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ROP and LOP as related to "the feel"


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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-

 

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40 minutes ago, MikeOH said:

Two guys on the internet ridicule the credentialed aeronautics prof.

Got it!

Did you look at the number on his chart?  Do you think you would notice being 60 knots or so slow????

What he is saying is correct.  But it is NOT "the Step."  The Step is a few knots.

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6 hours ago, Pinecone said:

Did you look at the number on his chart?  Do you think you would notice being 60 knots or so slow????

What he is saying is correct.  But it is NOT "the Step."  The Step is a few knots.

I post this response to those readers with an open mind.

Merely looking at the chart in the paper and failing to read Dr. Roger's actual point in presenting it will leave you uninformed.  Dr. Rogers is absolutely discussing "The Step".  In fact, if you bother to read his entire paper you will note he states, "We broke out the oxygen and climbed well into the teens to avoid the ice, got on "the step" to get that few extra knots,...".   Focusing on a personal observation about a curve without reading the context and reason why it was presented is unwise.

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Help me understand.  Most of my first several hundred hours were in C172's.   In my experience if I climbed to altitude and trimmed too soon, the ship would slog along at 98 knots.   Alternatively, climb 100' higher than your cruise altitude, nose it over to build speed, and trim to fly at 110 knots at your cruise altitude.  That ~12 knot difference is real for cruising at essentially the same power with a relatively draggy and underpowered airframe compared to our Mooneys.  I'm sure many of you have experienced it too.  Is that "the step"?  

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Let’s consider for a moment…

What it would take to make the step actually work… from a laws of physics point of view…

Then see if we have other examples of it in our complex Mooney lives….

 

Lets say our target cruising altitude is 10K’

1) We climb directly to 10k’ using Vy… or 120kias because we can… (probably won’t make a difference…)

2) Our cruise speed is 150kts true…. (Common cruise speed for some Mooneys…)

3) So we level off at 10k’… accelerate, and settle in on our power settings… often WOT, peak, and choice of rpm… (I like 2550…TopProp thing)

4) it takes some noticeable time after we level off….for everything to come to a steady state….

 

On the return flight… (I bump into a rule of flight level vs. heading…. Probably need 9k or 11k’… but ignore that for now…)

5) Select the new climb-to altitude… make it 11k’

6) The additional 1k’ climb to 11k’ gets accounted for… it isn’t forgotten….

7) a gentle cruise descent ensues… back to 10k’.

8) Arrive at 10k’, level off, and set power settings the same way… WOT, peak, and 2550…

9) There is no waiting for acceleration, as we traded altitude for speed… that energy was nicely stored in the extra climb…

10) A few minutes later… the same power settings net the same speed.… (how many minutes does it take to reach steady state again…?)

 

11) When performing a three way speed test… we usually wait a few minutes to arrive at steady state… because turns inevitably take some speed away…

12) If… airspeed improved our efficiency…   We would want to go fast to get efficient… and then arrive at altitude going fast and efficient…

13) I don’t recall any efficiency discussions except for the plane gets less draggy with altitude…

14) For NA planes… we get less power with altitude… so altitude definitely limits our reason to climb…

15) TC’d planes make this discussion slightly more interesting… full power is available in thin air…. Making things more efficient airframe wise…

16) Is there a step for TC’d planes… I don’t see one yet!

17) Climbing ROP in a TC’d plane… and cruising LOP…. May cause the math to not account for the different power levels…

18) In the end… we all reach a steady state that is set by air density and power available… completely independent of how we got there…

19) If anyone is a true believer in the step theory… let’s define what it is and how to test it Mooney style!

20) let’s keep in mind O’Tree’s @0TreeLemur mention of the C172, with the non laminar wing…. There may actually be two different operating points of where the split line forms on the leading edge… and being under powered… not being able to get to the most efficient way of operating that wing…   Hmmmmmmm…. Very interesting…

 

I could really get to like a new and different way to eke out more speed at the same power level I currently use…   :)
 

There is only one way to operate a laminar wing… fast and efficient… or was that just fast… or just efficient… :)

Best regards,

-a-

 

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On 9/21/2022 at 11:37 AM, A64Pilot said:

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

Other than seaplanes, that the only "step" I've heard of - a way to get to curse speed faster by adding a small descent.

i agree with those who say LOP and ROP should not have that much of an airspeed discrepancy or that anything below pattern speed should feel "mushy."

