On the step...

SkyHog said:
Yep. And that is exactly why the step (as many people define it) is a farce. They believe that they are getting something (speed or econony) for nothing.
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I'll agree to that. they are seeking some thing they know-nothing about.
 
azure said:
I assume he meant "It helps us achieve cruise speed more quickly", not "It gets us to cruise at a faster speed." I'll buy the former, and actually have been using the "step" method for years in my Cardinal. But I don't buy for a second that it improves your equilibrium cruise speed in the least. Only way to do that is to either increase power, or reduce drag.
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You are correct and I suppose it was poorly worded. What I have observed is that it speeds the transition from level off to cruise. (Perhaps not total time if you include the climb @FastEddieB) but that actual time spent getting settled down in cruise with trim & throttle set. At this point in my IR training, that's a help. And we only went 100' above assigned altitude, not 200' as I initially wrote.

I think I will try different approaches and time the results for my own curiosity. I'll even publish the results here when I get a chance.

The three techniques are:
1) Level off, set power and wait re-triming as you go. This should eventually result in the normal cruise speed but will take longer to get there.
2) Level off, leave full power in until at least at normal cruise speed re-trimming as you go. This should also result in normal cruise speed but will get there faster.
3) Climb 100' above altitude, descend using the descent to accelerate to something at or above normal cruise speed, then level off, set power and trim. This will also result in normal cruise speed.

I do agree that physics is physics and there is no free lunch. For a given power setting there is no way to have some magical higher speed by descending onto the altitude. What @Tom-D described is a way to get more power from the engine by leaning to max power (and then LOP if desired) which is perfectly safe at high enough altitudes (power less than ~75% for the lycosaurs I fly).

As a private pilot with ~250 hours total time I doubt I'll find anything that much more experienced pilots have not, but I'll probably learn something in the process.

John
 
jsstevens said:
I think I will try different approaches and time the results for my own curiosity. I'll even publish the results here when I get a chance.

The three techniques are:
1) Level off, set power and wait re-triming as you go. This should eventually result in the normal cruise speed but will take longer to get there.
2) Level off, leave full power in until at least at normal cruise speed re-trimming as you go. This should also result in normal cruise speed but will get there faster.
3) Climb 100' above altitude, descend using the descent to accelerate to something at or above normal cruise speed, then level off, set power and trim. This will also result in normal cruise speed.
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I predict #2, which is generally taught as SOP, will win. But eager to see a properly controlled experiment to confirm it.

From the Airplane Flying Handbook, Page 12-14 (bolded mine):


LEVEL OFF AND CRUISE

Upon leveling off at cruising altitude, the pilot should allow the airplane to accelerate at climb power until cruising airspeed is achieved, then cruise power and r.p.m. should be set. To extract the maximum cruise performance from any airplane, the power setting tables provided by the manufacturer should be closely followed. If the cylinder head and oil temperatures are within their normal ranges, the cowl flaps may be closed. When the engine temperatures have stabilized, the mixtures may be leaned per AFM/POH recommendations. The remainder of the “cruise” checklist should be completed by this point.
 
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Just a nit...172s are happy at full power to cruising altitude, but many airplanes aren't. For instance, 182s climb at 23 inches once beyond pattern altitude.

Maintain CLIMB power at level off.

100 above assigned altitude has no margin. It may still attract ATC attention, and is equal to the ACS tolerance.
 
MAKG1 said:
Just a nit...172s are happy at full power to cruising altitude, but many airplanes aren't. For instance, 182s climb at 23 inches once beyond pattern altitude.

Maintain CLIMB power at level off.

100 above assigned altitude has no margin. It may still attract ATC attention, and is equal to the ACS tolerance.
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I am aware of these points, thanks. Currently I am flying fixed prop C-172s.
 
Step thing is physical nonsense. However, I can see how the fallacy came about. I believe that it will result in full cruise speed in less time. If there's a physicist in the room, check my logic:

* In climb or acceleration phase, energy is being added to the system at roughly the same rate, as the power is set to maximum available (whether that's full throttle or not is aircraft dependent).
* In climb, drag is lower because speed is lower and drag rises as the square of velocity. In other words, energy is being removed from the system at lower rate in climb than acceleration.
* Hence, climb is a more efficient method of adding energy to the system. (Note, not the same as fuel efficiency, but this is about power use efficiency.)
* Dives can accelerate quicker than the engine alone.
* As a result, less time is spent getting to speed.

