Stall Surge on Tandems (or sport rigs)

[crazydiver 0]

I personally dont use the stall surge when landing tandems, however, I was thinking that there is no purpose to it...and heres why. I am interested in other physical properties of it that I am not thinking of. Here's my take...

when we put a canopy to the point directly before the stall, and let back up on the controls, essentially, the only acceleration and speed increase is the increase going back to full flight...so why would/should it give more lift on landing? In my theory, there is no speed increase past full flight with a stall surge. With carving turns yes, with riser turns yes, but the stall surge essentially just slows the canopy and pilot(s) down and then accelerates them back to normal full flight descent and thrust.

I'm interested in other takes on this and I would enjoy people correcting me, thats why I posted this...because I wonder if there is something i'm not seeing here.

I thought of this while hearing someone talking about not being able to land their "small parachute without swooping." Which is ridiculous. Eventually, the canopy must slow down its forward speed to the speed at which it would be at during a normal straight in landing so saying that a person can't land their parachute without swooping well is just poor piloting.

Edited for shitty spelling.

Cheers,
Travis

[AggieDave 6]

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I thought of this while hearing someone talking about not being able to land their "small parachute without swooping."

Hmmm...I know the canopies I've jumped (over 2.1:1) could be landed just fine with a straight in approach. I know folks who jump sub-100 canopies that say the same thing. The coaches I've talked to have stated that if they can't land right without a high performance landing, then they're doing something wrong. *shrug* Folks will believe what they want to believe, though.

As for the "stall/surge" method for tandems. If you do it high enough to allow the canopy to return to standard netural flight, then nope, no extra speed. It would be like doing it at 1000' then coming in for landing. Think of the dynamics being similar to doing a carving approach. You're doing something to make the canopy fly faster then it does in neutral flight. It recovers out of the dive but still maintains speed until it can't maintain that speed anymore and slows. It eventually slows to the point or returning to neutral flight. Obviously that's well over simplified, but I'm sure you understand the details in between. So you're entering your flare point with a bit more speed then what you canopy flies at while in neutral flight, and the speed helps with some lift.

I know it works well for me (gentle carve or stall/surge) when doing tandems, but that's just me. With that said I'll still come straight in and have good landing with a tandem. Its just a bit easier for me if I do something to slightly increase speed. Of course, I personally don't do any sort of full on hook maneuver with a tandem, but other TIs do with success.

Other TI's may find another method works better for them.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[skydivenagasaki 0]

Probably can't figure it out cause you can't figure out any canopy Course we've all seen my bullshit...

"and if you don't like it then 'Hey Fuck You'"
--The Beastie Boys--

[FlyinseivLP2 0]

Hmmm...I know the canopies I've jumped (over 2.1:1) could be landed just fine with a straight in approach. I know folks who jump sub-100 canopies that say the same thing. The coaches I've talked to have stated that if they can't land right without a high performance landing, then they're doing something wrong. *shrug* Folks will believe what they want to believe, though.

Yea I can land a velocity loaded at 2.5 straight in no problem too. But I want to see you land a Raven Reserve or something like that at the same wingloading. Canopy choice/design has something to do with it.

[AggieDave 6]

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Canopy choice/design has something to do with it.

Sure, but a certain amount of stupidity shouldn't be included in most folk's excuses. What I took away from the inital post are the folks jumping smaller Stilleto, or other high (or higher) performance canopies. Loading a canopy well beyond its design abilities isn't the greatest idea and the performance suffers hard. Obvisously there's a good debate right now about the high end of the market but there are many canopies that wingloadings are a given. Take the Raven, or the Spectre, or the Triathalon, etc.

As for a Velo loaded at 2.5:1, I'd have to land it straight in, since that would be a bit quick for me until I get some jumps on some stuff inbetween what I jump (and have jumped) and that.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[parachutist 1]

The stall surge is not good for landing your sport canopy, but it can temporarily increase forward speed and if done at exactly the right altitude it can provide for more lift (due to the extra speed) when flaring.

It increases speed because when you apply brakes to initiate the maneuver, the canopy slows down and the canopy is directly over your head, or slightly behind you (in full flight the canopy is slightly ahead of you). So when you let the brake toggles up, your canopy surges forward and you are now behind it. The canopy is racing forward trying to get back to full flight. Once it's in full flight your body is still behind the canopy, so your body swings forward as a pendulum.

If your body swings forward at just the right time (about the time that you're ready to start your flare), then you got the extra speed and therefore extra flare.
If the swing forward happens too high, then your body will swing back into normal position before flare time and you didn't gain anything.
If the swing forward happens too low (after you should have started your flare already), then you're going to impact the ground. When your body is swinging forward as a pendulum you have very little control. Flare won't give you much lift while you're swinging forward.

>>someone talking about not being able to land their "small parachute without
>>swooping." Which is ridiculous
Yes that generally makes listeners say "You've chosen the wrong canopy"

Chris

[Samurai136 0]

Keep in mind that flight characteristics of parachutes do not scale. Most of my tandem piloting experience is on the SET. Comparing the piloting techiniques of a SET loaded (usually) 1:1 to 1.2:1 (fatboys, heavily loaded) is totally different from piloting any other parachute at the same wingloading.

