I was looking around and came upon interesting info on making your own LRI, Lift Reserve Indicator, alias: AOA, Angle Of Attack for $60.
It looks equivalent to the LIR from InAir Instruments, LLC, which cost $450:
The instructions to make it are here and look very easy to duplicate:
It shows a nice drawing for making a probe out of a piece of aluminum bar. The gage is made from an off-the-shelf industrial differential pressure gage. The 2-1/6? dia. gage is mechanical and very sensitive. Specs for the gage:
This was off a Sonex Builders Web Site, and yes there are other home built kits out there. I would imagine the probe could be made from other materials and the face of the gage can be modified with color coded lift scale (provided in instructions).
Other Commercially available LRI, AOA
Other AOA gages utilize the same concept of differential pressure. Dynon & PSS (now sold by http://www.advanced-control-systems.com/
) uses variations on differential pressure. The Dynon AOA probe is incorporated in the Pitot, and the PSS system uses ports in the wing, top and bottom. The PSS also uses a flap position angle sensor to adjust the critical of angle of attack indication. The RV has a simple hinged flap, good for 2-3 mph, so a flap sensor is not super critical IMHO. On an aircraft with high lift devices like slats and slotted flaps it would be a must.
None of these units are reading angle of attack directly from a AOA vane, you see on Jets. The only "true" AOA is from right angle:
I have talk to the nice Gent who runs Riteangle. A visit to his web site and a look at installation photos is entertaining. He has new electronic display and incorporates a flap sensor. Worth a look. I think his product is in the $500+ range. The drag from his probe is reported to be less than 1mph at 200 mph from what I recall. That looks about right, a little more than the drag of a comm. antenna.
I think they are all nice products, but it hard to beat $60 for a do-it-yourself model. I see no reason that it would not be equivilant in most respects to the $450-$900 units. You could install the probe in your wing inspection cover. If you don't like it you could take it out and replace the cover. It looks like it would be worth the effort. I bought a Dynon AOA, since I already had the EFIS display and the probe was only $200 more. If anyone tries it, let us know how it works out.
Originally Posted by Dave Cole
I have used the same Minihelic differential pressure gauge with a drag rake for measuring wing profile drag .................Based on my experience, I don't think it would make a very useful AOA indicator.
That is interesting; I wonder if the brand of gage makes a difference. Even if it were affected by G loading, it would still be useful on a 1G approach. The commercial "LRI" unit uses a similar mechanical gage and is STC'ed? Hummmm. What gage do they use, because it sure looks like an off the shelf gage re-faced with a new scale. If I ever get my RV7 flying I may try it to compare it to the Dynon.