Flying over square
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knox
with all due respect, there are not lots of opinions at all.
There always seems to be facts and evidence based operations, and OWT's.
As for a thread on LOP v ROP
that will degenerate for sure, but let me say this, the lower case v in a title suggests one is opposed to the other, like Qld v NSW in a sport. One is opposed to the other scoring more points.
LOP is not opposed to ROP. ROP operations are perfectly valid and safe to do so provided they are conducted properly. Same for LOP ops. Heck ALL my takeoff and climbs are done ROP, and once climbing into the upper levels you are chasing best power and using a ROP setting that would not be wise at sea level. I often use ROP above 10'000. LOP is just more fuel efficient and kinder on your engine than running 100-200 ROP for not much speed loss.
Grasshopper you have much learning ahead of you!
with all due respect, there are not lots of opinions at all.
There always seems to be facts and evidence based operations, and OWT's.
As for a thread on LOP v ROP
that will degenerate for sure, but let me say this, the lower case v in a title suggests one is opposed to the other, like Qld v NSW in a sport. One is opposed to the other scoring more points.LOP is not opposed to ROP. ROP operations are perfectly valid and safe to do so provided they are conducted properly. Same for LOP ops. Heck ALL my takeoff and climbs are done ROP, and once climbing into the upper levels you are chasing best power and using a ROP setting that would not be wise at sea level. I often use ROP above 10'000. LOP is just more fuel efficient and kinder on your engine than running 100-200 ROP for not much speed loss.
Grasshopper you have much learning ahead of you!
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Yes, many OWTs and myths have featured in this thread.
One that has bobbed it head up, but not been addressed is the one about the act of "increasing pitch" on the prop on final approach which then "increases drag" and helps you to slow down.
There is a widespread myth about the effects of increasing prop RPM on final approach. I have heard some pilots express the view that the whole reason for increasing the prop RPM is to slow you down (!).
Some pilots seem to think that, because you are driving the blades to their fine pitch stops, this then causes drag - in the rearwards direction - which then causes the aircraft to decelerate.
To these pilots, the obvious question is: so what happens on takeoff, when the blades are again on the fine pitch stops (for the early stages of the takeoff, at least). Is the prop again causing drag, reducing the acceleration?
It must be clarified at this stage that the kind of "drag" we are talking about here is the drag that is acting in the direction opposite to that of the propeller thrust force. I shall refer to this drag as "thrust-opposing drag". It has the same effect on the aircraft as skin friction and induced drag.
A prop cannot produce thrust and thrust-opposing drag at the same time!
Yes, there is the induced drag that the prop blades produce, but the direction of that drag is such that, rather than opposing the aircraft forward motion, it opposes the prop rotation and creates the torque force that must be balanced by the engine torque.
But we are not talking about that drag; we are talking about the thrust-opposing drag that is sometimes provided by the prop(s).
As it turns out, there is an element of truth to the OWT which says that "increasing prop RPM on final slows you down".
Sometimes, increasing prop RPM will indeed cause the prop to commence generating thrust-opposing drag.
And sometimes not. It depends on whether the torque has gone negative or not.
Increasing the prop RPM causes a reduction in torque. If the engine torque prior to the reduction was a small positive value, then the reduction can be enough to cause the resultant to be negative.
If the resultant torque is negative, then the prop will be generating no thrust but rather, thrust-opposing drag. This situation is also known as "back-driving", "discing", "windmilling" and plain old "negative torque".
The key ingredient to this outcome was the small positive torque that existed before the act of increasing the prop RPM.
So, what this all means is: increasing prop RPM on final may or may not cause an increase in drag.
If an undesired drag from the prop should be experienced at any time - not just while on final approach - the remedy is simple: just increase the torque until it returns to a positive value.
To do that, just push the throttle lever forward a touch! If a turboprop, just push the power lever forward a touch!
Those levers are part of a set of controls that set the engine torque. The other part of that set are the prop RPM levers. We knew that didn't we?
One that has bobbed it head up, but not been addressed is the one about the act of "increasing pitch" on the prop on final approach which then "increases drag" and helps you to slow down.
There is a widespread myth about the effects of increasing prop RPM on final approach. I have heard some pilots express the view that the whole reason for increasing the prop RPM is to slow you down (!).
Some pilots seem to think that, because you are driving the blades to their fine pitch stops, this then causes drag - in the rearwards direction - which then causes the aircraft to decelerate.
To these pilots, the obvious question is: so what happens on takeoff, when the blades are again on the fine pitch stops (for the early stages of the takeoff, at least). Is the prop again causing drag, reducing the acceleration?
