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Thread: V-Tail Roll Moment

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    Registered User Tom Nalevanko's Avatar
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    V-Tail Roll Moment

    I was wondering/wandering and thinking about V-Tails. It seems to me that the standard type V-Tail a la Bonanza must also produce a roll moment as well when producing a yaw force. Am I correct on this? If so, is it significant such that it is felt in the Bonanza? Are the V sections somehow differentially offset to minimize the roll?

    Going further, could one produce roll, up and side forces with a V-Tail in a controlled manner with a different type of mixer such that one could minimize one of these parameters and maximize the others, for all combinations? Or, of course, combine them all?

    Thanks for any insight, discussion or anecdotes on this subject.

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    Rom
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    Re: V-Tail Roll Moment

    It seems as though adverse roll would be produced in a turn, requiring more aileron input.

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    Moderator Dana's Avatar
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    Re: V-Tail Roll Moment

    Even a single rudder produces a roll force opposite to the direction of yaw (unless the rudder is below the aircraft centerline). Because the rudder (or in the case of the Bonnanza, ruddervators) span is small compared to wingspan, the effect is small. I've never heard of it being an issue.

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    Re: V-Tail Roll Moment

    I don't think roll moment is a big issue (for the reasons Dana stated), but I've always disliked that elevator input results in bending moments that try to pry the two surfaces apart or squeeze them together. Add to that the fact that you cannot have a carry-through spar and it's no wonder that some Bonanzas (Bonanzai?) require reinforcement in the tail section. I also dislike the idea of efficiency loss during elevator use or trim because you generate two opposing forces that cancel each other out and only generate extra drag (due to cancelled forces and interference - the squeezing of the air between the two surfaces). Don't forget the added weight and complexity of a control-mixing system.

    V-tails look neat, but I like conventional tailsurfaces. Conventional surfaces have dedicated functions that they each do well, whereas a v-tail has mixed functions and does each function with mediocrity.

    Just my opinion...
    Bruce

    By the way... some of the newer military jets use elevator surfaces for roll control (or roll augmentation).
    Last edited by bmcj; May 6th, 2008 at 01:27 PM.

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    Re: V-Tail Roll Moment

    Powers and Bashforth were going to use a V tail on their plane, man what a linkage setup.

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    Registered User Tom Nalevanko's Avatar
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    Re: V-Tail Roll Moment

    Thanks for everyone's contribution. While I used the Bonanza V-Tail as an example, I'm thinking of a different use. I basically want to have an empennage-like set of control surfaces that give me X and Y forces and a moment. The moment should ideally always be one way but X and Y go both ways. And, unlike the Bonanza case, I want to have an input for the roll. And thus the problem of mixing all this together...

    I was hoping some erudite person could say 3 inputs ; 3 outputs. Should be able to be done. Or impossible without a 3rd surface....

    Blue skies as they are here in CMA,

    Tom

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    Registered User Tom Nalevanko's Avatar
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    Re: V-Tail Roll Moment

    Greg,
    I am not familiar with Powers and Bosworth; can you point me to a link or equivalent?
    Thanks,
    Tom

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    Super Moderator orion's Avatar
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    Re: V-Tail Roll Moment

    Harry Powers and Bruce Bashforth were behind the first production ultralight, the B1-RD. Later they developed the push/pull MiniMaster, sort of a scale Cessna 337. But the downturn in the ultralight business some years back came about the same time as they were finishing the MiniMaster and without the necessary backing, they were not able to put the MiniMaster into production, which essentially forced them out of the airplane business. The MiniMaster was about two or three years ahead of its time.

    I knew them quite well but I don't recall them ever taking about a "V" tail for anything. Might have been something early on.

    Regarding the Bonanza tail, the reinforcement that was necessary was on the leading edge - turns out that pulling out of a steep dive created a tremendous amount of low pressure on the leading edge of the tail surfaces, sufficient so that it caused the root rib to fail, which in turn was followed by skin to buckling, which in turn caused the leading edge to wrap itself around the main spar. The fix was relatively easy in that they simply pinned the root rib near the leading edge, to the side of the fuselage.

