The DI on my Cessna has failed. I suspect its 40 years old and probably overhauled about as many times. So I’m looking at buying a brand new unit.
Does anyone have any recommendation as to which brand is the best? In time I would be looking at replacing all the Vacuum instruments over 3 aircraft and I would like them all to be the same.
Why not replace them with electric ones with a built-in backup battery? This would do away with the need for regular cleaning and overhauls.
Sigmatek.
It seems curious why one would have a vacuum DI. It makes a lot of sense to have a vacuum AI (and indeed most King autopilot owners are stuck with the KI256, with no easy route that comes with the right paperwork) but a vac DI just means that if/when the vac pump goes, you lose both, and vac instruments suffer from bearing failure due to contamination, probably 10x more than electric ones.
Why not replace them with electric ones with a built-in backup battery? This would do away with the need for regular cleaning and overhauls.
All the standalone electric options seem to cost thousands, and you have the paperwork issue relative to the aircraft TC (unless there is a type specific STC).
DI – direction indicator, not attitude attitude indicator. Electric with back- up battery doesn’t apply.
With any vacuum gyros, contamination shouldn’t be an issue if filters are correctly maintained.
Peter wrote:
It seems curious why one would have a vacuum DI
It may be curious but that’s the norm in “steam gauge” aircraft. Of course you always have some backup for the DI in the form of the compass.
To me an Aspen unit seems to be the logical replacement for the basic instruments. If you have a VFR only aircraft the base VFR model is very reasonable, and can be software upgraded to a full HSI presentation for IFR use. To the OP: If the DI has gone the Attitude Indicator might not be far behind.
Peter wrote:
All the standalone electric options seem to cost thousands, and you have the paperwork issue relative to the aircraft TC (unless there is a type specific STC).
Isn’t that limited to aeroplanes with autopilots where AI is part of the system? E.g. S-TEC 50 won’t create that problem. Changing vacuum AI for electrical on an N-reg can be done as a minor alteration AFAIK.
PS: I would also think about Aspen.
Changing vacuum AI for electrical on an N-reg can be done as a minor alteration AFAIK.
Not so, sadly. You still need the redundancy. A while ago when I was writing this up I made some notes on this topic. Search for “KI256”. Also multiple threads here, with NCyankee being the expert.
an Aspen unit seems to be the logical replacement for the basic instruments
The EFD-1000 is a popular “high bang for the buck” option but at an installed cost of about 10x more than I suspect the OP wants to pay.
With any vacuum gyros, contamination shouldn’t be an issue if filters are correctly maintained.
IME, a KI256 lasts a few years at most. I have a spare on the shelf 
And I change all the filters at every Annual.
Out of interest – how much is an Aspen? I suspect my DI is heading towards an overhaul at the very least. If there’s a moderate chance that the AI is not far behind it, I’m wondering if it might make more sense to spend the overhaul money on an upgrade.
According to the price list it starts at 5k$ for the Evolution 1000 VFR PFD and 11k$ for the Evolution 1000 Pro PFD. Don’t know of the street prices, though.
Are there sensible alternatives?
