Post by volkerboehme on Aug 10, 2008 11:59:20 GMT -5
This is a clipping from a thread over at the Sim Outhouse Forum: the full thread is here:
www.sim-outhouse.com/sohforums/showthread.php?t=35023
******************************
B377 Flight Dynamics and handling criteria
Greetings 'Gibbons',
I am sorry to hear that you are puzzled by my B377 flight dynamics. MDLs, panels, gauges and sound files just sit there waiting for the flight dynamics to tell them how to react to user input.
Your question is based on the commonplace confusion between drag (IAS) and velocity (TAS) and further confusion concerning the dynamic relationship between velocity (TAS) and Mach.
Unless you were using a badly designed third party replacement panel both the real panel and the original FS panel supplied by Greg Pepper had an ASI which incorporated a 'Mach Bug'. The Mach Bug is a short
barber pole without the stripes. You have been ignoring the Mach Bug and allowing the ASI needle to merge with the Mach Bug.
It is your job to prevent this, either by reducing power or by seeking warmer air. Mach number depends only on velocity (TAS) and temperature. What altitude will allow maximum safe cruising velocity in a B377 varies hour by hour through the flight as current weight reduces and also hour by hour with the current weather. Flying propliners is a dynamic process and the B377 is a particularly difficult and complex propliner to master. What is safe one minute may be unsafe the next or vice versa, especially if you push propliners to the very limit of their safe performance envelope by using max cruise power.
The relevant section of the supplied on screen handling notes reads as follows;
***********************************
Max Cruise:
DO NOT EXCEED M0.52 - USE MACH BUG
COWL FLAPS - CLOSED
2100 RPM
41 inches MAP
If unable => 190 KIAS descend to lower level
Plan 650 GPH
Note: - Yields 295 KTAS at FL250
***********************************
You should not normally employ max cruise power unless very heavy or battling a headwind. Doing so gives you several dynamic problems to juggle. To invoke max cruise power you must not exceed an altitude at
which you can generate 41 inches of MAP and at the same time it is your job to seek the highest (semi circular compliant) cruising level that is compatible with a drag => 190 KIAS and that also does not cause the ASI needle to merge with the supplied Mach Bug which always shows the IAS = Mach 0.52 in the current weather.
When you have found the optimum current cruising level using the techniques described in detail in the supplied handling hints within the download you have achieved maximum safe cruising velocity for your
current weight in the current weather. That is the skill that the overspeed warning helps you to develop, though if you pay attention to the original ASI and its incorporated Mach Bug you will never commit either of the pilot errors that generate the overspeed warning.
When you do not need to battle significant headwinds and after you have burned off sufficient fuel you can make your life a lot easier by applying only economical cruise power and restricting your drag to
little more than 180 KIAS.
***********************************
Econ Cruise:
WARNING - not available at high weights
COWL FLAPS - CLOSED
2100 RPM
38 inches MAP
If unable => 180 KIAS descend to lower level
Plan 550 GPH
***********************************
Once you are light enough achieving a velocity of 290 KTAS in a B377 is not particularly difficult, but reaching a drag of 290 KIAS is abusive. The goal is to operate the aircraft carefully to avoid Mno = Mach 0.52 using the supplied Mach Bug and also to avoid Vno = 271 KIAS using the needle of the ASI; even when a drag of 271 KIAS is less than Mach 0.52 in warm air at low altitude. The main needle of any ASI tells you your drag (IAS), not your velocity (TAS).
****************************
Descent:
DO NOT EXCEED 271 KIAS
DO NOT EXCEED M0.52 - USE MACH BUG
AUTOMIXTURE - ON
COWL FLAPS - CRACKED
2100 RPM
REDUCE MAP in stages of 3 inches (per minute)
MINIMUM 17 INCHES MAP
****************************
The B377 was not certificated for flight above FL250. The pressurisation system could not cope. You should never attempt to climb higher and the colder air at higher altitude will restrict your safe cruising velocity even more anyway. The MAP you can generate will also be falling quickly at those altitudes. You will be entering 'coffin corner'. You may also have been ignoring the following part of the supplied on screen handling notes.
****************************
General:
NEVER EXCEED FL250 certification limit
NEVER EXCEED 305 KIAS
NEVER EXCEED M0.52 - USE MACH BUG
ROUGH AIR NEVER EXCEED 271 KIAS
GEAR DOWN NEVER EXCEED 200 KIAS
FLAP 1 never exceed 191 KIAS
FULL FLAP never exceed 162 KIAS
CLEAN STALL 115 KIAS at MLW
STALL with FULL FLAP 80 KIAS at MLW
****************************
Your primary goal is to avoid applying abusive drag (KIAS) for the current airframe configuration. You never know when you may run into rough air. Avoiding potentially abusive dynamic drag of 271 KIAS is easy
at any altitude, but the higher you climb, the colder the air, and the harder it becomes to avoid abusive transonic drag whose onset is at Mach 0.52.
