Flying over square
our Casa/caa/dot produced performance charts were pretty much the best in the world! but some legal muppet decided, that as they were not not produced by the manufacturer that CASA might get sued!
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I am surprised not more have mentioned the high MAP/low RPM settings introduced by Lindberg as posted by PLovett (#86). I remember watching a video of his techniques years ago but quality supporting material is not always easy to find.
High MAP & Low RPM, Advantages, Reduced Fuel Consumption, Long Engine Life, Running Aircraft Engines Over Square, Airplanes - EAI
In my time, flying schools with CSU SE/ME aircraft would not allow oversquare settings despite what was in the POH. Ignorance or caution, it didn't matter; they didn't allow it. Is this still the case today? With a few exceptions, I believe flying schools typically saw their pilots as not being mechanically aware; a sign of the times back then and probably more so today.
I wonder what the majority of round engine drivers think; oversquare: par for course perchance?
High MAP & Low RPM, Advantages, Reduced Fuel Consumption, Long Engine Life, Running Aircraft Engines Over Square, Airplanes - EAI
In my time, flying schools with CSU SE/ME aircraft would not allow oversquare settings despite what was in the POH. Ignorance or caution, it didn't matter; they didn't allow it. Is this still the case today? With a few exceptions, I believe flying schools typically saw their pilots as not being mechanically aware; a sign of the times back then and probably more so today.
I wonder what the majority of round engine drivers think; oversquare: par for course perchance?
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I consider myself a pretty experienced GA pilot. I was always taught and always teach to NEVER fly over square. It is the same as driving your car up a hill at low speed in a high gear. It causes detonation and does serious damage to your engine 
. I fell sorry for all your bosses who have to pay the maintenance bill!
. I fell sorry for all your bosses who have to pay the maintenance bill!
Grandpa Aerotart
Well PA38 it might surprise you to know that MOST of the pilots advocating over square operations, and Lean Of Peak EGT etc, on this thread are actually aircraft owners. Some have experience measured in 10s of 1000s of hrs spread across the entire spectrum of piston powered aircraft types.
WE pay for the maintenance on our OWN aircraft.
With all due respect, a thousand hours, or even 50000hrs, instructing in a PA38 does not add up to 'a pretty experienced GA pilot'...its 1 hour repeated 5000 times. Your comments demonstrate ignorance married to the unshakeable self assurance of youth.
Wotcha gonna do if one day you find yourself a PA31Captain?
WE pay for the maintenance on our OWN aircraft.
With all due respect, a thousand hours, or even 50000hrs, instructing in a PA38 does not add up to 'a pretty experienced GA pilot'...its 1 hour repeated 5000 times. Your comments demonstrate ignorance married to the unshakeable self assurance of youth.
Wotcha gonna do if one day you find yourself a PA31Captain?
Last edited by Chimbu chuckles; 10th Oct 2011 at 23:16.
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Surely this is a wind up
You say experienced, so 500 hours of doing the same misguided thing is still experienced, just like 4000 hours of doing the same misguided things, now you are really very experienced.
In all of your experience have you ever bothered to take the time and effort, maybe a hundred hours or more to research and learn. What's more have you ever flown with an EDM or EMS and truly tested your research?
This thread alone is not exactly the best education source alone, but had you read it through from the start, realized who exactly was behind the posts and what their experience is, you might start off by asking some good questions.
I see while editing to add these photos, the brains of the operation have arrived, so now would be a great time to look listen and learn, chances are I will learn some more too!
So...here are a few pics, please tell me what you think, Inlet or Exhaust valves? Good shape or not? How have they been run for hundreds of hours? Undersquare and ROP or Oversquare and LOP?
You say experienced, so 500 hours of doing the same misguided thing is still experienced, just like 4000 hours of doing the same misguided things, now you are really very experienced.
In all of your experience have you ever bothered to take the time and effort, maybe a hundred hours or more to research and learn. What's more have you ever flown with an EDM or EMS and truly tested your research?
This thread alone is not exactly the best education source alone, but had you read it through from the start, realized who exactly was behind the posts and what their experience is, you might start off by asking some good questions.
I see while editing to add these photos, the brains of the operation have arrived, so now would be a great time to look listen and learn, chances are I will learn some more too!
