Forums: Skydiving Disciplines: Swooping and Canopy Control:
High speed stalls

 


spankee  (Student)

Feb 21, 2011, 4:50 AM
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High speed stalls Can't Post

I have been advised in the past to find / approach the stall point in straght and level flight (up high!) for both toggles and rear risers.

I was wondering if this stall point i.e. position of toggles and risers would be the same or different if applied at high speed (for example in emergency recovery from an aborted swoop).

Has anybody experienced a high speed stall with their canopy or have any thoughts on this?


AggieDave  (D License)

Feb 21, 2011, 5:00 AM
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Re: [spankee] High speed stalls [In reply to] Can't Post

Quote:
I was wondering if this stall point i.e. position of toggles and risers would be the same or different if applied at high speed (for example in emergency recovery from an aborted swoop).

In my experience, the toggle stroke is much longer than the riser pull when entering that "problem."

If you have the chance, go up top and try some "recovery drills." Be alone under canopy (solo altitude clear and pulls are great for these), clear your airspace and smoothly initiate a diving maneuver. Immediately try to arrest your dive. Do the same with toggles and rear risers. See what the altitude difference between the two are. Also you will experience two similar, but different reactions from the canopy. You should be able to feel the difference as well.

A continuation along this thought:

Typically, though, when skydivers hurt themselves under canopy, by the time they made the low turn, it was much too late to recover from it. Although they would be better served to try to get under their wing and PLF for their life (using toggles to get there). Furthermore, there is no reason why someone should be trying to recover a too-low-turn-to-swoop on rears outside (and sometimes with in) a serious competition over water.

The first reaction to a chain of bad decisions that lead up to a low turn should be wing level. I like to teach "STOP!" That means, flare out and slow everything down. That gets people back under their canopy so they can have a chance of a PLF. It's hard to PLF if your canopy hits before you do!


Martini  (D 23756)

Feb 22, 2011, 8:50 PM
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Re: [spankee] High speed stalls [In reply to] Can't Post

Excellent question. I've often wondered the same thing but only as it applies to toggle input. During the sharp recovery arc created by strong brake input on a diving canopy the wing should experience a temporarily high wingload, higher wingload means higher stall speed. That part seems apparent but I'm only speculating. OTOH the wing may compensate for that effect by being more pressurized or from some other factor. My instincts tell me the canopy should enter a stall with less input during recovery but my experience doesn't agree. I hope someone with definitive answers will chime in.


floormonkey  (D License)

Feb 22, 2011, 10:23 PM
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Re: [Martini] High speed stalls [In reply to] Can't Post

Stalls are related to your angle of attack, not just your airspeed. When you pull your rear risers, it changes the angle of attack sooner (because more of your canopy deflects) then pulling on the toggles (longer time/distance to change the AoA). Stalls also are related to the shape of the wing you are flying.

Stalls are covered on pages 18-20 in The Parachute and its Pilot by Brian Germain.

They are also covered in the SIM (http://www.uspa.org/LinkClick.aspx?fileticket=eftnWLyVdVo%3d) on pages 50, 67, and 159ish.

And, of course, there's the article here on dz.com: http://www.dropzone.com/content/Detailed/637.html

That doesn't exactly answer the question, but with those resources and some clear airspace, you should be able to tell us on Monday.


morris

Feb 23, 2011, 9:18 AM
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Re: [AggieDave] High speed stalls [In reply to] Can't Post

