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Old 03-09-2004 | 12:25 PM
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Tony_M
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From: Feltham, UNITED KINGDOM
Default RE: Request For Comments

Looks good.

I think most aeronautical eng' students have, at some point in their career, come to the conclusion that a V/stab and rudder distributed evenly above and below the fuselage will produce a 'clean' yaw control with no adverse roll or pitch effects. The only problem with having so much fin below the fus' is that you cannot lower the tail at take off, which prevents the wing from creating enough AoA and therefore lift to leave the ground (unless you have a very long runway or big flaps. Apart from this little teaser, the principle is solid.

Similar to this, the aerodynamic advantages of having a v-tail with the fins angle down (inverted v-tail) are that a yaw command does not have an adverse roll effect, but actually compliments roll. The US's UAV (Predator?) uses the inverted v-tail, but you can see that tailplane clearance at TO and landing is very marginal only allowing an inch or two clearance during rotation and flare. This could be solved by using a twin boom fus'.

Because the moment arm is so small, I think you can 'raise' the whole V/stab without creating too many adverse effects. With todays programmable transmitters, its hardly an issue anymore since we can just remove unwanted effects by mixing in a compensating control coupling.

The final observation is that when you stick a propeller on the front and wash the fuselage with rotating air, you'll still get adverse roll/pitch effects at various speeds as the v/stab will be in various positions within this tube of rotating air depending on AoA, rudder deflection and fuselage shape.