From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: AOA systems
To: lml
Date: Fri, 05 May 2006 15:28:43 -0400
Message-ID: <web-1093607@logan.com>
In-Reply-To: <445B6284.104@lazy8.net>
References: <445B6284.104@lazy8.net>
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Posted for John Huft <aflyer@lazy8.net>:

  Thought I would offer some alternate thoughts on AOA systems
  
First, I agree that they are good. I have had the PSS "sport" model in my RV8
for 2 years.
  
  But I have an objection to the wing port system, and that is that it is
hooked into the existing pitot static system, and to the existing airspeed
pitot. The microprocessor "brain" has 4 pressure ports on it, two from the
wing top and bottom, and one static, and one airspeed pitot.
  
  This means that you don't have any redundancy. If something happens to the
pitot static system, or the airspeed pitot, your AOA won't work either. That
is where I would like to have a vane-type system that is independent of the
airspeed indicator. Also, it requires electricity, which isn't so bad with so
many of our planes being all electric, with redundant power sources.
  
  There is a new system coming that I haven't seen mentioned here, from
TruTrack. They are introducing a flat panel EFIS, and a vane-type AOA will be
a $250 option. The EFIS will not display maps, lightning, weather, etc., just
flight info...airspeed, heading, vert speed, roll and pitch. It uses the same
algorithms as the ADI
  
  http://www.trutrakflightsystems.com/ttfsinstruments.html
  
  i.e. no AHRS. This might give you a good backup for a dual chelton or what
ever you big money guys have in your huge panels :o)
  
  Something to consider.
  
  John
  RV8 "Nuisance"


[John... thank you for bringing that up.  It is certainly a consideration. 
 There was a Legacy lost a couple years ago to an incident in which there was 
an issue with the pitot system and as a result the pilot was receiving 
conflicting messages from the ASI, the AOA, the feel of the airplane and the 
view out the window.  Rather than continue the takeoff with known 
malfunctioning instruments he chose to abort, overran the end of the runway 
and wrecked the airplane.  Fortunately he walked away from the accident... the 
aircraft was pretty much totalled.  The reliance on pitot/static data without 
redundancy is probably the only design flaw in the system (however, not one 
that is without remedy, should the builder so desire... how many experimentals 
do you know of out there with completely redundant pitot/static systems.... 
probably not a lot).  However, reliance on the AOA without a "reasonableness" 
cross-check by the PIC is mentioned seriously in the operator's manual, and 
when confronted with conflicting instrument indications the pilot must use 
whatever other data is available to safely conduct flight operations. 
 Sometimes the only data on hand is what we can see out the window, hear with 
our ears, and feel with the seat of our pants.  Which takes us full circle to 
earlier comments about practiced and refined airmanship being among the top of 
the list of tools at our disposal.  This doesn't diminsish the usefulness of 
the (now Advanced Flight Systems) AOA, the pitot/static system, or any other 
instrument in the airplane... it just amplifies the fact that nothing is 
foolproof and that we all need to be the best pilots we possibly can be at all 
times we are enjoying our roles as P'sIC.  And that covers a lot of ground.

    <Marv>      ]