Forums: Skydiving Disciplines: Swooping and Canopy Control:
Penetrating strong winds.

 

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rendezvous  (C License)

Apr 1, 2002, 7:40 AM
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Penetrating strong winds. Can't Post

I have 48 jumps so keeping that in mind I would appreciate some insight to this. My last jump I missjudged the wind as it was quite calm down below and opened up downwind. At 3000 ft the wind was so strong that I had no penetration at all. It held me there until
I was at about 1000 ft and about the the same distance from the perimeter of my DZ landing area. Basically saying that from 3000 to 1000 ft I had no movement at all and then the wind mellowed down and I started moving. Anyway I choose an alternate area and landed. My question is what kind of options does a guy with my experience level have in a situation like that. How could I have been able to get some penetration to get a little close to the DZ considering I had altitude. Is trying the front risers out one of such options. If the canopy is being held by the wind will they be able to give penetration. I didn't use them since I thought for the little speed that I gained I would loose altitude too so I just used the extra altitude to look for a nice alternate and then try and position myself for it all the while trying not to let the wind come on my tail and take me further away.



flyhi  (D License)

Apr 1, 2002, 7:46 AM
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Re: Penetrating strong winds. [In reply to] Can't Post

Double front risers for penetration into the wind.
Double rear risers to run with the wind.

flyhiCool

"Marge, I'm coming to bed & I've been watching women's volleyball on ESPN."


SkydiveMonkey  (B 102345)

Apr 1, 2002, 7:50 AM
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Re: Penetrating strong winds. [In reply to] Can't Post

Don't forget though that if you're kit has a student CyPReS, double front risers could give you a high enough rate of descent to set it off. Best thing to do is watch other jumpers, and see what they're doing so you can judge what the wind is like.

When you participate in sporting events, its not whether you win or loose, its how drunk you get.


rendezvous  (C License)

Apr 1, 2002, 7:54 AM
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Re: Penetrating strong winds. [In reply to] Can't Post

No, I have the expert Cypres ( thats what the non student cypres is called, right ). With the front risers doesn't the descent happen at the steeper angle than what the normal glide angle for descent would be.



SkydiveMonkey  (B 102345)

Apr 1, 2002, 7:57 AM
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Re: Penetrating strong winds. [In reply to] Can't Post

It does, because you're changing the angle of incidence of the canopy (not to be confused with the angle of attack).

When you participate in sporting events, its not whether you win or loose, its how drunk you get.


Premier billvon  (D 16479)
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Apr 1, 2002, 10:27 AM
Post #6 of 30 (5729 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

>My question is what kind of options does a guy with my experience level have in
> a situation like that.

1. Pull your legs up; sit way back in your harness. Collapse your slider and pull it down. Get your arms in tight. This will reduce drag and increase your speed.

2. Loosen your chest strap. This will increase your glide, and may or may not help on really windy days. Experiment with it. (I hope it goes without saying that you should _not_ take your chest strap off until you land.)

3. Try front risers. This will increase your vertical speed significantly; it may also increase your forward speed a bit. Since you're simultaneously increasing your angle of incidence _and_ making your canopy less aerodynamic, the two may partially cancel out. Try a little front riser at first - no more than a few inches. Increase if that isn't effective. Note that if you're backing up, losing altitude quickly may be a good thing.

>so I just used the extra altitude to look for a nice alternate . . .

This is almost always your best option. If there's a decent alternate, and you can make that easily, that's a much better choice than trying to skim the trees to make it back to the DZ.

-bill von


Viking  (B 30397)

Apr 1, 2002, 1:20 PM
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Re: Penetrating strong winds. [In reply to] Can't Post

I remember you telling me that front risers would have helped me on that really windy day when we did that hop&pop. Do you think doing that would set off the Cypress?? What vertical speed is the student cypress set to go off at??

