Why does airspeed change when I adjust the prop?

"chris" wrote in message
ups.com...
This would also explain why so many pilots can
depend on voodoo or tea leaves to determine how they make the
adjustments, and yet they never have any problems.

--


Now that sort of statement is only going to **** off the people who
have kindly answered your question!!!

That's the goal.

This would also explain why so many pilots can
depend on voodoo or tea leaves to determine how they make the
adjustments, and yet they never have any problems.

--


Now that sort of statement is only going to **** off the people who
have kindly answered your question!!!

That's the goal.


Works rather well.

Peter Dohm wrote:
This would also explain why so many pilots can
depend on voodoo or tea leaves to determine how they make the
adjustments, and yet they never have any problems.

Now that sort of statement is only going to **** off the people who
have kindly answered your question!!!

Why? Others here have already chalked up some popular methods to old
wives' tales (aka "voodoo").

Getting two pilots to agree on anything, especially engine management,
is an interesting exercise ;-)

That's the goal.

Works rather well.

I'd say it would only work with people who are insecure or
troublemakers.

Kev

Now that sort of statement is only going to **** off the people who
have kindly answered your question!!!

That's the goal.


Works rather well.

Is there any doubt as to what "HE" really is doing here, after this
exchange?

And yet many enable HIM to remain here, by responding to HIS posts.

I don't get it.
--
Jim in NC

As to a good reason for adjusting throttle and prop in the old wives
tale's way -- sure. Take either case to an extreme: prop is at 1950,
you're putzing along at 1000 feet, decide you want to climb, grab hold
of and advance the throttle. I suspect your engine will suffer a bit at
25 inches and 1950: the phrase popping a gasket comes to mind. Maybe
it's just me, but I really try to be kind to the hardware because if
something breaks it's my checkbook that gets pulled out.

On the other hand, push the prop to high RPMs, then advance the
throttle, and the toque has someplace to go.

Now how about an example where the old wives approach isn't appropiate?

It's the old deal: there's lots of ways that work some of the time, I
figure to try to really stack the odds in my favor.



On Jan 17, 11:04 am, Newps wrote:
Tony wrote:
The habit of backing off throttle first, then reducing prop RPM, and
the habit of increasing RPM first, then advancing the throttle, is one
of those things that can save wear and tear, and maybe an engine. Can
anyone offer a good logical reason to do it any other way?Can you offer a good reason TO do it that way?

chris wrote:

Thomas Borchert wrote:
Chris,

OK, I stand corrected!! As I indicated in my first post I am a fixed
pitch pilot so I am quite short of knowledge in this area, and I am
always keen to learn more ...


Go for the avweb.com columns of John Deakin on engine management.

--


Hi, thanks for that - I didn't know about those columns, and the first
one I came across - the one I am reading right now is fascinating, so I
will keep on reading them..

Thanks heaps..

And in this world of political correctness we also have noise abatement
which means reducing power after take off and reducing climb rate
(which,at that critical point, in my opinion is a silly thing to do)

Tony writes:

As to a good reason for adjusting throttle and prop in the old wives
tale's way -- sure. Take either case to an extreme: prop is at 1950,
you're putzing along at 1000 feet, decide you want to climb, grab hold
of and advance the throttle. I suspect your engine will suffer a bit at
25 inches and 1950: the phrase popping a gasket comes to mind. Maybe
it's just me, but I really try to be kind to the hardware because if
something breaks it's my checkbook that gets pulled out.

You suspect? So you don't really know? By what mecanism is a gasket
blown, and where did you learn this?

Now how about an example where the old wives approach isn't appropiate?

Anywhere where the engineers don't back it up.

It's the old deal: there's lots of ways that work some of the time, I
figure to try to really stack the odds in my favor.

But if you don't know or can't explain the basis for your actions,
then basing them on long-standing urban legends is just as likely to
hurt you as it is to help you.

--
Transpose mxsmanic and gmail to reach me by e-mail.

chris writes:

Now that sort of statement is only going to **** off the people who
have kindly answered your question!!!

