Parachute Aerodynamics

[burtonjm 0]

Sounds like an interesting program. Still got the code kickin around?

This shit, right here, is OK

[theonlyski 8]

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Once I have made a program on my HP 48 GX graphing calculator to calculate the spot taking in account the speed and direction of winds aloft (given by a pilot forecast source) at every 3000 feet from ground to 12000 feet. I tested my program by making the calculation "by hand" and by using actually the calculated spot. When I tried to convince the people at the DZ to use that program at least for the first load, very few people were interested and some said my program was useless. As always, people are relying on the performances of their canopy to bring them back for landing until after a cut away they will lose their 2000.00$ canopy. We are doing a very technical type of sport but the skydivers really interested by the aerodynamics of a parachute are not part of the majority.

Give me the math, I'll put it in a Windows based app. A good excuse to get back to programming, and I'm sure some people would get good use out of it.

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[shah269 0]

Regarding aerodynamics.
I hate to say it but I would say very few really understand what keeps them up in the air and the concept of energy.
A few have a very good "feel" but those guys and gals are the few.
It's much like motorcycles. Very few have any idea what is between their legs all they know is that it looks good and goes fast. And then they bring the bike over to my place after owning it for two years and ask...how often should I do oil changes?


But I have a very dumb one an I hope you guys can help me because it counters what I knwo of Aero.
The other day when I was jumping there was significant traffic below me and I was using rear risers to flatten my flight. Which is fine...untill you have done it for about 5 min and are ready to land only to find out your arms are dead tired!

After landing one of my good friends who is an amazing swooper and very good and very experienced said I should try 75% toggle inputs, to slow up and to maintian altitude. To which i asked....but won't I "fall" he said no.

I don't get it? If my velocity is very low due to the heavy application of toggle inputs and I'm facing into the wind and i can tell by the sound of the wind that at most I'm doing 10mph....shouldn't I loose lift and slowly decend?

So I gave it a shot, and wouldn't you know it, I held 3500 ft for well...as long as I wanted to. What is this all about?
Thank you
Shah

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[wolfriverjoe 1,523]

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Regarding aerodynamics.
I hate to say it but I would say very few really understand what keeps them up in the air and the concept of energy.
A few have a very good "feel" but those guys and gals are the few...

...But I have a very dumb one an I hope you guys can help me because it counters what I know of Aero.
The other day when I was jumping there was significant traffic below me and I was using rear risers to flatten my flight. Which is fine...untill you have done it for about 5 min and are ready to land only to find out your arms are dead tired!

After landing one of my good friends who is an amazing swooper and very good and very experienced said I should try 75% toggle inputs, to slow up and to maintian altitude. To which i asked....but won't I "fall" he said no.

I don't get it? If my velocity is very low due to the heavy application of toggle inputs and I'm facing into the wind and i can tell by the sound of the wind that at most I'm doing 10mph....shouldn't I loose lift and slowly decend?

So I gave it a shot, and wouldn't you know it, I held 3500 ft for well...as long as I wanted to. What is this all about?
Thank you
Shah

First off, I agree with you about how few jumpers care about the aerodynamics (How many care about knowing how their gear is put together and maintained?)

The riser/brakes question gets a bit complicated.
The short answer is that there is an ideal speed that gives you the slowest descent. There is another, slightly different one that gives you the shallowest angle of descent too. In airplanes, there are somewhat similar things called Best rate of climb and best angle of climb airspeeds (Vy and Vx respectively).

These speeds are usually fairly slow, much slower than normal flight. You might want to experiment a bit to see how much input gives you the slowest descent (which is pretty hard to judge by yourself).

It's usually more efficient to use risers to slow to those speeds because the toggles deflect the canopy farther back and create more drag. The risers deflect the canopy over a wider area, generating the same lift with less drag. But at the price of very tired arms. And the difference in aerodynamic efficiency isn't all that much.

BTW, not a dumb question, just one that you didn't know the answer to.

"There are NO situations which do not call for a French Maid outfit." Lucky McSwervy

"~ya don't GET old by being weak & stupid!" - Airtwardo

[shah269 0]

THANK YOU!
I was simply amazed as to how slow I could fly with out "falling" out of the sky!
I started to pull on the toggles slowly untill they were at about 75% of where they would be for full flair and well...it got quiet and very still. And then I thought...ok now I should start loosing lift and fall......but nope! I looked at my alti and it looked to be stuck at 3500ish....5 min later.....still at the same spot.
What a nice thing to know! I wish they tought this in AFF. Because it really does give you a moment to sit back look around figure out where you are and how you will land.
Thank you!

