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cosmicgypsy

Toggle pressure and what effects it.

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It relates to load in the since that it will be a percentage of the load of the canopy. Load in this context is not wing loading but total suspended weight but is also controlled by g loading. If you are in a 2 g pull out the loading and control forces are doubled. 

 

Trim is a factor. The steeper the trim of the canopy the more the canopy will be front loaded. Nose down, front riser pressure higher. Flatter trimmed, front riser pressure lower. In terms of toggle pressure nose down means lighter toggles and flatter canopies heavier pressure. Some people will argue that the added airspeed of a steeper canopy increases the toggle pressure but I think they are confusing it with the g loading. To examine it rationally you have to look at the percentage of load on the toggles.

 

Lee

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6 hours ago, RiggerLee said:

Trim is a factor. The steeper the trim of the canopy the more the canopy will be front loaded. Nose down, front riser pressure higher. Flatter trimmed, front riser pressure lower.

That's interesting. Naïvely and without giving it much thought, I thought it was the opposite. The Katana, for example, is a notorious steeply trimmed canopy, and the front riser pressure is ridiculously low. 

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5 hours ago, Deimian said:

That's interesting. Naïvely and without giving it much thought, I thought it was the opposite. The Katana, for example, is a notorious steeply trimmed canopy, and the front riser pressure is ridiculously low. 

Also my experience. Flat trimmed canopies like Stilettos have higher front riser pressure.

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15 hours ago, RiggerLee said:

Trim is a factor. The steeper the trim of the canopy the more the canopy will be front loaded. Nose down, front riser pressure higher. Flatter trimmed, front riser pressure lower. In terms of toggle pressure nose down means lighter toggles and flatter canopies heavier pressure. Some people will argue that the added airspeed of a steeper canopy increases the toggle pressure but I think they are confusing it with the g loading. To examine it rationally you have to look at the percentage of load on the toggles.

 

Lee

 

8 hours ago, Deimian said:

That's interesting. Naïvely and without giving it much thought, I thought it was the opposite. The Katana, for example, is a notorious steeply trimmed canopy, and the front riser pressure is ridiculously low. 

 

2 hours ago, gowlerk said:

Also my experience. Flat trimmed canopies like Stilettos have higher front riser pressure.

That's interesting. And also my experience.

I know better than to argue much with Lee about this stuff. 

But, on a 288 Manta, I could pretty much do pull ups on the front risers. The canopy would barely deflect, even though I was pulling up enough to unweight the leg straps. 

 

Yet I could do 180s or more pulling a front riser on a Triathlon 190 and a Sabre2 170

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There are so many different factors involved, it gets confusing and I don't know the answers either.

Some variations:

1.  RiggerLee mentioned, "In terms of toggle pressure nose down means lighter toggles and flatter canopies heavier pressure."
I can't say how it is in general, but I recall one counter example. Have an old, large F-111 canopy (Titan 265) that I used to use for accuracy. It had high toggle pressure. I added an extra rapide link at each front riser (and even played with using 2 extras), so the canopy trimmed flatter and flew slower. The toggle pressure in turn went DOWN and was more pleasant to work in deep brakes.

2. Sometimes comparing a steep and shallow trimmed canopy is confounded by different styles and sizes of canopy. For example, one doesn't normally get to compare a (non-existent) Katana 280 against a Navigator 280. And is one comparing how much force it takes to pull a front riser down half an inch, or is one thinking of the final effect of pulling a front riser down?  After all, even if a small and large canopy have the exact same front riser forces, you might think, "Ugh, this big canopy is a boat, I'm hauling down the front riser and almost nothing is happening", while on the small canopy you whip nearly instantly into a sharp diving turn and even if you need a solid pull, you only need to do it for a second.

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I can compare JojoWings Raptor 135 (steep) vs Icarus World X-Fire 138 (shallow), I've recently flown both.

Raptor is very light on front risers and toggles are a real workout. On the other hand, X-Fire has much heavier fronts and the toggles are much lighter.

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Changes in suspended weight definitely change toggle pressure.

For example, if I jump the same Icarus 360 tandem canopy with a light-weight student, then a heavy weight student, toggle pressure dramatically increases.

With the light-weight student I can practice rear riser turns and rear riser flares before unstowing brakes, Then repeat the control check after releasing brake toggles. I like to practice rear riser manuvers in case I suffer a jammed toggle some day. Knock on wood!

OTOH, with a heavy student, any rear riser manuver is like trying to bend a steel crow-bar!

Hah!

Hah!

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On 1/11/2021 at 7:38 PM, RiggerLee said:

It relates to load in the since that it will be a percentage of the load of the canopy. Load in this context is not wing loading but total suspended weight but is also controlled by g loading. If you are in a 2 g pull out the loading and control forces are doubled. 

 

Trim is a factor. The steeper the trim of the canopy the more the canopy will be front loaded. Nose down, front riser pressure higher. Flatter trimmed, front riser pressure lower. In terms of toggle pressure nose down means lighter toggles and flatter canopies heavier pressure. Some people will argue that the added airspeed of a steeper canopy increases the toggle pressure but I think they are confusing it with the g loading. To examine it rationally you have to look at the percentage of load on the toggles.

 

Lee

So Lee, after reading and digesting a bit on this. Would it be safe to say that a canopy like something for accuracy or CRW would be trimmed more nose down? On the other side of that would something more for swooping be trimmed more nose up? Or do I have this backwards?