I'm not trying to make friends, I'm trying to get down to the truth.
Nobody seems to agree on anything in this domain, and I have to wonder
why. It seems to be a part of aviation that is filled with mythology,
rumor, and urban legend, but few hard facts appear to circulate, and
for some reason the actual recommendations of the engine and aircraft
manufacturers are often discounted in favor of rumors, which doesn't
seem very rational (although it is a fairly typical human behavior).

For my money it is nice to know the in-depth stuff but it simply isn't
necessary to be an aeronautical expert just to fly a light aircraft!

Perhaps not, but it does seem that one must know a great deal about
engines, which I find bizarre.

--
Transpose mxsmanic and gmail to reach me by e-mail.

I'm not trying to make friends, I'm trying to get down to the truth.
Nobody seems to agree on anything in this domain, and I have to wonder
why. It seems to be a part of aviation that is filled with mythology,
rumor, and urban legend, but few hard facts appear to circulate, and
for some reason the actual recommendations of the engine and aircraft
manufacturers are often discounted in favor of rumors, which doesn't
seem very rational (although it is a fairly typical human behavior).

There are a couple of reasons for this (besides ego). First, there are
many kinds of airplanes, and they are all different. Yes, they are all
basically the same (well, most of them anyway), but the differences can
bite if you're not aware of them. Stall charactaristics, engine design
and performance, wing shape, T- or conventional tail, canard... it goes
on. If you learn in one airplane, and from there "know" how airplanes
work, you may find that in a different airplane you know stuff that
ain't so.

There are rules of thumb developed to help bridge this - not running
oversquare is one of them. It's a convenient coincidence that the RPM
and MP numbers, in common units, line up the way they do, and line up
close to the edge of the envelope. Keeping undersquare is safe for most
(spam can) engines, running oversquare requires a peek at the POH to see
how much oversquare in this engine under these circumstances is ok. So
the rule of thumb gets taught, and it gets learned as a hard and fast rule.

Some limits and procedures are designed by lawyers. Consider the
Cirrus' spin recovery technique: pull the chute. I've never spun the
beast, but I bet it would recover conventionally if it didn't get too
far into the spin.

There is also some room for technique. There is no "best" power
setting, for example. What you use depends on what you want, and what
you're willing to give up. And whose airplane it is.

Also airplanes are expensive, and pilots are discouraged in a number of
ways from doing destructive testing on them. A lot of our knowledge
comes from the manuals (where the companies have done their own testing
and given us the digested results they choose), and the necessarily
limited experience of their own and their instructor, and authors of
books they've read.

In some cases the instrumentation just isn't good enough to achieve the
measurements you want. Some airplanes have no engine meters at all, you
pull back the mixture until the engine runs roughly, then you push it
back until it's smooth, then push it back "a little more". How much
more? However much your instructor taught you. (I've seen POHs that
are no better).

So why are the POHs not as good as they could be? I'm sure it's about
sales and liability. Anything that goes in a POH is fair game as "this
is why he crashed", right or wrong. If it's not there, there's nothing
to point to. And it costs money to do the research, so why not just
sell more airplanes by marketing instead?

So, us pilots are left to figure it out as best we can. Look at the
actual instruction booklet that came with the Piper J-3 cub, and see how
little it says.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

This would also explain why so many pilots can
depend on voodoo or tea leaves to determine how they make the
adjustments, and yet they never have any problems.

Now that sort of statement is only going to **** off the people who
have kindly answered your question!!!

Why? Others here have already chalked up some popular methods to old
wives' tales (aka "voodoo").

Getting two pilots to agree on anything, especially engine management,
is an interesting exercise ;-)

That's the goal.

Works rather well.

I'd say it would only work with people who are insecure or
troublemakers.

There were multiple issues at work in this thread, but it seems to me that
most of the contributors made an effort to provide real information, to the
best of each of our abilities, to the many lurkers--many of whom are current
and future pilots looking for all the information they can obtain.

Actually, I am impressed that MSFS simulates this part of an airplane's
opereation. I would have though that it was beyond the scope of typical
training useage in a PC based simulator. I have no idea how accurate it
might be, but I do give them credit for including it.

As to the issue of Mxsmanic, I am amazed that the thread went as far as it
did before he saw most of the common proceedures as "voodoo or tea leaves."
Perhaps we all just provided sufficient dialog until all of the views were
known.

Peter