andrewstewart 0 #1 October 17, 2003 Is there anyone who has jumped both a FOX/FLiK Vtec with covers and a Troll MDV that can give me a comparitive analysis? In the skydiving world I jump an Atair canopy but I have also jumped a FOX (just vtec, no covers) and thought it excellent also. Anyone qualified to comment? Thanks in advance, - A Share this post Link to post Share on other sites
TomAiello 26 #2 October 20, 2003 QuoteIs there anyone who has jumped both a FOX/FLiK Vtec with covers and a Troll MDV that can give me a comparitive analysis? I have only made a handful (less than five jumps) on the valved versions of these canopies. They pretty much fly and land just like the unvalved versions. The Vtec with covers system was developed by Basic Research following their own design program, and building on previous parachuting technologies (like their Vtec). The MDV is essentially an implementation of long-proven valve designs from the world of unpowered flight (paragliders, kites, etc) into a parachute. Although in most cases I've found that the parachuting technologies transfer (and develop) better to BASE, in this case I think the development history and track record of the paraglider type valve designs is pretty compelling. In my opinion, the MDV system is better than the Vtec with covers system in two ways, both having to do with the design of the valve itself (and the motion of the air into and within the canopy during the opening sequence). First, I believe the MDV will seal more perfectly in flight. This means that it will let the canopy fly more exactly like an un-valved canopy, which, ceterus paribus, will fly and land better than a the valved equivalent. These differences are marginal, though, and obviously so, as for several years many jumpers successfully flew and landed canopies with vents only (no valves). Second, I believe the direction of inflow at the end of the MDV "nozzle" is better oriented to speed the inflation process. Any valve will slow inflation as compared to the same inflation taking place without a valve or cover (i.e. with only the vent). [Note that this statement is true of all valves currently available--it is not necessarily true for all theoretical valve designs, some of which could, at least theoretically, actually perform better than a simple vent.] The trick is to design a valve that will impede the airflow the least. The MDV directs the airflow largely straight up (like a simple vent), impeding it the least. The "Vtec with cover" on the other hand, tends to deflect the air forward and aft, creating a longer lasting (as compared to the MDV) high pressure zone inside the valve. This means that the cover takes longer to close than the MDV after completion of it's inlet function. It also means that the canopy's internal equilibrium (i.e. the airflow that has to be in place for the canopy to be "flying") takes longer to establish. The bottom line is that the MDV system, if placed on an identical canopy, ought to yield a controllable canopy sooner than the Vtec with covers. In time difference, I am guessing this will gain you something measured in tenths of a second. Please note that the preceding discussion is all strictly theoretical. I've actually tested this by retrofitting canopies with MDV style valves--but have only compared PAC, MDV and simple vent, not Vtec with covers. I do not have any hard data to support my assertions on inflation difference--only the theoretical knowledge I gained testing other valve and vent systems. In summary, I think that the MDV comes closer to being a "perfect" inlet during inflation, as well as closer to being a "perfect" seal during flight.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Share this post Link to post Share on other sites
Zennie 0 #3 October 20, 2003 How does the Blackjack's design compare with VTEC/MDV? - Z "Always be yourself... unless you suck." - Joss Whedon Share this post Link to post Share on other sites
TomAiello 26 #4 October 20, 2003 QuoteHow does the Blackjack's design compare with VTEC/MDV? It's an oversimplification to compare the canopies directly, because the airfoil and trim are going to make such a huge difference to inflation. No one has yet succeeded in making an unvented canopy open better than a vented (or valved) one, but it is theoretically possible. Purely on the design of the valve, I think the PAC valve (which was the earliest design) is clearly inferior to the MDV. I also think that the Vtec Cover has an edge on the PAC valve, but that they are much closer together than either are to the MDV. So, on some totally ad hoc 1-10 valve rating scale, encompassing only these three valve systems, I'd say it's something like 3 for the PAC valve, 4 for the Vtec cover, and 8 for the MDV. Note that this does not speak to canopy design (which is, IMHO far more important) at all.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Share this post Link to post Share on other sites
Faber 0 #5 October 20, 2003 QuoteNo one has yet succeeded in making an unvented canopy open better than a vented (or valved) one, but it is theoretically possible. BR do NOT recomend Valves for ultra low freefalls(ie atleast sub 200ft freefalls),i know this as i asked them if it would be a good idea to my Fox,but as i like the low stuff they dont recomend it.But they SHOULD give a better flair. personaly i cant say as i only has 31jumps on a regular Fox and 36 on a vented fox.Just wahat i were told.. Stay safe Stefan Faber Share this post Link to post Share on other sites
TomAiello 26 #6 October 20, 2003 I'm pretty sure that BR recommends vents alone (i.e. straight Vtec) for sub 200' freefalls, and valves for all other jumps. I'm certain that an unvented FOX will be far worse than a valved one on a sub 200' freefall. A vented (but unvalved) one would be best of all, of course.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Share this post Link to post Share on other sites
Faber 0 #7 October 20, 2003 QuoteI'm certain that an unvented FOX will be far worse than a valved one on a sub 200' freefall. A vented (but unvalved) one would be best of all, of course. my point,i just think i didnt wrote it well..The right gear for the right jump. Would like a better flair through... Stay safe Stefan Faber Share this post Link to post Share on other sites
czechbase 0 #8 October 20, 2003 Now I'm confused. Does that mean an MDV canopy wouldn't be good for low stuff (200 feet or lower)?? For that I'd need just vents alone and no valves?www.motavi.com Share this post Link to post Share on other sites
TomAiello 26 #9 October 21, 2003 In my opinion, an MDV canopy would be fine for low stuff. A vent only canopy would be better, but a valved canopy (of whatever stripe) ought to serve you just fine. You'll probably need to revisit the vent/valve issues around 160 feet or so. But in the altitudes between 160 and 200 feet, valves should be ok. If given a choice, I'd take the vents there, but valves are definitely better than no secondary inlets at all.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Share this post Link to post Share on other sites
