Airlocks

[Yoshi 0]

I just overheard some perople talking about it at my dz.. wasnt sure if it was true...but I thought it made some sense.. the airlocks I know are designed to keep air in the cells..but wouldn't any fabric what so ever in the openings of the cells block air from entering???
-yoshi

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[PhreeZone 20]

Its a valve. It limits the air coming in the cell and increases the pressure of the air that is entering the cell. Think of it like its more of a funnel, it starts wide but gets forced into a small opening at the valve. The air that is being pushed through now has a higher pressure then the surounding air nd forces the canopy to stay pressureized the entire flight. Now when you hit the brakes you decrease the air entering the cell, but because the valve has kicked in it reduces the pressure loss and makes the canopy retain more pressure then an nonairlocked canopy. If the sirlock required speed to work the trim would be a lot less and it would be pointed straight down.

Brian designs his canopies for him to fly and if you like them too... thats an added plus but unlike PD/Icarus/Atair/PA/etc, he does'nt have to design them to fill a certian market. It sounds like Brian likes his canopy to be trimmed more aggressivly then someother companies do.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[billvon 2,990]

>but wouldn't any fabric what so ever in the openings of the cells
>block air from entering???

To some degree, yes. However, they are designed to do this as little as possible - the ideal valve presents 0% impedance in one direction and 100% in the other. Airlocks are not ideal valves, but they seem to work pretty well.

[billvon 2,990]

>Its a valve. It limits the air coming in the cell . . .

Well, it is designed not to - it's supposed to allow air to enter the cell with minimum impedance.

>and increases the pressure of the air that is entering the cell.

It does not increase pressure internally. A valve can't do that. It does, however, help keep pressure up when a normal canopy cannot maintain pressure. How much it does this is subject to debate of course.

>Now when you hit the brakes you decrease the air entering the
> cell . . .

Well, no. You do distort the canopy, and the airlocks help maintain higher pressure momentarily when that happens (and thus the distortion is momentarily resisted to some degree.) As you slow down ram pressure decreases as well.

[PhreeZone 20]

The Jedi I was looking at to get a better idea of how airlocks works sure did seem like it was slowing the intake of air just by forcing the air in a direction other then straight in. I think the design tries to minimize this, but from how I was picturing it, the forces would be there as it routes the air up and over the valve.

I was pretty sure the PCV system used a 2 flap system to trap the pressure better but it also would increase the impedance factor by routing the incoming air up then down again. Am I understanding is right?

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[polarbear 1]

You're saying that the airlock acts as a converging nozzle (forcing the air through a smaller area and thus increasing its presuure)? I hadn't thought about that, but it might be true. I don't think that is waht airlocks are specifically designed to do. I think the operating principle is just to hold air in the cell in the event the external pressure becomes greater than the internal pressure.

I would agree that the Samurai is trimmed steeply...mine comes DOWN, unless I get in brakes. I don't think airlocks require steeper trim...it just so happens that the canopies that have them are steep.

"Holy s*** that was f***in' cold!"

[PhreeZone 20]

I'm not saying... I'm asking... is that the right mental picture I had formed?

>external pressure becomes greater than the internal pressure.
Also I think this is reversed, if the internal becomes greater it would try to get to the lower pressure and thus it would leave the cell. Is that right or are you?

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[billvon 2,990]

>The Jedi I was looking at . . .sure did seem like it was slowing the
>intake of air just by forcing the air in a direction other then straight in.

If air regulary flowed through the canopy you would be correct. However, that happens for only a few seconds at deployment. Once inflated, there is nearly zero airflow through those valves - the only airflow comes from increasing air pressure as you descend, leaks through the ZP, and volume changes as the canopy distorts.

>You're saying that the airlock acts as a converging nozzle (forcing
> the air through a smaller area and thus increasing its presuure)?
>I hadn't thought about that, but it might be true.

Again, that's only an issue when air is flowing. That airlock can be modeled as a steady state (i.e. no significant air flowing past it) once the canopy is inflated.

To see this in action, check out debris in a cell of your canopy (say, a leaf that got left there during packing.) It may spin around in small eddies, and shift a bit, but will not get blown towards the back of the canopy because there's no significant airflow inside the cell.

[polarbear 1]

Quote

>external pressure becomes greater than the internal pressure.
Also I think this is reversed, if the internal becomes greater it would try to get to the lower pressure and thus it would leave the cell. Is that right or are you?

I think I am. If the internal pressure is greater, the cell will remain inflated (remember, I am talking about the pressure across the upper and lower skin, NOT the stagnation pressure at the nose). If the external pressure is greater, it will "squeeze" the cell closed.

"Holy s*** that was f***in' cold!"

[polarbear 1]

Quote

Again, that's only an issue when air is flowing. That airlock can be modeled as a steady state (i.e. no
significant air flowing past it) once the canopy is inflated.

Of course, that's right. Fluid Dynamics only works if the fluid is dynamic!

