Best Power vs Best Economy

[danb35]

I'm doing LOP without GAMIs, FWIW.

[Hank]

"Just make sure to climb 300' above final cruise altitude then descend to accelerate quickly so as to get her on the step."

I get on the step every time I change my oil. It's the only way to reach the oil filter. 

[201er]

What is "the step?"

[danb35]

The "step" is a myth.

[fantom]

Now that IS funny, Hank....

Personally, I use an ice chest as my oil changing step....seems I pick up a couple of knots that way ;-)

[Jeff_S]

What is "the step?"

The "step" in this context is generally referred to as an attitude in cruise flight where you have achieved an optimal balance between lift and drag forces which allows a faster airspeed. The maneuver referenced would certainly help to increase airspeed temporarily, as by climbing a bit higher than cruise altitude and then descending to cruise altitude you are reducing the downward (and drag inducing) force on the elevator. The "myth" part is that some people say this "step" can endure for long periods of time, while others claim that eventually at steady cruise altitude the forces should equalize back to the best airspeed you can accomplish given the plane's current weight/power configuration. I won't take a stand on that one...I've certainly felt like I was on "the step" from time to time, but I haven't measured how long it lasted.

A trick that does work for long-duration flight, and was referenced in a few threads on speed racing, is to configure your W&B with the safest allowable CG toward the tail of the plane. This will also reduce the drag-inducing downward force of the elevator and add a few knots of speed. Many folks will keep a 50lb bag of something in their baggage compartment if they are otherwise light on load to help with this.

[Jeff_S]

Sorry, editing doesn't work. In the above, I should have said "horizontal stabilizer" rather than "elevator" although I think you get my drift.

[The-sky-captain]

A good way to get a couple free knots in cruise is to slide the two front seats full aft. Like clockwork you will see the speed spool up every time. I don't do it much because I don't like the feeling of flying w/o being able to touch the rudder pedals.

[201er]

Is that meant as a joke? Or does the seat moment really play that much of a role?

Also, doesn't the Mooney have a very aerodynamically efficient trimming method compared to other planes by tilting the entire tail? Effectively it's like customizing the decalage for every configuration of flight without having to maintain elevator deflection.

[jetdriven]

The "step" is caused by having extra energy at level off from descending from above instead of letting the aircraft accelerate in level flight from climb airspeed.  AOPA did a test where they measured the time it took to accelerate to stabilized cruise speed.  If you count the time it took to climb 300' above your altitude the total time was exactly the same.    I suppose if it was grossly overloaded and you were climbing right at Vy perhaps there is some benefit to climbing 300' above your altitude and descending to it to speed up. 

Look out your left rear window next time you go fly.  The elevator will be deflected a couple degrees up and the counterweight will be sticking out below the stabilizer.  This is because your CG with one or two people is right near the forward limit.  When testing for the air race, we brought the CG back to the middle and the elevator displacement was less, it was almost aligned at zero.  In the 747 and CRJ an aft CG helps as well, near the rear limit the tail actually contributes lift as the incidence is positive with the CG aft. 

We have also found an extra 1 to 1.156 knots by moving the seats back in cruise.  Lots more room as well.  Not piper arrow" room, but hey, we arrive a half hour earlier with less fuel also.

 

[Shadrach]

Your kidding about the "Arrow Room", I'm sure...

201, the Mooney tail is a clean design and minimizes parasitic drag. However, CG affects "induced drag".  The tail is producing negative lift (pushing the tail down) against the weight of the everything "fore" of the center of lift (CL). Think of the CL as a fulcrum with the tail producing down force to compensate for the engine/prop/people etc...  The closer CG is to the CL, the less downward force necessary to sustain level flight. Less force = less induced drag = more speed... AFAIK, the CG is never behind CL in a certed AC as it is inherently unstable in some respects...but that's another thread.