Return of the Taliban Warthog

[Tom Harper]

This design is intended to provide a cheap sturdy platform for AP. Although termed Taliban Warthog by Vintage I prefer to call it 'Look Down' because it resembles a Florida game fish called Look Down Pompano (yum).

The idea here is to build a very sturdy airplane from foam board. Extremely short coupling is used to avoid the cost and fragility of long tail booms. Also the short coupling places the fuselage shell mostly forward of the wing where it can be utilized for payload. This design is a successor to a series of deltas. The problem with the deltas was low aspect ratio. This one has about a 7:1 aspect ratio. The wing is a NACA 6409 section from a Strucks New Ruler. It's mission is to fly a stable straight line for photography.

So far it does what is required of it. The rudder has a real challenge controlling that long wing. I went from aileron control (too much adverse yaw) to a large rudder only. The twin fins were cut down and a center rudder added. That worked but the rudder could still be larger (maybe next week).

Today we had a landing in the creosote that proved the model to be as rugged as hoped. It caught the bush in the lower left of the photo and spun around in the dirt. You can see that flights and mods have removed the eyeball decals. I'll put them back when testing is over.

The big wheels were added to help on rough fields and operation in the mud. They really work.

The problem now is engine run. The K&B .28 really rips on a Zinger 9X4 pusher but it won't stay running in the air. I assume the tank is too low so I will bring it out on top of the wing.

For those who may be interested, here are some pics:

[Sparky Paul]

Tom, on my AP pusher, the tank is directly ahead of the motor.. no fuel draw problems at all. It idles well, and runs forever on a 2oz tank... (OS 15 FP)
That's a GP Spirit Elite wing.

[Tom Harper]

Sparkster,

I can't figure it out. I have bought new fuel 5% and 15% nitro. I've raised the tank once. I've changed carbs. Changed glow plugs numerous times. Tried lean and rich mixtures. Sometimes it runs 30 or 40 seconds. Never more.

AAaaaarrrrgh!

Any wisdom?

[Sparky Paul]

Tom..
It sounds like there's dirt in the needle valve.
Clean out the entire fuel system.
Blow it clean from the engine side towards the tank, after pulling the needle.
Flush the tank, and replace all the tubing, if the tank is old or reused.
On my K&Bs I've sealed the carb to the crankcase with goopy, they're susceptible to airleaks there.

[Tom Harper]

Sparky,

Thanks. I think I'll replace the tank. I'll clean everything and will seal the carb joint. That's definitely a possible leak point.

I'll let you know how it works out.

[Sparky Paul]

The pinch bolt that holds the carb in place, goopy that too.
I've found it worthwhile on all the .20s and .28s I have.

[Tom Harper]

Sparky,

OK everything gets goopied.

BTW: I added three degrees of down thrust to the engine and it made a difference. The take off run is faster and it rotates and leaves the ground better.

[Tom Harper]

Sparky,

I cleaned the needle assembly and all the carb, parts. There was some galling between the carb barrel and the crankcase so I smoothed it out. Assembled everything with a thin coat of RTV. Raised the tank up so the center of the tank is level with the spray bar and the lines are clear of all bulkheads and obstacles. The engine now runs fine. It sags once in a while but I think we are down to running and adjustment.

Flew out an entire tank ~15 minutes. The wind was gusting from 5-10 mph. We were able to trim the model for hands off flying. Requires center on elevator and some left trim on rudder. To me that means the angle between the stab and wing is just right and that there is a lateral weight, alignment or warp problem.

The design has one very odd characteristic. It makes left turns very well. Nice and flat. When you turn right, however, it cranks the left wing way up, sticks it's nose in the air and eventually slurs around the turn. This action is not subtle. It does not like to turn right. I think there is a wing 'warp' but that is not enough to cause this. You can make a reasonable right turn by using down elevator.

I think the problem is gyroscopic precession from the prop. The long span damps out lateral precession when controlling pitch. But when you try to turn, it is felt as pitch up in a right turn and pitch down in left because of the short coupling. I'll check the wing for warps but I think there is more to it.

Is it worth it? So far I think so. The model is rugged. It came in dead stick today, stalled on a gust and went nose first into the creosote short of the field (pic below). You can see that it dug a hole in the sand (now under the fuse) then just bounced back and sat in the bushes. Landings like this with the Telemaster rent it assunder.

You can also see the amount of left trim in the rudder.

[vintage1]

Try each turn direction in the glide. That will tell you whether its asymmetric structure wise, rather than power wise.

I would expect that design to need significant side thrust...there isn't much to straighten out the propwash behind the prop at all...so its going to show a right roll tendency. You can see that from the left trim required.

Wihout ailerons and with not hugely massive dihedral I would expect it to be reluctant to turn against the torque.

You also have a LOT of fuselage side area forward, which is going to want to lift the nose in a bank.


Angling the rudder hinge line foward may help - giving a bit of 'down' elevator as it is applied.

