Beta Prop

And after discussing it with the rotary engine gang, the consensus is..
that you pass through this area of "chatter" fairly quickly.. either you
are engine driving prop.. or prop driving engine... but from a practical
matter you are not loitering in the power/thrust range that is teetering
between the two.

Every geared engine passes through this range several times on a given
flight, but rarely loiters there.

Even in ground ops.. you are pushing.. or pulling.. but rarely
straddling the fence.

Dave

Morgans wrote:
"Dave S" wrote in message
nk.net...

Wouldn't you have this "effect" ANY time you went from a thrusting to a
braking action with regards to thrust generated?

If I pulled power back, set the pitch to flat, and pushed the nose over,
wouldn't the prop be "driving" the engine in the manner you describe?

All of this is able to be done without a specific Beta range.

Dave


Actually, no. Kinda. g

When the engine is using HP to turn the prop, all is well, be it forward or
reverse thrust. The only difference the gearing sees is the thrust on the
shaft goes from pulling the shaft out, to pushing the shaft in, but the load
on the gears is the same. (all for tractor applications, in this case)

When the possible chattering comes in, is when you are gliding, and at a
very low power setting, and the *windmilling* prop is trying to turn the
engine, thus the prop is "making" HP to try to turn the engine- opposite
from normal.

I guess my point was that, whenever I have been with someone using beta,
they spent lots of time loitering there.
Positive thrust to get moving then hanging out in the zero thrust area with
little adjustments positive and negative during taxi.
I think I would hesitate to use a geared engine for taxing that way (like
turbine planes do)


"Dave S" wrote in message
nk.net...
And after discussing it with the rotary engine gang, the consensus is..
that you pass through this area of "chatter" fairly quickly.. either you
are engine driving prop.. or prop driving engine... but from a practical
matter you are not loitering in the power/thrust range that is teetering
between the two.

Every geared engine passes through this range several times on a given
flight, but rarely loiters there.

Even in ground ops.. you are pushing.. or pulling.. but rarely straddling
the fence.

Dave

Morgans wrote:
"Dave S" wrote in message
nk.net...

Wouldn't you have this "effect" ANY time you went from a thrusting to a
braking action with regards to thrust generated?

If I pulled power back, set the pitch to flat, and pushed the nose over,
wouldn't the prop be "driving" the engine in the manner you describe?

All of this is able to be done without a specific Beta range.

Dave


Actually, no. Kinda. g

When the engine is using HP to turn the prop, all is well, be it forward
or
reverse thrust. The only difference the gearing sees is the thrust on
the
shaft goes from pulling the shaft out, to pushing the shaft in, but the
load
on the gears is the same. (all for tractor applications, in this case)

When the possible chattering comes in, is when you are gliding, and at a
very low power setting, and the *windmilling* prop is trying to turn the
engine, thus the prop is "making" HP to try to turn the engine- opposite
from normal.

"PittsS1C" wrote

Positive thrust to get moving then hanging out in the zero thrust area
with
little adjustments positive and negative during taxi.
I think I would hesitate to use a geared engine for taxing that way (like
turbine planes do)

I can't say with 100% authority, but I don't see that as a problem. Just
because there is zero thrust, does not mean the engine/gearbox has zero
load. Even at beta, the prop is still moving a lot of air, but off of the
front and the back and ends of the prop, at the same time. Considerable HP
is still being used, and putting a constant, normal load on the gears.

Think of a "club" prop, for breaking in engines, or using on a "torque" type
dyno. It is indeed putting a load on the engine and gearbox, but it is not
trying to make thrust, so the test stand/dyno doesn't zoom down the length
of the driveway. g
--
Jim in NC

"Dave S" wrote

And after discussing it with the rotary engine gang, the consensus is..
that you pass through this area of "chatter" fairly quickly.. either you
are engine driving prop.. or prop driving engine... but from a practical
matter you are not loitering in the power/thrust range that is teetering
between the two.

All very true. You get pressure of the opposite side of the gears from
normal, but it would indeed be rare for it to get to the RPM where it is so
closely balanced, as to go from one to the other, rapidly.

All of this is reason to make the gears tight fitting, with little lash.
More lash gives time for the motion to set up with a "head start", providing
more force to break things. Broken things = bad. g
--
Jim in NC
--
Jim in NC