working out canopy speed

[pilotdave 0]

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It's fortunate that that's not true, or Boeing would have had to build hundreds of versions of each type of aircraft (and then watched them all crash) before they got one that flew. Mathematical approximations can get you very close to a correct answer

I think the point was that you can't apply simple formulas to figure out exact speeds. Yes, Boeing does use mathematical approximations to calculate lift/drag, etc, but those are based on millions of calculations done by computers. It's not as if they plug a few variables into a formula to come up with performance numbers.

Dave

[mikeat10500 12]

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>Higher wingload=faster(air speed)

That's true but . .,

>Less drag=faster(air speed)

That's not. A parachute is a very stable aircraft in both pitch and airspeed, and when you change the L/D by reducing drag, it tends to correct itself and remain at the same speed. You do get a better glide angle though (L/D is often how glide angle is expressed.)

This is true in aircraft as well. If you increase power (which is the same as decreasing drag in terms of the four-force diagram) the plane will initially speed up - then its nose will come up, it will slow down, and it will stabilize again at about the same airspeed, but this time at a higher climb angle.

Bill

So people use collapsible pilot chutes for what reason? (next question will include micro lines, and the move to low profile canopy design).
...mike

-----------------------------------
Mike Wheadon B-3715,HEMP#1
Higher Expectations for Modern Parachutists.

[billvon 2,991]

> So people use collapsible pilot chutes for what reason?

1. A better L/D means a better (shallower) glide. That's sometimes a selling point for canopies; it means you can make it back more often from a bad spot.

2. A shallower glide means you need less energy to plane out the canopy, so more energy is available to get a good planeout.

3. The speed only remains the same in stabilized glide. When you're not in a stable glide (i.e. you're flaring and planing out, or initiating a hook turn) then it can have a big effect:

-when planing out, the less drag you have the farther you go, since the only thing overcoming drag at that point is your momentum. Less drag means your momentum lasts longer.

-when starting a hook turn, the speed the canopy dives depends greatly on its drag, since you're essentially diving the canopy at the ground and greatly reducing lift momentarily.

4. On some canopies, the drag from the PC is so great that it can actually distort the canopy, and that messes up the aerodynamics of the wing.

> (next question will include micro lines, and the move to low profile
>canopy design).

Microlines: all the above except 4. Low profile canopy design: not really the same thing, since once you start changing the planform/trim angle/camber of the airfoil, you affect a _lot_ of parameters at once - not just drag.

[mjosparky 4]

"To date there has been little (if any) analytical work that can accurately predict the preformance of a given ram-air canopy". Taken for Helmut Heinrick short course on Decelerator systems engineering. Presented by Manley Butler, Preformance, Design and Construction Of Ram-Air inflated, Gliding Parachute Wings.
Sparky

My idea of a fair fight is clubbing baby seals

[mikeat10500 12]

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> So people use collapsible pilot chutes for what reason?

1. A better L/D means a better (shallower) glide. That's sometimes a selling point for canopies; it means you can make it back more often from a bad spot.

Better lift/drag ratio is just converting the greater available forward speed into the desired lift, through
canopy design, trim, etc.

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2. A shallower glide means you need less energy to plane out the canopy, so more energy is available to get a good planeout.

Energy can not be created or destroyed only converted...in this case...forward speed into lift.

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3. The speed only remains the same in stabilized glide. When you're not in a stable glide (i.e. you're flaring and planing out, or initiating a hook turn) then it can have a big effect:

Flaring...converts forward speed to lift( also induces extra unwanted drag)...when swooping...only convert
as much forward speed as required to keep you above ground level so as not to waist the forward speed...swoop far! Hook turns do not increase speed
as much as people think( 2-4mph) in the turn itself.

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-when planing out, the less drag you have the farther you go,

'cause more forward speed can generate more lift longer.

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since the only thing overcoming drag at that point is your momentum. Less drag means your momentum lasts longer.

-when starting a hook turn, the speed the canopy dives depends greatly on its drag, since you're essentially diving the canopy at the ground and greatly reducing lift momentarily.

4. On some canopies, the drag from the PC is so great that it can actually distort the canopy, and that messes up the aerodynamics of the wing.

