Bottom Skin Inlets

[imported_Tom Aiello]

I wrote this bit in another discussion. I've added a little to it, and was wondering if anyone here had any thoughts on it:

...
Bottom skin inlets do not have identical effects on all canopies.

The FOX has difficulties in steeply braked approaches, related to its shallow angle of attack. For this reason, secondary inlets greatly improve the flight performance of the Vtec FOX in deep brakes. The secondary inlets allow air inflow through the bottom skin, maintaining the canopy's internal pressurization even in brakes deep enough to stall a standard FOX.

The Mojo, on the other hand, has a relatively wider performance envelope. In very deep brakes, it tends to maintain pressurization far better than the FOX. I suspect that the effects of secondary inlets on the Mojo's flight profile would be far less pronounced than the effect on the FOX.

The Ace has an even wider flight envelope--and the effects of the secondary inlets are definitely less than they are on the FOX. In deep brake approaches, it's very difficult to tell the difference between the (unvented) Ace and the (vented) Blackjack.

The Troll also has a very wide flight envelope, so I would suspect that the effect of the MDV's, while probably quite dramatic on opening, are relatively limited (as with the Ace/Blackjack) in flight.

All of this should also relate to canopy openings. In general, the canopies with steeper angles of attack (greater down-angle on the nose, basically), should pressurize better at low airspeeds, and benefit less from the addition of secondary inlets. However, I think the effects of secondary inlets on openings are quite a bit more complex than their effects on canopy flight. For example, I expect that while the effect of adding secondary inlets to the Ace airfoil is relatively small on both openings and flight (more significant in openings, I think). But, while I have observed that adding the MDVs to the Troll has very significantly improved openings, I anticipate its effect on the flight profile to be rather less.

I don't know how this relates to the Flik. I suspect that its flight profile is very similar to that of the FOX, since the airfoil is identical. However, the trim is different, as is the aspect ratio, so no one really knows for certain. I am uncertain whether BR actually built any non-Vtec Fliks for testing. The Fliks I have seen in the possession of their test jumpers all had secondary inlets, so I rather suspect that the non-Vtec Flik saw minimal (if any) testing.
...

Thoughts, anyone?

--Tom Aiello
tbaiello@mac.com

[pyro]

Hey Tom.

Sorry about compiling all of these questions into one reply, but all of this has been on my mind lately and I did'nt want to scatter them all through the BB. This probably should be a separate post, so Mick if you see fit to move it, that's fine.
About a week and a half ago I had a toggle hang up on me for the first time. I was on a relatively low object, leaving very little time to correct it. After a couple tugs, which clearly distorted my canopy, it finally came free @ about 50 ft, and I landed w/o further incident.
I have a Fox 245 w/o Vtec, and I am using zoo toggles. I have never had a problem with them in the past, but I really don't want to see this happen again, so I am thinking about switching to LRT's. I'm pretty sure the reason for the hang-up was me. I am always on my toggles like lightning, and I probably just did'nt grab it them near the pin, but instead attacked them like skydiving toggles. Any comments and/or concerns before I make the switch?
Now the main reason that I wrote this is to discuss the flight characteristics of my canopy. After reviewing the video of this jump, and several other past jumps off of the same object, I have seen my canopy do some very ugly things. From the topside video, I am mainly seeing wave effect from nose to tail which lasts one or two times through the canopy. I believe this is caused by a lack of quick pressurization and me grabbing my toggles too quickly. At first, I was using the deep brake setting, and thought that might have been the problem(which, actually still might have contributed to it). But as I started jumping other people's gear, I decided that bottom skin inlets were definitely making a huge difference.
So...I have'nt decided on whether or not to get Vtec or the new Flik "ports". I'm not quite sure BR can even add the new ports to existing canopies like the Fox, or if they're still in the "testing" mode with just the Fliks. I have never personally seen the Flik in action, so I'm just going by info gathered on BR website and here. I would really like opinions on which people think are safest.
I am not a rigger, but I presently have an excellent one that will make modifications to my gear if I so ask. I plan on attending a rigger's course sometime this year. Until then, I have thought about having him add extra control lines to my canopy, and also another brake setting for a greater range of performance off of different objects. Where do I find specs for the additional control lines? Should I just have him measure the other cascading lines and use the same measurement? How do you test for the new brake setting(other than skydiving it, flying it in the desired setting, and guessing where that setting was once on the ground?).

Thanks,


}( Pyro }(

P.S. This message is not just intended for Tom, and I welcome all opinions.
P.S.S. I try to stay as technically competent as I can, but as I said before, I am not a rigger yet...so I hope I did'nt come off sounding like a tool here.

