Warrior cruise RPM settings

"Jay Honeck" wrote in message
news:Z7b1f.400967$x96.209528@attbi_s72...
What is "overspeed" on a fixed prop?

Same thing it is on a constant speed prop: the engine exceeds its maximum
allowed RPM.

"Max RPMs" on an O-320 (and, in fact, all aircraft engines) are so
retarded that the engine is really just loping along at 2700 rpm.

That's simply not true. In fact, the engine manual for any engine has very
specific guidelines about what the true maximum RPM is and how much you can
exceed that for how long before requiring some kind of maintenance. These
numbers are not far above the indicated redline.

Pete

What is "overspeed" on a fixed prop?

Same thing it is on a constant speed prop: the engine exceeds its maximum
allowed RPM.

Let me try that again. How can you overspeed an engine with a (properly)
fixed pitch prop?

"Max RPMs" on an O-320 (and, in fact, all aircraft engines) are so
retarded that the engine is really just loping along at 2700 rpm.

That's simply not true. In fact, the engine manual for any engine has
very specific guidelines about what the true maximum RPM is and how much
you can exceed that for how long before requiring some kind of
maintenance. These numbers are not far above the indicated redline.

I'm just passing along what my A&P has told me. He's got 42 years in the
engine rebuilding business, and is an award winning home builder and antique
aircraft restorer. According to him, our Lycoming/Continental engines are
purposefully designed to be slow-turning engines -- even at full throttle --
in order for them to survive all the way to TBO.

There is no harm running an O-320 with a fixed pitch prop at full throttle.
You'll make more noise, burn more gas, and go (a little) faster.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

"Jay Honeck" wrote in message
news:GZe1f.405624$_o.128570@attbi_s71...
Let me try that again. How can you overspeed an engine with a (properly)
fixed pitch prop?

In level cruise, full throttle is sufficient in some aircraft (may or may
not be in the particular Warrior in question). Even if full throttle is
not, anything that increases airspeed at full throttle is sufficient:
descent (intended or not) or wind shear, for example.

A propeller -- fixed-pitch, variable pitch, constant speed, whatever --
provides a load on the engine which in turns keeps the RPM below the
designed maximum. As airspeed increases, this load is reduced. Some
propellers (constant speed, for example) can increase blade pitch to
compensate and maintain a constant load on the engine. But a fixed-pitch
propeller does not have this option; RPM is determined solely by airspeed
and power setting. If you increase airspeed without reducing the power
setting, the RPM will increase (and of course, as I stated above, in some
installations full-power throttle is sufficient to exceed the designed
maximum RPM when in level cruise flight).

I'm just passing along what my A&P has told me. He's got 42 years in the
engine rebuilding business, and is an award winning home builder and
antique aircraft restorer. According to him, our Lycoming/Continental
engines are purposefully designed to be slow-turning engines -- even at
full throttle -- in order for them to survive all the way to TBO.

Your interpretation of even the statement you're attributing to your A&P
(and that's assuming you understood him correctly) doesn't support your
previous statement. An engine designed to turn at low RPM does not preclude
it being harmed at high RPM, and in fact if the design calls for low RPM
it's entirely possible (likely, even) that exceeding that low RPM would harm
the engine.

Beyond that, the reasoning given in your description of his statement is
flawed in any case. The primary reason aircraft engines turn slowly is so
that they match the needs of the propeller without adding a gearcase to the
installation.

There is no harm running an O-320 with a fixed pitch prop at full
throttle. You'll make more noise, burn more gas, and go (a little) faster.

Provided you do not exceed the manufacturer-determined maximum RPM, I will
agree with you 100%. However, one needs to be careful not to exceed that
maximum RPM, and running full-throttle makes it easier to exceed that
maximum RPM.

Pete

Let me try that again. How can you overspeed an engine with a (properly)
fixed pitch prop?

Push the nose down?

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

Jay Honeck wrote:

What is "overspeed" on a fixed prop?

Anything past redline on the tach.

"Max RPMs" on an O-320 (and, in fact, all aircraft engines) are so retarded
that the engine is really just loping along at 2700 rpm.

But the valve train on aircraft engines is deliberately lightly built. The
valves will "float" at a much lower rpm than a similar sized car engine. With
some aircraft, that's the limiting factor; with others, the prop tips might go
supersonic. Those are the two main limiting factors.

Granted, exceeding redline by 50 rpm or maybe 100 isn't likely to cause either
problem, but you don't know how far you can go before something comes apart.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.

Hence my question, because if I leave the throttle firewalled in either
the '67 172 (w/ 6 cyl continental) or the 81 Cherokee 161, the needle
WILL pass redline in level flight.

Ben Hallert
PP-ASEL

Ben Hallert wrote:
Hence my question, because if I leave the throttle firewalled in either
the '67 172 (w/ 6 cyl continental) or the 81 Cherokee 161, the needle
WILL pass redline in level flight.

Then don't do that. I've been told that the camshaft is the weak point on the
Lycoming engine. Being familiar with the problem of stuck valves on a
Continental O-200 (which has the same cylinders as the O-300), I expect that the
valves and rockers are the problem area there, but I'm not sure.

In any case, if you routinely exceed redline on the tach, you will learn what
your glide ratio is sooner than later.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.

I rent so the plane has to be back by a certain time. I've been trying to
land at all the airports in the state....

I hope you live in Rhode Island, not Texas or Califorinia!

I've been flying since 1946, and I STILL haven't been to every airport
in PA!

vince norris

Hence my question, because if I leave the throttle firewalled in either
the '67 172 (w/ 6 cyl continental) or the 81 Cherokee 161, the needle
WILL pass redline in level flight.

Perhaps you have a cruise prop on both aircraft, Ben? You shouldn't be
exceeding red line simply by going to full throttle in level flight,
*unless* your prop has been pitched differently than stock.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

That would be a climb prop, wouldn't it?

E-yup. I don't know why I ever try to post after 11 PM...
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"