I swear you must have footprints on the back of your helmet - chicagoskydiver


AggieDave  (D License)

Apr 1, 2002, 1:24 PM
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Re: Penetrating strong winds. [In reply to] Can't Post

Viking, he's not talking about pulling a screaming carve with the front risers, he's talking about pulling them just enough to change the angle of your canopy to give you more forward speed. I've had to do this a couple times with when the winds were kicking.

Question: does higher winds increase the arc that a canopy takes to recover from a hook or a dive? Or does it matter? What about into the wind, downwind, crosswind?

"Homer Simpson, smiling politely."


hooknswoop  (D License)

Apr 1, 2002, 1:37 PM
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Re: Penetrating strong winds. [In reply to] Can't Post

The wind speed does not change the recovery arc of a canopy- see the downwind turning thread.

Hook



Premier billvon  (D 16479)
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Apr 1, 2002, 1:47 PM
Post #10 of 30 (5698 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

>I remember you telling me that front risers would have helped me on that really
> windy day when we did that hop&pop.

>Do you think doing that would set off the Cypress?

Under a Manta? A cypres fires at 78mph. I'd be absolutely amazed if you could get a Manta to get to even 20mph vertical speed without collapsing it.

>What vertical speed is the student cypress set to go off at??

We use expert cypreses, not student cypreses, on our student rigs (which, I recall, is what you were jumping.)

-bill von


Premier quade  (D 22635)
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Apr 1, 2002, 2:22 PM
Post #11 of 30 (5691 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

In reply to:
The wind speed does not change the recovery arc of a canopy- see the downwind turning thread.
However, it may change your perception of what is happening.

It will appear that the arc becomes more verticle and, in fact, with respect to the ground it does. However, as far as control inputs and the canopy going through the air, nothing has changed.

Lemme try this little mind experiment on you and see if this makes sense. These numbers are just made up and not accurate, but should give you and idea of what I'm talking about.

First swoop. No wind. You have a smoke canister fired up and making smoke. Swoop starts 200 feet off the ground and is a perfect semi-circle. On the ground are 10 helium balloons tied to the ground spaced 20 feet apart up the windline. You start your swoop over the first balloon and toward the last balloon. Because the arc is 200 feet in radius, the bottom of your arc ends at the last balloon. Looked at from the side, the smoke trail is exactly what you'd expect -- a perfect semi-circle.

Next swoop. Winds equall your airspeed at the bottom of the arc. Same set up as before only this time as soon as you start your swoop, the balloons are released and allowed to drift with the wind. This time you end up over the ground just about where you started and the last balloon is just about where you are. (OK, maybe you're slightly past it but you get the general "drift".) The smoke trail however looks exactly as it did in the first example -- that is to say it describes a perfect semi-circle with the top of the arc 200 feet downwind of where you were at the bottom of the arc.

So, yes, depending on where you were looking at this experiment, you -could- say that the winds affected the arc and you dropped straight down, but in reality, the recovery arc through the air was identical.


quade

http://futurecam.com


Viking  (B 30397)

Apr 1, 2002, 3:12 PM
Post #12 of 30 (5670 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

Sweet i will try out some riser stuff on my next jump. hopefully the pd 260 will be available.
The only reason i was jumping that manta is b/c the blue 260 was out for repairs, and the other one was down for a repack.

I swear you must have footprints on the back of your helmet - chicagoskydiver


kallend  (D 23151)

Apr 2, 2002, 10:22 AM
Post #13 of 30 (5614 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

This is a very interesting topic.

The airspeed of a glider (or canopy) is primarily determined by wing loading and lift coefficient, while angle of glide is given by the Cl/Cd ratio.

Most canopies are trimmed to fly (full flight) at way above the best angle of glide speed in still air. So, in general, giving front riser input steepens the glide and takes you farther from the best angle speed, and rear risers flatten it. Even in modest winds, you will actually increase your range by using a little judicious rear riser and decrease it by using front risers (this sounds counter-intuitive, but look in the POH of any glider and you will see a Cl/Cd vs airspeed graph that glider pilots use to determine the speed for best range and you'll get the idea). There is a speed for best range for any windspeed, and *usually* this is below full-flight speed for a modern canopy in even moderate headwinds.

