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Peter Jenkins19/07/2019 23:42:11
1217 forum posts
132 photos

Be interesting to hear how you get on with the incidence check Martin.

Martin McIntosh20/07/2019 18:12:48
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2875 forum posts
1062 photos

Checked them both with a Great Planes laser meter, not entirely accurate but a good enough guide.

Wing incidence. Old, 1.8 deg., new, 2.6. Error may be due to friction in the laser bearings.

Down thrust, (difficult to measure because of the weight of the meter), old, 1.5 to 2.0, new, 1.5. All readings w.r.t. the tail.

So no real difference anywhere here. Must be down to the cg.

Now attempting to do the motor swap. I can fit the 155 in the Spit by using a tapped alloy plate behind the mount but the Stampe will be rather more difficult.

Martin McIntosh20/07/2019 18:25:35
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2875 forum posts
1062 photos

P.S.,

Whilst using the laser meter today I noticed that the elevator had developed a lot of play. On investigation I found that the servo arm was not seated properly and was a bit loose. Changed it and problem solved. This, however, would not cause the trouble I am having. (I think!).

Peter Jenkins20/07/2019 22:56:21
1217 forum posts
132 photos

0.8 deg on wing incidence is quite a lot Martin. I would consider reducing that and see if that helps.

Martin McIntosh20/07/2019 23:52:27
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2875 forum posts
1062 photos

Hi Peter,

Measuring with a straight edge rather than the laser, the incidence is most likely accurate to the plan. I cannot really see me having been that far out here.

Peter Jenkins21/07/2019 09:17:22
1217 forum posts
132 photos

Well Martin, I am still more inclined to a thrust line issue than CG issue. By the way, does operating the u/c cause any significant CG change?

Martin McIntosh21/07/2019 21:46:21
avatar
2875 forum posts
1062 photos

Hi Peter,

On this one I have used super light wheels which are unlikely to alter the cg measurably.

It is now definitely not the thrust line. The wing incidence should be as per plan. As I said, the laser is not that precise, indeed a click or two on the elevator trim could alter this reading considerably but it is a good guide.

Currently trying to modify a split mount to get the 155 in. Not easy.

Peter Jenkins21/07/2019 21:49:40
1217 forum posts
132 photos

Good luck Martin. Be interesting to hear how things pan out. Another learning opportunity.

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