Twin Boom Pusher Plane - neutrally unstable? - Page 3 - RC Groups
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Nov 15, 2012, 12:24 PM
Graham Dyer
pardus's Avatar
Originally Posted by kcaldwel
If changing the motor thrust line affected the power-off dive test results, it must have been out of trim in glide before the dive test. The dive test is only meaningful at all if the airplane is in trim near best L/D speed for a hands-off glide.

A better test for CG position is inverted flight. The amount of down elevator required inverted for level flight at the same speed as upright is a good indication of the stability margin - less down elevator, lower stability margin.

Thrust issues are easy to confuse with pitch trim and stability. The pattern guys have systematic trimming routines in a particular order to sort out which is which.

Yes I believe it was, having tried to get the pitch-up-on-power corrected, it seemingly was still trimmed nose down for the dive test which exacerbated the effect. Giving some up thrust I think has effectively given a bit of up force to the HS when adding power so negating a bit of the pitch up.

Anyway thanks for all the advice and info, hope this can also help someone else with a similar issue.
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Nov 15, 2012, 04:11 PM
Registered User
Good suggestions, guys. Thanks!

I'll let you know what I choose...
Nov 16, 2012, 12:12 PM
Registered User
"Thrust issues are easy to confuse with pitch trim and stability. The pattern guys have systematic trimming routines in a particular order to sort out which is which."

So what do you work on first? Pitch first, then thrust?

Jim R.
Nov 17, 2012, 08:13 AM
Registered User
richard hanson's Avatar
Just use the logical approach

once you get it in the air , trim the flying surfaces for an easy to fly trim.
the speed for this stage of trim should be a nice easy to fly cruise speed .
Once you get this sorted out - try lower power and higher power
If you see big differences in climb or dive as power changes- - First see if cg is reasonably close to correct - make gradual cg changes - finally- play with the thrust setups .
The old pattern trim charts are a decent starting point but getting sensitivity .
Here is the good part - with more experience in trimming -it all gets easier -
If you just chase the plane around - -it never gets easier
It is a learning curve - I have taken "trimmed" models which are difficult to land,etc., and by going thru the very basics, retrimmed the model for good manners.
You can't do the trimming on paper - you have to fly it to do it.
beleive it or not - once you "get it", you will find you can figure out the trim of someone elses model - by just watching them fly it.
Last edited by richard hanson; Nov 18, 2012 at 08:11 AM.
Jan 12, 2013, 04:32 AM
Registered User
Originally Posted by pardus
Looks familiar

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