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[kkeenan 14]

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Which is fine...untill you have done it for about 5 min and are ready to land only to find out your arms are dead tired!

There is probably a good gym in your town if you are too weak to properly control your parachute.

_____________________________________
Dude, you are so awesome...
Can I be on your ash jump ?

[shah269 0]

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Which is fine...untill you have done it for about 5 min and are ready to land only to find out your arms are dead tired!

There is probably a good gym in your town if you are too weak to properly control your parachute.

Student rigs don't have any loops so it's just hold on and pull up and hold. Easy to do but to hold for 5/10 min wooh what a work out.

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[airdolphin 0]

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...
untill you have done it for about 5 min and are ready to land only to find out your arms are dead tired!
...

If your canopy allows to pull the toggles all the way down without stalling it, then you can just put your thumbs through the hip rings (if available) and your arms won't be as tired.

Also, when using the rear risers you may choose to push them aside rather than pulling them down. This way you achieve two things: "effective shortening of rear lines" and thus higher angle of attack and more lift; and your canopy is better spread out (flattened out) and thus more effective as well.

[Earlybirdmel 0]

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In Switzerland, in order to get the A license you need to pass a written exam divided in 5 parts: Gear knowledge, "Jumping procedures", Aerodynamics, Meteorology, and Legislation.

Is there something similar in other countries? Just curious.

If I have missed this, I apoligise, but do we have written exam in the UK before being allowed to do first Static line or AAF?

[billvon 2,989]

>The other day when I was jumping there was significant traffic below me
>and I was using rear risers to flatten my flight.

You can also spread them instead of pulling them down. It takes less effort and has much the same effect.

>If my velocity is very low due to the heavy application of toggle inputs
>and I'm facing into the wind and i can tell by the sound of the wind that at
>most I'm doing 10mph....shouldn't I loose lift and slowly decend?

Pretty much no matter what you are doing under canopy, your lift equals your weight. There are several different things you might care about:

-Your time in the air
-Your L/D (glide ration with respect to the air)
-Your progress over the ground

The above are not the same, and wind conditions can affect the third.

Slight applications of brakes will reduce your speed and increase your L/D. Heavy brakes (but not stalling) will reduce your speed a lot and _decrease_ your L/D - but your descent rate may still be lower overall. In other words, you will be in the air longer, but at least in still air you won't go as far.

[theonlyski 8]

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Which is fine...untill you have done it for about 5 min and are ready to land only to find out your arms are dead tired!

There is probably a good gym in your town if you are too weak to properly control your parachute.

Student rigs don't have any loops so it's just hold on and pull up and hold. Easy to do but to hold for 5/10 min wooh what a work out.

My rig doesn't have loops on the rear risers... come to think of it, none of the ones Ive jumped have had them either.

Now, loops on the front risers... got those!

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[burtonjm 0]

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Which is fine...untill you have done it for about 5 min and are ready to land only to find out your arms are dead tired!

There is probably a good gym in your town if you are too weak to properly control your parachute.

Student rigs don't have any loops so it's just hold on and pull up and hold. Easy to do but to hold for 5/10 min wooh what a work out.

My rig doesn't have loops on the rear risers... come to think of it, none of the ones Ive jumped have had them either.

Now, loops on the front risers... got those!

I've never seen or heard of a rig that had loops on the rear risers...but what do I know

This shit, right here, is OK

[theonlyski 8]

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I've never seen or heard of a rig that had loops on the rear risers...but what do I know

I know, I was giving shah shit for this:

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The other day when I was jumping there was significant traffic below me and I was using rear risers to flatten my flight. Which is fine...untill you have done it for about 5 min and are ready to land only to find out your arms are dead tired!

&

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Student rigs don't have any loops so it's just hold on and pull up and hold. Easy to do but to hold for 5/10 min wooh what a work out.

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[shah269 0]

Dumb question, why not?
Is it because so you can more or less get the same effect via pushing the toggles down 75%?
Also wouldn't it be easier to do flat turns that way?
Sorry, just wondering.

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[timmyfitz 0]

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Also, when using the rear risers you may choose to push them aside rather than pulling them down. This way you achieve two things: "effective shortening of rear lines" and thus higher angle of attack and more lift; and your canopy is better spread out (flattened out) and thus more effective as well.

