REFLECTOR:Re:Pure Jet Velocity XL

[Brian Michalk]

On behalf of Richard, I would like to clarify some points.

Richard is not entirely speculating on the mach characteristics of our
airplanes.  No, he has not built or flown a Velocity, but he did for the
Berkut, and ran the company for a number of years.  He also has a Berkut (as
far as I know) that flew in the Reno Air Races, and I'm pretty sure his
portfolio allows him enough to extrapolate to our aircraft.  He knows our
canard airfoil, and the wing characteristics.

I'm not an aerodynamicist, and I am interested in an informative discussion
on a mach capable Velocity ... not that I want one, but what happens to one.

First, a swept wing has a much higher critical mach number than a straight
wing.  Since it is swept, doesn't the center of lift remain rather
stationary up to the point of critical mach?

What about the shock wave from the nose of the aircraft?  I suppose that
doesn't matter, because the aircraft would have to be supersonic before that
happened.  The main wing would already have had to go through transonic
flight.

So what about that canard?  It's a straight wing, thick airfoil, so it will
have a low critical mach number.  Richard mentioned somewhere between
.55-.65.  Once that happens, center of lift shifts back, as a shock wave
forms.  I'm not clear on the "mach stall" though.  Does airflow come
detached behind the shock wave?

If everything about the canard is true, then I could see that this would be
an unrecoverable situation, because mach drag only exists because the
aircraft is in transonic flight, and the part that will go transonic first
is the canard.  So what do you mean by your statement about Mcr?

>From what I've read, it seems the solutions to getting out of transonic
flight safely would be to modify the canard.  Make it sharper, make it have
less camber, and perhaps make it a pivoting canard such that there is no
elevator, but the entire canard rotates rather than using elevators to
change the angle of attack.  The article says an airplane with these
characteristics is not easy to fly.  I would imagine that it would have
abrupt stall characteristics.  In a canard airplane, why would that be such
a bad thing?  We already train to fly above the canard stall.  Why not have
a canard airfoil that is thinner, with a longer chord?


 Brian Michalk  <http://www.michalk.com>
Life is what you make of it ... never wish you had done something.
Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
musician, home-brewer, entrepreneur and barely single


> 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
>
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