So...here are a few pics, please tell me what you think, Inlet or Exhaust valves? Good shape or not? How have they been run for hundreds of hours? Undersquare and ROP or Oversquare and LOP?
Grandpa Aerotart
PA38 Captain full fine is indeed 1st gear...which is why we take off in full fine...then we climb in 2nd gear, on many aircraft you can actually leave it in 1st for the climb too and that can make perfect sense.
But usually we climb in 2nd and cruise in 3rd or 4th gear...sometimes we might even use overdrive (5th gear).
Or do you roar along the highway flogging your old banger in 1st all the time...maybe you drive an automatic?
Let me ask you a couple of questions - as an instructor you should blitz them.
1/. What does MP indicate?
2/. What else changes when you change prop RPM?
3/. What is the ONLY control in the cockpit that is capable of regulating engine power between 0% and 100%?
But usually we climb in 2nd and cruise in 3rd or 4th gear...sometimes we might even use overdrive (5th gear).
Or do you roar along the highway flogging your old banger in 1st all the time...maybe you drive an automatic?
Let me ask you a couple of questions - as an instructor you should blitz them.
1/. What does MP indicate?
2/. What else changes when you change prop RPM?
3/. What is the ONLY control in the cockpit that is capable of regulating engine power between 0% and 100%?
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1/. What does MP indicate? MP gauge is simply a pressure altitude meter. That is why when we are on the ground it indicates atmospheric pressure(QNH).
2/. What else changes when you change prop RPM? The experimental mean pitch will change. For basic forces on a prop. Lift, drag, weight, thrust, total reaction. A fixed pitched prop only has one best efficiency and therefore MP will always increase with an increase in altitude.
3/. What is the ONLY control in the cockpit that is capable of regulating engine power between 0% and 100%? Magnetos. With only one mag working, fuel burn rate will be less and power will be below 100%. With both mags off power will be relatively lower depending on altitude and airspeed. Some operators recommend only using 2 mags for takeoff and switching one off when in the cruise.
Ok smart guy, i have a few Q's for you.
1. If we have a hung start, what is the easiest way to remedy it?
2. When operating the PT6, what is the most fuel efficient stage of flight?
2/. What else changes when you change prop RPM? The experimental mean pitch will change. For basic forces on a prop. Lift, drag, weight, thrust, total reaction. A fixed pitched prop only has one best efficiency and therefore MP will always increase with an increase in altitude.
3/. What is the ONLY control in the cockpit that is capable of regulating engine power between 0% and 100%? Magnetos. With only one mag working, fuel burn rate will be less and power will be below 100%. With both mags off power will be relatively lower depending on altitude and airspeed. Some operators recommend only using 2 mags for takeoff and switching one off when in the cruise.
Ok smart guy, i have a few Q's for you.
1. If we have a hung start, what is the easiest way to remedy it?
2. When operating the PT6, what is the most fuel efficient stage of flight?
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Round engines ALWAYS oversquare
The following is a chart for the IO-720, but you'll find the engine you fly not greatly different. You can see that at 29.5" MAP you are permitted to operate between 2650 and 2300 RPM. Of course horsepower suffers, dropping from 400 to 350. At 1800 RPM you can operate up to 25" MAP max continuous.
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1. The MP gauge is simply a pressure altitude metre. That is why when parked on the ground it will show the atmospheric pressure(QNH).
2. When prop rpm is change the experimental mean pitch will change. Remember the four forces on a prop - lift, drag, weight, thrust, total reaction. This is not the case for reverse pitch however. That is why when we gain altitude with a fixed pitch prop the MP will rise but in a variable pitch prop it will remain constant below 10,000ft.
3. Magnetos are the only control that regulates the power. With both mags on we get 100% power or more(up to 110% depending on the day). When only one mag is on the power will be 100% but detonation can occur in diesel engines. With both mags off power will be considerably less. Some operators recommend running on both mags for takeoff but only one mag in the cruise to reduce SFC. (not recommended for diesel engines).
2. When prop rpm is change the experimental mean pitch will change. Remember the four forces on a prop - lift, drag, weight, thrust, total reaction. This is not the case for reverse pitch however. That is why when we gain altitude with a fixed pitch prop the MP will rise but in a variable pitch prop it will remain constant below 10,000ft.