The PC distorts the canopy because it slows down
the attachment point...holding it back...holding the
whole canopy back...more drag=less speed.

Think of a Tandem....big drogue...more drag=less
speed... drogue release time...less drag=faster... main inflates...more drag=slower

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> (next question will include micro lines, and the move to low profile
>canopy design).

Microlines: all the above except 4. Low profile canopy design: not really the same thing, since once you start changing the planform/trim angle/camber of the airfoil, you affect a _lot_ of parameters at once - not just drag.

Yes but I think they use,micro line, colapsible pilot chutes and low profile designs to reduce drag for an
increase in forward speed which inturn can be converted into lift.


Bill , I think I know what you are trying to say...that
canopies have a max or fixed speed( at a fixed wingload)...any loss of drag will only result the increased speed being converted to lift due to design
but this does not change less drag=faster...what you
choose to do with the energy that is not being wasted in drag is up to you, but more energy will be available if you reduce drag.
...mike

-----------------------------------
Mike Wheadon B-3715,HEMP#1
Higher Expectations for Modern Parachutists.

[apoil 0]

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Slowing down well its hard to change your wingloading during flight( though not impossible I'm sure) but you can induce drag by using toggles or
rear risers to create some lift and trade off air speed
(nothing is free in this world) or distorting the shape of the wing ( wing warping) .

While you can't change your base wingloading, other than by carrying ballast and dropping it, your effective wingloading can be changed both up and down during flight.

When you initiate a turn, causing a pendulum effect, the centrifugal force of your weight, swinging against the lines increases you wingloading - by a factor of 2 or 3 in extreme cases. This is one of the main reasons your canopy builds up so much speed in a high performance turn. Similarly, if you do a maneuver where the lines go slack such as a snap toggle turn, the wingloading will decrease. When you apply brakes suddenly and pendulum swing forward, again, you are decreasing the wingloading on your canopy.

[billvon 2,991]

>Better lift/drag ratio is just converting the greater available forward
> speed into the desired lift, through canopy design, trim, etc.

When you're flying, you don't really have any available forward speed. All you have is your potential energy from your altitude and your weight. A parachute can convert that energy into forward speed if it's designed well. You can change your forward speed by changing the trim of the canopy (i.e. front or rear risers) but you can't by just changing the amount of drag. It's sort of counterintuitive but it happens on powered aircraft and gliders as well.

>Hook turns do not increase speed
>as much as people think( 2-4mph) in the turn itself.

Not sure what you mean here - are you saying that, during the initiation of a hook turn, your speed only increases 2-4 mph?

>>when planing out, the less drag you have the farther you go,

>cause more forward speed can generate more lift longer.

Right, and that's why you get a longer planeout when you increase your speed by using front risers or a hook turn. When you compare a normal landing with a non-collasible with a normal landing under a collapsible PC, the difference is mainly in the loss of drag, allowing you to plane out further.

>Think of a Tandem....big drogue...more drag=less
>speed... drogue release time...less drag=faster... main
> inflates...more drag=slower

Freefall drag is very different than stabilized glide under a canopy. Completely different rules apply.

>any loss of drag will only result the increased speed being converted
> to lift due to design but this does not change less drag=faster

I think I agree. The first part of that is essentially correct - the extra 'thrust' you get by reducing drag is converted to a better glide angle rather than more speed - so if you reduce drag you get a better glide but your airspeed doesn't change. In some cases (like starting a hook turn, or planing out) you can keep that given speed for a longer time, or get excess speed and not lose it as quickly.

[kallend 2,027]

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>Higher wingload=faster(air speed)

That's true but . .,

>Less drag=faster(air speed)

That's not. A parachute is a very stable aircraft in both pitch and airspeed, and when you change the L/D by reducing drag, it tends to correct itself and remain at the same speed. You do get a better glide angle though (L/D is often how glide angle is expressed.)

This is true in aircraft as well. If you increase power (which is the same as decreasing drag in terms of the four-force diagram) the plane will initially speed up - then its nose will come up, it will slow down, and it will stabilize again at about the same airspeed, but this time at a higher climb angle.