Only in very strong winds will front risers will be best.

Reducing drag by tucking in arms and pulling up legs has more of an effect on flattening the glide than on increasing airspeed, and will work best in low to moderate winds. In winds strong enough to make you back up, reducing your drag will primarily keep you up there longer so you back up farther.

Anyone interested in the theory of this can find it in Barry Schiff's book "The Proficient Pilot" or in almost any book on soaring.

jk - licensed glider pilot too.



Premier billvon  (D 16479)
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Apr 2, 2002, 10:44 AM
Post #14 of 30 (5611 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

>In winds strong enough to make you back up, reducing your drag will primarily
>keep you up there longer so you back up farther.

I disagree here. If the drag reduction does not change the trim angle of the parachute (which I think is a good first approximation) then airspeed will stay the same but the groundspeed will increase (flattening the glide at same airspeed equals larger horizontal component.) So in winds that stop you or back you up slightly, I think you're better off reducing drag.

-bill von


Premier quade  (D 22635)
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Apr 2, 2002, 11:15 AM
Post #15 of 30 (5609 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

In reply to:
If the drag reduction does not change the trim angle of the parachute (which I think is a good first approximation) then airspeed will stay the same but the groundspeed will increase (flattening the glide at same airspeed equals larger horizontal component.)
Glide ratio is is defined as Clmax/D.

Since drag opposes thrust (induced thrust in the case of a glider or parachute), a reduction in drag without changing the AoA should result in an increase in airspeed as well as an increase in lift as a result of that increase in airspeed.

Imagine you were in a glider with the spoilers extended and then you retracted them. You would both increase your airspeed and extend your glide.


quade



http://futurecam.com


Premier billvon  (D 16479)
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Apr 2, 2002, 11:20 AM
Post #16 of 30 (5607 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

>Imagine you were in a glider with the spoilers extended and then you retracted
> them. You would both increase your airspeed and extend your glide.

Never flown anything with spoilers. But at least on the planes I fly, if I reduce power during the approach, my speed decreases. The nose drops. Speed then increases until it stabilizes at about the same speed as before, but with a higher rate of descent. The plane tries to maintain the same airspeed regardless of thrust. I would assume that reducing drag would have the same approximate effect as increasing thrust.



-bill von


Premier quade  (D 22635)
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Apr 2, 2002, 12:31 PM
Post #17 of 30 (5594 views)
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In reply to:
Speed then increases until it stabilizes at about the same speed as before, but with a higher rate of descent. The plane tries to maintain the same airspeed regardless of thrust.
Yeah, I know where you're going with this, but I don't think it's exactly the same thing as simply reducing power.

Yeah, the plane wants to return to that same angle of attack that's giving it a particular airspeed. It does that by lowering the nose (on a "normal" airplane at least) until thrust and drag equal each other again.

Hmmm, lemme think about this for a bit. I'm starting to chase my own tail on this one. Smile

If were in a C-172, engine out, trimmed for 65KIAS and then held the doors open against the airstream (creating a LOT of drag) would the aircraft maintain the same airspeed by lowering the nose? Well, it would definately lose a lot of airspeed initially wouldn't it? Yep. Would the nose drop? Yeah, I'm guessing. Would the airspeed remain the same? Maybe (probably).

Hmmm, let's see if that applies to me under canopy.

