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Correlation between elliptical canopies and aggressiveness?

 


20_kN  (B License)

Jan 19, 2018, 8:33 PM
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Correlation between elliptical canopies and aggressiveness? Can't Post

At one point awhile back when I was speaking to my instructor about buying a first rig he mentioned to get something nice and square and reasonably large. He said to avoid elliptical canopies as they are not suitable for beginners.

Well to my surprise I recently learned that several canopies that are marketed as appropriate for beginners are also listed as elliptical. For example, the Safire 2 and S Fire canopies are listed as elliptical on the manufacturer's website and I know the Safire 2 is not that aggressive as my DZ uses them for their students. I'm told the S Fire is basically just another version of the Safire 3 and it's listed as being a beginner canopy as well being elliptical.

By contrast, the Sabre 2 is listed as "semi-elliptical" by PD, but I think is understood to be a bit more aggressive than the Safire 2 despite the Safire 2 being listed as elliptical.

So what is the correlation between shape and aggressiveness assuming wing loadings between compared products are equal?


(This post was edited by 20_kN on Jan 19, 2018, 8:35 PM)


gowlerk  (C 3196)

Jan 19, 2018, 9:06 PM
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Re: [20_kN] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

Quote:
So what is the correlation between shape and aggressiveness assuming wing loadings between compared products are equal?


"aggressiveness" is not a quantifiable property. There are many ways to answer this question, canopy shape and performance are complicated subjects I will never grasp. But in general there is a trade off between stability and maneuverability in canopy design. The more tapered the shape of the canopy, sometimes incorrectly called elliptical, the easier it will be able to turn. Meaning it will be less stable, but more maneuverable.

You can start with that nugget. There is tons more.


AtrusBatleth  (A 79685)

Jan 19, 2018, 10:10 PM
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Re: [20_kN] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

I'm no canopy expert, I just jump an S-Fire as a beginner. I think "square" and "eliptical" are relative terms. I've seen plenty of obviously elliptical canopies of other jumpers (both front and rear edges are curved). The S-Fire I jump looks pretty square in comparison, but I suppose it curves a tiny bit. I could have sworn it was marketed as a "semi-eliptical" when I bought it but I agree, their website now calls it elliptical. Anyway, my opinion is if the manufacturers are saying it is a beginner/intermediate canopy it's probably going to behave pretty tame regardless of whether it's called square or elliptical.

PS - NZ Aerosports and Icarus Spain both manufactured Saffire-2 canopies for some time, then they had some kind of falling out over royalty payments or legal issues. NZ Aerosports came out with Saffire-3, and Icarus Spain came out with S-Fire. Sortof like how there was a family squabble that split the founding midwest farm equipment business into Blains Farm & Fleet vs. Mills Fleet Farm.


20_kN  (B License)

Jan 19, 2018, 11:14 PM
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Re: [AtrusBatleth] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

AtrusBatleth wrote:
I'm no canopy expert, I just jump an S-Fire as a beginner. I think "square" and "eliptical" are relative terms. I've seen plenty of obviously elliptical canopies of other jumpers (both front and rear edges are curved). The S-Fire I jump looks pretty square in comparison, but I suppose it curves a tiny bit. I could have sworn it was marketed as a "semi-eliptical" when I bought it but I agree, their website now calls it elliptical. Anyway, my opinion is if the manufacturers are saying it is a beginner/intermediate canopy it's probably going to behave pretty tame regardless of whether it's called square or elliptical.

PS - NZ Aerosports and Icarus Spain both manufactured Saffire-2 canopies for some time, then they had some kind of falling out over royalty payments or legal issues. NZ Aerosports came out with Saffire-3, and Icarus Spain came out with S-Fire. Sortof like how there was a family squabble that split the founding midwest farm equipment business into Blains Farm & Fleet vs. Mills Fleet Farm.

Are the S Fire and Safire 3 canopies completely identical, or are there some differences?

There seems to be an issue with the terms too. I havent seen any manufacturer label one of their canopies as "square" yet, but I see semi-elliptical, elliptical and "fully elliptical" whatever that means. Do these terms have any defined criteria, or is this purely marketing and what one brand might call "semi-elliptical" another might call square?


