Can someone guide me how to set the thrust angle and wing incidence for this type of rc airplane.On test flight i encountered some problems. The plane lifted fine after the takeoff roll as soon as it was some ten feet in the air i eased back on upelevator and it nosed down immediately , i managed to recover it though.At full throttle it tends to nose down and at half throttle it flies like its a bit tail heavy the tail wings are a bit lower than the horizontal line .My motor shaft is pointing upwards (looking from behind the aircraft) the wings and tail are almost at level .If i shim the leading edge of the wing a few mm and add some weight upfront will it do the trick.

You can't really solve this by altering the wing' geometry, though some engine upthrust may ameliorate the tendency.

The reason that you can't solve this is that it is not a "problem" ... it's merely a trait of that airframe layout. That is, it's perfectly normal. Some full-sized aircraft, with high-mounted engines, behave in the same way. They pitch down with power.




So, you can try some engine upthrust ... try 5 degrees or so.

You can mix in some elevator trim with throttle, such that increased power coincides with a little "up" trim.

You can just get used to re-trimming for each power setting.

Try building a small hand lunch model of your design and get to fly strait with a gentle glide slope. Tweak the moments, CG and incidences until you get good flight characteristics with it then put those on your full size powered model. Now you know that any bad habits are power related. Now you can play with thrust vectors until you find a good compromise.

Where is the engine on that thing anyway? Looks to be high mounted on the front of the wing.

I'm right there with ya though. I'm converting a Bird of Time to a pylon wing with a rear mounted motor off the back of the wing like the Thermal Charger.

I think your on the right track to increase the wing incidence doing so one mm at a time. If it was very sensitive on elevator, then moving the CG forward slightly will reduce that. That you were able to recover and land the plane, seems however to indicate that the CG was not grossly aft.

Engine up thrust is a rare thing. Down thrust is common on asymmetrical foils to counter the increasing lift as more power is applied. Given that your plane is increasingly trimming down with more power, it seems almost certain that it has negative wing incidence.

If your thrust line is well above the center of drag, any increase in power will pitch the plane down. This can be somewhat corrected by upthrust but often excessive upthrust is required to over come the pitching moment, especially if the motor is near or centered over the CG. Changing relative setting between wing and stab angles will not do it. If the plane handles nice with power off, leave those settings as they are.

Illl try to offset the motor thrust a bit more .Will double check the incidence aswell as the tendency to pitch down just after takeoff is quite alarming.Im trying to upload a small clip


http://www.youtube.com/watch?v=fyOpTSgwZsM

Your video clip looked like it was flying quite well. I did not note any serious dive at any time. If there is, it should not take much change in the thrust angle to correct it.

I heard a power increase just before it dove. If it was approaching at low power, it was trimmed up too much to produce a good low power glide slope. That fits with your description that at half power, it seemed tail heavy.

That leads me to believe it may not have been in good low power trim, therefore I stick with a position that an incidence problem may exist.

The first effort should be to check the balance. Then trim the plane for a proper low power glide slope. After which, take note of the elevator trim. If it is trimmed up, then in very small increments adjust the wing incidence up and if trimmed down, adjust the incidence down... but I'm betting it (elevator) is currently trimmed up. If so, then adjust the incidence up in small amounts till the elevator and stab are neutral with each other and a good low power glide slope exist.

Once the low power glide slope is good with a fairly neutral elevator/stab relationship, then it is time to correct high power pitch trim with thrust changes.

In most cases of asymmetrical wings, down thrust is needed to counter increasing lift of the wing at higher speeds but as Rodney pointed out, if the engine is high up, there is a couple between it and drag center that can affect the pitch and therefore the motor thrust setting. That thrust line will be a balance between pitch down of the engine drag couple and lift generated by the asymmetrical wing so it is anyone's guess to what thrust angle is needed.