RPM and MP
- Thread starter Coney
- Start date
MDPilot
Well-Known Member
Try reading Deakin's columns on the subject:
Manifold Pressure Sucks!
Those Marvelous Props!
Mixture Magic!
and
Putting It All Together!
Manifold Pressure Sucks!
Those Marvelous Props!
Mixture Magic!
and
Putting It All Together!
Grabo172
Well-Known Member
[ QUOTE ]
Okay. I just want to understand the relationship between throttle and prop control. When I adjust the throttle, the RPM and the MP change. But I thought the throttle controlled the MP and the prop knob (blue) controls the RPM. Hmmmm...
[/ QUOTE ]
The Throttle will control the MP and RPM will stay constant to only the extent where the engine isn't making enough power to keep the RPMs up at the setting the throttle contol is trying to maintain.
In other words, if there isn't enough oil pressure to maintain the piston at a certain position against the spring pressure, the RPM will change.
When at cruising power, smal adjustments in MP (say 19"-full throttle in a 172 RG or 182) shouldn't cause the RPM to change more that 10-20 RPM. If it is, you should have a mechanic check out the propeller control system.
Okay. I just want to understand the relationship between throttle and prop control. When I adjust the throttle, the RPM and the MP change. But I thought the throttle controlled the MP and the prop knob (blue) controls the RPM. Hmmmm...
[/ QUOTE ]
The Throttle will control the MP and RPM will stay constant to only the extent where the engine isn't making enough power to keep the RPMs up at the setting the throttle contol is trying to maintain.
In other words, if there isn't enough oil pressure to maintain the piston at a certain position against the spring pressure, the RPM will change.
When at cruising power, smal adjustments in MP (say 19"-full throttle in a 172 RG or 182) shouldn't cause the RPM to change more that 10-20 RPM. If it is, you should have a mechanic check out the propeller control system.
Looking4Lower
New Member
[ QUOTE ]
Try reading Deakin's columns on the subject:
Manifold Pressure Sucks!
Those Marvelous Props!
Mixture Magic!
and
Putting It All Together!
[/ QUOTE ]
I second that! These articles are pure genius - they clarified many mysteries about MP/RPM for me.
Try reading Deakin's columns on the subject:
Manifold Pressure Sucks!
Those Marvelous Props!
Mixture Magic!
and
Putting It All Together!
[/ QUOTE ]
I second that! These articles are pure genius - they clarified many mysteries about MP/RPM for me.
USMCmech
Well-Known Member
RPM = how fast the eingine is turning
MP = how hard the engine is working
Think of the prop control as the transmition of a car. If you try to take off with a low RPM setting the plane won't accelerate (trust me I know!) but a lower RPM is more eficient at cruise.
Below a certian throttle setting the prop just goes to low pitch/high RMP, so the RMP will change when you move the throttle.
PS, definatly read those articles by John Deakin, they're the best explainations I've seen anywhere.
MP = how hard the engine is working
Think of the prop control as the transmition of a car. If you try to take off with a low RPM setting the plane won't accelerate (trust me I know!) but a lower RPM is more eficient at cruise.
Below a certian throttle setting the prop just goes to low pitch/high RMP, so the RMP will change when you move the throttle.
PS, definatly read those articles by John Deakin, they're the best explainations I've seen anywhere.
ananoman
New Member
[ QUOTE ]
When I adjust the throttle, the RPM and the MP change. But I thought the throttle controlled the MP and the prop knob (blue) controls the RPM. Hmmmm...
[/ QUOTE ]
I can't add anything to what Deakin has already said, but at very low power settings like when the engine is at idle or you are taxiing, the prop is at its low pitch stop. The governor has no effect at these power settings (it can't increase the RPM because the prop is at its full low pitch stop and it cannot decrease the rpm because it is usually not possible to set a very low rpm below about 1500 on most small engines). It is usually possible to move the prop control from full increase to full decrease at idle without changing engine RPM (go ahead and try it, just go slow and stop pulling if you hear a decrease in RPM and whatever you do don't go into the feather detent on a twin).
When I adjust the throttle, the RPM and the MP change. But I thought the throttle controlled the MP and the prop knob (blue) controls the RPM. Hmmmm...
