[Dave Cogan]

I am looking to buy a standby Altimeter for an RV-7a.
In New Zealand you require a (TSOd preferably) altimeter for IFR to complement the AF-3500 EFIS.

I can get the ASI and Autopilot in the smaller 2.25" size but all the quality altimeters with the visual strips bellow 10,000ft are 3 1/8".

Any ideas on where to buy them in the smaller size?

 

[the_other_dougreeves]

I am looking to buy a standby Altimeter for an RV-7a.
In New Zealand you require a (TSOd preferably) altimeter for IFR to complement the AF-3500 EFIS.

I can get the ASI and Autopilot in the smaller 2.25" size but all the quality altimeters with the visual strips bellow 10,000ft are 3 1/8".

Any ideas on where to buy them in the smaller size?

The only 2.25" ones I know of are are made by UMA and are the 1 turn = 10k ft style.

 

[mburch]

If you can bear parting with $800, Winter makes a two-hand 2.25" altimeter that's used by glider guys:

http://www.wingsandwheels.com/page21.htm

mcb

 

[JonathanCook]

my plan was to install a 2.25 certified Altimeter as a backup until i discovered how much they cost. I am now planning on using a full size one.

 

[mandm1516]

2 1/4" Airspeed only $181, Airspeed/Altimeter combo $262. Smart Singles

Mike

 

[Captain Avgas]

I am looking to buy a standby Altimeter for an RV-7a.
In New Zealand you require a (TSOd preferably) altimeter for IFR to complement the AF-3500 EFIS.

I can get the ASI and Autopilot in the smaller 2.25" size but all the quality altimeters with the visual strips bellow 10,000ft are 3 1/8".

Any ideas on where to buy them in the smaller size?

Hi Dave, I see quite a lot of people doing "IFR" glass panels have the UMA 2.25 altimeter as back-up. But it would obviously be impossible to fly real IFR with that instrument because it only has one needle. I've therefore concluded that a lot of people who build "IFR" panels are not actually IFR pilots.

For instance with the UMA single needle instrument it would be impossible to fly to an approach minimum (or to even hold a precise altititude....any altitude) because the read-out is just way too coarse with a single needle.

It would also be impossible to recognise a slow rate of ascent or descent within a reasonable time frame. In other words...useless for the IMC environment.

The certified 2.25 instruments with 3 needles are worth megabucks (like US$3500 upwards). So that leaves ONLY the Winter 2.25 altimeter (model 4FGH40) which is generally used in gliders and goes up to 20k with 3 needles and has barometric adjustment.

It's still pricey at about $800 but it's the ONLY "reasonably" priced 2.25 analog altimeter on the market (that I'm aware of) that could be seriously used for an IFR approach. The downside of the Winter is that despite the price it is not really super accurate.....it has an error factor of up to 120 ft at 8000ft. That MAY place it outside TSO standards. However that may be OK for a back-up. More importantly it has an error of only 45 ft at 2000ft so that should make it OK for an instrument approach.

The electronic digital units recommended by others would also be useless for IFR work in my opinion. You need analog info to get proper trend data.

My best guess is that the AF3500 would easily meet the IFR altitude accuracy standards and an approved pressure calibration check of that device should prove that it is within certificated standards.

On that basis it probably does not matter that the Winter may not comply because it would only be a back-up....and I presume you do not legally require a back-up

Have you researched the matter further since your post. I'd be interested in your comments.

 

[SteinAir]

My personal take on IFR backups is this:

They're not intended to be used for flying approaches. They are intended to get your rear out of the clag and into the clear...period. Flying an approach on any set of 2.25" instruments after you've had some sort of primary failure (assuming it's electrical since this discussion started with Glass backups) is IMHO crazy. Plus, that also means you'd need some sort of working CDI as well as Nav/Comm, etc..

Personally, my thought is if you intend to fly approaches on "backups", then you should in reality have Dual Everything (including primary instruments), not backups. My thought is the backups are there as just that - a reason to keep you upright and to get you out of the "stuff" and for that the 2.25" stuff should be sufficient.

Just my 2 cents as usual.

Cheers,
Stein.

 

[Captain Avgas]

My personal take on IFR backups is this:

They're not intended to be used for flying approaches. They are intended to get your rear out of the clag and into the clear...period. Flying an approach on any set of 2.25" instruments after you've had some sort of primary failure (assuming it's electrical since this discussion started with Glass backups) is IMHO crazy. Plus, that also means you'd need some sort of working CDI as well as Nav/Comm, etc..

Personally, my thought is if you intend to fly approaches on "backups", then you should in reality have Dual Everything (including primary instruments), not backups. My thought is the backups are there as just that - a reason to keep you upright and to get you out of the "stuff" and for that the 2.25" stuff should be sufficient.

Just my 2 cents as usual.

Cheers,
Stein.

I obviously have a slightly different take on this than you. I perceive that one might HAVE to do an instrument approach to get back on the ground. And therefore in my opinion it makes sense to me that the back-up guages will allow you to do exactly that.

And of course there is always the possibility that the PFD might fail during an actual approach. When I did my Command Instrument Rating I was taught how to continue the approach with the T&B when the AH was suddenly rendered inoperable. Frankly I would imagine it might be a hellova lot easier completing the approach with a 2.25 AH than a standard size T&B

Stein, why do you say that it is "crazy" to do an approach on accurate 2.25 guages. Are you suggesting that they are too small to be readable. That of course would be another issue and I welcome any comments on that because I have never used 2.25 instruments so I am not in a position to say either way. But I have spoken to some glider pilots who say they find them comfortably readable....but of course they're not flying in IMC !!!

 

[Pirkka]

I'm also interested 2 1/4" altimeters which would look like "normal" unlike that UMA altimeter in above message or Smart singles. Non-TSOd would be just fine -- anyone found any?