How winds affect canopy flight...

[f94sbu 0]

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Real life of course will vary a lot! While the formula makes it all a gradual change, the overall change is significant -- the wind is about doubled a couple hundred feet up, compared to what one feels in one's face on the ground.

Just keep in mind that your canopy isn't (hopefully) flying at 5 feet altitude... How does your formula look like? It looks like it is very non-linear near ground where you normally don't fly your canopy.

rgds,
Stefan

[pchapman 279]

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Just keep in mind that your canopy isn't (hopefully) flying at 5 feet altitude... How does your formula look like? It looks like it is very non-linear near ground

The heights I chose were arbitrary, but the 15 ft level corresponds very roughly to a canopy on landing, and the 5 ft level corresponds to where we feel the wind in our face when standing on the ground.

The formula uses height ratios and an exponent, so yes it is quite non linear:
v2 = v1 x (h2/h1)^n where v1 is the known reference wind speed at height h1 above ground, v2 is the speed at a second height h2, and n is an exponent based on testing. The exponent n varies between .1 for smooth ocean and .2 for tall crops & low woods.

I can't comment on how well the various formulae and statistics out there are regarded by those in fields dealing with wind measurements. This one appeared reasonable, and good enough for a rough image of the kind of wind speed changes a skydiver may deal with during landing approach. (Being downwind of a large obstacle is another matter.)

[raymod2 1]

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5 ft height ------ 18 mph
15 ft height ------ 22 mph
33 ft height ------ 25 mph
100 ft height ------ 31 mph
200 ft height ------ 35 mph
(The above would be for a weather report of 25 mph winds, since a standard measuring height is 33 ft.)

This is very interesting. If true it would help explain the benefit of popping up during a downwind distance run.

[ntacfreefly 0]

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If true it would help explain the benefit of popping up during a downwind distance run.

Trajectory. We've been over this before Dan

To the mind that is still, the whole universe surrenders. ~ Lao-Tzu

It's all good, they're my brothers ~ Mariann Kramer

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If true it would help explain the benefit of popping up during a downwind distance run.

Trajectory. We've been over this before Dan

you say "Trajectory"
but there are more than one theory toward this. but they all point in the same direction. my theory is different.

[ntacfreefly 0]

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my theory is different

Hurl an object at 100 mph dead straight. Measure distance.

Hurl same object at same velocity with a 10 degree angle at launch. Measure distance.

Look at Olympian shot put, long jump, hammer throw, etc, etc, etc. They all follow the same principals. It's a balance between the best angle for the velocity of the object.

Not much 'theory' there Mark

To the mind that is still, the whole universe surrenders. ~ Lao-Tzu

It's all good, they're my brothers ~ Mariann Kramer

[marks 0]

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Not much 'theory' there Mark

I sat here and thought about it for a second, and you are correct.

trajectory, is "part" of the theory.

[ntacfreefly 0]

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trajectory, is "part" of the theory.

Now that I agree on

To the mind that is still, the whole universe surrenders. ~ Lao-Tzu

It's all good, they're my brothers ~ Mariann Kramer

[raymod2 1]

Ian, I just don't buy the "projectile trajectory" explanation. A canopy is not the same as a cannonball or a bullet. The difference is that a canopy generates lift. There is also one point that seems to get forgotten: A canopy must pass through a point where it is flying level (generally somewhere near the gates). To get it to rise after that you need to generate more lift than would be necessary to stay level. And more lift means more induced drag.

[Spizzzarko 0]

True a cannon ball is not like a canopy, but the mass of meat suspended below it sure is. If you have a lot of speed developed from a good turn then it is very easy to get a canopy to climb on it's own. The JVX really likes to climb from my observations, and those dudes are having a hard time keeping it on the water for free style especially when they are unloading the canopy by placing weight in the water.

[AggieDave 6]

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those dudes are having a hard time keeping it on the water for free style especially when they are unloading the canopy by placing weight in the water.

What about the guys on a JVX trying to do a standard CPC speed run with a carving course? Do they have trouble keeping the canopy in the course or from hitting blades due to the canopy trying to climb?

