Adding mass to the canopy?

[rmsmith 1]

Since the canopy tends to loose its kinetic energy before the pilot it would seem logical to add some mass to the canopy to increase the distance of the swoop. I can imagine that the dynamics involved during opening would be hard on the canopy. So, has anyone ever tried sewing some skinny shot bags along the chord of the loaded ribs starting from the nose of the canopy?

[pilotdave 0]

I don't think it would have the effect you want.

As the canopy slows down at the end of a swoop, there are two ways to maintain enough lift to continue to fly. Either change the camber of the airfoil or increase the angle of attack. Doing either increases drag, slowing the canopy down even more, but possibly allowing it to stay airborne a little longer, until it stalls.

Adding weight to the canopy doesn't really change that situation. Decreasing drag, or increasing the lift to drag ratio, is the only way you are going to produce equal lift at lower drag.

I'm willing to bet vortex generators will be coming along soon on canopies. Vortex generators can help delay separation as angle of attack increases, basically letting the wing fly at a lower speed (and also decreasing the drag on the wing when flying at a slow speed). Placed properly, I bet they'd help a canopy swoop farther. And I don't see why they couldn't be made out of little folds of stiff fabric.

Dave

[alan 1]

Don't vortex generators need some sort of airfoil in order to function? Just wondering how effective they would be on an inflatable, non-rigid airfoil that is at an angle of attack and airspeed that won't sustain pressurization of the airfoil.

alan

[pilotdave 0]

Well, I don't think they'd prevent canopy collapse if you reached that high an angle of attack or that low an airspeed. But I do think that they could in effect raise the L/D ratio at any given "high" angle of attack. Maybe not... maybe the "touchdown speed" of a canopy is too slow for vortex generators to have any effect... definitely a possibility. But if you can reduce separation at any given angle of attack, you reduce drag.

I'm definitely not a swooper. But if I did a normal approach and flare, planing out 3 feet off the ground, my canopy will slowly settle down with very little forward speed. If I did the same thing at say 50 feet over the ground and held the full flare, my canopy will eventually stall and fold back and come crashing in. So I'm not talking about preventing it from fully stalling and collapsing. I'm talking about maybe slightly delaying that first situation, allowing the canopy to fly just a little bit slower (and a little bit farther) before it begins to settle downward.

The speeds we're talking about are very slow though. I'm not sure vortex generators can be effective down to such low speeds. But who knows, myabe they'd be most effective half way through the swoop, not at the end, reducing drag and allowing the canopy to swoop a little farther anyway. Or maybe they'd create more drag than they'd save. But someone's gonna try it.

Dave

[rmsmith 1]

Quote

As the canopy slows down at the end of a swoop, there are two ways to maintain enough lift to continue to fly. Either change the camber of the airfoil or increase the angle of attack. Doing either increases drag, slowing the canopy down even more, but possibly allowing it to stay airborne a little longer, until it stalls.

It appears that as the canopy loses its kinetic energy it slows before the jumper does, and this increases the angle of incidence, which introduces yet more drag. Unfortunately, mass is a linear component of kinetic energy, so the addition of mass would yield a modest benefit. The introduction of depleted uranium projectiles was born of a desire for more kinetic energy at the distant end of the trajectory where reactive armor was found.

[alan 1]

Quote

But someone's gonna try it.

Probably, but my guess is that it will be more of a marketing ploy than an actual improvement in performance. The vortex generators will delay separation at high angles of attack. With a canopy, when it reaches the higher angles of attack near the end of a swoop, there is very little speed left to maintain pressurization of the canopy. In addition to that, the stagnation point has moved below the air inlet and further reduces the pressure that is needed to maintain the airfoil. I believe that at this point, low airspeed and high AOA, where the votex generator has the most potential to raise the L/D, on a non-rigid airfoil there is no airfoil left.....it won't be able to function.

Now perhaps if we borrow from the BASE people and put mesh on the bottom surface, use improved nose designs (R.A.G.E.), and improved airfoils, we can maybe get to a point where vortex generators may actually function.

alan