[Dwain]

This is very interesting but probably not the most relevant article. Bottom skin venting was introduced into the BASE world to improve slider down pressurization and canopy response to rear riser input with deep brakes set.
The improvements (and disadvantages) in certain flight characteristics are a secondary effect and rather inconsequential when compared to the safety improvements brought forward in terms of jumping low objects and/or avoiding object strike.
The main reason for having bottom skin vents on a canopy often gets forgotten as many tangent discussions arise from their use. The technology is simply for jumps where you exit low and/or where you open close to the wall.

Much of the comparisons in the above statements are incorrect because they do not consider the effect of bottom skin inlet valves. As someone who has tested a range of different valve prototypes, I can say with some certainty that valve design has a major impact on cell pressurization and (to a lesser extent) flare performance. A valve that significantly restricts inflow will result in noticeably slower cell pressurization. I suspect that one of the reasons that there isn’t as much noticeable difference with between a Ace and Blackjack on cell pressurization compared to a Standard FOX versus a Vtec/Valve FOX has more to do with the valve design (and perhaps location of the bottom skin vents) than the airfoil of the canopy (obviously however, angle of attack does play a role).
Place a Blackjack valve on a Vtec FOX and you get a canopy that pressurizes at a similar speed to a Blackjack. Place a FLiK valve on a Vtec FOX and you get a canopy that pressurizes like a Vtec FLiK . One of the reasons the Troll MDV is such a success is that they got their valve design right relatively fast.

"Noticeable effect" is also relational to skill level. A particular effect not noticeable to a poor canopy pilot may be very noticeable to an advanced pilot (who, for example, is in the process of trying to make a soft cross-wind landing on top of a flat 5-foot-diameter rock in the middle of a 45 degree boulder field). Unless you have the ability it's probably not fair to make blanket statements about a canopy’s performance. Number of jumps (or number of objects) has nothing to do with it - it's all about BASE canopy skill level and what you are trying to achieve with the canopy, which varies greatly from object to object and jumper to jumper (and thus the reason for difference of opinions).

In BASE lately there has been way too much focus on technology when compared to the general focus on advancing one’s own skill levels. In general an excellent canopy pilot on a ragged out old Pegasus will nearly always be in a much safer position than somebody with questionable skills under a Troll MDV or a Valved Vtec FLiK covered in body armor (just as an excellent tracker wearing jeans will always deploy further from the wall than the average Joe wearing Birdman Tracking pants, etc). More often than not, skill will far outperform technology.

My point is that many jumpers (both experienced and beginners) should redirect some of their interest in the finer points of BASE technology towards simply advancing their basic skill sets. Many newer jumpers have the belief that having the absolute best gear provides them with a good safety margin. It does to a point, but developing skill sets (and never being satisfied with your current ability) will take you much further in terms of safety.

Every jumper needs to constantly strive to improve their hardest launches, running exits, ability to take their intended delay (especially if you are packed slider up), sub-terminal and terminal tracking, body position on deployment, speed and correct reaction to off-headings, canopy control, and ability to land softly with a high degree accuracy. Until you have achieved these skill sets to a basic level of competency and consistency (which sadly is rare amongst the average BASE jumper), then discussing the finer detail points of BASE technology becomes somewhat redundant (albeit interesting).

>I am
>uncertain whether BR actually built any non-Vtec Fliks for
>testing. The Fliks I have seen in the possession of their
>test jumpers all had secondary inlets, so I rather suspect
>that the non-Vtec Flik saw minimal (if any) testing.

There are a great number of things that go on behind the scenes with all major BASE manufacturers. Most jumpers are not aware of the effort and cost that goes into designing, developing and testing new projects. There is also a high degree of secrecy involved. Just because you aren't aware of something doesn't mean it didn't happen. By the time the BASE population becomes aware of a new technology, usually that technology and/or its components have been under development, testing and refinement for a number of years (along with a large pile of similar concepts and prototypes that failed testing).

Be nice to the manufacturers. It’s a hard tedious task with very minimal financial gain. Nobody is getting rich producing BASE gear and the people doing it could easily make much more money in other fields.

[BASE_689]

>So...I have'nt decided on whether or not to get Vtec or the new Flik "ports".
>I'm not quite sure BR can even add the new ports to existing canopies
>like the Fox, or if they're still in the "testing" mode with just the Fliks.
Just done that. My Fox 245, already Vtec-ed, has just returned in my hands with the "covers" modification applied to it.
Not yet jumped on my Fox Vtec+covers, but it is an evidence that even on an old Fox you can get BR to do whatever you like: only Vtec or Vtec+covers or covers (on an already Vtec-ed Fox).

Stay safe out there
Blue Skies and Soft Walls
BASE #689 :D
e-mail: base_689@yahoo.com