[Sparky Paul]

Tom, I had an interesting occurence with the pusher twin I'd made from two planes, yesterday.
The wing is a plain dihedralled 88" span 2410 airfoil, the fuselage/tail is from the OS 15 pusher twin, which used the Spirit Elite wing.
The combination, with two GWS 300-D's with GWS 11x8 props wasn't anywhere near as "sprightly" as with the OS 15.. and it exhibited an alarming amount of vee-tail twist, something I'd never seen with the single pusher motor. And mostly to the right. I could see the vee twist on the boom, and the plane would pitch down.. and was reluctant turn right at all.
The vee apparently wasn't in the prop blast with the single motor, but both tips were directly behind the two.
I'm debating whether to proceed with it, or make a new fuselage with a different thickness CF boom, and possibly move the boom from the bottom to the top of the fuselage.
Or just go back to the centermounted glow motor and leave the vee low-mounted.
I ran my "Old Reliable" Gentle Lady into a Spanish bayonet yesterday, splitting the fuselage lengthwise, so that needs replacement.
And my C6D tractor twin-boomer got done in thoroughly by low-level turbulence this morning.. Time to cut wood again.. :(

[Tom Harper]

Vintage and Sparky,

Thanks for the comments. The forward area is an influence as I'll explain below. Also it turns well against torque and poorly with torque.

Made some measurements and found out some stuff!

The left wing panel is approx 1/2 degree positive referenced to the right (from rear of plane). It is not a warp - just that the last time I glued in a plywood dihedral brace I got the left panel an eentsy-beentsy bit positive. I doubt that I could do better if I cut out the brace and started again. This wing is forty years old and has been repaired many times so it is a bit bumpy when it comes to 1/2 degree alignments. I can average it out with the old heat gun.

That is not enough to account for the rudder trim. Sooooo I got to thinking (last resort) and ya know without any moment arm to speak of the only reference on the airplane is a spanwise line down the center of the wing. So I measured the cant of the wing. It was aligned with a square former in the fuselage. Turns out the left wing tip is leading by 2.25 inches and the right wing tip is trailing by 2.25 inches. Not too noticable in a 74" wing but it explains the yaw trim. The rudder had to hold the wing at right angles to the airstream.

That explains part of the turn problem. It liked to turn left but you had to force into a right turn. Thats because all of that area forward of the wing was cranked over to the left and you had to get it past center before the turn actually started.

So I filled and redrilled the wing mount holes and the wing is now straight. (of course the fuselage bulkhead looks crooked).

I think this will cure some ills but I am still leery of precession.

It will be windy for the next couple of days. Might get out Thursday.

Sparky,

Were the props counter roating? Did the booms twist with control or just propwash?

I really like my OS 15. What prop are you using? I've got Zinger 8x4 and 8x5.

[Sparky Paul]

Tom, the props turn the same direction on the pusher. counter clockwise when viewed from the front.
I'n using a Zinger 8x4 pusher on the OS 15..

[Tom Harper]

Last week was a disaster so I took a close look at everything. Turns out the model was a text book of misalignment. Some was creeping modification and repair and some just bad workmanship. I ripped it all apart and started over. Replaced the stab and rudder and opened and reglued the rear of the fuse. The short moment arm makes the usual alignment techniques worthless. So I got out a large mylar grid that my spouse has for quilting and used the lines as a reference.

The large cargo area in front of the wing was empty so I cut it down.

The results were great. The thing handles like an LT-40 and floats like a free flight. The short moment gives no problems at all.

The only problem was camera interference with the RC. It worked fine until the battery was about half discharged. Then every time the camera clicked (3 seconds) the model flipped on its back. It got progressively worse until the plane just spun into the ground from about fifty feet up. You can see in the third picture that the nose dug a hole in the ground but there was no damage at all.

Added a second battery pack for the camera, shielded the cable from the controller to the camera and moved the antenna. The problem is cured.

So, we had a great day. Got flights, got pictures and brought the airplane home in one piece.

[Sparky Paul]

Tom, The winds around here recently have been a problem... low level turbulence when launching near ground obstacles.. large Juniper bushes.. have had a couple of planes doing manuvers they just aren't intended to perform. And it can suck climb out of a plane.
But your camera controlled airplane is certainly one of the odder occurences.. :)
I'm looking to shave about 11 oz of ugly fat off my pod-planes, by going brushless and Li-po.. A mere $250 upgrade.. Yuck!
If I could drive to where I fly from sometimes, I'd take the glow planes, but walking a mile both ways carrying that extra stuff... too old for that.
And I prefer to be quiet.

[Tom Harper]

Sparky,

Yeah, it's wind season here too. Usually we can get in under it in the early morning. I think you have it worse than we do. It is windy outside now - about 25 mph and gusty. I hope to get in an hour of flying tomorrow, we'll see.

I cruise by the electrics counter when I am up in the big city, but I just can't do it yet. Too many bucks and a new thing to learn.

[vintage1]

Glad you got it all sorted.

Ive giot a similar problem in a model right now. Flies with full left trim in a straight line, glides staright with power off with full left trim

Wings are warped a bit to make it TURN LEFT AS WELL - where is all the right coming from?

ONLY time all that go left bias shows up is when I try and loop it - it does a left hand barrel roll!

I've got a fair bit of right thrust on it which I will pull out, but that should NOT affect the glide. Maybe the prop drag is turning it right as well

Oh well one step at a time. De warp the wings with the covering iron and pull the right thrust out and try again...

[Tom Harper]

Vintage,

Good luck with the iron!

[Tom Harper]

The K&B .28 Sportster was struggling to keep this thing in the air so I got a Norvel .25 - wow what a nice little power plant.

Had a good day at the field with solid take offs and good reliable runs for photography. But all of the previous crashes, repairs and mods took their toll. On the last approach the stab lifted and the plane did a very nice outside loop into the ground. The scheming airplane figured out a way to break the pusher prop - It came in up side down!

Anyway I think this is the end of the Taliban Warthog:

[vintage1]

Oh dear.

Still easy enough to build a new BETTER one.

I got my warps sorted and found a delightful little plane on my hands after all.