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FT 3D trimming for knife edge?

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Nick Farrow22/05/2017 10:07:16
157 forum posts
9 photos

Hi,

I having just got rid of a glitchy radio that sent my newly built Flitetest 3d ( https://www.youtube.com/watch?v=dIJUeQed7wk ) into the deck hard, twice that removed the wings. I'm trying to knife edge it. I built this to learn aeros/3D so I suspect I need some help!

My current efforts to knife edge (always wanted to do this!) are not good. Sometimes it goes from the horizontal('ish' i.e. rudder parallel to ground) into the vertical. I have this down to too much rudder and power, so pilot error?

The other trait, is that when KE it turns quite rapidly into a horizontal circle that flattens out. I thought this might be down to the elevator being 'up' slightly. As far as I can see the wings and stab are straight and level and line up with each other. Putting it into a steep dive shows it tracking straight as well neither pulling out or tucking in.It also flies straight and level so I'm not sure about the theory of the elevator being slightly 'up'.

Any suggestions for getting it trimmed correctly appreciated

Thanks

nick

Nigel R22/05/2017 10:51:56
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4082 forum posts
694 photos

A very Slight pull toward canopy or belly is quite normal. You can probably trim out most of that tendency.

Drifting up towards vertical is the pilot however!

Trimming fir good knife edge may require some c of g changes. There are some good guides in setting up models for this kind of aerobatic stuff. Triangulation trimming is the name I remember - try Google.

Delta Foxtrot22/05/2017 12:12:48
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566 forum posts
91 photos

Most of my models have required a small elevator to rudder mix for relaxed knife edge.

TIM Shaw22/05/2017 12:55:13
166 forum posts
41 photos

As above, but also be aware it is quite possible to apply too much ruder - try using as little as you can get away with to just hold level flight.

IF you still find it is pulling into a turn then you will need to compensate with elevator, and you might need some opposite aileron as well if its trying to roll with the rudder.

When you have worked out what the model is doing then you might be able to mix this compensation in - I have a scaled down Challenger which needs 10% up elevator slaved to left rudder, and 5% up elevator slaved to right rudder to stop it pulling towards the U/C for instance, but I would strongly advise you figure out what is going on before you reach for the mixes - its very easy to over - complicate things otherwise.

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