(This post was edited by 20_kN on Jan 19, 2018, 11:18 PM)


IJskonijn  (B License)

Jan 20, 2018, 3:43 AM
Post #5 of 16 (3047 views)
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Re: [20_kN] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

There is no clear correlation between how elliptical a canopy is vs how it flies. For an interesting listen and view, check John LeBlanc's seminar on planforms: https://www.youtube.com/watch?v=f-mUyy1fhjE


RMURRAY

Jan 20, 2018, 6:45 AM
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Re: [IJskonijn] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

thanks for that link. great stuff.


AtrusBatleth  (A 79685)

Jan 20, 2018, 8:18 AM
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Re: [20_kN] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

20_kN wrote:
Are the S Fire and Safire 3 canopies completely identical, or are there some differences?
They are different canopies. NZ developed the Saffire 3 and Icarus Spain developed the S-Fire after they parted ways, but they both represent the next iteration of the Saffire 2. I only found out about this after I ordered my S-Fire and got confused when I started seeing Saffire 3 being advertised.


ixlr82  (C 33491)

Jan 21, 2018, 12:36 AM
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Re: [IJskonijn] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

Yes. Thank you for that link. Clicked on it and spent the next 54 minutes learning about parachutes from someone who designs, modifies and test flies parachutes. And he refuses to get very technical, instead always bringing it back to the very pertinent, tangible and easy to understand aspects that are pertinent to real world skydivers.


Baksteen  (C 708753)

Jan 22, 2018, 1:28 AM
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Re: [20_kN] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

Call me cynical, but I suspect that an 'elliptical canopy, suitable for beginners' sells better than a 'semi-eliptical canopy, suitable for beginners', which sells better than a 'sqaure canopy, suitable for experts'.


(This post was edited by Baksteen on Jan 22, 2018, 1:28 AM)


kat00  (B License)

Jan 22, 2018, 11:28 AM
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Re: [20_kN] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

20_kN wrote:
Are the S Fire and Safire 3 canopies completely identical, or are there some differences?

There seems to be an issue with the terms too. I havent seen any manufacturer label one of their canopies as "square" yet, but I see semi-elliptical, elliptical and "fully elliptical" whatever that means. Do these terms have any defined criteria, or is this purely marketing and what one brand might call "semi-elliptical" another might call square?

The sfire and safire 3 are very close. I've flown both and have a slight preference for my safire 3. They both have a nice snivel and open softly. The flare is nice and easy on both. Turns recover fast and both are really docile.

Personally, I wouldn't focus on terms like elliptical and stuff. Find a canopy that is designed to fly well at lower wingloadings. These are the safires, pilots, sabres and various others. In the end, it really turns into personal preference. As a fellow newbish jumper, its really hard to find much of a difference in a pilot, sfire or safire 3 at the same 1.0 wingloading.

Try and demo some out if possible. All the canopies on the advised 1.0ish wingloading are tried and true canopies. It's just finding your personal preference.


daffes  (D License)

Jan 23, 2018, 9:44 AM
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Re: [20_kN] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

In the US, most beginner canopies after A license are:
Pilot (Aerodyne)
Pulse (very similar to the Pilot but by PD)
Safire 2, 3 (NZ Aerosports)
Sabre 2 (PD)

The first 2 are flatter and more docile, most people move away from those unless they go with Wingsuiting as their primary discipline. The last 2 demands a bit more of you both on openings and landings but achieve greater results with the proper technique, they are more suitable for someone focusing on canopy skills progression.

The classical canopies marketed as fully elliptical that people go to after 2-3 sizes of those listed above are the Crossfire and the Katana. You should definitely avoid them out of A license.


(This post was edited by daffes on Jan 23, 2018, 9:45 AM)


Joellercoaster  (D 105792)

Jan 25, 2018, 7:49 AM
Post #12 of 16 (1422 views)
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Re: [20_kN] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

I don't think anyone has addressed this in the thread yet so I'll have a go.

The word "elliptical" is certainly a marketing term, so you should take it (and literally anything else you read in a canopy blurb that's not a technical spec or a hard jump number recommendation or a max weight) with a huge grain of salt. But! It does have some use as a term used by skydivers to classify canopies, so I'll have a go.

Ram air canopies started off rectangular - and some of them still are: Navigator, Silhouette, Triathlon are all still made and still popular. Some people (including me sometimes) still jump the original Sabre, though it's not made any more. Colloquially, we call these "square".

