I posted this in another forum and a helpful person suggested I post it here. Any suggestions would be greatly appreciated. I’ve got the original RAF altimeters in my chipmunk. These are the type with the loop in the 1000′ hand. Both work fine but the kollsman windows are out of calibration – about 100′. It’s not a big deal because I only fly it vfr but I’d like them to be accurate. I know how to release the kollsman window on a standard altimeter but not on these. It may be that the altimeter has to be dismantled in which case I won’t try but if there’s simple way, I’d like to give it a try.
Here’s an old photo of my instrument panel.
Many thanks
Dave
By: Fieldhawk - 26th September 2011 at 12:46
Don’t muck around with something that you know little, or nothing, about. Send it to a recogised and CAA approved shop for calibration, then you will know that it is working properly and then, and only then, can you trust the reading.
Play safe – the alternative will be a disaster.
By: daverdla - 26th September 2011 at 11:57
FB,
It’s hopefully just a calibration error that can be corrected by setting the barometric pressure independently from the altitude. I have been stocking my cupboard with extras too. I just got a very nice looking never used altitude indicator for $23.00.
G – thanks very much – I’ll give it a try this week.
In case anyone is interested, here’s a link to the procedure for a “standard” altimeter.
By: Biggles of 266 - 26th September 2011 at 00:53
Undo the two screws holding the small plate under the knob. Remove the plate. The knob can then be pulled towards you and the scale can be adjusted intependantly from the hands.
Replace the plate.
Worked on mine.
G
By: Fournier Boy - 26th September 2011 at 00:42
Hi Daverlda
I’m not sure I follow! Do you mean the subscale is out of sync with the hands, but still linear? Normally my (limited) knowledge on Altimeter overhaul is that the bellows int he altimeter often take unfiltered static from the cockpit with no moisture trap, and after time, mildew/corrosion forms in the altimeter springs and bellows making it stick. Normally for cross referencing, I take it to 2 millibars difference (approx 70 ft) being acceptable for Annual renewal, to get it closer than that in these old instruments is pretty much an expensive waste of time in my eyes.
Purely personal thoughts though, i have a cupboard full of things units for when you find one that is simply “too bad”
FB
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September 25, 2011 at 11:58 pm