Post by Randy_Cain on Jan 26, 2009 19:55:38 GMT -5
This was posted in response to this thread:
calclassic.proboards55.com/index.cgi?board=general&action=display&thread=794
I've posted the response here as a reference.
Yours,
Randy Cain
Hi,
A response from FSAviator:
<<I too have had unpleasant experiences with FS9's horrific upper air wind changes but in this particular instance I am not convinced they were in play here.>>
I agree. Before I explain the two things that could have caused the symptoms you reported let me answer the question;
<<FS Aviator's PT goes into the subject of dealing with headwinds in a propliner but how does one deal with excessive tailwinds that reduce IAS significantly?>>
A change of wind vector alters speed (KTS) not profile drag (IAS). I will illustrate why in a moment, but your question is already answered in the 2008 Propliner Tutorial. Word searching the 2008 Propliner Tutorial for 'tailwind' provides guidance for all phases of flight. Searching instead for the main heading TAILWIND in upper case takes us directly to;
>>>>>>>>>>>>>
REACTION TO NO SIGNIFICANT HEADWIND OR A TAILWIND
Later during the same flight we notice that a leg (or legs) planned to take 20 minutes only took 19. Now we must react in the opposite way. We must seek a higher cruising level and we may reduce to one lesser stage of power from whatever we currently have applied. We never want our speed to exceed planned speed. We are being paid not only to reduce the TIME that our propliner suffers headwinds, we are also being paid to maximise the TIME it rides tailwinds. When we encounter a tailwind we climb in the hope of finding an even stronger tailwind at a higher semi circular cruising level and then we reduce power to enjoy the tailwind for as many minutes as possible.
This power reduction might potentially be a reduction from econ cruise power to long range cruise power. In some handling notes there will be an injunction against using LRC power until the weight is below a specified value or the fuel state is less than a specified percent.
In real life we discover these values by asking whichever crew member we appointed as Flight Engineer, (often this will be Pilot Not Flying = PNF), what they are. In MSFS we need to open the fuel and payload menu to obtain the answer or consult a Calclassic notepad.
The intention is, over the lifetime of the airliner, to maximise the time with a tailwind and minimise the time with a headwind. Over the long run it improves economy of operation and when simulating airline operations in propliners that is a major part of the 4D navigation process. If we always cruised at the same power setting we would spend more time flying with headwinds than with tailwinds. That would be very bad captaincy.
Real world aerial navigation is not a 2D process. It is very much a 4D process. The vast majority of the navigation task is the captaincy required to manage (reactively) the vertical profile of the flight and applied power versus perceived headwind. Simply planning and following the 2D course should be a tiny fraction of our navigation workload.
>>>>>>>>>>>>>>>>
When you assert wrongly that wind vectors vary profile drag (IAS) in flight you are confusing speed measured in KTS with profile drag measured in IAS. The Propliner Tutorial begins by explaining that speed and drag are different things and that the ASI in the cockpit can only measure profile drag.
Imagine we are in a small boat travelling at a speed of 10 KTS with a profile drag of 10 KIAS. There is no current. That profile drag (not our speed) is creating a visible and measurable bow wave. Now we meet a current going the other way at 10 KTS. *Our bow wave neither doubles nor disappears*. Our profile drag is still 10 KIAS. The bow wave is only the consequence of power we apply to the structure. The bow will not be stove in when we mead a current however fast. The bow has the same profile drag and bow wave whatever the current if we do not vary applied power or drop a see anchor. The current we have encountered and are immersed in cannot alter our drag (IAS) whatever direction it comes from. It can only alter our speed (KTS) relative to some land distant from our vessel.
Our profile drag is still 10 KIAS, our bow wave is unaltered, but our speed is now zero KTS. We do not progress relative to the distant land. Our speed still has zero influence over our profile drag producing the bow wave. If we meet a 15KTS current our speed will be minus 5 KTS but we will still have a bow wave that depends only on applied power. We control our profile drag (IAS = bow wave = structural failure probability) by moderating power to create the handling note target values and avoid the handling note limit values. Our speed (KTS), and only our speed, varies with the speed (KTS) of the currents we encounter. A wind is just a current of air. Currents have zero influence on drag in an aeroplane or a boat.
IAS measures profile drag on the vessel's structure
TAS measures aircraft velocity (how well it manoeuvres in flight or deforms in a collision)
KTS measures vessel speed (progress relative to some distant land)
The profile drag (IAS), shown on our ASI, to which the airframe is subjected by our choice of power input, is neither its velocity (TAS) nor its speed (KTS). This is at the very heart of navigation and is the 'eureka' moment that many FS users never come to terms with. An ASI does not register speed and it cannot register a change of speed, due to a change of current, or anything else. It only registers a change of profile drag on the pitot tube which we control with applied power or sea anchors (air brakes / flaps).
