PC size and canopy distortion during flight...

[lifewithoutanet 0]

I recently picked up a couple of new PCs: 46 and 48, each ZP, non-vented, to add to my 38 and 42. I really only needed the 46, but picked up both. Better to add more to the toolkit, no? When I decided on both, though, I was told the 48 probably wasn't necessary for what I was going to be doing and that with my canopy size (244/245), it would likely distort the canopy during flight. This makes sense, but at least I'll have the 48 if I ever need it, possibly for another canopy size (more on that in a moment).

So, we have charts for PC size based on deployment method and altitude, but has there been any research put into canopy distortion by a PC as it applies to canopy size/wingloading? I.E. "Wingloading at X, you can expect to see marked increase in canopy distortion with a Y inch PC and higher."

With that comes another question. What really factors into the distortion? For a highly loaded canopy, a larger pilot chute will wreak havoc on the system, but what is "highly loaded" in BASE? I don't think that what applies to a high-performance skydiving wing will translate linearly to BASE wingloading. But what's the delimeter?

For example, if the 48 was likely too big for my 244, what would that 48 do on a 266 vs a 222 over the same pilot?

Obviously, deployment should be the first consideration in choosing the appropriate sized PC.

-C.

Edit for clarity.

[TomAiello 25]

The only time I've been able to tell a real difference in flight is between a very large (48) PC and no PC at all (direct bag). Truthfully, I think BASE canopies are probably big enough that the effect of canopy distortion on the flight and flare are going to be pretty minimal.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[nicknitro71 0]

I did a litte math and here are the results:

At full canopy flight a PC will pull with the following forces:

~ 15 LBS for a 48"
~ 13.5 LBS for a 46"
~ 11.5 LBS for a 42"
~ 9.5 LBS for a 38"
~ 6.5 LBS for a 32"

That said I can only tell between a 42" and the 32" I use to for test jumping off planes. The canopy flares a bit better with the 32".

Memento Audere Semper

903

[leroydb 0]

care to share what formulas you used?

Leroy


..I knew I was an unwanted baby when I saw my bath toys were a toaster and a radio...

[crwper 7]

If I'm not mistaken, a lot of the distortion on smaller skydiving canopies results from the fact that they are very high aspect ratio. This means it is much easier to pull the center of the canopy back with respect to the endcells, for example. Because a BASE canopy is relatively low aspect ratio, I wouldn't expect a lot of distortion even with larger pilot chutes.

For what it's worth, we were jumping a 111-foot span a while back and noticed that the canopy never really had a chance to start flying before we touched down. I normally use a 48" F-111 pc for backup on the static line, but thought this would make little difference from such a low height, and might make a difference in the flight characteristics. So I did one jump without the pilot chute. There was no noticeable difference in the degree to which the canopy was flying when I hit the ground.

I should also mention, Dwain later pointed out that most premature breaks occur fairly late in the deployment sequence, so he hypothesized that a pilot chute likely would be helpful as backup even on a very low object.

Michael

P.S. Edited for clarity.

[DaveO 0]

I jump regularly with a jumper who weighs 120 lbs under a FOX 205. He uses a 48" ZP PC all the time with no problems.

"When it comes to BASE, I'll never give advice, only my opinion"

[Bryguy1224 11]

The canopy never had a chance to start flying from 111 feet. No way!!