The canopy will be flattened out only if the slider is pulled down past the risers at the point where you are spreading them out. At his level I doubt (but could be wrong) he is pulling the slider down.

[davelepka 4]

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Dumb question, why not?
Is it because so you can more or less get the same effect via pushing the toggles down 75%?
Also wouldn't it be easier to do flat turns that way?
Sorry, just wondering

In general, the control stroke for rear risers is quite short compared to toggles. If you used rear risers for falt turns, keeping mind you use a flat turn when you are low and needing to change direction with a min. altitude loss, if you were to stall one side of the parachute doing a flat rear riser turn, that would make a bad situation even worse. Stick with the toggles, and their long, forgiving control stroke when manuvering close to the ground.

In terms of rear riser loops, the main reason they don't exist is becasue toggles will give you a lower descent rate than rear risers, and therefore are the better option for getting back from a long upwind spot. When you have the wind at your back, you use the min descent rate to increase your exposure to the that wind and get the most distance from your given altitude.

Rear risers can lower your descent rate, and can do it inducing less drag allowing for a higher forward arispeed, but they cannot match the descent rate of deep brakes. You can use rear risers to get back from a long downwind spot, where keeping drag to a min and airspeed high is of value, but those spots are generally not that long, and if they are, you're just fucked anyway and are going to land off.

As an aside, I jump with a guy who installed rear riser loops on his rig. He's an older guy and for the sake of ease-of-operation, he wanted to loops in place in case he wanted to hang on his rears for any length of time.

As already mentioned, when coasting back from a long spot in deep brakes, see if you can't grab onto the lateral, hip ring, or the upsidedown 'V' made at by the legstraps at the hip. What this will do is transfer the work to your hands, and let you rest your arms and shoulders. The toggles are hooked over your hands, and your hands are doing all the work hanging onto whatever you can grab.

To go one step further, if you are jumping a student canopy, even in full lfight your descent rate will be quite low. Let it fly, and learn to manage the traffic. There shouldn't be that many canopies aloft by the time you reach the pattern, and those that are will be other students (very slow moving) or instructors and tandems (easy to work with). The point is that paying attention to traffic and sequencing yourself into the pattern are key skills to learn on the slower student canopy. As you move toward more of a 'sport' canopy, your descent rate and airspeed will both increase, and your time to sequence yourself will decrease. Having the experience of doing it on a slower canopy will help to prepare you for future jumps when you might not have the luxury of 'stopping' to wait for everyone else. Get in there and get it done (which is way different then 'git er done', which is retarded).

[shah269 0]

davelepka
Thank you.
Before I was educated about the deep toggle input hover, which by the way I still find amazing, I was in a situation where I was above tandems but not high enough so I grabbed my rear risers aimed my canopy into the wind and reduced my decent rate so as to increase the distance between me and the tandems. After about 5 min of "hanging" there was sufficient space for me to set up a clean landing.
Thus why I thought, "Well if I'm "hanging" here wouldn't some sort of loops hold on to."
But now that I know about the rear riser hover thing really is much easier on the upper body and easier to look around to make sure I'm out of the way.

Life through good thoughts, good words, and good deeds is necessary to ensure happiness and to keep chaos at bay.

The only thing that falls from the sky is birdshit and fools!

[riggerrob 643]

The disadvantage of rear riser "hang" loops is that they might be mistaken for steering toggles.

Kind of like the time a school ordered new main risers - for its student rigs - and they arrived with front riser dive loops. Those dive loops were cut off IMMEDIATELY!

[d123 1]

http://www.bpa.org.uk/doc_uploads/ellipticalleblanc.pdf

Not sure if is in any way helpfull but is something that comed in my mind when I've seen this subject.

Lock, Dock and Two Smoking Barrelrolls!

[erdnarob 1]

Hi Rob, I am thinking about having loops installed at the top of my rear risers but the other side with respect to the toggles. The reason for this is that in case of a broken steering line, I would have something solid to grab on and therefore I could land my Katana properly.
Two times, I got a knot of one steering line around the top channel which keeps the steering line excess (I have two channels). Since in both cases the knot was near the toggle, I could easily compensate with the other toggle to fly straight but when I was using the toggle on the knot side, I was actually pulling the whole riser. In this case, having loops installed on my rear risers would have been more convenient. I did some practice in the air and my landing was not too bad but it wasn't a stand up one. What do you think about that ?

Learn from others mistakes, you will never live long enough to make them all.