Spitfire

[fhrussell]

I came across this while Googling info on unstayed bi-plane rigs....

http://www.marine.bdg.com.au/spitfire_gallery.html

Just thought I'd share....

[Smoothride]

Wow--cool post.

Impressive on many levels.

Since the spitfire (airplane) was famous for it's elliptical wing, maybe some day the sailboat could have a semi-elliptical rigid sail? Among aviation circles, the elliptical wing is touted as the most efficient.

I don't know if it would look good or not, hmmm...

[CT 249]

I think you'll find that elliptical outlines are only the most efficient for a flat foil of given span, operating in untwisted uniform-speed flow, which doesn't exist very often in boats. The famous Spitfire wing outline was created so Mitchell could fit four machine guns in each wing, which meant a wide chord outboard.

[Smoothride]

Roger that CT249,

A fellow WWII aircraft enthusiast?

Sorry in advance for the novel...

Maybe not so good for sailing, but for airplanes:

Pretty much every engineering text that talks about elliptical wings cites the spitfire, and as for pilots--anyone worth their salt knows the 'spit was much beloved by it's aircrew.

The wing on the spit had washout or twist to prevent a tip stall before the wing root stalled. The spit's elliptical wing was thus bastardized from the start. The entire wing stalling at the same time would mean no roll control for the pilot during slow speed maneuvering near the stall (this would be bad for pattern work, approaches, and landing). This simply won't do. I don't know how much the twist messed with the lift distribution along the wing --root to tip-- but pilots loved that airplanes handling.

Low altitude ground attack spitfires actually had chopped off wingtips!! -- oh the humanity!!!! I guess it helped with roll control under about 20,000 ft, and they needed the maneuverability down low.

With all it's great qualities, the elliptical wing is too expensive to produce, I've always heard that since I was a little kid. Sure, it has the least induced drag for a wing form, but today's tapered wings with blended winglets have got to be close or better. Having flown aircraft with winglets while flying the same aircraft without them, they prove to be "smoother" flying airplanes, like comparing a Cadillac to a Honda, and they are more stable (directional stability). I wonder if the wonderful lift distribution across the elliptical wing felt similar to spitfire pilots...???

Cheers,

SR

Spitfire is one of the only foilers that I know of to use ballast(1100lb/ 500kg) in addition to crew weight-and won't be the last to do so.....
This is instead of a system such as that used on the Rave or Hobie Trifoler that uses the forward foils to generate righting moment with independent altitude control systems.

[catmando2]

Originally Posted by CT 249

I think you'll find that elliptical outlines are only the most efficient for a flat foil of given span, operating in untwisted uniform-speed flow, which doesn't exist very often in boats.

Had access to moulds for daggerboards, so used the bottom bit for the rudders on my powercat.

All the prop and rudder guys reckon these will be heaps better than the rudders thay can supply.

These are apparently scaled down spitfire wing tips.

Dave

[Smoothride]

Ahhh, most beautiful!!!

I built several model spitfires as a kid, and never tired of looking at them, there is something about that wing shape that appeals to almost everyone.

From our discussion here, the elliptical rudder may have less drag than a comparable-more rectangular one. Any thoughts on that?

Are you using hydraulic steering? If not, I wonder if feedback would be any different. My experience with drag saving devices tells me they make for a more "slippery" tactile/seat of pants feel which is usually a good thing (airplane wise--must be similar for boats though??).

[Smoothride]

Forgive me;

I just had to post this, even though this is not an airplane forum, this 3 view shows the inherent beauty of the classic 'spit. Quite a lot of wing area there, making for a slower roll rate. For the airplanes that operated lower in the more dense atmosphere for the ground attack role, they "clipped" the wings -- making the span less, destroying the beauty of the plan form, but increasing roll rate and maneuverability to counter anti-aircraft artilery (AAA) etc...

[catmando2]

Hi Smoothride, yes I will have hydraulic, but the other sailing cat's that have these as board's and rudder's used mechanical Spectra and chain steering.

These sailing cat's are arguably the fastest 40 footers in Australia, in the right hand's of course.

They always seem to outpoint all the other multi's and mono's on the race course and steer beughtifully.

Dave

[Smoothride]

Dave,

That's pretty interesting, and I never would have thought a scaled down spit's wing would be the rudder on a boat. What a cool idea.

I wonder how the "spitfire wing - rudder" compares to both a conventional rudder (rectangular?), and one of the foils on the canting keel boats. It would seem that the low aspect ratio of the spit rudder would have a higher "wing" loading than a high aspect one, such as a foil. Tell me if I'm geeking out too much, but I'm just interested in what that would mean for handling and feedback. hmmmm...

--SR

[catmando2]

I would argue that the square tip is better from the point of view that the designer of the boat's with these rudders have done the next lot of different design cat's with the square tip.

My last cat had square tip's as do most of the ones I sail on.

But the rounded tip's work on those other boat's and using the moulds sure made it easy for me.

Dave