Whenever you exceed Vno or Mno you will get an overspeed warning. It is not a mistake. It is there to help you to understand that you are potentially abusing the aircraft and have failed to follow the
comprehensive step by step on screen handling notes (press F10 and select the lowest icon with your mouse). They explain all the operating targets and all the operating limits of the aircraft. You must
differentiate between the operating targets, which you must pursue, hour after relentless hour, whilst always avoiding the operating limits.
The difference between drag (KIAS) and velocity (KTAS) is explained in more detail within my generic Propliner Tutorial available from the same place as the latest updates for Greg Pepper's B377 aircraft and panel which is Tom Gibson’s website at;
www.calclassic.com/
Look in the Tutorials section for ‘FSAviator's Propliner Flying in the Classic Era’. Hopefully that will resolve any lingering confusion, but the documentation supplied with a download is always the first place
to start looking for answers.
Hope that helps;
FSAviator
Greetings all,
I aplogise if this post has odd line spacing. I did not have time to correct it. There have been many questions raised in this thread. Let me try to clarify the issues that I think are still most widely misunderstood.
The issue of gauge compatibility is not being grasped. Third party gauges may contain non standard code that triggers 'events' when a threshold value set within the gauge is matched. The event may be one wholly absent from retail FS9, or the threshold for triggering the event is specific to the aircraft.
The consequence of the event may be coded within the air file, but can be coded within the same gauge, or a different gauge as a 'different multiplier' of a singular value in an air file. Gauges within panels may also be 'slaved' to one another passing data across a network of gauges. Remove one and you break the code interaction.
Remove the gauges developed for the project and you dumb the aircraft down to be no better than a default aircraft from FS9. That may be an awful lot of dumbing down. Third party developers develop their own gauge code to add events absent from retail FS9 and to make the simulation less generic and more aircraft/engine/system specific. The additional code in freeware products often exceeds the additional code in payware products. When users swap panels or gauges that contain third party gauges they have no idea what the result will be. The more 'developed' the aircraft the dumber the result is likely to be.
Be that as it may the only way to make any aircraft go faster is to learn how to fly it better. The handling notes explain how to fly it (better). They explain the concurrent handling targets for each phase and each power setting and the limits that apply to all of them. The fact that 'better' flying requires the user to achieve multiple concurrent targets introduces both complexity and options.
When the ASI needle merges with the Mach Bug we have a problem to solve. Certainly one of our captaincy options is to reduce MAP to economical cruise to ensure that the needle falls below the bug, but we have more captaincy options than reducing power and slowing down.
The premise is that we don't want to slow down. The first step is to apply the handling target MAP and rpm. If the drag target (for maximum cruising velocity) which is => 190 KIAS is > M0.52 the Mach Bug is actually telling us something more subtle than that we must slow down. It is telling us that we have climbed too high, into air that is too cold to be safe. What we may actually do is descend into warmer air until the dynamic drag target for maximum velocity (just over 190 KIAS) is associated with transonic drag that is just less than M0.52. Mach is how pilots measure transonic drag. Just like IAS, Mach is *not* a measure of velocity.
Most FS9 users have a very poor understanding of issues relating to Mach.
Transonic drag, and potentially fatal transonic shock, is generated at much less than Mach 0.52 in propliners and analogous aircraft including bombers. In a B377 Mach 0.52 is when the probability of transonic shock becomes 'dangerously' high.
Some posters have a misplaced belief in 'facts' researched from books. The 'speeds' we read about in books that appear to be 'facts' are just 50% probabilities across 365 days and nights at latitude 45 North or 45 South.
South of 45 North we have a better than 50% probability of being able to exceed 295 KTAS at certification ceiling (FL250) without exceeding M0.52 because the air is warmer (on average) towards the equator. In summer, or just by day versus night, we can fly faster without inducing the same transonic drag for the same reason.
The point is to grasp how difficult that makes captaincy and to explore the captaincy choices. No book can convey how theoretical and variable the numbers it states as 'fact' really are. One day, in a particular place, in a B377 it may be safe to attain only 285 KTAS and another day in different place it may be safe to attain 305 KTAS.
If we wish to maximise the velocity of a B377 we must seek the ever varying altitude that maximises TAS as weight and weather vary, using the target values in the handling notes, though of course in real life ATC would impose a different solution based on their rules and priorities.
It is not possible to deduce Mno from Vno. One does not become the other. They are concurrent. Regardless of current dynamic drag if transonic drag reaches M0.52 structural failure may now be only one gust of wind away. That is why it is potentially dangerous to cruise a B377 at a dynamic drag of only 191 KIAS, once the transonic drag reaches Mach 0.52.
The transonic drag itself is not really the problem though. The real problem is increasing probability of fatal transonic shock between Mno and Mne.
