AV8R Paul’s SuperSTOL XL

[AV8R Paul]

Working on the Tail Feathers, I wanted a flying tail.

[Clark in AZ]

Very nice! Can you tell how you came up with the design of the ribs?

[moving2time]

Paul, Did you change the pivot point of the hinge or leave it where it was? I can't tell from the images you posted. I have been contemplating something similar but wanted to relocate the hinge which is a real issue with the tube. If you move the pivot point aft then the trailing edge of the elevator is out past the horizontal stab. Wouldn't want to get into re-welding. Not one of my skills at the moment. Otherwise you are introducing a large open gap into the joint. You also going to modify the rudder? Thanks. Joe B

[AV8R Paul]

Very nice! Can you tell how you came up with the design of the ribs?

I started by Reverse Engineering other Designs: RV, Kitfox, Zenith STOL, etc., looking at the competitors ideas steal shamelessly the best design. I went to a Website (http://airfoiltools.com/), the web site has over 1600 commonly used airfoils. The website has a search for Airfoil Comparisons & a search for symmetrical airfoils, by the function of the design. I knew I wanted a Symmetrical Airfoil Design. I ended up landing on a NACA 4 Digit Airfoils. I also asked a friend of mine he recommended the NACA0012 Symmetrical, he also recommended I get a Airfoil Deign CAD package used by modelers, Airfoil Modeling Software CompuFoil #D v4.7.0.1. I looked at it and a few other Modeling Software Packages, and landed on this one because it would accommodate a 40+ inch wing cord. I purchased the full version and then ended up spending the next few weeks figuring out how to use the cad design tool. Then started laying out a symmetrical NACA four digit airfoils. I started with NACA0012 a very commonly used airfoil shape. I then plotted out all of the airfoil templates and started mocking ribs. The NACA0012 proved to have too thick of rib. The thickness equals 12% of the rib length for the longest 40 inch rib, which made the thickness of the rib 4.9 inches thick. It also made the elevator hinge faring very difficult to design. As I had said, I had also been looking at several other flying tail designs RV, Kitfox, Zenith, etc. I compared the airfoil to quite a few and found the NACA0012 to be a little more aggressive than most used, and looking at the Zenith they use an aggressive inverted non-symmetrical wing. I looked at the NACA0010, NACA0008, & NACA0006. I finally picked the NACA0008. A NACA0008 is 8% of 41 inches or 3.3 inches thick, which made it a little easier to design the hinge. Looking at all of the engineering data, I finally decided that anything was better than a flat tail. The RV across the way has what looks like a NACA0008 or a NACA0010, but I’m guessing it would be the NACA0008. I plotted out the NACA0008 and started the laying out the elevator hinge interface. At first I could only get about 23 Degrees of up and down elevator. I finally relented and started doing a simple CAD layout of the interface to determine the hinge interface design, and now I am getting +/-35 degrees, more than needed but it will not limit the movement. The Rib Spacing was dictated by some of the welded tubes and design features in the Horizontal stabilizer & elevator. The first rib had to be sufficiently spaced from the fuselage to assure there was clearance for the bolt. There needed to be a rib at the longest Rib, and then at the the welded tubes. See attached photo layout and Pivot Hinge Designs:

[AV8R Paul]

Paul, Did you change the pivot point of the hinge or leave it where it was? I can't tell from the images you posted. I have been contemplating something similar but wanted to relocate the hinge which is a real issue with the tube. If you move the pivot point aft then the trailing edge of the elevator is out past the horizontal stab. Wouldn't want to get into re-welding. Not one of my skills at the moment. Otherwise you are introducing a large open gap into the joint. You also going to modify the rudder? Thanks. Joe B

I was not willing to redesign the hinge points. I had someone recommend that, but I want to get into a flying airplane in my lifetime. I was not willing to go to that much trouble.

[Clark in AZ]

WOW! Thank you for taking the time to explain all of that. Very interesting! It all looks great and I can't wait to see it covered. I'm so interested because I just sent my deposit on a SuperSTOL kit today. Not the XL though. I was lazy and purchased their flying tail. I gave some consideration to doing something along the lines of what you are undertaking but thought better of it. I too want to fly it in my lifetime. Curious if you considered a flat bottom airfoil for more lift or were you more interested in speed?

