About constant speed props and commercial maneuvers

Hilton wrote:

If you're trying to analyze maneuvers by using energy, you're not
going to
get anywhere fast. You are converting chemical energy into heat
energy,
kinetic energy, grav. potential energy, etc. The air is sapping a
varying
amount of energy from you as you climb, turn, change AOA, etc etc.
As the
prop speeds up, or slows down, and/or the AOA of the prop changes,
effeciency ratios change. When you're climbing, the engine is
getting
hotter and it can be argued that even that would affect the
efficiency/effectiveness of the engine. Thrust/power curves are
constantly
changing. The list going on.

Thats my point. You're supposed to finish a lazy 8 at the same altitude
and airspeed as what you started with. The beauty of the lazy 8 is how
you start out in perfect equilibrium, disrupt that equilibrium by
changing all kinds of things, then returning back to the equilibrium
you started with. It tells you all sorts of things about the airplane.
Its probably my favorite commercial maneuver. Anyways, you need to add
power someway to replenish the energy lost due to induced drag, prop
drag, "changes in thrust/power curves" as you put it, in order to bring
yourself back to that equilibrium. And it's not just the engine either.
You lose energy from banking the wings too.

Pretend you're in a plane which has a low horsepower engine and a high
fixed blade AOA. This gives you a (relativly) fast cruise speed, but
hardly any torque left over to handle climbs. If you were to do a lazy
8, it would be a lot harder. As you pull up the airspeed slows down
causing the prop to impose more stress on the engine. This slows down
engine RPM and horsepower drops sharply down the performance curve.
You're putting the plane in a condition where it is horribly
inefficient. The results of all this is a very little altitude
increase, along with a huge decrease in airspeed at the 90 degree point
of the maneuver. Now for the second half, you can't return to that
equilibrium you started with because you lost too much. you're going to
have to live with being outside PTS by either diving lower than your
starting altitude, or leveling off too slow.

Now if you have a plane that was specifically designed to handle these
changes, then you're not going to lose as much power so its going to be
easier. You'll still lose power in the climb even with a constant speed
prop for various reasons, but its not going to be nearly as much. You
still "lose energy" by banking and increased drag.

So I guess my point is that it's impossible to do a lazy 8, unless
either your plane is 100% efficient (which is physically impossible),
or you somehow add power. This is spliting hairs, and you may only lose
3 or 4 knots of "energy", but theoretically its true.


It is?


I've been lead to believe so. That might be due to the fact that even
though the control surfaces are roughly the same surface area as
compared to a Skyhawk, the bonanza is faster, allowing the plane to be
more responsive. I start my training in the bonanza in about another
week, so I'll see for myself soon.


Keep posting!


OK I will!

"buttman" wrote in message
ups.com...
Thats my point. You're supposed to finish a lazy 8 at the same altitude
and airspeed as what you started with. The beauty of the lazy 8 is how
you start out in perfect equilibrium, disrupt that equilibrium by
changing all kinds of things, then returning back to the equilibrium
you started with.

I agree with those who suggest you are over-complicating the issue.

Yes, the lazy eight should finish up at about the same altitude and airspeed
as you had when you started the maneuver. But IMHO, the biggest factor in
aiding you to that goal, other than flying the maneuver correctly, is
selecting an appropriate power setting.

Throughout the maneuver, your power setting is "wrong" for the flight
attitude and configuration (clean). You are either slowing down or speeding
up. Ideally, you'll wind up as much slower than your equilibrium point as
you wind up faster than it, and in the end it all comes out even. To
accomplish this, you either need to compensate by spending more or less time
in the decelerating or accelerating portion of the maneuver (as
appropriate), or you need to select a power setting that puts those end
point roughly the same distance from the middle equilibrium point.

I am, of course, oversimplifying the whole "middle, low end, high end" part
of this discussion. The end points may or may not be exactly the same
distance from the ideal middle point, from an absolute airspeed point of
view. But the basic idea is true, regardless: there's an appropriate
"center point" around which you fly the maneuver, and your power setting
determines that center point (assuming the rest of the maneuver is flown the
same...you can rush or slow down portions of the maneuver to compensate for
a "wrong" center point, of course).

I believe that you are right, that a constant speed prop provides a more
constant contribution of power throughout the maneuver. But, for one thing,
the maneuver is as much about drag (force) as it is about power (force over
distance over time). Since your airspeed is constantly changing, you're not
really producing a constant balance between engine output and drag anyway.

For another thing, I believe that in the context of the maneuver, the
difference in power output between a fixed pitch prop and a constant speed
prop isn't significant. Not compared to the other issues surrounding the
maneuver (flying it smoothly, and choosing an appropriate power setting for
the maneuver).

I think of it this way: as far as preserving your equilibrium, it's not
really that important how much energy the engine is providing at any given
point during the maneuver. The only thing that's important there is how
much extra energy the engine provides, TOTAL, throughout the maneuver.
Regardless of the type of prop installed, you control this directly through
the choice of the power setting used. If you finish the maneuver fast, your
power setting was too high; slow, your power setting was too low. It works
the same regardless of the type of prop.

