Physics/Canopy Question

[kelel01 1]

Here's the setup: two identical Sabres with people of identical wingloadings are flying with 0 wind beginning at 3,000 feet.

Canopy Pilot A goes into half brakes, and Canopy Pilot B flies in full flight (both straight)-- who will land first?

Kallend?
Kelly

[DALAILAMA 0]

Canopy B
The angle of attack on A is greater and therefore he will loose altitude faster.

"Dropzone.com, where uneducated people measuring penises, has become an art form"

[quade 3]

Too many unknowns to give a definitive statement, but under -my- Spectre I can tell you that its rate of decent is slower in half-brakes.

quade -
The World's Most Boring Skydiver

[quade 3]

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The angle of attack on A is greater and therefore he will loose altitude faster.

Not always true. In fact, the entire statement is pretty misleading without any regard to airspeed.

quade -
The World's Most Boring Skydiver

[Jimbo 0]

Assuming that both canopies have the same trim (not an unreasonable assumption, I think) and have the same suspended weight, should airspeed even been an issue?

-
Jim

"Like" - The modern day comma
Good bye, my friends. You are missed.

[pilotdave 0]

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Canopy B
The angle of attack on A is greater and therefore he will loose altitude faster.

If A will lose altitude faster, why will B land first?

Dave

[Nightingale 0]

I was wondering the same.

[FrogNog 1]

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Canopy B
The angle of attack on A is greater and therefore he will loose altitude faster.

I think a much earlier effect to consider is that in half brakes, the airfoil shape is wildly different from full flight.

The angle of attack of the canopy after it has stabilized in flight will be more dependent on the airfoil shape than vice versa. (In a wing inflated by airspeed, certainly there is some bidirectional dependence between airfoil and angle of attack.)

From what I remember about hang gliding (and it's applicable to a lot more flying than that), the characteristic in question here is "sink" (rate). And all the canopies I've jumped (in my entire 14 months in the sport ) have a lower sink in partial brakes than in full flight. The sink isn't low throughout the entire brake range - but it reaches a nadir somewhere in the brake range and is higher in full flight and full brakes. (Duh - just before the canopy stops flying and falls out of the sky. )

[And, while I'm here, "lose" means when something goes away, i.e. it is lost (verb, pronounced "looz"). "Loose" means something that is not fixed, tied down, or retained (adjective) or the act of setting something free or untying / unfixing it (verb - pronounced "loos", as is the adjective).]

-=-=-=-=-
Pull.

[hookitt 0]

If the nose is pointed up more the angle of attack is greater.

If the Nose is pointed down more, the angle of attack is less.
==========

If you read his response it reads that canopy B will descend quicker because the angle of attack is greater on A.

My canopy will stay up longer in half brakes than in full flight. Most canopies will. I can't think of any canopies out there that would descend quicker in half brakes.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[ryoder 1,381]

"A" goes into half brakes which effectively makes the airfoil thicker. A thicker airfoil will fly slower and produce the same lift at a lower speed than the unbraked airfoil. The two canopies will have about the same glide ratio, but the unbraked canopy will land first.

"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

[teason 0]

I think the theory you citing is that a canopy in half brakes produces more lift at a cost of more drag.

It would depend a great deal on how the canopy is trimmed and how far the tail is pulled down in that jumper's half mode. (I've jumped canopies that nearly stalled at my half brake point because of poorly set brake lines)

But fine points aside, Canopy A is capable of producing more lift. As you pull your toggles down, The shape of your canopy changes. Air is moving faster over the canopy relative to under it. To oversimplify; the greater difference in air speed means lower air pressure on top and therefore creates the greater lift.

The canopy also produces more drag which in turn slows the forward speed reducing lift.

There is a point where the canopy produces greater lift for the drag produced. Go beyond that point and the increased drag reduces the wing's efficiency.
It's like a pilot flying with flaps!

As for angle of attack, I don't believe it changes because you are not affecting the length of you A,B,C and D lines. I think that this is a symantic thing. Your glide slope is what is affected.
... I think...

I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

[pilotdave 0]

Pulling the brakes changes the effective camber of the airfoil, not really the thickness ratio. It's like putting the flaps down on a plane. Completely changes the L/D ratio and should change the glide ratio. Experience might tell you that it's not a very big change in glide ratio.... I don't know.

Dave

[pilotdave 0]

Both canopies are producing the same amount of lift... L=weight for any wing in unnaccelerated flight. If L
Dave

[kallend 1,621]

Quote

Here's the setup: two identical Sabres with people of identical wingloadings are flying with 0 wind beginning at 3,000 feet.

Canopy Pilot A goes into half brakes, and Canopy Pilot B flies in full flight (both straight)-- who will land first?

Kallend?
Kelly

Sabres? Beats me. On my Stiletto at my WL, half brakes definitely produce a lower descent rate than full glide.

...