Couple that with the psychological impact of interaction with the aircraft being more engaging than just leveling and waiting, the time will also feel shorter.

My theory, anyway. Haven't tested it. I can try it in my 172, but my guess is that the greater the difference between climb speed and cruise, the more you'll see the effect. The 172...not much difference.
 
Let'sgoflying! said:
The other thing that leads me to believe it does not exist is that airliners, who are all about chasing the knot, would be all over this like a nasty rash if it were true.
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The airlines must definitely DID believe in it, but that was back when they were flying piston prop liners in the flight levels.
 
jsstevens said:
I am aware of these points, thanks. Currently I am flying fixed prop C-172s.
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Another one to watch is that you don't exceed 70% power. You won't if the climb is really high, but power is roughly proportional to RPM, so you'll make more of it at higher airspeed, with the same throttle. It's a factor for lower cruise altitudes, where full throttle may exceed 70% power in cruise, but not in a climb.

172s can take quite some time to accelerate after a Vy climb, even if it is only 30 knots slower than cruise.

172SP's approximate 70% power with the tach green arc (which has three steps). Earlier ones, you'll have to get from the cruise performance tables.
 
<----- put in the "its a crock" column. It would be nice if you could get on "the step" and stay there but once you hit a thermal or a bump its all shot.
 
MAKG1 said:
Another one to watch is that you don't exceed 70% power. You won't if the climb is really high, but power is roughly proportional to RPM, so you'll make more of it at higher airspeed, with the same throttle. It's a factor for lower cruise altitudes, where full throttle may exceed 70% power in cruise, but not in a climb.

172s can take quite some time to accelerate after a Vy climb, even if it is only 30 knots slower than cruise.

172SP's approximate 70% power with the tach green arc (which has three steps). Earlier ones, you'll have to get from the cruise performance tables.
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Which 172 variant and where in the POH does it say not to exceed 70% power in cruise?
 
MAKG1 said:
Another one to watch is that you don't exceed 70% power. You won't if the climb is really high, but power is roughly proportional to RPM, so you'll make more of it at higher airspeed, with the same throttle. It's a factor for lower cruise altitudes, where full throttle may exceed 70% power in cruise, but not in a climb.

172s can take quite some time to accelerate after a Vy climb, even if it is only 30 knots slower than cruise.

172SP's approximate 70% power with the tach green arc (which has three steps). Earlier ones, you'll have to get from the cruise performance tables.
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Don't apply Lycoming's data to all 172. the 0-300 can run leaned to best power all its life and love you for it.
 
Greg Bockelman said:
Just so I can verify what I think I already know, how do you do that?
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In your case with 34V, set cruise power, (2450RPM) lean to the vibration, then enrichen to smooth running then trim to level flight.
OR
set 2450 RPM trim level, lean until a climb is shown on the VSI, trim level, repeat as Necessary until you lean and show a dive, then enrichen until you gain level flight.
that will be lean best power in either case on the 0-300.
 
Tom-D said:
In your case with 34V, set cruise power, (2450RPM) lean to the vibration, then enrichen to smooth running then trim to level flight.
OR
set 2450 RPM trim level, lean until a climb is shown on the VSI, trim level, repeat as Necessary until you lean and show a dive, then enrichen until you gain level flight.
that will be lean best power in either case on the 0-300.
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Ok. Thanks.
 
Charles Lindbergh flew two combat aircraft during ww2 . One was the corsair the other was the P38. The majority of his flying was in the P38 with which he taught the other pilots how to achieve best fuel consumption and longer range by optimum engine settings. He flew many combat missions. The P38 did not have radial engines.
 
MAKG1 said:
It's in the 172N and 172S manufacturer cruise checklists (but it's 75% power). That's all I can check easily at the moment.
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Can you provide an excerpt? My copy of the 172N POH says this:

Clipboard01.png

and my copy of the 172S POH says this:

Clipboard02.png

Which seems to imply cruise above 75% is OK (as long as you follow their recommendations, of course).
 
MAKG1 said:
Vx is the boundary between front and back side in steady flight.
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Vx is calculated as the airspeed at which thrust available - thrust required is the greatest and doesn't have much to do with the minimum power required curve.
 