Then manufacturers discovered that if you tapered the ends, they would turn faster (and thus dive harder) and fly more efficiently, and maybe quicker through the air due to reduced drag. This is the "high performance" part of ellipticality.

When tapered in a small way, this contributes mostly only good things to an otherwise square canopy - snappier turns, better glide and possibly flare (although it tends to make openings a little more wandery). Some manufacturers refer to these as "lightly elliptical" or "semi-elliptical", and they include wildly popular canopies such as the Sabre2, Pilot, Safire2/3, S-Fire, Spectre and many others. Confusingly, some manufacturers refer to things in this class as "elliptical" or even "fully elliptical", though it's not common.

Tapering beyong this point keeps upping the performance factor in terms of speed and roll and agility, but now you are starting to pay for it. Quick to roll and dive can mean quick to get into trouble - and highly tapered canopies have a tendency to oversteer and/or stay diving once you stop pulling things. If you get cut off in the pattern under your aggressively tapered Mamba, you need to have your reflexes under control and not yank on a toggle to evade, or you might find yourself in a bad place you're too low to get out of again. They are also definitely more prone to bad behaviour on opening! Popular canopies in this class include the Stiletto, Mamba, Zulu, Crossfire2/3, Katana and X-Fire. This is what people generally mean when they say "fully elliptical", or simply "elliptical" for short. There are lots of different shapes in this class, but they all have a noticeable taper on one or both edges.

NOTE: Some places have hard jump number requirements attached to canopies in this group, and for strong reasons.

(All modern cross-braced canopies are, of course, fully elliptical. But those are a whole 'nother thing.)

There is a lot of subtlety I'm missing out here - the models in my groups don't all fly alike and there are plenty or other factors involved, like steepness of trim, reliability of opening and recovery arc, that differentiate them. But, I hope this has answered your question about the word and how it's generally used, a little more directly.


(This post was edited by Joellercoaster on Jan 25, 2018, 7:50 AM)


freeflyfree  (D 28117)

Jan 25, 2018, 8:14 AM
Post #13 of 16 (1383 views)
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Re: [Joellercoaster] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

When you have an hour to burn, John LeBlanc talks about the evolution of planform shapes:

https://www.youtube.com/watch?v=f-mUyy1fhjE


frontfloater  (D License)

Jan 28, 2018, 4:16 PM
Post #14 of 16 (1069 views)
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Re: [freeflyfree] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

I also recommend that you (and everyone else) read this excellent article by Mr LeBlanc :

http://www.performancedesigns.com/docs/wingload.pdf

It cuts through many widely-held but wrong beliefs and assumptions about wing-loading and flight performance.

BOB


shadeland  (D 34638)

Jan 28, 2018, 5:50 PM
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Re: [Joellercoaster] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

Joellercoaster wrote:
I don't think anyone has addressed this in the thread yet so I'll have a go.

The word "elliptical" is certainly a marketing term, so you should take it (and literally anything else you read in a canopy blurb that's not a technical spec or a hard jump number recommendation or a max weight) with a huge grain of salt. But! It does have some use as a term used by skydivers to classify canopies, so I'll have a go.

Ram air canopies started off rectangular - and some of them still are: Navigator, Silhouette, Triathlon are all still made and still popular. Some people (including me sometimes) still jump the original Sabre, though it's not made any more. Colloquially, we call these "square".

Then manufacturers discovered that if you tapered the ends, they would turn faster (and thus dive harder) and fly more efficiently, and maybe quicker through the air due to reduced drag. This is the "high performance" part of ellipticality.

When tapered in a small way, this contributes mostly only good things to an otherwise square canopy - snappier turns, better glide and possibly flare (although it tends to make openings a little more wandery). Some manufacturers refer to these as "lightly elliptical" or "semi-elliptical", and they include wildly popular canopies such as the Sabre2, Pilot, Safire2/3, S-Fire, Spectre and many others. Confusingly, some manufacturers refer to things in this class as "elliptical" or even "fully elliptical", though it's not common.

