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BMAC615

A License on >1:1 WL?

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12 hours ago, 20kN said:

 Changing the wingloading absolutely does change the glide ratio. If you increase the loading high enough, there comes a point where the canopy becomes overloaded and it's vertical decent rate increases substantially with little increase in horizontal speed. This is very apparent in XRW where canopy pilots will hook wingsuiters on their feet and suspend their weight, after which their canopy falls out of the sky with no noticeable increase in forward speed.

Do you have a reference for this? If it's generally true but then breaks down at the extremes such as with XRW, could we agree that it's practically true in the context of this discussion?

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8 hours ago, nwt said:

Do you have a reference for this? If it's generally true but then breaks down at the extremes such as with XRW, could we agree that it's practically true in the context of this discussion?

I think it’s on you and @Kenzdik96 to provide a reference that glide ratio remains constant independent of WL as he is the one who initially made the claim.

Edited by BMAC615

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1 hour ago, BMAC615 said:

I think it’s on you and @Kenzdik96 to provide a reference that glide ratio remains constant independent of WL as he is the one who initially made the claim.

Glide ratio is numerically equal to the lift/drag ratio.  Adding weight increases the forward speed, but also increases drag in the same proportion, so the ratio remains the same.  You can google "glide ratio is independent of weight" and see any number of articles on the subject, and none to the contrary.

The flight path angle with respect to the horizon depends on the glide ratio and winds.  When flying in a headwind, a more heavily loaded canopy will have a shallower angle than a lightly loaded one.  When flying with a tailwind, it is the more lightly loaded canopy that will have a shallower angle.  In both cases, the glide ratio is the same.  The airspeed is different, and the amount of time of exposure to the wind conditions is different.

Do not equate glide ratio with the flight path angle with respect to the horizon.

 

 

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1 hour ago, BMAC615 said:

I think it’s on you and @Kenzdik96 to provide a reference that glide ratio remains constant independent of WL as he is the one who initially made the claim.

https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/glider_handbook/media/gfh_ch03.pdf

From page 3-8:

Quote

Increasing the mass of a glider by adding water ballast,
for example, shifts the glide polar down and to the
right. [Figure 3-18] The minimum sink rate is therefore
increased, so as expected, the extra weight makes it harder
to climb in thermals. However, the best glide ratio remains
approximately the same, but now occurs at a higher airspeed

 

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23 minutes ago, BMAC615 said:

Thank you for clearing that up. Back to the original topic: what are the coaches, instructors and S&TA’s thoughts on an A License flying a Sabre 170 w/ an exit weight of 225 lbs @ 1.32 WL?

Why are we so focused on talking about this one specific dude behind his back?

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1 hour ago, nwt said:

Why are we so focused on talking about this one specific dude behind his back?

Why are you so focused on talking about topics besides the specific subject of this thread? This “specific dude” is an example. This scenario seems to be prevalent across many DZs and has been for decades.

If you are a coach, instructor or S&TA, I’d like your opinion about this scenario. If you aren’t a coach, instructor or S&TA or would like to be a pedant about WL notation or the dynamics of WL in relation to glide ratio, please start another thread.

I’d like to keep the discussion focused to those who are rated and give advice regarding canopy choice and their thoughts about this specific scenario to gain insight about the type of advice they give to new skydivers who are choosing a first rig.

Are you a coach, instructor or S&TA? What are your thoughts on an A License flying a Sabre 170 w/ an exit weight of 225+ lbs @ 1.3+?

Edited by BMAC615
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On 2/12/2021 at 9:00 PM, 20kN said:

 Changing the wingloading absolutely does change the glide ratio. If you increase the loading high enough, there comes a point where the canopy becomes overloaded and it's vertical decent rate increases substantially with little increase in horizontal speed. This is very apparent in XRW where canopy pilots will hook wingsuiters on their feet and suspend their weight, after which their canopy falls out of the sky with no noticeable increase in forward speed.

You're also adding the drag of the wingsuiter (at what body position?), and it is way down low on the whole canopy & pilot system, which also tends to angle the canopy more nose down. So I think that's a different situation overall; it is about more than just more weight   There are unmanned military canopy systems that fly just fine at wing loadings of 5 or 10 without dropping out of the sky.

"And now back to your regularly scheduled novice wing loading arguments."

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On 2/12/2021 at 9:00 PM, 20kN said:

 Changing the wingloading absolutely does change the glide ratio. If you increase the loading high enough, there comes a point where the canopy becomes overloaded and it's vertical decent rate increases substantially with little increase in horizontal speed. This is very apparent in XRW where canopy pilots will hook wingsuiters on their feet and suspend their weight, after which their canopy falls out of the sky with no noticeable increase in forward speed.

You're also adding the drag of the wingsuiter (at what body position?), and it is way down low on the whole canopy & pilot system, which also tends to angle the canopy more nose down. So I think that's a different situation overall; it is about more than just more weight   There are unmanned military canopy systems that fly just fine at wing loadings of 5 or 10 without dropping out of the sky.

"And now back to your regularly scheduled novice wing loading arguments."

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(edited)
On 2/13/2021 at 7:38 PM, BMAC615 said:

Thank you for clearing that up. Back to the original topic: what are the coaches, instructors and S&TA’s thoughts on an A License flying a Sabre 170 w/ an exit weight of 225 lbs @ 1.32 WL?

