What's the real difference?

[rgoper 0]

Quote

Yeah, who can forget when they pulled the wool over our eyes and said we were jumping SQUARE parachutes

ya know, ya got a point there, which no one can argue. LOL.

--Richard--
"We Will Not Be Shaken By Thugs, And Terroist"

[cobaltdan 0]

hey richard,

i think you misunderstood my post.

i call any canopy that does not use the exact same rib in every position an "elliptical".

all "tapered" and "semi" canopies are "elliptical".
those terms are marketing names and most times do not give any indication of the "degree of taper". they are used to describe whether the canopy is high or low performance.

understand that the "degree of taper" or the "ellipticalness" as people like to say (i hate this) is only 1 variable of many in a canopy design and will not give you an indication of performance without knowing all the other variables. i.e. there are straight leading edge canopies with tail tapers that are far more radical than the many high performance dual taper ellipticals... there are begineer canopies with more agressively tapered planforms than the competition swoop machines...etc.

i call a duck a duck. from day 1 i have always stated all our canopies are elliptical from student to base to tandem to swoop machines. i have never used terms like semi or tapered in our marketing, because i find it misleading.

sincerely,

dan<><>

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[AndyMan 7]

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i call any canopy that does not use the exact same rib in every position an "elliptical".

Just to add confusion to the water, I believe the Aerodyne Diablo has different ribs in each position. Despite it's straight leading edge, is it Eliptical?

I put a similar question to hook: You said having a straight leading edge but tapered tail makes a canopy "tapered". What other canopies beside the Diablo fit this definition?

_Am

__

You put the fun in "funnel" - craichead.

[cobaltdan 0]

yes the diablo is elliptical.

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[Hooknswoop 19]

I count all three of those as sem-elliptical, tapered trailing edge w/ a straight leading edge.

Hook

[kallend 2,105]

An ellipse is a curve, and if it is of finite extent the curve contains no straight line segments.

A P51 has tapered wings, a Spitfire has elliptical. If you have any doubts about the different planforms, just compare a P51 wing with a Spitfire wing.

[Hooknswoop 19]

Quote

I put a similar question to hook: You said having a straight leading edge but tapered tail makes a canopy "tapered". What other canopies beside the Diablo fit this definition?

I didn't look back, but I am fairly sure I said a straight leaading edge and a tapered trailing edge (like a Cessna 182 wing), I call semi-elliptical. Semi, becuase only the tail is tapered and elliptical becaue that is the accepted terminology. I have never seen a truely elliptical canopy, only tapered canopies.

Other canopies that I group into the semi-elliptical catagory are the Safire, Spectre, Sabre2, Hornet, Silouette, and Diablo.

Square canopies; Sabre, Monarch, Triatholon, and all ram-air reserves.

Ellipticals; FX, VX, Crossfire, Stiletto, Velocity, Vengance, Samari, Batwing, Cobalt, and Heatwave.

Just the system that works for me.

Hook

[Hooknswoop 19]

Quote

An ellipse is a curve, and if it is of finite extent the curve contains no straight line segments.

A P51 has tapered wings, a Spitfire has elliptical. If you have any doubts about the different planforms, just compare a P51 wing with a Spitfire wing.

I agree, no doubt in my mind.

Hook

[riggerrob 643]

Diablo has three center cells that look to be all the same size. Taper is limited to the outboard trailing edges. The Diablo leading edge is straight.
The reverse would be a Swept wing Jedi with a straight trailing edge, but tapered/swept leading edges.

[billvon 3,063]

All this discussion is fine, but it reminds me of the office arguments along the lines of "It's not a xerox! It's a reproduction! And that's not scotch tape, it's transparent tape." Yeah, technically correct, but somewhat misleading. I have scotch tape, transparent shipping tape, and electrical tape in my office, and using those terms uniquely identifies them - even though both the gaffer's tape and electrical tape are technically mislabeled.

I usually use "square" to refer to rectangular canopies with straight front and back edges. I use "elliptical" to refer to canopies whose tips are narrower than their centers. Very elliptical canopies (like the Stiletto) have much narrower tips, less elliptical canopies (like the Spectre) are barely narrower at the tips. The reason I think this terminology is OK is that I can use it and everyone seems to understand me; when people talk to me using that terminology I understand them. Using the term "tapered" usually leads to a discussion along the lines of "Oh, I thought it was sort of elliptical. It's like a square, then?"

People who discuss canopies discuss them primarily in terms of performance, not geometry. Given that, the terms elliptical and square(with ellipticals having varying degrees of aggressiveness) seems to make the most sense.

[alan 1]

This may help a little.
http://www.afn.org/skydive/sta/highperf.pdf
It is a little hard to read though, the quality of the scan or whatever was poor.

alan

[pilotdave 0]

I just want to point out that generally, for a wing, an elliptical planform is the most efficient possible wing. This is only true for low speed aircraft of course because shockwaves will form at high speeds. But a tapered wing is simply an approximation to an elliptical wing which is far easier to design and construct. I'm sure this is true for parachutes too. As it turns out, a properly tapered wing is only slightly less efficient than a truly elliptical wing. This is why most general aviation aircraft have tapered wings, but almost none have elliptical wings. So, whether a canopy truly curves in the shape of an ellipse or just tapers doesnt make a whole lot of difference aerodynamically. To really learn about wing planform design and airfoil selection, you really need an aircraft design or aerodynamics book. This stuff gets really mathematical really fast though.

By the way I'm a senior in aerospace engineering. Right now I'm taking an aircraft design class. We happened to cover wing taper today. Last friday we studied the aerodynamics of tailgate aircraft, specifically the skyvan. I was so entertained! Turns out keeping it boxy in the back makes it MORE aerodynamic than if it was rounded off. Who knew? (ok, maybe the shorts brothers)

Dave

[SkyMissy 0]

You guys do understand that no skydiving canopy is truly elliptical, right? These terms all try to reflect how CLOSE to an ellipse the canopy's shape comes. An ellipse has no straight lines, unlike canopies. Paragliding canopies come a lot closer to an ellipse, but still don't quite cut it. You guys are arguing over arbitrary, made-up terms. Modern canopies have differing degrees of taper.

Peace!


Okay, I'm the idiot. I posted this after reading only the 1st page of posts! Already covered.

________________________________________________
Mike