Tapering beyong this point keeps upping the performance factor in terms of speed and roll and agility, but now you are starting to pay for it. Quick to roll and dive can mean quick to get into trouble - and highly tapered canopies have a tendency to oversteer and/or stay diving once you stop pulling things. If you get cut off in the pattern under your aggressively tapered Mamba, you need to have your reflexes under control and not yank on a toggle to evade, or you might find yourself in a bad place you're too low to get out of again. They are also definitely more prone to bad behaviour on opening! Popular canopies in this class include the Stiletto, Mamba, Zulu, Crossfire2/3, Katana and X-Fire. This is what people generally mean when they say "fully elliptical", or simply "elliptical" for short. There are lots of different shapes in this class, but they all have a noticeable taper on one or both edges.

NOTE: Some places have hard jump number requirements attached to canopies in this group, and for strong reasons.

(All modern cross-braced canopies are, of course, fully elliptical. But those are a whole 'nother thing.)

There is a lot of subtlety I'm missing out here - the models in my groups don't all fly alike and there are plenty or other factors involved, like steepness of trim, reliability of opening and recovery arc, that differentiate them. But, I hope this has answered your question about the word and how it's generally used, a little more directly.

Joellercoaster has the right answer here. To suppilment this, and from John Le Blanc's talk, I put together diagrams of planforms from various canopies for my canopy course.

The first image shows three planforms. The next shows you what they represent. Even the navigator is tapered, and would probably be considered "semi-ellipitcal". Not many non-reserves are rectangular. I can't think of any modern canopy that is.

Fun fact: The original Sabre is completely rectangular: No tapering.


(This post was edited by shadeland on Jan 28, 2018, 5:51 PM)
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RiggerLee

Jan 29, 2018, 8:59 AM
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Re: [shadeland] Correlation between elliptical canopies and aggressiveness? [In reply to] Can't Post

In regards to LaBlanks lecture on elliptical wings and plane forms.

The first thing you have to understand is that the theoretical optimum of an elliptical wing is actually a theoretical optimization of an elliptical lift distribution span wise across the wing. This is to reduce the induced drag component of the wing to a min. In theory the most efficient way to do that is through the area of the wing. He touches on all the trade offs in his lecture.

As to the difference in taper in the leading vs the trailing edge. What he fails to mention in relation tto that is the fact that the aerodynamic center of the wing is not at the center of the cord. This is why you see a lot of wings, like the spit fire, with greater taper on the leading edge. When you model an aircraft, this is kind of an old school discrription but very relevant to WWII, you look at locations of CG, wing AC, and tail AC. From this comes your basic stability. Looking closer at your wing. you examine it as a span wise line through the aerodynamic center of each wing section. Each wing section can be reduced to it's lift and drag and moment acting through the point of it's aerodynamic center. Generally a point 1/4 of the way back along the cord line. So you talk about the 1/4 cord point of that wing station. So let's design a wing. I take a straight line and and decide how big and how long and in this case how elliptical I want the wing to be. That gives me a span width and cord of the wing. That plugs into all of my stability equations and I can design the plane. Fine. So I go to build it. Well the 1/4 cord point of each rib arranged in a straight line gives you a wing with 3 times as much taper on the trailing edge then on the front. You get a Spit Fire wing. That is what an elliptical wing looks like.

It doesn't have to be this way. You can build the wing symmetrically. But what you are doing is warping the wing. Reducing it to the span wise line of lift, that line is now bowed. Now you can do some interesting things with this. It could affect where the center of lift is for example, under certain conditions. Let say in a side slip. Is the wing is swept back, which is kind of what we are talking about, then you will have more lift on one wing then on the other. This can affect the yaw/roll coupling. It affects how the aircraft turns and behaves dynamically in yaw and roll.

Same thing in a canopy. Even a bit more so. Keep in mind that the wing of a canopy wants to sit above your head stable at one point. But if you think about it each section of the canopy wants to sit above your head at it's own point based on it's own angle of attack which is dependent on induced drag of the wing and its individual effective angle of attack. Also keep in mind that a canopy is totally dependent on it's yaw pitch relation ship to roll into a turn. I've talked to people trying to model canopy dynamics and they have had at most moderate success. They've been hard pressed to get a model that matches even the most basic perturbation in a canopy. So their model in theory looks great. They are getting pretty good actual test data now when they jump it but the two don't match up. So it's still kind of in the voodoo phase. Lots of test data, lots of experience. They know what the variables are and pretty much what they do but to try a new design they pretty much have to build it. I don't know any one successfully predicting the dynamic behavior of there designs by computer model prior to test jumping the way we can with a rigid air frame.

Lee



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