In reply to:
Quote:
The first reaction to a chain of bad decisions that lead up to a low turn should be wing level.
Id like to add something as wing level might not be precise enough.
Being in a too low diving turn the emergency rule is "1.Pitch,2.Roll!"
You need to slow down your rate of descent asap, to stop turning has not the highest priority.
For whatever reason people often stop the turn first before they try to bring the pitch up to stop the descent, wasting time/alti. In a real emergency, if executed correctly, you might arrive at groundlevel while still turning, but without the REAL danger of a high rate of descent. The opposite szenario is way more dangerous.
This can be drilled up high.
Initiate a diving turn, lets say to the left.
Wrong:
Hit the right toggle to stop the turn, continue with both toggles to stop the dive.
Correct:
Hit both toggles to stop the dive, continue pulling the right toggle to stop the turn.
Done this way youll end up in level flight while still turning (before you continue to apply toggleinput on the right) = carving as hell (fun!).
Try both "versions" to feel the difference.
Exception from the rule:
If your turn is that aggressive that your wing is level with the horizon some stopping of the roll (= bringing the wing back up) is necessary to make the + of pitch really stopping your dive as fast as possible.
In this situation you should nevertheless start pulling down both toggles from the beginning on, just pull a bit more/faster on the right side...
Regarding the original question:
At a slow airspeed the air is able to "follow" the profil for longer (a more deflected wing) than at a higher airspeed. Therefore the stallpoint is reached sooner at higher airspeeds, bad news.
But there is a way around this!
Imagine this drill:
Aggressive turn, stop turning, canopy on final heading, recovery just starts (up high please), hit both toggles hard, all the way, trying to end up in level flight (or even climbing big time) asap.
In this szenario there is a maximum speed you can pull down your toggles without creating a highspeed stall. Now imagine pulling your toggles only half way down.
What is the benefit?
If you are pulling less distance, you can pull even faster without creating a stall.
The speed of the input is of way more importance for the overall outcome than the distance (inches) of the input!
So you can recover even faster while pulling less distance but faster!! Not kidding!
In a real emergence this brings another benefit into the picture.
Szenarion 1, pulling all the way:
The aggressive toggleinput will bring you from way behind to somewhere in front of your wing/somewhere in front of the neutral position under the wing. From this "place" behind you, your canopy will pass over your head (overshooting) to the front before returning to neutral flight. Not something you wanna have if the ground is right there...
Szenario 2, pulling half way down:
While being swung in front, being in 1/2 brakes, watch your wing (up high) as the wing comes back over your head, the moment it (the wing) is about passing over to the front, apply what is left of toggleinput! This will avoid the chute from overshooting! In a real emergency you might even be able to create a nice soft landing with a well executed flare from half brakes. But this should just be an option if you know your wing very(!) well, otherwise and if in doubt, Id always recommend a PLF...


Martini  (D 23756)

Feb 23, 2011, 11:44 AM
Post #6 of 15 (1278 views)
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Re: [floormonkey] High speed stalls [In reply to] Can't Post

Quote:
That doesn't exactly answer the question, but with those resources and some clear airspace, you should be able to tell us on Monday.

It snowed 8" here today and it's not even noon yet. Shocked


Thanks for the response and the links. Most of the discussions are theory, this from the SIM:
D. H igh-sp eed stall
1. Occurs at any speed when the canopy reaches too high
of an angle of attack
2. Easily induced as a result of distorting the wing too far
during a rear-riser flare

Little info on actual performance though. Brian's info in "The Parachute and its Pilot", which I own, is far more detailed of course but the original question remains. So yes, I'll just have to do a high hop n pop and play with the stall point, I'll try to do it on one of my Sabres and also on my Xaos to see if there is any real difference. BTW not only have I never stalled a wing digging out a low hook but I don't remember ever seeing it happen watching swoop videos that inlude plenty of low digs.


(This post was edited by Martini on Feb 23, 2011, 12:15 PM)


d123  (B 6134)

Feb 23, 2011, 9:39 PM
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Re: [morris] High speed stalls [In reply to] Can't Post

If we had an "I like" button for each post, I would press it for your post in a heartbeat.


phoenixlpr  (D 3049)

Feb 23, 2011, 10:30 PM
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Re: [d123] High speed stalls [In reply to] Can't Post

In reply to:
If we had an "I like" button for each post, I would press it for your post in a heartbeat.
It sounds like you already spent too much time on a certain social(???) site.Tongue


morris

Feb 24, 2011, 6:39 AM
Post #9 of 15 (1134 views)
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Re: [d123] High speed stalls [In reply to] Can't Post

!Thank you!
Good to hear that the time to write this kind of stuff isnt wasted. Im not a native speaker and Im not typing fast, this takes time...

And in reply to:
BTW not only have I never stalled a wing digging out a low hook but I don't remember ever seeing it happen watching swoop videos that inlude plenty of low digs.

I guess we dont need to talk about the dangers and limitations of digging out on rears, rearisersstalls, blablabla...
Digging out on toggles can create stalls. I agree that this isnt happen often and that you really need to apply some very serious input to create that kind of result, but Ive seen it more than once.
In my courses persons are experimenting with "emergency flares" and ultra fast recoverys.
Most of them are not creating togglesstalls - but some do/are able to.
If they dont, one reason (among others) might be that the are not applying the most aggressive possible input ("Ok, on this one, try to break your brakelines!" :-) ).
But if someone is about hitting the ground, he might hit the toggles hard enough to get "his chute in trouble"...
However, most of the times - in real emergencies/accidents/low turn situations - people are not apply enough input to avoid hitting the ground because they are scared of stalling the wing (not knowing their wing well enough!) while they actually are still far away from stalling it.
So practising/experimenting with different types of "serious toggle inputs" for fastest possible recovery is always a good idea...
I need to go...