[/ QUOTE ]
I can't add anything to what Deakin has already said, but at very low power settings like when the engine is at idle or you are taxiing, the prop is at its low pitch stop. The governor has no effect at these power settings (it can't increase the RPM because the prop is at its full low pitch stop and it cannot decrease the rpm because it is usually not possible to set a very low rpm below about 1500 on most small engines). It is usually possible to move the prop control from full increase to full decrease at idle without changing engine RPM (go ahead and try it, just go slow and stop pulling if you hear a decrease in RPM and whatever you do don't go into the feather detent on a twin).
[ QUOTE ]
Try reading Deakin's columns on the subject:
Manifold Pressure Sucks!
Those Marvelous Props!
Mixture Magic!
and
Putting It All Together!
[/ QUOTE ]
I had the pleasure of meeting him briefly at Camarillo Airport after havnig watched him take a zero around the pattern a few times. After having read a lot about the C-46, getting to see them in operation here in AK was very cool. It would be fun to fly one of those at some point, in fact, even got an offer for a ride-along from one operator up that I seriously need to take someone up on.
Also, bought his book, and while good, basically 90% of it is straight from his column's on AvWeb. I'm very interested in reading the book he's promised specifically on piston engine management. Anyone here have any thoughts on the whole LOP concept?
Try reading Deakin's columns on the subject:
Manifold Pressure Sucks!
Those Marvelous Props!
Mixture Magic!
and
Putting It All Together!
[/ QUOTE ]
I had the pleasure of meeting him briefly at Camarillo Airport after havnig watched him take a zero around the pattern a few times. After having read a lot about the C-46, getting to see them in operation here in AK was very cool. It would be fun to fly one of those at some point, in fact, even got an offer for a ride-along from one operator up that I seriously need to take someone up on.
Also, bought his book, and while good, basically 90% of it is straight from his column's on AvWeb. I'm very interested in reading the book he's promised specifically on piston engine management. Anyone here have any thoughts on the whole LOP concept?
seagull
Well-Known Member
John Deakin. Now there's a name I don't see too often anymore, although I think he might still hang at www.avsig.com, I haven't seen him post there in a while. Quite the character, that's for sure, (in a good way), used to banter with him often!
USMCmech
Well-Known Member
[ QUOTE ]
Anyone here have any thoughts on the whole LOP concept?
[/ QUOTE ]
Flying with the throttle wide open and reducing power by leaning out the mixture well past peak EGT is actually a very old procedure. Virtually all of the old piston engine airliners were flown this way.
First off, a brief lesson for any newbies.
The mixture of an airplane engine is controled manually by the pilot. On airplanes with a constant speed propeller the way you know if the mixture is correct is by watching the Exaust Gas Temp guage. When the perfect mixture ratio is achived the EGT will be hotest. This is known a peak EGT.
Now running at peak EGT will really heat up the engine. Most pilots richen the mixture to add more fuel. This extra fuel dose not burn because there isn't enough air for it. Instead it absorbes some of the heat from the engine and carries it away.
What you can also do is lean out the mixture past peak EGT. This is starving the engine for fuel. Now instead of extra fuel to carry away the heat, you have extra air to accomplish the same thing. (air is a heck of a lt cheaper than 100LL). By defintion "lean of peak" is cooler than peak EGT.
The drawback of running LOP is that power drops of dramaticly as you go past peak. If you don't monitor this carefully you will either be going really slow, or (if you're a shade too rich) really abusing your engine.
Now the main reason that this procedure was forgotten was due to instumenation. The old DC-4s and Connies had flight enginiers to monitor a multitude of guages. The Cessnas and Bonanzas useually only have an already busy pilot, and a single EGT guage. So pilots could only aproximatly guess wether they were at the right mixture setting. Since everyone wanted to be cautious they ran rich. This let them go fast and kept their engines cool.
Now that the new multi bar engine monitors have become so cheap. Pilots can get much better info about what is going on inside their engine. Now you can adjust your mixture at precisely the right setting for your flight.
The other problem with running LOP is that most carburated and many fuel injected engines have very poor matching of airflow from diffrent cylinders. Old radials useuall had really good distribution. This means that each cylinder is reaching peak EGT at diffrent times. When this happens, vibration gets pretty bad. Most engines with fixed pitch props are leaned out till they start vibrating, then you richen up a little.