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8 hours ago, MikeOH said:

I post this response to those readers with an open mind.

Merely looking at the chart in the paper and failing to read Dr. Roger's actual point in presenting it will leave you uninformed.  Dr. Rogers is absolutely discussing "The Step".  In fact, if you bother to read his entire paper you will note he states, "We broke out the oxygen and climbed well into the teens to avoid the ice, got on "the step" to get that few extra knots,...".   Focusing on a personal observation about a curve without reading the context and reason why it was presented is unwise.

I went back and read the whole thing.

He still doesn't prove a step.   He just points out that at high altitudes it helps to accelerate by climbing a bit higher and then diving to get to the cruise speed.

The same thing can be done by leaving climb power on, leveling off and letting the airplane accelerate.

MANY other people have done actual comparison tests that show there is no step, but that it can take a while to accelerate to your final cruise speed.  His scientific method is lacking.  We did this and this happened.  Without testing other ways to accomplish the same thing.

There is a corner situation where the power available is so low that climb power and cruise power are the same.  But that only occurs near the service ceiling.

The U2 at 80,000 feet is getting into this area.  Plus the "coffin corner" were the stall speed and Vne are very close.

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3 minutes ago, midlifeflyer said:

 

i agree with those who say LOP and ROP should not have that much of an airspeed discrepancy or that anything below pattern speed should feel "mushy."

The speed discrepancy is easy to validate, Look at a chart for best power, if it’s a 75% power chart and your a 200 HP Lycoming, then that’s 150 HP of course.

Go out and fly the chart conditions but at LOP, remember fuel flow, multiply that fuel flow by 14, that will give HP. It will be significantly lower than 150. To see the speed difference, just enrichen until best power EGT (100 ROP)

The difference is pretty significant, but fuel flow is an even bigger difference, proving if you will that even though power is down efficiency is up.

I don’t know where this myth of I can go just as fast LOP as I can ROP came from, it’s actually true in certain circumstances like much more MP is available than what your flying at, but those are unusual circumstances, but you just cannot make the same power with any mixture other than best power as you can best power with the same MP, it’s called that for a reason. But you can burn significantly less fuel in most conditions if you give up a little speed LOP

TANSTAAFL

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28 minutes ago, Pinecone said:

 

There is a corner situation where the power available is so low that climb power and cruise power are the same.  But that only occurs near the service ceiling.

 

Depending on what you define cruise power as it occurs much lower than service ceiling, if you define cruise as 75% is occurs 8,000 or so 65% about 12,000 roughly, maybe a little higher. NA generic airplane. 

I know the step is a myth, but I have had as much as a 5 kt difference in speed in identical conditions from one day to the next that I cannot explain, so I can see where the myth comes from, because I can’t explain the true airspeed difference myself, and the step explains it.

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9 hours ago, 0TreeLemur said:

Help me understand.  Most of my first several hundred hours were in C172's.   In my experience if I climbed to altitude and trimmed too soon, the ship would slog along at 98 knots.   Alternatively, climb 100' higher than your cruise altitude, nose it over to build speed, and trim to fly at 110 knots at your cruise altitude.  That ~12 knot difference is real for cruising at essentially the same power with a relatively draggy and underpowered airframe compared to our Mooneys.  I'm sure many of you have experienced it too.  Is that "the step"?  

This is what I would personally call “on step”.   If you don’t dive to get to cruise trim, you will eventually get there from level flight, but it takes longer.  I haven’t run the numbers, but I suspect your overall leg time is longer when approaching trim speed from below or from level.  To me getting on step is getting to trim speed faster.  
 

Thinking out loud, As others have alluded, on step likely comes from a nautical term.  To me, when a boat or seaplane is “on step”, it is at its optimal trim configuration for the power available.  It takes time and perhaps some work and perhaps trimming to get there.  I do t think the term “on step” as used in aviation is a bad term if used to indicate “trimmed out at optimal speed”.  You can  and will get “on step” from target altitude or below, it just takes a lot longer.  It is also easy to fall “off step”, when you have some sinking air….we’ve all experienced these conditions.