Saturday I went out and tried three different methods of getting to cruise. I flew a C-172N. My method was to fly at stable cruise: 98 KIAS, 2300 RPM, 2500'. Start the timer and smoothly pull up and go to full power. Using 80 KIAS for cruise climb and targeting 3500'. Once stable at cruise altitude of 3500', 2300 RPM and 98 KIAS, stop the timer.

First time I leveled off at 3500' and pulled the power back to cruise immediately. Trimming and adjusting bit by bit until stable at cruise. Time: 3:35.

Second time I continued the climb until at 3600', then pushed over to get back to 3500' leveled off, set power and as soon as speed stablized, time: 2:25.

Third time I leveled off and left the power at full until I reached cruise speed then powered back to cruise. Time: 2:59.

These are not the results I expected. I really thought the full power until cruise would be fastest.

I'd like to conduct multiple trials of each with a second set of eyes to watch for traffic so I could pay more attention to flying a precise profile. Still, the results seem to be significant.

John
 
Gotta love the scientific method.

Again, not the results I'd have expected.

Since you seem to be a good skeptic, let's see if you can replicate your results.

What was your approximate rate of climb? Interesting to know how long climbing the extra 100' took.

Where are you located?
 
Those results are more or less exactly what I'd expect. Of course keeping full power in a descent will get you the best acceleration. And in an airplane that climbs at 90 and cruises at 100, you'll get the climb time back pretty easily. You may get different results at high altitude, where the climb takes a lot of effort.

A better test would be with a slippery, low power aircraft like a Mooney or maybe a Cardinal RG, where the acceleration phase takes a while.

But the "step" claim is that the descent gives you a higher cruise speed, not just a faster acceleration phase. You didn't test that.
 
FastEddieB said:
Gotta love the scientific method.

Again, not the results I'd have expected.

Since you seem to be a good skeptic, let's see if you can replicate your results.

What was your approximate rate of climb? Interesting to know how long climbing the extra 100' took.

Where are you located?
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Central Florida. I was west of Orlando Executive KORL and south of Leesburg KLEE around 9AM when I did the tests. I believe I was getting a little better than 500 fpm once the initial zoom was over.

John
 
MAKG1 said:
Those results are more or less exactly what I'd expect. Of course keeping full power in a descent will get you the best acceleration. And in an airplane that climbs at 90 and cruises at 100, you'll get the climb time back pretty easily. You may get different results at high altitude, where the climb takes a lot of effort.

A better test would be with a slippery, low power aircraft like a Mooney or maybe a Cardinal RG, where the acceleration phase takes a while.

But the "step" claim is that the descent gives you a higher cruise speed, not just a faster acceleration phase. You didn't test that.
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Well, I did test it in that I wound up at the same cruise speed using the same power setting for all three tests. But I don't believe the step as described can really get you more speed for the same power.

And it would be very interesting to see with a slippery plane and a bigger difference between climb and cruise speed. Any volunteers?

John
 
MAKG1 said:
Those results are more or less exactly what I'd expect. Of course keeping full power in a descent will get you the best acceleration. And in an airplane that climbs at 90 and cruises at 100, you'll get the climb time back pretty easily. You may get different results at high altitude, where the climb takes a lot of effort.

A better test would be with a slippery, low power aircraft like a Mooney or maybe a Cardinal RG, where the acceleration phase takes a while.

But the "step" claim is that the descent gives you a higher cruise speed, not just a faster acceleration phase. You didn't test that.
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Would love to oblige a test with my Cardinal RG but I am still without a medical.

Although the original "step" claim is a higher cruise speed as you say, I'm not sure anyone here really believes that. At least, it was my perception that the argument was over the claim that the same cruise speed could be achieved faster with the "step" method.

Anyway my expectation for a Cardinal RG would be pretty much the same results, maybe slightly greater difference between full power level flight until cruise vs. accelerate full power in a 100 ft descent.

Actually, rereading John's test description I'm not sure what the power setting was after the descent while waiting for the speed to stabilize (second method). "Set power and as soon as speed stabilized"... what? Or was the "and" extraneous? (i.e. accelerate in the descent and maintain full power until speed stabilized? vs. throttle back as soon as level at 3500 and wait for speed to stabilize?)... :confused:
 
azure said:
Would love to oblige a test with my Cardinal RG but I am still without a medical.

Although the original "step" claim is a higher cruise speed as you say, I'm not sure anyone here really believes that. At least, it was my perception that the argument was over the claim that the same cruise speed could be achieved faster with the "step" method.