It must be clarified at this stage that the kind of "drag" we are talking about here is the drag that is acting in the direction opposite to that of the propeller thrust force. I shall refer to this drag as "thrust-opposing drag". It has the same effect on the aircraft as skin friction and induced drag.
The wing produces lift + drag simultaneously, does it not?
Yes, there is the induced drag that the prop blades produce, but the direction of that drag is such that, rather than opposing the aircraft forward motion, it opposes the prop rotation and creates the torque force that must be balanced by the engine torque.
But we are not talking about that drag; we are talking about the thrust-opposing drag that is sometimes provided by the prop(s).
As it turns out, there is an element of truth to the OWT which says that "increasing prop RPM on final slows you down".
Sometimes, increasing prop RPM will indeed cause the prop to commence generating thrust-opposing drag.
And sometimes not. It depends on whether the torque has gone negative or not.
Increasing the prop RPM causes a reduction in torque. If the engine torque prior to the reduction was a small positive value, then the reduction can be enough to cause the resultant to be negative.
If the resultant torque is negative, then the prop will be generating no thrust but rather, thrust-opposing drag. This situation is also known as "back-driving", "discing", "windmilling" and plain old "negative torque".
The key ingredient to this outcome was the small positive torque that existed before the act of increasing the prop RPM.
So, what this all means is: increasing prop RPM on final may or may not cause an increase in drag.
If an undesired drag from the prop should be experienced at any time - not just while on final approach - the remedy is simple: just increase the torque until it returns to a positive value.
To do that, just push the throttle lever forward a touch! If a turboprop, just push the power lever forward a touch!
Those levers are part of a set of controls that set the engine torque. The other part of that set are the prop RPM levers. We knew that didn't we?
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Radial history...
An instructor told me that this mythical rule comes from Radial Engine procedures (non-geared).
There is an abundance of info on the benefits of running Lyco/Conti engines oversquare and LOP.
Check your engine manual.
It will very clearly show (in a table MAP vs RPM vs Alt) the oversquare limits.
There is an abundance of info on the benefits of running Lyco/Conti engines oversquare and LOP.
Check your engine manual.
It will very clearly show (in a table MAP vs RPM vs Alt) the oversquare limits.
FGD135
Maybe I've oversimplified the effect, but was I actually wrong? You do understand that relative airflow changes depending on rpm AND airspeed?
ie. On final and ready to start your T/O roll are WAY different
This was only one part of the reason for setting pitch fine on short final. I see benefit in having the engine ready for a go around if required, especially in the post PPL training environment where the instinctive manipulation of controls in the correct order has not yet developed. More importantly, perusing my collection of flight manuals for finals checks;
Beech;
55 Props low pitch (high rpm)
58 Same
65 Advance to full low pitch at min appch speed
80 Props low pitch
76 Props high rpm
Britten Norman
BN2 props fully fine
Cessna;
172RG Prop high rpm
182 Same
206 Same
208 Prop max
210 Prop high rpm
303 Props high rpm
310 Props full forward
337 Props high rpm
340 Props full forward
401 Props forward
Decathlon Prop full increase rpm
DH8 Condition levers max rpm
Mooney M20 Prop full increase
Partenavia P68 Props full forward
A-viator Condition Levers Max 100% Np
Are we seeing a pattern here?
You are going to have to look hard to find an exception.
It's not an OWT.
Maybe I've oversimplified the effect, but was I actually wrong? You do understand that relative airflow changes depending on rpm AND airspeed?
ie. On final and ready to start your T/O roll are WAY different
This was only one part of the reason for setting pitch fine on short final. I see benefit in having the engine ready for a go around if required, especially in the post PPL training environment where the instinctive manipulation of controls in the correct order has not yet developed. More importantly, perusing my collection of flight manuals for finals checks;
Beech;
55 Props low pitch (high rpm)
58 Same
65 Advance to full low pitch at min appch speed
80 Props low pitch
76 Props high rpm
Britten Norman
BN2 props fully fine
Cessna;
172RG Prop high rpm
182 Same
206 Same
208 Prop max
210 Prop high rpm
303 Props high rpm
310 Props full forward
337 Props high rpm
340 Props full forward
401 Props forward
Decathlon Prop full increase rpm
DH8 Condition levers max rpm
Mooney M20 Prop full increase
Partenavia P68 Props full forward
A-viator Condition Levers Max 100% Np
Are we seeing a pattern here?
You are going to have to look hard to find an exception.
It's not an OWT.
Last edited by MakeItHappenCaptain; 28th Sep 2011 at 15:16.
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Continental.
But i,ll probably get blasted out of the park on this one too.
