ROP and LOP as related to "the feel"

[211º]

During recent flights, I have been doing more rich of peak flying. (Mostly because I have included some shorter cross country's that don't get anywhere near my reserve of 10 gallons of fuel remaining).

Anyway, maybe this is just a happy perception, but it seems like the plane just operates better when flying a little faster.

It seems like my altitude hold works better (Brittain) and that there is overall less wandering. I kind of wonder if it has something to do with "mushiness" or being on/off step. It's about 15 mph IAS difference.

Has anybody else noticed something like this?

[takair]

13 minutes ago, 211º said:

During recent flights, I have been doing more rich of peak flying. (Mostly because I have included some shorter cross country's that don't get anywhere near my reserve of 10 gallons of fuel remaining).

Anyway, maybe this is just a happy perception, but it seems like the plane just operates better when flying a little faster.

It seems like my altitude hold works better (Brittain) and that there is overall less wandering. I kind of wonder if it has something to do with "mushiness" or being on/off step. It's about 15 mph IAS difference.

Has anybody else noticed something like this?

Yes….I think your perception is real.  Remind me, what power settings are you using and what airspeed?  I find mine to trim up better and generally be more stable (hands off) with speed.  The PC and altitude hold is probably optimized at about 150mph….bottom of my yellow.  It does well at lower speeds, but works harder and you will generally see more activity.  

[N201MKTurbo]

Because I have a turbo, I believe I can make more power LOP than ROP. Well more airspeed without the cylinders going over 380. This happens with about 1.5 GPH less fuel flow. 
 

Without a turbo, you will always make more power ROP.

[Ragsf15e]

38 minutes ago, 211º said:

During recent flights, I have been doing more rich of peak flying. (Mostly because I have included some shorter cross country's that don't get anywhere near my reserve of 10 gallons of fuel remaining).

Anyway, maybe this is just a happy perception, but it seems like the plane just operates better when flying a little faster.

It seems like my altitude hold works better (Brittain) and that there is overall less wandering. I kind of wonder if it has something to do with "mushiness" or being on/off step. It's about 15 mph IAS difference.

Has anybody else noticed something like this?

I do think it feels more solid faster, but 15mph between rop and lop is too much.  I usually fly about 65% power at 10k and see about 5mph different.  Maybe you’re too deep lop?

[211º]

9 hours ago, takair said:

Yes….I think your perception is real.  Remind me, what power settings are you using and what airspeed?  I find mine to trim up better and generally be more stable (hands off) with speed.  The PC and altitude hold is probably optimized at about 150mph….bottom of my yellow.  It does well at lower speeds, but works harder and you will generally see more activity.  

I was at 6000 at 22/2400 (just under 10gph) I think - about 145-149 IAS - I was thinking that as I still have variation in the IAS that I should open the decay valve another 1/16 turn.

It is good to know that it isn't just "my feel" but that others have noticed it too.

[211º]

9 hours ago, Ragsf15e said:

I do think it feels more solid faster, but 15mph between rop and lop is too much.  I usually fly about 65% power at 10k and see about 5mph different.  Maybe you’re too deep lop?

That could be - I know that my fuel totalizer is off about 7% (so I'm guessing that the fuel flow is also off about 8%.  In the long past, I have almost always flown at LOP 21/2350 and get about 134± IAS, but as Rob noted, there is more mushiness and the IAS varies more too.

(Oh, and I consider it totalizer being off about 7% a feature - I'd rather have more fuel - always - than less... been there and once was enough.)

[Shadrach]

11 hours ago, 211º said:

During recent flights, I have been doing more rich of peak flying. (Mostly because I have included some shorter cross country's that don't get anywhere near my reserve of 10 gallons of fuel remaining).

Anyway, maybe this is just a happy perception, but it seems like the plane just operates better when flying a little faster.

It seems like my altitude hold works better (Brittain) and that there is overall less wandering. I kind of wonder if it has something to do with "mushiness" or being on/off step. It's about 15 mph IAS difference.

Has anybody else noticed something like this?