Anyway my expectation for a Cardinal RG would be pretty much the same results, maybe slightly greater difference between full power level flight until cruise vs. accelerate full power in a 100 ft descent.

Actually, rereading John's test description I'm not sure what the power setting was after the descent while waiting for the speed to stabilize (second method). "Set power and as soon as speed stabilized"... what? Or was the "and" extraneous? (i.e. accelerate in the descent and maintain full power until speed stabilized? vs. throttle back as soon as level at 3500 and wait for speed to stabilize?)... :confused:
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I left the power at full until I reached cruise speed and altitude on the climb above test, so yes I was descending at full power.

John
 
Yes that was a very good Time to Cruise Speed test.
But not a Step Theory test.
 
Let'sgoflying! said:
Yes that was a very good Time to Cruise Speed test.
But not a Step Theory test.
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What should I have done differently in trial #2 to test the step theory? I set power after descending (accelerating above cruise speed) and let the speed stabilize. It stopped at the same IAS as all the other trials. What am I missing?

John
 
jsstevens said:
I left the power at full until I reached cruise speed and altitude on the climb above test, so yes I was descending at full power.

John
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I realized this is incorrect. I left full power in until I had descended to my target altitude actually accelerating to above cruise (~105KIAS) then reduced power to cruise. Power settings would be more accurate in a CS prop setup. I'm using RPM and my best estimation of throttle setting with a little fiddling to nail 2300 as speed stabilizes.

John
 
jsstevens said:
I realized this is incorrect. I left full power in until I had descended to my target altitude actually accelerating to above cruise (~105KIAS) then reduced power to cruise. Power settings would be more accurate in a CS prop setup. I'm using RPM and my best estimation of throttle setting with a little fiddling to nail 2300 as speed stabilizes.

John
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Okay - I do not throttle back until expected ROP cruise speed is achieved from below. IIRC that usually happens *after* returning to my desired cruise altitude so I maintain full power for a bit at cruise altitude and do not need to slow back to cruise speed. An exception would be if there is a strong updraft helping my acceleration.

Since I generally run LOP, my next step is to do the "big pull", after which I gradually lose 5-10 kts of airspeed.
 
That is a great test. It shows that maybe climbing above the target altitude and descending on the step may result in quicker stabilized flight allowing us to multi task better or do other things sooner.

It would be interesting to see a time-to-distance test to see which is fastest A to B for those who prioritize time savings.

Finally, it would be nice to know total fuel burn for distance travelled. Climbing above target altitude and descending on the step seems to have less full throttle time but the distance traveled is also less by the time cruise speed is achieved.

These are questions that have always kept me up at night, thrashing around:D
 
Landshark said:
That is a great test. It shows that maybe climbing above the target altitude and descending on the step may result in quicker stabilized flight allowing us to multi task better or do other things sooner.

It would be interesting to see a time-to-distance test to see which is fastest A to B for those who prioritize time savings.

Finally, it would be nice to know total fuel burn for distance travelled. Climbing above target altitude and descending on the step seems to have less full throttle time but the distance traveled is also less by the time cruise speed is achieved.

These are questions that have always kept me up at night, thrashing around:D
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For the case I tried (C-172) the distances are so small I'd never be able to fly the rest consistently enough to measure a difference. A few degrees of wandering off course for a few minutes would make more difference.

John
 
Analogy?

Would a dragster have a higher top speed or E.T. at the end of a run if the dragstrip had a slight "hump" in it?

Similar logic, right? Or just dumb? o_O
 
I think you need to do each method 3 times, not just once. That will help get rid of some possible other reasons. Then use statistics.
 
jsstevens said:
I realized this is incorrect. I left full power in until I had descended to my target altitude actually accelerating to above cruise (~105KIAS) then reduced power to cruise. Power settings would be more accurate in a CS prop setup. I'm using RPM and my best estimation of throttle setting with a little fiddling to nail 2300 as speed stabilizes.

John
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Interesting. My guess is that the best time to cruise speed would be the one where you climb exactly enough above cruise altitude that you get to precisely cruise speed at the desired altitude at full power. Maybe try it again with a 50' overclimb? I'll see if I can find time to play in my plane, too, though being a 172S, it's pretty damn similar to yours. (Though I tend to cruise at 2500 RPM and 115-120 knots.)
 
jsstevens said:
What should I have done differently in trial #2 to test the step theory? I set power after descending (accelerating above cruise speed) and let the speed stabilize. It stopped at the same IAS as all the other trials. What am I missing?

