Rear risers V Brakes glide chart

[yuri_base 1]

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But if you float in a headwind, you stay longer in the adverse winds.

If you have at least some ground speed, floating longer (while having the same ground speed) will move you farther forward. And if you're going backwards, why did you jump?

The components of the sustained airspeed of a flying body with adjusted lift and drag coefficients Kl and Kd are

Vx = Kl/(Kl^2 + Kd^2)^(3/4)
Vy = Kd/(Kl^2 + Kd^2)^(3/4)

In a presence of a headwind W the glide ratio is

G = (Vx - W)/Vy

If you take the derivative of the glide to the drag coefficient, you will find out that it's negative (decreasing drag increases glide) for windspeeds up to

W = Vx*(G0^2 + 1)/(G0^2 - 0.5) > Vx

where G0=L/D, the glide without the wind. So, unless you're being pushed backwards, bringing the knees up increases your glide.

The effect you describe (decreasing drag of a suspended weight will change the trim) is of the second order of magnitude, since a) the increase in the angle of attack will be partially compensated by increased L/D, and b) the pilot is still supposed to readjust the trim to maximize the glide when bringing the knees up.

I brought the math up just for the fun of oiling the rusting braincells , but everybody knows from experience that bringing knees up gives noticeable improvement to glide, wind or no wind.

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[kallend 1,726]

IF YOU FOLLOWED THE THREAD, this sub-thread started:

"Pulling your knees up improves the glide ..."

To which I replied:


"In all situations? Can you prove it?"

Thank you, Yuri, for proving my point, that there is a situation when it makes things worse

FACT: decreasing your drag is more beneficial running with the wind than going into a headwind, as I stated and as you have shown mathematically. Decreasing your drag is of decreasing effectiveness as the headwind gets stronger, as I stated and as you have shown mathematically. Eventually, if you are backing up, decreasing your drag is detrimental, etc....

As for what everyone knows, everyone used to know that the Earth is flat, the stars are attached to crystal spheres surrounding the Earth and disease is caused by bad air.

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

[adamT 0]

I have never experienced a reduction in body drag resulting in a loss of forward speed, just the opposite actually. So i maintain that reducing body drag will always be beneficial even when going backwards.
I don't know the math. But i have plenty of real world experience referencing other canopies, the ground, and the sound of the air, and that is enough proof for me.

[kallend 1,726]

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But i have plenty of real world experience

So do people who believe in the "45 degree rule".

...

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

[adamT 0]

So how about you explain your methods (canopy, wingloading, reference) that have proved to you that when you decrease the drag of your body your forward speed also decreases. The 45 degree rule is easily observed as bullshit. So far you haven't present any real world test that prove your statements. I have given several of my actual real life experiences in controlled situations that prove otherwise, and you haven't attempted to address them.
Please indulge us.

[kallend 1,726]

Quote

So how about you explain your methods (canopy, wingloading, reference) that have proved to you that when you decrease the drag of your body your forward speed also decreases. The 45 degree rule is easily observed as bullshit. So far you haven't present any real world test that prove your statements. I have given several of my actual real life experiences in controlled situations that prove otherwise, and you haven't attempted to address them.
Please indulge us.

Yuri's done the math for you (but never trust math and physics, they're way over-rated.

OTOH, imagine you're being blown backwards but could reduce your drag to zero. Your airspeed would remain essentially unchanged (because you'd still fly at the speed required for the lift to equal your weight) but you'd never come down at all. If you dive you'll pick up speed that you can't dissipate without climbing again. So you'd keep blowing backwards forever.

A more detailed analysis was done here some 5 years ago www.dropzone.com/cgi-bin/forum/gforum.cgi?post=120238#120238

...

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

[adamT 0]

Well that thread was just more of the same sitting around talking instead of going out and experimenting. I now can accept your original statement that is some conditions it may be detrimental. But I still think you are underestimating the effect that drag has on your forward speed. Next time you are flying next to someone with a similar wing, play with it. Watch how reducing your body drag will drive you forward relative to them. And don't just play with pulling your knees up. Try putting your heals on your ass, leaning forward through the harness and arching hard.
I see though that if you are backing up at a rapid rate and the reduction in drag still doesn't allow you to move forward, then it could hurt you. What do you think a reduction in body drag combined with front riser input would do?

And I don support you in that a modern canopy at anything above student wingloadings best gilde will be with a little bit of rears even into a moderate headwind.

[adamT 0]

That "I don support" is "I do support"