Idea: Pivoting contraption for PCs

[guest]

I don't know if this has been tried or if it is even an issue. I realize pilot chutes are the cause of offheadings more often then not. Out of the hundreds (low hundreds) of off heading BASE deployments I've now seen it very much appears that the canopy is turning right as it leaves the pack tray. The pilot chute bridle can also appear to be visibly wound up slightly at this point too. I was curious if the pilot chute is providing some torque (spinning) to cause this. It seems like it would be more apparent on the multi as it has more area to torque with. So if this is the case (and someone explain why it wouldn't be) then wouldn't a PC that can spin freely be more effective?

Just a thought.

[imported_Tom Aiello]

I think it might be the case. However, I'm uncertain how much impact the torque of the twisted bridle would have on the pack job.

Is it possible that another culprit might be wrapping the bridle around one of the "ears" of the pack job? If you do that, you can have a length of bridle several inches long exerting cross pressure on a relatively wide piece of fabric during extraction.

Hmmm. I don't know. A "bridle swivel" might help, but I'd be reluctant to add another piece to the system without being sure it would improve things.

--Tom Aiello
tbaiello@ucdavis.edu

[guest]

Out of curiosity I just wound up the bridle and tore the shrivel flap off slowly and kept tension on it. It definitly spun the shrivel flap around.

[guest]

If the PC has not migrated to a point directly behind the jumper prior to canopy extraction, it makes sense for this off center extraction force to contribute to an off heading opening.

However, a swivel at the canopy attatchement point is not going to change this extraction angle. A swivel will only eliminate the torque created at the canopy attachment point. This amount of torque is likely insignificant as the bridle, canopy, and attachment stitching are soft, not rigid bodies.
Example: Picture a water skier being pulled behind a boat, going from side to side. Would the skier notice if the tow rope were tied directly to an eyelet on the boat, vs. a swivel to an eyelet??? Only if the rope were replaced with a long steel bar that was welded to the boat would a swivel matter.

The best medecine against PC based off-headings is using the proper sized PC for the delay, bridle girth hitch centered on PC binding tapes, and a moderate toss (just enough to get clean air).

MB

[crwper]

I think an even better analogy is... If the skier was directly behind the boat, and flipped the handle over 180 degrees, how much effect is that going to have on the boat? Is the boat going to flip over as well? Probably not. I think the pilot chute would have about the same effect on your deploying canopy.

If, however, the skier moves over to the side as far as he can, because he's using the pull of the boat, he can probably exert a substantial sideways force on the tail of the boat, and affect its direction somewhat. Similarly, I think people are justified in saying that an orbiting pilot chute, which would exert an off-center force on the deploying canopy proportional to its drag, which is in turn a function of your speed, could affect heading.

Michael

[space]

Hi Justin, Torque is a product of force multiplied by distance. force is tangential to the angle of the anchor(distance), in laymens terms, if you had a steerable kite, the highest loading would be when it was directly down wind on the same level.. and lesser when it was away from this point.. If you had a rotating PC, as long as its in the High load area, it (twist would be very close to non consequential) would do the most effective job of extracting the canopy best within regard to jumper position,, as the canopy´s best deployment scenario is following the PC straight to the max loading vector, not in an orbiting, meandering journey there, the same as a skilled deckhand on the MS river can roll the line off a timberhead20ft above on a lock wall by inducing a 180 in the line and progressing it to the eye over the timberhead by sheer momentum..BTDT,..
take care, space..

[guest]

If you can't handle a 180, don't BASE jump.

[guest]

I was referring to a swiveling device not a pivot. I got tongue tied.

For us engineering types this is an interesting topic. If you aren't going to contribute go away.

x(

[space]

I can measure the torque in the above scenario of twisted bridle, how many twists would you want? It just happens to be my field of work (torque sensors)..and for you engineer types, I´m almost finished creating the world´s first 3D torque scanner..figger that one out.. hehe..
3DTS #1
take care,
space

[guest]

Is there some equation that one of the variables is number of turns and it gets the amount of torque force out of it? I'm just curious if the amount of torque produced is enough force to turn the canopy. 10 twists maybe?

[guest]

I can't say whether or not bridle torque might play a significant role in off-heading openings, not having had a lot of experience either first- or second-hand with them. I think, though, that your biggest problem isn't going to be with finding an equation for torque as a function of number of turns but rather with defining "turn the canopy".

As has been noted already, winds, thermals, packjob, and such will probably make any quantitative discussion of the issue moot. Qualitative is always worthwhile, though...

[space]

It (sensor calibration) was 27.17 mV/Nm. Got a reading of 1mV with 20 (360°) twists at 5kg axial. Couldn´t get any thing from 10 full twists,
this equals 3.68 Newton grams of force in a radial curve perpendicular to the angle of the bridle , or the best relative value I can come up with is it is like the force you have in your hand hanging straight down when holding 3.6 grams as compared when you don´t. divide by 2 and you get your 10 (full) twist value. Hope this helps. Let me know if I can do any more tests in this arena..you can check out www.fastechnology.com for our capabilities.
take care,
space

[Tom B]

I disagree.

I think p/c lag behind body position and prevailing weather conditions and pack jobs as causes of off headings.

But its good that people are thinking outside the square anyway.

[guest]

Agree with Tom B.. Space has long attributed off-headings to orbiting p.c.'s with #1 probable cause being improper bridle attachement to p.c.. This makes excellent sense, but...seems to me that the "burble" above a jumper is extremely unstable airflow because of an imperfect "wing" so to speak and that unstable airflow is gonna play havoc with p.c. stability anyway. Therefore,direct bags or 50' bridles are the solution!:7
My two cents is first keep it simple and second...prepare and deal with it.
Ciao

[space]

Hey Doc, spores for thought, With an orbiter, it aint in your burble..longer bridles can help if only attatched to a stable extractor such as a symmetric PC or astrodome,,,DB lacks the geometric orientation that a stable PCa has in ref to winds,Oh yeah, you need to update your Ciao: come see me,
take care,
space,,