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I have a Dynon D60 efis and an analog guage. During test flying the efis is reading 5-8 knots lower than the round guage. Any ideas? If it was a leak wouldn't it affect both? The only adjustment I've found for the Dynon is the zero set and I have done that. Any help would be appreciated.
Do they both use the same static source? That can make a difference in the reading. Are the static lines for the Dynon and the steam gauge plumbed together? If the Dynon uses an external source but the gauge uses cabin air, that would explain the difference in the readings.Quote:
Originally Posted by JHD
I once tried out a car-type electronic compass that included an altimeter setting in my Fly Baby. During runup, the altimeter would rise 100-200 feet due to the lower pressure in the cockpit.
Ron Wanttaja
Yes they both use the same staic source. There is a t-connection at the efis that feeds the analog guage.
There is instalation error, not yours, but from the physical instalation of the instruments. Also, the instruments will have insturment error which will be different for each airspeed indicator. I would think that the instalation error ought to be the same since its running on the same lines, but yiu may want to check all connections. Perhaps the difference may just be the instrument error. Recall, that POH performance data is based on calibrated airspeed which will be different that indicated airspeed.
Have you considered checking against a mamometer.(sp?)
What is the age of the analog airspeed instrument? They do have a spring and gearing involved I believe. If the analog ASI was purchased used and has not been calibrated in a while, it may be off that much. I believe that they read high when they get fatigued.
As mentioned earlier in this thread, you can test them at home and I think that there was an article about that topic in Sport Aviation not too long ago.
Best of luck,
Wes
N78PS
The airspeed indicator in my airplane has an adjustment knob where you align the altitude you are flying with the outside air temperature so the indicator will display not only indicated air speed but also true air speed. If your airspeed indicator has this TAS adjustment knob, it may be causing the difference you are seeing. Does the Dynon have adjustments for altitude and temperature correrction so it can indicate TAS. If so, make sure both the steam gage and the Dynon have the same settings.
Mick,
I kind of doubt the Dynon is showing TAS. I looked at their website and it shows TAS on the D100, but makes no mention of it on the D60. Normal flying would be by IAS, with TAS shown as a digital presentation on the PFD. I'd bet my guess on either instrument error as mentioned above or an issue with the ADAHRS in the Dynon, having the system tested/calibrated would be the best bet.
Jim
buddyamine has a different model dynon but a similar problem in his light-sport aircraft. shared pitot and static ports, t-fittings to each unit, but analog reads 4-5 mph slower than dynon. so we read the manual, calibrated and recal'd dynon. still there. made up a manometer setup, by golly the dynon was real close and the analog was 4-5 low. no adjustment. so we marked the analog gauge red/yellow/green ranges to be right, planned to ignore the numbers on the face. went to the logbook to make a note of why the range markings didn't match the numbers, lo&behold a tag dropped out. before the analog was installed, the manufacturer tested it. noted on the installation paperwork "this indicator reads 8 kph slow at 165kts which is within limits". now isn't that interesting. why would an instrument with mph markings have a note that it was off in kph when measuring knots? and what d'ya suppose the limits are? o well. your mileage may vary.Quote:
Originally Posted by JHD
Thank you all for the info. The airspeed indicator is new and so is the Dynon. I will look for leaks. If I can establish which one is right I will mark the other one.