Altitude for opening

[imported_Mac]

I have posted this on the Tech Forum but no one seems to be using that much! :P


After a recent trip (a big thanks to those who helped me out for that trip!!) and a non jumpers perception of opening heights I have some curiosity on time taken for deployment and the factors governing this.

I ask this after 3 jumpers similar delays, same sized PC's (46" - 2 non load tapes, 1 with - all without caps) all with velcro rigs (2 one type 1 other - 2 newer velcro 1 older), 3 noticably different packing methods, similar wing loadings, 3 different canopy sizes (2 same type canopy 1 other), 1 launched head high (very) 1 not so head high and 1 unknown (as i could not see myself and the non jumper could not comment on my angle but generally I launch near to 45 and flatter than my perception of the first 2 jumpers I watched).

I would be interested to hear the views of people on what can and cant effect the time for PC throw to pressurisation to confirm / change my thoughts and open my eyes to other aspects.

Thanks for your time taken to answer.

Be Safe............. Be still learning the basics!

Michael
:+

[imported_Tom Aiello]

>I have posted this on the Tech Forum but no one seems to be using that much!

I can't seem to find it on the tech forum. I wonder if there is some issue with postings there.

>I would be interested to hear the views of people on what can and cant effect the time for PC throw to pressurisation

I'm not sure if you're thinking of time from PC pitch to PC inflation, or PC pitch to canopy inflation.

Some general thoughts. I've tried to organize them into what I think has most effect and least effect.

Time to PC pressurization:
a) type of deployment: Hand held deployments inflate quicker and more consistently than stowed deployments.

b) bridle length: A PC on a shorter bridle will reach bridle extension sooner and begin to inflate sooner. This is NOT a recommendation that you shorten your bridle, as that can cause various other problems.

c) direction of pitch: A PC pitched straight up will reach bridle extension sooner, and begin inflation sooner.

d) manner of PC folding: There are various methods of PC folding. Some produce inflation faster than others. I've heard various people with different theories on which folding methods work best.

Canopy inflation time:
a) reefing system (for example, slider): obviously, a slider is the best method for changing (slowing) inflation.

b) airspeed at deployment (i.e. delay-relative wind): canopies deployed into greater relative wind will inflate faster.

c) secondary inlets: canopies with secondary inlets (valves or vents) will inflate noticeably faster, as well as reaching riser responsiveness sooner in the inflation sequence.

c) wind at deployment (absolute wind): tailwinds can noticeably slow inflation, and headwinds can quicken it.

d) type of canopy: Canopies with steeper angles of attack will generally inflate faster. Crossporting can also increase inflation speed, as can other canopy design factors.

e) age of canopy: As canopies age, their inflations become noticeably less consistent. This generally results in slower inflation, but can also create an occasional very fast inflation.

f) packing technique: In my experience, packing technique is one of the least important factors effecting inflation speed. In my opinion, it only becomes important with virtually all other factors equal, and at very low (sub 200') altitudes.

--Tom Aiello
tbaiello@mac.com

[david]

Hey Tom,
How about the weight of the canopy? I jump a FOX 285 V-tec and a buddy of mine jumps a FOX 205 V-tec. Using the same packing technique and same size and make of PC the 205 is always pressurized and flying before the 285. I'm talking on go and throws, not on any sort of delay. This is just my opinion of what I have seen. Does anybody else have any thoughts on this?

[Faber]

I were told that smaler canopies opens faster.Dont know why,and dont have any facts.

[jules]

Smaller canopy - less mass - easier for PC to drag off back?

Jules

[346]

Yes, less mass is one factor - requires less force to extract.

You'll probably find that the lines of the smaller canopy are also shorter due to the canopy being smaller making line stretch take slightly less time than a larger canopy lifting off at the same speed.

Span-wise and Chord-wise expansion of a smaller canopy will take slightly less time than a larger canopy due to smaller dimensions.

Pressurization of a smaller canopy will take slightly less time than a larger canopy due to smaller internal volume.

Each of these things are just small fractions of a second, but they can add up.

There are trade-offs, of course. A smaller canopy needs to fly faster than a larger canopy to generate same amount of lift, so a smaller canopy will generate less lift than a larger canopy at a given speed. Because of the decreased lift, a smaller canopy will tend to stall at a higher airspeed than a larger canopy (assuming the same suspended weight, etc).

Mark

[imported_Tom Aiello]

Sorry, I've been trying to post for some time now (unsuccessfully). I do think that smaller canopies inflate faster. I have also heard speculation that canopies with higher wingloadings inflate faster.

Now let's see if this posts...

--Tom Aiello
tbaiello@mac.com