Boy , haven't had much response from you guys, but here's another question: I have a 72" glider with a standard tail, I'd like to increase performance. Someone suggested cutting the wings down to 60" and putting a v-tail on it. what is the conversion formula? And what is the formula for tail dimensions in relation to the wing surface area?

Increse horizontal stab and elevator surface areas 30%

Set the angle between the V-tail surfaces at 110 to 120 deg. (90 will function... but is very draggy when giving elevator control, more than 130 and you have virtually no yaw control)

The performance you want to change is? Without a stated goal... its hard to give the changes needed.

The V-tail can aid in many areas. Becuase of a reduction in frontal area (drag). And educed tail weight means less ballast needed at the nose. So you can get a speed increase and increased duration in marginal lift.

Reducing span sounds like you may want increased speed and/or roll rate. Without knowing the aircraft, the appx 15% wing area reduction could give more problems than help...

Changing to a V-tail AND a major change in the wing planform at the same time... It may be time to look at a different aircraft kit.

the glider in question is a Bob Martin Coyote. It is a nice plane, but a little sluggish. The directions state it can be cut to 60", but i'd like to go one step further and convert to a v-tail. I'm ALWAYS looking for speed! So I wanna go faster!
If I cut the wings, won't I also need to decrease the tail area?

Currently the wing span is 72", wing area is 639 sq. inches wing loading is 10oz. Root chord is 10", tip is 7.5". Fuse length is 36"

I guess it is in my hobbyist nature. Haven't you EVER put modifications on a plane? Carbon, glass, change dihedral? Adjust incidence? Or even scratch built? Just to see what happens? If you take a risk in mods to improve performance, doesn't it feel GOOD when it works?
Some guys like the hobby to relax, some like to build, others just fly. I like to experiment. The Coyote is a cool plane, I have one now flying, and another in the box on the shelf for a later time.
The guy that designed it, probably flew and experimented on it plenty.
And I'm sure he wrote the directions. The directions state: "...if you have great lift regularly, clip off 6" from each tip and watch it become even more impressive."
So has anyone done this?

Rimshot -- how much have you experimented with the CG on your Coyote? Is its sluggishness limited to speed, or is it slow to respond to control inputs as well? Weight and balance is starting to sound more and more to me like a reversible place to experiment before doing some of the bigger chnages.

Gentle Spirit -- great post, but I have to add a caveat to your statement that, "Performance increases dramatically when each half of the wing is the same size." I do remember an old Ken Willard article where he found the opposite to hold when he tested the assumption with a standard size plane. He replaced one outer panel with a tip plate, balanced and flew to find that the plane didn't need to be retrimmed -- and he did it with the other outer panel, too. Actually, I'm into a little assymmetry, so I kinda like the look of a plane with a long wing and a short wing. BTW, if your plane's a Gentle Spirit, then I must have a Spirited Lady... opposite combination.

Thanks for all of your input guys, I've decided not to do the conversion. I've been flying this coyote every weekend now for months. I like it the way it is. Although, after the last reply, I think I'll start playing with the CG! Something I never really considered. I figured if it doesn't pull up after a dive, and inverted needs little or no down stick, the CG was perfect, but what the hell, I'll experiment! So thanks and happy flying!