great write-up. It looks like you are getting close to your dream plane.

It also looks like you did the final assembly at Kitfox Aircraft facility.

Looks good.

Ralph

[DesertFox4]

Excellent post Trent. Sounds like the STI delivers exactly as advertised.

[efwd]

Thats so cool Trent. Wonder when I will buy mine. To be honest though, seeing that pic of the sweep set up brought back some anxiety that I was experiencing back at that stage. Not sure Im ready to do that again just yet.