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

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To get it to rise after that you need to generate more lift than would be necessary to stay level. And more lift means more induced drag

you can generate more speed if your body, "weight" is a pendulum. and when your body swings out in front of the canopy it pitches it upward. that way you don't add any input and the canopy climbs at full efficiency. although this is just one point of view, there are other ways, and ideas to do the "pop up" thing your talking about. do it too much, and it hurts you. do it to little not much help. do it just right, and you will go sailing. It kinda "just happens"

and to answer dave's question. that isn't the canopy not being able to stay down on the water, it is the pilot. or stay down in the course. if you have problems popping out of the course in speed runs, try not using your rears to turn, you need to use more harness and straighten out the turn. if you arent straight, and you have all that speed, turning with your rears will pop you out of the course.

you will climb off the water even more when your going downwind. try using toggles instead of rears if your not hitting it just right and are climbing off the water.

if your body pendulums too much when your trying to stay on the water, the same thing happens, your body gets out in front of the canopy, which pitches it up, and causes it to climb.

[raymod2 1]

I doubt any canopy will climb on its own when you have it tipped over going through a carving course.

[Spizzzarko 0]

The popping up technique is more for distance runs than anything. With Speed yes you are leaned over in the traditional carving speed runs, but it has been run as a straight course in the past, so there is nothing preventing the competition director from changing it in the future.

[audacium 0]

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To get it to rise after that you need to generate more lift than would be necessary to stay level. And more lift means more induced drag.

Actually, induced drag diminishes with more speed, it is parasitic drag that increases with speed. So, in order to know whether total drag increases with speed you have to know where you are on the "total drag curve".

That is an interesting question: Are canopies at the minimum of the total drag curve when flown at trim speed and without any inputs from the pilot? It would be entirely possible for the canopy designer to move this point a little bit towards "accelerated flight", ie, after front riser input or after a steep turn.Then a canopy would have its best glide at higher speeds than trim speed.

Does anyone know about this?

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Eduard

[Pendragon 1]

Canopies are not trimmed to be at min drag (also happens to be min sink) at the toggles-up position - they are trimmed much faster. This is to give the canopy good flaring characteristics I believe. Less drag would come from some rear riser input.

BTW - you are both right;

- Induced drag diminishes with speed
- More lift (i.e. slower speed on an unpowered wing) means more induced drag

Just opposite ways of saying the same thing

Richard

--
BASE #1182
Muff #3573
PFI #52; UK WSI #13

[audacium 0]

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Canopies are not trimmed to be at min drag (also happens to be min sink) at the toggles-up position - they are trimmed much faster. This is to give the canopy good flaring characteristics I believe. Less drag would come from some rear riser input.

Thanks. I think min drag means best glide, while min sink happens at max lift which means more drag?

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BTW - you are both right;

- Induced drag diminishes with speed
- More lift (i.e. slower speed on an unpowered wing) means more induced drag

Hm, I think we are mixing two things: If I do not change the configuration of my (unpowered) wing then going faster with this wing will produce more lift but less induced drag. I think what you are saying is "if I increase the angle of attack and thus increase the lift coefficient C_L, I will go slower and the induced drag will rise (because I go slower)". But this is a changed configuation. I was talking about coming out of a carve turn or so with increased speed, but with pilot not giving any inputs for a moment (that is, when leveling out)

What do you think?

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Eduard

[Pendragon 1]

For an unpowered wing like a parachute, min sink is at that point when the wing is most efficient (min drag).

Max glide is always faster: obviously with a tail wind, it gets very close to min sink (spend more time getting blown in the right direction). By way of demonstration, consider a canopy with a min sink airspeed of 20 mph going into a 20 mph headwind. By definition, ground speed = 0 (and glide ratio = 0). However, increase the angle of attack and speed the wing up, forward penetration increases so you get glide.

Max glide speed is highly dependent on the horizontal wind speed.

Regarding your second point, coming out of a carving turn puts your canopy beyond its normal flying speed - you've put the wing in a dive, gravity has accelerated you and you're coming out with a surge of speed which results in lift as the excess speed the wing has to fly is converted into lift (at a constant angle of attack). This is a temporary effect though, as we all know.

