Page 1 of 1

Pondering the need for speed

PostPosted: Tue Jan 19, 2016 2:01 pm
by scubarider2
Well, you know for a couple years now I have been toying with the idea of selling my bird and building another. I even put it up for sale for about a month and then took it off. I love my plane. I am pretty different from most of the Highlander owners in that I like taking mine on trips and am not interested in the short field take offs and landings. I am based on a 3000ft grass strip and only really fly into other airports. So I have "cleaned up" my plane as much as I can even constructed the ONLY wheel pants out there. I have the Rotax 912uls 100hp with a Sensenich 3-blade prop. At max cruise speed I am getting right at 105-110mph. I don't want to give up my plane for more speed thinking about a few things and want some feedback.
I am pondering for this summer about pulling the wings, which are currently the Highlander wing, and replacing them with the Escapade wing. I would install the new aluminum tanks (now have the fiberglass ones that bled into the motor), try and work on the camber and any other mods to increase the cruise speed. Any and all opinons and suggestions are welcome. :shock:
Thanks everyone!!!
Your moderator,

Re: Pondering the need for speed

PostPosted: Wed Jan 20, 2016 1:49 pm
by Johnny C!
I am planning to get my wheel pants made & installed
this spring. Also, Troy & Steve Henry suggested I go with
a 2 blade Ivo, which I did. I can get 100 mph at 5400 rpm,
with my 912 Rotax, and still get really good take off
performance, more than enough for conventional

I just found this, also...

I have added flap gap seals, I feathered the trailing
edge of my main landing gear, and have recently
faired over the forward landing gear mounts on my

I am going to fill the flap to fuse gap, and fair in the
exposed flap & aileron pulleys, soon as well.

One other thing I would like to do is build fairings for
my bungies, as well.

I have the Highlander wings & tail feathers. I'll bet your
Escapade tail feather are helping you on your cruise



Re: Pondering the need for speed

PostPosted: Wed Jan 20, 2016 8:53 pm
by av8rps
I own a 80 hp Kitfox 4 on amphib floats, and it is probably all out 15 mph faster than my 100 hp Highlander is on wheels with an open tube gear and 850 tires. But I have a pretty fast Kitfox compared to many. And actually, same goes for my Highlander (108+ mph at 5450 using a Sensenich 2 blade, and still climbs like a rocketship).

Now I'm confident the Kitfox 4 on floats can't be "cleaner" than my Highlander on wheels, so I think it is safe to say the speed comes all from the wing. The newer Kitfoxes use a Harry Riblett airfoil design that modified the early Kitfox wing (identical to our Highlander I'm pretty certain) to remove most of the undercamber from the bottom of the wing, added a leading edge extension that created a sharper angle as opposed to the round tube leading edge, and added a set of Hoerner styled wingtips to reduce tip vortices / drag. The ultimate example of that cleanup was first represented in a Model 4 Kitfox Speedster, which used a 28'8" wing (vs the std 32 ft), used streamlined wing, jury, and horizontal stab struts, wheel pants, and a smaller tailwheel. I personally got to fly that airplane in the early 90's with a 80 hp 912 that used a ground adjustable GSC wood prop (pretty, but very inefficent) and it would fly almost 140 mph at 5500 rpm. There were many of us that would've never believed an 80 hp Kitfox could ever go that fast. But it did.

And probably 10 yrs ago, Kitfox entered there factory model 7 tri gear in the Sun 100 air race, and even with 2 guys in it, it had an average speed of 139 mph running a 100 hp 912.

So again, it's mostly in the wing. I personally don't believe an Escapade wing and / or tail feathers will gain you much of anything. It's still the same airfoil.

So if it were me I'd get the loftings for the Kitfox Riblett airfoil (they're floating around on the Net at the Kitfox / and / or the Avid forums. I have a copy of Ribletts letter explaining why to do it with the dimensions somewhere in my stuff too if you can't find it) and modify your existing wing. You could use a Kitfox leading edge extrusion along with Speedster / Hoerner wingtips. I'd probably just make some foam pieces to add to the lower Highlander ribs, AND I would add some false ribs between the main ribs on the bottom of the wing. Just look at a newer Kitfox wing bottom and you'll see what I mean by that. Tbat is very important if you are looking for speed, as early Model 4's didn't have enough of them between main ribs, and those airplanes are slower than the later versions with more false ribs. I believe that is because the faster you go the more the airfoil will go back towards the undercambered shape, caused by presuure.

Oh, and while I think the Ivo 2 blade is probably a little quicker than some three blades, I doubt very much it is any quicker than the Sensenich 3 blade as that is a very nice prop, and I'm told it is the one the Rv 12 guys prefer for speed. My experiments with props on my Kitfox have proven to me that my Kitfox flies significantly faster with a 66 inch 3 blade than with a 72 inch of the same design. But climb with the small blade sucks, so I've settled in with a 68 " three blade. On a Highlander with a 912uls I'd go for the 69 or 70 inch 3 blade, and 72 if I was wanting a bit more STOL. Props like the 75 inch and up are optimized for STOL and probably not practical for you.

