REFLECTOR: AOA perspective

["Al Gietzen" <alventures@email.msn.com>]

Interesting to see the postings regarding angle of attack meters (AOA); especially systems costing over $1400, and mounting in the wing.

 

What is it we want from these?  In spite of marketing claims, I think its usefulness is pretty much limited to giving a good consistent indication of incipient stall, regardless of loading, temp., density altitude, etc.  I'd say that this is an instrument that is conspicuous by its absence from the panels of standard tractor pull; stabilizer-in-the-back airplanes that are subject to the stall-spin accident.  But a prime motivation for driving an airplane with a wing in the front is that it avoids this type accident.

 

So I think its possible usefulness to us is to know when the canard is going to stall so we can make consistent landings which aren't any hotter than necessary (or not hot enough) for the conditions.  So we need it on the canard; not the wing.  I also think that order to calibrate these instruments, you need to take the airfoil to stall speed, so we could never calibrate one for the main wing without being in deep _____ . . . . , you know; stall! 

 

Installation of any system using differential pressure ports is not so easy in our canards, especially if we got the canard from our friends at Dynamic Wing.  Or, if you haven't built your canard yet, a very inexpensive installation is a differential pressure gauge, a small pressure port (like a static port) on the leading edge of the airfoil, and another such port on the bottom of the airfoil 12 1/2% of the chord length from the leading edge.  Measure the pressure difference between the two; calibrate it by marking the reading on your gauge just at the point of incipient stall of the airfoil.

 

Now even simpler; since the leading edge port is subject to a bug splatter or dirt or ice, one can instead use the dynamic pressure you already have from your pitot tube.  It gives you less of a differenttial pressure range to work with, but I helped a friend with this type installation on his Lancair 360 and it works just dandy.  A pitot tube mounted in the slightly disturbed flow on the side of the fuselage may be a bit different, but it probably would also work.

 

When asked if they thought an AOA (stall) meter would be helpful, the guys at the EZ Squadron sort of shrugged and said they didn't think so.  If you pressed them, they'd probably say that they land hot anyway because otherwise mushy aileron response, adverse yaw, and lack of visibility over the nose makes them nervous. 

 

What about you Velocity fliers (if any of you have read this far)?  Would you like to have one of these on your airplane?  I'd like your feedback, because I'm giving serious thought to making this installation.

 

Al Gietzen  RGE