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Old 04-09-2010, 08:56 PM
flybye flybye is offline
Join Date: Feb 2008
Location: Border
Posts: 113
Default AOA design. GRT vs AFS

In comparing the EFIS offerings of GRT and AFS, they take different approaches to the design of their AOA systems. AFS measures differential pressure from the leading edge of the wing while GRT's output is derived from an algorithm. I'm attracted to GRT's system since it overcomes the need to measure air pressure where there's always the possibility of blockage from insects ice etc. Has there been any third party evaluation of these two systems? Does GRT make any trade-off in not requiring measured inputs of air pressure?
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Old 04-09-2010, 09:29 PM
vmirv8bldr's Avatar
vmirv8bldr vmirv8bldr is offline
Join Date: Jun 2005
Location: Eastvale, CA
Posts: 378
Default Measured vs Calculated

I don't know the inner workings of either completely, but it seems to me the AFS is measured while the GRT is calculated. In general, measured quantities are usually more accurate than calculated. I believe the AOA's in commercial liners and Military planes are measurements of differential pressures as well, similar to the AFS. People smarter than me, please correct me if I'm wrong. I would love to see a side by side comparison.....

I do not work for either company, and I bought the AFS AOA and GRT EFIS.
(Technically, I bought them before GRT offered the AOA feature.)

You could always opt for the mechanical do-hickey that hangs a vane off the wing....
Bart Filipiak
Eastvale, CA
RV-8 N74VB

Barrett IO-390
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Old 04-10-2010, 07:34 AM
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Ironflight Ironflight is offline
VAF Moderator / Line Boy
Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,464

I have not flown the AFS unit, but have quite a few flight hours with the GRT, and have reviewed and commented on it here before. If you want a full-time indication of AOA, no matter if you are at th top of a loop, then a measured system is probably the way to go. If you are looking for AOA on approach, then the GRT system is quite adequate - because it is calculated, and requires computation, it is not perfect in highly dynamic situations, but gives good data within a limited set of operational parameters.

The biggest plus with the GRT AOA is that it is free with the EFIS, and requires no plumbing or installation. The biggest problem is that the display is on the EFIS, and generally out of the field of view when you are in maneuvering flight (because you're looking out the window). A remote reading head that mounts on the glareshield would be a great addition!

Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
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