pilot chute design question (stupid maybe...)

[finflyer]

Hi

I was wondering has anyone ever tried to design a rotating pilot chute? A pilot chute rotating fast around its centerline axis would propably oscillate less (because of momentum) and if also equipped with AV's would lead to an improvement on on-heading openings. The rotation would be induced by small angled air outlets near the mesh/F-1111(ZP) seam.

There would surely be some drawbacks also, like twists in the bridle and maybe some unexpected issues. How to build one symmetrically enough and so on.

This is just a late night thought, so you can take it like that if you want. But, has anyone aver thouhgt, tried or tested this kind of design? And does anyone think it should be?

Vesa
#845

[base428]

Interesting idea.

You can use a stainless steel swivel to prevent the bridle from twisting, but how would you actually make it rotate?

Yes, the gyroscopic effect of a spinning PC would help keep it from oscillating.

------------
Jason Bell (BASE428)
Email: jbell@vertical-visions.com
Web: www.vertical-visions.com or www.bridgeday.info

[finflyer]

>You can use a stainless steel swivel to prevent the bridle
>from twisting, but how would you actually make it rotate?

Yes, I thought about the possibility of an SS swivel, but for me it's just another part to fail and add complexity. But of course it would be possible that way.

I would build a number of directed holes partially covered with lids about an inch up from the mesh/top fabric seam. Those angled holes would direct outcoming air at an angle with the circular radius of the pilot chute.

That would force the air that is now spilling randomly out of the pilot chute and causing oscillation to start spinning the pilot chute around it's centerline axis.

have to try to draw it as my English may not be good enough to describe it...

finflyer
#845

[Tree]

I think that this would be a tough sell. PC's are pretty reliable today, and the vented ones even better. I just don't see occilating PCs as the culprit for most off headings. I've seen video were a PC was clearly to blame, but it is either an old design, poorly made, or incorrectly rigged. Body position, cross winds, and (to a lesser extend) packing are still the primary cuprits. Not to mention, the rotating PC would be complicated, compared to a standard or vented pc. Nice idea, but it would be a hard sell and I don't know anyone who would want to test jump them (testing being the first several thousand field jumps).

My 2 cents.

Tree :-)

[imported_Tom Aiello]

The U.S. military tested this design. For a PC, it might work great (they couldn't make anything larger than about 2 meters, and they were looking at recovery parachutes, so I'm not sure how much work they did on it). Perhaps 311 can dig out his reference manual (mine's in California), and give us the statistics on stability, but as I recall it was more stable than any other design (or did an annular parachute have it edged?).

My real concern would be deployment. Since it's intended to spin, you'd have to make sure the deployment was appropriately staged. In other words, if it started spinning before it got to bridle stretch (especially if it did so in the midst of flailing wads of bridle), you might experience some problems. Picture a rotating pilot chute binding up in the bridle prior to extension--instant total. Constructing it out of F-111 (so it would reach extension prior to inflation) might help.

Anyway, I'll see if I can find the book and copy out the relevant portions. If you really want to see all the technical data, you can buy the book on Amazon.com:

Amazon.com: Parachute Recovery Systems Design Manual (9780915516858): T. W. Knacke: Books (http://www.amazon.com/exec/obidos/tg/detail/-/0915516853/qid=1070897701//ref=sr_8_xs_ap_i0_xgl14/002-3293300-0234437?v=glance&s=books&n=507846)

--Tom Aiello
tbaiello@mac.com

[jason]

I'm not convinced that this would have any effect at all. If you've got substantial mass toward the edge of the thing (a la bicycle wheel) then yeah, there's a significant tendency to stay on-axis. But we're talking pilot chutes here. Imagine spinning something about half the mass of your t-shirt. Worse, still, if you've got most of the mass at the center -- say, in a handle.

Couple that with the fact that, even on a steel swivel, a spinning pilot chute will transfer *some* rotation to the canopy (how much depending on how well you've maintained the swivel, but always some), and it seems to me that the small-or-zero gains are far outweighed by the certainly-nonzero risks.

Just my two cents...

[crwper]

Also... I think it's worth recalling that a gyroscope will tend not to _rotate_, but _translation_ is another thing altogether. My understanding is that pilot chute oscillation is mainly caused by the latter... My gut says you would wind up with a pilot chute which still oscillates, but stays on-axis while it does this. Know what I mean?

Michael

[AdamF__ CR]

What you are describing is a rotofoil. It's pretty common in non-personel applications.

However, aside from the bridle twisting (which can be remedied with a device called a para-swivel), a rotofoil does not spin on the axis of the bridle. Instead it tend to spiral in a tight radius which does little to help with our needs.

While we were researching the development of our AV Pilot Chutes we tried rotofoils and other variants but there was always a trade-off in either low-speed stability, inflation, drag, price or reliability.



Adam Filippino
Consoidated Rigging, Inc.

[finflyer]

Thanks for a reply Mr. Filippino. Nice to know it's been tried and tested. Don't have to do it myself then :D

finflyer
#845