Quick-disconnect connector force spec

[EdBundy]

Hi all
Does anyone on the forum have any experience or information regarding quick release (quick-disconnect, or QD) connectors? We're integrating a helmet system into a helicopter and for emergency egress purposes fitted the helmet loom with a QD connector.

The problem is that we cannot find a standard against which to measure our new installation, making qualification a bit tricky. The connector is a COTS item, which according to its specs, should disconnect at 13.8 lbf. A quick review of the company's compliance tests show that the connector disconnects at 16 lbf (Discrepancy 1). These tests were done using an ideal-circumstance scenario, i.e. no pins, prefectly aligned shells, etc.

We then did our own tests and found that the connector disconnects at between 22 and 28 lbf in real-world conditions. (Discrepancy 2). So our issues are:
a) To what do we really qualify to, does such a standard exist?
b) How do I convince the flight test pilot that he won't break his neck during an emergency egress?

Any light on this topic will be greatly appreciated!

Regards,
Ed

 

[moon161]

b) This is an interesting problem. Depending on what generates the force to pull the connector, and the geometry, injuring or trapping the pilot seems possible, even when the circumstance presumes a fit, adrenalized person.

The best circumstance I can think of is a pull handle that gives the pilot some slack so they can jerk it out. If an ejector system generates the motion, it seems like the harness should pull their head back into the headrest as the seat moves out.

If the actual work to pull the connector out is small enough, jerking it out w/ your head doesn't seem bad, especially if your neck is tensed so that the weight of your body helps you.

I'd be careful with this, possibly bring a biomed or Orthopedist in on this. I'm sure I've exceeded this force in bike and car crashes that I've walked away from (except for one), but the spine and neck aren't too hard to mess up if loaded out of column.

In summary:
1. It seems better if inertia, external support or another limb generate the force to pull it out.
2. Ask someone who really knows and get it on paper.

Of course you're way to far down the design process to ask this question, but could you use bluetooth for this instead?

 

[kontiki99]

Years ago, I was a parachute rigger for ejections seat parachutes.

I have no engineering experience in the area.

Seems to me, helmet disconnect ought to be on the seat. That way egress does not impose any loads on the crewpersons neck.

Crewperson then only has to deal with disconnecting the helmet when it somes time to separate from the seat.

That's how I vaguely remember the O2 and g-suit hose connections being set up.

It probably is possible to mount a strain relief on something that can take a load like the parachute harness.

Crew and harness should stay together for the whole ride.

 

[moon161]

Egress might be post crash only. I think only the russian Ka 50 has an ejection system.

 

[EdBundy]

Hi all

Thanks for the insights - gives me some food for thought. That being said, there is such a miriad of design standards and testing procedures out there that one would think at least one of them deals with allowable QD forces. Having the connector break on the seat is not feasible since the seat stay with the heli during emergency egress. This is a manual open-the-door-and-run-like-hell scenario. What other heli's have is a system that instructs the pilot(s) to manually disconnect the helmet loom before egress - something we would rather avoid as it adds another checklist point to an already hectic situation. Bluetooth will unfortunately not work due to lag, system and EMI issues. So far I have found an OLD navy spec which states the helmet QD force should be 18+-2 lbf, but was hoping to find something newer (like a DEF-STAN, SAE or MIL spec).

BTW egress implies any emergency situation, so crash land, engine fire on ground, all of these requires a quick getaway.

Regards,
Ed

 

[MintJulep]

How about a flying lead from the helmet and clip the connector to a lash tab on the flight suit. Take the force on the shoulder instead of the neck.

 

[moon161]

I'd brainstorm a bunch of options and mock it up w/ lumber, a moveable connector and flight gear. Remember to orient things so that you can generate a force directly in line w/ the connector. Tying into the flight gear seems like a good way to go.

 

[EdBundy]

Thanks for the insights, but the question remains - to what do I qualify it? Usually we qualify our designs to FAR29, but this is beyond the scope of FAR29 so I'm looking for some other supporting standard, i.e. something our CAA would accept. Myself, the electrical designer and one of the flight test pilots have done release tests in situ on the now-installed system and it works well as is, with the loom on the helmet and the QD connector on the airframe. No undue forces and no excessive resistance on the QD. So I know it's practically OK; I want to make it technically OK. If no standard exists then a statement to the effect of "was tested by flight and design personnel and found sufficient" but obviously this is still open to interpretation given the population scatter. A standard clears up much confusion.