Hands off glide and I decide to fool around with a spare tandem drouge that was laying around the drop zone. Let's see, I'm flying at maybe 25 knots and throw the drouge. Wow, it's creating a lot of drag back there. Does the nose of the wing lower to compensate? I don't think so, not appreciably anyway. It's pretty much fixed because of the line tension. I'd definately be slowing down and I'd also be going down at a faster rate because the wing isn't creating as much lift. Wow, doesn't look like I'm going to make it back to the grass, better chop the drouge. There, now I'm back up to speed. I wonder what losing even more drag would do?


quade



http://futurecam.com


kallend  (D 23151)

Apr 2, 2002, 5:22 PM
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Re: Penetrating strong winds. [In reply to] Can't Post

<<<Imagine you were in a glider with the spoilers extended and then you retracted them. You would both increase your
airspeed and extend your glide.>>>

maybe - but not by much. This is not a good analogy anyway since spoilers also destroy lift over a large fraction of the wing. Spoilers are primarily used to control angle of descent.

To a first approximation, for unaccelerated flight the airspeed is sqrt(2*L/(rho*Cl)) so that the lift balances the weight, where L is wing loading, Cl is lift coefficient, rho is air density. Unless the dive angle is particularly steep (so there are some trig terms to worry about), the drag coefficient doesn't have much effect on airspeed but it does have a big effect on glide ratio.

Risers change the trim angle angle therefore change Cl, which is why using front or rear risers does have an effect on airspeed.

Doesn't anyone want to take up my claim that for low to moderate headwinds on a modern canopy you are likely better off with rear risers? It's heresy at my DZ.



kallend  (D 23151)

Apr 2, 2002, 5:37 PM
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Re: Penetrating strong winds. [In reply to] Can't Post

<<< Speed then increases until it stabilizes at about the same speed as before, but with a higher rate of descent.
The plane tries to maintain the same airspeed regardless of thrust.



Yeah, I know where you're going with this, but I don't think it's exactly the same thing as simply reducing power.

Yeah, the plane wants to return to that same angle of attack that's giving it a particular airspeed. It does that by lowering
the nose (on a "normal" airplane at least) until thrust and drag equal each other again.>>>

Another dangerous analogy - it all depends on the angle of the thrustline. I've experimented with just this on my Mooney (M20G, N3910N). In level stable cruise at 65% power, if I open the throttle it starts to climb AND THE AIRSPEED DROPS! OTOH, if I close the throttle, it starts to dive and the airspeed INCREASES. I interpret this to mean that there is slight upthrust on the engine.

<<< I wonder what losing even more drag would do?>>>

You could lose all the drag and you still wouldn't go faster in unaccelerated stable flight than the speed at which the lift produced is equal to your weight.

Your airspeed is primarily controlled by the lift coefficient and wing loading. Only when your dive angle exceeds 45 degrees does drag become more important than lift.



Premier quade  (D 22635)
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Apr 2, 2002, 5:38 PM
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Re: Penetrating strong winds. [In reply to] Can't Post

Ok, you didn't like my glider & spoiler example. What about the drouge under canopy example?

In reply to:
Doesn't anyone want to take up my claim that for low to moderate headwinds on a modern canopy you are likely better off with rear risers? It's heresy at my DZ.
Depends on what you're calling light to moderate.

In no wind I'd say you're probably better off (depending on the exact canopy) to have the brakes unstowed and ride the rear risers.

In headwinds near the forward speed of the canopy, I'd say you're better off with the brakes unstowed and on front risers as much as you can stand so that you decend quicker and are therefore exposed to the wind for the least amount of time.

Somewhere between these two extremes there must be a transition point, but there probably isn't a general rule that fits all canopies equally.

So, what are you calling low to moderate?


quade

http://futurecam.com


kallend  (D 23151)

Apr 2, 2002, 5:47 PM
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Re: Penetrating strong winds. [In reply to] Can't Post

<<<So, what are you calling low to moderate?>>>

Last year I spent some time talking about this with John leBlanc. His numbers for a Stiletto are that best glide speed in still air is around 15-18kts, whereas the trim speed is more like 25 - 30kts.

Glider pilots usually like to add 1/2 headwind speed to the still air best speed for maximum range in a headwind. This is a rule of thumb.

So - assuming (dangerously) that a Stiletto behaves much like a glider, a 20kt headwind would require an airspeed of around 25 - 28 kts for best range. This is somewhere around the trim speed.

