REFLECTOR:Re:Pure Jet Velocity XL

[Andreas Christou]

At 07:55 PM 2/7/04, Richard Riley wrote:
>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.

Richard,

It is always disconcerting to read contributions like this, which raise 
fears based on very little factual information, and a great deal of 
speculation.

It is also rather annoying that anyone reading your e-mail would be excused 
from assuming you are referring to the Velocity Jet as shown on the 
http://x-jets.com/ web site. I can't imagine you are, because you have not 
discussed this aircraft with me or my partner at any time, and I have no 
idea where you get the numbers and engine type that you quote.

Let me say quite clearly to everyone on this list, that we do not feel 
compelled to operate outside of the envelope of a standard Velocity XL RG.

Whether you choose turbojet power or a reciprocating engine, The VNE and 
Critical Mach Speed of the airframe remain the same. A jet engine is simply 
a very good power to weight ratio, not a license to exceed VNE or other 
airframe limits including Mcr.

Those limits have been estimated for our airframe, and prudent placard 
limits have been set. All this was done at a very early stage, before an 
engine choice was finalized. We did not simply bolt a jet engine on the 
back end and cross our fingers. All the systems on our plane have been 
designed for routine flight above 20K. Our project represents a safety 
conscious and carefully engineered next step in Experimental aviation. If 
you are curious, just watch for more news on the web site.

The engine, by the way, is a GE-T58-8F  NOT a Honeywell T55. The Mcr of the 
Main wing airfoil is the lowest at M=.54, which  equates approximately to 
240 Kts IAS at 25K, 218 Kts IAS at 25K, and 199 Kts IAS at 29K. The 
reference you give is excellent. However, it would be better to read it 
from the start of the 
chapter  http://142.26.194.131/aerodynamics1/High-Speed/default.htm  with 
particular note of the way drag increases as Mcr is approached. Also note 
how Mcr may be increased.

Best Regards,

Andreas P Christou
andreas@x-jets.com