Gap seals and airfoil shapes for tail surfaces

[haribole]

Would someone have pictures of gap seals for the tail surfaces?

Trying to make wood strips for the horiz and vert stabs, Papa Foxtrot mentioned this:

"If the stab rib is X in length, then then max thickness is .09X at .3X. Then use the bottom of the airfoil template as the "french curve" to draw the airfoil."

I understand the first part, but don't quite get the second part about using the bottom of the airfoil template.... would some one have drawings for these wood strips for a 4 place? It seems Avipro has the pieces for sale and Mark suggested I call Bob, but if someone has already made these, don't want to bother Bob.

Thanks
Hari

[jaredyates]

I just had the good fortune of visiting Pat to see his airplane recently. I didn't take any pictures, but it looked like his wooden strips only provided shape to the horizonatal stabilizer, not the elevator. So at the hinge line, his new horizontal stabilizer was the same thickness as it was before the wood strips. In this sense it differs from the profiled tail of the Patrol and LSA, where there is an airfoil shape that spans the chord of both the elevator and the horizontal stabilizer, at least as I understand it, not having built an LSA or Patrol.

[John Rheney]

The leading edge of the elevators are a larger diameter than the trailing edge, so the taper is already build into the elevators. At least that's the way mine are built. If this is true of all 4 place BH then the profile of the elevators is built in already.

[John Rheney]

Hari: I'm using data from here:

http://airfoiltools.com/plotter/index?airfoil=naca0006-il

to scale the profiles for the stabilizers. I don't think the lower airfoil profile for the 4-place BH is what we are looking for.

[Battson]

There was a thread on this topic a little while back, you can probably find it with a search. I posted these photos:







You don't need to use wooden formers on the elevator surfaces.


Personally I find the elevator quite touchy at high speed, I would not want increased effectiveness, just for my 2c. They are big elevators.
That said - I suggest the Pitts or Piper Pacer gap seals would work well.

[RatherBFlying]

Battson, how did you secure these nut plates? I can't find your original write up. Did you find some extra long rivets, or do they just swell and wedge themselves within the wood?

[Battson]

I used epoxy glue and rivets, I just let them swell and hold into the wood. It worked well and 10 years later they are all going strong, not issues whatsoever.

[alaskabearhawk]

As far as numbers so, we had quite a discussion about stab airfoil shapes off-group (the good ol’ days) a few years back. I borrowed the templates and rib form blocks from Pat Fagan and used those as patterns for new blocks. The measurements were a little different for my stab, so I made all new blocks. I did measure the templates and the thickest part is right around a third back from the front. If the rib was 18 inches long, the thickest part would be 6 inches back. The ratio was about 12 to 1 (+ -) for thickness. For every 12 inches in length, it’s 1 inch wide at about a third back. The 18.5 inch rib was 1.5 inches wide at 6 inches from the tip. Likewise for a 26 inch long rib. It was 2.3125 inches wide (2 5/16ths) at about 8.5 inches from the tip.

Bob said any symmetrical airfoil with the widest point at 30% of the chord would work. After doing a bit of research, I found out that all 4-series NACA airfoils are at their widest at 30% and the NACA series from 0006 to 0012 have been used for exactly that…the horizontal stab on many designs. I eyeballed a plot of the NACA 0006, 0009, 0010 and 0012 airfoils against the small, grainy pictures of the Patrol ribs on the parts section of the Bearhawk Store site. Out of all those, the 0006 looked the closest.

https://www.youtube.com/watch?v=rUyTOwfnQiI&list=UUJZsfzVIbZt78P78Uks8q-A

Gap seal optiohs: http://www.wingsandwheels.com/page28.htm

[haribole]

Thanks everyone.

Thanks Battson, for your 2c I am absolute newbie to flying and have no clue about what I am getting into. What you say makes sense to me. Initially when I read about better control authority with the airfoil shaped stabilizers, I thought this would be a good thing to have, now it does look like I would be better off without these. However the gap seals would improve performance, so will stick to those and perhaps visit the airfoil shaping later when I have some experience flying with the vanilla bearhawk.

thanks Alaskabearhawk, the wingsandwheels looks like a great site for the gap seals.

[alaskabearhawk]

The profiled horizontal stab doesn't affect the action of the elevators...or at least shouldn't. Two different animals. Just about all aircraft save a few of the small ones we fly have an airfoil shape. The idea is you can reduce the negative incidence from a neg 4 to a neg 2 and reduce drag. Bob said the 4 place files fine without it. But based on his design and handling of the Patrol, if he were to do it again he would design it with a profiled horizontal and vertical stab. FWIW, I know Pat Fagan likes his.

[Battson]

I have mine set at negative 3 degrees and you would not want to be any closer to zero.

Agree with your other comments, the aerofoil shape is about increasing the aerodynamic efficiency of the tail, but this has the effect of making the elevators more effective too as I understand it. Calculation suggests the stabiliser will be something like 25% more effective for an aerofoil compared to a "flat plate". This sounds empirically correct, because I found a 25% reduction in angle of attach of the stabiliser to be best.

[Papa Foxtrot]

I just had the good fortune of visiting Pat to see his airplane recently. I didn't take any pictures, but it looked like his wooden strips only provided shape to the horizonatal stabilizer, not the elevator. So at the hinge line, his new horizontal stabilizer was the same thickness as it was before the wood strips. In this sense it differs from the profiled tail of the Patrol and LSA, where there is an airfoil shape that spans the chord of both the elevator and the horizontal stabilizer, at least as I understand it, not having built an LSA or Patrol.

Actually, the elevator and rudder ribs on both the Patrol and LSA(I have plans for both) are straight bends like the 4 place. Only the horiz. and vert. stabs. are an airfoil profile.

[alaskabearhawk]

The variation seen is a size difference of tubing diameter between the elevator/rudder spar and trailing edge, making it look like it has an airfoil shape.

[Papa Foxtrot]

Bob said any symmetrical airfoil with the widest point at 30% of the chord would work. After doing a bit of research, I found out that all 4-series NACA airfoils are at their widest at 30% and the NACA series from 0006 to 0012 have been used for exactly that…the horizontal stab on many designs. I eyeballed a plot of the NACA 0006, 0009, 0010 and 0012 airfoils against the small, grainy pictures of the Patrol ribs on the parts section of the Bearhawk Store site. Out of all those, the 0006 looked the closest.

Interesting. I want to start with the horiz. tail to work on my welding skills before beginning the wing. I've got Compufoil and Profili - I'll have to play with the NACA 0006 to see if I can put together some patterns.