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down thrust angel - 4/25/2012 3:10 PM   
jeffk464


 

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Status: offline 		What thrust angle is best for an aerobatic plane assuming zero incidence on wing and tail.

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RE: down thrust angel - 4/25/2012 3:25 PM   
LesUyeda



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Status: offline 		Zero incidence, and go fly. Adjust depending on the flight characteristics of the particular plane.

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RE: down thrust angel - 4/25/2012 3:43 PM   
All Day Dan


 

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RE: down thrust angel - 4/25/2012 5:30 PM   
tschuy


 

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Status: offline 		Thats if you have a fully symmetrical rib.  Then zero degrees is correct.



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RE: down thrust angel - 4/25/2012 7:40 PM   
rlipsett


 

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Status: offline 		flat bottom wings require more down thrust

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RE: down thrust angel - 4/26/2012 4:31 AM   
jeffk464


 

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RE: down thrust angel - 4/26/2012 9:55 PM   
BMatthews



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Status: offline 		It also depends on the CG location. Make it "stable" by moving the CG forward and you end up using up trim to compensate. And with the up trim the wing to tail isn't at 0-0 anymore and you find you need some downthrust. But if you set the CG back so the model is nearly or fully neutral for pitch stability then you'll find you need little or no downthrust.

If it's your intention to set it up that sensitive then by all means to for 0-0-0 for engine-wing-tail. If you find you need a slight shimming later then it's easy enough to add a sliver or two.

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RE: down thrust angel - 5/2/2012 5:47 PM   
David Bathe



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Status: offline 		Guys, without wanting to sound seriously  .
Lets talk about setting up an average, low wing aerobat.
There is no such thing as a 0-0-0 set up... apart from on the bench.
The moment to test fly your 0-0-0 model you'll have to add up elevator trim... thus lowering the stab
That's because a symetrical airfoil needs a positive incidence to generate lift (to fly), not much but it there, say about 0.5deg.
Thus you dial in the up trim (lower the stab) on your imaginative 0-0-0 model to give the aerofoil the desired incidence and what do you end up with?
Posítive engine, wing and stab incidence! NOT 0-0-0

There'll be those out there that say... "Mines 0-0-0 i don't add up evevator"
That'll be because you've got a rearward CG... thus the tail wieght is lowering the stab enabling the wing to establish a positive incidence.
The results are the same, positive incidence on all... not 0-0-0.

Thus the standard bench set-up is:
Leaving aside right thrust (2.5-3.5 deg depending on engine/prop)

Engine: 0.5 negative (to counter the positive wing)
Wing: 0.5 positive (so it'll fly)
Stab: Zero.
 
Try it... it's a far more pure set-up than the imaginary 0-0-0. AKA +-+-+.
 


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RE: down thrust angel - 5/6/2012 8:01 PM   
kiwi4


 

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Just because you added trim to get a positive incidance ,the plane is still 0-0-0. Zero in relation to the plane it self is relitive at all angles.The addition of trim doesnot negate the true angle of its parent surface,the plane remains at 0-0-0. The plane being zero in flight attitude to the oncoming air is a differant subject.Kiwi4

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RE: down thrust angel - 5/9/2012 1:33 PM   
David Bathe



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Status: offline 		Indeed you are correct.
I was of course refering to the latter sinario.
Thanks for setting that straight.


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RE: down thrust angel - 5/9/2012 5:42 PM   
ARUP


 

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Status: offline 		The Cassutt in my Gallery is 0-0-0 with symmetrical airfoil. Thrust wing and stab on same datum line. It has a little right thrust for 'P' factor. Great flying model and tiny tailfeathers very effective because c.g. is at the rearmost limits.

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