tIANci

I just got a sketch built plane and I am having some problems with my maiden flight and last few flights. After getting the plane in trim I will fly it at half throttle, it holds properly. When I power up to full it pulls hard UP and RIGHT. I would then be fighting to trim it out again. What might be the cause ... engine thrust issues? The engine is mounted at 45 degrees, 10 o'clock. Thanks.

FHHuber

From the way we normally reference things... 45 deg would be a HUGE offset and so would the "10 oclock"..... Its hard to imagine seeing these angles actually used anywhere. (well... maybe he's got it ROTATED 45 from vertical...)

We may be referencing from different prespectives... or its one rather wild design... or it will be WAY out and its kind of amazing that it would be controllable at all... (if the prop doesn't hit the wing AND the landing gear...) if its that far out.

I have GOT to see a picture of this one.[:-]

combatpigg

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HI FHHUBER! I think he means the engine is rotated on the plane radially, so the muffler clears the wing, or something like that. It sounds like the engine could use some down thrust . The pulling to the right could be a speed related problem caused by a crooked plane.

Montague

I'm guessing that when you say the engine is mounted at 45 degrees, you mean the cylinder is rotated 45 degrees, so the engine isn't upright or on it's side? At least that's what I'm hoping you mean. If that is the case then I can say that the way the engine is mounted, rotation wise, is not important.

What is important is where the crankshaft is pointing in relation to the rest of the airplane. You'll want to aim the engine's crankshaft "down" (in relation to the airframe) a few degress.

The right turning could also be engine thrust, but I'm guessing it's something else. Try adding some downthrust and see how it flys. And check the alignment of the wing and stab as well.

BMatthews

The model trim and balance along with the wing and stabilizer surfaces and engine thrustline angles all come together. And then there are misalignments and warps to consider. Without going over the whole airplane and checking EVERYTHING it's impossible to say what the problem is.

I'd start with a very complete measurement of the model to confirm wing and tail surface alignment angles to within one degree and do the same with the engine. Check for any warps in the wing and control surface misalignments as well.

In an otherwise properly aligned model with 2 or 3 degrees of downthrust already in place I would say that your balance point is too far forward. This results in requireing more angle between the wing and tail. When that angle is quite large it emphasises the sensitivity to power to make the model climb. In THAT case moving the balance point back a little and re-trimming the elevator to compensate will reduce the model's sensitivity to climb strongly under power.

But it's in your own best intrest to carefully check the model over first. It's bad enough with a kit or ARF but with a scratch built model who knows what angles were built into it.

tIANci

Hahahahaa ... HUber its not an OSPREY! Its 45 degrees radially. Anyways, the plane was built true and I think its the engine thrust. I added in a washer to get some down and left thrust. Thanks for the feedback guys ... anyways here are some pics of the plane.

FHHuber

The engine cylinder orientation is going to have virtually no effect on the model performance. so there's usually no need to mention it when discussing a thrust line problem.

You had me wondering "how the heck coulsd someone come up with that thrustline?" when I first saw it.. 45 deg (assumed)down and 10 o-clock (viewed from above...) would be about 60 deg left. (lets spin sideways and dive like heck[X(]) I knew I was misunderstanding it somehow.

a088008

Firstly, what are your trim settings when you are flying at full throttle? This will tell you what you are fighting against. So, you need to adjust the thrustline to produce the same forces, but in reverse, at the front of the plane.

It is clear from the pictures that you have way too much left and up (as far as the thrustline goes). Center the thrustline with the center line of the fuselage and then add 3 degrees DOWN. Fly it and see how it behaves.
I think you will still find the model rolling to the right a bit. That is due to the prop wash on that huge flat fuselage. You can then add 3 degrees LEFT thrust and see what happens.

tIANci

Apreciate the info! Thanks a lot!!! BTW the plane is trimmed on full power ... then when I go back to half throttle it is like 'out of trim' and I re-trim it, hence when I go back to full throttle the problem starts over again ... I will fix the thrust first.

LouW

From BMatthews reply:

In almost every case, an airplane that pitches up sharply with addition of power is nose heavy. It's hard to tell from the pictures, but it appears that the wing is set at a positive incidence angle. If that is the case, when balanced properly, it will require down elevator to trim at most any speed. The normal setup for that type of aircraft is zero incidence for both wing and tail.

BMatthews

Lou, I think that's just the pic. Looking at the wing tip former and tail they appear to be 0-0.

Ian, you're onto the correct path now. Trim the controls for flight at low throttle and then adjust the thrust to hold the same trim at high throttle.

If you NEED upthrust when it's all said and done, as you do appear to have in the pic, then I would suggest that your balance point is way too far back in your efforts to get 3D performance. Trim the model to fly level at just above idle. Then dive it at a 45 and let the controls go to nuetral and watch the model. If it tries to tuck you're balanced too far back (behind the neutral point actually), if it dives at the same angle you're spot on and if it pulls up back to level then you're a trifle positively stable. For 3D aero stuff you want to be trimmed to the middle option, dead neutral.

Once trimmed to that neutral point if you still find that you need upthrust on the engine (WRT the wing's chord line) then I would suggest that the model is not as truly built as you think. No model of this type planform and airfoil should require up thrust is it isn't out of whack somewhere.