Basejumper.com - archive

Please correct me if I'm wrong at any point of my logic - critical angle of attack after which a canopy stalls is the same for all jumpers weight (given the same canopy type, size etc.), but because of a canopy trim, the heavier jumper loads the front of the canopy more, effectively decreasing the angle of attack in comparison to the lighter jumper. So in order for the heavier jumper to stall the canopy, he needs to first increase the angle of attack to the point where the lighter jumper was originally, and then both of them have the same range of angle of attack before reaching the stall.

This is why if we assume the heavier jumper has set his DBS right before the stall for his weight, if the lighter jumper jumps his canopy, it will stall.

PS. Another related question - for the same canopy model and size, for the same angle of attack, a heavier jumper will have more forward and downward speed compared to a lighter one, so given they both sets up DBS right before the stall point for their weights, the heavier jumper will always have more forward and downward speed than the lighter one.

So in theory, if a lighter jumper could set up his DBS to achieve zero forward speed, but this DBS would require him to set it up just before the stall point, the heavier jumper with the same canopy type and size would not be able to achieve zero forward speed with his DBS as the lighter jumper, because of his bigger weight, he would need to achieve a higher angle of attack that the lighter jumper, and that would put him into a stall. To achieve the zero forward speed with his DBS, the heavier jumper would need to upsize his canopy.

What do you mean by "Stall" are you referring to depressurization & collapse of the canopy, or just moving backwards?

If deep brake settings are set too deep the canopy will stay inflated but move backwards, I saw an object strike because of that. Not sure how a non vented canopy would behave in that attitude. I am also not sure that if held for long enough, would the canopy depressurize & collapse?

My deep brake settings came preset & function as designed, i have little to no forward speed after opening.

A heavier jumper will have
more wing loading which
means they can wring a
canopy out more before
it folds up & goes home.

what do you weigh and what size/type canopy do u have dude?

??? explain please. Are you saying more weight is on the A lines than on the D lines?

FLiCK 293 & I weigh about 210.

fatty!!!!!!!!!

+1!!!!!

The distribution of load between front and rear risers is a function of canopy trim only, not weight. If you draw a triangle N-T-J representing nose, tail, and jumper, the lengths of its sides are determined only by canopy chord length, A-lines length, and brake lines length. It is a fixed triangle no matter what weight is attached at the bottom. And the orientation of this triangle is also fixed, since the position of center of lift&drag is a function of trim only.

So, if the load is distributed like 60/40 front/rear for a light jumper, it'll be the same 60/40 for a heavy one.


As discussed in the other thread "How a rear riser stall differs from a braked stall?", ram air parachute stall (at least, for docile, low aspect ratio wings we have in BASE) occurs at very high angle of attack, close to 90 degrees, when airflow suddenly switches from nose-to-tail to tail-to-nose, accompanied by significant distortion of shape and depressurization.

For light and heavy jumpers on the same canopy, there will be a small difference in the stall point, and I believe it is due to different pressures of the poorly inflated canopy which affects its shape and thus the onset of the backward airflow. The heavier jumper will have higher overall speed than a lighter one on the same size canopy, so the ram air pressure will be roughly proportional to weight. The higher the pressure, the better the canopy can maintain its shape. So, for heavier jumper, stall will occur "later" than for light one. If the canopy brake setting is dialed in for heavy jumper, the lighter one jumping the same canopy may experience surprising stall/backward surge on opening.

I know his comments are confusing, but if you put it in the light of "This guy has only ever seen a parachute on YouTube and is just wasting people's time asking questions that betray a complete ignorance of the way parachutes work" it all makes more sense.