John
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"On the step" as talked about in the original post refers to this magical extra couple knots that you gain, and are able to sustain, by going above the target altitude, and descending under cruise power until you hit your target altitude with the couple extra knots due to descending. The plane will supposedly stabilize with a couple extra knots even using the same cruise power setting, essentially getting something (more speed) for nothing (same power).

If you want to run the test:

Trial 1: Climb using full power or climb power. Then level off at target altitude and simultaneously reduce power to cruise power. Let the plane slowly accelerate to maximum cruise speed under cruise power. Note maximum speed achieved.

Trial 2: Climb 100 feet or so above target altitude using full power or climb power. Descend to target altitude using cruise power. Level off at target altitude, keeping cruise power, and let speed stabilize. Note maximum stabilized speed.

If Trial 2 is a couple knots faster, being "on the step" is a thing and we should all fall in line.
If both trials produce the same speed, consider this myth busted:)
 
jsstevens said:
First time I leveled off at 3500' and pulled the power back to cruise immediately. Trimming and adjusting bit by bit until stable at cruise. Time: 3:35.

Second time I continued the climb until at 3600', then pushed over to get back to 3500' leveled off, set power and as soon as speed stablized, time: 2:25.

Third time I leveled off and left the power at full until I reached cruise speed then powered back to cruise. Time: 2:59.
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Landshark said:
If Trial 2 is a couple knots faster, being "on the step" is a thing and we should all fall in line.
If both trials produce the same speed, consider this myth busted:)
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To be fair; if there were any advantage at all (fuel consumption, time to cruise speed, etc), "on the step" is at least partially proven correct.

I also am a skeptic; I'd like to see the tests repeated, and maybe one with a climb 200' higher than target altitude, just for fun.

I feel like if there were any advantage in the slightest, every carrier out there would be having its pilots do that.

I really appreciate your time in doing this, @jsstevens and the rest.
 
I don't know if airliners are routinely assigned a block altitude to climb and descend at their discretion. Without a block altitude, going 100 or 200 feet or more above cruising altitude would be a big problem with ATC. Second, I believe airliners travel much closer to the critical Mach number. Any overspeed in the descent could lead to a dangerous Mach stall.

Perhaps those two things prohibit the airliners from using these techniques. However, for our VFR GA planes, we have no such limitations. We just need the data to see if there is any benefit.
 
jsstevens said:
Saturday I went out and tried three different methods of getting to cruise. I flew a C-172N. My method was to fly at stable cruise: 98 KIAS, 2300 RPM, 2500'. Start the timer and smoothly pull up and go to full power. Using 80 KIAS for cruise climb and targeting 3500'. Once stable at cruise altitude of 3500', 2300 RPM and 98 KIAS, stop the timer.

First time I leveled off at 3500' and pulled the power back to cruise immediately. Trimming and adjusting bit by bit until stable at cruise. Time: 3:35.

Second time I continued the climb until at 3600', then pushed over to get back to 3500' leveled off, set power and as soon as speed stablized, time: 2:25.

Third time I leveled off and left the power at full until I reached cruise speed then powered back to cruise. Time: 2:59.

These are not the results I expected. I really thought the full power until cruise would be fastest.

I'd like to conduct multiple trials of each with a second set of eyes to watch for traffic so I could pay more attention to flying a precise profile. Still, the results seem to be significant.

John
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Nice expirement!
Since all 3 cases have a climb at steady 500 fpm to start, I suggest starting the stopwatch while in the climb about 100 feet before the target altitude, to remove some variability.

More data! More flying!
 
JoeFromKS said:
Nice expirement!
Since all 3 cases have a climb at steady 500 fpm to start, I suggest starting the stopwatch while in the climb about 100 feet before the target altitude, to remove some variability.

More data! More flying!
Click to expand...

Thanks for the compliment. The climbs started at higher rates because I was dissipating the extra speed then stabilized at 500fpm and 80KIAS. I agree that in theory they should be the same and in practice they are probably not exactly because I can't fly that consistently/accurately. But it would be hard to figure out exactly where to start the stopwatch in the climb.

I do have an airplane (and no instructor again) for Saturday so I may run another trial or two.

John
 
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