Post by volkerboehme on Aug 10, 2008 12:08:50 GMT -5
I will try to answer all the questions that have arisen in a single reply which should hopefully also explain why the answers are what they are.
Cowl flaps control air flow through the cowling. For a radial engine profile drag (KIAS) is the same thing as cooling. When flying an aeroplane with radial engines we use cowl flaps to manually augment engine (cooling) drag. The cowl flaps can vary the engine cooling drag from slight to massive.
In the B377 openings of more than 5 inches are used to cool the engines on the ground, when they have very little natural airflow.
The higher the power of each engine, the more heat it produces, and the more manually induced cooling drag it needs if natural profile drag (KIAS) is low.
When we are climbing in METO power with low natural cooling drag (= 170 KIAS) we must augment that low natural profile drag by opening the cowl flaps 4 to 5 inches.
Once we are climbing with (less) climb power and with increased natural profile drag (=> 175 KIAS) we have more natural cooling for less power and we can reduce cowl flap opening to only 3 inches. Once we level off and reduce to max cruise power we need less cooling and our natural profile drag will rise (=> 190 KIAS). Now we can close the cowl flaps to zero inches to minimise engine drag.
The cowlings themselves deliver enough natural engine drag to cool max cruise power when the profile drag is => 190 KIAS without any manual engine drag augmentation via cowl flaps. The B377 is very powerful and so the cowl flaps can add huge quantities of engine drag. Even when set to 3 inches to cool climb power they promote a lot of additional engine drag (cooling).
Much later we will be light enough to cruise in econ power. With only econ power applied the natural profile (cooling) drag is adequate => 180 KIAS.
If we climb too high our natural cooling drag (KIAS) will decay and become inadequate. If we try to remedy that by opening cowl flaps we add engine drag, slow down and lose more natural cooling (KIAS). We create a vicious circle that ends in a stall. We must never climb above our current operational ceiling.
That is what the one line statements in the handling notes ‘explain’. KIAS is profile (cooling) drag. Our Air Speed Indicator tells us our natural profile drag in KIAS and the handling notes tell us how low we can allow it to be, plus how much we must augment the engine cooling drag manually, and by how many inches of cowl flap opening, power setting, by power setting.
The real world flight engineers tables and procedures work differently, but the aircraft performance envelope is the same either way if we follow the (recently revised) FS9 handling notes. We will learn to fly the real flight plan 4D profile, for our current weight, and our current weather, constrained in all the right ways.
Retail FS9 does not replicate any of this. Consequently very few aircraft available for purchase or download replicate this reality. However all the relevant aircraft available from Calclassic.com have 'realistic' user variable engine drag augmentation encoded via a mixture of air file code and gauge code to make up for that important deficiency within retail FS9.
The density altitude at which profile drag will decay to 175 KIAS, in climb power, at 500 VSI, following a max gross (UAL variant) B377 departure, with the cowl flaps opened 3 inches depends on the weather at the time. In the International Standard Atmosphere it will happen just below 9000 feet causing the FS9 user to level off at 9000 feet to burn off fuel before beginning the long series of 2000 foot interval step climbs, each of which terminates at a semi circular ATC cruising level (see Propliner Tutorial).
In real life, or with real variable weather, or a variable weather theme in use within FS9, some days perhaps below 7000. or maybe above 10,000. However initial operational ceiling is very unlikely to be around 18,000 feet in any weather in the circumstances above.
Either 500 VSI was not sustained, or => 175 KIAS was not sustained, or more than climb power was employed, or the departure was not at UAL max gross, or the cowl flaps were not set to 3 inches to provide 'adequate' cooling with climb power in use, or the panel used lacked the gauge code to control variable engine drag correctly. Using the bundled Calclassic panel is mandatory. It provides all of the code that retail FS9 lacks.