The only sure way to survive a canopy collision is not to have one.

[quade 3]

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Assuming that both canopies have the same trim (not an unreasonable assumption, I think) and have the same suspended weight, should airspeed even been an issue?

Yes.

Most canopies are trimmed to fly at least slightly faster than best glide speed. By judiciously applying a small amount of rear risers (increasing the AoA) you -can- slow down the canopy -slightly- and improve the glide.

Think about it. You've just increased the AoA, slowed down AND increased the glide.

For -every- airfoil there is ONE (and ONLY one) AoA that will produce the maximum glide ratio. If you increased OR DECREASED the AoA you'd shorten the glide ratio.

Further, for every airfoil and wingloading there is a specific AoA that will produce the lowest decent rate. This is NOT the same AoA as the one for maximum glide ratio. It is -always- a higher AoA than the one for maximum glide ratio.

So, the canopy at full flight -will probably- have a glide ratio that can be improved upon simply by -slightly- increasing the AoA and the time aloft can -probably- be lengthend by increasing it even further -- to a point.

Obviously if you go past that point you will decend faster and if you -really- increase the AoA you'll eventually stall the canopy.

quade -
The World's Most Boring Skydiver

[acrojunky 0]

Quote

Here's the setup: two identical Sabres with people of identical wingloadings are flying with 0 wind beginning at 3,000 feet.

Canopy Pilot A goes into half brakes, and Canopy Pilot B flies in full flight (both straight)-- who will land first?

Kallend?

God guys BbBbBbBbBbBbBbBbBbBbBbBbBbbbbbbbbbbbbb beeeebeeeebeeebeeebee will land first because it was not slowed down/trimed to a flatter glide angle so B will have a greater desent rate. end of storie

Kelly

[JYorkster 0]

What are you really asking? By "first" do you mean in time or distance? These are different questions, and I think people are giving you different answers based on how they interpreted the question.

A better glide ratio will make you go further and probably also take more time. Half brakes may or may not give you a better glide ratio in zero wind. It may bring you down slower, but in a more vertical descent. If you are in high wind that is pushing you the direction you want to go, this could be beneficial. Some canopies drastically lose forward speed in half brakes, but get very floaty...think of it like a round canopy. Low descent rate aided by wind can get you where you want to go.

Just my 2 cents,

Rock

[nael 0]

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God guys BbBbBbBbBbBbBbBbBbBbBbBbBbbbbbbbbbbbbb beeeebeeeebeeebeeebee will land first because it was not slowed down/trimed to a flatter glide angle so B will have a greater desent rate. end of storie

Thats what I thought, but I'm a 29 jump wonder, and I have very very very limited understanding of how a canopy flies, but isnt it obvious that a canopy being flown in half breaks will stay in the air longer than a canopy in full drive?? Seems pretty logical to me, if all other factors are the same for both canopies.

www.TerminalSports.com.auAustralia's largest skydive gear store

[kelel01 1]

Good question: time, not distance. Who will land first time-wise.

Good answers so far, guys! Thanks! This was to settle a dispute.
Kelly

[Rdutch 0]

How about C: Me in my Velocity 90 in 3/4 brakes, I will land after both of them.

Ray
Small and fast what every girl dreams of!

[rehmwa 2]

Funny conversation with lots of digressions and non-pertinent info.

angle of attack, distance, airspeed, none of that matters to the question. The only thing that matters is descent rate.

The half braked canopy will land second since its descent rate is less.

The distance question is much more interesting.

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[DALAILAMA 0]

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The two canopies will have about the same glide ratio, but the unbraked canopy will land first.

I agree that the canopy at full flight will land first due to his angle of attack, but it is impossible for the same cxanopies to have the same glide ratio.

"Dropzone.com, where uneducated people measuring penises, has become an art form"

[DontPanic 0]

As a student, I have been voraciously reading the posts and training articles I've found on this site, and I ran across some articles on canopy control that address this question in general (I'm not sure if it applies to a Sabre).

Following the link for "Survival Skills for Canopy Control" in the training section, theres a chapter on getting the most out of your canopy: http://www.skydiveaz.com/resources/book_chp4.htm

If a read the article correctly, a canopy at half brakes will have the slower descent rate, but not cover as much ground. In full flight mode, you'll cover more ground even though you are descending faster.

Another article even suggests that applying alittle front riser can increase the ground you cover even more, while also increasing you descent rate.

[Push 0]

I have a different question. Does there exist a canopy that lands faster in half brakes than in full flight?

Every single canopy I've jumped, and every canopy I've ever seen anyone jump, floats when you put on the brakes. Everyone recommend putting on brakes to float.

-- Toggle Whippin' Yahoo
Skydiving is easy. All you have to do is relax while plummetting at 120 mph from 10,000' with nothing but some nylon and webbing to save you.

[d604 0]

Brakes does not affect the angle of attack, risers do. But since the question was simple who will land first, then B.