PD Reserve Sizing

[lnd906 0]

General wisdom states that the reserve size should be the same as the main; but, PD Reserves aren't sized as mains are. Why are these reserves made in different sizes than PD mains? So if someone if jumping, for example, a 150 main, what would be considered the same as 150 (143 v. 160)? Is this intended to encourage the purchase of a slightly larger reserve? If so, why are container reserve trays generally smaller than the main trays?

I'm not searching for "what reserve to get" advice, simply curious. I've searched all over and have yet to find a clear answer to this (perhaps there isn't one), so I apologize if this has been asked before.

[billeisele 130]

9 cell vs. 7 cell, and exact size matching isn't accurate anyway, different folks measure them different ways

Give one city to the thugs so they can all live together. I vote for Chicago where they have strict gun laws.

[skytribe 17]

The sizes of PD reserves match the sizes of Lightning canopies and the old F111 PD 7 cells canopies.

7 cell vs 9 cell, Modern canopies can be tapered or elliptical as against rectangular planform which will also effect surface area.

[mjosparky 4]

Go to PD's web site. If you can't find what you are looking for call talk to someone there.

My idea of a fair fight is clubbing baby seals

[pchapman 279]

lnd906

General wisdom states that the reserve size should be the same as the main;

That's not to be taken too strictly, and is just a very rough guide. It's hard to argue for a reserve too much smaller than your main (unless you're jumping a main much bigger than your ability level -- eg, a big demo or accuracy canopy). And it's hard to argue for jumping a reserve way bigger than your main (unless your main is a super tiny swooper).

It just happens that in the medium to large size range, manufacturers have tended to make rigs with the reserve size a little smaller than the main size. I'm only guessing how the skydiving community settled into that rut, but I think the idea is if you are competent and can handle a size X main day in and day out, and you don't want to carry extra bulk around, then surely you're OK with size X minus 1 on rare occasions when you're not looking for the perfect landing but just want to get down without serious injury.

Certainly one can still make the argument that when you might be in a crappy spot or even injured, a little extra square footage might be nice.

Similar to rig sizing, since the time people have been jumping both square mains and reserves, I think common reserves have tended to be sized a little smaller than the typical main. Before that time, people were used to a reserve ride being a little rough anyway -- thumping in under a round reserve.

[riggerrob 643]

Fashion changed when square reserves came into fashion during the early 1980s. In 1981, Para-Flite introduced the first decent square reserve: the 5-cell, 176-180 square foot Swift. A couple of years later, Precision introduced the 7-cell, 176 square foot Raven 1 reserve. Back then most skydivers were jumping mains in the 200 to 230 square foot range.
The next major change cane during the late 1980s when acid-mesh grounded large numbers of round reserves, sending skydivers scrambling to buy (proven, trusted) Swift and Raven reserves. Fortunately those Swifts and Ravens packed into the same volume (400 cubic inches) as the 26 foot diameter LoPos that they replaced.

By 1990, most skydivers were still jumping main canopies with more than 200 hundred square feet of F-111, with only smaller women jumping 176 square foot mains.

Then things got confusing when Parachutes de France introduced zero porosity fabric making much smaller mains practical.

[hackish 8]

I think the practical reality is that a 160 versus 170 is not going to make a huge difference. When you couple that with the non-eliptical ,thicker wing and non-performance oriented trim angle on a reserve, the 160 is more likely to fly like a lower performance canopy as compared to the larger main.

Rig designers need to keep the shape of the reserve tray consistent with their design, so while there is a bit of wiggle room on the reserve versus main size it just doesn't physically work well to have a 300in^3 reserve and a 200in^3 main. You still need to match the width and height of the two while keeping the entire rig length comfortable with the height of the jumper.

-Michael

[Quagmirian 40]

Ah, I happen to have a good theory for PD's odd sizing of their 7 cells and reserves. The chord length, and therefore rib pattern, of the 143 for example is exactly the same as on a 170 PD 9 Cell. This means fewer patterns floating round the factory. Of course, now they use laser cutters but the old sizing method has remained. That's my guess anyway.