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HobbiStar 60 MK III wants to CLIMB

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Old 09-27-2018, 08:02 AM
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Jack_K
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Default HobbiStar 60 MK III wants to CLIMB

I have a Hobbistar 60 MK III that a friend gave me. He crashed it and didn't have time to repair it. The wing was perfect, just some torn covering. No problem to fix that.

The fuselage was not bad. It had a small break on one side that looked like something had punched it. I was able to straighten that and added a 1/16" piece of plywood about 2" x 3" on the inside surface of that side. Epoxied it.

The vertical fin was broken off. I added 3 dowels, make from chop sticks, into the fin and into the fuselage and glued with 30 minute epoxy. A small amount of Monokote on the fuselage side, new motor mount, servos, OS 61FX, and 12x6 prop. It looked almost new. CG was right on at 3", per the manual.

When I flew it, it took off like a race plane! That 61FX is a powerhouse. It wanted to climb, and climb it did. I ended up with full down trim on my DX9 and it flew almost level. During the flight the muffler flew off (had been repaired with JB Weld), so I landed it.

Looking at the elevators now, I see they are at 10 degrees down.

When I repaired it nothing was changed in the wing saddle, wing incidence, tail incidence, or firewall. It's a different kind of motor mount, but a brand new one mounted flush on the firewall.

Any ideas why it wants to climb like that?
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Old 09-27-2018, 10:12 AM
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r ward
 
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I recently noticed that two different brands of new motor mounts that I have , have different angles between mounting surface(firewall) and engine beams. one is square with the firewall and one has a slight upward or downward draft to the beams. so one could theoretically mount an engine with up or down thrust, depending on which way he oriented the mount on the firewall.
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Old 09-30-2018, 02:08 AM
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jetmech05
 
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when you throttle down does the tendency to climb stop? If so itís a thrust angle issue.
Bear in mind flat bottom wings do climb under power. But if itís very noticeable it could be the thrust angle
so does the airplane not want to flair or slow down on approach? Could be the CG.
Is the airplane sensitive in pitch? The more you fly the worse it is? LOok at CG.
let us know what you find
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Old 09-30-2018, 06:59 AM
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Jack_K
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Originally Posted by jetmech05 View Post
when you throttle down does the tendency to climb stop? If so itís a thrust angle issue.
Bear in mind flat bottom wings do climb under power. But if itís very noticeable it could be the thrust angle
so does the airplane not want to flair or slow down on approach? Could be the CG.
Is the airplane sensitive in pitch? The more you fly the worse it is? LOok at CG.
let us know what you find
As I said, the CG is at 3". That's what the manual says. I added a 1/16" thick washer behind each upper engine mounting bolt. Been too rainy to fly since then.
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Old 10-09-2018, 04:50 AM
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r ward
 
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a little down thrust, as you did, might be all it needs. at this point,.... it's a "try it and see" process,...know the different ways to affect that tendency, is just as important as knowing how to eliminate it.. as said a flat bottom wing will climb when giving some power. you might try just a bit of negative incidence on the main wing, or a tiny bit of positive incidence on the horizontal stab and live with the tendency to climb on throttle. although you shoot for level flight on throttle,...it's not absolutely necessary,.... as long as you know it's there.
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