REFLECTOR:Pure Jet Velocity KL

[reflector@tvbf.org]

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.  Andreas has also made
>some remarkable mod's to the control and heating systems. Check them
>out
>
>Mike W.