Rich thanks for the long and informative email. Hopefully you'll let me know when you come up with a new plan - know my wife would be happiest with a BRS (any brand that works) in the aircraft so hoping to hear good news before long on the topic!
I keep hoping there's a way to go out the top, I hate the idea of cables wrapped around the exterior, seems so tacky since I'm talking about a finished airplane.
Your welcome! What keeps the Kitfox community going is dedicated information sharing.
In regards to the location of the cables and the launch direction of the rocket, take a look at the BRS drawings that are referenced in my previous message. One of the drawings portrays the cables as being top mounted along the windshield line, attached to the frame at the front. Check it out!
You're referring to the 3575 PDF's on the 'other forum' link right? unless I'm mistaken, aren't they all showing downward firing? Seems like in a close-to-ground deployment shooting downward is the last think you want....
Am I missing the correct photo you are referring me to?
one thing to consider with a rocket deployed parachute ,..almost all kitfox's that have the BRS system has them either pointing down or out the side,..and I'm wondering if this is to reduce the initial shock of deployment of the chute,..I'm thinking a rocket going straight up dragging the chute behind it and then being suddenly at the end of it's rope ...literally,..was there a reason for side or down departure of the rocket and chute system?,..this would inherently make the rocket go into an arc,.. which would swing from the bottom or the side curving to the top,..which would drastically reduce the shock to the harness on the airframe,..
lexan is some tuff stuff,..you can take a hammer to it,..if you watch some of the tests that lexan has been subject to,.. also on myth busters,..like cannons tossing frozen chickens at it ..sometimes the chicken is deflected,..that's 5 to 6 lbs of frozen chicken bouncing off the lexan under force,..probably more force then the BRS rocket will exert on it,..one would be better off to make the turtle deck so it would eject under the pressure of the rocket then trying to poke a hole thru it ..if the rocket did poke thru ..now the chute has to follow thru that same jagged hole the rocket made in the lexan if it indeed did penetrate it..
I'd like to see the results of a thru turtle deck test,..not with just a rocket going thru but the chute as well following it,..expensive test though .
Drawing 3575-B is the most valuable for illustrating the installation of the cables along the top of the frame. However, the different firing orientations of the rocket (as has been discussed in several threads) is subject to discussion and I haven't been able to discern a superior orientation.
However, if the exit is to be through the top, the lexan needs to be "pre-cut" to allow the rocket to exit. SkyPirate was right-on about the resistance ability of lexan - you sure wouldn't want a ballistic rocket bouncing around inside the cabin!
The BRS factory engineers suggested cutting a section of the lexan (can't remember the exact dimensions, maybe it was 12" square) and then gluing it back in with thin bridging strips so the whole piece would would break away easily when contacted by the exiting rocket.
BTW, to keep this thread more intact, I've attached the BRS drawings we've been talking about.
Thanks for adding those files - great care for all future readers...
I somehow never saw the band install pdf.
Well none of those actually show upward firing - seems like velcro etc could be utilized for a quick release of the turtledeck, about anything that will not catch air in flight and still hold it on would be suitable right?
Someone wrote somwhere that 'firing down is to prevent from getting wrapped up in the event of a folded back wing in flight' but seems to me like straight up would be 1. faster acting in low altitude and 2. if a wing is folded back there's a 100% chance that if that side wing is folded back it WILL hang up the riser line that goes around the side and down underneath. I just don't undersatnd how mounting at the bottom is smart at all.
How far back can we mount one, can we go far enough back that it goes aft of the turtledeck? Or is that just too far for weight and balance?
Here's another question: is it smart to buy used BRS chutes ? Will they sell you risers and hardware only from BRS for the kitfox if I got a used one?
Good questions about mounting location and direction of launching. The only thing I can directly comment on is the idea of using Velcro to adhere a breakaway lexan panel.
Someone at BRS recommended AGAINST using Velcro because of two reasons: a) It's adherence is too strong for the rocket and b) Velcro does not uniformly release and a non-uniform release could cause the rocket to exit at a poor or outright impossible angle. That's why they recommended the cut-out lexan panel held in place with thin (relatively weak) bridging strips glued to the turtledeck/windshield to hold the panel in place but still break away cleanly when impacted by the rocket.
...which could potentially blow out in a forward slip.
I still think this is why most of these installs go out the bottom, though a perforated fabric (mine appears to have been "scored" with a pinwheel as suggested earlier). It doesn't show in the photos, but there is an "X" pattern of very fine holes in the fabric, I assume made with a tool that looks like a little pizza cutter, but has pins on the wheel (looking for a picture on the net now).
The "out the bottom" deployment is not the prettiest, especially in my case, and fairly destructive to the a/c. But still seems to be the best way to go.
Last edited by Av8r3400; 01-18-2010 at 07:16 AM.
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I agree with your comments about the risk of going through the turtledeck, but what about my question of mounting aft of the
turtledeck facing up? Bad weight and balance ?
As Mike Berglund was building his Vixen with BRS in baggage compartment,
we were also concerned about the strength of Lexan. He cut a hole in
the turtledeck and I thermoformed a simple airfoil shaped cover from very
thin ABS. We feel the rocket would go through this without deflection.
Re: BRS Install photos in Model 3?
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