The place for technical discussions about GA and flying.
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By flyer5
I noticed an advert on FlightGlobal for a Honeywell inertial platform - for about $1500.

An INS for a small plane would be a brilliant back-up for GPS. Has anyone seen anybody selling these. or talking about developing them?
Modern solid state gyros are much more accurate than the old stuff. A new one might keep sufficient accuracy to be useful in case of gps failure.

But how often do gps actually fail? Now that’s not going to wind anyone up is it?

And I wonder if those who would want a backup are the ones who would not like a little black box.

If Garmin were to work on the G5 it wouldn’t be that much of a change to use the sensors it already has to output a inertial derived location.
We put a state of the art INS in our work research jet a few years ago. It cost over £400k and drifts about 1.5nm per hour.

Which is fine - regulatory compliance is met, and after 6 hours towards the North Pole, where GPS and the compass are equally untrustworthy, and there is nothing else to use - it is quite good enough to find an NDB.

But for light aircraft ops? VOR/DME, GLONAS and ded-reckoning all strike me as a rather better bet.

T67M liked this
VOR/DME I guess was the basis of Area Nav a while back. Are you aware of any cheap boxes you can buy that will feed SkyDemon using VOR/DME?

Your point about Glonass implies it mitigates GPS drop out to some degree. I saw the following which partly supports that (it is focusing on naval navigation but I doubt that makes a huge difference):

The results from the static test showed that the jammer has effect on large distances,
and that the different receivers used react differently when exposed to jamming.
Further, the carrier-to-noise ratios for Glonass are less affected by the jammer, and
the receiver is able to track Glonass satellites with lower carrier-to-noise ratios than
GPS satellites. We have seen that utilizing Glonass satellites in addition to GPS
satellites in the receiver contribute to a later loss of position fix and an earlier
calculation of new position under difficult jamming conditions.
The dynamic test showed that the marine grade GPS receiver is easy to jam. A weak
jamming signal caused the GPS receivers to give misleading information without
any warning ....
As Glonass signals has shown to be more resistant to jamming than GPS signals,
applying the Glonass system in addition to GPS might provide benefits with regards
to reliability and redundancy, especially for maritime navigation in Northern areas
where the Glonass satellites also have higher elevation and better coverage than
GPS. ... sequence=1
flyer5 wrote:I've heard of 10 nm drift after crossing the Atlantic but that was a long time ago. So what are we talking - 50 years ago?

Not that long! It was about 20 years ago on a 747-400 so using units still in use today! I haven’t looked recently as the twin GPS units now used are so accurate :D
Genghis the Engineer wrote: a second hand Bendix-King KNS80 would do the job
Actually that would be a good idea (£600 ballpark) if I owned my own plane. But those of us who fly miscellaneous club aircraft hired by the hour it's better to have something portable and battery driven.
You won't carry-on an INS, it needs to be installed near the airframe CG, very firmly attached, and calibrated to the airframe dynamics.

Plenty of high end phones now however incorporate GLONASS receivers, and a few Galileo receivers, if you are tablet obsessive who declines to look out of the window and use a chart.

I'd have thought that most club rental aircraft have VORs in at the very least?

Genghis the Engineer wrote:Flyer5, a second hand Bendix-King KNS80 would do the job, but I doubt it will feed SkyDemon.


I've used our Narco NS800 8 station RNAV for 25 plus years, from long before GPS was freely and cheaply available for GA.(Place 8 remains our airstrip tuned off CLN)

We've has a couple of replacement gas displays and had if FM immunised and it keeps on going:

So well in fact that when we upgraded to GNS 430W we kept 800 if only for its DME.

Great bit of kit. admittedly slightly less useful in darkest Europe where there seems to be a dearth of VOR/DMEs.

I fire it up as backup every time I fly except for local bimbles.

Solution looking for a problem?

VFR - GPS Backed up by window plus map/compass/timer
IFR - IFR approved GPS kit backed up by VOR/DME/ILS/NDB/radio.
Flyin'Dutch' wrote:Solution looking for a problem?

VFR - GPS Backed up by window plus map/compass/timer.
I started flying over half a century ago. I can remember when you would request a QDM from a passing airfield. In those days you would make a wish to the Pools Fairy for a Decca Navigator or fiendishly expensive Doppler Inertial. Fifty years later to buy your first SkyDemon/Airbox is far beyond your wildest dreams.

I know officially you are still supposed to fly VFR with pilotage and DR, and many people cling on to the old days of lines on maps and dials and mental calculations, but recently flying the magenta line has started to be accepted. It has probably been driven by airspace busts but once people accept that a GPS-driven map is more reliable at keeping jets into Stansted free from disruptions then it's a small step to accept the old ways are actually second best wherever you are.

It's relaxing flying along not really knowing where you are half the time but neatly spotting your destination a minute or so before the time showing on your log but around areas of congested airspace maybe it's 'stop when the fun stops' and check where you are compared to the boundary lines minute by minute.
Nick liked this
Just out of interest I checked the inertial drift on a one hour flight yesterday and it was 1.5nm....
If you’re worried about GPS reliability, I would have 2 devices, one running iOS, one Android and each running different nav programs. If GPS goes down totally, a PA28 getting lost will be the least of their problems, all North Atlantic traffic will have to stop for example. My belief is that the GPS system satellites are much more robust than we think.