 

I’ll offer a dissenting opinion. Yes, control feel/authority diminishes as speeds are reduced, but I don’t think the speeds mentioned are low enough to be called “mushy”.  I personally think control feel and harmony is actually best around 120kias.
These airframes are capable of operating over an altitude range that yields pretty large deltas in IAS. Once trimmed, I don’t notice a remarkable difference in stability between 150kias vs 120kias. Perhaps your autopilot’s inputs are better suited to the pitch outputs at higher speed. No question that the input for a pitch correction will be less at higher speed.

I’m not sure what you mean by “on/off step”? 

Your LOP speed loss is suspect. I’ve never seen a 15MIAS loss between LOP and ROP. More like 5MIAS under most scenarios and that’s probably running leaner than necessary.

Given that you are comfortable with the notion of running LOP, I’m curious why you would chose to deliberately throttle and prop back to 22”x2400 when you could likely go just as fast or faster on less gas by running WOT at 2500 and how ever far LOP necessary to keep CHTs <350. My guess is that’d be 20ish LOP at that altitude.

[A64Pilot]

55 minutes ago, Shadrach said:

 

I’m not sure what you mean by “on/off step”? 

Your LOP speed loss is suspect. I’ve never seen a 15MIAS loss between LOP and ROP. More like 5MIAS under most scenarios and that’s probably running leaner than necessary.

Step is an old possibly wives tale, especially prevalent among Mooney guys. The idea is the aircraft actually gets on “step” once it exceeds some speed and if power is reduced some it may stay on step traveling faster than the identical power setting if off step. Reduce power too much and she falls off step and slows significantly, think boat on plane. 

‘The idea is either climb a couple of hundred ft higher than assigned, then leaving climb power in to descend to assigned altitude, then reduce to cruise power. The idea being that the steady state speed will be higher than if you climbed to assigned and immediately reduced to cruise power.

Some say you can feel the tail riding high and one way to tell your on step is to look over your shoulder and look at the elevator, the leading edge of the elevator will have significant height above the horizontal indicating down elevator, or trim will be nose down.

Some are adamant about it.

I think under some conditions the difference in best power and LOP airspeed can be significant, fuel flow too of course.

https://books.google.com/books?id=szhF30LW2wcC&pg=PA75&lpg=PA75&dq=putting+a+mooney+on+step&source=bl&ots=ec_BN3OmT5&sig=ACfU3U02dKYNGuILhRNTx2-6lJz8H01y6A&hl=en&sa=X&ved=2ahUKEwjSuKDkkab6AhWCfjABHb8XBNsQ6AF6BAgfEAM#v=onepage&q&f=false

[Shadrach]

1 hour ago, A64Pilot said:

Step is an old possibly wives tale, especially prevalent among Mooney guys. The idea is the aircraft actually gets on “step” once it exceeds some speed and if power is reduced some it may stay on step traveling faster than the identical power setting if off step. Reduce power too much and she falls off step and slows significantly, think boat on plane. 

‘The idea is either climb a couple of hundred ft higher than assigned, then leaving climb power in to descend to assigned altitude, then reduce to cruise power. The idea being that the steady state speed will be higher than if you climbed to assigned and immediately reduced to cruise power.

Some say you can feel the tail riding high and one way to tell your on step is to look over your shoulder and look at the elevator, the leading edge of the elevator will have significant height above the horizontal indicating down elevator, or trim will be nose down.

Some are adamant about it.

I think under some conditions the difference in best power and LOP airspeed can be significant, fuel flow too of course.

https://books.google.com/books?id=szhF30LW2wcC&pg=PA75&lpg=PA75&dq=putting+a+mooney+on+step&source=bl&ots=ec_BN3OmT5&sig=ACfU3U02dKYNGuILhRNTx2-6lJz8H01y6A&hl=en&sa=X&ved=2ahUKEwjSuKDkkab6AhWCfjABHb8XBNsQ6AF6BAgfEAM#v=onepage&q&f=false

Great article! My favorite line is below:

pilots are veritable treasuries of misinformation about airplanes and flight. Most of what they say about the theory of flight, as opposed to practical techniques, should be given polite assent and then forgotten. Like the hazards, or lack of them, of downwind turns, the existence or non-existence of the "step" has generated millions of words in hangars and flight schools all around the world, most of them assuredly gibberish.