Thanks again,
Clark

[AV8R Paul]

WOW! Thank you for taking the time to explain all of that. Very interesting! It all looks great and I can't wait to see it covered. I'm so interested because I just sent my deposit on a SuperSTOL kit today. Not the XL though. I was lazy and purchased their flying tail. I gave some consideration to doing something along the lines of what you are undertaking but thought better of it. I too want to fly it in my lifetime. Curious if you considered a flat bottom airfoil for more lift or were you more interested in speed?

Thanks again,
Clark

Clark, I am a retired engineer. I actually enjoy doing the design work. Changing from a flat tail to a airfoil shape will reduce the drag significantly. I have an old engineering video engineering wind tunnel test somewhere that shows a rod versus an airfoil shape, the drag of the rod was something like 9 times greater than that of a airfoil shape the same thickness. The SuperSTOL is a little nose heavy, and using a flat bottom airfoil shape to add lift to the tail may exacerbate the problem.

You might consider using a Edge Performance Rotax Engine, it produces 150 HP. It is a Rotax 912ULS, with a custom fuel injection, & a Turbo. BadAss Power Sports out of Canada is the North America Distributor, http://badasspowersports.com/badass-sho ... e-engines/. I would highly recommend going that route if you are planning to install a Rotax. The fuel injection gets rid of the Rotax Carbs, and balancing issues. I was actually planning on building a SuperSTOL, using one until I got a ride in Troy’s Titan 180 HP.

[kenryan]

Why not an inverted airfoil, like Zenith uses on their STOL designs?

[Clark in AZ]

Paul,

Yes, I too got a ride in Troy's beast but I couldn't justify loosing the extra weight of the motor and extended fuse right off the top of the useful load. I still want to be able to carry two with a lot of "stuff" and full fuel. I was also put off by the fuel burn on that Titan. I know you can fly it somewhat miserly but most won't, me being one of them. Troy told me how much it set him back flying off the 40 hours on that, it was a chunk of change.

So, I'm looking at several engine options, Rotax 915 (if they ever release it), Yamaha APEX (150hp, Steve Henry's completing work on this), or maybe the new Yamaha 998 turbo (180-200hp), if none of those work out, then the fall back would be a Rotax big bore 912is. So, at least 140hp one way or the other.

Thanks for posting the link to the other Rotax, that looks interesting too! Fuel injected and turbo'd, just what I want.

Keep the excellent posts coming!

[AV8R Paul]

Why not an inverted airfoil, like Zenith uses on their STOL designs?

In talking with Chris Wallen, he put on a symmetrical airfoil similar to the factory design, and he felt it performed as well.

[av8rps]

I am really enjoying this thread as Paul is obviously quite a builder and engineer. You're going to have a mega cool Super STOL when you are done. I can hardly wait to hear how it flies with your mods.

[AV8R Paul]

I am really enjoying this thread as Paul is obviously quite a builder and engineer. You're going to have a mega cool Super STOL when you are done. I can hardly wait to hear how it flies with your mods.

I’ve decided it’s now or never. I really like having my hand in the build process, and Chris Wallen has been great to work with so far. I’ll be glad when he gets done with his current project. I decided to go with the Garmin G5 versus two steam gauges, a little weight savings to counter my weight gain from the ribs. I hope I like the choice, it does everything and more than airspeed & altimiter. I know I will like the G3 touch screen with maps.

I guess I’m blowing part of my daughters inheritance.

[av8rps]

We all only go around once

[SheepdogRD]

I guess I’m blowing part of my daughters inheritance.

My attorney told me a long time ago the money doesn't become an inheritance until we die. Up 'til then, it's our money.

And I suspect your daughter would rather have an outrageous Dad who takes her for rides in his maxed-out SuperSTOL than a guy who invests quietly and builds nothing. Those memories will make her life richer than the cash.

[AV8R Paul]

I guess I’m blowing part of my daughters inheritance.

My attorney told me a long time ago the money doesn't become an inheritance until we die. Up 'til then, it's our money.

And I suspect your daughter would rather have an outrageous Dad who takes her for rides in his maxed-out SuperSTOL than a guy who invests quietly and builds nothing. Those memories will make her life richer than the cash.

Richard,
So true! It’s not quite maxed out, Chris Wallen has been checking my list of wants.
How is your project coming along?
Today I completed the elevator hinge Interface, and cut out the ribs for the Co-Pilots side.