Why did this happen?

[matttrudeau 0]

So I made my first AFF jump this weekend. Everything went great. Excellent exit, good awareness, and good practice ripcord pulls. But when I was about 100 feet off the ground approaching the landing area my canopy felt like it almost collapsed on one side for a moment. The wind that day was bisecting the runway so I was parallel to the runway and then turned left into the wind. People on the ground told me that I was too close to being over the runway and it caused thermals which made my canopy shake. Is this right? Also, I'm only 145 pounds and I was under a Navigator 240. Being so under loaded, would this cause the canopy to react to more turbulance? One more thing, could I approach the landing zone in half brakes to help with turbulance until I approach and go in at full speed until flair? Thanks for you help!

[SkydiveMonkey 0]

Thermals coming off a runway will cause turbulance and your canopy will buck a little. In turbulence, you want your canopy to stay pressurised, and that means letting the canopy fly on full drive. Lightly loaded canopies like student ones will be more suseptible (sp?) to turbulence, but due to their big size, it won't be as much of a problem if one or two cells close off as on a smaller canopy.
When I grow up, I want to be a post whore

[rendezvous 0]

If you are experiencing turbulance let the canopy fly, full flight. Don't apply any breaks.

[hobbes4star 0]

if you ever feel turbulence let it fly, that way the canopy stays rigid with air pressure and is less likely to collapse
why jump when you can fly

[billvon 2,691]

>One more thing, could I approach the landing zone in half brakes to help with
>turbulance until I approach and go in at full speed until flair?
Yes, but that's something you should discuss with your instructors. If you do it too low you can land very hard since the canopy will not recover before the flare. Generally, 1/4 to 1/2 brakes will help your canopy remain inflated through turbulence. If you do have to land in 1/4 brakes, it is doable on a larger canopy as long as you don't let them back up.
Again, this is background only. Ask your instructors before you decide what to do in the future.
-bill von

[Michele 1]

Hey, Matt! Great to see you here!
Congratulations on making it into the air - told you it was amazing!
I have absolutely no tips other than to say talk to your instructors, contantly ask them questions, and listen to what they say!
Pleased to see you in the sky, Matt!
Ceils and Pinks-
Michele
If you really want to, you can seize the day; if you really want to, you can fly away...
~enya~

[polarbear 1]

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Generally, 1/4 to 1/2 brakes will help your canopy remain inflated through turbulence.

That seems a little counter-intuitive to me. The faster the canopy flies, the higher the pressure in the cells and thus the more stable. I had operated under the belief that flying in brakes will help the canopy reinflate more quickly in the event of a collapse, but flying in full flight results in higher cell pressure and reduces the likelihood of the collapse. Any thoughts?
I suppose that it has some to do with where the stagnation point is on the cell mouth...if pulling the brakes in a little moves the stagnation point closer to the center of the cell mouth, I suppose that might make it less susceptible to turbulence. I fly in full flight and make smooth, light control inputs.

[Geoff 0]

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Generally, 1/4 to 1/2 brakes will help your canopy remain inflated through turbulence

This one's been debated here a few times, but I really don't agree, and neither do PD.
"Contrary to what some people have been told, flying in brakes does not necessarily help keep the canopy pressurized. Aerodynamically, the canopy is actually more susceptible to turbulence in brakes. Years ago, flying in half brakes seemed to make some of the earliest canopy designs more stable in turbulence, though they were obviously very different from modern canopies. Flying in brakes is definitely not the best technique to use with the canopies we're flying today, although a lot of skydivers are still told to use this technique. "
....taken from here.
Geoff

[GrumpySmurf 0]

This is just guessing, so I might be out to lunch.
Seems 'turbulence' (as we experience it) comes in two forms -1) horizontal - generally moving in a path parallel to the ground - rotors off buildings, or disturbances at the point of contact between winds at different altitudes going in different directions and/or speeds.
2) vertical - perpendicular to the ground - thermals off a plowed field or runway.
The best way to get through a disturbance is probably to get through it as quickly as possible - horizontal by passing down through it or vertical by passing horizontally through it. Flying in any sort of brakes is going to slow you down in both the vertical decent and horizontal translation. The longer you remain in the disturbance, the greater the chance of it messing up your day?
Like I said, wild guess out to left field.

