Manifold Pressure
Joined: Mar 2000
Posts: 3,130
Likes: 17
From: U.K.
It was definately me. My assertation that Lcomings etc. like being around 75% comes from experience of a/c that have been looked after and flown properly and from people far more experienced than me, both engineers and pilots.
As an ex-engineer with too many hours sat watching a dyno, when an engine is designed the are usually optimised for the power setting they will spend most of their life at. This is especially precient with an engine as crude as the average light a/c engine. Since the introduction of fuel injection, electronic ignition and especially variable valve timing we can now have engines that are good across the rev range, but if you remeber back to a car/bike engines of a few years ago, then they were always better at one thing than another i.e great top end, no pull low down. How much technology do we have in lycomings?
If you read the charts in most POH's, then you can get the correct power settings without needing a fuel flow meter.
If you have a sufficiently powerful a/c, TB20 for example, then pulling the power back after T/O isn't an issue. The problem is when it is done in a lower power machine for example a TB10, which doesn't really have much excess power. 500'AGL is about the lowest height I'd recommend for pulling the power back, but I have met people who do it lower. This is normallly followed by a rollicking followed by a discussion about carb icing and engine failures.
Cruise climbing is a very different regime of flight than the initial climb and a lower power setting is obviously sensible.
As an ex-engineer with too many hours sat watching a dyno, when an engine is designed the are usually optimised for the power setting they will spend most of their life at. This is especially precient with an engine as crude as the average light a/c engine. Since the introduction of fuel injection, electronic ignition and especially variable valve timing we can now have engines that are good across the rev range, but if you remeber back to a car/bike engines of a few years ago, then they were always better at one thing than another i.e great top end, no pull low down. How much technology do we have in lycomings?
If you read the charts in most POH's, then you can get the correct power settings without needing a fuel flow meter.
If you have a sufficiently powerful a/c, TB20 for example, then pulling the power back after T/O isn't an issue. The problem is when it is done in a lower power machine for example a TB10, which doesn't really have much excess power. 500'AGL is about the lowest height I'd recommend for pulling the power back, but I have met people who do it lower. This is normallly followed by a rollicking followed by a discussion about carb icing and engine failures.
Cruise climbing is a very different regime of flight than the initial climb and a lower power setting is obviously sensible.
Joined: Jun 2003
Posts: 13,787
Likes: 0
From: EuroGA.org
FFF
There is nothing wrong with a cruise climb power setting, right after takeoff, terrain permitting - except that the airflow around the engine won't be what it is at level cruise and I would think many/most engines would eventually overheat if you did it at say Vx. And do you have a CHT gauge, and a working one?
I've never seen a working one in any of at least a dozen hire planes. Now I have an EDM700 which is very interesting to watch in different situations.
If the POH says something is OK, then it should be OK. The danger is in using rules like 25/2500 generally.
SAS
I agree re the power settings without a flowmeter - provided you apply the correct altitude compensation to the MP value, about 0.5" to 1" extra (or so) per 1000ft - this is because the fuel metering (or a carb) doesn't measure mass flow; it measures air by something between volume flow and mass flow, whereas it measures the fuel by mass only. But few spamcans fly high enough for this to matter.
There is nothing wrong with a cruise climb power setting, right after takeoff, terrain permitting - except that the airflow around the engine won't be what it is at level cruise and I would think many/most engines would eventually overheat if you did it at say Vx. And do you have a CHT gauge, and a working one?
I've never seen a working one in any of at least a dozen hire planes. Now I have an EDM700 which is very interesting to watch in different situations.If the POH says something is OK, then it should be OK. The danger is in using rules like 25/2500 generally.
SAS
I agree re the power settings without a flowmeter - provided you apply the correct altitude compensation to the MP value, about 0.5" to 1" extra (or so) per 1000ft - this is because the fuel metering (or a carb) doesn't measure mass flow; it measures air by something between volume flow and mass flow, whereas it measures the fuel by mass only. But few spamcans fly high enough for this to matter.
Joined: Sep 2001
Posts: 343
Likes: 0
From: Melbourne, Australia
Most POH have MAP/RPM combinations for % power. You want a 75% power climb? It's probably there for you. You want 85%? Probly find that too. Since these figures come from test cell work by the engine manufacturer, you'd be pretty hard pressed to convince anyone who is semi intelligent that "word of mouth", or the "know all down the road" knows better. These work just fine. That's why they are there. Comparing car and aircraft engines together is a completely fallacious argument. An aircraft engine spends 90 % of it's life producing 65 % or more of it's rated power. Your average car engine spends 90 % of it's life producing 15% of it's power. Two completely different objectives.
PPruNaholic!
Joined: Aug 2000
Posts: 1,615
Likes: 0
From: Buckinghamshire
Most POH have MAP/RPM combinations for % power
Joined: Mar 2000
Posts: 3,130
Likes: 17
From: U.K.
Dale,
That was the whole point of the comment. Engines are designed for the type of use they are most likely to get, how that makes something fallacious I don't know. But comparing like with similar is the easiest way of creating an understanding.
That was the whole point of the comment. Engines are designed for the type of use they are most likely to get, how that makes something fallacious I don't know. But comparing like with similar is the easiest way of creating an understanding.
Joined: Mar 2000
Posts: 3,130
Likes: 17
From: U.K.
Apples and oranges? I.C engines are all similar in basic designs and designers of all types face the same problems.
Not everybody on this board is a technical genius (I know I certainly am not) and drawing parallells can help get a point across. Whether it is 100% on the nail, isn't relevant to this discussion. The basic principles are.
I have spent many hours with students looking blankly at me when explaining theory, especially in regard to piston engines. Putting the explanation in the context of what people are familiar with helps hugely. If it gets the point across and helps promote understanding, then that's all that matters.
Not everybody on this board is a technical genius (I know I certainly am not) and drawing parallells can help get a point across. Whether it is 100% on the nail, isn't relevant to this discussion. The basic principles are.
I have spent many hours with students looking blankly at me when explaining theory, especially in regard to piston engines. Putting the explanation in the context of what people are familiar with helps hugely. If it gets the point across and helps promote understanding, then that's all that matters.