[...]
So I guess my point is that it's impossible to do a lazy 8, unless
either your plane is 100% efficient (which is physically impossible),
or you somehow add power. This is spliting hairs, and you may only lose
3 or 4 knots of "energy", but theoretically its true.

Well, I'm not aware of any airplane in which it's impossible to do a lazy
eight without changing the power during the maneuver. So I'd say that
"point" of yours is obviously incorrect. In your example of a
low-horsepower, high-prop-pitch airplane, all you should need to do is use a
slightly higher power setting for your entry into the maneuver. Of course,
that presumes such an airplane and frankly, people don't usually go around
putting high-pitch fixed-pitch props on low horsepower airplanes.

[talk about ease of performing the maneuver between
fixed-pitch and CS props]

It is?

I've been lead to believe so. That might be due to the fact that even
though the control surfaces are roughly the same surface area as
compared to a Skyhawk, the bonanza is faster, allowing the plane to be
more responsive. I start my training in the bonanza in about another
week, so I'll see for myself soon.

My experience has been that of the three airplanes I flew a lazy eight in --
a C172, a C177RG, and my Lake Renegade -- the easiest airplane for the
maneuver was the Cardinal and the hardest was the Lake, both of which have
constant speed props. IMHO, control feel on the Cessnas is better, and I
especially like the stabilator on the Cardinal (not everyone feels this way
). Even in the Lake, once I got the power setting figured out, the
maneuver went pretty smoothly, as it should. (I needed a lower power
setting...flying the maneuver near Va, as I was doing with the Cessnas, was
too fast an entry and I wound up too fast at the end).

Frankly, even in the C172 the maneuver is fairly easy as long as you fly it
by the numbers and don't try to rush it. Like you, I find the lazy eights
to be one of the more enjoyable of the commercial maneuvers, but it does
require a relaxed, smooth hand on the controls. Provide that, and I don't
see why it shouldn't go well in just about any airplane, constant speed prop
or not.

Pete

buttman wrote:

Thats my point. You're supposed to finish a lazy 8 at the same altitude
and airspeed as what you started with. The beauty of the lazy 8 is how
you start out in perfect equilibrium, disrupt that equilibrium by
changing all kinds of things, then returning back to the equilibrium
you started with. It tells you all sorts of things about the airplane.

Define equilibrium. Technically speaking, at the moment you arrive at your
'starting point', your pitch is changing, your bank angle is changing, your
altitude is changing, your VSI is changing, your energy state is changing,
your airspeed is changing, your governer is changing...

I think it's way too deep to look at the energy aspects of a lazy-8. I
think Peter's advise is the best; i.e. nail your power settings which is
what you've also alluded to. Personally, I think the key to flying the
lazy-8 is to ensure that your pitching and banking moments are out of sync
with one another. I think too many CFIs teach them to be in sync which is
wrong. I 'fired' my CSEL CFI for that reason and another reason related to
my 'comfort level' while flying with him.

Hilton

"Hilton" wrote in message
ink.net...
[...] Personally, I think the key to flying the
lazy-8 is to ensure that your pitching and banking moments are out of sync
with one another. I think too many CFIs teach them to be in sync which is
wrong.

I wouldn't be surprised if there's a different way to teach the maneuver for
every CFI that's out there.

However, the CFI that had the most success (out of two) teaching me the lazy
eight was the one who showed me that you pretty much only have to use
aileron right at the beginning of the maneuver. A little bit of roll input,
and then just a nice slow increase in back pressure (with ailerons neutral),
causes just the right amount of increase in bank angle throughout the first
half of the maneuver.

I'm not sure what "out of sync with each other" means (or "in sync" for that
matter), and maybe it just means the same as what I have found to work well.
Can you elaborate on your terminology?

Pete

Peter wrote:

I'm not sure what "out of sync with each other" means (or "in sync" for
that
matter), and maybe it just means the same as what I have found to work
well.
Can you elaborate on your terminology?

Sure. At the start of the maneuver, no pitch, no bank, etc... Start
banking and pitching. Now, the maximum pitch occurs at the 45 degree point,
at which point the pitch is reduced to level at the 90 degree point in the
maneuver, and then the minimum pitch (max down) occurs at the 135 degree
point. So, the minimum and maximum pitch up and down occur at the 45, 135,
etc degree positions. However, the bank is zero at the start, and maximum
at the 90 degree position, and then zero again at the 'bottom'. So the
minimum and maximum bank left and right occur at the 0, 90, 180, etc
positions.

IMHO, if a student is simultaneously pitching and banking 'in sync', they
are doing it wrong. Recap: At the start, you start pitching and banking.
When you get to the 45 degree position, you keep increasing the bank, but
start decreasing the pitch etc. I believe the Jeppesen book shows this
well.

Hilton