    "V" tail configurations can have the same type of structural arrangement a conventional tail, just with a minor geometric modification at the root. As such, a carry-through structure is not that big a deal.

    But the real problem in this type of mixing is control rigidity. Given the number of connections and joints, it is easy for a bit of slop to work itself into the system. These complex assemblies must be done in a very precise manner or you increase the chance of flutter.

    The main argument for "V" tail configurations was generally based around manufacturing in that both surfaces are the same so the assembly could see a bit of fabrication efficiency and possibly, a bit of interfearance drag reduction. But while that's true theoretically, the actual benefit is very small. Since stability requirements deal with net projected areas, the size of the "V" surfaces must be so that they deliver the same effectiveness as a conventional configuration. This forces the surfaces to be fairly sizable, thus negating any potential material savings in production, or drag in flight.
    "To live is to learn; to learn is to live" (author unknown)

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    Re: V-Tail Roll Moment

    The V tail was going on their "all aluminum" ultralight.
    Hydroformed aluminum ribs (I made the forming tools).
    Aluminum skins held on with 3M tape.
    And of course the all aluminum V tail.

    I think they both went to work at FSI on the Arlington airport after B&P went down. I tried to look them up recently but no luck. My shop was right next to theirs in the mid 80s at the Arlington Ultralight Airpark

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    Super Moderator orion's Avatar
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    Re: V-Tail Roll Moment

    I'm assuming then that that was the MiniMaster since that was built in precisely that manner. I guess they had a difficult time figuring out how to do the "V" with the twin boom arrangement.

    Although, now that you mention it, I do remember Bruce saying that they had the rib tools for the MiniMaster from another project - maybe that was it. But I didn't see that one - I'll ask Bruce next time I talk to him.

    Bruce worked for a number of different places since then including Bayliner and Glasair. Now he works as a production manager for a shop that manufactures UAVs - the company is owned by the same gentleman who is behind Dynon Avionics.
    "To live is to learn; to learn is to live" (author unknown)

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    Re: V-Tail Roll Moment

    The ultralight project was going on about the same time they were laying up the mold for the Minimaster. They got out a prototype (of the ultralight), but it just sat there at the end of the building. I thought it was pretty cool and was trying to figure out how I could angle my way into one

    Ask Bruce if they need any machined parts
    Wonder what happened to Harry?

    Oh, and the ultralight was a single boom unit. They were trying aluminum irrigation tube around 5" or 6" in diameter. I bought a piece at Cenex as I was trying to gather up parts for my own
    Last edited by Greg Mueller; May 6th, 2008 at 03:23 PM.

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    Super Moderator orion's Avatar
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    Re: V-Tail Roll Moment

    Do you by chance have any pictures?
    "To live is to learn; to learn is to live" (author unknown)

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    Re: V-Tail Roll Moment

    I was just trying to think if I did, but if I do, I don't know where they would be. And of course they'd be film based from back then.
    Also in the building there was a Beaver dealer, a Quicksilver dealer, Steve (what's his name) the Kasperwing guy and of course the Scott's Cadet shop/dealership. Those were the days.
    My shop was known as GM Machine at that time

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    Moderator Dana's Avatar
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    Re: V-Tail Roll Moment

    There should be a small drag decrease from the decrease in wetted area (two surfaces vs. three, even though they're larger than the single surfaces)... though I'm sure it's more a marketing thing than anything else.

    There'a also the Lazair ultralight, which had an inverted V-tail, so the any rolling forces were in the same direction as the yaw forces... and they also put tailwheels on the tail surfaces.

    For primary roll control in a low speed aircraft, nowhere near enough authority... and for roll augmentation not worth the control complexity in anything but a fly by wire aircraft, where control mixing is "free" via software.

    -Dana

    Can a Cessna 150 truly "slip the surly bonds of Earth"?

  15. #15
    Super Moderator orion's Avatar
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    Re: V-Tail Roll Moment

    There is no effective decrease in whetted area since the projected area is what you need. The only drag reduction is due to the fewer intersections. But that's really only in theory. In the practical sense, there's just too many drawbacks and penalties for application in anything that requires any level of performance.
    "To live is to learn; to learn is to live" (author unknown)

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