Snaps

[JOddino]

I would say it is when the slope goes to zero.  Many lift curves go flat for
quite a few degrees of angle of attack before the slope goes negative
especially on low aspect ratio wings.  We always said a surface was stalled
when the slope dropped to zero.
We always strove for a low time constant meaning a short time between
establishing an angle of attack and the vehicle pitching.  To do a snap as
people are describing we'd need a long time constant where we can create a
large angle of attack before generating a pitch acceleration.  Larger
control surfaces ?
Jim
----- Original Message ----- 
From: "Jerry Budd" <jbudd at QNET.COM>
To: <discussion at nsrca.org>
Sent: Wednesday, April 14, 2004 4:26 PM
Subject: Re: Snaps


> Not quite.
>
> A wing is stalled when the lift curve slope changes sign, meaning
> that a further increase in angle of attack (AOA) results in a
> reduction in lift, due to increased separation of the airflow
> disrupting the pressure distribution over the top of the wing.  The
> AOA (also refered to as "alpha" in the flight test world) at which
> the lift curve slope changes from positive to negative is where the
> maximum lift coefficient (CL-max) of the wing (or vehicle) is reached
> and is typically found to occur around 18 to 30 degrees alpha.  It's
> a function of a whole lot of things like aspect ratio, planform,
> control surface deflection, Reynolds #, Mach#, etc.  It is NOT a
> function of airspeed.
>
> But I digress...
>
> Jerry
>
>
> >I was taught that a wing is stalled when it will no longer support the
> >aircraft in flight. You would be losing altitude if in level flight until
> >airflow is returned over the wing to support the weight of the aircraft.
> >Granted this is over simplification but when you ask about laminar flow
> >separation I understood that you can have separation when in a well
trimmed
> >plane and still not lose much altitude but I believe this is getting into
> >semantics and not germane to models being judged for snapping or not
> >snapping.
> >
> >                          del
> >                NSRCA - 473
> >----- Original Message -----
> >From: "Adam Glatt" <adam.g at sasktel.net>
> >To: <discussion at nsrca.org>
> >Sent: Wednesday, April 14, 2004 10:44 AM
> >Subject: Re: Snaps
> >
> >
> >>  Isn't the definition of a stalled wing just that it doesn't have
laminar
> >>  flow?  That is entirely possible in a downline with sharp elevator
input
> >  > (think less extreme version of a TOC plane's parachute or wall).
>
> -- 
> ___________
> Jerry Budd
> mailto:jbudd at qnet.com
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