Airbag trigger points

[patprimmer]

Does anybody here know the forces necessary to set of an airbag, or more to the point, the safe limit in use, so as to avoid accidental discharge.

The reason for the question, is that on a recent trip to a desolate area of outback Australia, I assisted a mid sized 4 X 4 bus which was bogged.

It must have weighed 5 or 6 tonnes. I was in an Isuzu 4 X 4 station waggon that weighs 2 tonnes.

When I hit the end of the rope, at about 35 kph (20mph) the rear wheels were pulled from the ground, and the impact was enough for me to suddenly think "Oh no, the air bag".

We retrieved the bus, to everyones amazement, and no damage was done.

How hard could I hit the rope without risk of setting off the airbag.

Why isn't the fuse that disables the airbag clearly marked.

Why arn't there warnings that the airbag might deploy in such violent manovers.

This location was so isolated, that it might have taken up to 48 hours for help to arrive Regards
pat

 

[GregLocock]

Well, last point first - even if your airbag had gone off there's no reason to stop driving the car, if that's what you meant.

I've just looked through the airbag schematics for an EF Falcon.

Typical crash pulses are in the 20 to 80 g range at the sensor(s), which is obviously far more than you can generate with a rope. So far as I can tell if 2 out of three crash sensors are activated then the airbag goes off. However, anecdotally, naughty people can set them off by hitting the bumper in a particular way with a baseball bat.

We deactivate the airbag by disconnecting it in the steering wheel and adding a dummy load, but then we usually want the electric side of it to work. There are a total of four fuses in the system, at least one of which is in the passenger compartment fusebox, and labelled as such. I imagine that removing this will generate a fault code and disable the airbag system. Cheers

Greg Locock

 

[patprimmer]

Greg

Thanks for the info, it is reassuring. If it had been 5 or less, I would really worry.


The last point was to make the point that it was necessary to recover the vehicle, rather than go to get more help.

I know you can still drive the vehicle after deployment, but I certainly would rather avoid the expense and injury (even if only minor) that a deployment would cause. Regards
pat

 

[TrekLawler]

Greg,
Hello, I was searcing the old posts and ran across this one. Since I am doing some customizing on a vehicle which includes removing the airbag. Could you please let me know what the dummy load you referred to is and what the elctrical values of this load are. Any help would be appreciated.

Thank you,
Trek Lawler

 

[GregLocock]

It is an air bag simulator - ie a plastic box with connectors on it. This is a service part. I'd /guess/ that a 2.2 ohm resistor is hidden inside it. Obviously a given airbag might have a different resistor. Problem is, measuring resistances like that is tricky and you may set the airbag off if you try and measure it.

Anyway, there should be sufficient clues in the workshop manual for you to work out the required resistance.

Cheers

Greg Locock

 

[Nigel]

have a client that has requested that I develope an airbag system for his helicopter. The purpose is to reduce the potential for cyclic headstrike injuries during a crash.

Are there any other helicopter owner opperators out there that think this would be a useful addition to helicopters?

Are there any engineers with any comments about this? I am wanting to develope a simple system based on a 3 axis accelerometer and automotive style glare shield mounted airbag.

Obviously, this system will need to be FAA approved on a no hazard basis and it must function correctly.

Nigel Waterhouse B Eng (Hon's)
Can-Am Aerospace,LLC, Canadian Aircraft Certification Centre

http://www.canamaero.com

 

[SolderingGunslinger]

As an old rotor-head, I would think that a design utilizing a side stick as opposed to having the cyclic between the knees would make the implementation of an air bag easier...if not unnecessary. The stick would be low enough along the thigh of the pilot (Obviously on the opposite side of the pilot from the collective) that any possible head impact would require the body to bend in a most unnatural and catastrophic way.

My concern about an air bag in the cockpit is the event of a malfunction in the airbag system which would render the aircraft difficult or impossible to fly. Getting a light rotor wing aircraft into autorotation can be difficult enough without a loose-floppy airbag in your way.

I remain,

The Old Soldering Gunslinger

 

[patprimmer]

What is wrong with correctly designed seats and good harness type seat belts and helmets. It works well in motor racing.

It does not work in passenger cars due to fashion implications and driver discipline or lack thereof. I imagine these factors should be less apparent where the operator needs an aircraft licence.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

While I'm not the biggest fan of airbags, they do seem to offer additional safety benefits over and above a conventional 3 point harness. Once you go to 5 point then the next ideal would be a HANS device, but that might make moving your head too difficult.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

An accidental or poorly timed deployment of an airbag, like during a serious but possibly survivable mid air collision, or maybe a lightning strike? might have more serious implications in an aircraft than in a car.

In a car just before the airbag goes off, the car is almost certainly already in a position where control could not be be regained, and the only strategy is heavy braking with a reasonable chance of not hitting anything else at high speed, but in an aircraft, there can be time to attempt to recover control before hitting the ground at high speed, so long as the pilot is not hampered.

If held in place by a 5 point harness, and with some head restraint built into the seat, I would think should give as good a protection as an airbag, and it continues to work in subsequent impacts.

I should qualify this as being thoughts and personal observations only, with no hard data to support it.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[AMDSpeedTeam]

Dear Pat:

You say that you hitted the end of the rope at 35+km/h (an elastic rope I suppose) and you want to hit it even faster? You dont really want to do that!! Trust me, I ripped out the anchorage point of a series III Landy only at 40 km/h and it went trough my back door (I own a Landy too) at one zillion km/h of speed, destroying my back door AND a 4 gallon water filled Jerrycan! I still have cold sweat about that.

 

[zeusfaber]

Nigel,

how much of the desired benefit could you get from some sort of harness power retraction unit (a la Martin Baker)?

A.