[RV10Rob]

Just finished my static/transponder IFR certification?I?m good for another 2 years. As the technician was tapping the glass of his altimeter to keep the needle from getting stuck, I was wondering how accurate my Dynon D100 altimeter is compared to his calibrated mechanical altimeter. In other words, what?s more likely to be accurate: his or mine? How accurate is the altimeter in the typical experimental EFIS?

As an aside, to get our altimeters to agree, I had to adjust the altimeter correction to -40 in 2011 and -60 this year.

-Rob

 

[SteinAir]

Just finished my static/transponder IFR certification?I?m good for another 2 years. As the technician was tapping the glass of his altimeter to keep the needle from getting stuck, I was wondering how accurate my Dynon D100 altimeter is compared to his calibrated mechanical altimeter. In other words, what?s more likely to be accurate: his or mine? How accurate is the altimeter in the typical experimental EFIS?

As an aside, to get our altimeters to agree, I had to adjust the altimeter correction to -40 in 2011 and -60 this year.

-Rob

If he's using an old aneroid altimeter then it's likely your Dynon is many times more accurate! Both can and do drift, and depending on a number of variations either could be more accurate at different data points, but on the whole the digital instruments are often superior by quite a wide margin within our standard operating envelope of an RV.

Cheers,
Stein

 

[Walt]

His "calibrated" altimeter "should" be accurate to about 0.01 in of mercury which equates to about half the acceptable limit per CFR 43 (e). He will have a correction card with his "calibrated" altimeter in order to meet that spec.
If you're interested here is the FAA document on calibration for barometry equipment.

As Stein stated, the Dynon may indeed be more accurate than his setup.

However, not all of us have such outdated equipment! My pitot-static test box meets the latest RVSM requirements for accuracy:
(and I don't have to tap on the glass)

Altitude Performance (NIST Traceable)
Range: -1,500 ft. to 55,000 ft.
Resolution: 1 ft.
Accuracy:

±2 ft. @ 0 ft.

±5 ft. @ 35,000 ft.

±12 ft. @ 55,000 ft.


The airspeed performance is equally amazing:

Airspeed Performance
Range: 10 to 600 Knots
Resolution: 0.5 Knots
Accuracy:

±0.5 Knots@ 20 knots

±0.5 Knots @ 100 knots

±0.5 Knots @ 600 knots

I guarantee your Dynon can't meet those specs!

 

[RV10Rob]

Thanks, guys... this of course begs the question of whether I've erroneously adjusted my altimeter. I'm sure it's within spec, but I have it "adjusted" 60' right now, which is a lot on an ILS with 200' minumums.

-Rob

 

[jimgreen]

When my new Dynon D100 was tested last year the max deviation was 20'.
2/3 of the data points were 10' or less. Truly amazing.
Of course there could be significant static position error which wouldn't show up in the test.

How accurately does your altimeter read field elevation when set to altimeter setting from the tower?

 

[Walt]

Thanks, guys... this of course begs the question of whether I've erroneously adjusted my altimeter. I'm sure it's within spec, but I have it "adjusted" 60' right now, which is a lot on an ILS with 200' minumums.

-Rob

I don't really follow what you mean by the above "adjusted" 60'.

As Jim stated above what do you read on the ground when adjusted to local baro?

IFR Tolerances are shown below which can be found in CFR 43 Appendix E (copied below)

Altitude ------------------- Tolerance +/- Ft

¥1,000 ............................................ 20
0 ................................................... 20
500 ................................................ 20
1,000 ............................................. 20
1,500 ............................................. 25
2,000 ............................................. 30
3,000 ............................................. 30
4,000 ............................................. 35
6,000 ............................................. 40
8,000 ............................................. 60
10,000 ........................................... 80
12,000 ........................................... 90
14,000 ........................................... 100
16,000 ........................................... 110
18,000 ........................................... 120
20,000 ........................................... 130
22,000 ........................................... 140
25,000 ........................................... 155
30,000 ........................................... 180
35,000 ........................................... 205
40,000 ........................................... 230
45,000 ........................................... 255
50,000 ........................................... 280

 

[Brantel]

He's talking about ALT alt offset parameter. It's the only ALT adjustment available to the end user on the Dynon system.

 

[Walt]

He's talking about ALT alt offset parameter. It's the only ALT adjustment available to the end user on the Dynon system.

Thanks, forgot we were talking about the Dynon offset adjustment.

 

[RV10Rob]

Thanks, guys... next time I fly, I'll compare what I'm reading to a known elevation. I'll let you know what I find.

-Rob

 

[RV10Rob]

Checked it yesterday. It indicated 620' in a spot that's listed as 600' on the airport diagram. Good enough for me.

-Rob