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Old Dec 03, 2012, 07:41 AM
KK4QIN
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United States, GA, Cornelia
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Best thing to do: don't do anything yet, power the plane up, the take pictures of everything and post here
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Old Dec 03, 2012, 02:18 PM
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Nose diving Bixler

Attached are photos, thanks for looking.

Motor is a Suppo 2200Kv 2212/6, prop 6x5.5, 30 amp esc

I added the camera this morning before seeing this email. It was placed for checking the field of view, will fly without it next time.
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Last edited by uavrat; Dec 16, 2012 at 09:33 PM.
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Old Dec 03, 2012, 02:32 PM
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Why is the motor mounted so high? you are still using a 6" prop. That extra height give added leverage to make the plane dive. Also the thrust line won't be where it was designed to be. I believe it should be through the CoG, that is the CoG in all directions.

Also did you free up the hinges? There could be some stiffness there.
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Old Dec 03, 2012, 02:37 PM
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Motor Mount: good question. Yes, props is 6x5.5 with the 2200kv motor.

I am planning to install a lower Kv/Larger prop combo. Someone told me: "the height would not matter, only the angle. And as long as I stayed on the same angle as the original design I should be OK". Maybe not, huh?

Hinges all freed up.
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Old Dec 03, 2012, 02:39 PM
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But I forgot to mention, even with the power-off glide tests with CG set to either 60 or 70 mm from leading edge I still got the nose-in effect. That is how I worked out moving the CG back further and further, so that I could glide it by hand, and bring it in smoothly with the controls, dead stick.
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Old Dec 03, 2012, 05:58 PM
KK4QIN
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United States, GA, Cornelia
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It looks like your elevator has a bit of down in it.. The motor angle shouldn't matter a whole lot. Check your control services for slop. Try to move them around some with your hands.

Also, are you setting this up for FPV?
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Old Dec 03, 2012, 08:06 PM
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Could the angle of the camera on that plywood at the front be creating nose down? And it does look like there is some down elevator.

On the prop height, I think of it like pushing something, a box for example, along the ground. If you put your hand at the base of the box and push, it slides along the ground easily. As you move your hand higher up the box to push, it will start to fall over at a certain point instead of sliding. Applying this logic to the height of the prop, as it goes higher, it moves further away from the cg in all directions as Mac50L pointed out and "falls over" or noses down.
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Old Dec 04, 2012, 09:35 AM
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Thanks for responding.

I will check the elevator today, and slop in the surfaces, if I can get out at lunch.

Camera - yes I am setting up for FPV, but I have not flown this with the camera. I just installed it yesterday morning, before I saw of this feedback/request for photos. I'll pull it off for the next test flights. On another aircraft I have with a nose camera that piece of plywood actually puts a bit of nose-up into the aircraft. But each aircraft is a bit different, not sure how it would react on this one.

I think another good point is that launching with 25 to 40% throttle is enough. Other birds I have were better at 70%, but not this one! That is a point worth noting.
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Old Dec 04, 2012, 09:43 AM
KK4QIN
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United States, GA, Cornelia
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Quote:
Originally Posted by uavrat View Post
Thanks for responding.

I will check the elevator today, and slop in the surfaces, if I can get out at lunch.

Camera - yes I am setting up for FPV, but I have not flown this with the camera. I just installed it yesterday morning, before I saw of this feedback/request for photos. I'll pull it off for the next test flights. On another aircraft I have with a nose camera that piece of plywood actually puts a bit of nose-up into the aircraft. But each aircraft is a bit different, not sure how it would react on this one.

I think another good point is that launching with 25 to 40% throttle is enough. Other birds I have were better at 70%, but not this one! That is a point worth noting.
No problem. When you do that, check back with us.

Also what is your flying experience? You might want to hold off on FPV if you are just getting into the hobby.
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Old Dec 04, 2012, 10:36 AM
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I'm not all that experienced, but I've been flying since last spring, and FPV on a couple of fixed-wing trainers since this past summer. Usually a Gamma 370 with front camera, 5.8Ghz. Simple, functional, easy to fix....
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Old Dec 04, 2012, 01:50 PM
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OK, was able to take two flights today at lunch.

Elevator: set to neutral when controls at center. Same for ailerons. There is some wiggle in the elevator itself. It is aileron-taped in place.

Again i tried moving that CG forward a bit from 90mm, with a glide test it still noses in with a hard turn to the left.

CG set same around 90mm. Launch about the same, 40% throttle, a not too hard toss and it glides down (but not nosing in) and then I increase power slowly and it starts to climb.

Once I get it all up and flying around at a comfortable altitude, to make it trim I have to slow the throttle down to about 40% and trim the elevator down quite a bit. There it flies level. If I leave the elevator at neutral it wants to nose up all the time, and I am constantly on the down-elevator stick.

Power up above 50% throttle and she starts nosing down. If I use 50+% power then I really have to keep the elevator up to make it stay neutral or climb. Which feels very wrong.

It floats amazingly well, but is just hinky launching and then trimming out.
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Old Dec 04, 2012, 02:02 PM
Just Me
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It's the height of that motor that's causing you most of the problems with the pitch down on throttle up. It's like a lever...the longer it is the more torque is being applied to the CG. You might have some other fine tuning yet to do but that motor either has to come down to the original height or the thrust angle has to be adjusted.
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Old Dec 04, 2012, 02:07 PM
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That is the conclusion I am coming to as well. I wanted to run a slow motor/big prop, long flight and a few others are doing that. But it might be that this plane is not the one to go that route.

I should just install the original motor at the original height. Get a baseline function test, then decide. Back to the man cave to reconfigure.....
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Old Dec 04, 2012, 04:28 PM
Just Me
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With the correct adjustment on thrust angle you should be able to have the motor at the height
you have it and use the larger prop.
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Old Dec 04, 2012, 09:05 PM
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I agree with the others that the motor height is the main problem. With the standard thrust angle the greater the distance from the lateral axis the more downward force will be applied because of the increased torque resulting in pitch. That is why this increases under power, the torque offsets your trim adjustments as power increases. As Brner indicates, there are two solutions. Move the motor to the original position or decrease the thrust angle, that is tilt the motor slightly back, That will reduce the downward component of the force. Of course it will take trial and error to find the sweet spot.
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