I am sure a young Mr. Garrison could not have imagined that in 2022 we would be cataloging and curating our gibberish online for posterity...

[A64Pilot]

Step or no step I climb slightly above assigned  say 100’, then slowly descend to assigned then reduce power. There may or may not be a step, but doing that gets me to trimmed airspeed much quicker.

Step is hard to refute though I’ve had as much as 5 kts true airspeed difference in identical conditions, and can’t explain why.

Probably lack of precision in instrumentation and calculation I guess

[PT20J]

The Mooney’s (up through the J) have low drag, but not a great excess of power. The low drag gives a greater spread between climb speed and cruise speed than say a C-172, but the lack of power makes acceleration slow, and the acceleration decreases exponentially as the speed increases because thrust decreases with airspeed and drag increases as airspeed squared. So, transitioning from climb to cruise takes a while in a Mooney. If you are impatient, you can level off above your cruise altitude and use gravity to help the airplane accelerate as you descend. If you are patient, you can level off at altitude and accelerate. Either way will get you to the same place eventually. Just don’t reduce power until you get to cruise speed - a common mistake. 

[Hank]

48 minutes ago, PT20J said:

The Mooney’s (up through the J) have low drag, but not a great excess of power. The low drag gives a greater spread between climb speed and cruise speed than say a C-172, but the lack of power makes acceleration slow, and the acceleration decreases exponentially as the speed increases because thrust decreases with airspeed and drag increases as airspeed squared. So, transitioning from climb to cruise takes a while in a Mooney. If you are impatient, you can level off above your cruise altitude and use gravity to help the airplane accelerate as you descend. If you are patient, you can level off at altitude and accelerate. Either way will get you to the same place eventually. Just don’t reduce power until you get to cruise speed - a common mistake. 

Yep. Coming home from the Summit at 8000', I had to climb for traffic. Cruise had been 143 mph, climb slowed down to 100 mph at the end, leveled off and accelerated back to 120-125 mph then seemed to stop. Leaned her out and viola, 140 mph again. The leveled-off acceleration was not quick . . . Neither was slowing back down to cruise speed about ten minutes later when they dropped me back to 8000'.  

Unrelated question:  when two IFR aircraft are on converging / crossing courses, how does ATC decide which one to move?

[Greg Ellis]

13 minutes ago, Hank said:

Unrelated question:  when two IFR aircraft are on converging / crossing courses, how does ATC decide which one to move?

Usually the one I am flying. 

[201er]

5 hours ago, Shadrach said:

I’ll offer a dissenting opinion. Yes, control feel/authority diminishes as speeds are reduced, but I don’t think the speeds mentioned are low enough to be called “mushy”.  I personally think control feel and harmony is actually best around 120kias.

Maybe Carson was onto something after all and not just some random number...

[201er]

17 hours ago, 211º said:

Anyway, maybe this is just a happy perception, but it seems like the plane just operates better when flying a little faster.

It seems like my altitude hold works better (Brittain) and that there is overall less wandering. I kind of wonder if it has something to do with "mushiness" or being on/off step. It's about 15 mph IAS difference.

 

You can also fly at a lower altitude to accomplish similar result while flying LOP. Higher IAS can be achieved LOP down lower.

Then again, you're in enroute cruise so who cares? You're not performing lazy eights and turns around a point so just fly fast and efficient.

[takair]

10 hours ago, 211º said:

I was at 6000 at 22/2400 (just under 10gph) I think - about 145-149 IAS - I was thinking that as I still have variation in the IAS that I should open the decay valve another 1/16 turn.

It is good to know that it isn't just "my feel" but that others have noticed it too.

Probably fair to share that Dave and I worked on getting his altitude hold tuned.  Great learning experience.   When I set up your dynertial on my plane I was using about 150mph and up….so it was definitely optimized for a higher speed.  This is likely why you have had to adjust the decay and may require additional adjustment if you typically fly at a lower speed. 