My Mooney M20 actually slows down as you increase power, unless you re-trim nose-down. And vice versa. Confuses the passengers no end!

...

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

[kallend 2,027]

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It's fortunate that that's not true, or Boeing would have had to build hundreds of versions of each type of aircraft (and then watched them all crash) before they got one that flew. Mathematical approximations can get you very close to a correct answer

I think the point was that you can't apply simple formulas to figure out exact speeds. Yes, Boeing does use mathematical approximations to calculate lift/drag, etc, but those are based on millions of calculations done by computers. It's not as if they plug a few variables into a formula to come up with performance numbers.

Dave

Ummm - there were very successful aircraft designers before computers were available. The Spirt of St. Louis is an example, as are the Spitfire, B29, Lancaster, Mosquito and P51. There's an interesting chapter in Hoerner's book on Fluid Dynamic Drag about the design of the Messerschmidt Bf109 and how they calculated its performance - very accurately, as it turns out, using simple fluid dynamics.

...

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

[mikeat10500 12]

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When all the data is not available I use a SWAG
calculation...I came up with 44.3mph!

Hope your friend gets well soon....mike

No one is even going to ask what SWAG stands for...are they?

-----------------------------------
Mike Wheadon B-3715,HEMP#1
Higher Expectations for Modern Parachutists.

[quade 4]

I woulda thunk everyone already knew it is a standard engineering term that stands for;

Silly
Wild
Assed
Guess

quade -
The World's Most Boring Skydiver

[mikeat10500 12]

Close enough...Scientific Wild Ass Guess.

-----------------------------------
Mike Wheadon B-3715,HEMP#1
Higher Expectations for Modern Parachutists.

[quade 4]

Actually, in my business we use WAG (Wild Ass Guess) and SWAG means, Stuff We Are Getting -- freebies, like t-shirts and other tchoskies -- but of course, context is everything when it comes to slang.

quade -
The World's Most Boring Skydiver

[Clownburner 0]

And that second meaning, actually is an 'invented' acronym from the original use of the word "Swag" which dates to 1660 and (among other things) means "goods acquired by unlawful means : LOOT b : SPOILS, PROFITS"

7CP#1 | BTR#2 | Payaso en fuego Rodriguez
"I want hot chicks in my boobies!"- McBeth

[sducoach 0]

[;)Hey Guys,
If you truly want some good info. Go to PD's page and check out Scott Miller's articles. You will find out, as Bill I think you know, wing loading equals speed. Increase wing loading, increase speed. Reduced drag, equals speed, decrease parasitic drag, increase speed because. We are working with a fixed thrust (gravity) so the L/D ratio can and will be changed but. Increased speed (velocity) causes increases in parasitic drag. Going in circles?? Yes unless you can make very large reductions in parasitic drag such as collapsible PC's.

Great line guys!

Tell me the formula you used, or how you calculated the speed with your SWAG.

Blues,

J.E.

James 4:8

[mikeat10500 12]

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Hey Guys,
If you truly want some good info. Go to PD's page and check out Scott Miller's articles.

Cool...I'll check that out!

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Great line guys!

Tell me the formula you used, or how you calculated the speed with your SWAG.

Sadly...I guessed (Wild Ass but in no way scientific) soley based on the extent of your friends injures.I now believe I guessed aprox 10 mph to high(based on wingloading vrs air speed info available).

I had the misfortune this weekend of dispatching my first student that resulted in an injury(minor). I know people will get hurt in the sport but I still hate to see it.

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Blues,

J.E.

I wish your friend a speedy recovery.

-----------------------------------
Mike Wheadon B-3715,HEMP#1
Higher Expectations for Modern Parachutists.

[sducoach 0]

Sorry to hear that. All we can do is instill the information. They must execute when they need to. After any type of incident/accident I always do a "hot" debrief on/of myself. First impressions, subjective, objective, application, and plan.

"SOAP"
Subjective: How I feel about it which includes emotions.
Objective: Just the facts.
Application: Specific cause and effect of the facts and how it related to the problem.
Plan: How to implement what I have learned from the facts and reduce the chance of a recurrence.

FYI.

Blues,

J.E.

James 4:8