I'm wondering how you guys are comparing "high performance techniques" on a tandem loaded maybe 1.2:1 to "high performance techniques" on a sport parachute that is 4 times smaller and loaded twice as much.

They're totally different. Generally speaking, tandem mains are trimmed to fly very flat compared to a sport parachute. That's one factor in why the "stall/surge" technique works. Although, I've never thought of it a proper stall. It's more of a deep-brake flat turn/ "sinking it in" technique than a stall.

Usually to stall a tandem, you need the passenger to pull the toggles down to their knees and hold it there. The "stall/ surge" landing technique never really gets there.

"Buttons aren't toys." - Trillian
Ken

[davelepka 4]

The stall/surge does give you speed beyind full flight. The momentum of the canopy moving forward from far behind you carries it beyond full flight to a point out in front of you (aka a dive). It will return to full flight soon after that, so timing is key.

Every canopy can be landed without swooping. The higher you load, the higher the stall speed will be, and faster the stall will develop.

Canopies with very high loadings will often have a stall speed faster than jumpers can run. The 'sliding your feet on the grass' method (aka the Flintstone brakes) are one way to combat this. By pitting your landing gear down early, you partially unload the canopy, and raise the stall speed.

This is one reason jumper get dropped on their ass in distance comps. They have no Flintstone braking, and when the canopy stalls, you'll notice a good bit of forward speed still exists. The other reason is to go further.

Every techinque for canopy piloting works on any size canopy at any loading. The things that change are the altitude loss, turn rate, stall speed, and the speed at which the stall. As long as you account for these factors, you can do any manuver with any canopy.

[davelepka 4]

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Usually to stall a tandem, you need the passenger to pull the toggles down to their knees and hold it there. The "stall/ surge" landing technique never really gets there.

"Stall/surge" is just a name. You don't actually reach the stall point. Doing that on final would be beyond stupid.

The 'stall' is really a deep braked slow flight.

[phoenixlpr 0]

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But I want to see you land a Raven Reserve or something like that at the same wingloading.

Just for the record, what is the maximum recommended wing load for Raven Reserve? Is it 1.3?

[murps2000 86]

By pitting your landing gear down early, you partially unload the canopy, and raise the stall speed.
***

You mean lower the stall speed, correct?

[diablopilot 2]

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But I want to see you land a Raven Reserve or something like that at the same wingloading. Canopy choice/design has something to do with it.

True, but I have landed a "Raven" at over a 1.5 loading just fine. Now I wouldn't try landing a "MICRO RAVEN" at much over 1.3 but then they were not designed for it. The R-Max lands fine at those loadings and higher....as do the SMART and PDR's I've tried.

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You're not as good as you think you are. Seriously.

[davelepka 4]

Yeah, sorry.

[Calvin19 0]

If you want a crazy Aerodynamics answer, keep reading...

Any kind of suspension-ramair canopy such as skydiving canopies and paragliders/powered parachutes have an EXTREMELY pitch Stable characteristic when compared to all other forms of aircraft.

Pitch stability, can easily be modeled as a ball rolling back and forth in a bowl... If something is pitch stable, the bowl will not allow the ball the roll out of it, when disrupted (stallsurge) it will roll back and forth until it lays dormant in the middle of the bowl. Ram air suspension canopies have bowls with very steep sides, so they recover quickly(small, highly loaded canopies have the same, just less steep)

Basicaly this means that when you disturb the canopies dormant (level) flight, it will speed up to faster than its dormant flight on recovery(speed and lift are less than needed to sustain flight), then slow down (because speed/lift are in exess, therefor work is done against gravity) to below its dormant flight after its dive(, and again will gain speed above its dormant flight...

Thereticaly this cycle will continue, but keep getting smallerin value, but with the inefieciency of skydiving canopies, it becomes unoticeable after 1 or 2 cycles.

BUT....

of course the whole point of this stall/surge teqnique is not to give more forward speed but to give less (as in 0) vertical speed at the right moment when landing. So, if the canopy is effeicient enough to use this excess forward speed to produce enough lift and not break the students legs... then we are good.

SOOOO....


to answer the question, from an aerodynamics perspective, i would say the stall/surge method is a functional teqnique for landing a parachute... especialy when using risers for canopy acceleration is not a great option.

[diablopilot 2]

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to answer the question, from an aerodynamics perspective, i would say the stall/surge method is a functional teqnique for landing a parachute... especialy when using risers for canopy acceleration is not a great option.

However from a practical standpoint you'll probably have a different opinion if you ever make more than a few hundred landings under a tandem canopy with a student.

It's not just for fun that TI's have been using that technique for 15+ years, and millions of landings.

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You're not as good as you think you are. Seriously.

[Calvin19 0]

[reply
It's not just for fun that TI's have been using that technique for 15+ years, and millions of landings.