0
Sabrekakkonen

Flat gliding canopy with long recovery arc

Recommended Posts

I'm not sure you can have both. I think that's where the trade off is. If you think about it the recovery arc is determined normal component or lift of the canopy. So it relates to your Cl. Flatter gliding canopies have a higher Cl/Cd ratio. So for a flat glide ether you are trimmed flat with a high Cl or you have a low Cd, drag.

Don't confuse this with wing loading. At a higher wing loading you have to go faster to make the same amount of lift and that force has a greater mass to affect to form the arc. So you're moving farther along the path and not turning the path as much. Longer arc.

In terms of the actual design. If you wanted to build a flat flying canopy with a long recovery arc you would have to minimize it's drag. Higher aspect ratio. Cleaner trailing edge, little false ribs. Thinner airfoil. Smoother nose. Fewer lines, cross braced. Things like this can reduce the parasite and induced drag of the canopy. There are trade offs for all of them as well. For example a thinner airfoil might have a lower Cl which actually hurts you in this. A high aspect ratio implies longer lines which increases line drag and also affects the dynamics of how the canopy pitches.

On the second front of wing loading. A more highly loaded canopy has an inherently longer recovery arc. That's why as you down size, reducing your lift area you find that you are not just flying faster but turning radius, recovery arc, is much longer. This is part of why people tend to plant them selves in the ground after they down size if the hook at there normal altitude.

Lee
Lee
[email protected]
www.velocitysportswear.com

Share this post


Link to post
Share on other sites
Flat glide angle implies a shallow angle of attack (flat) producing slow forward speed (less drag) and slow rate of descent.

OTOH swoopers like to increase forward speed in order to build up excess speed that they translate into longer horizontal swoops. They increase forward speed by diving or turning their canopies. Diving is easier with canopies that already have steep angles of attack.

Share this post


Link to post
Share on other sites
Quote

Flat glide angle implies a shallow angle of attack (flat) producing slow forward speed (less drag) and slow rate of descent.



Slower airspeed actually means less parasite drag and more induced drag (drag resulting from lift). The attached graph illustrates this principle.

Share this post


Link to post
Share on other sites
Define "flat"...

I've had the same question, as I fly a Pilot and felt the recovery arc was more positive than I preferred after just a few jumps. Going down one size didn't help. So, options from there?

Sabre 2 seems like it flies almost as flat as the Pilot when you want it to, but will dive easier and recover more gradually. I've not flown one, so I'm basing that assumption on input from others and lots of video.

I have, however, recently flown the Zulu and I freakin loved it. Only two jumps, but both openings (terminal) were picture perfect and it was a blast to fly. Compared to the Pilot, it of course did everything faster, required a fraction of the effort on front risers and had a longer (maybe 1.5-2 times) recovery that was nice and smooth. Huge power in the flare. I was at an unfamiliar DZ and it was pretty windy, so I didn't get a great feel for its ability to get back from a long spot, but the rep tells me it glides flatter than the Crossfire 2 or Katana, but with a recovery arc somewhere between those two.

I can't wait to fly one some more!

Share this post


Link to post
Share on other sites
I sometimes wonder to what degree a recovery arc difference is a true or perceived one, or is a function of the inputs.

Take two canopies with the same actual recovery arc. One turns more quickly, and has lighter front risers.

I bet many who crank a 270 with that one will say it has a longer recovery arc because they got into the dive quicker and could hold it better in deep front riser for the turn. So they came out of the turn with more speed and a steeper dive, leading to a longer recovery arc -- even if the two canopies performed the same if the setups were identical in turn rate and dive angle.

So NO it doesn't have a longer recovery arc on one sense, but YES it does in another, given typical human performance that makes it easier to get a longer recovery on one.

It would mean that assumptions about input conditions on any test would have to be considered.

It could be a partial explanation as to why a canopy claimed to be flat flying at the same time seems to have a fairly long recovery arc.

(Other factors would still apply. If two canopies had the same flat glide angle, but one was a more efficient design and flew faster, it would likely have a larger recovery arc.)

Share this post


Link to post
Share on other sites

Here's my experience...

On back to back jumps, flying the Pilot and the Zulu, I can tell you that if you put both of them in a steep dive, then release all inputs, the pilot pulls out MUCH quicker, you can feel it pull more g's during the recovery than on the Zulu. The Zulu was also going faster when all input was released and recovery allowed on it's own, but once again, it did not recover as aggressively as the Pilot, the difference was very noticeable. The same was true after either aggressive toggle turn or front riser dive.

I think there's more at play here than just how steep the canopy trim is. I'm guessing the lineset also differs in where it places the pilots weight under the canopy, thus affecting pitch stability.

Take for instance a fixed wing glider. If you move the center of gravity forward, it will become more pitch stable, so if you put it in a dive, then let go, it will recover more quickly on it's own to the trimmed airspeed. If you move the c/g rearward, it will handle more neutral, and take longer to recover from the same maneuver. If you move it back TOO far, it will go past neutral stability and into the realm of negative dynamic pitch stability. If you then put it into a dive and let go, it will actually pitch over steeper as the airspeed builds and will NOT recover on it's own. You can see this by examining the elevator trim setting required to attain level flight at a constant airspeed. On a perfectly balanced c/g, the elevator will be trimmed exactly neutral, or very slightly up (depending on your definition of perfectly balanced [sly;). With a more forward c/g, you'll need to dial in some more nose up trim to maintain level flight, and if you move it rearward, you'll actually be trimmed slightly nose down to stay level. Now, if you pitch over and gain speed with some nose down trim dialed in, then let go, things get interesting in a hurry!

Some hot rod canopies seem to stay in whatever pitch you put them in until you tell them otherwise. I suspect this has more than a little to do with where the center of gravity is in relation to the center of lift on the wing...

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

0