Re: [valentin] Design a new type of base canopy
It's an interesting question. I've pondered this my self a bit. We've been totaly focased on openings and minamizing malfunctions. and yah that's important I mean we often jump with only one chute but there are other ballancing issues. I can hear the bitching and screaming starting now but with a background in areonatical engineering I can tell you that all designs are a compermise between opposeing an contraditory design requirements. It alway pisses me off when some one bragging about their new design clames to have the highest possable glide angle with the highest possable forward speed with the lowest... you get it.
So here are some thoughts. First off I think glide angle is a bigger deal then people think. There are a lot of jumps out there where that is really a limiting factor. The ability to reach the landing area or the good landing area. Out fly the tree, tallus, etc. We don't generaly hear about fatalities from this but I wonder how many ingeries and hard landings there are? Exmple, look in the incedents right now where he cliped that building.
Size only plays into this when you start talking about wind. A small canopy is a disadantage in every other way. But wind is an issue. Ever see a poler graph for an airplane? You can plot maximum range based on a wind speed for each angle of the compass. Heading into the wind you actualy drop the nose a bit below max glide to get better penertration and down wind your flyinng almost at min sink to take advantage of the wind. There's a lot more range and leway with a more efficent airplane or glider. I don't have good raw numbers to work from to draw you one but basically we are really screwed with any kind of head wind.
But lets talk about other ways to improve our effecentcy rather then reduicing our surface area.
That anker we drag around is a killer. Even on high jumps where you can get away with a 36 that's still a huge anker your dragging behind you from the top of your canopy. There are several things you can do about this. It's out of favor now but we used to jump a sleave in the Sorceror. The canopy had one small fold at the bottom and then the rest of the sleave S folded into the bottom tray. It was lose and soft not hard or bulky or prone to spinning. I've heard of a few nasty off heading on short delays but I had good luck with it and put a lot of jumps on it in the 1000+ ft range of delay. I had a big #8 grommet in the top and it was good about slideing back and swallowing the PC colapsing it. People had less luck with this when they tryed t use them in single canopy rigs. They were tighter around the canopy and more like a brick. More prone to spin. This could be used with a large grommet like that or wih a more traditional colapsable pc provided there was enough slack in the bag to allow the canopy to slump if nessasary. That is the advantage of useing a ring against a grommet.
I'm going to toss out an idea here that is going to sound a bit strange but bear with me and think about it. I have not played with this but I don't see why it would not work. It's a way to build a colapsable pc to work with a tail pocket. Say you had a multi or even just the center and rear rings. Normaly a split bridal supports all of these rings evenly and lifts them all to line streatch. Then they spread out as the canopy opens. It doesn't hender the opening of the cannopy and I don't recall hearing of any intanglements. Say you had the same system but with the upper bridal built like a tradetinal collapsable bridal with kill line. The lower lines are still split. The kill line runs down like all the rest but it passes through the center front ring and then goes to the back ring. So now you have the four original bridal lines + the new vectran kill line. The canopy is lifted to line streatch by the original lines. There is no force on the kill line till it reaches line streach. Then the spreading of the canopy pulls the kill line in. Note all the slack to do so is all ready right there. There is nothing inhibiting theopening of the canopy. The pc is just pulled closer to the canopy by the kill line as it spreads. This happens in the burbal of opening and has been used on CRW canopies for years. The bridals are shorter an PC's smaller bt I don't think that could affect any thing. and 90% of the canopy can open regardless even if the line were to intangle. As the canopy flies the pc inverts it self as it normaly would but there is no need for it to do that in order for the canopy to open so this should cause no delay in opening. Again I haven't actualy put it on a canopy and played with it but I think it should work.
AR. It kills us. It was very fashenable to try and have the lowest AR for a while. Most canopies are n the 2.0 range depending on how you measure them. That so sucks. A rectangle is not a very efficent plane form but what really kills you is the AR. Look, a seven cell is a seven cell. Same lines, same number of cells every thing. Slider down off heading occure as the canopy is lifted to line streatch. The pack job doesn't know how wide the canopy is. Cord affects the shape of the packed canopy not span. We lose nothing be going to a slightly wider canopy. Slider up openings are a lot more complicated but look at the designs and wing loading we skydive with. I jumped a Mavrick as a slider up canopy when I started. It had a little thinner section. Depending on how you measured it I want to say the AR was about 2.27. It was one of the best flying canopies I ever had.