[billvon 2,691]

>Flying in brakes is definitely not the best technique to use with the canopies
> we're flying today, although a lot of skydivers are still told to use this technique.
Most student skydivers are not jumping Sabres or Stilettos, much less more modern canopies. In my experience, 1/4 brakes helps keep larger F111 canopies inflated in turbulence.
-bill von

[skybytch 259]

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This one's been debated here a few times, but I really don't agree, and neither do PD

I can only speak from personal experience here... this weekend for example. It was really bumpy at Perris. Hands off on my Spectre (loaded at about 1.0) and it was bucking and turning without input. I went to quarter brakes and it flew fine. Everytime I let up on the brakes the canopy would start bucking and turning and dropping on me.
So, imho, on my canopy anyway, flying in quarter brakes works.
pull & flare,
lisa
---
On the other hand...you have different fingers

[skyhawk 2]

a tip dont reach out ive had this happen to me a couple of times and ive reached out to protect myself, but im still flaring so it just increases the turn and hurts Opinions are like a-holes everyone has one, the only one that does you any good is yours and all that comes out is shit

[billvon 2,691]

>The best way to get through a disturbance is probably to get through it as quickly
> as possible - horizontal by passing down through it or vertical by passing
>horizontally through it.
Turbulence is defined as change in wind over time. If it goes from 10kts to 15kts in 30 seconds it's a non event. If it goes from 10 to 15kts in 1/2 second you will feel a very significant bump. By flying faster you traverse the change more quickly and thus see more turbulence. (Note that a hot air balloon, the slowest possible vehicle. very rarely sees turbulence even on bad days.)
In addition, it is worth noting that pilots of aircraft slow down in turbulence to avoid overstressing their aircraft.
>The longer you remain in the disturbance, the greater the chance of it messing
> up your day?
True - but the faster you fly through it the worse it will be (albeit for a shorter time.) On the plus side your canopy is better pressurized at the higher speed. Which is the better plan depends on your canopy, altitude, and type of turbulence. I've found that for larger canopies, 1/4 to 1/2 brakes is generally the best solution. For smaller canopies at altitude, full flight generally works the best.
-bill von

[puffdaddy 0]

Hi Bill
Have to agree with you there. Flying with some brakes makes a lot of difference to how the canopy reacts. A common thing tought to paraglider pilots in strong turbulence is to apply some brakes to keep the cell pressure up in the canopy. In one of the other post here Polarbear indicated that this sounded counter intuitive him. Just think about a situation of end-cell closure. You do deep pumps on the brakes to re-inflate the cells. That action is pressurizing the canopy. With modern canopies I believe that hands -up flying and the correct wing loading makes the difference.

[polarbear 1]

Hmmm...I'm not sure that pumping brakes increases cell pressure. Slower flight=lower stagnation pressure=lower cell pressure. I suppose this would be true in steady state. If you had a highly pressurized canopy, and then pulled the brakes down, it would sort of be like squeazing the air out of the canopy during packing...at first it ballons up in high pressure, but eventually the pressure subsides.
On most canopies, the end cells actually have a lower angle of attack then the center cells because of the anhedral angle. This means the stagnation point is closer to the top surface. I had been thinking that end cell closure resulted from the mouth of the end cell getting pinned down by the stagnation point. Pulling the toggles (or rear risers) increases the angle of attack, helping to move the stagnation point off of the pinned-down cell mouth. In addition, the pressure is momentarily increased in a transient, as described above. Together, these cause the end cell to inflate.
In steady state, I don't see how flying in brakes creates higher cell pressurization
I suppose that's all pretty academic. In the end I guess it depends on the canopy.

[GrumpySmurf 0]

Ahh, thanks for clearing that up - now I feel educated So if any of you are on a commercial flight, and some yutz starts yelling from the back, towards the pilot (during turbulence), "Slow down dammit!" - it's me

[alan 1]

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(Note that a hot air balloon, the slowest possible vehicle. very rarely sees turbulence even on bad days.)
In addition, it is worth noting that pilots of aircraft slow down in turbulence to avoid overstressing their aircraft.

