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Cirrus descent rate under parachute less with wind?

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Cirrus descent rate under parachute less with wind?

Old 31st Mar 2020, 11:42
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Cirrus descent rate under parachute less with wind?

In the youtube video below Paul Bertorelli states at 4.07 that a Cirrus with parachute deployed descends at a rate of 1700 fpm but will have a lower rate of descent if there is a wind.


Can someone explain that? To me the aircraft has no form of control with the parachute deployed as the indicated airspeed will be zero in a constant wind however strong and there is no way of harnessing the wind strength to form lift.
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Old 31st Mar 2020, 11:57
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The aircraft and parachute will not move at the same speed as the wind because of drag. Therefore there will a small residual airflow over the wings which may generate a LITTLE lift.
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Old 31st Mar 2020, 13:16
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Originally Posted by Groundloop View Post
The aircraft and parachute will not move at the same speed as the wind because of drag. Therefore there will a small residual airflow over the wings which may generate a LITTLE lift.
If they move at different speeds the distance between them would have to increase😀 So any small transient changes in speed between them due to drag or pendulum effect would have to cancel out.
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Old 31st Mar 2020, 22:59
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Drag is the reason the plane and parachute will very quickly stabilise at the wind speed.
Only severe windshear would have the plane and parachute at different speeds while still attached to one another, a situation which might occur near the ground.
However it would be possible for them to gain height in strong updrafts.
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Old 1st Apr 2020, 01:28
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In still air the parachute will be directly above the aircraft and both will go straight down.
In a wind the parachute will above and ahead of the aircraft and both will decend at an angle. There are 2 vectors, horizontal and vertical, the aircraft will take longer to reach the ground, simple trigonometry.
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Old 1st Apr 2020, 02:51
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Having jumped round canopies in high winds I can tell you that your position hanging in the harness does not change relative to the canopy ie you still hang directly below the canopy apex, nor does the rate of descent change with wind, why Paul states what he does I have no idea. One advantage landing with wind is that the horizontal impetus throws you into a landing roll, rather than coming straight down and landing like a bag of spuds. There are wind limits of course, have memories of a barb wire fence arresting horizontal passage across across a very wet and muddy wheat field. Good training for a to be fixed wing naval aviator.
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Old 1st Apr 2020, 09:28
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Originally Posted by The Ancient Geek View Post
In still air the parachute will be directly above the aircraft and both will go straight down.
In a wind the parachute will above and ahead of the aircraft and both will decend at an angle. There are 2 vectors, horizontal and vertical, the aircraft will take longer to reach the ground, simple trigonometry.
It may be simple trigonometry, but you've done it wrong.

If the wind is constant all the way down, it will make no difference to the descent rate (and probably very little even if the wind does vary). The aircraft will take the same time to reach the ground compared with there being no wind.

If there is wind, then the overall velocity of the aircraft (the sum of the descent and wind vectors) will be higher than with no wind - but only as measured by an observer stationary relative to the ground. For an observer say in a balloon, drifting with the wind, there will be no difference.

The claim in the original video is incorrect.

Paul
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Old 1st Apr 2020, 11:18
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Originally Posted by The Ancient Geek View Post
In still air the parachute will be directly above the aircraft and both will go straight down.
In a wind the parachute will above and ahead of the aircraft and both will decend at an angle. There are 2 vectors, horizontal and vertical, the aircraft will take longer to reach the ground, simple trigonometry.
Nope, you’re getting ground and wind speed confused. They are totally, totally, totally unrelated. You could be in a 50,000kts wind, if the air is stable then you’d be hanging quite happily, quite vertically, everything pointing to the centre of the Earth. It just so happens to be spinning below at a great speed.
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Old 1st Apr 2020, 11:38
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Irrespective of the debate above I find 1700 fpm as rather uncomfortable when hitting solid ground...
​​
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Old 1st Apr 2020, 13:44
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Originally Posted by megan View Post
Having jumped round canopies in high winds I can tell you that your position hanging in the harness does not change relative to the canopy ie you still hang directly below the canopy apex, nor does the rate of descent change with wind, why Paul states what he does I have no idea. One advantage landing with wind is that the horizontal impetus throws you into a landing roll, rather than coming straight down and landing like a bag of spuds. There are wind limits of course, have memories of a barb wire fence arresting horizontal passage across across a very wet and muddy wheat field. Good training for a to be fixed wing naval aviator.
This is the only explanation. The video statement is wrong, and misleading.
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Old 1st Apr 2020, 13:53
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Hmmm as my normal descent on finals would be about 400 ft/min then 1,700 ft/ min sounds a lot.

I make it (1700 / 60) x (60 / 88) = 19.3 mph. suppose its a good bit slower than without the parachute but it still seems a tad quick to me. That's why I've never had the urge to leap out of a serviceable aeroplane.
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Old 1st Apr 2020, 14:41
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I find 1700 fpm as rather uncomfortable when hitting solid ground...
Me too!

That's why I've never had the urge to leap out of a serviceable aeroplane.
Me either! Though I flew jumpers for years. The happy difference for the sport parachutist, as opposed to the Cirrus passenger, is that the sport parachutist has the ability to flare the parachute for a softer landing, and regularly impressed me with well timed flares, and feather soft touchdowns. If I understand correctly, the returning Russian space vehicles use last moment rockets to arrest the descent rate - okay, I guess it works, but the civil aviation standards would never allow certifying such a system! The Cirrus does not know when it's about to hit.

