So, I started a spares collection, because if I have a spare on the shelf, the active unit in the plane won’t ever break.
But how do I keep them in good health? Just keeping a vacuum driven instrument in an airtight box with some desiccant on a shelf can’t be enough, right? All the little bearings and whatnots surely need some vacuum induced action every once in a while, right? How do I keep them happy?
Sounds like a fun project: Vacuum cleaner powered workout rig for bored steam avionics (don’t forget the relief valve). But then arises the next question: Who moves the instruments around? Because the gyro bearing is probably the bearing which is least affected by a little stickyness.
Keeping spares is a great idea.
I keep them in the house where it is warm and dry.
For spinning up, say once a year, I constructed this with an old vacuum pump and a cheap chinese motor from Ebay.
However I don’t have any electric gyro instruments as spares. The KG102 would need a power connection to spin it up. The KI525 has no gyros – it is just a slaved HSI.
I replaced the KG102 with the Sandel SG102. It is a plug-compatible replacement, with just some very specific limitations (no stepper motor outputs, IIRC) if you don’t use the additional functions.
Keeping spares is an expensive hobby, too ;-)
If I’m looking at it right, that is an old vacuum pump directly driven by an electric motor, correct? Almost free, yay. What is the RPM range for a vacuum pump? I can probably run the setup with a drill and score points for membership in the CB (cheap bastards) club, although using a vacuum cleaner would probably get a better score.
I was thinking I could probably pick up a proper electric backup vacuum system for peanuts, with all the solid state stuff on the market, but easy does it.
My plane is 12V, so I should be able to spin up the KG-102 from basically any old 12V battery laying around. The connectors look typical, and I already have way too many different crimping tools, thanks in part to EuroGA’s help in an earlier thread on crimping tools
Now I have to go and find / order some fittings for the vacuum connectors. Endless, vicious circle of gathering… ;-) Although with the forced replacement of components based on time (thanks, EASA) I’ll probably be able to find some in the trash bin sooner or later.
A vac pump spins at something like 1.5x crankshaft rpm. A standard capacitor-start single phase motor runs (at 50Hz, 2 pole motor) at 1500rpm off-load. So you get the sort of vacuum you should get slightly above engine idle. It works fine – I can confirm.
To get higher rpm you need a DC motor (an electric drill would do), or a 3 phase motor driven from a variable speed inverter e.g.
You had me at “can confirm” :-) thank you!
I would consider not trying to “keep them moving” during storage (at the risk of damaging something by messing with pressure or not using the adequate dust filters) but rather keep them packed and dry and investing the money for the “movement rig” into an avionics shop doing a “cleaning and greasing” service before installation.
I do see value in your approach, Malibuflyer, but it kind of defeats the purpose of having a spare ready for installation if I need it to go to a shop before I can use it. I’m looking into picking up a whole electric standby vacuum system on the cheap to make sure the cure I apply is not worse than the disease; I already have a vacuum pump and filter that silently became trash in the CAMO’s eyes.
Agree – it is really the question of what you are solving for:
If it’s really about “having a cold standby” that you could screw into the panel within minutes to avoid aircraft on the ground, I fully agree that your solution is a (perhaps the only) feasible one. In those cases, however, I assume that your fleet is so big that we are more talking about storing them a year rather than 10 years before use.
If it is more for “having a spare one because you never know if when mine is failing in 8 years I will find one on the used market at a reasonable price” then some days for the shop might not hurt too much.
And by the way the second use case does make lot’s of sense: The prices for such used equipement differ by orders of magnitude whether you “need to buy one now because yours failed” or you “happen to find one from someone that just updated his avionics”
Keeping spares makes a dramatic difference to downtime / AOG issues.
It also makes it possible to do quick troubleshooting, by swapping stuff.
It also means regular component overhauls (mags etc) have zero downtime.
Otherwise, to get replacement items, you need to have a very good “relationship” with a shop which is willing to lend you stuff. That sort of thing does exist but in every case I have known it was done with a shop
Most aircraft owners are in some sort of “middle ground” where they don’t have access to some handy facility like that.
It works best with an N-reg and a friendly freelance A&P who can sign off the swap in the logbook. I am not sure if any EASA66 guy is similarly authorised; isn’t there a “radio license” of some sort?
Another advantage is that you can buy up these spares at time and place of your choosing, on US Ebay for example, and not when you are stuck somewhere and over a barrel. Recently a kind ex owner gave me a Shadin fuel totaliser (the panel instrument). This is worth at least 1k. I may not need it for years, but…
