REFLECTOR:Re:Pure Jet Velocity XL

Jim Sower reflector@tvbf.org
Wed, 11 Feb 2004 11:44:25 -0600


<... modify the canard ... Make it sharper, make it have less camber ... make it a
pivoting canard such that there is no elevator ...>
Either of these mods would squander any assurance you had that the canard would stall
first and protect you from "deep stall".

Additionally, flutter will rear its ugly head at altitude since its onset is
determined by TAS as well as IAS.  I've no clue what effect Mach would have on
flutter, but Mach stall is certainly unrecoverable and terminal, and I believe flutter
would precede it.

I believe a canard airplane is a very poor choice for hi-alt hi-speed operations ....
Jim S.




Brian Michalk wrote:

> 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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--
Jim Sower ... Destiny's Plaything
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T