sail aerodynamics

Hi Leo.
I mean rigid wings with leading edge tubercles, i.e.
Cheers.

 

They might have some benefits, but they could also be quite expensive to fabricate.

Another difficulty might be that the tubercules on a whale fluke are matched to the way the whale flexes that tail. What works on a "flapping" tail might not be as beneficial on a rigid wing.

I'm guessing though.
Leo.

 

i cant find it and might as well ask you aerodynamicists, for a while i've been i've been
looking for inf on wobly, say fabric or inflatable foils and possibly endcap on bi-planes

 

What did you want to know about it Yipster?

(BTW, That's the coolest three-blade razor I've ever seen!)

Leo.

 

perhaps also see my post #203 page 14 on inflatable battens and yeah, have to shave, i know

what i dont is, as with the tubercled leading edge how wobly planforms as in old planes and kites
are behavin, ever heard of a endcap expiriment on a bi-plane, neighter did i but do wonder...

 

More, extended and bigger battens are coming to get us?

 

You might check out "Effect of Regular Surface Perturbations on Flow Over an Airfoil." Santhanakrishnan and Jacob, U of Kentucky

If you google it, it should come up- my printout does not have the web address on it.

It's about low re bumpy inflato wings (like a modified E398 section), and the bumps are 90 degrees to the direction we are talking about, but cool things happen at low re.

 

interesting link, i was looking for chordwise perturbations as in those foils
but spanned i see back also in nasa's blow-up wings big blue V mars lander

 

You might check out the X plane site= they're throwing around ideas for a Mars plane, some inflatos there-

 

Harvard professor's reference

I was going to move this 'whale' posting to its own subject thread, but it appears as too many have already responded to it.

There's a paragraph at Harvard Professor Michael Brenner's pages at
http://www.seas.harvard.edu/brenner/Research%203.html

"We have been interested in understanding the aerodynamic mechanism for
this stall-delay. Recent work with Ernst van Nierop and Silas Alben
demonstrates the mechanism for the observed increase in stall angle.
Although the bumps have been compared to vortex generators, we propose a
different mechanism: we demonstrate that the bumps alter the pressure
distribution on the wing such that separation of the boundary is delayed
behind bumps; this ultimately leads to a gradualonset of stall and
higher stall angle. Our mechanism predicts that as the amplitude of the
bumps is increased, the lift curve flattens out leading to potentially
desirable control properties. Model airplane builders have started
experimenting with this type of wing shape."

 

Leading edge projections.

Not being any kind of an aerodynamic expert myself, I see two possibilities for this performance enhancement.

1.) that the projections are creating vortexes, which break away from the upper surface later, or

2.) they break the wing up into separate lifting sections at the leading edge, but let them join as one, further back, thus delaying upper surface separation which seems to start pretty far forward.

A good way to see which one is correct would be to build a wing with cut water like, fence projections, which only extend forward, but have the same spacing, while keeping the rest of the wing shape exactly the same.

It would be interesting if the enhanced performance goes or stays, or is simply reduced.

Such an experiment, IMHO, could go a long way toward sorting out what is really going on.

The reason I suspect that the second theory might be right is that I heard of an Experimental Aircraft Association lecture about stalls and flat spins in airplanes.

The lecturer was a test pilot who would try to deliberately put a planes into flat spins (he had a way to escape if the spin got unstoppable) . Most of the light planes he tested, he was able to.

He then tried to see if he could create a spin proof wing. He did this by creating a solid leading edge projection near the tip of each wing that was a significant portion of its span in length along the wing. It, of course created an ugly notch where it ended, but it worked. He could not get the plane into a flat spin.

He then tried to fair this projection into the rest of the leading edge. It didn't work. The plane was able to get into a flat spin again, just as before.

My take on this story is that the wing ended up with two distinct lifting surfaces at the leading edge. This way either all the wing was producing lift or at least part of it was. It would be the projection part of the span or the inward part. And this would all happen during at least part of each turn of the spin, making the spin wobbly and unstable.

I imagine that once he fared out the notch, created by the projection, he created an unbroken leading edge. This way, if the separation started anywhere along the span at all, it would end up encompassing the entire span under these more extreme conditions.

This, I imagine, is because fluid molecules tend to play 'follow the leader'. Once part of the flow breaks away, the rest seems inclined to follow. Maybe this is why weather patterns seem to be heavily influenced by mountain ranges of even modest heights.

To make a safe airplane, you need only to make the outer end of the wing have its separation last. This way, if the plane stalls, the wings will be more inclined to stay level. This is done by making the pitch of the outer span less than the pitch of the inner span, creating a slight twist in the wing. This does not prevent a stall, or even delay it, but only tries to keep the airplane from tipping sideways once it happens.

 

Try reading my website at www.ivorbittle.co.uk

 

Two things-

1) the bumps on the whale fin and the idealized bumps on the 'man made fin' are not the same- the 'man made fin' has it's bumps at 90 degrees to the whale's bumps(?).

2) as long as wing sails have surfaced, here's something you might be interested in, if you haven't seen it before- "An Autonomous Wing Sailed Catamaran" Phd thesis by Gabriel H. Elkhaim (the Atlantis project):


http://www.soe.ucsc.edu/~elkaim/Documents/Catalyst_BoatArticle.pdf


Paul

 

seen that interesting ucsc doc before but now i was thinking that was the santa cruz boardwalk i saw in the opening pictures background but no, this world IS changing and i appologise for bluring this perfect thread, i'm gonna reread it again!

 

Paul,
I am new to forums. I looked for experience with one and now realise that I should not have taken part at all. Forgive me. I shall not make the same mistake again. Re Gabriel Elkaim-I would like to see a history of all the revolutionary devices that have been promoted for aero- and hydro- dynamic devices over the years.
Ivor Bittle