Now a second confusion. Turbulence in the fluid is a separate issue but is being muddled with strength of current. Turbulence can be caused by 'mixing of currents' or 'rate of change of the speed of the current', but that must be differentiated from the strength of the current. A fast current may have zero turbulence. Severe turbulence may exist where there is no current. There is zero correlation.
Big waves and strong currents are different things.
Our bow wave varies in turbulent seas. Our drag increases as we smash into a huge wave, but then it rapidly diminishes. The bow may be stove in or the tail may be ripped off before it diminishes. When profile drag (IAS) suddenly increases structural failure may occur, when it suddenly diminishes an aeroplane may stall. It is only the profile drag (IAS) on the wings that supports our weight. Waves smashing into the bow and turbulent flows over the pitot tube can, and do, vary profile drag (IAS), but that has nothing to do with whether a current is even present.
Variation of current causing variation of KTS is not at all the same thing as variation of wave size (turbulence) causing change of IAS.
Your report cites an increasing and prolonged decrease in profile drag (IAS). That prolonged change cannot have been caused by either a change of current (wind vector) or a change of wave state (turbulence).
The consequence of turbulence (big waves) is rapidly fluctuating profile drag (IAS). Since any such increase may rip the tail off (stove the bow in) we must reduce power and reduce our target profile drag (IAS) whenever we encounter significant turbulence (big waves), even though that may make stall more likely in an aeroplane. Stall is better than structural failure.
We do *not* reduce power when we meet strong currents opposed to our bow. Strong currents which vary KTS and big waves which vary IAS are not the same thing and they require different captaincy responses.
<<Was flying the BSAA Montevideo - Buenos Aires segment in a Lancastrian MkII........Suddenly IAS dropped 40+ mph....,As wind velocity increased, IAS continued to decay and the Lanc seemed close to stalling.>>
Your incident report is clear. Your attribution of cause is false. The strength of the current you were immersed in, whatever its direction of travel, was irrelevant. It could not alter profile drag (IAS). So something else did. There are only two possibilities. Change of POWER and change of DRAG. There are three logical reasons why those two things might happen in MSFS.
1) Bogus drag imposed by the gauge code
It may or may not apply here, but many FD supplied for use in MSFS have 'cheat modes'. Some suddenly auto deploy invisible air brakes (sea anchors) when they should not, because the gauge code is bugged or the developer had some misconceived notion about flight dynamics.
2) Progressive engine failure in the gauge code
Some releases have 'engine failure code' which reduces power causing persistent loss of bow wave = profile drag = IAS for reasons which are lost on the user, but which represent mismanagement by the user, at least according to the developer.
Maybe your Merlin engines overheated whilst cruising in very hot air that was ISA + 23C. Maybe you failed to open the radiator gills sufficiently on all engines for that extreme outside air temperature. Ice was the least of your engine management problems! Maybe the developer imposed a failure for reasons you have not understood. Maybe the failure code malfunctioned.
If you were punished with code that varied mixture to emulate user engine mismanagement and consequential partial failure there may have been no loss of MAP. It can be very hard to tell when a developer decides to punish you. We have no way of knowing what gauge code may be in every propliner downloaded or purchased. You should investigate whether your aircraft specific operating manual cites engine cooling, radiator gill status and progressive engine failures. If not you should ask the developer what they think happened in the forum where they provide support.
Unless you accidently reduced thrust. or accidentally altered aircraft drag configuration you were almost certainly afflicted by developer gauge code that you did not expect to run, and you probably have no idea what you did to cause it to run. If your aircraft specific operating manual does not explain the incident I believe only the developer will be able to explain what third party code was invoked to cause persistent loss of profile drag on the pitot tube (IAS).
3) Sudden false change in altitude density.
Using real METARS invokes risk of real human data input error. If the real meteorologist or data entry clerk entered 19.92 inches when they intended to enter 29.92 real pilots will read it and realise it is human error. Computers won't. Our computers just reduce altitude density at all altitudes massively in an instant. If you are high enough in relation to the encoded engine specific critical altitude MAP falls accordingly at constant throttle opening. The sudden loss of applied power causes profile drag = bow wave = IAS to decay very fast at first, and then much slower, potentially and eventually to stall.
However since you do not report a sudden change of actual height or displayed altitude this is much less likely in relation to your incident than fake air brake code or fake mixture code invoked by the developer from the gauges.
Prolonged or progressive decay of profile drag (IAS) in level flight can ONLY relate to power change, or aircraft configuration drag change, never to wind vector (current) or turbulence (wave state).