Engine manufacturers have guide lines, why F with that.
1000,s of hrs below 500 ft. I,m still here. What would i know.
But i,ll probably get blasted out of the park on this one too.
Engine manufacturers have guide lines, why F with that.
1000,s of hrs below 500 ft. I,m still here. What would i know.
Contis? Not as a rule, but Aztec C is the one exception I did find.
Props high cruise rpm
Amplified explanation is to prevent engine overspeed in the event of sudden throttle openings, but this is the only one I've found.
Props high cruise rpm
Amplified explanation is to prevent engine overspeed in the event of sudden throttle openings, but this is the only one I've found.
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Yes the learning never stops in this industry, I'll be a grasshopper for a longtime yet
I'm mainly flying lyc's at the mo and I came across this from the manufacturer
http://www.lycoming.textron.com/support/troubleshooting/resources/SSP700A.pdf
Knox
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Knox, have a thread search for the terms ROP, LOP, lean, etc. There have been some great threads on the matter in the past. Mr Chimbu and Jaba in particular comes to mind as posting some great info on those.
Then of course reading through Pelican's Perch. Then reading it again. Then several more times.
The Lyc/TCM references have lots of good info, but also some bad stuff. I've seen pages where the classic CHT/EGT graph is displayed, sometimes even with 50LOP shown as "best economy", but then a warning about "there be dragons here".
They often state a risk of detonation, overheating, and engine damage. Yet, what is the best measure of engine temperature (and therefore internal pressure)? CHT. Which is shown as dropping of sharply when LOP, to a CHT that would require 200 degrees+ if ROP. But don't take my word for it though, I'm just a faceless internet name. The words of Chimbu and Jaba, etc however, I would trust.
Then of course reading through Pelican's Perch. Then reading it again. Then several more times.
The Lyc/TCM references have lots of good info, but also some bad stuff. I've seen pages where the classic CHT/EGT graph is displayed, sometimes even with 50LOP shown as "best economy", but then a warning about "there be dragons here".
They often state a risk of detonation, overheating, and engine damage. Yet, what is the best measure of engine temperature (and therefore internal pressure)? CHT. Which is shown as dropping of sharply when LOP, to a CHT that would require 200 degrees+ if ROP. But don't take my word for it though, I'm just a faceless internet name. The words of Chimbu and Jaba, etc however, I would trust.
If the APS (Advanced Pilots Seminars) come back to OZ at any stage, be sure to go along.
You can do them on line but it wouldn't be the same.
Or as suggested - Read pelicans perch.
They are a great bunch of presenters and will turn verything you are tought on its ear.
Even had the pleasure of dinner and beers with Braly and Atkinson at Darling Harbour. What a pair of characters.
Of interest is they provide the Operating Handbook for the Curtis Wright radial engine which was run LOP.
As Jaba says - It's not necessarily LOP v ROP. I follow what the APS semimars taught but still run ROP.
You can do them on line but it wouldn't be the same.
Or as suggested - Read pelicans perch.
They are a great bunch of presenters and will turn verything you are tought on its ear.
Even had the pleasure of dinner and beers with Braly and Atkinson at Darling Harbour. What a pair of characters.
Of interest is they provide the Operating Handbook for the Curtis Wright radial engine which was run LOP.
As Jaba says - It's not necessarily LOP v ROP. I follow what the APS semimars taught but still run ROP.
Last edited by rioncentu; 29th Sep 2011 at 00:34.
The 1979 Piper Aztec F that I flew for a while had charts for both square settings such as climb 25"/2500 RPM, cruise at 23"/2300RPPM(which we used), and also charts for over square settings such as cruise of 26"/2400 RPM.
Old timer who flew PA-24's and PA-30's in the 60's, said they always operated them over-square, and always got better than TBO on the engines.
Regarding the max RPM for landing, most of the turbo-props I have flown:
EMB110 props stayed at 91% for Landing,
Beech 90 props at 1700 or 1900 RPM for landing(variation due to various models and if Raisebeck modified etc). Also some of these versions had a requirement in the AFM for the props to be increased to 1900 RPM during an ILS approach.
Beech 200/300 props go up to 1900 RPM for landing for three bladed versions.
Shorts 330, props were placed into climb setting in the event of a go around.
Old timer who flew PA-24's and PA-30's in the 60's, said they always operated them over-square, and always got better than TBO on the engines.
Regarding the max RPM for landing, most of the turbo-props I have flown:
EMB110 props stayed at 91% for Landing,
Beech 90 props at 1700 or 1900 RPM for landing(variation due to various models and if Raisebeck modified etc). Also some of these versions had a requirement in the AFM for the props to be increased to 1900 RPM during an ILS approach.
