There are some similarities between high elevator tail sections and T-Foil rudders. However there are a lot of differences and the tail sections have moveable surfaces which complicates things. Articles from the 1950's and 1960's might have some basic data. I would understand winglet first

No, but has anyone seen an aircraft with two fuselages and two tail rudders?


Has anyone seen what brought an end to A-class development in this? Rules? Drifting conditions downwind when some degree of bow down often is used to reduce transom drag.?
Would be interesting to see what was the reasoning for abandoning it as it seem to be very promesing.

BR
Patrik

Luiz, your rudder is unique. It would not be my solution but it from what I read, a lot of testing has been and it works. My concern would be "if you stall the rudder do you stall the lifting surface". If you push too hard on the rudder at speed do you make things much much worse instead of just worse.

The P-38 Lightning comes to mind when you ask about two fuselages. A very beautiful plane in my opinion: http://www.richard-seaman.com/Aircraft/AirShows/Chino2004/Sampler/P38.jpg
If you look at some of the planes Burt Rutan and Scaled Composites have done, you can find other examples, like Steve Fossets "Global Flyer" and others.

Have the A's even tried this? If they have, I guess their hullshape and length is is such that they dont need it to keep their rigs stable. Much the same reason the C-class dont use them.

Yes:

P38 Lightning http://en.wikipedia.org/wiki/P-38_Lightning

Cessna 337
http://en.wikipedia.org/wiki/Cessna_337

Not sure what this proves other than an unhealthy knowledge of aircraft <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Actually, twin rudder is reasonably common: http://en.wikipedia.org/wiki/Twin_tail

I'll get my anorak.

Paul

http://en.wikipedia.org/wiki/Image:B-25_Flying.jpg

This plane has IMHO something very much like an L form...

So does the cessna and the P-38 although, not fully symetrical anyway.

In A-cats, there is a clear difference due to hull shape from older boats to newer on how much they nod, I believe that is one of the things driving wavepiercing bows and so?

All the best
Patrik

My A is very stable in pitch. I can't see a lot of advantage in that area. If I want to lift the rudders in light air, I sit on the front crossbeam. There are easier ways to handle these problems.

Foiled rudders have been looked at to reduce drag. But, you don't gain that much compared to the pain.

Maybe we need to rethink this. If I build foiled rudders for my 14 you can be certain, that they will fit my A.

The 14's are different. Mine is really unstable in pitch. Anything would help.

Carl, what I meant was that when adopting that bow down attitude a foiled rudder would both hinder (downwards lift) it and, as lift and drag is coupled, slow the boat down.

I'm comparing a Auscat Mk3 with Marstroem boats and to me it seems as there is a clear difference in pitching behaviour.

It would be most interesting if you did try foiled rudders on your A-cat.

I don't think the A's are a good platform for T-foils. Their general make-up is such that gains would indeed be very limited. This also hints at the fact that other cat design, which are significantly different when compared to the A's can most definately benefit alot from application of T-foils.

For example I feel the A's are rather narrow compared to their length and mast height. Much more then other cats. They are therefor much more limited by capsizing then pitching. Wider boats like most of the non-A-class designs are much more limited in pitching the capsizing here the T-foils can be a great advantage. Probably increasingly so with decreasing hull length.

WOuter

Carl,

I guess if my rudder stalls the foil placed on the side where the flow is detached will also stall. I see no reason for the other foil to stall together. Since the stalled foil still generates lots of lift, this is not a reason for concern. Reataching the flow is as easy as placing the rudder in a lower angle of attack. Then, of course, I want to test it in real life.

As far as I know, the A Class initially banned rudder foils similar to mine. They were close to the surface and the concept was that they would increase the effective waterline. They probably worked well, otherwise it wouldn't be necessary to ban them.

I don't remember where I read this, so take it as an unconfirmed rumour.

Carl,

You are focusing on stability only. As I wrote before in this thread, most of the time the T foil provides upwards lift.

When the foil's lift is up, weight must be moved further aft to maintain the same pitch attitude. When lift is upwards the wetted surface is reduced. If this causes a (friction) drag reduction bigger than the foil's drag, their contribution is positive to performance.

Only when the boat pitches down the T foil provides downwards lift. Downward lift increases wetted surface. That adds to the foil drag to slow down the boat. This exchange of speed for stability is usefull when sailing in the limit. The rest of the time moving the weight aft is faster.

It could be seen as unhealthy not to know of the p38...