FSAviator
calclassic.proboards55.com/index.cgi?board=general&action=display&thread=794
I've posted the response here as a reference.
Yours,
Randy Cain
Hi,
A response from FSAviator:
<<I too have had unpleasant experiences with FS9's horrific upper air wind changes but in this particular instance I am not convinced they were in play here.>>
I agree. Before I explain the two things that could have caused the symptoms you reported let me answer the question;
<<FS Aviator's PT goes into the subject of dealing with headwinds in a propliner but how does one deal with excessive tailwinds that reduce IAS significantly?>>
A change of wind vector alters speed (KTS) not profile drag (IAS). I will illustrate why in a moment, but your question is already answered in the 2008 Propliner Tutorial. Word searching the 2008 Propliner Tutorial for 'tailwind' provides guidance for all phases of flight. Searching instead for the main heading TAILWIND in upper case takes us directly to;
>>>>>>>>>>>>>
REACTION TO NO SIGNIFICANT HEADWIND OR A TAILWIND
Later during the same flight we notice that a leg (or legs) planned to take 20 minutes only took 19. Now we must react in the opposite way. We must seek a higher cruising level and we may reduce to one lesser stage of power from whatever we currently have applied. We never want our speed to exceed planned speed. We are being paid not only to reduce the TIME that our propliner suffers headwinds, we are also being paid to maximise the TIME it rides tailwinds. When we encounter a tailwind we climb in the hope of finding an even stronger tailwind at a higher semi circular cruising level and then we reduce power to enjoy the tailwind for as many minutes as possible.
This power reduction might potentially be a reduction from econ cruise power to long range cruise power. In some handling notes there will be an injunction against using LRC power until the weight is below a specified value or the fuel state is less than a specified percent.
In real life we discover these values by asking whichever crew member we appointed as Flight Engineer, (often this will be Pilot Not Flying = PNF), what they are. In MSFS we need to open the fuel and payload menu to obtain the answer or consult a Calclassic notepad.
The intention is, over the lifetime of the airliner, to maximise the time with a tailwind and minimise the time with a headwind. Over the long run it improves economy of operation and when simulating airline operations in propliners that is a major part of the 4D navigation process. If we always cruised at the same power setting we would spend more time flying with headwinds than with tailwinds. That would be very bad captaincy.
Real world aerial navigation is not a 2D process. It is very much a 4D process. The vast majority of the navigation task is the captaincy required to manage (reactively) the vertical profile of the flight and applied power versus perceived headwind. Simply planning and following the 2D course should be a tiny fraction of our navigation workload.
>>>>>>>>>>>>>>>>
When you assert wrongly that wind vectors vary profile drag (IAS) in flight you are confusing speed measured in KTS with profile drag measured in IAS. The Propliner Tutorial begins by explaining that speed and drag are different things and that the ASI in the cockpit can only measure profile drag.
Imagine we are in a small boat travelling at a speed of 10 KTS with a profile drag of 10 KIAS. There is no current. That profile drag (not our speed) is creating a visible and measurable bow wave. Now we meet a current going the other way at 10 KTS. *Our bow wave neither doubles nor disappears*. Our profile drag is still 10 KIAS. The bow wave is only the consequence of power we apply to the structure. The bow will not be stove in when we mead a current however fast. The bow has the same profile drag and bow wave whatever the current if we do not vary applied power or drop a see anchor. The current we have encountered and are immersed in cannot alter our drag (IAS) whatever direction it comes from. It can only alter our speed (KTS) relative to some land distant from our vessel.
Our profile drag is still 10 KIAS, our bow wave is unaltered, but our speed is now zero KTS. We do not progress relative to the distant land. Our speed still has zero influence over our profile drag producing the bow wave. If we meet a 15KTS current our speed will be minus 5 KTS but we will still have a bow wave that depends only on applied power. We control our profile drag (IAS = bow wave = structural failure probability) by moderating power to create the handling note target values and avoid the handling note limit values. Our speed (KTS), and only our speed, varies with the speed (KTS) of the currents we encounter. A wind is just a current of air. Currents have zero influence on drag in an aeroplane or a boat.
IAS measures profile drag on the vessel's structure
TAS measures aircraft velocity (how well it manoeuvres in flight or deforms in a collision)
KTS measures vessel speed (progress relative to some distant land)
The profile drag (IAS), shown on our ASI, to which the airframe is subjected by our choice of power input, is neither its velocity (TAS) nor its speed (KTS). This is at the very heart of navigation and is the 'eureka' moment that many FS users never come to terms with. An ASI does not register speed and it cannot register a change of speed, due to a change of current, or anything else. It only registers a change of profile drag on the pitot tube which we control with applied power or sea anchors (air brakes / flaps).
