1. posterid:2018744
  2. AOA

Re: AOA

Jay Scheevel
 

Hi All,

Some time ago, I did some airflow modeling on the tandem wing configuration of the Q-2 (LS1 canard and Eppler 1212 main wing). I have posted a diagram on Q-list group site that shows two models that I ran:

http://groups.yahoo.com/group/Q-LIST/photos/album/576675737/pic/1308193526/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

The model on the bottom of the diagram shows that the canard can fly at a high AOA (near stall angle) but because of the downwash from the canard, the main wing will be flying at a slightly higher(2-3 degrees) angle of attack than it does when the canard is flying at a low AOA (as shown in the top example in the diagram).

In this respect, the downwash does far more to prevent the main wing from stalling than does the angle of airplane as a whole. Because of this downwash effect on the main wing's AOA, mounting an AOA instrument on the main wing would be folly. The critical AOA is that of the canard, NOT the main wing so the canard is where the AOA instrument should be located (at least in the case of the Dynon-style pitot-based system).

By the way, if you fly the Q-2 inverted (negative G's), the downwash from the canard will be more pronounced on the main wing and will eliminate most or all of the lift from the main wing. And although the main wing is not technically "stalled", it will generate virtually no lift and the Q will enter a deep inverted stall. Positive G maneuvers won't do this, but negative G's will. This is why having the main wing mounted near the top of the fuselage and the canard mounted near the base of the fuselage is important to the stability of this design.

After I did this modeling, I realized that the main wing will never really stall, but it is capable of producing insufficient lift because of downwash from the canard. This may be an academic distinction, but it helps me think about how our unique design works.

Cheers,
Jay Scheevel -- Tri-Q, still building.

--- In Q-LIST@..., Mike Dwyer <q2pilot@...> wrote:


Oh, I do see that I misread Bob's main wing comment. Yes, lets not stall the main wing. That would be very bad. I suppose an electronic AOA could be set to go red near the main wing stall point... but a properly consructed and loaded aircraft hopefully never gets near that angle due to the canard stalling first. Thanks for the correction Lynn!



Mike Dwyer Q200 N3QP


________________________________
To: Q-LIST@...
From: q2pilot@...
Date: Tue, 3 Apr 2012 19:33:54 -0400
Subject: RE: [Q-LIST] AOA



Nope, never stalled that, the plane won't let me stall the rear wing,
thank goodness!
Mike

Sent from my Windows Phone
________________________________
From: N142LF
Sent: 4/3/2012 7:22 PM
To: Q-LIST@...
Subject: Re: [Q-LIST] AOA

Mike,
I don't think you are stalling the main wing all the time.

LJ French

Short & simple from my mobile

On Apr 3, 2012, at 5:36 PM, Mike Dwyer
wrote:

Let me take a shot at Bob's question. First it's got nothing to do
with Plenums so I changed the subject line to AOA.


Bob wrote:
I am looking at electronic instruments to replace the 30 year old
instruments in my plane, N19WT. One of the glass instruments has the

ability to report angle of attack from a $200 pitot. Since I'm rebuilding,
this has me interested.



My Comment:

Most of the fancy electronic AOA systems do not give you much resolution,

just a relative indication of AOA. It's a ok toy.




Bob wrote:
I can see measuring the wing angle of attack (aka., fuselage angle) makes
some sense. If the plane is aft-loaded, the angle of attack indicator
would let me know early on that there is a problem.





My comment:

No, it won't, other than the $1500 system the others don't have much
resolution.



Bob wrote:
In our canard airplanes, a stalled main wing is bad news.


My comment:

Really. I guess I should quit stalling mine then. I always thought it
was a non-event.



Fly More, Type Less!

Mike Dwyer Q200 N3QP

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