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Re: Airfoil tail

PostPosted: Mon Dec 19, 2016 5:21 pm
by AV8R Paul
Man you nailed the issue, it all boils down to money $$$$$$$$$$$$. But whats a little $$$$$$$$$$, when we are crazy enough to spend $100,000 to build an airplane. The Next Draggy Tube would be the Landing Gear, cut a foot out of them and it would also help.

I wanted to add one thing to the discussion. In looking at all of the number the one thing that is missing is the Actual Cross Section of an Airfoil that would be required to encompass the existing Tube Diameters of the Horizontal Stabilizer & Elevator. See the Green Number with Question Marks, the thicker Cross Section would result in a larger Load Factor. Would it be 1.1 or 1.5, I don't know. The only way we could determine that is to build scaled mock ups of both to determine the exact Load Factor. Just FYI, my wife just walked out of the room, her only comment Damn your are an Engineer!

As you can see from the Sketch, I have been cogitating the issue. FYI you can click on the picture and get a more legible photo of it.

By the Way Merry Christmas & Happy New Year to All Ya'll ! ! !

dkshow wrote:These are quite draggy airplanes. I think the best way to make a SS go faster would be to take the shocks and the gear off... All those round tubes hanging out there in the breeze pulls incredibly hard in the wrong direction. Unfortunately, we sort of need the gear for the landing part unless you only plan on doing it once. Try this, drive down the road at say 65mph, now stick a broom stick out the window and see how tough it is to hold it. Just the struts alone is a lot of drag. I'm not sure the best way to reduce it but I think you could pick up a bit of the top end by working on losing some of that drag. Didn't Troy say in the beginning that the SS wing was 10 slower and 10 faster than the Highlander? That could have been before the SS gear I suppose. I think horsepower and the right prop is the key to a faster SS honestly. Everything is a trade off, do you want to go fast or leave the ground fast.

I'd love to have the best of all worlds, something tells me I don't have enough money.

Re: Airfoil tail

PostPosted: Mon Dec 19, 2016 5:50 pm
by Clark in AZ
Really interesting thread!

Would a flat bottom airfoil be beneficial to the SS by producing more lift for the tail thereby reducing the nose high flight characteristic? Also, how much weight are we talking about adding? Unfortunately all that weight it way out on the arm of the tail...

Re: Airfoil tail

PostPosted: Mon Dec 19, 2016 6:52 pm
by kenryan
dkshow wrote:These are quite draggy airplanes. I think the best way to make a SS go faster would be to take the shocks and the gear off... All those round tubes hanging out there in the breeze pulls incredibly hard in the wrong direction. Unfortunately, we sort of need the gear for the landing part unless you only plan on doing it once. Try this, drive down the road at say 65mph, now stick a broom stick out the window and see how tough it is to hold it. Just the struts alone is a lot of drag. I'm not sure the best way to reduce it but I think you could pick up a bit of the top end by working on losing some of that drag. Didn't Troy say in the beginning that the SS wing was 10 slower and 10 faster than the Highlander? That could have been before the SS gear I suppose. I think horsepower and the right prop is the key to a faster SS honestly. Everything is a trade off, do you want to go fast or leave the ground fast.


Increasing speed by using horsepower can require burning a lot more fuel. More fuel means heavier which means increased AOA which means more drag ... not to mention reduced range. I'll be happy to accept the "natural" speed of the airframe. I just wanna get this thing done!

Re: Airfoil tail

PostPosted: Mon Dec 19, 2016 7:15 pm
by dkshow
Ken,
All those things are true...and that's just your wisdom speaking again. I enjoy experimenting and finding ways to make something better but a SS will never be "fast". I don't know who said it, "it might not be fast but man it sure is slow!". One thing to not lose sight of is just how fun and easy these airplanes are to fly. It's easy to get all wrapped up in just how slow or fast will it go, it also happens to handle really nicely and just fun. Put 15-20mph on your nose and things get really really slow, when you start landing in 10-15 ft it's just surreal. There really aren't words for that feeling.

