LeSving wrote:
At which alt?
It doesn’t say, but at 65% power TAS doesn’t increase more than 11% between MSL and service ceiling, while IAS doesn’t decrease more than 8%, so I would expect the 1 kt figure to be sufficiently precise to be used at all altitudes.
Airborne_Again wrote:
The Cessna 172S POH says that “at normal power settings below 65%” you should get a 1 kt speed increase for each 125 lbs below MTOM.
At which alt?
Peter wrote:
Weight doesn’t seem to affect the cruise speed for a given fuel flow, on the normal SEP tourer types, much. On the TB20 I can hardly tell. Maybe 2kt from light to MTOW.
The Cessna 172S POH says that “at normal power settings below 65%” you should get a 1 kt speed increase for each 125 lbs below MTOM. That’s not much and, given that the total useful load of our 172S aircraft is ≈800 lbs, will probably not be noticeable.
EDIT: Corrected useful load.
Airborne_Again wrote:
But I don’t think that’s what people usually refer to as the “step” since this happens way below cruise speed
Yes not specific to minimum drag, it can happen at any speed value but it has to be the average value from some “lucky random steps” not some exact value from “smart deterministic steps”, for the latter the end result will be the same when things settle down irrespective of how you get there 
Away from the stall and sound barrier, flying mechanics are smooth and continuous, pushing against the air is unlike pushing under solid stick-friction forces
https://en.wikipedia.org/wiki/Stick-slip_phenomenon
Weight doesn’t seem to affect the cruise speed for a given fuel flow, on the normal SEP tourer types, much. On the TB20 I can hardly tell. Maybe 2kt from light to MTOW.
I reckon a lot of people are drastically mis-using the mixture. I read about TB20s being cruised at 16GPH…
And yes TAS v. IAS is a traditional one, but for someone who holds a PPL??
I would think prop and rigging. Weight also, weight can easily be varied
It’s clear that if you’re below minimum drag speed, then accelerate past that speed by descent and finally level off you will end up with a higher airspeed at the same power. But I don’t think that’s what people usually refer to as the “step” since this happens way below cruise speed — except at altitudes near the aircraft ceiling.
Airborne_Again wrote:
We’ve had a long discussion about that supposed effect.
I hadn’t seen that thread. I’ve just skimmed and it doesn’t appear to me that it is a supposed effect which doesn’t exist.
I think I agree with Pilot DAR’s statement towards the end in that he has measured / noticed it and in discussion thinks it may be more pronounced in draggier airframes.
I know this is a fact around Minimal drag speed, you can go from one regime to another by just pushing or pulling the yoke as soon as you have some altitude, without touching the engine setting.
Airborne_Again wrote:
We’ve had a long discussion about that supposed effect.
Not sure what was the conclusion on that discussion? but it is mathematically correct
You will average lower speed when X fluctuates vs speed at average value of X0
X can be power, altitude, heading, pitch….
This depends on “concavity” of the Speed-vs-X curve and it’s symmetry around X0, say one will find that climbing at (VY+5kts)+/-5kts achieves better average climb rate than (VY+/-5kts), as the drag curve is rather flat on the VY+5kts side but the back of the drag curve is steep on the VY-5kts, the same principal would applies to altitude & gravity
Obviously when things settle down it does not matter how you get there…but things never settle down and the maths bellow applies 
https://en.wikipedia.org/wiki/Jensen%27s_inequality
If one like graphs
