Asymmetrical UAV/AP - Page 12 - RC Groups
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Apr 30, 2012, 05:02 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar


Removed the thrust offset.

Cleaned up the rudder hinge.

Rebuilt the elevator - rounded LE for center line hinge

Working on aluminum can motor cowl

Aileron will take a while

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May 01, 2012, 05:11 PM
Registered User
UnDetekted's Avatar
Originally Posted by Tom Harper
1) Oscillation - It is critically damped in a right turn but oscillates in a left turn. Well, duh! All of that left thrust increases system gain to the left and critically damps to the right.

2) Power - So, why the power increase? Speed, weight and altitude are constant so lift must be constant. In a left turn the single left side aileron decreases lift on that wing panel. Two things must happen in response: the autopilot must increase angle of attack to maintain lift and it must correct for adverse yaw. That results in a significant drag increase and a compensating increase in power. More power = more system gain resulting in oscillation.

3) Cure - Remove the left thrust - Add a right side aileron - Increase rudder area.

Recall that our best flights were our first few flights with no left thrust (actually, I think there was some right thrust?). As such, I'd say your conclusions are valid. However, I doubt we need more rudder area as it has not showed any lack of effectiveness.

May 01, 2012, 05:37 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar

The Left Turn Problem


I watched the video this morning and had the same thought. It seemed to handle the left turns fine.

May 01, 2012, 06:23 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar


I've been using tape for so long that I had to search for hinges. I salvaged these from a box of stuff.

Don't like to glop up hinges with CA or epoxy, also have had binding problems with 3 point hinges. So, I pinned them with toothpicks - no glop. That gives them some float so they are self aligning.

Oct 12, 2012, 06:16 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar

Patina of maturity

Asym now carries the patina of experience. It's had a couple bad crashes. Nothing design related - equipment and crew.

I added the right aileron and have spent a lot of time on the electronics. I believe everything is cleaned up. We shall see this weekend.

One of the project criteria was ease of field assembly. The Asym has fallen short in that regard. It takes two people 15 or twenty minytes to assemble this thing. That takes time and can lead to errors.

So, I did some measurements and found that the model will travel on the package cover of the Land Rover. That, and some autopilot packaging changes, removes over half of the assembly time.

Should be back in the air by Sunday.

Oct 14, 2012, 12:58 PM
Lift is cheap - Drag sucks
Tom Harper's Avatar

A bit windy

Nice day but a bit of a gusting wind. Hand launch was uneventful.

This was the first flight after the addition of the right aileron. CG and lateral balance look good. Needs a calmer day to get the trim adjusted.

Still having Autopilot problems, will work on them this week.

Brought it home in one piece, so it was a successful day!

Oct 14, 2012, 10:11 PM
Registered User
HELModels's Avatar
It sure looks unique in flight, like it was built with a purpose in mind.

Oct 15, 2012, 04:24 AM
Registered User
Looks very sleek for sure. But those low set tail and wing seem made to catch in any possible clump of grass or bush even in the smoothest landing. I understand that it will spoil the aerodynamics a bit, but wouldn't it be better off with a few wire skids under the nose and wings?
Oct 15, 2012, 09:00 AM
Lift is cheap - Drag sucks
Tom Harper's Avatar
Thanks guys,

It has 1/4" square spruce longerons on the bottom of the fuselage and pod. So far they have been sufficient.

I am concerned about field operations. This thing is big. We have been using a county road for landing - narrow with lots of sand (photo). Be interesting to see how it does.


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