Some aircraft have no promulgated Mach limits because nobody had figured out they needed them. Others, even in a power dive in very cold air are so fragile that their Vno and Vne are so low that they would always be destroyed by dynamic drag before low temperature became a factor and induced transonic shock. Nobody dies from transonic shock in a hang glider, but dozens of big strong aircraft that were nowhere near their dynamic drag limit have been lost to transonic shock at less then Mach 0.4.
In real life there are many drag limits to observe. Back when FS developers had little idea exactly how the air file was supposed to work we reached a de facto agreement to encode the Mach drag limit that users should observe as Mno for piston engined public transport aircraft, but Mne instead for piston engined combat aircraft. This reflects in a broad way the different 'rules of engagement' that apply to different roles.
Consequently the values encoded within FS9 flight dynamics for aircraft with different 'roles' are not strictly comparable.
The B-29 structure was a little weaker than that of the B377 because it had extra holes cut out for combat applications.
There is no reason to suppose that the B-29 had Mno or Mne greater than the stronger B377. However the crew of a B-29 would be both more likely and more willing to allow the aircraft to reach almost Mne whilst cruising if the circumstances were compelling.
These values must be researched carefully and encoded in the flight dynamics. They do matter. They are used by FS9. What confuses FS9 users is the fact that the aircraft.cfg is a file used by different .exe files within retail FS9, not just by FS9.exe. Some values are used only by FSEdit, some only by the FS9 flight planner. FS9 is a single product, but it is not a single program.
The B-29 was 'unsafe' beyond a dynamic drag of 300 MIAS (which actually rounds up to 261 KIAS) versus 271 KIAS for the stronger B377. Stratocruiser Mne was M0.585 and Superfortress Mne was the same or just slightly less. Both aircraft were exceptionally transonic shock tolerant by the large aircraft standards of the 1940s.
Some of the previous generation of WW2 strategic bombers had been unsafe at more than 165 MIAS (145 KIAS) in cold air. Their 'Mne' was well below M0.40. Aircraft that happen to have been designed during the same war do not share a common transonic drag tolerance and most had transonic drag tolerance nowhere near the levels that have been proposed in this thread or elsewhere in the FS community.
Moving to assorted matters raised by later posters in this thread.
All the DC-7 variants available for download from calclassic.com have had fully functional mainwheel air brakes for many years.
Descent planning is explored in principle and in detail in different parts of the propliner tutorial.
Prop pitch v thrust modelling is much better than it needs to be in FS9. Throttling back does not create drag. It creates less thrust. Bogus drag can however be added to air files to create 'real easy' flight dynamics if the target consumer is thought to relish them. All the relevant problems encountered by FS9 users are due to deficient or inappropriate flight planning of top of descent and unrealistic VSI/IAS targeting by users, not flight model or flight dynamics issues.
Concerning IAS and dynamic drag. The needle on the ASI moves in proportion to the square of the current drag in pounds. This difference matters to scientists, but IAS is how pilots measure the drag of the air on their aircraft. Why do pilots still use this strange frame of reference?
The propensity of a structure to fail does not depend on the force of the drag in pounds. It depends on the associated IAS. The propensity to fail follows the same 'square law'. IAS is the propensity of drag to rip things apart. In an aeroplane we need IAS as our dynamic drag reference. It tells us directly when the tail or the flaps or the gear will fail, so we end up using IAS to meet our drag target for best climb gradient (Vx) or best climb rate (Vy) and so on, and so on. In a B377 IAS is a relevant target during maximum cruise planning, but for reasons which I will explain shortly, in most aircraft it is not.
FS9 users think of KIAS as the reference for limiting the drag that is slowing them down, (or preventing them from climbing better), and learn to differentiate the concept of *drag* (measured by pilots in KIAS) from (aircraft or wind) *speed* (measured by pilots in KTS), and differentiate both of those concepts from *velocity* (measured by pilots in KTAS).
The following extract from the Propliner Tutorial may further increase understanding of how to maximise aircraft velocity and manage drag as a flight progresses. The worked example is for the DC-6B.
>>>>>>>>
DRAG.
The lower we fly the slower we fly in any aircraft. We are ramming more air molecules and they slow us down (a lot). Whenever we fly any aircraft we must work hard to maximise our velocity (TAS) whilst restraining our drag (IAS).
From the DC-6B handling notes.
*************
Econ Cruise (FL160 to FL225):
COWL FLAPS = CLOSED
MAP = 31
RPM = 1800
CHT < 232C
Plan 370 USG per hour
Note - yields 258 KTAS at FL220 @ 83000lbs
*************
Econ cruise MAP and rpm delivers a drag of about 182 KIAS at any level but it depends on current weight and that varies a lot over ten hours of flight. This is the most economical drag for cruising. The only altitude at which the drag and the velocity are equal is sea level. 182 KIAS = 182 KTAS at sea level but 182 KIAS = 258 KTAS at FL220.
