from what i read is that the placement of the horizontal tail is crucial in that when a plane is in a flat spin, the horizontal blocks air from getting to the rudder on the vertical tail. In a v tail, the horizontal is the rudder so in a flat spin, the control surface has air.I've never heard that and don't see any reason for that to be true. However, I suspect that a V-tail may affect spin recovery (good or bad?).
From the Type Certificate Data sheet for the PA-38 Tomahawk, found here:The Tomahawk is not rated for intentional spins.
Some schools probably prohibited spins in their Traumahawks because the recovery could get exciting. I've never flown one but ours guys that have say that it likes to drop off into a spin the other direction when you recover from the first spin. And they said it wasn't as bad as some made out, but that may be since we Canucks teach spins all the time and are familiar with them, while many US schools stay away from them altogether. The FAA doesn't mandate spin training, while Transport Canada does.Huh. Wasn't at the time, IIRC. There was a big to-do about "the trainer you couldn't spin." That's my memory of the situation, though, and perhaps I'm wrong. Or perhaps there's some difference between the Tomahawk I and Tomahawk II. I mostly flew the former. I know that we did spin one (instructor and myself), with a caveat from him to "...not tell anyone back at the school." Quite a ride.
Thanks for the update, Dan.
pic 1,2,3 Moni motor glider, pic 4 Monerai glider, hope it helps.skier said:...but I was wondering if anyone knew of anyplace to find out how the rudder and elevator controls are mixed such that there are only 2 movable surfaces on the tail?
Well, I've done one spin in a Tomahawk, and was a passenger for the one immediately before that. My limited experience is that she sure likes to roll over going from the stall into the first turn (more so than others I've experienced), and flatten out just a bit if you let the turns develop. Not a lot of flattening, nor dangerously, but it was an exciting ride. Exit from the spin was non-eventful for me. Seems like you'd have to be pretty ham-fisted to break into a spin the other way upon exit, but again, I have very limited experience with this airplane in that regard.Some schools probably prohibited spins in their Traumahawks because the recovery could get exciting. I've never flown one but ours guys that have say that it likes to drop off into a spin the other direction when you recover from the first spin. And they said it wasn't as bad as some made out, ...
Not necessarily. Billski made that point about total area requirements. Just because they are dual-function doesn't excuse you from needing the requisite amount of vertical and horizontal projected area:
thanks bruce, i glossed over that the first time =)Originally Posted by wsimpso1
By the time you get projected areas equal for tail volume, you have the same total wetted area. And then there is control authority and interference between the foils, which actually drives you to more wetted area than with a three surface tail.
Which is because it's true in theory. If you simply look at the formulas your total tail area will go down.There are aero studies on this... All sorts of folks think that you should be able to carry less total tailplane wetted area and one less set of interfaces, so it should have less drag.
I did a design project for a 737-sized airliner and we chose for a V-tail, despite the fact that we were warned that it wasn't more efficient in reality. Some of the issues:I forget the whole explanation, but the upshot is this: Anytime you build with less total tailplane wetted area than what you would use on a conventional tail, it's stability is poor and its control authority at low airspeeds is inadequate... And when you build with just that amount, you will not have enough control authority if you are carrying some rudder, like landing in a crosswind. So you end up having to go bigger than with a conventional tail.
The best (albeit non-scientific) explanation I ever heard was from an old aero professor at CalPoly. Very practical guy. He said that, fancy math aside, all you're doing with a V-tail is rotating a conventional tail 45° and redistributing the area. Same as rotating the fletchings on an arrow 45°. "Why would simply rotating the tail like that result in less required tail area for a given amount of stability?" Good question. It won't. And since a conventional tail usually has a little more area in the horizontal tail than the vertical, distributing the total area into two equally-sized fins spaced at 45° will result in the pitch axis being 'shortchanged' a bit - which means more total area required to make up for that....I forget the whole explanation, but the upshot is this: Anytime you build with less total tailplane wetted area than what you would use on a conventional tail, it's stability is poor and its control authority at low airspeeds is inadequate... And when you build with just that amount, you will not have enough control authority if you are carrying some rudder, like landing in a crosswind. So you end up having to go bigger than with a conventional tail. ...
What is best? Depends on what you want to do. Years ago I started messing around with X-plane and one of the things I tries was to put a "V" tail on the little plane I'm building. I started with the assumptions mentioned in this thread - that is 45 deg and total equal area. Turns out, in X-plane anyway, that just slightly less area at 30 deg gave me the desired balance between dutch roll and spiral stability while still maintaining the original control authority. Real world might be different? Decided to stay "per plans"tin response to Topaz, i have read that people are having the v tail at 35 degrees from horizontal, but in my mind, you woul want them at 45 degrees.. whats best?