"Holy s*** that was f***in' cold!"

[Yoshi 0]

I guess that answers my question..it is really interesting though..I never really thought about air passing through the cells..rather it just going into the cells and stays until landing..
good point..
yoshi

_________________________________________
this space for rent.

[TomAiello 26]

Quote

To see this in action, check out debris in a cell of your canopy (say, a leaf that got left there during packing.) It may spin around in small eddies, and shift a bit, but will not get blown towards the back of the canopy because there's no significant airflow inside the cell.

I'm not sure this is true. Adam Filipino at CR did some tests when he designed his valved BASE canopies. He put streamers inside the cells and used them as indicators of airflow inside the cell (he was trying to figure out where to place and how to orient the valves).

Anyway, after seeing the test results (and a bit of the raw footage), I'm pretty convinced that there is a significant airflow inside the cells. It looks to me like a series of rotors, getting progressively smaller, moving back into the tail. The rotors, if I recall correctly, tend to flow across the inside of the topskin, then come down and create a reverse flow along the interior of the bottom skin.

At any rate, when you are talking about valves or vents on the canopy, I do not believe it is accurate to model the internal airflow as stagnant. There is air moving around in there, and it can interact negatively (or positively) with secondary canopy inlets or valves.

-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

[cobaltdan 0]

i am just back froma week of drop tests and trying to catch up.

a think the minor confusion is about definitions.

collapse: when a canopy is no longer in flight supporting the jumper.

airlock canopies can collapse in turbulence, same as a non airlocked canopy. keeping the air in does not prevent this.


sincerely,

dan

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[cobaltdan 0]

hi jerm,

just back from a week of test drops and trying to catch up and overcome some computer problems...

anyway, i think the confusion is about definitions:

collapse: when a canopy is no longer is in flight supporting the jumper.

in turbulence locking air in a cell changes how the canopy collapses but it still collapses.

again fly an airlock because you like how it flies, do not fly one because you believe it will save you over an open cell canopy in turbulence, it will not.

be safe.

dan <><>

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[Jonsmann 0]

I would define it:
Stall: Flow separation from the top skin caused by too high an AOA. You no longer have a flying wing.
Collapse: Massive deformation of the canopy, usually caused by too low cell pressurisation.

A collapse is not identical to a stall, but a collapse can result from a stall. Airlocks can delay a collapse following a low speed stall.

- Jacques

[jerm 0]

Quote

anyway, i think the confusion is about definitions:

collapse: when a canopy is no longer is in flight supporting the jumper.

in turbulence locking air in a cell changes how the canopy collapses but it still collapses.

I'm not an aerospace engineer, but your definition sounds like a symptom of a collapse. I would tend to define a collapse as the canopy deforming to a point where it is no longer a wing capable of flight.

I believe was using the term 'catastrophic collapse', which i would further refine to mean a rapid deformation/deflation of the wing, causing loss of flight.

Brian has a great little demo 1 cell airlocked parafoil, and one non-airlocked... inflate both, and clap them between your hands one at a time.....

The non-airlocked one deflates rapidly and your hands hit as though there were nothing between them.

The airlocked one will stop your hands dead in their tracks and slowly leak air as you continue to squeeze, all the while maintaining it's shape.


Airlocks can not keep a rotor from spinning you into the ground, or a downdraft dropping you to the ground.... they CAN HELP keep air in your canopy when the turbulence would have rapidly squeezed it out of another canopy -- which gives you BETTER chance of keeping a viable wing above your head.

Landing without injury is not necessarily evidence that you didn't fuck up... it just means you got away with it this time

[billvon 2,990]

>Collapse: Massive deformation of the canopy, usually caused by too
>low cell pressurisation.

I disagree here, since, to my knowledge, there has never been a test of cell pressurization during a collapse. In addition, parachutes like the Paradactyl (which have _zero_ cell pressurization since they have no cells) can remain flying. Generally, collapses occur during turbulence, and when the force from the changing airspeeds seen in turbulence is sufficient to overcome the "normal" force provided by your weight on the lines, the canopy can collapse. High pressurization may help a bit, but is a tiny factor compared to the hundreds of pounds of force on the lines from the normal loading of the parachute.

[billvon 2,990]

>airlock canopies can collapse in turbulence, same as a non airlocked
>canopy. keeping the air in does not prevent this.

While I agree that both canopies can collapse, I do notice a slight increase in stability in turbulence between two similarly loaded canopies, one with airlocks and one without - specificially, the Lotus 135ish size vs the Sabre2 135. It was noticeable enough that I would prefer the Lotus in turbulence simply because it needed less input to keep it flying straight, and needed less "help" during the planeout to prevent getting dropped or turned. As I have said before, this may be due to other factors, such as the crossbracing effect the airlocks have on the nose of the canopy. Nevertheless, a jumper might well choose an airlocked canopy due to its perceived higher rigidity, regardless of the cause of that rigidity.