With piston engines fuel consumption per mile (range) is nearly constant versus altitude. It is the velocity at which we can traverse that range that differs (a lot).
We can fly 1820 miles at low level in a DC-6B and take ten hours, or we can do it at FL220 and take seven. Entirely our choice. We use the same amount of fuel either way but should fly the DC-6B with a drag of 182 KIAS at a velocity of 258 KTAS up at operational ceiling, not down at low level ramming much thicker air with a velocity of only 182 KTAS.
WE must not apply abusive power at low level to try to get the drag up to 258 KIAS. Abusive power forces an aircraft to fly noticeably nose down. Using the fuel to increase drag (IAS) is not a substitute for using it to increase velocity (TAS). Available excess power is used to create climb power to reach the thinnest possible air.
The tail becomes stressed if we add too much drag. DC-6B Vno is 251 KIAS. If we push the drag on the tail beyond 251 KIAS it may suffer structural failure if we encounter turbulence. We should target a drag below 251 KIAS even in descent.
The only way to fly fast is to fly high. Sure we can fly lower than the operational ceiling, but we are wasting huge amounts of time. It will take many extra hours to complete even a medium haul.
Air molecules exert great drag on aeroplanes. We must keep the IAS down and the TAS high by flying as high as possible in the thinnest possible air.
Most FS9 users never quite grasp the difference between drag (IAS) and velocity (TAS). Consequently they end up trying to increase the wrong one
ACCELERATION and DECELERATION in aircraft.
Most MSFS users have never flown an aircraft, but have operated terrestrial vehicles. Everything they have ever learned about terrestrial vehicles leads them to believe that any vehicle is easier to accelerate going downhill than going uphill. The whole point about aircraft, and the only reason airliners exist, is that aircraft are incredibly easy to accelerate when going uphill and almost impossible to accelerate when going downhill.
If that sounds unlikely then you are bound to be flying unrealistically.
It takes FS9 users, (and many real pilots), a long time to understand that if a fighter pilot power dives his fighter from 250 KIAS at 40,000 feet to 400 KIAS at low level he has decelerated from about 500 KTAS to about 400 KTAS. As the fighter pilot dives hard and watches the ASI needle proceed from 250 to 400 he is watching the drag rise, he hears the wind noise screaming ever louder as he decelerates a hundred knots in no time at all.
A drag of 400 KIAS at low level ensures that the fighter is much slower than it is with a drag of 250 KIAS at high level. It's just a lot more drag, so we hear much more wind noise. Wind noise isn't an indicator of velocity, it's just an indicator of drag. IAS isn't an indicator of velocity, it's just an indicator of drag.
In a DC-6B we must take care that the drag does not rise above 165 KIAS until we have finished accelerating the aircraft, which will be at least 30 minutes after take off. We must keep the drag low and point it up hill or it will not accelerate. So long as we keep going up hill it will accelerate so fast that we can reduce MAP from 45 inches in the stage 1 climb to just 37 inches in stage 3 climb during the final stage of the acceleration. We start the acceleration burning 600 gallons per hour and finish it burning only 480 gallons per hour. We cannot accelerate a DC-6B by applying 37 inches and burning only 480 USG/hr at low level. We can only do it at the top of a long, long hill climb. In an aeroplane climbing enables acceleration and diving promotes deceleration. When climbing we need less and less power to go faster and faster. The aeroplane is the exact opposite of a terrestrial vehicle. That's the whole point.
Airliners cannot fly fast at low level. They do not have enough power. To fly fast an airliner must accelerate for as long as possible, and the only way to accelerate an aircraft, for more than a couple of minutes, is to point it uphill and keep on going uphill into thinner and thinner air for as long as possible.
At sea level a drag of 160 KIAS delivers a velocity of 160 KTAS, but after going up hill in a DC-6B at a drag of about 160 KIAS for 30 minutes we will have reached about FL160 and we will have accelerated to a velocity of 205 KTAS. If we departed at max gross in a DC-6B we will be around our current operational ceiling by then so we will reduce power further to 31 inches and allow the drag to rise to just over 180 KIAS allowing the aircraft to accelerate further to a velocity of 231 KTAS.
To go faster (accelerate) we must step climb again and again as weight reduces hour by hour. Many hours later we can cruise at 258 KTAS up at FL220, still with only 182 KIAS of drag. We will have turned a ten hour flight into a seven hour flight by climbing and sustaining operational ceiling as weight reduces.
End of extract.
>>>>>>>
The dynamic drag of passing air molecules (measured by pilots in KIAS) slows aircraft down and prevents them from achieving high velocity (measured by pilots in KTAS). Transonic drag (measured by pilots in Mach) also slows aircraft down and prevents them from achieving high velocity. Both exist together. One does not become the other. They don't 'convert'. The limits that depend on temperature have no dependency at all on the limits that don't.
