REFLECTOR:Pure Jet Velocity KL

reflector@tvbf.org reflector@tvbf.org
Sun, 08 Feb 2004 09:50:02 -0500


I agree with Richards asssessment of the very real danger of running the velocity airframe beyond it's designed VNE, although even the velocity has significant drag at those high speeds (drag increases as the sqare of speed - re: accidentally increasing the speed in a dive) I did not see anything on the Jet site that suggested that they were going to run past the published VNE (maybe I missed that)- I think that the customer just wants to have the "cool" factor of running a jet back there- nothing wrong with decreasing the T.O. distance by 25-40%, and allowing operation of the aircraft at say 30k feet with pressure oxy system as long as they do not exceed the current VNE indicated- which would be a really good ground speed at that altitude.  I would be much more worried about losing the elevator or ailerons due to flutter than stalling the canard due to the shock wave - I really don't think that the airframe could be pushed to that speed without loosing at least one of the co
ntrol surfaces.

----- Original Message -----
From: Greg Poole <gpoole@zeta.org.au>
Date: Saturday, February 7, 2004 10:49 pm
Subject: Re: REFLECTOR:Pure Jet Velocity KL

> 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, 
> withoutthe
> > 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.
> >
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