Forums: Skydiving: Safety and Training:
Becoming unconscious under open canopy

 

First page Previous page 1 2 3 4 Next page Last page  View All

evh  (D License)

Jul 5, 2005, 2:23 PM
Post #76 of 87 (455 views)
Shortcut
Re: [cchandler] Becoming unconscious under open canopy [In reply to] Can't Post

In reply to:
If an airplane, or parachute, is exposed to increased wind velocity (gust) from a particular direction, the airplane, or parachute, will move in the opposite direction (or decrease it's velocity) an amount equal to the velocity of the gust. The aircraft will NOT turn.

It will move, but it will also turn. If it didn't it would be unstable.
Airplanes rotate around their centre of gravity (at about 1/3 of the chord). The surface area (seen from the side) behind the C.O.G. is always much larger than in front of it (weathervane effect?), even for the Wright plane.


cchandler  (D 12392)

Jul 5, 2005, 2:33 PM
Post #77 of 87 (443 views)
Shortcut
Re: [tso-d_chris] Becoming unconscious under open canopy [In reply to] Can't Post

Will a canopy (or airplane) turn in turbulence? Sure it will. We see that all the time.

However, the reason the canopy turns is not because of "wind." The canopy turns because the amount of drag or lift on the airfoil is not symetrical over it's entire span. Sounds like what happens during a toggle input?

Rising airmasses (thermals) and orographic turbulence (from trees, terrain, buildings) may affect only a part of the airfoil. If the change in drag or lift on that segment of the parachute is significant enough, it will manifest as a turn.

Additionally, our semi-rigid airfoils may change shape over a portion of the airfoil, thus changing the flight characteristics of the entire canopy and possibly causing a turn.


(This post was edited by cchandler on Jul 5, 2005, 2:33 PM)


tso-d_chris

Jul 5, 2005, 2:41 PM
Post #78 of 87 (431 views)
Shortcut
Re: [cchandler] Becoming unconscious under open canopy [In reply to] Can't Post

In reply to:
The canopy turns because the amount of drag or lift on the airfoil is not symetrical over it's entire span.

Or its chord. Same forces, coming from a different direction. Same result about the vertical axis.


kelpdiver  (B 7)

Jul 5, 2005, 2:47 PM
Post #79 of 87 (426 views)
Shortcut
Re: [tso-d_chris] Becoming unconscious under open canopy [In reply to] Can't Post

In reply to:
If there is no reference to the ground, you have no way of knowing whether your claim is true or not.

compass. Effectively the same way a plane navigates (yeah, I know they use a device that is more inertial). If you were opening at 14k over cloud cover, it would be foolish not to carry one.


tso-d_chris

Jul 5, 2005, 2:59 PM
Post #80 of 87 (422 views)
Shortcut
Re: [kelpdiver] Becoming unconscious under open canopy [In reply to] Can't Post

In reply to:
compass. Effectively the same way a plane navigates

Sounds reasonable.


cchandler  (D 12392)

Jul 5, 2005, 3:04 PM
Post #81 of 87 (424 views)
Shortcut
Re: [tso-d_chris] Becoming unconscious under open canopy [In reply to] Can't Post

Quote:
If there is no reference to the ground, you have no way of knowing whether your claim is true or not.

You are correct that one cannot determine ground track. That's the whole point to my imaginary "above the clouds" parachute jump.

One could use the sun as a heading reference, or a compass, as suggested by a subsequent post. I recall a night 8 stack I was on a few years back. The pilot of the stack used the moon as a heading reference as we were above an undercast. He made timed turns to maintain orientation to the DZ. Yes we all landed on the DZ after descending thru the clouds at 2500 feet.Shocked

Remember, for the sake of our discusion, it's all about the flight of the canopy in the air.


Premier billvon  (D 16479)
Moderator
Jul 5, 2005, 3:11 PM
Post #82 of 87 (421 views)
Shortcut
Re: [cchandler] Becoming unconscious under open canopy [In reply to] Can't Post

>Will a canopy (or airplane) turn in turbulence? Sure it will. We see
>that all the time.

Agreed.

>However, the reason the canopy turns is not because of "wind." The
> canopy turns because the amount of drag or lift on the airfoil is not
> symetrical over it's entire span.

Nope. Same thing would happen with a dart, or a glider, or a windsock, or a tetrahedron. It faces into the relative wind because it is designed with its center of pressure behind its center of mass (or center of rotation, in the case of the ground-mounted things.) When the wind changes direction, forces on the 'tail' overpower forces on the 'nose' and cause a turn in the direction of the relative wind.