The handling notes specify the targets that users must pursue to allow velocity to maximise. These targets do not just differ in value from aircraft to aircraft. The type of target differs depending on what type of limits constrain performance of that particular aircraft. The B377 handling notes promulgate the combination of dynamic drag (KIAS) and transonic drag and/or shock tolerance (Mach) that allows velocity (KTAS) to maximise. During an air race (with no wind) pilots must work hard to target the promulgated combination of KIAS and Mach that maximises velocity (KTAS).
In a B377 maximum velocity is only available when having already restricted current dynamic drag to just over 190 KIAS the transonic drag is fractionally under M0.52. This condition exists only along a single thermocline of fixed temperature in the Earth's atmosphere. Its altitude varies minute by minute and mile by mile. All other conditions reduce available cruising velocity in a B377.
The maximum possible velocity of a B377 varies with weight and the weather, but regardless the variable maximum is always achieved by restricting dynamic drag to => 190 KIAS and transonic drag to <= M0.52. Our operating targets (specified in the handling notes) never change with weight or weather in FS9. It is the resulting maximum velocity (Vmax) that varies and is constrained by both weight and weather.
The real world operations manual may provide a wider range of combinations for a wide range of unusual weather conditions. However those manuals are copyright and if we want them we have to pay for them. They cannot (legally) be given away within freeware.
Either way we cannot target a KTAS or MTAS incorrectly published as a 'fact' in the 'Boys Bumper Book of Big Planes'. In real life or in FS9 we have no idea what its value will be today, in this weather, at this weight. We can only target the same dynamic drag (IAS) and transonic drag (Mach) each day and everywhere, which is precisely why our propliner cockpit has no TAS gauge. When max cruising a B377 we have two target drags. We must work hard to control all types of drag until the velocity maximises to whatever the maximum may be at this moment, at this weight, in this weather. We control and optimise all the types of drag by varying altitude
We must step climb hour by laborious hour, in accordance with the handling notes and the propliner tutorial. Our cruising velocity will be much less than that claimed as 'fact' in the 'Bumper Book of Big Planes' until we are light enough to reach the optimum thermocline. If later still we make the captaincy mistake of climbing above that optimum thermocline (maximum) cruising velocity will diminish.
Sometimesthe optimum thermocline will be above the certification ceiling of the aircraft. We cannot achieve 'book' velocity at all on those days. On other days we may encounter 'unusually' warm air just below certification ceiling. On those days we will be able to exceed a dynamic drag of 191 KIAS at FL250 without exceeding the maximum safe transonic drag of M0.52 and we will be able to exceed 'book' maximum velocity (295 KTAS) without risk of sudden structural failure. We may be able to reach 305 KTAS..... or not. It just depends on all the above.
Most post war piston propliners (including the DC-6B) have much simpler handling criteria than the B377 because they have superchargers (rather than turbo chargers). Most piston propliners (or bombers) can withstand much less transonic drag than a B377 or B-29 but their engines produce so little power that they have no possibility of reaching an unsafe transonic drag in level flight. Most must however exercise caution during early descent from high level cruise. The relevant limits are specified in their individual handling notes.
How to maximise the speed of a B377 during an air race would involve a whole different answer. The original question asked about maximising the velocity of a B377, not maximising its speed, and they are very different concepts. How to maximise the speed (KTS) of a B377 between A and B whilst using FS9 involves more complex captaincy decisions and is more complicated, but is anyway explained in later parts of the Propliner Tutorial. Part 1 only explains how to maximise cruising velocity (KTAS).
By now everyone should have grasped that aircraft dynamic drag (KIAS), aircraft speed (KTS) and aircraft velocity (KTAS) are three different things and maximising any one of them requires different captaincy decisions. Learning how to make the correct captaincy decisions to maximise a chosen performance attribute of a given aeroplane is how we learn to fly any aeroplane (better).
We all have to acquire the knowledge and develop the skill to maximise it in a different environment every time we fly. The relevant skill is the skill of captaincy. The best pilot will achieve the highest mean velocity. That is the point of air racing. If all the aircraft are identical the best pilot wins. They don't cross the line together. Maximum velocity (in any power setting) is a function of pilot (captaincy) skill.
The handling notes promulgate the targets and the propliner tutorial explains the captaincy decisions so that FS9 users can understand which set of targets to pursue to maximise a specific attribute of performance. Nobody in any forum has to guess wildly about any of the values discussed in this thread or how to achieve them by making skilful captaincy decisions whilst using the B377 within FS9. All the answers were always in the B377 download and the associated web tutorial.
Did anyone really suppose that the knowledge base and skill required to captain a Boeing Stratocruiser well was going to be minimal? Remember the skills learned in a video game are worth nothing in the real world, but the skills needed to use a flight simulator competently are worth hundreds of dollars per hour in the real world. That is what makes flight simulation more interesting and demanding than video gaming.
