Control authority of V-tail vs. Cruciform - Page 2 - RC Groups
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Jun 12, 2012, 11:39 AM
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Not only the span of the V tail is small compared to the wing . The V tail also adds to the dihedral effect. So, as the plane yaws, the fixed portion of the V tail on the "outside" of the yaw will see a higher AOA compared to the one inside, and while this probably won't be enough to roll the plane towards the yaw, it will cancel out at least part of the adverse roll. That said, i have seen inverted split V tails on booms further outboard of the wing used to get "proverse" roll. However, the wing spar must be rigid enough to cancel out the tail induced torsion of the wing that would again generate adverse roll.
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Jun 12, 2012, 11:50 AM
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Don Stackhouse's Avatar
The structural weight of that system also tends to be higher, as well as the whetted area and drag.

The alternative, an inverted V-tail hanging under a single tail boom, tends to use the tail as a part of the landing gear, which imposes more structural loads and more weight.
Jun 12, 2012, 12:05 PM
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Hmm, swept flying wing with stub booms near the wingtips ?
Jun 12, 2012, 12:07 PM
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Don Stackhouse's Avatar
I've tried that. Can have some benefits, but aeroelastics get really tricky.
Jun 13, 2012, 01:42 PM
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Yes, in my post #14 I should have used the term "adverse roll," not "adverse yaw." Thanks for the correction for this aging bear.

Jim R...
...who yaws more than he rolls, and he never rolled much.
Jun 21, 2012, 01:03 PM
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Originally Posted by Don Stackhouse
I've tried that. Can have some benefits, but aeroelastics get really tricky.
hi don,

interesting reading. was looking for info on swept flying wing with dihedral and inward canted winglets to combine roll and yaw, like an inverted v, and at the same time reducing some of the combined dihedral effect of sweep and dihedral, and came across this.

i need the sweep to have most of my 'hull' forward of cg as well as pitch up in extreme ground effect and dihedral to increase water clearance

i imagine i could join the winglets to make a boxtail to stiffen up against aeroelastics although i would rather a not have a horizontal tail as with reduced downwash in ground effect it tends to aggravate the pitchdown normally experienced in ground effect due aft movement of cp.


Jun 21, 2012, 01:11 PM
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Don Stackhouse's Avatar
What you just described falls into the general category of a "joined wing" aircraft. The big problem is that the plane ends up being a "tandem wing" arrangement, which has some aerodynamic penalties.

One problem I ran into with inward-canted winglets on the tips of a flying wing is that with large yaw disturbances, the more-forward wingtip tended to tuck downwards and the rearward one upwards, which could tend to roll the plane over into a vertically downward knife-edge maneuver. The plane would show very little tendency to recover, instead trying to do its impression of a lawn dart with the wing tip, stabbing the wingtip violently into the ground.

A "C" wing (vertical winglet at the tip, with an inward-pointing horizontal surface from its top end) did much better, but that much more complex shape made the structural issues quite a bit more difficult.

Dr.Kroo at Stanford University has done quite a bit of work with C wings.
Last edited by Don Stackhouse; Jun 21, 2012 at 01:17 PM.
Jun 21, 2012, 01:20 PM
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omg that is serious! i guess with a very low AR like i have in mind it would not be as extreme. being close together the winglets would not be as far from each other as in a higher AR in a large yaw disturbance.

stability so close to the ground in gusty conditions is a very high priority.
Jun 21, 2012, 01:28 PM
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Don Stackhouse's Avatar
It's more of an issue if you have a plane with very weak yaw damping (like a lot of flying wings) and a fair amount of yaw inertia. On something like that, a significant yaw disturbance tends to keep going, until you get to some pretty extreme yaw angles. At that point, you have to consider what the plane does when flying sideways. On a plane with less span and yaw inertia, and a decent vertical tail moment arm, it's less of a problem.
Jun 21, 2012, 03:07 PM
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here is a rough sketch of the planform, but without winglet
Jun 21, 2012, 03:08 PM
vespa's Avatar
You'll need a lot of anhedral to make that thing stable!
Jun 21, 2012, 03:17 PM
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i was thinking with large, possibly large enough to be joined in an inverted v, anhedral wingtips at about 30 to 35 degrees from horizontal.
Jun 21, 2012, 03:35 PM
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would it still need a lot of anhedral with elevons only, no tail?
Jun 21, 2012, 03:45 PM
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Don Stackhouse's Avatar
You would have problems, anhedral or not. The anhedral counteracts the excessive dihedral effect of the sweep at high angles of attack, but makes the plane statically unstable in roll at low alpha.
Jun 21, 2012, 03:47 PM
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well i cant have anhedral because of wave clearance. my first thought was with so much sweep plus dihedral i would not need a tail. then i thought of the winglets canted in.

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