AAD/Wingsuit question

[mccordia 74]

Is there anyone who has any knowledge about FXC AAD and wingsuits?
In some countries the older type AAD's are still quite common in use, though you rarely see em here (aside from student gear)

With the 'intake' part of the unit located on the MLW down on the chest, I could imagine the slighly higher pressured air underneath the body would/could slighly alter the units working (fooling it into thinking it's lower then it actually is)

Is there any information regarding this subject? Or is the pressure difference so minimal its neglectable?

dont turn this into a pro/con AAD discussion..its just a question regarding the working of the device, based on which a recommendation can be made when someone asks about jumping sayd AAD with a wingsuit

JC
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[phoenixlpr 0]

We have FXCs on student gear only. I have not seen anyone jumping FXC anything else than student gear.

[mccordia 74]

My personal view on FXC and wingsuits is 'rather not', but Ive seen some people jump older gear/units (sans wingsuit) in some of the baltic countries, and wondered about that combination.

JC
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[dragon2 2]

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We have FXCs on student gear only. I have not seen anyone jumping FXC anything else than student gear.

We have a few younger jumpers with FXC's on our DZ. Not many but they exist. Haven't had one for a wingsuit student yet, but, good point

ciel bleu,
Saskia

[mccordia 74]

The thing that sparked my interest, is the sudden high pressure you can generate after flaring out from a dive. Something students can also accidently do on first jumps if they have a wild ride.

The FXC activates just based on a certain airpressure. The sudden peak in pressure, bellow the body/chest, where the FXC intake is also situated, could (I think) make for scary situations.

JC
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[phoenixlpr 0]

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The FXC activates just based on a certain airpressure. The sudden peak in pressure, bellow the body/chest, where the FXC intake is also situated, could (I think) make for scary situations.

I don't think that could yield to anything if they open over 1000m as they should.

[LouDiamond 1]

Are you refering to the 12000 or Astra model? The FXC ( known as the Astra to many these days) has been in use for years both on the military and sport side of parachuting. Some foreign militaries are still using the older units(model 12000-25). The quick answer to your question,according to the FXC engineer I spoke with on the phone, is yes. BUT, it is highly unlikely that using one on a wingsuit dive could cause it to become confused and operate outside of its parameters any more than any of the other AADs on the market. The changes in pressure would have to be extremely high,even for a wingsuit planing out after a dive( 300 ft per second change in 3 seconds according to the engineer).However,the one show stopper in my and the engineer I spoke withs opinion where the unit could be fooled into firing higher than 1000 ft is where the jumper goes from their stomach to their back and then back to their stomach. The pressure changes could be significant enough to cause a higher firing altitude. FXC has not done any testing with wingsuits(according to the engineer I spoke with) so they are not 100% certain that there doesn't exist other circumstances where the unit might be fooled into functioning outside of its paramaeters. As always, nothing is infallable and proper use and understanding of how a device is meant to be used by the manufacturers specs is paramount to correct utilization.

FXC homepage

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[sdctlc 0]

Scott,

Are you saying the engineer sad what you related about the 12000 or the Astra?

Scott C.

"He who Hesitates Shall Inherit the Earth!"

[LouDiamond 1]

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Scott,

Are you saying the engineer sad what you related about the 12000 or the Astra?

Scott C.

The model I am refering to and that I discussed with the engineer is the Astra.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[mccordia 74]

The one I was refering to is the FXC12000.

Ive been to some dropzones in the baltic corner, where ts quite common to see people walking around with 'slighly older' rigs and AADs.

Thou most people upgrade their gear at some point, its not unthinkable that some people may actually try flying a wingsuit with the older 12000 units.

There are several thinkable moves with a wingsuit, that can cause severe pressure drops/rises, which would not fool the calculated activation of 'modern' AADs. But seeing as the air pressure at +- 1000 ft is all it takes for a 'mechanical' device like the FXC 12000 to fire, I believe a high powered flare-outs after a dive (especialy when done at lower altitudes, close to opening height) could give the device the higher airpressure on the chest needed to actually activate.