FSAviator.
www.sim-outhouse.com/sohforums/showthread.php?t=35023
******************************
B377 Flight Dynamics and handling criteria
Greetings 'Gibbons',
I am sorry to hear that you are puzzled by my B377 flight dynamics. MDLs, panels, gauges and sound files just sit there waiting for the flight dynamics to tell them how to react to user input.
Your question is based on the commonplace confusion between drag (IAS) and velocity (TAS) and further confusion concerning the dynamic relationship between velocity (TAS) and Mach.
Unless you were using a badly designed third party replacement panel both the real panel and the original FS panel supplied by Greg Pepper had an ASI which incorporated a 'Mach Bug'. The Mach Bug is a short
barber pole without the stripes. You have been ignoring the Mach Bug and allowing the ASI needle to merge with the Mach Bug.
It is your job to prevent this, either by reducing power or by seeking warmer air. Mach number depends only on velocity (TAS) and temperature. What altitude will allow maximum safe cruising velocity in a B377 varies hour by hour through the flight as current weight reduces and also hour by hour with the current weather. Flying propliners is a dynamic process and the B377 is a particularly difficult and complex propliner to master. What is safe one minute may be unsafe the next or vice versa, especially if you push propliners to the very limit of their safe performance envelope by using max cruise power.
The relevant section of the supplied on screen handling notes reads as follows;
***********************************
Max Cruise:
DO NOT EXCEED M0.52 - USE MACH BUG
COWL FLAPS - CLOSED
2100 RPM
41 inches MAP
If unable => 190 KIAS descend to lower level
Plan 650 GPH
Note: - Yields 295 KTAS at FL250
***********************************
You should not normally employ max cruise power unless very heavy or battling a headwind. Doing so gives you several dynamic problems to juggle. To invoke max cruise power you must not exceed an altitude at
which you can generate 41 inches of MAP and at the same time it is your job to seek the highest (semi circular compliant) cruising level that is compatible with a drag => 190 KIAS and that also does not cause the ASI needle to merge with the supplied Mach Bug which always shows the IAS = Mach 0.52 in the current weather.
When you have found the optimum current cruising level using the techniques described in detail in the supplied handling hints within the download you have achieved maximum safe cruising velocity for your
current weight in the current weather. That is the skill that the overspeed warning helps you to develop, though if you pay attention to the original ASI and its incorporated Mach Bug you will never commit either of the pilot errors that generate the overspeed warning.
When you do not need to battle significant headwinds and after you have burned off sufficient fuel you can make your life a lot easier by applying only economical cruise power and restricting your drag to
little more than 180 KIAS.
***********************************
Econ Cruise:
WARNING - not available at high weights
COWL FLAPS - CLOSED
2100 RPM
38 inches MAP
If unable => 180 KIAS descend to lower level
Plan 550 GPH
***********************************
Once you are light enough achieving a velocity of 290 KTAS in a B377 is not particularly difficult, but reaching a drag of 290 KIAS is abusive. The goal is to operate the aircraft carefully to avoid Mno = Mach 0.52 using the supplied Mach Bug and also to avoid Vno = 271 KIAS using the needle of the ASI; even when a drag of 271 KIAS is less than Mach 0.52 in warm air at low altitude. The main needle of any ASI tells you your drag (IAS), not your velocity (TAS).
****************************
Descent:
DO NOT EXCEED 271 KIAS
DO NOT EXCEED M0.52 - USE MACH BUG
AUTOMIXTURE - ON
COWL FLAPS - CRACKED
2100 RPM
REDUCE MAP in stages of 3 inches (per minute)
MINIMUM 17 INCHES MAP
****************************
The B377 was not certificated for flight above FL250. The pressurisation system could not cope. You should never attempt to climb higher and the colder air at higher altitude will restrict your safe cruising velocity even more anyway. The MAP you can generate will also be falling quickly at those altitudes. You will be entering 'coffin corner'. You may also have been ignoring the following part of the supplied on screen handling notes.
****************************
General:
NEVER EXCEED FL250 certification limit
NEVER EXCEED 305 KIAS
NEVER EXCEED M0.52 - USE MACH BUG
ROUGH AIR NEVER EXCEED 271 KIAS
GEAR DOWN NEVER EXCEED 200 KIAS
FLAP 1 never exceed 191 KIAS
FULL FLAP never exceed 162 KIAS
CLEAN STALL 115 KIAS at MLW
STALL with FULL FLAP 80 KIAS at MLW
****************************
Your primary goal is to avoid applying abusive drag (KIAS) for the current airframe configuration. You never know when you may run into rough air. Avoiding potentially abusive dynamic drag of 271 KIAS is easy
at any altitude, but the higher you climb, the colder the air, and the harder it becomes to avoid abusive transonic drag whose onset is at Mach 0.52.
Whenever you exceed Vno or Mno you will get an overspeed warning. It is not a mistake. It is there to help you to understand that you are potentially abusing the aircraft and have failed to follow the
comprehensive step by step on screen handling notes (press F10 and select the lowest icon with your mouse). They explain all the operating targets and all the operating limits of the aircraft. You must
differentiate between the operating targets, which you must pursue, hour after relentless hour, whilst always avoiding the operating limits.
The difference between drag (KIAS) and velocity (KTAS) is explained in more detail within my generic Propliner Tutorial available from the same place as the latest updates for Greg Pepper's B377 aircraft and panel which is Tom Gibson’s website at;
www.calclassic.com/
Look in the Tutorials section for ‘FSAviator's Propliner Flying in the Classic Era’. Hopefully that will resolve any lingering confusion, but the documentation supplied with a download is always the first place
to start looking for answers.
Hope that helps;
FSAviator
Greetings all,
I aplogise if this post has odd line spacing. I did not have time to correct it. There have been many questions raised in this thread. Let me try to clarify the issues that I think are still most widely misunderstood.
The issue of gauge compatibility is not being grasped. Third party gauges may contain non standard code that triggers 'events' when a threshold value set within the gauge is matched. The event may be one wholly absent from retail FS9, or the threshold for triggering the event is specific to the aircraft.
The consequence of the event may be coded within the air file, but can be coded within the same gauge, or a different gauge as a 'different multiplier' of a singular value in an air file. Gauges within panels may also be 'slaved' to one another passing data across a network of gauges. Remove one and you break the code interaction.
Remove the gauges developed for the project and you dumb the aircraft down to be no better than a default aircraft from FS9. That may be an awful lot of dumbing down. Third party developers develop their own gauge code to add events absent from retail FS9 and to make the simulation less generic and more aircraft/engine/system specific. The additional code in freeware products often exceeds the additional code in payware products. When users swap panels or gauges that contain third party gauges they have no idea what the result will be. The more 'developed' the aircraft the dumber the result is likely to be.
Be that as it may the only way to make any aircraft go faster is to learn how to fly it better. The handling notes explain how to fly it (better). They explain the concurrent handling targets for each phase and each power setting and the limits that apply to all of them. The fact that 'better' flying requires the user to achieve multiple concurrent targets introduces both complexity and options.
When the ASI needle merges with the Mach Bug we have a problem to solve. Certainly one of our captaincy options is to reduce MAP to economical cruise to ensure that the needle falls below the bug, but we have more captaincy options than reducing power and slowing down.
The premise is that we don't want to slow down. The first step is to apply the handling target MAP and rpm. If the drag target (for maximum cruising velocity) which is => 190 KIAS is > M0.52 the Mach Bug is actually telling us something more subtle than that we must slow down. It is telling us that we have climbed too high, into air that is too cold to be safe. What we may actually do is descend into warmer air until the dynamic drag target for maximum velocity (just over 190 KIAS) is associated with transonic drag that is just less than M0.52. Mach is how pilots measure transonic drag. Just like IAS, Mach is *not* a measure of velocity.
Most FS9 users have a very poor understanding of issues relating to Mach.
Transonic drag, and potentially fatal transonic shock, is generated at much less than Mach 0.52 in propliners and analogous aircraft including bombers. In a B377 Mach 0.52 is when the probability of transonic shock becomes 'dangerously' high.
Some posters have a misplaced belief in 'facts' researched from books. The 'speeds' we read about in books that appear to be 'facts' are just 50% probabilities across 365 days and nights at latitude 45 North or 45 South.
South of 45 North we have a better than 50% probability of being able to exceed 295 KTAS at certification ceiling (FL250) without exceeding M0.52 because the air is warmer (on average) towards the equator. In summer, or just by day versus night, we can fly faster without inducing the same transonic drag for the same reason.
The point is to grasp how difficult that makes captaincy and to explore the captaincy choices. No book can convey how theoretical and variable the numbers it states as 'fact' really are. One day, in a particular place, in a B377 it may be safe to attain only 285 KTAS and another day in different place it may be safe to attain 305 KTAS.
If we wish to maximise the velocity of a B377 we must seek the ever varying altitude that maximises TAS as weight and weather vary, using the target values in the handling notes, though of course in real life ATC would impose a different solution based on their rules and priorities.
It is not possible to deduce Mno from Vno. One does not become the other. They are concurrent. Regardless of current dynamic drag if transonic drag reaches M0.52 structural failure may now be only one gust of wind away. That is why it is potentially dangerous to cruise a B377 at a dynamic drag of only 191 KIAS, once the transonic drag reaches Mach 0.52.
The transonic drag itself is not really the problem though. The real problem is increasing probability of fatal transonic shock between Mno and Mne.
