V-tails are inherently unstable due to a reduced lift slope and I'm amazed that they've done as well as they have.
Consider a 45deg V. Put it on a stick at 0deg decalage. Put wing (no dihedral) at 0deg also. Now put stick at 10deg incidence.
Wing goes to 10deg incidence. Tail incidence (in plane of tail surface) is 7deg ( 10*cos45 ). This generates a lift vector approx 70% as large as a flat stab. This smaller vector is 45deg from vertical so the net result is generating lift at half the rate of the wing or a flat stab. Equivalent to giving up as it approaches stall and down in a dive. NG
This cosine squared effect works the other way also so wing dihedral results in longitudinal stability. Tip dihedral moreso due to cos sq. Tip plates on flat wing gain no stability.
More surprising than sucessful indoor models with V-tails are the UAV's made by name brand companies, which sometimes fall out of the sky and nobody understands why.
Off the soapbox,
H
To: Indoor_Construction_at_yahoogroups.com
From: engineer_at_anchorparachutes.com
Date: Tue, 6 Oct 2009 18:03:23 +0000
Subject: [Indoor_Construction] Use of V-Tail stabs
In the past, I have seen some minor use of V-tail Stabs, are there good reasons for this or are they no better than traditional arrangements.
_________________________________________________________________
Hotmail: Trusted email with powerful SPAM protection.
http://clk.atdmt.com/GBL/go/177141665/direct/01/
Received on Wed Oct 07 2009 - 01:05:39 CEST