Cosmic 

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You have that backwards. Swooping canopies are trimmed nose down. They need that to get the necessary speed for a swoop. Accuracy canopies are trimmed very flat, so they are slow and give the pilot time to correct and hit the target. CRW canopies are something in between.

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3 hours ago, Deimian said:

You have that backwards. Swooping canopies are trimmed nose down. They need that to get the necessary speed for a swoop. Accuracy canopies are trimmed very flat, so they are slow and give the pilot time to correct and hit the target. CRW canopies are something in between.

Got it. Thanks

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I missed part of the conversation but I'll try to clarify my remarks. 

First some of the examples given have been comparing different canopies one being steeper then the other. Often what they mean by that is that one has a longer dive then the other which is not exactly the same thing. In doing this they are also comparing two different air foils, plane forms, break line configurations etc. So for example the location of the maximum thickness may be at a different location cord wise on an air foil. Or it may be thicker. The pitching moment may be different affecting the pitch stiffness. The point is that you tend to be stuck comparing Apple's and oranges which tends to be anecdotal. 

 

I'm looking at this from my experience tinkering with crw canopies. Crw canopies are one of the very few examples where you can get the same canopy in different trim configurations. Steep of flat. Short or long. You name it. And that's just the starting point. No crw dog deserving of his hook knife has ever been able to resist tinkering with and retrimming their canopy.

 

I mostly did bigger way stuff but this was kind of the thought process at the time at least among the people I knew. Keep in mind that the ideas of how best to set up your canopy are constantly evolving and vary from one team to another.

So of the three disciplines rotation sequential and eight way. Their thought was that in rotation you wanted to be able to drop as fast as possible relative to the formation. Ether by stalling back over the top and dropping through the wakes behind the stack or by turning off to the side and cutting back in behind it in a quick sashay. The thought was you wanted the canopies as flat as you could get away with. You wanted the stack to be floaty. But more important you wanted the rotating canopy to be maxed out on Cl. When he popped the toggles or rears to drag him back over the top of the stack you wanted to already be on the edge of stall so there was no more lift to pop you high up off the top of the stack. Pretty much the same thing if you were going to turn off to the side. You didn't want extra lift. So basically you trimmed it real flat adding an extra link and then trimming the lines. Some of the canopies were so flat that you flared them with the front risers.

 

The the thought process was reversed with sequential. They had the thought that in flying peaches or changing slots that you wanted to be able to float relative to the formation. They trimmed steep to be able to get on the rears and float relative to the other canopies with out dropping behind. Or at least that was the idea behind the old expresses. 

 

So you got to play with the same canopies at both ends of the spectrum. This is where my observations come from. That when you trim the canopy flat the fronts become soft and are easy to pull down. When you trim it steep. The load on the front risers increases. One secret of pulling down the fronts on a heavy canopy is to tap the breaks to rock it back before grabbing the fronts as it rocks back forward. It will soften it up enough to let you get locked in. Part of that is the angle of attack and part the dynamic easing of the load. 

 

The increase in load towards the front of the canopy is why I tell people that it's in some ways safer to trim a canopy more nose down when tinkering. More lift at the front of the canopy improves the stability and you have plenty of room to increase the Cl so you can have flare authority to kill your sink rate on landing. Contrast that with a very flat trim on the same canopy which tends towards soft front risers. When you try to flare there is nothing left. It just stalls. That is why you wind up doing front riser approaches may be with a bit of turn and killing your sink rate by letting up on the front risers and just finish out the landing with your toggles hoping you can slide or run it out. Going flatter is defenintly trickier and should be approached with more caution.

 

That got longer then I intended. This information is some what out of date. I hear the newer crw canopies are much nicer and not even scarry to land. I would really like to put some jumps on them some day. But right now I'm stuck here in isolation playing nurse maid.

 

Lee

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4 hours ago, RiggerLee said:

Often what they mean by that is that one has a longer dive then the other which is not exactly the same thing.

True, for the canopies I've compared above (X-Fire and Raptor) I assumed that longer cycle on Raptor + greater vertical speed meant that Raptor was steeper. Though I just checked the trim charts and yeah, Raptor really is steeper (trimmed more nose down). The fact that they're two completely different planforms and shapes in general remains.

Does anyone know of any example of two canopies where one has a longer cycle but is trimmed more flat than the other one? I know it's a far fetched question, but can't hurt to ask.

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On 1/25/2021 at 9:57 PM, RiggerLee said:

I missed part of the conversation but I'll try to clarify my remarks. 

First some of the examples given have been comparing different canopies one being steeper then the other. Often what they mean by that is that one has a longer dive then the other which is not exactly the same thing. In doing this they are also comparing two different air foils, plane forms, break line configurations etc. So for example the location of the maximum thickness may be at a different location cord wise on an air foil. Or it may be thicker. The pitching moment may be different affecting the pitch stiffness. The point is that you tend to be stuck comparing Apple's and oranges which tends to be anecdotal...

Ok. Thank you.

Your comparisons are very much 'apples to apples', where the only real thing changing is trim. 

Mine are much more 'apples to bunny rabbits', where everything changes. 

As I noted, I'm very reluctant to disagree with you on this because your knowledge and experience is so far beyond mine (again, 'apples to bunny rabbits').

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