>Additionally, our semi-rigid airfoils may change shape over a
>portion of the airfoil, thus changing the flight characteristics of
>the entire canopy and possibly causing a turn.

Rigid wing aircraft do the same thing.


cchandler  (D 12392)

Jul 5, 2005, 4:26 PM
Post #83 of 87 (407 views)
Shortcut
Re: [billvon] Becoming unconscious under open canopy [In reply to] Can't Post

Yes Bill, the relative wind, which is the wind opposite the direction of flight! Wink


(This post was edited by cchandler on Jul 5, 2005, 4:27 PM)


Premier billvon  (D 16479)
Moderator
Jul 5, 2005, 4:47 PM
Post #84 of 87 (402 views)
Shortcut
Re: [cchandler] Becoming unconscious under open canopy [In reply to] Can't Post

>Yes Bill, the relative wind, which is the wind opposite the direction of flight!

Right, and if you change the real wind, you change the relative wind too - at least until the aircraft adjusts to the 'new' relative wind.


pilotdave  (D License)

Jul 5, 2005, 6:50 PM
Post #85 of 87 (394 views)
Shortcut
Re: [cchandler] Becoming unconscious under open canopy [In reply to] Can't Post

Quote:
As far as having a "tail" in the front and it not working, let's keep it our secret and not tell the Wright Brothers.
http://www.nasm.si.edu/...00/wright_flight.jpg

Hehe, c'mon, you know better than that... you're looking at that picture backwards. The vertical tails ARE in the back. The stabilators were in the front.

A plane most definitely WILL weathervane in a sideslip (caused by pilot input OR a crosswind gust). Think about what happens when you kick the rudder and bring it back to neutral. The plane flies slightly sideways for a short time, then weathervanes back into the relative wind. Same thing happens when a gust of wind hits the plane from the side. The plane won't instantaneously change flight paths (relative to the ground) because of inertia.

This is simple stability and control. The response of the aircraft in yaw (yaw moment) to a disturbance in sideslip angle. An aircraft with neutral stability in yaw would produce no yaw moment when exposed to a sideslip. That would mean a disturbance in yaw (like the pilot momentarily kicking ae rudder pedal) would produce no tendency for the aircraft to reduce that sideslip. The plane would just continue to fly with a sideslip, slightly skewed (in relation to the relative wind, not the ground).

I'm only talking about airflow with respect to the aircraft. Picture a top view of an airplane. Theres a straight line connecting the nose and the tail. Zero sideslip means the relative wind is parallel to that aircraft longitudinal axis. A sideslip is any deviation in the angle between the relative wind and the longitudinal axis. What causes that sideslip doesn't matter. It can be wind from monther nature, pilot input, or a bigass fan. The aircraft reaction will be the same.

Dave


(This post was edited by pilotdave on Jul 5, 2005, 6:51 PM)


JohnMitchell  (D 6462)

Jul 5, 2005, 9:46 PM
Post #86 of 87 (383 views)
Shortcut
Re: [tso-d_chris] Becoming unconscious under open canopy [In reply to] Can't Post

In reply to:
[And, to clarify, I WAS WRONG ABOUT IT ALWAYS PREFERRING A DOWNWIND HEADING. .
For the second time, I'll tell you. THAT WAS ALL I WAS SAYING YOU WERE WRONG ABOUT THE WHOLE TIME.

Excuse me, was I screaming again?Tongue

I never said canopies don't move around in turbulent, gusty winds. That's moronic, seriously. I was simply stating that they don't prefer downwind over upwind, they just move around where ever they get blown. And so do I. Cool


tso-d_chris

Jul 6, 2005, 6:58 AM
Post #87 of 87 (363 views)
Shortcut
Re: [JohnMitchell] Becoming unconscious under open canopy [In reply to] Can't Post

In reply to:
For the second time, I'll tell you. THAT WAS ALL I WAS SAYING YOU WERE WRONG ABOUT THE WHOLE TIME.

Excuse me, was I screaming again?

Sorry, I wasn't meaning to yell at you. Tongue

Initially, I would have been more accurate if I had said:

A canopy will not maintain a heading all by itself. It has a preferred orientation relative to the positive acceleration of the airmass in which it is flying. However, the canopy can only change heading on its own during periods of time in which the airmass is actually accellerating.

Does that sound better? Wink


First page Previous page 1 2 3 4 Next page Last page  View All

Forums : Skydiving : Safety and Training

 


Search for (options)