Re: Snap roll vs. Va

"Rich Stowell" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Most things in aviation are related to the wings-level, 1-g stall
> speed, Vso. The maneuvering speed, Va, is actually the stall speed of
> the airplane at the design limit, and it is related to Vso by the
> square root of the g-load. (Of course, all of these are CAS, so you
> may have to do some massaging through the airseed calibration data to
> convert back and forth between IAS and CAS to find the numbers you
> must read on the airspeed indicator.)
>
> For example, in aerobatic airplanes like the Citabria which were
> certificated at +5.0 g's (at max. gross), Va = 2.24 x Vso. In
> aerobatic airplanes certificated at +6.0 g's (at max. gross), Va =
> 2.45 x Vso.
>
> In terms of the snap roll entry speed (and snap rolls are really
> accelerated stall/spins), the speed will naturally fall somewhere
> between Vso and either 2.24 or 2.45 x Vso.
>
> In Eric Muller's book, Flight Unlimited, he recommends intially
> practicing snap rolls at 1.5 x Vso, so there's a starting point. In my
> experience, I'd recommend around 1.6 x Vso as a good "recommended"
> snap roll speed, which translates into a 2.5-g pull to stall/spin the
> airplane at that speed. The MAXIMUM snap roll speed should probably be
> no greater than about 1.7 to 1.8 x Vso...
>
> Hope this helps (and HI Ken!),
>
> Rich
> http://www.richstowell.com

Don't forget that the structural g limit is for a symmetrical stall and is
reduced to 2/3 for an asymmetric stall - therefore the absolute max snap
roll speed at MAUW for a 6g airframe is 2xVso.
Also, this speed should decrease at lighter weights by the ratio of the
square roots of the weights. Vso at weight w = Vso x sqrt(w)/sqrt(MAUW),
this can make a 10% difference to Vso so could easily affect the max snap
speed by 10kts or more.

Dave Sawdon