Superstol Flying Tail Pics

[CanadianSheepHunter]

I just weighed the flying tail including both horizontal Stabilizers and both elevators and the trim tab it weighs 19 lbs 2 oz.

[CanadianSheepHunter]

The original non flying tail including both horizontal stabilizers, both Elevators and trim tab is 17 lbs 3 oz...so the flying tail adds nearly 2 lbs ...adds 1 lb 15 oz

[dkshow]

Paul,

I love how clean the tail is on your airplane. Absolutely beautiful job. I hope I get to see yours up close in person someday. If I ever get to build another one I'll have lots of questions for you.

I have a flying Tail as well I used a NACA0008 airfoil, made wooden ribs, with a leading edge cuff from the leading edge all the way to the high point of the rib to eliminate 90% of the scalloping and to make a true airfoil shape. My airfoil goes from the leading edge of the Horizontal all of the way thru to the trailing edge of the elevator. I also have the Vertical Stabilizer and Rudder done.

[CanadianSheepHunter]

I just weighed the flying tail including both horizontal Stabilizers and both elevators and the trim tab it weighs 19 lbs 2 oz.

I forgot to add the Strakes/Fences which are 2 lbs 5 oz = 21 lbs 7 oz Total for the flying tail

[Clark in AZ]

Ok, silly question for all of you. I am covering my "flying tail" and was contacted by someone viewing my blog that stated I have my horizontal stabs upside down.

Here is a pic of what I consider my LEFT horizontal stab while covering.

20200314_145845 - 800x450.jpg

This shows the bottom covered and the top to be covered. The tall side of the ribs facing up? I was told that this is upside down. He said the tall side of the ribs should face down to force the tail down in flight.

Conversely, I was told that the purpose of the "flying tail" is to force the tail up to give a more level attitude in flight?

So, do I have the correct orientation?

Here is a pic showing the "top" covered...

20200315_185741 - 800x450.jpg

Thanks,
Clark

[danerazz]

You would have to contact Just Aircraft to confirm, but USUALLY an asymmetric airfoil tail looks like a wing upside down. On a conventional airplane (not a canard) the center of lift is behind the CG, and creates an upward moment on the tail. Your tail will ALWAYS need to produce “downward” lift, or there will be serious stability issues, including some frightening and possibly unrecoverable stall characteristics.

So, USUALLY an airfoil tail has the more cambered side down, so it produces downward lift and eases the burden from the elevator, if properly designed can alleviate trim changes with airspeed changes, and prevent or delay tail stall through improved airflow.

So, yes, your tail should LIKELY be “upside down” when installed, and I would be VERY surprised if it was not, and it is extremely important you verify this with the factory.

If there was an issue with needing to force the tail up, which I know has been discussed frequently about the SS, to me would point more to a wing angle of incidence issue or gross aft CG issue, than a “need positive lift on the tail” issue.

If you force the tail up to get a more level flight attitude, one of two things would be happening (or somewhere in between):

1) you lower the wing angle of attack (wing attached to fuselage; lower nose = lower wing AOA). The wing produces less lift and you descend.

2) you have a very heavy tail, and the POSITIVE LIFT of an “upright” airfoil tail produces lift thus reducing weight and thus the required lift from the wing, requiring a lower AOA.

The problem with #2 is it doesn’t work like that. In level flight, for a given wing at a given CG and a given airspeed, there will also be a given tail-lifting moment created by the wing. There needs to be a given amount of down-lift on the tail to keep the nose up. If you reduce this downward lift the nose drops. This is a good thing; it gives you positive stability and makes stall recoveries possible versus impossible. It is akin to aft CG.

So if you are in level flight and the nose is too high, you need to change the angle of the wing with respect to the fuselage (and the tail with it) or figure out if you have a gross CG issue.

[BDA]

Larger airfoil on the bottom gives more pitch authority at slow speed.

The small airfoil on the top does give you more level flight attitude at speed.

[Clark in AZ]

Great, thanks for the responses guys. I will call the factory in the morning and confirm.

Clark

[danerazz]

Larger airfoil on the bottom gives more pitch authority at slow speed.