Not saying it is dangerous..but if it is, this may even be one of the things that should also listed in first flight briefings. Just like no pull-out, pilotchute pouch on leg etc. (though the pilotchute on the leg would maybe be possible again with some of tonys designs)




Anyways...I was thinking about the FXC/Wingsuit after a question from someone over email (who I advised not to use it) and couldnt find any previous posts or any other written recomendition/documentation on this matter..

Though there is only a small chance that anyone may actually try jumping an FXC equipt rig with a wingsuit, it could definately seriously ruin someones day. Maybe its a good idea to either test or put out a preventive bulletin regarding this matter?

JC
FlyLikeBrick
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[jakee 1,564]

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But seeing as the air pressure at +- 1000 ft is all it takes for a 'mechanical' device like the FXC 12000 to fire,

No, I don't believe that's true. The FXC 12000 combines both air pressure (altitude, user adjustable) and rate of change of airpressure (vertical speed, 44mph+) in its firing criteria, like an electronic AAD. Unlike an electronic AAD it can't figure out when it's being fooled.

Still wouldn't like to see someone flocking with one though!

Do you want to have an ideagasm?

[LouDiamond 1]

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I believe a high powered flare-outs after a dive (especialy when done at lower altitudes, close to opening height) could give the device the higher airpressure on the chest needed to actually activate.

The FXC 12000 is also a barometrical activated device,albeit older than the Astra.The engineer I spoke with said that it was possible but the rate of pressure change would have to be significant for a duration longer than a flare out would typically be. However, he conceeded that it was possible.

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Maybe its a good idea to either test or put out a preventive bulletin regarding this matter?

FXC has not tested their units (12000 or Astra) for wingsuit use per the conversation I had earlier. I was given no indication that they would persue this either. I think it would be premature and possibly litigious for anyone OTHER than FXC to issue a bulletin of any type without proper documentation and testing of the FXC products in a wingsuiting environment.


My take on the situation based on my conversation and what the engineer told me is that the possibility of a higher than normal activation could possibly occur if there were enough of the correct variables. I would recommend that until FXC can provide guidance on the use of its products with wingsuits that Instructors explain to both FFC students and experienced wingsuit pilots who use an FXC, that there exists the possibility of a premature activation of the unit at altitudes higher than specified by the manufacturer. Of course the alternative is to not use/turn on the FXC device on wingsuit dives, if it does not violate any applicable AAD useage requirements and the user is OK with it.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[sdctlc 0]

Scott,

I have a Astra and have been using one for about a year now with wingsuits. I have a friend that has been using one for more then 2 years in his rig. I switched to the Astra as I had a cypress that expired in my rig previously and had ready access to the Astra when I made the switch. Using this unit, I have done a good number of transitions belly to back and to belly again but with out and AAD incident. As I see it wingsuiting can be very easy to generate parameters outside of normal "Skydiving AAD" presets. I think it would be interesting to check out what the other manufacturers stance is on wingsuits and how it would potentially affect their units.

My concern was the acceleration from Low WS vertical speeds to a tumble and if the flying at the Low speeds right from the start of a jump following exit would create an issue with the units not arming themselves by not figuring out that it was on a jump.

Below is the response I received in an E-mail. I took out the engineers name as I dont think it is relevant but the info might be helpful. I have to admit that as a NON engineer it was a little confusing. I would be interested in the thought that people have to not only this response and an ASTRA but also to what I would expect to be similar "Issues" with other modern AAD's. I left in the mod info to indicate that this ASTRA is at the current revision in software as should any other ASTRA being used today in skydiving.

Scott C.


From:
Sent: Monday, May 21, 2007 12:13 PM
Subject: ASTRA explanation for Scott C.

