Happy-flier
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Posts: 286
Joined: Sat Dec 25, 1999 4:41 pm

Trying To Understand V-tail Theory

Wed Nov 10, 2004 1:40 pm

For the longest time I have had the desire to understand the physics behind the V-tail design. I like this tail design for the simple reason that it seems to be one of the best configurations for a hypothetical roof-mounted, single-engine jet- (or ducted-fan-) powered version of something like a Lake amphibian. (I'm not designing one, but it never hurts to dream a little ...  Big grin). The other ideal tail type for such an aircraft would probably be an ordinary horizontal stabilizer possessing two vertical stabilizers at the end of each stabilizer - kind of like a Connie tail, but obviously without the central fin.

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And, so, here are some of my questions:

  • How do you perform lateral maneuvres in a V-tail aircraft when the tail assembly must also function to control pitch?

  • How do you correct for a crosswind during takeoff?

  • How do sideslips get done in a V-tail aircraft?


  • Just some basic ones to get going. Many thanks in advance.
    May the wind be always at your back . . . except during takeoff & landing.
     
    cancidas
    Posts: 3985
    Joined: Thu Jul 03, 2003 7:34 am

    RE: Trying To Understand V-tail Theory

    Wed Nov 10, 2004 3:49 pm

    while i never flew a v-tail aircraft this was once explained to me by a half-drunk pilot out at the airport. according to him, control inputs were the same as they are on an aircraft with conventional control surfaces. the mechanism for those ruddervarots actually handles any differences. i didn't exactly believe him then. wonder if i should at all, anyone have a better explanation?
    "...cannot the kingdom of salvation take me home."
     
    QantasA332
    Posts: 1473
    Joined: Sat Dec 13, 2003 5:47 pm

    RE: Trying To Understand V-tail Theory

    Wed Nov 10, 2004 5:35 pm

    As far as yaw/pitch control goes, v-tail arrangments require a complex control mixer which the pilot of such an aircraft may be able to explain to you better than I can. I assume such a mixer is just some sort of automatically balanced input-deflection balancer which produces the desired movement.

    V-tails are quite prone to dutch roll problems (due to their large effective dihedral), and they impose greater loads on the tail section of aircraft than do normal tail designs. However, V-tails provide good spin-recovery characteristics and produce slightly less drag than conventional tails (through a reduction in interference drag, not parasite drag - after all, the same total surface area is needed to maintain the same stability and control forces).

    Cheers,
    QantasA332
     
    LeanOfPeak
    Posts: 496
    Joined: Thu Oct 21, 2004 2:18 am

    RE: Trying To Understand V-tail Theory

    Thu Nov 11, 2004 1:32 am

    Everyone so far is right.

    To give you an impression of how messy the control mixing is...

    Both ruddervators deflect up or down to control pitch (So that the horizontal components fight each other and cancel out and a pure pitching moment is obtained).

    For yaw, one ruddervator deflects up and the other deflects down (So that the vertical components fight each other and cancel out and a pure yawing moment is obtained).

    And for a given input of yoke position and rudder pedal position, there is a specific configuration of those two control surfaces that matches it.
     
    PPGMD
    Posts: 2398
    Joined: Sun Sep 30, 2001 5:39 am

    RE: Trying To Understand V-tail Theory

    Thu Nov 11, 2004 2:20 am

    Cancidas,

    You got a better explanation than I did when I first asked how it worked. The MX guy's answer was PFM.

    LeanOfPeak,

    That's exactly how I have seen how the they work in flight. Now there is an issue, the V-tail models have less overall rudder authority than the conventional tail models. Which can be an issue when you are landing at airports with a single runway, sometimes you simple run out of enough rudder to line yourself up.

    The V-tails are fun to fly, but there advantages are few, you get at most a couple of knots over the convention tail, smaller engine bonanzas, and they have a knack of flying off in flight (I kid on that one, but there was an issue, that required the issuing of an AD). It is kind of fun flying them, but in the end it's not much different than any other doctor killer, it just looks cool with the V-tail.
    At worst, you screw up and die.
     
    wingscrubber
    Posts: 806
    Joined: Fri Sep 07, 2001 1:38 am

    RE: Trying To Understand V-tail Theory

    Sat Nov 13, 2004 5:55 am

    I had this explained to me on my aircraft maintenance course at college by a guy who'd worked on bonanzas, leanofpeak is exactly right but you must consider that in terms of the control mixing, the pitch/elevator function of the flight surfaces has priority over the rudder function. I was told that this is achieved through a sprung link in the rudder control, so if pitch and yaw inputs are made at the same time the pitch input can overcome that of the yaw on whichever flight surface is required to move. I did a really cool diagram of how it all works...if I had it I'd scan it in and show you but no idea where it is heh.  Smile/happy/getting dizzy

    -Pete
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