I think PT20J is correct about what is perceived as the “step”….it is really just getting to trim speed.  If leveling right at or below target, a Mooney takes quite some time….multiple minutes to get to trim speed.  The dynertial system can make it even more interesting since you need to anticipate its inputs too and the resultant trim might not be perfect every time.  Someone above mentioned climbing above target and settling to target, this can reduce getting to trim speed faster…by multiple minutes.  Another consideration is that when at a higher speed, one has more reserve energy.  So, at 120mph, if you get below target altitude, it can take more pitch or more time to get back on target altitude.  This might give that feeling of slower response as opposed to higher speeds where the reserve energy more rapidly gets you back on target altitude….basically trading airspeed for altitude.  If you have more airspeed, you can convert it to altitude faster.  The autopilot has similar constraints, but it has more limited knowledge and less things to help it come back to target.  For example, when hand flying, you may fine tune the trim and power, but the dynertial only has its limited authority on the elevator, so it will behave slightly differently….especially since set up for a higher target speed.

[MikeOH]

This guy was an aeronautics professor at Embry-Riddle.

Decide for yourself if he's full of it: https://www.nar-associates.com/technical-flying/step/step_wide_screen.pdf

 

[211º]

I’m looking forward to continued collection of data. 

[Andy95W]

If “the step” was really a thing for airplanes, the airlines would be doing it.  Saving even a tiny % over a thousand flight hours a day is a crapload of JetA (and money).

[Fly Boomer]

17 hours ago, PT20J said:

Either way will get you to the same place eventually. Just don’t reduce power until you get to cruise speed - a common mistake

As John Deakin used to say "When we level off at our target altitude, what's the first thing we are going to do?  That's right, we are going to do nothing."

[Fly Boomer]

6 hours ago, MikeOH said:

This guy was an aeronautics professor at Embry-Riddle.

Decide for yourself if he's full of it: https://www.nar-associates.com/technical-flying/step/step_wide_screen.pdf

 

In spite of his estimable resume, this reads like a sober explanation of how obese people gain weight on 900 calories a day.

[Pinecone]

He is right, but that is NOT the step.  The step is a few knots more.

You would almost have to pull the power before leveling off to see what he is talking about.   At 55%, he is talking about 80 knots difference.

[MikeOH]

Two guys on the internet ridicule the credentialed aeronautics prof.

Got it!

[carusoam]

On 9/21/2022 at 8:10 AM, 211º said:

 

(Oh, and I consider it totalizer being off about 7% a feature - I'd rather have more fuel - always - than less... been there and once was enough.)

Flying based on a feeling…?

has the extra challenge of not being reliant on instruments…

Of course… if your instruments aren’t calibrated… they are doubly hard to rely on…

 

laws of physics don’t allow the step to actually exist…

But, in practice… it allows people to get their cruise set up done nicely and predictably… (works for some)

 

Just don’t tell everyone you fly the step… or you have somehow proven that it exists… 

 

Flying by the facts of your instruments… doesn’t sound as much fun as flying by the seat of your pants…

Flying by feelings, in IMC… Is the entry step of the death spiral…

 

I prefer to make decisions based on accurate instrumentation…   

But, have been known to use some pretty ancient instruments with a big safety margin…

Getting your FF and FL sensors calibrated is a common challenge around here… the sooner the better…

 

PP thoughts and encouragement only…

Best regards,

-a-

 

[PT20J]

It is well known that since the power required curve is u shaped and the power available curve is in the shape of an inverted u that the two curves intersect at two points. That’s why it takes so much power to fly at minimum controlled airspeed. 

All the article points out is that at high altitudes with a normally aspirated engine, the power available is so low that the two intersection points can be close together and it is possible to settle on the lower one unintentionally if arriving at cruise from a climb speed below both points.

This is a plausible origin of the notion of the step. 

David Rogers website has a number of fascinating papers, all carefully written and most with detailed mathematical analysis. 

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