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!