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19 hours ago, PT20J said:

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. 

Skip
 

 

I’ve had that happen a few times on a hot day trying to use LOP/peak up around 12,000’.  Hit a little downdraft, speed drops off and it’s never coming back.  Realized density alt was well over 14k.  We just don’t have a ton of excess power up there, especially LOP.

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14 hours ago, A64Pilot said:

I know the step is a myth, 

I guess I'm the only one who can understand what Dr. Rogers wrote.  Oh well, bias is a powerful thing.  His paper does NOT contradict physics despite @carusoam protestations.

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On 9/22/2022 at 10:59 PM, MikeOH said:

I post this response to those readers with an open mind.

Merely looking at the chart in the paper and failing to read Dr. Roger's actual point in presenting it will leave you uninformed.  Dr. Rogers is absolutely discussing "The Step".  In fact, if you bother to read his entire paper you will note he states, "We broke out the oxygen and climbed well into the teens to avoid the ice, got on "the step" to get that few extra knots,...".   Focusing on a personal observation about a curve without reading the context and reason why it was presented is unwise.

I respect Dr. Rogers, but this paper is mostly academic navel gazing.  Respectfully, you are misunderstanding. His graph perfectly depicts what he is saying in the narrative. He is simply describing what can happen when power is reduced to a level that puts the airplane behind the power curve (minimum velocity for thrust) before allowing it to accelerate. This is a scenario he creates by reducing power as he arrives at target altitude rather than letting the aircraft accelerate before reducing power.  

As thrust drops, the min velocity and max velocity for a given thrust get closer and closer until they meet at absolute ceiling for a given thrust.  You don’t need to climb to 15,000’ to demonstrate this, you could do it at 5,000’ by doing a reduced power climb so that the airplane is just climbing at say 100fpm at Vy, then level at the target altitude and immediately reduce power another 10% before the plane has accelerated. 

The whole paper can be summarized by saying - at low thrust levels the spread between minimum and maximum velocities narrows. Reducing thrust to a level with a minimum velocity in the vicinity of climb velocity may result in a condition where the aircraft is behind the power curve and incapable of accelerating at the reduced thrust level.

 

 

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The thing about flying and about flying Mooneys - it is both fun to fly fast and fun to figure stuff out.

Yesterday I flew a long cross country and played around with things a little bit in flight. This morning, I stepped into the Infinity Pool of Mooneyspace, LOP, ROP, FF, and calculating HP.

I think that I figured a few things out... and figured out a few things to look into.

First, I think that I have been so conservative (scared?) of the red box that I have been super-conservative when it comes to 65% power. My go to setting to know that I'm under 65% power at any altitude is 21/2350 and 7.0 gph. This setting is probably somewhere around 15x7/200 52% power. It has treated me well when on long XCs - I can fly for 6 hours (easily) and land with more than 10 gallons in the tanks (my current minimum landing criteria).

But on yesterday's flight, I flew ROP at 23/2400 (10.5 gph) with an IAS of about 151 mph giving a rough calculated TAS of about 172 mph (7,000 ft)

The difference between 55% power and 135 mph IAS and 151 mph IAS was quite fun - the airplane just feels tighter (and less mushy).

As others have noted above (and I'll paraphrase) - there is just more inertia at 151 mph to overcome slight altitude climb corrections than at 55%... and maybe that is a better quasi-definition of "step".

@kortopates put together a nice table that I'm going to play/flight test for a while. 

While I've always appreciated the efficiency of the Mooney in getting me between Cinti and KC, I'm liking trying to figure out how to do it even better now.

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7 hours ago, Shadrach said:

I respect Dr. Rogers, but this paper is mostly academic navel gazing.  Respectfully, you are misunderstanding. His graph perfectly depicts what he is saying in the narrative. He is simply describing what can happen when power is reduced to a level that puts the airplane behind the power curve (minimum velocity for thrust) before allowing it to accelerate. This is a scenario he creates by reducing power as he arrives at target altitude rather than letting the aircraft accelerate before reducing power.  