3. Magnetos are the only control that regulates the power. With both mags on we get 100% power or more(up to 110% depending on the day). When only one mag is on the power will be 100% but detonation can occur in diesel engines. With both mags off power will be considerably less. Some operators recommend running on both mags for takeoff but only one mag in the cruise to reduce SFC. (not recommended for diesel engines).
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surely pa38 just came along for sh*ts and giggles.... i read his reply elsewhere and it was actually good.
if not, pa38, you should 1st, put your bong back in the cupboard, 2nd read this thread in its entirety....ALL of it! and some of the articles linked in responses.
T28D.....3!!!!! do you have any hair left???
Cheers
Jas
if not, pa38, you should 1st, put your bong back in the cupboard, 2nd read this thread in its entirety....ALL of it! and some of the articles linked in responses.
T28D.....3!!!!! do you have any hair left???
Cheers
Jas
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Ohhh dear........... T28D and I will bang heads on many topics, and I am sure we are at odds on many more, but it seems that we do have a common appreciation for the fact based science of engine operation.
I have to say I can't agree more 
Now PA38.......Chimbu asked a bunch of serious questions, the most serious one and the one most understood is the one you took the piss out of.
Have a go at Q3 would you, or we might stop taking pity on you and call you a Troll....which will usually end up in you being banned. How sad that would be
PS: Can you please tell me all about those valve pictures?
Wow 38 I own 3 round engines, and I must admit in 50 years of operations I never knew all that !!
You are a legend, please stop instructing .
You are a legend, please stop instructing .
Now PA38.......Chimbu asked a bunch of serious questions, the most serious one and the one most understood is the one you took the piss out of.
Have a go at Q3 would you, or we might stop taking pity on you and call you a Troll....which will usually end up in you being banned. How sad that would be
PS: Can you please tell me all about those valve pictures?
Last edited by Jabawocky; 11th Oct 2011 at 04:52.
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Jas T28D.....3!!!!! do you have any hair left??? Sure do I love round engines.
One of the real misunderstandings about round engines is they are said to be unreliable.
Absolute poppycock, once a round engine is running in steady state they are remarkably reliable, fact is if you consider the firing order 1,3,5,7,9,2,4,6,8 it becomes obvious there is less stress on the whole engine than say a horizontally opposed engine.
They fire sequentially around the master rod so the forces are not across the engine rather tangential to the output in simple terms.
Most big radials have quite sophisticated magneto systems which control any pre ignition.
My Wright 1820 is 52.5 inches 2700 rpm at takeoff developing 1425 HP, climbs at 36 inches 2400 rpm, cruise 30 inches 2000 rpm and coming home 1700 rpm 20 Inches
Oversquare all the way.
Likewise the Pratt 985 are 36 inches at 2300 rpm for takeoff, climb 33inches at 2100 rpm, cruise 29 inches at 1850 rpm and come home 20 inches at 1700 rpm.
Never a hint of detonation, why one must wonder ?? well because it is well within the thermal limits of the engine and there is no internal overcompressed mixture or overload on the engine.
BTW the Auto Mixture on the Wright 1820 is set LOP as they all are and I get a really nice soft grey exhaust colour, CHT 150 degrees C engine happy and leakdown pressures all above 75/80 .
So 38 what am I doing wrong with my engine handling ??
One of the real misunderstandings about round engines is they are said to be unreliable.
Absolute poppycock, once a round engine is running in steady state they are remarkably reliable, fact is if you consider the firing order 1,3,5,7,9,2,4,6,8 it becomes obvious there is less stress on the whole engine than say a horizontally opposed engine.
They fire sequentially around the master rod so the forces are not across the engine rather tangential to the output in simple terms.
Most big radials have quite sophisticated magneto systems which control any pre ignition.
My Wright 1820 is 52.5 inches 2700 rpm at takeoff developing 1425 HP, climbs at 36 inches 2400 rpm, cruise 30 inches 2000 rpm and coming home 1700 rpm 20 Inches
Oversquare all the way.
