Exceeding VNE (V *never exceed* !!!) is a VERY risky proposition. The
Berkut
used carbon fiber all over the place and the much higher stiffness and
lower
weight
of the carbon will help a lot with this problem.
I'm not an aero engineer, but this is aero-structural interaction and I
have
studied it
a bit. Any real aero engs out there please correct this if I get it
wrong.
Apparently
the biggest issue is flutter of the aero surfaces (wings, horizontal
stab,
fin) The
natural vibration frequency of a vibrating object is proportional to
(K/M)^0.5
which is the square root of the stiffness (K) divided by the mass (M).
So, to
increase the natural frequency (where flutter can occur), you need to
increase
K (stiffness) and/or decrease M (mass). Carbon is about 3X the
stiffness of
glass, so this is very helpful when trying to increase the Vne of an
existing design.
Substituting carbon for glass increases K. Since most carbon is also
stronger (note
that stiffness and strength are NOT the same, nor are they particularly
closely related)
than glass, you can use less, so you may also decrease M, also good.
This
just tells you
about the general direction you are blindly wandering in - generally
towards
death and
destruction or generally away. Not good enough in my book. Test
pilots
make the big
bucks by going out and finding out whether the calculated Vne is
actually
safe. If you get
it wrong, the pieces are usually scattered over a very wide area. You
really need to do
a proper ground vibration survey (needs smart people & expensive
equipment) to
find out what the whole surface flutter situation is going to be like.
This is very dangerous ground to be working in without proper knowledge.
A lot
of "eyeball engineering" will work just fine up to about 150, perhaps
200 mph.
When you start looking 300 mph in the face, the rules are changing and
the laws
of physics are extremely nasty.
Remember the famous saying of one of the 20th century's great
philosophers -
Harry Callahan: "A man has GOT to know his limitations."
My saying is "The laws of physics will be strictly enforced"
. . . .and they'll kill you in a heartbeat without remorse.
Ya'll be careful out there in the "experimental" part of the flight
envelope.
Bill Freeman
Long EZ builder & pilot
BSME, MSME
EAA Technical Counselor
Geeze Bill,
You're worse than my mother! :-) I can assure you that I have no desire to
become hair teeth and eyeballs all over the ground somewhere, nor am I
looking for a smoking crater to crawl out of. I really don't want to try for
300 mph in a long EZ. Certainly not unmodified. Unfortunately, the Berkut is
out of my current price range. And the engineering required to design and
test a proper airframe would put the price of said airframe up past the
Berkut!! So absent a proper airframe, I'm very comfortable just trying to
make an extremely efficient aircraft. 200 is fast enough for me. It will get
you from point A to point B in a hurry. Plus the faster the plane, the
greater the pain (in an off field landing) Something that I definitely have
in mind, since this IS an EXPERIMENTAL engine. I was being somewhat tongue
in cheek with Paul when discussing trying to go 300 mph.
One of my friends used to be a factory test pilot. He would take the new
planes off the assembly line, fly them to altitude, put it in a dive,
accelerate to VNE and bump the stick in all directions to try and induce
flutter. Talk about pucker factor!!
My real goal with the design I posted was drag reduction, and reduced weight
= better efficiency and performance without sacrificing slow speed handling
or fuel burn. The power of the one rotor engine is somewhere in neighborhood
of 100 hp, which is the same as the original aircraft. I seriously doubt
that the drag reduction would be enough to allow a speed over 220 mph. There
just is not enough HP. But the fuel burn would be reduced and the power
required to cruise would be much less. In a long EZ same story with two
rotors. In fact a single rotor would be enough for the Long, especially with
a CS prop. I believe that Burt's original Long had an 0-200 in it and
actually outperformed Dick's 160 hp aircraft initially. What I would really
like to do is make a single-rotor turbo-compound aluminum engine with a CS
prop. THAT would really sip the fuel.
Light, slick, and efficient is much better than heavy, dirty, and wasteful.
Monty
Hey I am with you Monty. Turbo compound IMHO has not been given the respect
it deserves. Especially a wankel version with no broken exhaust valves
to pass through and destroy the turbine. First of all you get 20% more HP
right off the bat with no increase in waste heat load and no additional
fuel burn. That would put a one rotor wankel up to an easy 100 HP and perhaps
120 or so turbo charged or peripheral ports.
It must be about ten years ago that Don Sherman, and Prof. of automotive engineering
at Michigan University Ann Arbor and son of the one time president of GM,
Dr. Ed Cole Jr. and I were on our way to the Detroit auto show and I brought
the subject up. Not long after that NASA looked into it and they wrote a report
saying it was highly desirable and feasible. I always wondered if Ed had said
something to some one at NASA. Never the less no hardware work was done on it.
Perhaps you can search the NASA data base Monty and find that report.
Paul Lamar
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