The small airfoil on the top does give you more level flight attitude at speed.

If the wing produces the lift required for level flight at 7 degrees nose up, then unless you change the wing, airspeed, weight or CG it will fly level at 7 degrees nose up. If the tail raises the tail, you will descend. The airfoil keeps the flow attached and gives better authority, and with an inverted asymmetric airfoil producing downward lift the elevator will not be deflected as much and thus reduces the tail AOA so it can remain effective at lower air speeds.

I think any sense of a more level flight attitude is purely psychological.

[Clark in AZ]

Well, just for the record, Jak from the factory told me the large side of the flying tail ribs face downward. I did have mine backwards, thanks to Ken Kitzmann for pointing it out to me. Also, thanks to those that posted in response here.

Clark

[BDA]

I agree you cant just raise the tail
But
I can do level flight with nose angle at 20* nose up too, with more power to counteract the drag.

The planes with airfoil tail fly with tail higher than flat tail - flown side by side.

We have also seen flap gap seal bring the tail up.

Near as I can tell the center of lift for this wing is not far enough back and/ or the tail has too high angle of incidence (negative). Gap seal fixes center of lift, airfoil fixes incidence.

And dont forget - elevator creates camber which “gives” more lift to the opposite side of deflection.

Power for altitude
Pitch for speed.

[danerazz]

Right, but all those things affect the drag and efficiency of the surface which has an effect on moments and efficiency, interaction with prop wash, etc.

If the airfoil tail produces adequate downforce with less drag then the wing will need to produce less lift at a given speed, which would equate to a lower pitch.

I know you can do level flight at different pitches, but not at the same airspeed/flap configuration.

[BDA]

If the airfoil tail produces adequate downforce with less drag then the wing will need to produce less lift at a given speed, which would equate to a lower pitch.

Yes, this.

Its all about pitch drag

[CanadianSheepHunter]

Well, just for the record, Jak from the factory told me the large side of the flying tail ribs face downward. I did have mine backwards, thanks to Ken Kitzmann for pointing it out to me. Also, thanks to those that posted in response here.

Clark

Your very welcome Sir...we are all in this together !

[R Rinker]

For the sake of discussion I'll add some thoughts about a subject I know nothing about, then maybe someone who does know can explain it.

A 'flying tail' is a horizontal stabilizer that produces lift vertically, either up or down depending on which way it's mounted. I soled in a Cardinal, and it is a joy to fly with it's incredible responsive pitch control. If the 'flying' stabilizer is not moveable then the lifting force (either up or down) will be constant for any given configuration. When the Super Stol was designed and prototyped, the drag effect on pitch, of 29" tundra tires hanging at a large fulcrum position was not fully appreciated. Therefore to achieve level flight with a neural stick it was necessary to set the horizontal stabilizer at an angle that would produce a constant pressure pushing the tail down to counter the drag of the tires pulling the nose down. Ideally, this level flight pitch issue would have been satisfied by the incidence of the wing and overall basic design of the entire airplane. Added to this, the Super Stol is a short coupled design. The overall length of the fuselage places the tail surface closer to the wing giving it less of a fulcrum than if it was farther back, thus making it less effective and requiring greater pressures to achieve necessary force. The 'flying tail' is one way to achieve these forces instead of increasing the angle of the stabilizer. To produce a downward pull to counter the drag of the tires the airfoil must be placed upside down.
Another design of a so called flying tail is a simple aerodynamic curve on the stabilizer, top & bottom to reduce drag and not produce any lift in either direction. Any corrections or additions............??

In spins and high angles of attack, the wing and tail can block off the airflow over the other tail surfaces making them unresponsive. Designers have often found that the only part of the vertical stabilizer that has any effect in a spin, is that part which extends 'below' the horizontal stabilizer. Thus they have sometimes had to redesign a rudder to extend below the horizontal stabilizer, for the sole purpose of spin recovery to pass certification. In the Super Stol, that part of the rudder has been trimmed off so it won't contact the ground if the tail wheel gets torn off in landing. Early builds only used one bolt to attach the tailwheel to the stinger...now the standard is two high strength bolts because tail wheels were coming off.