REFLECTOR:Pure Jet Velocity KL

[Greg Poole]

Quite sobering comment Richard!

Greg in learning mode.
Sydney.

----- Original Message ----- 
From: <richard@riley.net>
To: <reflector@tvbf.org>
Sent: Sunday, February 08, 2004 11:55 AM
Subject: Re: REFLECTOR:Pure Jet Velocity KL


> I have said this before, and said it directly to some of the people who
are
> building these airplanes.
>
> A jet canard is a fatal accident just waiting for someone to open up the
> throttle.
>
> The canard will mach stall well before the main wing.  John Roncz believes
> that the 1145MS will hit it's critical mach at  somewhere between .55 -
.65
> mach.  The GU and the Velocity canard are probably in the same
> neighborhood.  At 25k that's only 380 mph.  At 700 lbs thrust, these
> converted T-55's can get that in in level flight.  Even if not, without
the
> drag of a prop and some residual thrust at idle, you could start out at
300
> mph at altitude, pull back the throttle, drop the nose and be through your
> critical mach in a few seconds.
>
> If the canard mach stalls, you're dead.  There will be no possible way to
> recover.  Aerodynamically, it will be as if the canard has come off the
> airplane.  The elevators will have no effect at all.  Putting out the
> landing brake and gear won't do nearly enough.  You'll just go faster and
> faster until something flutters to destruction or you hit the ground.
>
> I can't say this clearly enough.  This is not something you can sneak up
> on, stretch the envelope and back off from.  This is a sudden,
> unrecoverable, unpredictable, 100% lethal failure mode.
>
> Here's a primmer
>
> http://142.26.194.131/aerodynamics1/High-Speed/Page2c.html
>
> The important 'graph -
>
> "The second form of drag, due to the shockwave is unique to the normal
> shock wave. The shock wave tends to stop the boundary layer, causing the
> flow to separate and thereby producing effects almost the same as a
> stall.  Thus, the term "Mach Stall" has been coined.
>
> The diagram to the left shows a wing with the lift being disrupted and the
> drag greatly increased by a Mach Stall. In a mach stall the aircraft
> experiences a loss of lift, increase in drag and usually a tendency to
> pitch nose down. In other words it has most of the same symptoms as a low
> speed stall except the angle of attack is quite small and the TAS is very
> high."
>
> So, you're flying along very fast.  How fast?  Hard to say, but above .5
> mach.  You decide you're going to drop a couple of hundred feet to dip
> below some clouds.  As you do so you go just a LITTLE bit faster.
>
> Your canard stalls.  Just like it would if you were going very slowly, at
a
> high angle of attack.  What happens?  The nose drops.  You go faster.  The
> stall remains.  The nose drops more.  You go faster.  The stall remains.
>
> Eventually you tie the low altitude record.
>
> The canard we're flying couldn't be worse for delaying the onset of shock
> waves.  It's a thick section, narrow chord, and with no sweep at all.  The
> main wings are actually not bad, well swept, wide chord, not too
> thick.  But, as with the low speed stall, it's the canard that matters.
>
> The Vne of these airplanes should be no more than 300 mph.  And it should
> be considered a Vinstantdeath.
>
>
>
> At 03:10 PM 2/6/04 -0500, you wrote:
> >Hi Group,
> >
> >If you're interested in seeing a pure jet Velocity XL being built, go to
> >www.x-jets.com. Click on "projects" then click on "Velocity Jets."
> >
> >It's being built at 44N Skyachers in New York.&nbsp; Andreas has also
made
> >some remarkable mod's to the control and heating systems. Check them
> >out
> >
> >Mike W.
>
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