REFLECTOR: 65VT/ angle-of-attack system

[Douglas Holub]

I look forward to testing that when I start flying off my 40 hours sometime 
in this century.

Doug
----- Original Message ----- 
From: "Jim Sower" <canarder at frontiernet.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Tuesday, October 05, 2004 11:46 AM
Subject: Re: REFLECTOR: 65VT/ angle-of-attack system


> Max glide, climb and Vx, Vy are usually the bottom of a fairly wide 
> bucket, and the departures either side of the POH specs are pretty 
> gradual, so if you're in the ballpark, your results will be very close to 
> optimum.  I tend to go just a little faster than the specs on account of 
> the heavy front seat.  AoA indicators are not typically accurate enough 
> (fine enough granularity) to be all that useful for stuff like that 
> anyway.  At least that's what I recall from tactical jets in the 60s and 
> 70s.  The big deal as I see it for GA AoA is to prevent approach turn 
> stalls, and that's not a problem with canards.
>
> As I see it .... Jim S.
>
>
>
> Douglas Holub wrote:
>
>> So, would you say that the airspeed indicator is just as useful as an AOA 
>> indicator for establishing maximum glide or maximum rate of climb?  Or 
>> would Vx and Vy vary more with CG and weight than an AOA indicator would?
>>
>>     ----- Original Message -----
>>     *From:* Jim Sower <mailto:canarder at frontiernet.net>
>>     *To:* Velocity Aircraft Owners and Builders list
>>     <mailto:reflector at tvbf.org>
>>     *Sent:* Monday, October 04, 2004 8:54 PM
>>     *Subject:* Re: REFLECTOR: 65VT/ angle-of-attack system
>>
>>     Al,
>>     <...The relative AOA of the two airfoils is fixed. ...>
>>     Actually, they're not.  AoA / incidence are respectively the
>>     angle(s) between the chord of the airfoil and the airstream /
>>     fuselage centerline respectively.  The airfoil chord line is the
>>     line between the "stagnation point" on the nose of the airfoil to
>>     the tip of the trailing edge.  Wing flap or canard elevator
>>     deflection increase the camber of the airfoil and increase both
>>     the incidence angle and the AoA.  An AoA indicator measures
>>     airflow relative to a *fixed* line (the fuselage centerline?) and
>>     assumes *fixed *incidence angle (which is not the case with a
>>     canard unless you never deflect the elevator).
>>
>>     <...could be useful for determining canard stall at one
>>     configuration; full elevator deflection ...>
>>     Actually, the canard stall does not always occur at full elevator
>>     deflection either.
>>     With aft CG, relatively little elevator deflection rotates the
>>     fuselage considerably, and the the canard will stall at an AoA
>>     that consists of the largish fuselage AoA plus the relatively
>>     small increase in incidence caused by relatively small elevator
>>     deflection.
>>
>>     With forward CG, it takes much more (full?) elevator deflection to
>>     rotate the fuselage less, for the canard to stall.  Here, the
>>     fuselage AoA is much smaller, but the canard incidence increase is
>>     much larger with full elevator deflection.
>>     The canard stalls in both instances, but the "AoA" that the
>>     transducer sees is a good bit lower at forward CG than at aft CG.
>>
>>     You may recall from your Cessna days that the airplane had to be
>>     pretty cocked up to stall clean, and much less so to stall with
>>     the flaps down.  The AoA of the *airfoil* was not that much
>>     different clean or dirty, but the incidence of the chord line
>>     increased radically when you lowered the flaps.  By the same
>>     token, cruising at, say 70 kts the airplane had relatively level
>>     attitude, but drop the flaps and maintain 70 kts straight and
>>     level and you were looking at the trees.  The AoA of the airfoil
>>     didn't change radically, but the angle between the wing chord line
>>     and the fuselage did.
>>
>>     So for a canard, AoA is a little like teats on a bull .... Jim S.
>>
>>
>>     Al Gietzen wrote:
>>
>>>Angle of Attack is a very useful tool for conventional plan form 
>>>airplanes.  It is of little value for canard type aircraft since the wing 
>>>you're trying to observe is the canard, and the incidence and aerodynamic 
>>>properties (like stall AoA) are constantly changing (with elevator 
>>>deflection).
>>>It just doesn't tell you anything particularly useful ... Jim S.
>>>
>>>Good point, Jim.  However, I do think that it could be useful for
>>>determining canard stall at one configuration; full elevator deflection.
>>>Using the pressure port system, I'd expect installation on the main wing
>>>will work fine; you just need to calibrate it the canard stall point. 
>>>The
>>>relative AOA of the two airfoils is fixed.
>>>
>>>Al
>>>
>>>__
>>>
>
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