Now a second confusion. Turbulence in the fluid is a separate issue but is being muddled with strength of current. Turbulence can be caused by 'mixing of currents' or 'rate of change of the speed of the current', but that must be differentiated from the strength of the current. A fast current may have zero turbulence. Severe turbulence may exist where there is no current. There is zero correlation.
Big waves and strong currents are different things.
Our bow wave varies in turbulent seas. Our drag increases as we smash into a huge wave, but then it rapidly diminishes. The bow may be stove in or the tail may be ripped off before it diminishes. When profile drag (IAS) suddenly increases structural failure may occur, when it suddenly diminishes an aeroplane may stall. It is only the profile drag (IAS) on the wings that supports our weight. Waves smashing into the bow and turbulent flows over the pitot tube can, and do, vary profile drag (IAS), but that has nothing to do with whether a current is even present.
Variation of current causing variation of KTS is not at all the same thing as variation of wave size (turbulence) causing change of IAS.
Your report cites an increasing and prolonged decrease in profile drag (IAS). That prolonged change cannot have been caused by either a change of current (wind vector) or a change of wave state (turbulence).
The consequence of turbulence (big waves) is rapidly fluctuating profile drag (IAS). Since any such increase may rip the tail off (stove the bow in) we must reduce power and reduce our target profile drag (IAS) whenever we encounter significant turbulence (big waves), even though that may make stall more likely in an aeroplane. Stall is better than structural failure.
We do *not* reduce power when we meet strong currents opposed to our bow. Strong currents which vary KTS and big waves which vary IAS are not the same thing and they require different captaincy responses.
<<Was flying the BSAA Montevideo - Buenos Aires segment in a Lancastrian MkII........Suddenly IAS dropped 40+ mph....,As wind velocity increased, IAS continued to decay and the Lanc seemed close to stalling.>>
Your incident report is clear. Your attribution of cause is false. The strength of the current you were immersed in, whatever its direction of travel, was irrelevant. It could not alter profile drag (IAS). So something else did. There are only two possibilities. Change of POWER and change of DRAG. There are three logical reasons why those two things might happen in MSFS.
1) Bogus drag imposed by the gauge code
It may or may not apply here, but many FD supplied for use in MSFS have 'cheat modes'. Some suddenly auto deploy invisible air brakes (sea anchors) when they should not, because the gauge code is bugged or the developer had some misconceived notion about flight dynamics.
2) Progressive engine failure in the gauge code
Some releases have 'engine failure code' which reduces power causing persistent loss of bow wave = profile drag = IAS for reasons which are lost on the user, but which represent mismanagement by the user, at least according to the developer.
Maybe your Merlin engines overheated whilst cruising in very hot air that was ISA + 23C. Maybe you failed to open the radiator gills sufficiently on all engines for that extreme outside air temperature. Ice was the least of your engine management problems! Maybe the developer imposed a failure for reasons you have not understood. Maybe the failure code malfunctioned.
If you were punished with code that varied mixture to emulate user engine mismanagement and consequential partial failure there may have been no loss of MAP. It can be very hard to tell when a developer decides to punish you. We have no way of knowing what gauge code may be in every propliner downloaded or purchased. You should investigate whether your aircraft specific operating manual cites engine cooling, radiator gill status and progressive engine failures. If not you should ask the developer what they think happened in the forum where they provide support.
Unless you accidently reduced thrust. or accidentally altered aircraft drag configuration you were almost certainly afflicted by developer gauge code that you did not expect to run, and you probably have no idea what you did to cause it to run. If your aircraft specific operating manual does not explain the incident I believe only the developer will be able to explain what third party code was invoked to cause persistent loss of profile drag on the pitot tube (IAS).
3) Sudden false change in altitude density.
Using real METARS invokes risk of real human data input error. If the real meteorologist or data entry clerk entered 19.92 inches when they intended to enter 29.92 real pilots will read it and realise it is human error. Computers won't. Our computers just reduce altitude density at all altitudes massively in an instant. If you are high enough in relation to the encoded engine specific critical altitude MAP falls accordingly at constant throttle opening. The sudden loss of applied power causes profile drag = bow wave = IAS to decay very fast at first, and then much slower, potentially and eventually to stall.
However since you do not report a sudden change of actual height or displayed altitude this is much less likely in relation to your incident than fake air brake code or fake mixture code invoked by the developer from the gauges.
Prolonged or progressive decay of profile drag (IAS) in level flight can ONLY relate to power change, or aircraft configuration drag change, never to wind vector (current) or turbulence (wave state).
FSAviator