Vertical tail airfoil for pusher

[Protech Racing]

I think that you have a tolerance stack. IE the soft tail, the smallish swept rudder, the P factor , etc.
Stiffen up the tail , add some P factor offset and maybe a trim tab . IMHO

 

[Protech Racing]

Maybe the carbon guys can aadvise about wrapping your tube.
also points of interest might be stuffing another round or square tube inside with the help of an oven and large freezer.
You also might experiment with moving the tube anchor to the side to reduce p factor after you are sure that the thrust line offset is not creating a vector bounce off of the vertical.
Other options : gurney flap the rudder.
A small tip plate will also increase the rudder power.

 

[Victor Bravo]

Eugene, I agree with others here, the FIRST thing you have to do is isolate where the issue is coming from. You need to know for a fact whether your tailboom is flexing... or twisting. Once you know that this is or is not the problem, then and only then can you design a plan to rectify the problem.

 

[berridos]

I would experiment with the engine mount incidence and not take the 1,5º as definitve.

 

[Victor Bravo]

A Go-Pro type camera pointing toward the tail, a piece of aluminum with a 1/4" hole in it, and four zip-ties will provide some very useful information on the very first flight.

 

[Vigilant1]

It would be useful to see how closely the needed rudder input matches the power level. Compare needed rudder at, say, 80 knots under these conditions:
1) Climb and full power
2) Level flight and, say, 50 percent power.
3) Slight descent with idle power.

Maybe the yaw is due, at least in part,, to some type of rigging problem. The closer that the yaw is tied to power setting, the better the case for fixing it with a thrust line adjustment (so the "remedy" is at least somewhat proportional to the "disease," both will vary with power level).

 

[Protech Racing]

You could set the right wing down a half degree

 

[berridos]

Maybe the high rudder deflection required bends/torsions the fin and tailarm, sort of a feedback loop.
attach a laser pen to the fin that points somewhere you can see the point migrate when deflecting rudder. Some cardboard attached in the nose.

 

[TLAR]

I would experiment with the engine mount incidence and not take the 1,5º as definitve.

The very first thing I would do, verify

 

[Eugene]

Thanks guys for all your input. Unfortunately no experiments possible anymore. I did enough of playing around for years. My airplane is ready for surgery. Part that painted in blue will be amputated pretty soon.


Will try to build composite tail. Old tail was for sure not a good match for this airplane. It was bouncing around in flight and it was driving me crazy. 120 mm tube is simply not stiff enough for this job.

I was hoping that there is straightforward procedure to deal with P factor for pusher airplanes in LSA world. But sounds like if it's sized up correctly and is stiff enough then may be a little bit of trim tab deflection will do it. So, nothing is ever straightforward in experimental aviation. That's OK, I did it to myself.

On standard Skyboy with 100 hp engine during landing if you decided to go around and apply full power at the relatively low speed = airplane will depart to the left at 45° angle and will not listen to the right pedal until building up more speed.

https://drive.google.com/file/d/0B9ZeEB_79LEPUFZNbmdoOWNVVDA/view?usp=sharing

 

[Eugene]

You can see from this video that tail is moving in near perfect no wind condition.

Loading…

drive.google.com

IMG_4087.MOV

drive.google.com

 

[Victor Bravo]

May I suggest removing more than just what is painted blue? IMHO look into a carbon tube replacement for the tailboom. You can pick one that is far stiffer (more wall thickness), or you can pick one that is a larger diameter, and get the extra stiffness that way.

As you design the flying surfaces, build in the ability to adjust the mounting angles by using shims, or lead screws, or tabs with different holes in them, etc.

 

[Eugene]

May I suggest removing more than just what is painted blue?

Airframe on Skyboy build around this tube forming strong structure. I don't have any problems with it. Only with tail


New carbon tail will connect to this airframe as "plug-and-play" at 4 points as I show on pictures below.



At least 2 aeronautical engineers telling me that it is very possible to do. Not very cheap and not very fast, but it is very possible. And this is direction I will be going. Vertical stabilizer will be part of new tail boom. And that is why I was wondering if I should build 1° or 2° angle into it.

 

[BBerson]

Make it adjustable with a stack of washers or something.

 

[Eugene]

Make it adjustable with a stack of washers or something.

Not sure how built as one unit with one mold composite tail boom/vertical fin combination can be made adjustable.

 

[Protech Racing]

Not sure how built as one unit with one mold composite tail boom/vertical fin combination can be made adjustable.

Make the entire boom adjustable.

 

[Eugene]

Make the entire boom adjustable.

Wow! I don't think this will be my option. New tail boom will slide somehow over old leftover 120 mm tube to make tight fit. I'm not sure how it's gonna look like, but assuming there will be no play at all. There shouldn't be any play or possibility for any adjustments.



When it's all said and done my airplane hopefully will look similar to this one. Maybe I should find out if they have built-in fin angle on Seamax and copy?

 

[BBerson]

. And that is why I was wondering if I should build 1° or 2° angle into it.

The vertical tail angle could be determined with a flight test on the Skyboy first. Pull the boom over to the right 2° with a cable and a turnbuckle.

 

[Vigilant1]

Just to mention it: That counter-rotating prop thingamajig that henryk frequently brings up might address some of the issues being experienced.
Henryk, where are you?

 

[henryk]

Just to mention it: That counter-rotating prop thingamajig that henryk frequently brings up might address some of the issues being experienced.
Henryk, where are you?

-I am alive,
CR propellers too...

=circa 30 % more thrust,
=NO giroscopic effects,

IMG_6622.mp4

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=focused,linear flow,

Dym - zwolnione tempo.mp4

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=reactione momentum equal to the motor momentum...