Bias constructed canopies

[andyhughes 0]

I've not been in the sport long enough to see any of these... but i've read about a few models of square canopies that were constructed on the bias. Apparently there were problems with this construction method (hence the block construction used in pretty much all modern squares), and i was wondering exactly what the problems were exactly?

[mjosparky 3]

Bias and block construction applied to round canopies only. What you are probably thinking of is “Span” construction. ParaFlite made a few in the 80’s.

Sparky

My idea of a fair fight is clubbing baby seals

[highspeeddirt 0]

spanwise construction is more labor intensive as the whole top or bottom has to be sewn together BEFORE any ribs attach. only way it is less labor intensive (hence cheaper)is iff you space the ribs out to save on the number of seams .BUT performance suffers due do the rather large inlet opening at the fron of each cell. abot the only true advantage is that its harder to build a canopy witha built in turn using spanwise construction.

[mark 102]

Quote

Bias and block construction applied to round canopies only. What you are probably thinking of is “Span” construction. ParaFlite made a few in the 80’s.

Sparky

Para-Flite (now Airborne Systems) is still making span-constructed canopies: MC4/MC5, Dragonfly (not the Django one), MegaFly, etc.

Mark

[riggerrob 558]

Trivial point: Precision built a few ram-air canopies (Batwing, P-124A and Raven Dash M reserve) with span-wise bottom skins, but chord-wise top skins.

Aerodynamically, a perfectly flat bottom skin is fine, but you only need chord-wise construction to allow precise tailoring of complex, top-skin curves.

[councilman24 36]

More specifically, bias construction refers to the seams being at an angle, usually 45 degrees, to the warp and fill of the fabric. Block constructed means the seams are, for the most part parallel to the warp and fill. Of course the radial seams, being the side of a 'pie' shaped gore aren't parallel to each other or to the warp.

All ram air parachutes are, for the most part, 'block' constructed whether spanwise constructed or chordwise constructed. Of course there are curves and slight angles to the warp and weave.

The angled seams you see in the photo here http://paragear.com/templates/parachutes.asp?group=351&level=2&parent=337
indicate it's biased constructed.

Ask any seamstress what the bias of the fabric is and they can show you.

I'm old for my age.
Terry Urban
D-8631
FAA DPRE

[DrewEckhardt 0]

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abot the only true advantage is that its harder to build a canopy witha built in turn using spanwise construction.

Batwings with the right different colored panels on the bottom (span-wise) and top (chord-wise) skins looked nice with light behind them.

[andyhughes 0]

Quote

All ram air parachutes are, for the most part, 'block' constructed whether spanwise constructed or chordwise constructed. Of course there are curves and slight angles to the warp and weave.

In terms of the way the fabric is loaded, makes sense for the top skin and bottom skin. But for ribs and d-ribs, is there any specific reason why these are also cut on the block with tapes at 45 degees (aprox) to the chord line or is this just "market convention". We don't see bias cut ribs with tape parallel/perpendicular to the chord (which may reduce amount of tape neeeded), and was wondering why?

[dumstuntzz 0]

thats because para flite invented it Elek Puskas was the patent holder.

[dumstuntzz 0]

if you made a rib bias constructed, it would have to be made out of 2 or more pices of fabric. a bolt of fabric is only something like 60 -65 '' wide. take a rib that is 10 feet long and then lay it across the fabric on the bias and you will see wahat i mean. early strong tandem mains actually were (are) bias constructed ribs.

[andyhughes 0]

Nice one. Thanks for the info.

Andy