danielcroft  (D 31103)

Feb 24, 2011, 4:28 PM
Post #10 of 15 (1071 views)
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Re: [morris] High speed stalls [In reply to] Can't Post

I'll second that "like" thank you Morris. I have some testing to do early this season. Smile


AggieDave  (D License)

Feb 24, 2011, 6:03 PM
Post #11 of 15 (1058 views)
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Re: [danielcroft] High speed stalls [In reply to] Can't Post

In reply to:
I'll second that "like" thank you Morris.

Same here, although I'm hesitant to really talk/teach about rolling out with out the wing level as a survival skill to all but the more advanced canopy pilots. The majority of people I'm teaching and the majority of the people reading here would do better to focus on keeping out of those situations, flat turns and to get the wing over their head and PLF to save their life.


Calvin19  (D 29712)

Feb 24, 2011, 8:22 PM
Post #12 of 15 (1050 views)
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Re: [spankee] High speed stalls [In reply to] Can't Post

This is a accelerated spin-stall. Asymmetric obviously. The loading is increased about 3 fold. (this is a speed glider wing, easily capable of that).
The wing fully stalls, yaws, and spins me up. good times. I did this a few more times on that flight at different riser loads (weight shift input).

http://vimeo.com/16226960


morris

Feb 25, 2011, 5:39 AM
Post #13 of 15 (1002 views)
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Re: [AggieDave] High speed stalls [In reply to] Can't Post

Quote:
Same here, although I'm hesitant to really talk/teach about rolling out with out the wing level as a survival skill to all but the more advanced canopy pilots. The majority of people I'm teaching and the majority of the people reading here would do better to focus on keeping out of those situations, flat turns and to get the wing over their head and PLF to save their life.

Dave, Im with you, agree on everything of the above/everything youre saying 100%!


stayhigh  (F 111)

Feb 25, 2011, 6:46 AM
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Re: [morris] High speed stalls [In reply to] Can't Post

can you reach high speed toggle stall, even when your toggle is set long enough so that you can't ever stall em???


morris

Feb 25, 2011, 11:01 AM
Post #15 of 15 (953 views)
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Re: [stayhigh] High speed stalls [In reply to] Can't Post

"...even when your toggle is set long enough so that you cant ever stall em???"
How long?
How far "out of reach" is the stallpoint?
As always the answer to your question depends on many things (type of canopy, WL, blablabla) but if you want me to keep it as simple as possible Id have to say "yes, you can!"
Depending on how far "out of reach" your togglestallpoint is and - in the first place - how aggressive your input is, you will very likely be able to stall it. If you are going for the most extrem possible input ("trying to break the brakelines") the stallpoint will very likely being "within reach". If you are giving it at try and it doesnt stall, ask yourself if youve really been shooting for the most aggressive ("I-wanna-break-the line") type of input. Most people dont dare to give that much of an input (or sometimes arent even able to for physical reasons) in a "training-szenario" - something that can be different if they are about impacting the ground...
However - now it gets important - I DON`T RECOMMEND to achieve this kind of stall to anyone. As this might sound opposite to what Ive written above (somewhere), let me explain:
I have persons experimenting with aggressive inputs, doing this the goal is not to create this kind of result, were not going that far. The goal is to get familiar with way more aggressive inputs than what persons are usually used to, to have them applying an input aggressive enough to safe them, if the time comes they need it.
(Hopefully never,"stay out" comes first, see Dave above!)
Once in a while someone is "obeying too much" to what Im telling him and skipping a step (or three or four, many...) on the way towards more and more aggressive inputs (the last one was a soldier) and those are the once coming down "Holy ____!"
If you go for it, dont blame me for ANY outcome, including being "scared as hell/to death" (chutes dont like it at all!!), cut-aways (by the way, Optimums rock!) or worse!
Dont be scared to experiment with "reasonabel inputs" as it really takes something to "get in trouble", but keep this in mind!

I dont wanna say anything more detailed as anything Im able to do here is "written only" and as I mentioned, Im not even a native speaker.
Of course the internet is better than "by trial and error only" but this - as anything that might be dangerous - is something that belongs under the supervision of a qualified coach with a reasonable reputation.
Problem is:
How does someone know if something can "result in trouble" or worse??
See, always a good idea to see a good canopycoach!

Hope this answered your question well enough...



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