catmandu
Well Known Member
EDIT: Just looked at 2020 pricing and it seems there is no longer a cost advantage, oh well.
When I originally got the sensed-AOA upgrade to my GRT Sport SX, I fashioned my own AOA sensing port by putting a drilled piece of tapered bar stock behind my pitot probe at a 45 degree angle, since the access plate to the aileron bell crank was right there. That worked fine, the GRT was able to use that pressure point to calculate the displayed AOA in conjunction with the pitot pressure from the separate, already installed heated pitot probe.
After cleaning up my panel and electrical system, my plane is a more reliable IFR platform. In that vein, it only made sense that I should have heat available to the AOA pressure port as well. The GRT installation manual only says "This probe is available from several third-party sources, or may be fabricated by the builder . . . " In reality, there are only two purpose built dual pressure heated probes out there, and the price point was hard for me to swallow.
I did find Alpha Systems had a heated AOA probe option for about half the price of the others, but it is really a system designed just for AOA. But looking at the geometry of the two pressure ports on their probe gave me hope that it might work for both pitot and AOA. I called and talked to the owner, and he said that some folks were in fact using one of the ports in his probe for pitot pressure (but, boy, he really wanted me to buy his complete setup, quite the salesman!). So I bit the bullet and ordered a probe. If it did not work, I figured I could talk my partners in the certified airplane into buying the rest of the STC'd Alpha Systems equipment and not be out any money.
I installed the Alpha Systems probe and did a test flight. Unfortunately, IAS was off quite a bit (30 knots slow at cruise power settings). But after consultation with a really smart friend, I modified the probe to get better total pressure to the GRT. I made it so the pitot port entry hole was perpendicular to the ram direction, enlarged the port entry hole and ram direction leg to 0.25" (to match the upward oriented leg in the rest of the probe), and then slightly tapered the probe edges away from the port to minimize turbulence. Something in there did the trick, three leg GPS runs confirm TAS to be within one knot from 60 to 160 knots. Sensed-AOA also works as advertised. So, one less probe, heated for safety, and a couple AMU's cheaper than I thought it would be. Successful experiment for my Experimental!
When I originally got the sensed-AOA upgrade to my GRT Sport SX, I fashioned my own AOA sensing port by putting a drilled piece of tapered bar stock behind my pitot probe at a 45 degree angle, since the access plate to the aileron bell crank was right there. That worked fine, the GRT was able to use that pressure point to calculate the displayed AOA in conjunction with the pitot pressure from the separate, already installed heated pitot probe.
After cleaning up my panel and electrical system, my plane is a more reliable IFR platform. In that vein, it only made sense that I should have heat available to the AOA pressure port as well. The GRT installation manual only says "This probe is available from several third-party sources, or may be fabricated by the builder . . . " In reality, there are only two purpose built dual pressure heated probes out there, and the price point was hard for me to swallow.
I did find Alpha Systems had a heated AOA probe option for about half the price of the others, but it is really a system designed just for AOA. But looking at the geometry of the two pressure ports on their probe gave me hope that it might work for both pitot and AOA. I called and talked to the owner, and he said that some folks were in fact using one of the ports in his probe for pitot pressure (but, boy, he really wanted me to buy his complete setup, quite the salesman!). So I bit the bullet and ordered a probe. If it did not work, I figured I could talk my partners in the certified airplane into buying the rest of the STC'd Alpha Systems equipment and not be out any money.
I installed the Alpha Systems probe and did a test flight. Unfortunately, IAS was off quite a bit (30 knots slow at cruise power settings). But after consultation with a really smart friend, I modified the probe to get better total pressure to the GRT. I made it so the pitot port entry hole was perpendicular to the ram direction, enlarged the port entry hole and ram direction leg to 0.25" (to match the upward oriented leg in the rest of the probe), and then slightly tapered the probe edges away from the port to minimize turbulence. Something in there did the trick, three leg GPS runs confirm TAS to be within one knot from 60 to 160 knots. Sensed-AOA also works as advertised. So, one less probe, heated for safety, and a couple AMU's cheaper than I thought it would be. Successful experiment for my Experimental!
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