Beech 200/300 props go up to 1900 RPM for landing for three bladed versions.
Shorts 330, props were placed into climb setting in the event of a go around.
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MIHC
I am not sure anyone said full fine on short final was an OWT of sorts, if I did say that well clearly I am losing the plot. What I did say.....
So if it makes you feel better going full fine on final, well do so, just dont go boring downwind at 120 knots and back to 2700RPM making an almight noise that only winds up the people who leave near to the aerodrome. They get enough on takeoff so halve the number of 2700RPM events
Despite what your instructor once taught you, you can learn a whole new more neighbour friendly and sensible "checklist" that is not dangerous and is "better" in some ways.
I am not sure anyone said full fine on short final was an OWT of sorts, if I did say that well clearly I am losing the plot. What I did say.....
Why not land with the pitch control still set from the cruise. say 2300 RPM. Why not, in the event of a baulked landing, RED/BLUE/BLACK, in about the time you read that, or if you can do all at the same time, who cares. It will not make any difference. Now you are climbing away at full bore max rate.
Despite what your instructor once taught you, you can learn a whole new more neighbour friendly and sensible "checklist" that is not dangerous and is "better" in some ways.
Jabba, that was what I was taught as well, perhaps those old experienced grey haired instructors and CP's know something afterall!!!
Bet not too many operaters of GTSIO-520 get the pilots to shove the prop levers to max on downwind or final?
Bet not too many operaters of GTSIO-520 get the pilots to shove the prop levers to max on downwind or final?
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MIHC,
As Jaba has said, nobody is saying that "prop up" on final is an OWT.
My post was purely to address the myths that surround this practice.
Personally, I bring the prop levers up on final approach (in accordance with the SOP for the type), but I don't do it until the props are already on the fine pitch stops.
How does one know when the props are on the fine pitch stops? Go back and look at post #25 by Lasiorhinus.
As Jaba has said, nobody is saying that "prop up" on final is an OWT.
My post was purely to address the myths that surround this practice.
Personally, I bring the prop levers up on final approach (in accordance with the SOP for the type), but I don't do it until the props are already on the fine pitch stops.
How does one know when the props are on the fine pitch stops? Go back and look at post #25 by Lasiorhinus.
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The angle of attack of the propeller is changing with the RPM change. At high RPM (full fine) the propeller may have a negative angle of attack, and is acting as a big braking disc. When you are in low RPM (full coarse) the opposite happens, there may still be an angle of attack on the blades which produces thrust (or lift).
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One must be really careful with any geared engine not to allow the propellor to drive the engine, i.e. maintain positive manifold pressure and enough blade angle to always load the engine, on big radials this is really important as it gets serious expensive very quickly if you miss handle them !!
R1820 on final 1800 rpm 20 inches, forget the fine pitch bit close the throttle as you flare and the propellor comes back to fine as the power comes off during the roll out.
Even the non geared R985 Pratt is same , don't let the prop drive the engine, the counter weights get really unhappy.
Round engines require finesse, absolutely reliable if you treat them well.
Geared Continental is similar hold coarse until the round out power reduction.
R1820 on final 1800 rpm 20 inches, forget the fine pitch bit close the throttle as you flare and the propellor comes back to fine as the power comes off during the roll out.
Even the non geared R985 Pratt is same , don't let the prop drive the engine, the counter weights get really unhappy.
Round engines require finesse, absolutely reliable if you treat them well.
Geared Continental is similar hold coarse until the round out power reduction.
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Having read all of this, given it some consideration, read a few more bits and pieces, I thought it was time I posted something a little more serious.
To me, not going fully fine on short final has ants on it. (I am going to restrict my reply to Flat non geared Piston engine types)
Many pilots are ham fisted and just ram the pitch lever forward. If you have a bit of power on still, the chance of beating the governor are huge. You don't whack full back stick to rotate, so why treat a condition lever different?
I thought about what was being suggested with leaving the prop in the cruise setting for landing and almost thought it wasn't a bad idea, and that it could do no harm. No harm to the engine, but a whole load of harm when needed. It isn't going to be the short period of over square that does the damage, its going to be the simple lack of performance, and i think that engine damage is going to be the least of the worries. I thought about it long enough that I thought I might go and fly some practice approaches with that set-up and see what eventuates(at a safe height)
Then reality hit me.....the CSU equipped type I fly the most, would kill you in this configuration...lord knows its killed enough when being flown by the book.
PA-32-300!
