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Peter Jenkins19/07/2019 23:42:11
1281 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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2947 forum posts
1083 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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2947 forum posts
1083 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
1281 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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2947 forum posts
1083 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
1281 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
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2947 forum posts
1083 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
1281 forum posts
132 photos

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

Martin McIntosh29/08/2019 16:18:36
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2947 forum posts
1083 photos

The 155 is now fitted but suffered from vibration on the test runs/flight which was traced to the motor fixing screws which have now been changed to M4`s as in the old Spit. The cg was readjusted back to as per plan and test flown today. I added a few clicks of down trim (not even noticeable on the ground) and it now flies much more happily for some reason. Maybe there was simply too much power for this lighter airframe before. Had to curtail it due to severe changes in the motor mixture but I think I have traced this to a small split in the filter line. Will try again when the wind is next down the strip.

Peter Jenkins30/08/2019 00:15:47
1281 forum posts
132 photos

How very curious Martin. Could this be due to gyroscopic force from the presumably larger and heavier prop on the 180?

Peter

Martin McIntosh30/08/2019 08:51:10
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2947 forum posts
1083 photos

Nope, its not the prop Peter. Both engines like an 18x8, in this case a G-Sonic composite. I have also used wooden ones on both model versions.

Peter Jenkins30/08/2019 08:53:42
1281 forum posts
132 photos

Curiouser and curiouser Martin. However, you seem to have overcome the original problem so all's well. Be nice to know why though!

Martin McIntosh12/09/2019 20:10:44
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2947 forum posts
1083 photos

Fixed the fuel line problem and took it up again a couple of days ago. No motor troubles and no vices; flies just like the other one. Must simply have been over powered for the much lighter airframe. Thanks for your inputs. It will be at the RCM&E fly-in at the weekend.

Peter Jenkins12/09/2019 20:36:21
1281 forum posts
132 photos

Well done Martin. Interesting that over powering was what you think caused the problem.

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