So to answer your question, I would call low to moderate
something less than 20kts.




ltdiver  (D 20506)

Apr 2, 2002, 7:05 PM
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Re: Penetrating strong winds. [In reply to] Can't Post

In reply to:
I've had to do this a couple times with when the winds were kicking.
Just don't try this when you have turbulant winds, IMHO. I tried it one hot, very windy day, when my Spectre-135 was backing up, not driving forward, and the canopy collapsed when I was about 30 feet off the ground (coming in straight for landing). My reflexive reaction to the sudden loss of lift was a startle reflex and my arms flew back up and let the risers go! My canopy reinflated and I landed unhurt.
My friends in the packing area all reported that they thought I was 'toast' when they saw the canopy collapse. I got 'you're the luckiest girl in the world' from one of the skygods.

Just my .02,
ltdiver

____________________________________________
LightDiverCam


Premier billvon  (D 16479)
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Apr 2, 2002, 10:44 PM
Post #23 of 30 (5525 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

>In level stable cruise at 65% power, if I open the throttle it starts to climb AND
> THE AIRSPEED DROPS!

Well, yeah, and if you do the same thing on a Lake amphibian the opposite happens. But those are due to off-center thrust affecting the attitude of the plane, not a change in pitch stability.

>You could lose all the drag and you still wouldn't go faster in unaccelerated
> stable flight than the speed at which the lift produced is equal to your weight.

Again, your airspeed wouldn't change, but your horizontal speed would increase a bit.

-bill von


kallend  (D 23151)

Apr 3, 2002, 7:46 AM
Post #24 of 30 (5507 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

>>You could lose all the drag and you still wouldn't go faster in unaccelerated
>> stable flight than the speed at which the lift produced is equal to your weight.

> Again, your airspeed wouldn't change, but your horizontal speed would increase a bit.

For a 3:1 glide ratio, the glide angle is 18.4 degrees, and the horizontal component of airspeed is cos(18.4) = .948 times airspeed.

So if you lose ALL drag (including the drag of the canopy) your forward component of velocity will increase by roughly 5% (or, typically, 1.5kts). On the other hand, you will be up there forever since your glide ratio now becomes infinite. So IMO, if you're backing up at more than 1.5 kts you are worse off reducing your drag to zero than using it to get down more quickly.

I'm not sure how much drag can be reduced anyway. In freefall (belly to wind) my drag = my exit weight = 190lbf. At canopy speed, belly to wind, the drag is reduced by the square of the speed ratio and will therefore be about 12lbf. Maybe I can reduce this to 10lbf by tucking up. The total drag will be approx 1/3 of the lift (for a 3:1 glide) or 63 lbf . So the most drag reduction I can expect is likely to be about 3%, and this in turn will lead to an increase in the forward component of airspeed by less than 0.5% or about 0.15kt.





Premier quade  (D 22635)
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Apr 3, 2002, 7:56 AM
Post #25 of 30 (5502 views)
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Re: Penetrating strong winds. [In reply to] Can't Post

In reply to:
Another dangerous analogy - it all depends on the angle of the thrustline. I've experimented with just this on my Mooney (M20G, N3910N). In level stable cruise at 65% power, if I open the throttle it starts to climb AND THE AIRSPEED DROPS! OTOH, if I close the throttle, it starts to dive and the airspeed INCREASES. I interpret this to mean that there is slight upthrust on the engine.
If you go back and read my original post, I said on a "normal" airplane. Smile

In reply to:
You could lose all the drag and you still wouldn't go faster in unaccelerated stable flight than the speed at which the lift produced is equal to your weight.
You still haven't addressed my analogy of deploying a drogue while under canopy. Certainly THAT would make you go slower wouldn't it? If adding drag makes you go slower, then I don't understand why it's unreasonable to assume that reducing drag would make you go at least a little faster.

Just curious, do you have a collapsible pilot chute?


quade


http://futurecam.com


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