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:

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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, 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.
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Thoughts, anyone?

--Tom Aiello
tbaiello@mac.com

[Dwain]

I posted this some time ago in the technical section, but it never appeared. So here it is again.
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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 was simply introduced for jumps where you exit low and/or where you open close to the wall.

Much of the comparisons in the above post 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 between a Ace and Blackjack with cell pressurization (compared to a say Standard FOX versus a Vtec/Valve FOX or a Troll versus a Troll MDV) has more to do with the valve design (and perhaps location of the bottom skin vents) than the airfoil of the canopy.
Place a Blackjack valve on a Vtec FOX and you get a canopy that pressurizes like 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 particular 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 jumper / canopy pilot on a ragged out old Pegasus will nearly always be in a much safer position than somebody with questionable skills covered in body armor under a Troll MDV or a FLiK Valved Vtec (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 a strong focus on 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 canopy manufacturers. Most jumpers are not aware of the effort and cost that goes into designing, developing and testing new products. 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 general 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 other concepts and prototypes that failed testing). The gear of tomorrow is being designed today.

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.