The problem with the M3 program was that, when the aircraft flew above 1700 feet and then back down to 1400 feet during the climb, the ASTRA would fire whenever it measured a 400 foot drop in altitude during a 3 second interval. This situation occurred once or twice because the pilot was flying a low altitude holding pattern during the use of M3 units, and it resulted in a firing just after exiting from the aircraft. The M3B program added the feature that if the altitude goes above 1700 feet again after going down to 1400 feet, the 3 second search for a 400 foot drop stops and the ASTRA will again look for 1400 feet to start the 3 second measurement interval. So, if Scott is flying up and down in his wing suit just below 1700 feet and at least once below 1400 feet, the ASTRA might fire as high as 1300 feet instead of 1000 feet when it measures a drop of 400 feet in 3 seconds.

The only other concern with the use of wing suits is the increase of air pressure caused by speed through the air. An air speed of 170 miles per hour against the Astra Control Unit is estimated to cause it to read 1000 feet below the altitude pressure. This effect varies as the square of the air speed. Therefore an air speed of 40mph may decrease the altitude reading by 55 feet. Values of the change in altitude reading at other air speeds are left for Scott to evaluate. Tumbling complicates the situation because the Astra moves in and out of the air stream, going from increase to decrease and back to increase in pressure with respect to the pressure at the altitude. The Astra will fire if it senses an air pressure increase equivalent to 400 feet from the start of a 3 second interval regardless of what was happening previously. When the air pressure at the end of a 3 second interval is equivalent to 400 feet above the initial ground level reading, the Astra disarms and goes back into the mode that looks for 1700 feet above ground level (equivalent to turning the unit off and then back on except that the initial ground level reading is not updated). In other words, a steady high rate of air speed at a low enough altitude could disarm the Astra.

Regards,

FXC Engineering

"He who Hesitates Shall Inherit the Earth!"

[LouDiamond 1]

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I think it would be interesting to check out what the other manufacturers stance is on wingsuits and how it would potentially affect their units.

This question is outside of the question that Mccordia originally asked but to answer your question, I have personally spoken to Helmut (Cypress), Jo (Vigil) and Karel(Argus) about their AADs and the use of wingsuits. All of whom have confirmed with me that their products will perform as designed when used with a wingsuit. The only exception, which is already well known about, is that it is possible to fly slower than the activation speeds, below the activation altitudes when in full flight and not have the unit activate.

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My concern was the acceleration from Low WS vertical speeds to a tumble and if the flying at the Low speeds right from the start of a jump following exit would create an issue with the units not arming themselves by not figuring out that it was on a jump.

On the FXC, this arming issues is addressed as it arms as soon as it ascends above 1700 feet AGL.


The response in the e-mail statement seems to focus more on ascending above the arming altitude and then dropping below it and then ascending while in the aircraft. This is also a known issue with other AADs on the market and really doesn't address the high pressure located under the wingsuit jumper during flight as mccordia originally asked. It also suggests that headdown or freeflying speeds above 170 mph may cause it to think it is lower than it actually is. In regards to the slower airspeeds, the difference of 55 feet is negligible when talking about hard decks for activation as it is still higher than other AADs activation altitudes.

My observation is that there is a difference of 100 feet ( 300 vs 400) in the parameters mentioned in your e-mail and in what I was told over the phone.

At any rate, I think that the fact that you(and others probably) have used one without issue on wingsuit jumps shows that it can operate within it's design paramaters but based on what you received in your e-mail and what I discussed with the engineer suggests that there exists a possibility for a premature or higher than specified activation of the unit in certain instances during a wingsuit and or freefly flight. Therefore, I will reiterate what I posted above:
I would recommend that until FXC can provide guidance on the use of its products with wingsuits that Instructors explain to both FFC students and experienced wingsuit pilots who use an FXC, that there exists the possibility of a premature activation of the unit at altitudes higher than specified by the manufacturer.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING