EFIS ASI Adjustment?

[s19flyer]

I have a D-100 and an analog ASI, both of which are new. I did an accuracy check today using my Garmin 396 and the analog ASI is dead on with the Garmin. The D-100 is reading 6-7mph low. Is there any way to adjust for this or just not worry about such a small difference?

 

[dynonsupport]

There's isn't a way to adjust the IAS in the way that you're describing. But, historically, units that we get back that supposedly have IAS accuracy problems in fact are well-calibrated. There is an zero pressure calibration SETUP>SPDCAL that is designed to set the zero pressure reference point which in turn can affect VERY low airspeed accuracy only, but this doesn't change the entire airspeed curve.

Note that your 396 won't correspond with an airspeed indicator except in zero wind conditions and near sea level. There are involved methods that you can use that can help tease out the actual right IAS numbers you'd expect to have given GPS legs along with OAT/altitude info, and unless you've done one of them, don't trust the fact your GPS and analog match but your Dynon doesn't. The most likely source of systemic problems is pitot/static system error, for what it's worth. The fact that your other instrument is closer to GPS doesn't say anything about its accuracy.

The gold standard(s) are a known good pitot/static test set or water manometer if you have access to one.

All the same, we'll take a look at a unit if you really think it's your Dynon. But almost always, they check out fine.

 

[DBRV10]

I bet you a six pack, you had a head wind.....and your analogue ASI is wrong

Get an A&P or whatever the instrument guy is called and his test box to check the whole system, pitot and static.

Then once you are sure there are no leaks and all is accurate, go do a static error check by doing a indicated or displayed TAS Vs GPS box test. This confirms if your static has any dynamic errors.

Also check both ASI are in the same units. KNOTS/MPH or KPH

 

[s19flyer]

There's isn't a way to adjust the IAS in the way that you're describing. But, historically, units that we get back that supposedly have IAS accuracy problems in fact are well-calibrated. There is an zero pressure calibration SETUP>SPDCAL that is designed to set the zero pressure reference point which in turn can affect VERY low airspeed accuracy only, but this doesn't change the entire airspeed curve.

Note that your 396 won't correspond with an airspeed indicator except in zero wind conditions and near sea level. There are involved methods that you can use that can help tease out the actual right IAS numbers you'd expect to have given GPS legs along with OAT/altitude info, and unless you've done one of them, don't trust the fact your GPS and analog match but your Dynon doesn't. The most likely source of systemic problems is pitot/static system error, for what it's worth. The fact that your other instrument is closer to GPS doesn't say anything about its accuracy.

The gold standard(s) are a known good pitot/static test set or water manometer if you have access to one.

All the same, we'll take a look at a unit if you really think it's your Dynon. But almost always, they check out fine.

I did use a measured course (triangle) and that's how I got my numbers. Having that small of a difference is not really that big of a deal but I just wondered if there was a way to close the gap.

The analog and Dynon use the same static and pitot lines so I thought they should read closer than that.

No big deal but I'll check stall speeds on both, do a zero cal and call it good.

the analog is just a backup in case of power loss.

Thanks for the response.

 

[s19flyer]

I bet you a six pack, you had a head wind.....and your analogue ASI is wrong 

Get an A&P or whatever the instrument guy is called and his test box to check the whole system, pitot and static.

Then once you are sure there are no leaks and all is accurate, go do a static error check by doing a indicated or displayed TAS Vs GPS box test. This confirms if your static has any dynamic errors.

Also check both ASI are in the same units. KNOTS/MPH or KPH

Yep I may have to take you up on that bet  ;D

Did several checks in different directions, then averaged for the diff. And yes I do need a static test. Both units are set to MPH. Dynon AOA/PITOT that is 6" below the wing and static in factory location(s). Both on same pitot/static line but they indicate the difference that I found also.

Later and thanks for the info.

 

[s19flyer]

I bet you a six pack, you had a head wind.....and your analogue ASI is wrong 

Get an A&P or whatever the instrument guy is called and his test box to check the whole system, pitot and static.

Then once you are sure there are no leaks and all is accurate, go do a static error check by doing a indicated or displayed TAS Vs GPS box test. This confirms if your static has any dynamic errors.

Also check both ASI are in the same units. KNOTS/MPH or KPH

Yep I may have to take you up on that bet  ;D

Did several checks in different directions, then averaged for the diff. And yes I do need a static test. Both units are set to MPH. Dynon AOA/PITOT that is 6" below the wing and static in factory location(s). Both on same pitot/static line but they indicate the difference that I found also.

Later and thanks for the info.

Well I'm waiting on that six pack ;D

Did the zero pressure cal and the Dynon/analog/GPS are now all within <2mph apart.

Happy Camper