HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jun 12, 2012, 11:39 AM
Registered User
Joined Oct 2004
2,913 Posts
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.
Brandano is offline Find More Posts by Brandano
Reply With Quote
Sign up now
to remove ads between posts
Old Jun 12, 2012, 11:50 AM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,146 Posts
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.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Reply With Quote
Old Jun 12, 2012, 12:05 PM
Registered User
Joined Oct 2004
2,913 Posts
Hmm, swept flying wing with stub booms near the wingtips ?
Brandano is offline Find More Posts by Brandano
Reply With Quote
Old Jun 12, 2012, 12:07 PM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,146 Posts
I've tried that. Can have some benefits, but aeroelastics get really tricky.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Reply With Quote
Old Jun 13, 2012, 01:42 PM
Registered User
Blacksburg, VA 24060 USA
Joined Feb 2000
3,232 Posts
Don,

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.
JRuggiero is offline Find More Posts by JRuggiero
Reply With Quote
Old Jun 21, 2012, 01:03 PM
Registered User
Joined Mar 2011
792 Posts
Quote:
Originally Posted by Don Stackhouse View Post
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.

rgds

armour
captarmour is offline Find More Posts by captarmour
Reply With Quote
Old Jun 21, 2012, 01:11 PM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,146 Posts
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.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Last edited by Don Stackhouse; Jun 21, 2012 at 01:17 PM.
Reply With Quote
Old Jun 21, 2012, 01:20 PM
Registered User
Joined Mar 2011
792 Posts
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.
captarmour is offline Find More Posts by captarmour
Reply With Quote
Old Jun 21, 2012, 01:28 PM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,146 Posts
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.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Reply With Quote
Old Jun 21, 2012, 03:07 PM
Registered User
Joined Mar 2011
792 Posts
here is a rough sketch of the planform, but without winglet
captarmour is offline Find More Posts by captarmour
Reply With Quote
Old Jun 21, 2012, 03:08 PM
War is over (if you want it)
vespa's Avatar
Thousand Oaks, CA
Joined Mar 2004
2,665 Posts
You'll need a lot of anhedral to make that thing stable!
vespa is offline Find More Posts by vespa
Reply With Quote
Old Jun 21, 2012, 03:17 PM
Registered User
Joined Mar 2011
792 Posts
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.
captarmour is offline Find More Posts by captarmour
Reply With Quote
Old Jun 21, 2012, 03:35 PM
Registered User
Joined Mar 2011
792 Posts
would it still need a lot of anhedral with elevons only, no tail?
captarmour is offline Find More Posts by captarmour
Reply With Quote
Old Jun 21, 2012, 03:45 PM
Registered User
Don Stackhouse's Avatar
United States, OH, Bradford
Joined Jun 2005
4,146 Posts
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.
Don Stackhouse is offline Find More Posts by Don Stackhouse
Reply With Quote
Old Jun 21, 2012, 03:47 PM
Registered User
Joined Mar 2011
792 Posts
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.
captarmour is offline Find More Posts by captarmour
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Split v-tail suitable for yaw control? VTOLicious Modeling Science 27 Apr 06, 2012 03:05 PM
Discussion MKS Nuke 3: any good for V tail controls? Masterpiece Radios 0 Oct 21, 2011 10:35 AM
Discussion v-tail vs inverted v-tail tymbrewolf Foamies (Scratchbuilt) 17 Jan 07, 2011 05:42 PM
Discussion t tail vs v tail vs conventional SPARTMAN Sailplane Talk 8 Nov 09, 2006 01:29 PM
SS V Tail vs Inverted V Tail CRASHED AGAIN Parkflyers 9 Oct 29, 2004 11:24 PM