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  1. #1
    Mike Switzer's Avatar
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    BRS installation guidelines

    Does anyone know where I can find an article on the installation of a BRS chute in an experimental aircraft? Or has anyone here done it?

    I would like to include one in my design but I have some concerns.

    (And yes, I have looked at their website if there is any relevant engineering information there I can't find it)

    My biggest concern is if I try to put it near the CG of the aircraft it will be either fore or aft of the baggage compartment, which puts it either immediately behind the passenger's seat or directly in front of the fuel tank, neither of which seems like a good choice.

  2. #2
    Dana's Avatar
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    The anchor point should be at or near the CG but the canister and rocket can be anywhere it can fire into clear air and not foul the lines during deployment.

  3. #3
    Mike Switzer's Avatar
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    Well, if I can use a single anchor point that would make it easier, what little was on their web site talked about multiple attachment points.

    A 2 seat tandem layout doesn't give you a whole lot of options for where to put the rocket if you are trying to keep it away from both the seats & the fuel tanks.

  4. #4
    Mike Switzer's Avatar
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    You know, I'm sitting here thinking, if the objective is to impact at a survivable speed in the event of 1) power failure over rough terrain or 2) a unrecoverable stall/spin situation, I wonder if a drogue chute installation might not work as well. I don't really care what direction I am facing or if the airframe requires repair, as long as the occupants survive.

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    Eric Witherspoon's Avatar
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    Do you have a type that your design is comparable to? That might generate some ideas. My plane (Sonex) is a 2-seat, side-by-side low wing. I have seen photos of similar planes (CH-601 or one of the follow-on types) where they put the BRS behind the seat, and ran cables on the OUTSIDE of the fuselage on either side of the canopy to the forward attach points. These external cables were faired in with some sort of break-away (light) coverings, so there would be 2 attach points near the front of the wing, and 2 attach points near the back of the wing. One Sonex builder posted to the type-specific Yahoo group that he put the BRS behind the seat such that it fires DOWN out a hole in the bottom of the fuselage, and the airplane would recover inverted, hanging from the main spar, I believe. Though in the Sonex, it's quite a compromise, as a BRS and its mount/attach hardware will use up all of the factory-allowed behind-seat weight, and with 2 aboard, the airplane is running near/at most aft allowed cg.

    But to answer your general question, yes, people have added BRS to homebuilts. Have you tried contacting the company directly? They might have resources available to help a potential customer become a paying customer...
    Murphy's 13th: Every solution breeds new problems...

    http://www.spoonworld.com

  6. #6
    Mike Switzer's Avatar
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    I'm building something loosely based on a Long EZ, with a baggage compartment behind the passenger, the only one I know of that had a chute was N3R & since Tim had a stroke in flight the chute didn't matter...

    He put it behind the passenger seat but there was nobody back there usually...

  7. #7
    Matt Gonitzke's Avatar
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    Quote Originally Posted by Mike Switzer View Post
    You know, I'm sitting here thinking, if the objective is to impact at a survivable speed in the event of 1) power failure over rough terrain or 2) a unrecoverable stall/spin situation, I wonder if a drogue chute installation might not work as well. I don't really care what direction I am facing or if the airframe requires repair, as long as the occupants survive.
    This morning I ran across a video of some sort of aerobatic aircraft that lost a wing in a negative-G maneuver, and it appeared to have a drogue chute, as it was hanging by the tail after parachute deployment. The pilot walked away after it came down. And of course, I didn't think to save the link so I could post it here...

  8. #8
    Mike Switzer's Avatar
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    Thank Matt, I will hunt for that later tonite if Comcast doesn't slow down too much, it would sure make for an easier installation.

  9. #9
    steveinindy's Avatar
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    directly in front of the fuel tank, neither of which seems like a good choice.
    How big is your aircraft again in terms of weight? If it's on the lighter side, you might look into the Second Chantz compressed air ballistic parachute. It doesn't have the nasty habit of starting fires like the BRS system does (mostly because BRS is more often than not deployed after the aircraft hits the ground and the control lines are damaged).

    . I don't really care what direction I am facing or if the airframe requires repair, as long as the occupants survive.
    Then you probably want to come down vertically in a level attitude or even 10 or 20 degrees nose up by which the tail and rear gear would be the first to touch down. The problem with a lot of homebuilts is that they turn turtle if they are in a nose low attitude upon touchdown and we don't do the best job of including head protection in our designs whether they are canopy equipped or not.

