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lsbrv7a(at)yahoo.com
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 Posted: Wed Mar 29, 2006 1:59 pm Post subject: Tip tanks and spins |
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It depends on the mission. My son the aero engineer made this comment.
Dad,
The writer of this article does have some valid things to say. I think it imprudent to say that even a little gas in the tip tanks could be fatal, given that no information about the airplanes stability coefficients or moments of inertia is provided. However, I do think that unless you have that data it would be unwise to take too big of a chance. There are other interesting advantages to putting more weight in the tips; one, roll stability (the aircrafts tendency to be upset by air perturbations) can be enhanced. Two, the weight in the tips could lower the stresses in the wing spar root (hence the airbus A340 hangs its engines way out on the wing).
There is a way to measure estimates for the spin stability coefficients but its not terribly easy.
Sherman Butler
RV-7a Empennage
Idaho Falls
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klwerner(at)comcast.net
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| Posted: Wed Mar 29, 2006 2:16 pm Post subject: Tip tanks and spins |
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That brings up another question that I have regarding Wing Spar Root stress (not necessarily in the RV-Series though):
Let me just say that in this scenario one would be able to switch between all tanks, ... not draining one into the other.
Would it be best to burn most fuel of the Mains before switching to the Tips?
Or would one first burn most of the Tips before going to the Mains?
Which way would be better in a fully switchable 4-Tank System?
Thanks,
do not archive
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Bob Barrow
Joined: 11 Jan 2006
Posts: 29
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| Posted: Wed Mar 29, 2006 4:06 pm Post subject: Tip tanks and spins |
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Jon Johanson reports that with standard Vans wing tips on his RV4 the plane
will recover from a spin by simply releasing all control inputs
(specifically rudder). With the tip tanks installed (and fully empty) the
aircraft requires positive spin recovery inputs to stop the spin (works
within 1/4 turn). So there is some information that is relevant. By adding
approx 6 lb of mass to each tip his RV went from requiring no spin recovery
inputs to requiring positive spin recovery inputs. It is still safe...but
different conditions apply.
This leads me to the conclusion that 6 lb of additional mass at the wing tip
of an RV can in fact make a real difference in terms of spin recovery
characteristics.
If just 1 gal of fuel remained in the tips that would increase the tip tank
mass by another 6 lb. Am I saying that would definitely, absolutely,
positively cause real spin recovery problems...no I am not. I'm just saying
that it *could*...and I don't intend going there to find out.
My goal will be to instal a tip tank system that ensures that I have zero
fuel in the tips when I do not require tip fuel for a mission (which will be
most of the time).
| Quote: |
It depends on the mission. My son the aero engineer made this comment.
Dad,
The writer of this article does have some valid things to say. I think
it imprudent to say that even a little gas in the tip tanks could be fatal,
given that no information about the airplanes stability coefficients or
moments of inertia is provided.
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