Author Topic: ENL recording sensitivity  (Read 7261 times)

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Brett

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ENL recording sensitivity
« on: December 06, 2012, 03:10:43 PM »
I have had a jet engine installed in my JS1. Looking at the IGC trace recorded by the ClearNav the trace "just" picks up engine use - instead of showing red on the trace the green trace line is a sort of green/yellow.
Is there a way of increasing the ENL sensitivity so it picks up the jet noise more effectively to satisfy the scorer?
As an aside the LX9000 on a friends jet powered JS1 shows nothing at all when the engine is in use.

Evan Ludeman / T8

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Re: ENL recording sensitivity
« Reply #1 on: December 06, 2012, 05:14:30 PM »
The ENL sensor is frequency selective.  This is necessary to avoid false positive indications from opening a vent window at high speed, etc.  We're aware of the issue with jets, not certain what we might do about it at this point.  As you've noted, other manufacturers face the same quandary.

Just curious: what's the jet sound like in the cockpit (volume, character)?
Evan Ludeman / T8

Brett

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Re: ENL recording sensitivity
« Reply #2 on: December 06, 2012, 07:11:03 PM »
Thanks Evan.
The jet is surprisingly quiet in the cockpit - certainly much less noisy than the roar from the business end.
As it spools up it moves through frequency bands which give the high pitched whine for a few seconds, but at useable thrust levels these are supersonic I assume as there is just a muted roar like a big hair dryer or vacuum cleaner.
I turn the comm volume up a bit to be able to hear what's being said but don't bother with hearing defenders.
Brett

Evan Ludeman / T8

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Re: ENL recording sensitivity
« Reply #3 on: December 06, 2012, 07:30:41 PM »
Maybe engine noise isn't the way to track usage. 

This must be the first time in history that anyone wished that their jet airplane was louder ;D.

update:  It turns out that this is an IGC issue.  We don't actually have a free hand as far as the bandwidth, filters, sensitivity and so forth.  I'm informed that there was in fact a hell of a lot of work to get this right... for propeller driven motorgliders.

« Last Edit: December 07, 2012, 05:54:55 AM by Evan Ludeman / T8 »
Evan Ludeman / T8

John Galloway

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Re: ENL recording sensitivity
« Reply #4 on: December 17, 2012, 04:12:09 AM »
My jet JS1 is scheduled for build completion in October 2013.   LX Nav make a MOP sensor for installation in the engine compartment for jets (and electrics) so I will be limited to choosing an LX 9000/8000 unless ClearNav come up with something similar.

John Galloway

Evan Ludeman / T8

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Re: ENL recording sensitivity
« Reply #5 on: December 18, 2012, 03:04:47 AM »
We've discussed this, very briefly.

I suspect the IGC is going to have a problem with any sort of remote sensor. 

The simple way to do it with CN equipment would be to locate the CNv ADC closer to the engine.  There's no way at this moment to know if that will work, but it seems much more likely to get approved than a remote sensor.

A better solution might be to have a look at the noise spectrum of the jet in the cockpit vs normal soaring flight and see if there's some bandwidth and SPL threshold that can be identified as useful for ENL yet not troublesome for false alarms.  If anyone has a good idea of how to get this done, I'm all ears.
Evan Ludeman / T8

John Galloway

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Re: ENL recording sensitivity
« Reply #6 on: December 18, 2012, 03:32:34 AM »
Evan,

The LX Nav remote MOP sensor is IGC approved so there does not seem to me to be any theoretical reason for others not to be.  The remote sensor is electronically sealed and the data transfer between it and the FR is encrypted. See para 7.6 of the LX 9000 IGC approval document:

http://www.fai.org/gnss-recording-devices/igc-approved-flight-recorders

and:

http://www.lxnav.com/products/mop.html

John

Evan Ludeman / T8

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Re: ENL recording sensitivity
« Reply #7 on: December 18, 2012, 04:53:02 AM »
Ah yes, I see now.  Thanks for pointing this out.
Evan Ludeman / T8