Re: Airfoil tail

PostPosted: Mon Dec 19, 2016 8:39 pm
by av8rps
Troy and I talked prior to him developing the Super STOL as he had originally planned to build a 4 place one-off 180 hp Lycoming powered homebuilt Helio Courier for himself, after being so impressed with flying Gary's Helio. But I suggested he just turn his already great STOL Highlander into a Super STOL aircraft by putting a Helio type retractable slatted wing on it, but to eliminate the undercambered wing altogether in favor of a faster airfoil that would allow it to cruise faster, while flying slower when the slats are out. Just like the Helio.

Well, I think that concept would have worked great, but then Troy had the brainstorm of adding the huge extended gear, which of course really ended up being a critical part of the Super STOL's huge success. Unfortunately that great gear more than destroyed the speed benefits of having retractable slats on the wing. Of course, I'm like most of you on this forum. If I really want the ultimate booney basher I'm gonna go for the Super STOL. It's one of the very best STOL aircraft ever created. But if I can live with landing in a 100 ft instead of 25, and would like a little better cross country capability, I'll opt for the Highlander. I think both models are phenomenal aircraft.

For those that think the wing airfoil is not the primary cause of our drag / slow cruise speed, just compare your Just Aircraft model to a Kitfox with the same power and you will discover a large difference in cruise speed. I'm willing to bet if you put the Riblett airfoil the Kitfox uses on a Highlander you will gain 15 to 20 mph in top speed. How do I feel so confident to say that? Simple, when Kitfox had Riblett modify the original Dean Wilson undercambered airfoil, they suddenly had an airplane that flew 15 to 20 mph faster than the old airfoil. And the best part, it flew almost as slow. So with all that said, I am confident a Riblett airfoil like Kitfox uses on a Highlander would really make it a performer. The fuselage and tail and landing gear are just not that different between the Highlander and the Kitfox, so you could maybe end up with a 140 mph top speed Highlander, like the newer Kitfox can do. I have a 110 to 115 mph ( top speed) Highlander, and it generally is a fast one.

Ok, if I were to put a Riblett airfoil on a Highlander, I would airfoil the tail, just because. And I would also fair the tail struts like I did on my Kitfox (the Kitfox only uses steel rod struts on the lower part of the horizontal stabilizer, which makes it easier to streamline than cables).

It would be really interesting to see what a Super STOL would do for speed without that big gear. But I agree with Troy, "That would take all the fun out of it" :wink:

Re: Airfoil tail

PostPosted: Sat Dec 31, 2016 2:15 am
by BDA
Trial fit for plug formed aluminum ribs on vertical

Re: Airfoil tail

PostPosted: Sat Dec 31, 2016 2:29 am
by BDA
Another view

Re: Airfoil tail

PostPosted: Sat Dec 31, 2016 3:34 pm
by R Rinker
I haven't read the entire thread, but wanted to comment on the flying tail concept. For me the advantage of a flying tail is not to reduce drag but for slow speed control response. I've only flown in a couple Super Stol's and not as PIC in any. It definitely is controllable, but pilots used to fast, responsive aircraft are not comfortable, and one new builder was so uncomfortable that he put his up for sale. This may be more of a pilot experience issue, as to what one is comfortable with, but it makes the point of control response, or how fast the aircraft responses to control input. It would seem obvious that the faster the aircraft responds, the more control is available when on the edge. I did my initial pilot training (over 30 years ago) in a 172, but then got a few hours in a Cardinal and soloed in the Cardinal, then finished my training in the 172. There was an amazing difference with the Cardinals flying tail. It gives a very solid feeling of control and instant response. A lot of people find the Cardinal way "too touchy", but I loved it. The response made it so much easier to do precision work of a landing. So if you take that kind of response and add it to the extreme slow flight regime in a Super Stol and it would make a world of difference. When coming in (or sometimes going out) wobbling around & getting hit by unexpected shearing, if that airplane is solidly responding quickly to input, you are going to feel a lot more joy and do a lot more accurate job getting it done... I believe this is the universal feeling of those with experience in a flying tail. With the Cardinal it can be a little annoying at speeds above the very slow flight envelope, but the Super Stol is all about the slow fight envelope to operate where not much anything else will....