The handling notes cannot tell us where we will encounter operational ceiling. It varies with weight and weather every time we fly. That is what makes flight simulation using realistic flight dynamics interesting. Our operation of the same aeroplane over the same route, will be differ correctly with weight and weather. The significance of operational ceiling is explained within the Propliner Tutorial. The handling notes tell us how to discover what it is, at our current weight, in the current weather.
The reason that propliners sometimes fly for thousands of miles at altitudes well below their current operational ceiling is to avoid headwinds at higher altitudes that would reduce their cruising speed (KTS), even though the propliner would achieve much higher cruising velocity (KTAS) at higher altitudes.
Today a cruising velocity of 265 KTAS into a 150 KTS headwind vector at FL250 yields a cruising speed of only 115 KTS.
The Air Speed Indicator only ever tells us our profile drag (which depending on the weather today might be 180 KIAS). Our cruise profile drag (180 KIAS) tells us nothing about our cruise velocity (265 KTAS) or our cruise speed (115 KTS). We never use KIAS to calculate speed or velocity. It is just a drag.
As aircraft captain we must react to significant headwinds in various ways. Today, if the headwind vector 14000 feet lower at FL90 is only 20 KTS we may choose to cruise with a profile drag of 180 KIAS and a velocity of 205 KTAS at a speed of 185 KTS travelling 38% faster at much lower velocity at a much lower altitude.
The differences between KIAS (profile drag), KTAS (velocity), and KTS (speed) are explained in the Propliner Tutorial along with elementary tactics for battling headwinds in FS9; within which we can never use real world techniques because we cannot obtain forecast winds aloft.
Finally back in the days of FS8 when I created the flight dynamics for the B377 I was working in part from fragments of the real BOAC manual. I made the BOAC version the default version. Within that default FS8 aircraft.cfg I included instructions for altering the BOAC version into other versions. I placed all the payload at CoG to make that easy.
Then FS9 came along. The flight dynamics (FD) had to be rewritten because Microsoft had dumbed down the flight models (FM) in FS9. The instructions for converting one version to another are present in the UAL version, but doesn't work now since the payload has been converted to the FS2004 format and you need to consider the CG since the load is not all at 0.
FSAviator.
Cowl flaps control air flow through the cowling. For a radial engine profile drag (KIAS) is the same thing as cooling. When flying an aeroplane with radial engines we use cowl flaps to manually augment engine (cooling) drag. The cowl flaps can vary the engine cooling drag from slight to massive.
In the B377 openings of more than 5 inches are used to cool the engines on the ground, when they have very little natural airflow.
The higher the power of each engine, the more heat it produces, and the more manually induced cooling drag it needs if natural profile drag (KIAS) is low.
When we are climbing in METO power with low natural cooling drag (= 170 KIAS) we must augment that low natural profile drag by opening the cowl flaps 4 to 5 inches.
Once we are climbing with (less) climb power and with increased natural profile drag (=> 175 KIAS) we have more natural cooling for less power and we can reduce cowl flap opening to only 3 inches. Once we level off and reduce to max cruise power we need less cooling and our natural profile drag will rise (=> 190 KIAS). Now we can close the cowl flaps to zero inches to minimise engine drag.
The cowlings themselves deliver enough natural engine drag to cool max cruise power when the profile drag is => 190 KIAS without any manual engine drag augmentation via cowl flaps. The B377 is very powerful and so the cowl flaps can add huge quantities of engine drag. Even when set to 3 inches to cool climb power they promote a lot of additional engine drag (cooling).
Much later we will be light enough to cruise in econ power. With only econ power applied the natural profile (cooling) drag is adequate => 180 KIAS.
If we climb too high our natural cooling drag (KIAS) will decay and become inadequate. If we try to remedy that by opening cowl flaps we add engine drag, slow down and lose more natural cooling (KIAS). We create a vicious circle that ends in a stall. We must never climb above our current operational ceiling.
That is what the one line statements in the handling notes ‘explain’. KIAS is profile (cooling) drag. Our Air Speed Indicator tells us our natural profile drag in KIAS and the handling notes tell us how low we can allow it to be, plus how much we must augment the engine cooling drag manually, and by how many inches of cowl flap opening, power setting, by power setting.
