SS horizontal stab/elevator on regular highlander

[danerazz]

Title says it all: anybody do this? Looking for more authority at low speed…feels like the tail is giving up.

SS has a larger area. Other option might be airfoil mod.

[Tralika]

Yes, you can order the "Flying Horizontal Stab" with your Highlander kit. I know someone who did it. If you are thinking of modifying your existing standard Horizontal Stab it might be tricky. I'm not sure if you could remove the standard stab and install the flying stab. The angle might be different. That would involve getting under the fabric to move the front attachment point. The folks at Just should be able to tell you.

[danerazz]

Is the SS stab attach different? It looks like it is a rectangular shape instead of the swept, then bigger elevator balance tips.

[Tralika]

Don't know. Just Aircraft would be the experts on that.

[BDA]

Call Chris Wallen.
Use the Symetrical horizontal that he is building, much more authority and less drag. See my thread here on the flying tail, mine is a little thicker than his for extreme slow flight, but same concept.
The reason these tails are giving up at slow speed is because they are built to provide down force to counter act the wing lift at speed. When you go really slow the wing is not making the lift that it is at speed and that downforce is not needed. What you need at that reversal is lift on the tail.
So with a symetrical airfoil horizontal, you have lift on the top when you need it.

[danerazz]

You have a nose down moment generated by the wing, the tail needs to pull down almost all the time during flight. I am running out of “down” tail authority. It is not a wing stall, but the tail quits pushing down at high angles of attack. This is helped by aft CG, but doesn’t really solve it.

The angle of the horizontal stab is so high that the air moving over the top delaminates and the elevator has no authority. An airfoil tail helps because it keeps the airflow attached longer and at lower airspeed, giving the tail more authority.

There isn’t a problem of the wing pitching moment decreasing. As you slow and increase angle of attack the downwash of the wing (especially with flaps) adds turbulence to the airflow over the tail. This hurts tail authority as well.

Adding some power increases the airflow over the tail, which helps too, but then the airspeed tries to come up and you climb, which is counterproductive.

All that being said, the airfoil tail would likely help; both by adding weight/aft CG and increasing the effectiveness of the tail.

[BDA]

Yes, the airfoil tail makes a HUGE difference with elevator authority. Partly because of the nose radius of the airfoil preventing a sharp angle change to airflow.

I also saw a gain in elevator authority when I put VG,s on the TOP of the horizontal stab, 1" back from leading edge (I know this goes counter to all accepted theory about how a tail works) - but it does work. This also adds pitching moment, so I have to be careful with the throttle when I have nothing in the baggage area - which is almost never. I can also carry more weight in the baggage area now.

When I flew flat tail superstols, before my build, I was not satisfied w the amount of tail authority and how early it gave up. So I added the airfoil and the VGs, now I have enough elevator, at any airspeed, to fully stall the wing. The original setup was safer for sure, because it was nearly impossible to stall the wing (slats), but you didn't have the ability to go as slow as the wing would allow.

Highlander is a different beast, I am sure the airfoil would help, don't know how much.

[marl59]

Danerazz, my last Yamaha powered Highlander had the flat tail. My current on has the symmetrical Airfoil Tail which Chris Wallen made up for me from a flat tail. Also, he provided strakes that mount to the end of the horiz stab between the elevator horn and the elevator horns. Here is how I would compare the two. Both had gap seals, both had VGs about 3.5" forward from the elevator hinges. They fly very differently. The flat tail would drop nicely at high angles of attack and I could add a little elevator authority with small amounts of power. I really got used to the way it landed and liked the tail drop/increased angle of attack at low speeds. I could touch down tail first with the stick in my gut and a little shot of power just before touchdown.

The airfoil tail keeps producing lift at lower air speeds. The tail drop is not nearly as pronounced with the airfoil tail. It keeps flying longer in the landings. So I'm still trying different things to get the tail down. So far, with about 20 flight hours, I haven't been able to get the tail to touch before the mains. But, I can land at slower ground speeds, (airspeed is not working any longer), and have more elevator authority at those slower speeds. I can't explain why all of this is but I believe when I get the right technique worked out that the plane will land slower. Currently, at altitude, I'm stalling at 32mph with full flaps. Not sure if this comparison helps. BTW- I'm loving my 160 HP Yamaha Apex power!

[danerazz]

BDA:

The behavior you describe (tail giving up before the wing stalls) is what I am seeing. It is tough to get a 3-point landing unless I carry just tiny bit of power and have an aft CG.

If I add too much power (not much at all) it will climb.

In stall testing, the wing never really gives up on power-off stalls. The nose comes down a little (but still not “nose-down”) and it just kind of slowly descends in a relatively level attitude. It is pretty clear that the tail quits working and causes this.

If I keep just a little bit of power on the stall breaks and you get a pronounced nose dip as one would normally expect.

I’d really like a little more elevator in the landing flare.

[marl59]

Danerazz, I'd say you would have more elevator authority in the landing flare with the airfoil tail.

[BucF16]

Hi Dane, For what it's worth, I have Chris' flying stab. I have not flown yet, so I have nothing to report. I sent my flat stab to him and he modified it. It came back powder coated.

I was to have my Apex Highlander flying by now having retired at AAL last summer..............But Flight Safety called and made me an offer that was too good to pass over. Check ride on the Cessna Longitude early May. Then back to work on the big green machine.

[danerazz]

Makes sense; you are right near KCMH. I was working at CAE at DFW for a year and a half. They offered us jobs, but I’ll stick with the one I’ve got for now.

[Biggles]

Hi All.
I’m in New Zealand and rebuilding our SSTOL after a crash.
Nearly finished but I want to include a faired horizontal stabiliser.
Too expensive to freight to US and back so will do the mod here.
Can somebody please send me the dimensions for the thickness
So I can determine the thickness/chord ratio and how far back from the leading edge is the thickest point.
Thanks and regards
Biggles

[BDA]

Biggles, send me a text on Messenger or Facebook and I will send you what I have. Mine is an XL that I fly at 2,100# gross, so I wanted more tail, my horizontal is thicker than what the Wallen or factory tail is - but it works pretty good!
I called Chris Wallen and had him send me his ribs w the airfoil in them - and welded them to my tail, I adjusted for a thicker airfoil tho.
There should be pics on my "Alaskan Superstol" Thread here.