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BASE #1182
Muff #3573
PFI #52; UK WSI #13

[meatbomb 0]

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you will climb off the water even more when your going downwind.

Didn't we just have a thread about this...oh wait...

Over a longer period, with a shallower climb angle perhaps? Or just the perception thing causing different inputs?

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Swoopert, CS-Aiiiiiii!
Piccies

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you will climb off the water even more when your going downwind.

Didn't we just have a thread about this...oh wait...

Over a longer period, with a shallower climb angle perhaps? Or just the perception thing causing different inputs?

I'm not really sure why you climb off the water more when going downwind. I think it may be because of too much input because your perception is off and you add too much input too quick, which will cause you to swing underneath and then it climbs. I still think it is because of the pilot and not the canopy.

[audacium 0]

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For an unpowered wing like a parachute, min sink is at that point when the wing is most efficient (min drag).

Max glide is always faster: obviously with a tail wind, it gets very close to min sink (spend more time getting blown in the right direction). By way of demonstration, consider a canopy with a min sink airspeed of 20 mph going into a 20 mph headwind. By definition, ground speed = 0 (and glide ratio = 0). However, increase the angle of attack and speed the wing up, forward penetration increases so you get glide.

Max glide speed is highly dependent on the horizontal wind speed.

The above is not correct, sorry, at least not in this generality.

The speeds for best glide and for minimum sink are in general NOT the same. Practical example: For paragliders (another unpowered wing) they are definitely not. Best glide usually happens at trim speed (ie, without any inputs), while minimum sink happens when some brake (about 20%) is applied. But the wing goes slower of course, glide ratio gets worse.

Theory: Best glide happens when the wing is most efficient, and that is when total drag is at a minimum (which makes sense). Do a calculation for example with one common polar equation (C_d = C_d0 + k c_l^2). Minimize total drag, and you will arrive at the exact same condition for best glide, and vice versa. The calculation for minimum sink is different and will result in a worse glide ratio.

Minimum sink happens at values for the lift coefficient much higher than they are for best glide (and thus at slower speeds). In fact, total drag rises more than lift increases and thus glide ratio gets worse (again, paragliders glide worse at minimum sink, but when using thermals it is min sink which is relevant but not the glide ratio).

Also, two things should not be mixed: how the wing flies in the air, thus, its inherent glide ratio, etc., and what that means for glide ratio etc. relative to the ground. For better penetration into a head wind you decrease, not increase the angle of attack (I think you simply wrote the opposite of what you wanted to.)

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Regarding your second point, coming out of a carving turn puts your canopy beyond its normal flying speed - you've put the wing in a dive, gravity has accelerated you and you're coming out with a surge of speed which results in lift as the excess speed the wing has to fly is converted into lift (at a constant angle of attack). This is a temporary effect though, as we all know.

Exactly, and this is what I was saying in reply to raymod2 "more lift means more induced drag": in the discussed case of coming out of a fast turn, when hitting the gates, more lift is generated but not necessarily more drag. When the canopy rises instead of levelling out it means lift grows proportionally more than drag rises, right?


All the best, Eduard.

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Eduard

[raymod2 1]

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Exactly, and this is what I was saying in reply to raymod2 "more lift means more induced drag": in the discussed case of coming out of a fast turn, when hitting the gates, more lift is generated but not necessarily more drag.

Please refer to the following URL:

http://en.wikipedia.org/wiki/Lift-induced_drag

Here they give the formula for induced drag:

k * L^2            

Di = ------------------------------

0.5 * rho0 * Ve^2 * S * pi * A

Notice the term L^2 in the numerator. This means that induced drag is proportional to the square of the lift.

[audacium 0]

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Notice the term L^2 in the numerator. This means that induced drag is proportional to the square of the lift.

I stand corrected, when I answered I was thinking of level flight with constant lift which obviously does not apply here as we were talking about more lift due to more speed, sorry for the confusion...

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Eduard