A descent rate of 1700 fpm exceeds some helicopter autorotation rates I have flow, and they're a little alarming. When I changed the prop from two to three blade on my flying boat, the power off, full fine propeller pitch glide went from 800 fpm, to 1300 fpm. This was an alarming rate in this plane, and I really think that a flare to a safe landing from even 1300 fpm would be challenging. (I found that selecting full coarse propeller greatly improved the glide).

a 19 mph stop is painful. Cirrus gets credit for energy absorbent seats, which I'm sure really help, but it's still a hard stop. In times past, when car seatbelt use was being encouraged, there was a road safety car simulator, which subjected the occupant to a 5 mph crash force, even that was a jerk.

I can't imagine a Cirrus parachute descent rate low enough, combined with all other factors, to make me comfortable with the system. But that's my personal opinion, I respect that others feel differently, and that is entirely their privilege too...
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Old 1st Apr 2020, 15:14
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Sometimes that Cirrus pushes pilots to do stupid things because of the chute...they should read this thread. It's a nice plane but it's still a limited SE
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Old 1st Apr 2020, 15:32
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If I had an engine failure in a Cirrus and could not reach an airfield I would rather glide down and land in a suitable field. Is that what is recommended or do they suggest pulling the parachute handle?

I remember seeing at an airshow a light sport aircraft with a ballistic parachute. It was designed to come down right wing low under the 'chute so the right wing would hit first and concertina thus absorbing energy before it would straighten up and land on the gear. Very clever.
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Old 2nd Apr 2020, 03:38
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1,700 ft/ min sounds a lot
Just for comparison sake the maximum rate of descent permitted in my jumping days was 1,260 ft/min (21 ft/sec) with a 170 pound individual. The main we used was a 28 ft diameter (same as used in the F-86 at the time, same container as well, descent rate 19.8 ft/sec with 235 pound load) with a 24 ft diameter chest mounted reserve. Big guys would use a 35 ft diameter main and 28 ft reserve.
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Old 2nd Apr 2020, 09:52
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Originally Posted by The Ancient Geek View Post
In still air the parachute will be directly above the aircraft and both will go straight down.
In a wind the parachute will above and ahead of the aircraft and both will decend at an angle. There are 2 vectors, horizontal and vertical, the aircraft will take longer to reach the ground, simple trigonometry.
This is completely wrong. The load on the parachute falls at the same rate regardless of any wind. It is a pity that (wrong) opinions are dressed up as statements of fact - when they are not. Dressing it up with irrelevant maths, vectors, trigonometry etc doesn't make it right.
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Old 2nd Apr 2020, 10:36
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Originally Posted by The Ancient Geek View Post
In still air the parachute will be directly above the aircraft and both will go straight down.
In a wind the parachute will above and ahead of the aircraft and both will decend at an angle. There are 2 vectors, horizontal and vertical, the aircraft will take longer to reach the ground, simple trigonometry.
No it won't. The vertical component is the same. However the wind ADDS a horizonal component.
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Old 2nd Apr 2020, 12:36
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Okay, I don't know which answer is right, with a wind, the cirrus has more time before arriving to earth, or not. It's a worthwhile discussion and thinking point while we're not flying, but it's not worth rudeness, nor emotion, so reign it in! Everyone is entitled to their opinion, politely expressed, someone's opinion is probably correct. It won't hurt anyone for a trigonometry review, which is why I have not deleted a couple of posts, nor locked the thread. The principles here are worth discussion, but they're not worth an argument.

So, someone(s) who knows a lot more about trigonometry than I, please feel welcomed to post some math with lines at angles, and the rest of us will learn something we will hopefully never use!

You moderator, Pilot DAR....
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Old 2nd Apr 2020, 14:21
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Originally Posted by Pilot DAR View Post
Okay, I don't know which answer is right, with a wind, the cirrus has more time before arriving to earth, or not. It's a worthwhile discussion and thinking point while we're not flying, but it's not worth rudeness, nor emotion, so reign it in! Everyone is entitled to their opinion, politely expressed, someone's opinion is probably correct. It won't hurt anyone for a trigonometry review, which is why I have not deleted a couple of posts, nor locked the thread. The principles here are worth discussion, but they're not worth an argument.

So, someone(s) who knows a lot more about trigonometry than I, please feel welcomed to post some math with lines at angles, and the rest of us will learn something we will hopefully never use!

You moderator, Pilot DAR....
In my view it will only take longer if there is some sort of uplift. And, of course, it could encounter sink. As any glider pilot knows, both of these are possible on an absolutely still day.
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Old 2nd Apr 2020, 15:59
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Okay then. As already posted by some, any wind velocity will not reduce the descent rate as incorrectly stated in the video. Descent rate will not change. However impact velocity will increase. Notwithstanding aforementioned vertical wind currents obviously. Here is the relevent equation and trig:


...so in a sense the video has it the wrong way around because wind drift is going to make the impact worse. QED

Last edited by oggers; 3rd Apr 2020 at 09:06.
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