I know this is almost blastfomy but would it really be so great a sin to jump a nine cell. I know, I know, I know. Hear me out. They got a bad name at bridge day. Some body would show up with a PD nine cell or a Saber, a small canopy, and put a 48 in pc on it. The damn thing would look like it was broken in half by the pc. Huge distortion. But no one ever thought twice about jumping the same canopy with a 36 in pc when they skydived and that's more what we're talking about here right. Plus if you had a collapsable... They're more prone to mallfunctions. Really? If you're old enough think back to PD nine cells and Fallcons. Now I've seen malls on all kinds of canopies over the years includeing seven cells and reserves. a good potion of the time I could trace the source of the mall and rarely was it the canopy. We're not talking about crossbraces at 2.5 here. and some of those were nice flying canopies. The extra AR shure would help. You could say they don't stall as well but if you move the inside break line inward a bit they're almost as stable in a stall as a seven cell. Lastly you get too much center cell strip and slump with them becaus of the exter cell on each side. Well if that really worries you jump a multi. At that point you're no worse off then you are jumping a seven cell with a single bridal.
Would it kill us to have a lip on the canopy? a leading edge lip like a Saber. Hear me out. It's a big nose. Do we really need all of that inlet area? we're talking about a slider up canopy not a vented pilot chute assist canopy set up for hairy staticline jumps under 200 ft. It might slow the openings a bit and on some canopies that would be a god send. Frankly there are other factors that have a much greater effect on that then a lip. In full flight you'll see it dimple in. The dimpled part is doing nothing for you but at least you have the air above the dimple contained in the canopy where as at least part of that is normally lost. Here is where it shines. as you apply breaks and the pressure coeficent shifts around the canopy and the lip pops out. Now it is pressureized from the inside trapping that air forming a smooth top surface. Basically it's a variable geometry inlet. Where you want the inlet on the nose varries with angle of attack and spilling air over the top skin out of the canopy kills your proformance. You'll get a lot better float in breaks and better flare.
Slider up do we really need daccron lines? Let me help you out here. I jumped spector for years slider up. Shrinks like a bitch as fast as the slider comes down and plays hell with your break setting but it does fly nice. We do have some thing called vectran now that at least the break lines could be made from.
I don't buy into the whole zp thing. We jump at such light wing loading that F111 is pretty tight. You could put 500 jumps on an F111 canopy before it really started to show. Base is a rougher enviroment but by then a canopy is nearing retirement any way. You might offer it s a marketing thing but I don't think you'll get that much real binnefit from it.
Here's another out side the box for you. Trailing edge. Yah we draw our ribs with nice pointy ends. Ever do crew and fly by the trailing edge of some ones canopy? try it some time. I mean close enough to touch it, It's also fun to pull on their pc
. If you haven't done this I'll help you with the answer. It's not sharp then or in any way aerodynamic. In fact In the middle of the half cell it wants to turn into a rounded half circle. It goes from something shar at the rib to a radious of almost the width of the half cell / pi. On a 260 sqft canopy we're talking a 6 in radious on the trailing edge of the canopy. and that's about on with what you'll see if you fly up and try to grab it. Nobody's stupid enough to build wings like that but us. Never see that any where else. You think it doesn't matter? There used to be this old guy here named Chafen. He used to build canopies. One odd thing about them was his ribs didn't go all the way to the trailing edge. Don't ask me why but the whole trailing edge inflated round like that. I was playing with one of his canopies and decided to try a little expearament. I sewed the top and bottom skin togather up to the rib. Basically turned it into a normal canopy. Ugly but it worked. There was a noticable improvement in performance all around. Just that alone made a huge diffrence but I think we can do one better. Try ad follow me on this. Say the unloaded rib ended short of the trailing edge. say at the .75c where the D lines are. and the bottom skin was cut in a saw tooth to that point so that it formed a cone smoothly tapering to a point at the trailing edge. So that the air makes a smooth transition to a thin single layer edge. I think there was a europen reserve from PDF, Springo?, but being french they only got it half right and still had a double surface all the way to the trailing edge loseing all real bennefit. Help me out if I'm remembering this wrong. As to how to do this... You could make the bottom skin seam slant up wards to meet that point but that makes it torked relative to the bottom skin load bearing seam. that presents problems with the bottom skin pannel onless you make it facceted in which case it will probbable wrinkle. If you reduiced the highth of the rid moveing the whole seam upwards that problem goes away. You have an uneven bottom skin but what of it? It's that bad any way from the normal shifting of the rib upwards. But now the angle of the bottom skin supports the top skin almost like a cross brace. smoothing the top of the canopy which is what really counts any way.
I'm tired of writeing. Neck sore. I'll try and think more on it. Good luck. and feel free to make fun of me all ou like. Flame away at all my heretical views. I wont be offended.
Lee