The reality phase was reflecting back on a few flights and recalling the power used on some approaches. One in particular in my memory was my first time into Great Lakes. Unfamiliar strip, unexpected sink, first approach to that kind of gradient, almost max weight............ 2600 rpm...yes thats right almost full power
Do I want to be in an aeroplane that suffers from reverse command, with cruise RPM set on short final, and power not available the moment i want it? NO not yesterday, today, tomorrow or EVER!. It is bad enough that you have to pre-empt your power needs and wind it up early, than to be dealing with having to go for a second lever to get the power you need...or worse forgetting its set for cruise.
Sorry but it just seems a bit d0pey to me to give yourself something extra to do in a pressure situation, when you can pre-empt that situation by setting the aeroplane up for what you may need BEFORE you need it.
Having limited time in a 210 (the only comparable type so far mentioned) I cannot really comment on the comparison, other to say, that the 210 would probably give you the time to react and get the prop lever forward, but a chog 6 won't!. You are already on the back of the drag curve, so the chog 6 happily decelerates. Really not a place you want to be in.
-------------------------------------------------------------------
Mixture management.
I concur with not touching the mixture for the begining of the descent.
In an injected/csu equipped, I like to have the mix at roughly 75% forward when i level off for the circuit(with a keen eye on the cht/egt), and go for 100% at the same time I go fully fine on the prop....another thing i don't have to deal with in the event of a go-around. Once on the ground I'll wind the mixture back again as part of my post landing clean-up to avoid fouling. I find in PXG, 6 turns works just fine.
----------------------------------------------------------------------
At the end of the day, it does come down to your POH, anything else is the realm of test pilots.....hence they get paid the big bucks and get to write the stories that tell you how to fly it.
Leaving pitch in the cruise setting for landing to me is a NWT.....and if you have flown the chog 6, then you would know the circuit setting is different to the cruise in both MAP and RPM.
Cheers Big Ears
To me, not going fully fine on short final has ants on it. (I am going to restrict my reply to Flat non geared Piston engine types)
Many pilots are ham fisted and just ram the pitch lever forward. If you have a bit of power on still, the chance of beating the governor are huge. You don't whack full back stick to rotate, so why treat a condition lever different?
I thought about what was being suggested with leaving the prop in the cruise setting for landing and almost thought it wasn't a bad idea, and that it could do no harm. No harm to the engine, but a whole load of harm when needed. It isn't going to be the short period of over square that does the damage, its going to be the simple lack of performance, and i think that engine damage is going to be the least of the worries. I thought about it long enough that I thought I might go and fly some practice approaches with that set-up and see what eventuates(at a safe height)
Then reality hit me.....the CSU equipped type I fly the most, would kill you in this configuration...lord knows its killed enough when being flown by the book.
PA-32-300!
The reality phase was reflecting back on a few flights and recalling the power used on some approaches. One in particular in my memory was my first time into Great Lakes. Unfamiliar strip, unexpected sink, first approach to that kind of gradient, almost max weight............ 2600 rpm...yes thats right almost full power
Do I want to be in an aeroplane that suffers from reverse command, with cruise RPM set on short final, and power not available the moment i want it? NO not yesterday, today, tomorrow or EVER!. It is bad enough that you have to pre-empt your power needs and wind it up early, than to be dealing with having to go for a second lever to get the power you need...or worse forgetting its set for cruise.
Sorry but it just seems a bit d0pey to me to give yourself something extra to do in a pressure situation, when you can pre-empt that situation by setting the aeroplane up for what you may need BEFORE you need it.
Having limited time in a 210 (the only comparable type so far mentioned) I cannot really comment on the comparison, other to say, that the 210 would probably give you the time to react and get the prop lever forward, but a chog 6 won't!. You are already on the back of the drag curve, so the chog 6 happily decelerates. Really not a place you want to be in.
-------------------------------------------------------------------
Mixture management.
I concur with not touching the mixture for the begining of the descent.
In an injected/csu equipped, I like to have the mix at roughly 75% forward when i level off for the circuit(with a keen eye on the cht/egt), and go for 100% at the same time I go fully fine on the prop....another thing i don't have to deal with in the event of a go-around. Once on the ground I'll wind the mixture back again as part of my post landing clean-up to avoid fouling. I find in PXG, 6 turns works just fine.
----------------------------------------------------------------------
At the end of the day, it does come down to your POH, anything else is the realm of test pilots.....hence they get paid the big bucks and get to write the stories that tell you how to fly it.
Leaving pitch in the cruise setting for landing to me is a NWT.....and if you have flown the chog 6, then you would know the circuit setting is different to the cruise in both MAP and RPM.
Cheers Big Ears