As thrust drops, the min velocity and max velocity for a given thrust get closer and closer until they meet at absolute ceiling for a given thrust.  You don’t need to climb to 15,000’ to demonstrate this, you could do it at 5,000’ by doing a reduced power climb so that the airplane is just climbing at say 100fpm at Vy, then level at the target altitude and immediately reduce power another 10% before the plane has accelerated. 

The whole paper can be summarized by saying - at low thrust levels the spread between minimum and maximum velocities narrows. Reducing thrust to a level with a minimum velocity in the vicinity of climb speed may result in a condition where the aircraft is behind the power curve and incapable of accelerating at the reduced thrust level.

 

 

Well, I think you will be surprised to know we are in violent agreement on most of this!  You actually read the paper and got his point!  We are going to have to agree to disagree on the "academic navel gazing" value and, I suspect, the definition of "The Step", however:D

The fact that this issue arises at 'edge' cases is exactly why I think he wrote the paper (he even says you have to "hunt" for it), and it is a valuable paper to read and understand.  At high DA situations I think you can find yourself at an insufficient speed to accelerate to proper cruise without realizing it (turbulence, airspeed errors, claiming a bit steeper than you thought, for example).  To me that is why the practice of descending into your cruise altitude became common (especially with earlier, underpowered, aircraft as he describes) and the term "The Step" was coined.  While there are many analogs with boating and aviation, trying to force a term to be synonymous for both is sometimes inaccurate.  I'm sure others are going to disagree with Dr. Roger's using this definition, but I'm not one of them!

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3 hours ago, MikeOH said:

Well, I think you will be surprised to know we are in violent agreement on most of this!  You actually read the paper and got his point!  We are going to have to agree to disagree on the "academic navel gazing" value and, I suspect, the definition of "The Step", however:D

The fact that this issue arises at 'edge' cases is exactly why I think he wrote the paper (he even says you have to "hunt" for it), and it is a valuable paper to read and understand.  At high DA situations I think you can find yourself at an insufficient speed to accelerate to proper cruise without realizing it (turbulence, airspeed errors, claiming a bit steeper than you thought, for example).  To me that is why the practice of descending into your cruise altitude became common (especially with earlier, underpowered, aircraft as he describes) and the term "The Step" was coined.  While there are many analogs with boating and aviation, trying to force a term to be synonymous for both is sometimes inaccurate.  I'm sure others are going to disagree with Dr. Roger's using this definition, but I'm not one of them!

Fair enough. I disagree that what he is describing is “the step”.  If one has sufficient power reserve to over shoot and then descend to cruise altitude, one has sufficient power reserve to accelerate to cruise. Whether it’s the best use of resources, I can’t say.  To be clear, I am not suggesting that using gravity to accelerate is a bad idea. On the contrary, I think it’s a fine idea, but it’s not getting on “the step”. 

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3 hours ago, Shadrach said:

Fair enough. I disagree that what he is describing is “the step”.  If one has sufficient power reserve to over shoot and then descend to cruise altitude, one has sufficient power reserve to accelerate to cruise. Whether it’s the best use of resources, I can’t say.  To be clear, I am not suggesting that using gravity to accelerate is a bad idea. On the contrary, I think it’s a fine idea, but it’s not getting on “the step”. 

Dr. Rogers is defining "the step" that way with his description.  I think it is logical.  And, I would say that you have enough power to overshoot your desired altitude, you are just operating below the speed that would allow you to accelerate if you merely directly level off.

It would seem that you, and others, want to define "the step" as some mythical creature that is unobtainable without defying the laws of physics; thus, not real.  Doesn't seem logical, to me:D

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5 minutes ago, MikeOH said:

Dr. Rogers is defining "the step" that way with his description.  I think it is logical.  And, I would say that you have enough power to overshoot your desired altitude, you are just operating below the speed that would allow you to accelerate if you merely directly level off.

It would seem that you, and others, want to define "the step" as some mythical creature that is unobtainable without defying the laws of physics; thus, not real.  Doesn't seem logical, to me:D

I think the step is mythical. It’s conceivable to me that something like it may exist above absolute ceiling. Which is to say that if the hand of God were able to lift your airplane above its absolute ceiling and let it gain speed in the descent, it may be able to sustain flight at a higher altitude and at a greater speed than it would attain climbing under its own power. It will take someone smarter me to calculate whether that is true.

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