View Full Version : Difference Between V-Tail & Stright Tail

12-20-2006, 07:02 PM
I'm a new member to Wattflyer and to sailplanes, but I've flown fuel and gas planes for years. Now it's time to appreciate the beauty of flight through sailplanes.
I've been looking for information on the difference between V-tail and stright tail as far as how the launch goes and how they fly in general. If you guys know of a email that talks about this, please let me know. Maybe one of our old timers could comment on this.:D
Thanks, Charlie

Sky Sharkster
12-20-2006, 11:28 PM
Hello Charlie, Welcome to Wattflyer! As far as tail comfiguration, here's a couple of threads;
And I'll add my $ .02; For gliders, I like "T" tails best, "Cruciform" or conventional tails next, and "V"s the least. Now I'm sure you'll get lots of differing opinions on this but my experience has been that "V's have a tendency to wobble or "dutch roll" thru turns that a conventional tailed-model will "carve" in a much smoother manner.
Maybe it's a matter of setting the model up; The elevator throw is generally much less than the rudder deflection on a sailplane but lots of "V"s have an equal amount of deflection for the "ruddervators". This may stall the elevator and the whole tail loses its effectiveness. Maybe the overall size of the tail surface is too small compared to a flat tail. I don't really know, and many highly competitive gliders and e-gliders use "V"s (and "T"s) with no problem. This is just my personal experience.
Good Luck and Thermals!

12-21-2006, 03:55 PM
Thanks Ron, that's good to know. I've always like the old fashion configuration, but was wondering...I think now, I'll just wait before I tried one.

12-22-2006, 03:22 AM
Ol Guy, now ya done it! Now I'm gonna have to hunt for my 30 yr old copy of Stick And Rudder. I remember a chapter on the V tail Beechcraft Bonanza as he described how an airplane flies- like nobody has been able to describe it before or since. I wish he could have seen Rutan's layouts. Would love to read his take on the White Knight and SS1.. but I digress badly... :D

If by the Old Fashioned kind, you mean the surfaces in the FRONT of the contraption pre 1910, your first deep slip will be your last! It was nice to have structure out front when you crashed to break, knowing your bones were next... but the yaw was a bear! Oh... not THAT old? Good! :D

I helped my longtime wingman build a Lazair ultralight that had an Inverted V Tail and it was amazing to see how well it flat-turned while I followed behind it. My trike being slower, that was my usual view of him when we ventured out! :D

I have a Candy HLG with a V tail that flies pretty well but was a lot more trouble to keep aligned and true than a standard tail. You'd need to be a Swiss watchmaker to trim it up without a computer radio!

It seems less precise in controlling the pitch and yaw axies since it does so indirectly as a balance between the 2 surfaces whereas a cruciform tail does it directly, being in plane with those 2 forces. Even tho the V tail is one less surface out in the breeze, they still come close to the area of a 3 piece tail so the advantage of less drag is minimal.

Keep it simple!

Sparky Paul
12-22-2006, 03:39 AM

If by the Old Fashioned kind, you mean the surfaces in the FRONT of the contraption pre 1910, your first deep slip will be your last! It was nice to have structure out front when you crashed to break, knowing your bones were next... but the yaw was a bear! Oh... not THAT old? Good! :D

Speaking of that "feature" (in the Microsoft lexicon)... Willi Coppens, a Belgian Air Force WWI ace, describes one of his instructors trying out one of those new-fangled "banked turns",,,, and slipping into the ground in his Farman.
It was his first and last. :(

12-22-2006, 05:31 PM
Thanks for your help, but for now I think I'll stick to the T-tail.

12-26-2006, 11:29 AM
I look at tail designs as being in two groups:

Fixed Stab
Floating Stab

The V tail is typically a fixed stab design with moveable rudervators.

One advantage of a V tail over a "standard low stab with the fin on top" designs is that you are less likely to catch the tail on the grass when belly landing your glider. Look at the Hybrid to visualize this:

V tails are reputed to be lighter and have less frontal area to create drag. They consist of a fixed V stab with a moveable surfaces. Many like them and many hate them. They can be challenging to trim properly but they remain popular.

In comparison, if we consider the Spirit to have a standard fixed stab with an elevator design, see example, we see that the H stab is low and easily catches when landing. I have broken the stab loose on my Spirit many times.

T tails are very popular on scale gliders and full sized gliders but have been all but abandoned for modern non-scale thermal ships as the support post adds weight and the mechanism for the elevator can also add weight. We see an example here:

Fully floating stabs - easy incidence adjustment

The high mounted fully floating stab provides ground clearence and incidence adjustment that you can't do with a fixed stab. If the incident of the V tail Hybrid or the fixed stab Spirit is off, you have to remount/shim it or use the moveable surface to compensate, creating drag.

The BOT is an example of a high mount fully floating stab. Ground clearence is provided and no problems with incidence errors. Just trim to best incidence while flying.

If we look at the Thermal Dancer, we see one of the newer tail designs that grows out of the hand launch community. I believe these are called X tails. The floating stab/elevator sits in front of the fin. It has good ground clearence and no fixed incidence issues.

Stab is high and fully articulated, or fully floating. This keeps it off the ground AND eliminates trim problems caused by having a fixed H stab that is at a poor incidence with the wing. You just trim for best incidence while you are flying. Changing weather, heat and whatever that might change the body of the plane does not prevent you from having an ideal incidence. :)

It was Gordy Soar, a well know contest pilot, who pointed out the benefits of a floating stab design. I had not thought of it up till that moment. But after working with all these tail types I find I like fully floating stabs best. I think V tails are fine and have a nice look. A plane I am currently interested in, the Renny, has a V tail.

All things being equal I would avoid the fixed stabs, not because there is anything wrong with them but because I feel the floating stab offers advantages. ;)

I have not noted any characteristic launching issues with any of the designs.

Hope that made sense.

12-26-2006, 05:05 PM
Thanks Ed for sharing your experience.

01-02-2007, 07:40 AM
I also found my Filip600Spory's V-tail a bear to trim out correctly. But once done she flew great. I did however dial in a healthy dollop of differential in the ailerons, thereby minimizing the need of rudder in turns. Plus I just like the v-tail "look".