I don't think these are good points. The balloon does not rely on airspeed to remain inflated and flying. Powered, fixed wing ac fly at speeds and altitudes where turbulence is greater and have a greater possibility of transitioning the ac into exceeding the vne. Do fixed wing pilots also reduce airspeed in the landing pattern (we generally fly our canopies under 3000' agl) when it is turbulent? Do they increase the flap setting? There is much less of a gap between the cruise and stall speeds our canopies than on fixed wing ac. If we fly in brakes, we are flying even closer to the stall speed and suddern turbulence may be more likely to be enough to cause a stall. Remember, we are flying non-rigid, ram-air wings, generally at relatively low altitudes, at relatively low airspeeds that do not come even close to a vne, although I doubt that any manufacturers even publish one for a parachute (well, maybe max. deployment speed, but how often do we approach that after we have begun flying the canopy). Collapse is the issue, not overstressing. The aoa is not constant on all ram-airs. Some may have a degree of wash out designed into the wing and others may not. For an older F-111 type canopy, the technology wasn't used, so adding 1/4 brakes increased the aoa at the wing tips and helped prevent them from deflating and assisted in a more rapid re-inflation if there was a collapse. Newer designs incorporate technology that helps to keep the wing tips inflated during turbulence without the need to fly in brakes. So, in my opinion, to some degree, it seems as if everyone is at least a little bit correct here.
alan

[Spy38W 0]

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Do fixed wing pilots also reduce airspeed in the landing pattern when it is turbulent? Do they increase the flap setting?

No and No, on final approach we typically increase the speed by 1/2 the gust factor, and use a partial flap setting.
--
Give them a sip of the darkside, and they just thirst for more.

[billvon 2,691]

>Powered, fixed wing ac fly at speeds and altitudes where turbulence is greater
>and have a greater possibility of transitioning the ac into exceeding the vne.
That's not why they reduce speed. They reduce speed so that a sudden attitude change caused by turbulence will not overstress the airframe. This can happen even below Vne.
>If we fly in brakes, we are flying even closer to the stall speed and suddern
>turbulence may be more likely to be enough to cause a stall.
Agreed, and this is why I recommend 1/4 to 1/2 brakes for larger canopies. The difference between full flight and 1/4 brakes is perhaps 3-4 mph; not that significant when it comes to avoiding a stall. However, if you _do_ stall part of the wing, partial brakes is a very good position to be in. It is how your canopy is designed to reinflate to begin with, and it is a good position to land in if you are stalled.
Smaller canopies cannot be landed safely when stalled (i.e. cannot be sunk in like an accuracy canopy.) In addition, the difference between 1/4 brakes and full flight is much more significant. Therefore the above doesn't apply.
-bill von

[alan 1]

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That's not why they reduce speed. They reduce speed so that a sudden attitude change caused by turbulence will not overstress the airframe. This can happen even below Vne.

That doesn't invalidate the point I was making. Yes, an ac may be overstressed without exceeding the vne, but exceeding the vne _implies_ that the ac may be overstressed. You ignored the meat of the post to nit pik on semantics.

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Agreed, and this is why I recommend 1/4 to 1/2 brakes for larger canopies. ........

Yes, here we agree. My post was an attempt to bridge the gap between what worked on older design F-111 type canopies and the newer zero-P elliptical designs. At least that was what I thought I was doing when I posted the comments quoted below.
"For an older F-111 type canopy, the technology wasn't used, so adding 1/4 brakes increased the aoa at the wing tips and helped prevent them from deflating and assisted in a more rapid re-inflation if there was a collapse. Newer designs incorporate technology that helps to keep the wing tips inflated during turbulence without the need to fly in brakes. So, in my opinion, to some degree, it seems as if everyone is at least a little bit correct here."
alan

[billvon 2,691]

>Yes, an ac may be overstressed without exceeding the vne, but exceeding the
> vne _implies_ that the ac may be overstressed.
That's not where the definition of Vne comes from. It is a number that comes from a great many variables, including prop overspeed, control surface flutter, max trim range, safe engine power output, etc. A plane flying faster than Vne is not generally overstressed - a plane below Vne but above structural cruise will be overstressed if the pilot performs a maximum-lift manuever (or hits turbulence that does the same.)
Since canopies are very easily "overstressed" when pulling negative G's (in fact, they can't pull them at all; they collapse) it might pay to consider that aircraft slow down to avoid overstress. As you pointed out, they also increase speed to avoid gust-induced stalls when on final, so aircraft have a range of speeds that make them more immune to both stall and overstress when flying in turbulence. If you can apply rigid wing performance to flexible wing stability at all, it would pay to consider whether this "safe" range is above, at or below a canopy's trim airspeed.
-bill von