GAMI has come out with a line of fuel injectors that fixes this by precisely matching fuel flow to each cylinder with the correct airflow.
A computerized graphic engine monitor, GAMIjectors, and LASAR ignition will be required equipment on any plane I own in the future.
Now that you can closely monitor your engine and it won't vibrate like crazy, it is possible to cruise at 50-100 deg LOP without destroying your engine or sacrificing speed.
Look at the mixture curve chart in the "mixture magic" article (I couldn't figure out how to post it). It explaines this pretty well.
Anyone here have any thoughts on the whole LOP concept?
[/ QUOTE ]
Flying with the throttle wide open and reducing power by leaning out the mixture well past peak EGT is actually a very old procedure. Virtually all of the old piston engine airliners were flown this way.
First off, a brief lesson for any newbies.
The mixture of an airplane engine is controled manually by the pilot. On airplanes with a constant speed propeller the way you know if the mixture is correct is by watching the Exaust Gas Temp guage. When the perfect mixture ratio is achived the EGT will be hotest. This is known a peak EGT.
Now running at peak EGT will really heat up the engine. Most pilots richen the mixture to add more fuel. This extra fuel dose not burn because there isn't enough air for it. Instead it absorbes some of the heat from the engine and carries it away.
What you can also do is lean out the mixture past peak EGT. This is starving the engine for fuel. Now instead of extra fuel to carry away the heat, you have extra air to accomplish the same thing. (air is a heck of a lt cheaper than 100LL). By defintion "lean of peak" is cooler than peak EGT.
The drawback of running LOP is that power drops of dramaticly as you go past peak. If you don't monitor this carefully you will either be going really slow, or (if you're a shade too rich) really abusing your engine.
Now the main reason that this procedure was forgotten was due to instumenation. The old DC-4s and Connies had flight enginiers to monitor a multitude of guages. The Cessnas and Bonanzas useually only have an already busy pilot, and a single EGT guage. So pilots could only aproximatly guess wether they were at the right mixture setting. Since everyone wanted to be cautious they ran rich. This let them go fast and kept their engines cool.
Now that the new multi bar engine monitors have become so cheap. Pilots can get much better info about what is going on inside their engine. Now you can adjust your mixture at precisely the right setting for your flight.
The other problem with running LOP is that most carburated and many fuel injected engines have very poor matching of airflow from diffrent cylinders. Old radials useuall had really good distribution. This means that each cylinder is reaching peak EGT at diffrent times. When this happens, vibration gets pretty bad. Most engines with fixed pitch props are leaned out till they start vibrating, then you richen up a little.
GAMI has come out with a line of fuel injectors that fixes this by precisely matching fuel flow to each cylinder with the correct airflow.
A computerized graphic engine monitor, GAMIjectors, and LASAR ignition will be required equipment on any plane I own in the future.
Now that you can closely monitor your engine and it won't vibrate like crazy, it is possible to cruise at 50-100 deg LOP without destroying your engine or sacrificing speed.
Look at the mixture curve chart in the "mixture magic" article (I couldn't figure out how to post it). It explaines this pretty well.
ROFCIBC
Well-Known Member
[ QUOTE ]
John Deakin. Now there's a name I don't see too often anymore, although I think he might still hang at www.avsig.com, I haven't seen him post there in a while. Quite the character, that's for sure, (in a good way), used to banter with him often!
[/ QUOTE ]
Gawd...."Deakin!"...I too remember him from putzing aroung on the avisig bulletin board of my old CompuServe days. Didn't know it still existed.
There was another guy over there that used to take issue with about everything any body ever posted but can't recall the name. Been too many years ago!
John Deakin. Now there's a name I don't see too often anymore, although I think he might still hang at www.avsig.com, I haven't seen him post there in a while. Quite the character, that's for sure, (in a good way), used to banter with him often!
[/ QUOTE ]
Gawd...."Deakin!"...I too remember him from putzing aroung on the avisig bulletin board of my old CompuServe days. Didn't know it still existed.
There was another guy over there that used to take issue with about everything any body ever posted but can't recall the name. Been too many years ago!