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I don't know how many people have said that in the last 7 years
and then lived to regret it once they had their airplane flying :)
HP in an airplane is like money. You can never have too much
as long as it does not significantly increases the weight.
Once you change the six port flywheel to a auto tx flex plate there
is no difference in engine weight.

It is a safety thing. You can get in situations all the time
where you need more HP. Climbing over clouds in the flat lands
and climbing over mountains and clouds in the mountains are just
two examples. Taking off on a hot day at something other than
sea level is another. When you get two people and luggage in a
150 HP airplane you will wish you had more HP. A low HP airplane
limits your options.

Sure you get 150 HP at sea level and 67 degrees F  but what about
5000 feet or 12,000 feet on a hot day. At 8000 feet you are
down to 120 HP.

You don't have to use the HP if you don't need it.

Drivabilty means nothing in an aircraft engine.
Mazda has a whole different set of requirements than we do. Torque
at less than 5000 RPM means nothing to us but it means everything
in a car engine. One misfire per minute at idle means a lot to
car emissions. It means nothing to us. Apples and Oranges.

Why are you putting a 2.85:1 gear box in there if you don't need
7000 RPM and HP?


Paul Lamar ...No rotor no motor.


Paul,

The reason Van's doesn't want people using engines with more power has to do
with flutter margins. More power or a turbocharger will let the plane reach
a higher true airspeed at altitude, even though indicated airspeed may still
be in the green.

At higher true airspeeds the control surfaces will be more susceptible to
flutter because it is the speed of the air, not the dynamic pressure that
counts when it comes to the excitations that set the vibration in motion.

Van's has an article on this on their website that makes a pretty good case
for staying within the recommended power range.

http://www.vansaircraft.com/pdf/hp_limts.pdf


While I agree that it's hard to have too much power, I also don't like the
idea of an airplane that can exceed flutter margins at altitude. You would
have to exercise real self-control every time you fly up there.

And Van's planes have pretty good power loading anyway -- RV9, even with 150
horsepower will have about 10 pounds per horsepower. That's a lot better
than a lot of small planes.

Regards,

Gordon.

-------------------------------------------------------
Yes he has been saying that for years but people like
Dave Anders have gone 256 MPH in his RV4. Tracy Saylor goes
238 MPH in his RV6. Tracy Crook goes 220 MPH. This is mainly
drag speaking. The Harmon Rocket is a six cyl. stuffed into an RV4.
It is not much faster but it sure does climb.

Also Tracy Crook has never had problems with cracks in the
RV tail surface. A lot of other people with Lyc's do. Has to due
with the low vibration levels of the rotary compared to
the Lyc. Engine vibration is also a factor in flutter.

HP has little to do with top speed. It mainly improves
takeoff and climb. Top speed is proportional to the cube
root of HP.

Van is also concerned with weight. A 150 HP A/C engine is ligther
than a 200 HP A/C engine. Van does not like people stuffing
heavier six cylinder engines in four cylinder airplanes.

If you have an engine that weighs 300 pounds no matter what
and it will put out 150 HP or 200 HP where is the big decision?

Nobody is forcing anyone to exceed vne. You exceed vne
at your own peril.

Paul Lamar ...No rotor no motor.


Paul,

You don't have to exceed VNE to see a high enough true airspeed that could
cause flutter.

VNE is indicated airspeed, not true airspeed. As you go higher and the air
gets thinner, your IAS can remain the same -- and well within the green arc
-- while your true airspeed goes higher.

With flutter, it is the true speed of the air passing over the airframe that
is critical -- because it has to do with the frequency of the vibrations.
Just like an engine has certain critical frequencies, it will be susceptible
at certain engine speeds.

If you're flying at 12,000 feet and you encounter a gust, you should be okay
in terms of structural integrity as long as you are in the green arc. That's
because even though your true airspeed is higher, the dynamic pressure your
airframe is seeing is the same as it would be at a lower speed and higher
air pressure. So the increased angle of attack caused by the gust will not
break your airplane, as long as you are in the green arc.

However, this does not protect you against flutter. If you encounter that
same gust while going at the same speed, well within the green, it will not
break your airplane, but it could set your tail vibrating. And because you
are going at a higher true airspeed, the frequencies may not damp out as
they would at lower true airspeed.

Have a look at that Van's article; it has a first-hand report from an RV4
pilot who was going high to climb over some clouds. With his IAS well in the
green, he got a scary shaking in his tail as he executed a 360 to avoid
towering cumulus. And this guy should be a pretty good stick -- his day job
is driving an F-16.

So even if you stay well within VNE you could still get flutter if your true
airspeed is high enough.


Regards,

Gordon.

So what you are saying is one cannot relie on the markings of
one's airspeed indicator. Does the FAA know about that?
Perhaps he built the airplane himself and he did not balance
things properly. Either that the RV4 has insufficient margin
of safety in the tail flutter which I find hard to believe
given all the people flying them and the total absence of
flutter induced crashes. Another possibility is the tail was
painted by somebody that did not rebalance the surfaces.

Paul Lamar ...No rotor no motor.

I think the Columbia 400 steps into this problem of IAS and altitude with
relation to flutter.

-dave

Best Regards /Mit freundlichen Gruessen,
  dave ( at ) arb.net http://arb.net

What Van is saying is he set the vne too high on the RV4.
Vne is whatever Van says it is. Never exceed speed under
any and all conceivable conditions the air plane is designed
for. If the ceiling is 17,000 feet then flutter below
that altitude and the vne marked on the air speed indicator
should not occur.

So what you are saying Gordon is people should not climb over
the design ceiling of the RV4 and/or exceed the vne. I'll buy that.

This reminds me somewhat of an argument we had on here about
the flat plate drag coefficient. I think it was Burt Rutan
that said the drag coefficient of a one square foot flate plate
was something other than one. Sheess! That is the definition
of a drag coefficient of one for the last 100 years. You hold
a one square foot flat plate up in the air stream, measure the
drag and divide by by the dynamic pressure and that gives you
a number for flat plate drag coefficient. It should and will
be ONE.