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Trimming YAK-54 don't know where to go

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Old 12-19-2007, 09:30 AM
  #1
niche
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Default Trimming YAK-54 don't know where to go

Hello
I have a YAK 54 scratchbuilt from original real scale drawings and few fine tunes
The Stab and the engine have both 1° negative , downtrust, wing incidence is zero.

The plane is a around 63" Span, pretty much for 0.60 engine and it holds a Moki 1.35 swinging APC 17x6 (I fly at almost 10.000 ft, very thin air)
The issue I am having is that the plane flies straight with almost halfway of trim down at half throttle, when I give full power the plane just starts going up almost 45° steep (regardless the elevator trim down I add)

I tried to see whether was the engine trust, at straight level I cut the engine and the planes remains straight, I was wondering it could be balance (it's slightly tail heavy) but when approaching for landing the plane just goes smooth (no nose up tendency).

On vertical dive, the plane goes slightly up tendency.
As you see I have reach the point where don't know where to go, I don't know if because is kind of overpowered with the moki I have to add uptrust altough as I mentioned before it doesn't look like an engine trust issue.

Any help or hint will be more than welcome
Regards
Omar
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Old 12-20-2007, 01:33 PM
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Default RE: Trimming YAK-54 don't know where to go

These references discuss many aspects of trim and have checklists

http://www.flyrc.com/articles/03-16-...airplane.shtml
http://www.modelaircraft.org/Mag/FTG...31/31main.html
http://www.nsrca.org/trimA.htm
http://www.palosrc.com/instructors/trim-chrt.htm
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Old 12-20-2007, 02:19 PM
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Default RE: Trimming YAK-54 don't know where to go

My first impression is its tail heavy. What does it do when you roll inverted and let go? Does it dive, need no elevator or climb? If either no elevator or it climbs, its tailheavy for sure.
What does it do when you pull vertical at full power and let go?

I'm not clear on the engine thrusr. You mentioned 1 deg down thrust but latrer said you have up thrust.
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Old 12-20-2007, 03:38 PM
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Default RE: Trimming YAK-54 don't know where to go

Mike
Sorry Iwas not clear
I meant that the engine has one degree downtrust.
About tendency when inverted (after half roll) it trends to go nose down, I have to add significat down to keep it level
I don't recall what it does when in vertical climb and let go at full power I'll try next flight.
I had a trimming chart in my field bow and it says that to know whether it has some problem with the wing incidence I had to make it flight knife edge and see nose (up or down) trend, in my case with 65% of rudder it seemed to be straight, don't if I am mistaking there
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