2.25" Altimeters????

A recent post by prkaye got me thinking and it never occurred to me that you could not buy a reasonably priced 2.25" "sensitive" altimeter for a backup instrument.

Is there a source for these that is not obvious? If not, I have may have some rework to do to my panel plans.

What are the thoughts about using a non-sensitive (one arm) altimeter as a backup instrument? I noticed most if not all of the panel pics on Stein's website have one armed ones installed.

Brian,

Here's a 2.25" altimeter from Winter. (Stand by to have heart palpitations at the price). William Soaring Products

Here's an alternate source of the same unit. Their prices are slightly lower: Wings and Wheels Soaring Supplies (Scroll down to the 4th photo).

As far as I know, the Winter altimeters are the only sub-$1000 2.25" altimeters you can get.

Brantel said:

A recent post by prkaye got me thinking and it never occurred to me that you could not buy a reasonably priced 2.25" "sensitive" altimeter for a backup instrument.

Is there a source for these that is not obvious? If not, I have may have some rework to do to my panel plans.

What are the thoughts about using a non-sensitive (one arm) altimeter as a backup instrument? I noticed most if not all of the panel pics on Stein's website have one armed ones installed.

Click to expand...

Yes of course,
have a look at our Infinitec ALT-1 or even the Infinitec ASX-1 which gives you both altimeter and airspeed indicator in a single 2.25" housing (standard "round" 2.25" housing, front or rear mount).

The price may pleasantly surprise you too...

Rainier
CEO MGL Avionics

UMA Instruments makes single-pointer 2.25" altimeters. 10k or 20k faces, inches for us, mbar for everyone else.

About $250. Order direct from UMA or your fav supplier. Stein lists 'em, but says he's out of stock. If you order from UMA, you should be able to get internal EL lighting.

TODR

I looked at the MGL Alt-2 and am very tempted by it for a number of reasons (e.g it doubles as a VSI and has an encoder).
My BIG hesitation is that it requries power. That kills my goal of having a set of critical flight instruments that continues to work in the event of total electrical failure.
Now, if the MGL altimeter had a built-in battery backup that could keep it going for up to say an hour... then I would be sold on this solution.

I do not believe the UMA ones are considered "sensitive".

Falcon has a 2.25" single-pointer that they claim is "sensitive", but the only definition of "sensitive" i have ever seen (Wikipedia) means an altimeter with multiple pointers so you don't have to interpolate to get better than 100ft resolution. So I don't know if the Falcon one would really count as sensitive.

The nice thing about the Winter unit is that I believe it meets JAA certification, which I believe is a foreign equivalent of TSO.

At Oshkosh this year, a UMA sales guy told me they were working on a 2.25" sensitive altimeter that would be cheaper than the Winter one (although still expensive). I hope it works out, since I will need a small standby altimeter and I'm in the same boat as the rest of you guys!

mcb

I have a 2 1/4" UMA in my panel for a back up. After looking at it for 350 hrs I would not recommend it. The first problem is that it is impossible to set the barometric pressure because the Kollsman window is so small you can not read the setting and the scale reads in increments of .4 inches. The only way to set the thing is to a known altitude. Interpreting the single needle to anything closer than 500' is a challenge. I have the 0 to 20,000 feet version wich makes the scale even harder to read. Additionally I have noticed that even when I set the thing to field elevation on take off it will have as much as a 500' error when I get to 8,500'. I too have been looking for something better and will probably go with the electronic unit from MGL.

Martin Sutter
building and flying RV's since 1988

Rainier,

Looks like you could sell three of these things today if you can give us a good solution for backup power????

prkaye said:

Now, if the MGL altimeter had a built-in battery backup that could keep it going for up to say an hour... then I would be sold on this solution.

Click to expand...

I believe I read somewhere that the Infinity Singles by MGL can run on a 9 volt battery for over an hour, so if any of your instrumentation already has a battery backup, couldn't you just hook this up to it as well? Otherwise you could buy a separate battery backup from MGL--the one for the Enigma is $30, the one for the Odyssey is $40.

Brantel said:

What are the thoughts about using a non-sensitive (one arm) altimeter as a backup instrument? I noticed most if not all of the panel pics on Stein's website have one armed ones installed.

Click to expand...

Well ... what do *you* think about it? It will be your butt in the airplane. I think it's up to you and your DAR in terms of them approving the operating limitations for the aircraft, right?

Personally, I'd be Ok with it if it saves $750. It's not enough to fly a precision approach. I can't see a reason to go with the 20k unit in an RV - 10k unit would provide better reading precision.

TODR

the_other_dougreeves said:

UMA Instruments makes single-pointer 2.25" altimeters. 10k or 20k faces, inches for us, mbar for everyone else.

About $250. Order direct from UMA or your fav supplier. Stein lists 'em, but says he's out of stock. If you order from UMA, you should be able to get internal EL lighting.

TODR

Click to expand...

No internal EL lighting in their 2.25" ALT's, only the ASI's, etc.. We often have them in stock, but also many time don't. UMA is often slooooow in deliveries!

Cheers,
Stein

I do have the single-pointer UMA installed and when I asked about doing a pitot-static check for IFR, was told they wouldn't pass me with that Altimeter installed. It's OK as a VFR stand-by, but I wouldn't use it for IFR. I had two options, remove it, or cover it so it wasn't visable. My plan is to replace with the newer sensitive altimeter from UMA when it's available.

You know Rainier's Infinity instruments make a person start to rethink some things...

I can add his Infinity instrument to my backup plan and come out better:

I was planning 2.25" backup instruments as follows:

ASI
TT ADI
ALT

With Rainier's solution, I could have

ALT/ASI on the same instrument
True AI/T&B/Magnetic Compass on the same instrument

More information with one less instrument and a couple hundred cheaper!

Brantel said:

Rainier,

Looks like you could sell three of these things today if you can give us a good solution for backup power????

Click to expand...

OK, that's an easy one...

Well, many of these units are used for backup purposes on larger aircraft or as primaries on smaller types.
One big factor is the really low power consumption of these things and low voltage requirements.
This means, in a nutshell, you could use a small 9V transistor radio battery to power these things quite happily for perhaps close to 10 hours or so (depending on the battery chemistry kind).

So, one way (there would be others of course) would be to stick a 9V battery in a holder from Radio shack (perhaps behind the panel where you can get to it), then use two diodes and a small switch. One diode connectes the power to the main bus, the other connects via the small switch to the 9V battery.
In practise, you would do your preflight like such: Main bus off, backup switch on - check to see if instrument works OK, then switch on main bus.
The higher voltage from the main bus would then stop any current flowing from the 9V battery - but if the bus goes down, the ALT-1 would continue to function as if nothing happened and will be visible even at night due to the backlight.
The switch prevents the battery from running down when you're done flying. If you have a main power switch with a spare set of contacts you could use those - but then you would need some other means to check if the backup is working when main power is down.

Another option would be to use a rechargeable 9V battery (such as a NiMh) with another diode from the main bus and a resistor in series to trickle charge the battery when the main bus has power.

For a more comprehensive backup instrument our Flight-II has become quite popular - but it needs a 3.1/8" hole. It's almost a small EFIS for next to nothing and even can give you engine RPM and fuel related stuff like flow and level apart from all primary flight stuff.
The Flight-II BTW is soon going to be available in a new, round housing as well as are all other maxi-singles. The new range will be known as "Velocity".

Rainier
CEO MGL Avionics