Likewise the Pratt 985 are 36 inches at 2300 rpm for takeoff, climb 33inches at 2100 rpm, cruise 29 inches at 1850 rpm and come home 20 inches at 1700 rpm.
Never a hint of detonation, why one must wonder ?? well because it is well within the thermal limits of the engine and there is no internal overcompressed mixture or overload on the engine.
BTW the Auto Mixture on the Wright 1820 is set LOP as they all are and I get a really nice soft grey exhaust colour, CHT 150 degrees C engine happy and leakdown pressures all above 75/80 .
So 38 what am I doing wrong with my engine handling ??
Grandpa Aerotart
Well THAT is a relief - relax T28...one thing our mate is NOT is a Flying Instructor.
PA38 'captain' I am sure you have heard the expression 'Google is your friend'...in your case its simply not true.
On the outside chance you're (maybe - BIG maybe) a student pilot, not merely a troll, I will correct your homework.
1/. Reasonable attempt - at least you didn't suggest it indicated 'power'. A knowledgeable pilot would have answered 'The Manifold Pressure Gauge measures Air Pressure in the induction manifold downstream of the throttle butterfly. On the ground with the engine shut down it should indicate field barometric pressure.
2/. Fail. A knowledgeable pilot would have answered (within the context of this thread) 'when propeller rpm is varied the speed of the engine driven fuel pump is also varied'. For FULL marks he might also mention that, particularly in a direct drive/non geared engine, the speed of the pistons sucking air into the cylinders is also varied thus, together with the changed fuel pump speed, varying the fuel/air ratio. Lower RPM with everything else held constant LEANS the mixture and higher RPM en-richens the mixture.
3/. UTTER fail. A knowledgeable pilot would have answered 'The mixture control is the only control that can vary power through the range 0% (idle cutoff) to 100% (somewhat leaner than full rich).'
PA38 'captain' I am sure you have heard the expression 'Google is your friend'...in your case its simply not true.
1. The MP gauge is simply a pressure altitude metre. That is why when parked on the ground it will show the atmospheric pressure(QNH).
2. When prop rpm is change the experimental mean pitch will change. Remember the four forces on a prop - lift, drag, weight, thrust, total reaction. This is not the case for reverse pitch however. That is why when we gain altitude with a fixed pitch prop the MP will rise but in a variable pitch prop it will remain constant below 10,000ft.
3. Magnetos are the only control that regulates the power. With both mags on we get 100% power or more(up to 110% depending on the day). When only one mag is on the power will be 100% but detonation can occur in diesel engines. With both mags off power will be considerably less. Some operators recommend running on both mags for takeoff but only one mag in the cruise to reduce SFC. (not recommended for diesel engines).
2. When prop rpm is change the experimental mean pitch will change. Remember the four forces on a prop - lift, drag, weight, thrust, total reaction. This is not the case for reverse pitch however. That is why when we gain altitude with a fixed pitch prop the MP will rise but in a variable pitch prop it will remain constant below 10,000ft.
3. Magnetos are the only control that regulates the power. With both mags on we get 100% power or more(up to 110% depending on the day). When only one mag is on the power will be 100% but detonation can occur in diesel engines. With both mags off power will be considerably less. Some operators recommend running on both mags for takeoff but only one mag in the cruise to reduce SFC. (not recommended for diesel engines).
1/. Reasonable attempt - at least you didn't suggest it indicated 'power'. A knowledgeable pilot would have answered 'The Manifold Pressure Gauge measures Air Pressure in the induction manifold downstream of the throttle butterfly. On the ground with the engine shut down it should indicate field barometric pressure.
2/. Fail. A knowledgeable pilot would have answered (within the context of this thread) 'when propeller rpm is varied the speed of the engine driven fuel pump is also varied'. For FULL marks he might also mention that, particularly in a direct drive/non geared engine, the speed of the pistons sucking air into the cylinders is also varied thus, together with the changed fuel pump speed, varying the fuel/air ratio. Lower RPM with everything else held constant LEANS the mixture and higher RPM en-richens the mixture.
3/. UTTER fail. A knowledgeable pilot would have answered 'The mixture control is the only control that can vary power through the range 0% (idle cutoff) to 100% (somewhat leaner than full rich).'