    Mike, you know if you want my input on the survivability aspects, I'm happy to help since that's the area where I know the most about.

    I think Eric may be right - but it shows landing nose down is a survivable option
    Close to 70% of what most pilots currently generally consider to be invariably fatal crashes are survivable. Most spin/stall crashes don't absolutely exceed the human tolerance limits in a way that's not amenable to the proper use of engineering. However, I will point out that a nose down landing is not exactly ideal if one can avoid it. The limits for serious and fatal injury (which are different than the "no or minor injury" limits we often see trotted out for light aircraft designs) are higher in a longitudinal impact than a vertical one, but it's also a lot easier to dissipate the energy of a controlled vertical impact before it gets to an occupant.

    *You absolutly need the best restraint system that you can install.
    No offense, but given the 10-20% rate of restraint failures in GA aircraft (much higher in some models), one needs the best restraint system (or at least a better one) in almost any situation.

    the restraints will be right out of a race car so that won't be a problem
    Remember that a lot of the failures of restraints systems are due not to the webbing or buckles failure but due to the attachment points at the fuselage failing. Failure of the seat attachment points is another significant problem that needs more attention than it receives.

    *Trees may penetrate the windshield before impact.
    That's amazingly rather uncommon in a way that is significant. It's much more common- especially in composite aircraft- for the tree to penetrate/crush through the fuselage even in a crash that should be survivable. However, I see your point.

    Bob - my engine & fuel will be in the rear (some fuel in the wings) but nothing up front to speak of but electronics (& my feet)
    So a nose down impact is even less of a good idea without something very solid up there to take the brunt of the impact.

    Injury threshold: +17Gx (Eyeballs in)
    -12Gx (eyeballs out) See Col Stapp 1954 or so.
    +25Gz (Eyeballs down)
    -15Gz (Eyeballs up)
    The "injury threshold" in that case is not really the same as you would encounter in an aircraft scenario. This is mostly due to the fact that the forces in a paratrooper are going to be directly applied to the torso rather than to the airframe along with the mitigating factors of the seat, restraint, etc. Just something to keep in mind as those numbers (assuming you're quoting from the study I think you are) were designed to determine limits a paratrooper could withstand without needing to go to sick call or be put on restricted duty.

    One of the big problems with discussing "G" with non-survivability engineers is that they often forget it's not simply a matter of "X G = serious or fatal injury" but where the force was applied (over how much of the body) and how rapidly it was applied (onset) and duration. For example, a fall from standing height backwards and striking the back of your head on the sidewalk (as though someone fainted for example)- a common and very survivable event- imparts something on the order of 300 G for a split second to the back of the head. Most people survive without a skull fracture and maybe just a bad headache or concussion. The same level of force applied to the whole body for 0.35 seconds of more longitudinally (eyes out, -Gx) would likely result in the body fragmenting. Turn the subject around and decelerate them in excess of 100 G and there may be some negative effects but most people could survive it. Stapp himself argued that the rear facing "eyes in" (+Gx) whole body limit for life-threatening injury was probably in excess of 200 G based on his studies with monkeys. Unfortunately, no research board on the planet would approve testing that in humans so we're left to extrapolate from crash data (inaccurate as it is) and other indirect sources.

    One last thought Mike. If you could mount the chute in the nose, and desc tail first, you have all that structure behind you to sacrifice while eating up energy.
    The biggest issue in that scenario though becomes the strong likelihood of the entire thing winding up on its back and pinning Mike and his passenger in the aircraft which could introduce an increased risk of death due to post-crash fire or positional or traumatic asphyxia.

    About that Sonex that deploys out the belly and descends inverted. Someone is yanking our chain. No overhead structure, Real bad if landed in boulders or water. Sad songs and slow walks follow.
    Amen to that.

    After a couple emails (and lack of response after my last reply) I am getting the distinct impression the folks at BRS aren't that interested in the application of their products in experimental aircraft...
    That's the impression I got.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  10. #10
    Mike Switzer's Avatar
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    Quote Originally Posted by steveinindy View Post
    That's the impression I got.
    After the response I got from BRS I have pretty much decided to just wear a seat parachute. Eliminates a couple engineering problems & makes things simpler.

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