One last comment. I've always made an effort to streamline my planes first by approaching the parts of the aircraft that are out in clean air, out of the prop wash and boundary layer of the fuselage. I think you get much better results quicker. A good example is on a Kitfox: many guys believe a round cowl is just too much drag, so they switch to a smooth cowl and gain nothing. Why, because right in front of that cowl is a draggy 6 ft prop. Granted, on a fast plane a cowl can make a big difference. But on planes like ours adding wider wing strut fairings, fairings where the strut meet the wing spar, jury strut fairings, and tail fairings (the boundary layer reattaches to the fuselage near the tail typically) are more likely to make bigger improvements quicker. I would later start working on fairings for landing gear to fuselage, struts to fuselage, etc, etc., the parts and pieces that essentially fly in the boundary layer.

Whew, lots of typing. Hopefully my jibberish here will help you to gain that speed you're after. I've thought about doing all that myself many, many times. But I hardly have time to fly my planes these days, much less improving them...

Re: Pondering the need for speed

PostPosted: Fri Jan 22, 2016 10:05 am
by scubarider2
Thanks for your reply. Do you have some pictures of what you did for mods? Would love to see them. Even better you should fly over when the weather gets better. :mrgreen: :mrgreen: 8)

Re: Pondering the need for speed

PostPosted: Fri Jan 22, 2016 10:25 am
by scubarider2
AV, thanks for your reply! Great information. My thoughts were to possibly move to the Escapade wing and do mods to it as I built them. Some of what you mentioned. Overall I would love to see my bird cruise at 120mph which I think may be possible with some heavy speed mods and cleaning up everything. Well, that is my hope anyway. I need to talk to the guys at JUST to see their thoughts.

Re: Pondering the need for speed

PostPosted: Fri Jan 22, 2016 12:23 pm
by FlyerChief
Hi Dennis,
Maybe you need to look to the Cessna Sky Catcher for inspiration when it comes to speed. It's a high wing that cruises at about 130 mph. They make pretty extensive use of fairings at all of the attach points to reduce drag and a flat bottom wing like the Kitfox that Paul mentioned. I think the flying wires create a lot of drag too.


Re: Pondering the need for speed

PostPosted: Fri Jan 22, 2016 8:51 pm
by av8rps

It will be interesting to hear whay Troy has to say about using Escapade wings. The newer Kitfox that did the Sun 100 race at 139 mph used a 32 ft wing. What we've learned on our Kitfoxes is that if you have a 650 lb or less Kitfox, the shorter 29' Speedster wing will give best cruise. But the short wing on the heavier airplanes actually makes it fly slower, probably because it has to fly at higher angles of attack to support the higher empty weight, thereby increasing induced drag.

So with that said, I doubt a shorter wing will help a Highlander cruise. But I know an airfoil change will :)

Re: Pondering the need for speed

PostPosted: Sat Jan 23, 2016 9:34 am
by av8rps
I forgot to mention, it might be worth your time reading this kitfox forum link. it has stats on a new kitfox with big bush tires and a 75 inch prop that cruises at 120 mph at 5,000 rpm. Again, the new kitfox wing is just a minor mod to the wings we use.

Re: Pondering the need for speed

PostPosted: Sat Jan 23, 2016 1:30 pm
by jjacky
Hi Scubaraider...I'm confused by what you wrote about your fuel tanks ("now have the fiberglass ones that bled into the motor") there a problem with the fiberglass tanks?

Re: Pondering the need for speed

PostPosted: Mon Jan 25, 2016 1:37 pm
by scubarider2
Thanks again everyone. Yes I will look at the Kitfox threads. Also, I more than likely will NOT go with the Escapade wing for the very reason you stated about drag and lift. I am looking at going with some different mods for the wing though. Will upadte everyone when I proceed and give you some numbers. Weather is not really good right now. Hopefully soon.
Yes, I did and still do have a problem with the fiberglass tanks. I got sold a batch that were not cured properly. I ran the first couple hundred hours with them and started to notice the engine was getting weaker (lower compression) and it was almost impossible to get an oil burp. So I took it to a mechanic who did a compression check and he told me that it looked like I had 2000 hours on it. I was heartbroken because I take such good care of that motor. So right about that time a few others were also complaining so the company came up with a "fix". Had to "wash" the tanks until the whitish material was gone. I did that which was expensive. After that Troy agreed to have Billy look at the motor and replace anything that was wrong. So he replaced the valves. Almost like having a brand new motor. Now at 475 hours I am experiencing the same thing again. Harder to burp, seems weaker again... I always change the oil/filter at 25 hours. I use high octane non-ethonol the majority of the time and 100LL when I have to when traveling. It looks like I do not have any option other than to replace the fiberglass tanks. I have not discussed any of this with Troy yet because I have not decided the best thing to do. Either way it is going to be expensive and labor intensive. Neither of which I am excited about.