jjconstant
Well Known Member
Hi All
I'm scratching my head over something that has me befuddled.
On my return trip from Sun Valley, ID to Livermore, CA I was at 12,500' and showing 7.2gph fuel burn, 136kts indicated and 169kts true on my GRT Horizon EFIS. Ground speed showed 148kts with an outside air temp of 44F.
After I said "woo-hoo" to myself I very quickly said "better verify fuel burn and airspeed when I get home."
I refueled at home an the totalizer was dead on, so the fuel burn portion of the data was correct.
The next day I did both a wind triangle and a 4 leg gps airspeed calibration run and ran them through the various spreadsheets available.
Results: my "indicated" true airspeed (true airspeed shown on the EFIS, which I think is simply calculated from the indicated airspeed on the EFIS, using the air/data info about temp and pressure) is about 12 kts higher than the calibrated/calculated speeds from my testing. This result passes the sniff test of being right in the ball part of what I was expecting/hoping for when I had a finished airplane, on that sort of fuel burn.
The part that has me befuddled is that means that my indicated airspeed is off by a considerable amount, even though it has passed the pitot static check with flying colors. The EFIS specifically prevents you from adjusting the indicated airspeed so that it will agree with backup instrumentation, but you CAN adjust the True Airspeed shown by doing a true airspeed calibration procedure.
So a couple of questions:
1. After doing the true airspeed calibration will the True Airspeed shown on the EFIS actually be Calibrated Airspeed?
2. I thought true airspeed was basically indicated airspeed with a calculated adjustment for temperature and pressure. Does this mean that my indicated is really far off and can't be corrected, even though it passed an IFR standards pitot/static check? I have a Gretz heated pitot tube, with the static vents integrated into the rear top and bottom of the heated tube. It would be a challenge to change the static vent situation, but my assumption has been that the geometry was well worked out.
Thanks for the help
Jeremy Constant
I'm scratching my head over something that has me befuddled.
On my return trip from Sun Valley, ID to Livermore, CA I was at 12,500' and showing 7.2gph fuel burn, 136kts indicated and 169kts true on my GRT Horizon EFIS. Ground speed showed 148kts with an outside air temp of 44F.
After I said "woo-hoo" to myself I very quickly said "better verify fuel burn and airspeed when I get home."
I refueled at home an the totalizer was dead on, so the fuel burn portion of the data was correct.
The next day I did both a wind triangle and a 4 leg gps airspeed calibration run and ran them through the various spreadsheets available.
Results: my "indicated" true airspeed (true airspeed shown on the EFIS, which I think is simply calculated from the indicated airspeed on the EFIS, using the air/data info about temp and pressure) is about 12 kts higher than the calibrated/calculated speeds from my testing. This result passes the sniff test of being right in the ball part of what I was expecting/hoping for when I had a finished airplane, on that sort of fuel burn.
The part that has me befuddled is that means that my indicated airspeed is off by a considerable amount, even though it has passed the pitot static check with flying colors. The EFIS specifically prevents you from adjusting the indicated airspeed so that it will agree with backup instrumentation, but you CAN adjust the True Airspeed shown by doing a true airspeed calibration procedure.
So a couple of questions:
1. After doing the true airspeed calibration will the True Airspeed shown on the EFIS actually be Calibrated Airspeed?
2. I thought true airspeed was basically indicated airspeed with a calculated adjustment for temperature and pressure. Does this mean that my indicated is really far off and can't be corrected, even though it passed an IFR standards pitot/static check? I have a Gretz heated pitot tube, with the static vents integrated into the rear top and bottom of the heated tube. It would be a challenge to change the static vent situation, but my assumption has been that the geometry was well worked out.
Thanks for the help
Jeremy Constant