Forums: Skydiving: General Skydiving Discussions: Re: [The111] Collapses and Turbulence: Article: Edit Log


BrianSGermain  (D 11154)

Jan 31, 2006, 3:18 PM

Views: 9159
Re: [The111] Collapses and Turbulence: Article

That is an interesting brain-teaser. Yes, the loss of groundspeed is a lesser precent of the overall airspeed when you are flying faster. But the issue is not groundspeed at all when we are talking about turbulence.

It is:
1) How long are you in the bad air
(downdraft, updraft or choas)
And:
2) Is the variance of the fluid going to effect the flight path?

Number one is clear. The faster you are flying, the sooner you will pop out of the nasty stuff into clean air. The second issue, partially predicated on the first, is a more complex question that requires all of the relevant details.

The example you presented is a helicopter, which is a very different set of dynamics. Not to say that helicopters do not suffer in turbulence, but the effects will be somewhat different, and I do not pretend to be an expert in that field. Actually, I do not pretend to know everthing about parachutes either. I just seem to be saddled with this responsibility of the "go-to" guy for this kind of question. So I will try...

The flight path of a parachute is based on
1) Lift
2) Drag
3) Flying Environment

The first two partner up to give us our efficiency, calculated by L/D resulting in glide ratio. The flying environment is a variable that includes vertical air movement (+ and -) as well as chaos which reduces the efficiency of the airfoil. If the flow of air over the wing is disrupted and becomes less "laminar", the drag will increase and the lift will decrease. Increasing the airspeed will increase both forces, Lift and Drag. This does not necessarily result in a linear correlation between the variables as they are altered by the conditions, but it stands to reason that the higher the airspeed, the less the percentage of the whole the loss of both figures will represent.

If airplanes did not weigh as much, we might choose to increase the airspeed in bad air due to this assumption, but we do not. We slow down. This is beacuse of the limited ability of the airframe to handle the stress. If you increase the airspeed, you increase the forces on the aircraft as the loading on the wings varies positive and negative. This is why there is "maneuvering speed" on your airspeed indicator. If you fly too fast in turbulent air, your wings may fall off. That sucks...

Parachutes are quite different. The mass of the suspended load is far less than an airplane, and parachutes are designed to handle quite a bit of stress for opening shock. This means that there is pretty much no chance of you flying so fast that the positive "g's" actually bust your parachute. Good thing. Not to mention, negative "g's" are not an issue at all, as all that does is release the line tension and collapse the parachute. Not good for descent rate, but you parachute will fare well from the encounter.

This all suggestes that the first issue is the most important. Flying fast will keep you from lingering in the oatmeal air, and will super-pressurize the parachute to handle the hits. As far as we are concerned, the faster the better, as long as the maneuvers utilzed to create the airspeed maintain significant line tension to keep the skeleton of your system intact.

OK, that was the most verbose answer I could have given. Sorry about that. On cold winter days, a little mental masterbation can be a good thing.

Anybody got a towel?
;)


(This post was edited by BrianSGermain on Jan 31, 2006, 3:24 PM)


Edit Log:
Post edited by BrianSGermain () on Jan 31, 2006, 3:20 PM
Post edited by BrianSGermain () on Jan 31, 2006, 3:22 PM
Post edited by BrianSGermain () on Jan 31, 2006, 3:24 PM


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