I think you already know the answer to that question. It's not smart. Can some people get lucky and not get hurt? Sure. But I have also seen A license guys break bones under a WL of 0.8. It's a sliding scale. How much risk do you want to take? In the case of an A license holder flying 1.3, I'd say the needle on the risk scale is in the red. It also depends on the canopy itself. Is this a canopy with a super flat glide that has a low decent rate, or a Katana that just falls out of the sky? Does the canopy have massive flare power and you could shut it down on a downwinder, or is it a mushy 7-cell that flares like a semi-truck on ice? Those all play a role as well.

Edited by 20kN
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10 hours ago, 20kN said:

I think you already know the answer to that question. It's not smart. Can some people get lucky and not get hurt? Sure. But I have also seen A license guys break bones under a WL of 0.8. It's a sliding scale. How much risk do you want to take? In the case of an A license holder flying 1.3, I'd say the needle on the risk scale is in the red. It also depends on the canopy itself. Is this a canopy with a super flat glide that has a low decent rate, or a Katana that just falls out of the sky? Does the canopy have massive flare power and you could shut it down on a downwinder, or is it a mushy 7-cell that flares like a semi-truck on ice? Those all play a role as well.

I think we’re in agreement that it’s not smart, but, this isn’t an isolated event. I’m interested in hearing from some who thinks this is smart and agrees with the instructors and S&TA of this situation?

“I have also seen A license guys break bones under a WL of 0.8.“  We can agree on this as well, but, how much worse would it have been had the WL been >.8?

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On 2/8/2021 at 7:44 PM, nwt said:

I understand this. I'm asking can we please stop because it's stupid.

Actually, it is not only not stupid, it is specifically correct and even what you yourself asked for... "express wingloading as pounds per square foot"....
"1.2 pound per 1 square foot" is literally notated as "1.2:1"

Often we use a short hand of "1.2" to express the same thing, but you _are_ being provided with _exactly_ what you're asking for...

 

JW



 

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1 hour ago, fcajump said:

"1.2 pound per 1 square foot" is literally notated as "1.2:1"

No, it isn't. Neither is miles per hour or pounds per square inch, etc. Pounds per square foot is no different. When the cop asks you how fast you were going, do you respond with "50:1"? Do you fill your tires to "35:1"?

An example where this notation is actually appropriate is canopy aspect ratio, which is the ratio of width to length, is unitless, and will be the same value regardless of the measurement system in use.

Edited by nwt

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13 hours ago, nwt said:

No, it isn't. Neither is miles per hour or pounds per square inch, etc. Pounds per square foot is no different. When the cop asks you how fast you were going, do you respond with "50:1"? Do you fill your tires to "35:1"?

An example where this notation is actually appropriate is canopy aspect ratio, which is the ratio of width to length, is unitless, and will be the same value regardless of the measurement system in use.

i would think of it as a ratio, 1.2 lbs per 1 sq ft of canopy would be written as 1.2:1.  i remembered that from a math course years ago, but i looked it up just to make sure.  you have to hit definition to expand it.

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On 6/4/2021 at 4:25 PM, nwt said:

No, it isn't. Neither is miles per hour or pounds per square inch, etc. Pounds per square foot is no different. When the cop asks you how fast you were going, do you respond with "50:1"? Do you fill your tires to "35:1"?

An example where this notation is actually appropriate is canopy aspect ratio, which is the ratio of width to length, is unitless, and will be the same value regardless of the measurement system in use.

People can express it however they want regardless of what you think.

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On 6/5/2021 at 6:25 AM, sfzombie13 said:

i would think of it as a ratio, 1.2 lbs per 1 sq ft of canopy would be written as 1.2:1.  i remembered that from a math course years ago, but i looked it up just to make sure.  you have to hit definition to expand it.

Okay, you might be right that it isn't technically incorrect, but it doesn't make any sense to use this notation in this context. Do you drive 55:1 or fill your tires to 35:1? 

Look at the examples in the link you gave. They are all comparisons of a count of "things" to a count of other "things" and none of them can be described by standard units of measure. Boys:apples, girls:oranges, wins:losses, etc.

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2 hours ago, nwt said:

Okay, you might be right that it isn't technically incorrect, but it doesn't make any sense to use this notation in this context. Do you drive 55:1 or fill your tires to 35:1? 

Look at the examples in the link you gave. They are all comparisons of a count of "things" to a count of other "things" and none of them can be described by standard units of measure. Boys:apples, girls:oranges, wins:losses, etc.

Technically correct is the best kind of correct. You’ve been wrong in the past, you’re wrong now and will be wrong in the future, get over yourself.

Edited by BMAC615

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5 hours ago, nwt said:

Okay, you might be right that it isn't technically incorrect, but it doesn't make any sense to use this notation in this context. Do you drive 55:1 or fill your tires to 35:1? 

Look at the examples in the link you gave. They are all comparisons of a count of "things" to a count of other "things" and none of them can be described by standard units of measure. Boys:apples, girls:oranges, wins:losses, etc.

Ok. I was taught to express canopy loading a s a ratio, dividing he weight by the footage to express it  as "this many pounds is being carried by each square foot of canopy."

This number gives an approximation of the expected performance. For stuff like students and downsizing progression and also for CRW.
 

Since you don't like the 'ratio' expression, how would you like to see it?
What sort of notation do you think would be better?


Edit to add:

Wendy's remonstration came while I was composing this. Not sure if this counts as what she doesn't want. 

Edited by wolfriverjoe

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