The real world flight engineers tables and procedures work differently, but the aircraft performance envelope is the same either way if we follow the (recently revised) FS9 handling notes. We will learn to fly the real flight plan 4D profile, for our current weight, and our current weather, constrained in all the right ways.
Retail FS9 does not replicate any of this. Consequently very few aircraft available for purchase or download replicate this reality. However all the relevant aircraft available from Calclassic.com have 'realistic' user variable engine drag augmentation encoded via a mixture of air file code and gauge code to make up for that important deficiency within retail FS9.
The density altitude at which profile drag will decay to 175 KIAS, in climb power, at 500 VSI, following a max gross (UAL variant) B377 departure, with the cowl flaps opened 3 inches depends on the weather at the time. In the International Standard Atmosphere it will happen just below 9000 feet causing the FS9 user to level off at 9000 feet to burn off fuel before beginning the long series of 2000 foot interval step climbs, each of which terminates at a semi circular ATC cruising level (see Propliner Tutorial).
In real life, or with real variable weather, or a variable weather theme in use within FS9, some days perhaps below 7000. or maybe above 10,000. However initial operational ceiling is very unlikely to be around 18,000 feet in any weather in the circumstances above.
Either 500 VSI was not sustained, or => 175 KIAS was not sustained, or more than climb power was employed, or the departure was not at UAL max gross, or the cowl flaps were not set to 3 inches to provide 'adequate' cooling with climb power in use, or the panel used lacked the gauge code to control variable engine drag correctly. Using the bundled Calclassic panel is mandatory. It provides all of the code that retail FS9 lacks.
The handling notes cannot tell us where we will encounter operational ceiling. It varies with weight and weather every time we fly. That is what makes flight simulation using realistic flight dynamics interesting. Our operation of the same aeroplane over the same route, will be differ correctly with weight and weather. The significance of operational ceiling is explained within the Propliner Tutorial. The handling notes tell us how to discover what it is, at our current weight, in the current weather.
The reason that propliners sometimes fly for thousands of miles at altitudes well below their current operational ceiling is to avoid headwinds at higher altitudes that would reduce their cruising speed (KTS), even though the propliner would achieve much higher cruising velocity (KTAS) at higher altitudes.
Today a cruising velocity of 265 KTAS into a 150 KTS headwind vector at FL250 yields a cruising speed of only 115 KTS.
The Air Speed Indicator only ever tells us our profile drag (which depending on the weather today might be 180 KIAS). Our cruise profile drag (180 KIAS) tells us nothing about our cruise velocity (265 KTAS) or our cruise speed (115 KTS). We never use KIAS to calculate speed or velocity. It is just a drag.
As aircraft captain we must react to significant headwinds in various ways. Today, if the headwind vector 14000 feet lower at FL90 is only 20 KTS we may choose to cruise with a profile drag of 180 KIAS and a velocity of 205 KTAS at a speed of 185 KTS travelling 38% faster at much lower velocity at a much lower altitude.
The differences between KIAS (profile drag), KTAS (velocity), and KTS (speed) are explained in the Propliner Tutorial along with elementary tactics for battling headwinds in FS9; within which we can never use real world techniques because we cannot obtain forecast winds aloft.
Finally back in the days of FS8 when I created the flight dynamics for the B377 I was working in part from fragments of the real BOAC manual. I made the BOAC version the default version. Within that default FS8 aircraft.cfg I included instructions for altering the BOAC version into other versions. I placed all the payload at CoG to make that easy.
Then FS9 came along. The flight dynamics (FD) had to be rewritten because Microsoft had dumbed down the flight models (FM) in FS9. The instructions for converting one version to another are present in the UAL version, but doesn't work now since the payload has been converted to the FS2004 format and you need to consider the CG since the load is not all at 0.
FSAviator.