Some aircraft have no promulgated Mach limits because nobody had figured out they needed them. Others, even in a power dive in very cold air are so fragile that their Vno and Vne are so low that they would always be destroyed by dynamic drag before low temperature became a factor and induced transonic shock. Nobody dies from transonic shock in a hang glider, but dozens of big strong aircraft that were nowhere near their dynamic drag limit have been lost to transonic shock at less then Mach 0.4.
In real life there are many drag limits to observe. Back when FS developers had little idea exactly how the air file was supposed to work we reached a de facto agreement to encode the Mach drag limit that users should observe as Mno for piston engined public transport aircraft, but Mne instead for piston engined combat aircraft. This reflects in a broad way the different 'rules of engagement' that apply to different roles.
Consequently the values encoded within FS9 flight dynamics for aircraft with different 'roles' are not strictly comparable.
The B-29 structure was a little weaker than that of the B377 because it had extra holes cut out for combat applications.
There is no reason to suppose that the B-29 had Mno or Mne greater than the stronger B377. However the crew of a B-29 would be both more likely and more willing to allow the aircraft to reach almost Mne whilst cruising if the circumstances were compelling.
These values must be researched carefully and encoded in the flight dynamics. They do matter. They are used by FS9. What confuses FS9 users is the fact that the aircraft.cfg is a file used by different .exe files within retail FS9, not just by FS9.exe. Some values are used only by FSEdit, some only by the FS9 flight planner. FS9 is a single product, but it is not a single program.
The B-29 was 'unsafe' beyond a dynamic drag of 300 MIAS (which actually rounds up to 261 KIAS) versus 271 KIAS for the stronger B377. Stratocruiser Mne was M0.585 and Superfortress Mne was the same or just slightly less. Both aircraft were exceptionally transonic shock tolerant by the large aircraft standards of the 1940s.
Some of the previous generation of WW2 strategic bombers had been unsafe at more than 165 MIAS (145 KIAS) in cold air. Their 'Mne' was well below M0.40. Aircraft that happen to have been designed during the same war do not share a common transonic drag tolerance and most had transonic drag tolerance nowhere near the levels that have been proposed in this thread or elsewhere in the FS community.
Moving to assorted matters raised by later posters in this thread.
All the DC-7 variants available for download from calclassic.com have had fully functional mainwheel air brakes for many years.
Descent planning is explored in principle and in detail in different parts of the propliner tutorial.
Prop pitch v thrust modelling is much better than it needs to be in FS9. Throttling back does not create drag. It creates less thrust. Bogus drag can however be added to air files to create 'real easy' flight dynamics if the target consumer is thought to relish them. All the relevant problems encountered by FS9 users are due to deficient or inappropriate flight planning of top of descent and unrealistic VSI/IAS targeting by users, not flight model or flight dynamics issues.
Concerning IAS and dynamic drag. The needle on the ASI moves in proportion to the square of the current drag in pounds. This difference matters to scientists, but IAS is how pilots measure the drag of the air on their aircraft. Why do pilots still use this strange frame of reference?
The propensity of a structure to fail does not depend on the force of the drag in pounds. It depends on the associated IAS. The propensity to fail follows the same 'square law'. IAS is the propensity of drag to rip things apart. In an aeroplane we need IAS as our dynamic drag reference. It tells us directly when the tail or the flaps or the gear will fail, so we end up using IAS to meet our drag target for best climb gradient (Vx) or best climb rate (Vy) and so on, and so on. In a B377 IAS is a relevant target during maximum cruise planning, but for reasons which I will explain shortly, in most aircraft it is not.
FS9 users think of KIAS as the reference for limiting the drag that is slowing them down, (or preventing them from climbing better), and learn to differentiate the concept of *drag* (measured by pilots in KIAS) from (aircraft or wind) *speed* (measured by pilots in KTS), and differentiate both of those concepts from *velocity* (measured by pilots in KTAS).
The following extract from the Propliner Tutorial may further increase understanding of how to maximise aircraft velocity and manage drag as a flight progresses. The worked example is for the DC-6B.
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DRAG.
The lower we fly the slower we fly in any aircraft. We are ramming more air molecules and they slow us down (a lot). Whenever we fly any aircraft we must work hard to maximise our velocity (TAS) whilst restraining our drag (IAS).
From the DC-6B handling notes.
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Econ Cruise (FL160 to FL225):
COWL FLAPS = CLOSED
MAP = 31
RPM = 1800
CHT < 232C
Plan 370 USG per hour
Note - yields 258 KTAS at FL220 @ 83000lbs
*************
Econ cruise MAP and rpm delivers a drag of about 182 KIAS at any level but it depends on current weight and that varies a lot over ten hours of flight. This is the most economical drag for cruising. The only altitude at which the drag and the velocity are equal is sea level. 182 KIAS = 182 KTAS at sea level but 182 KIAS = 258 KTAS at FL220.
With piston engines fuel consumption per mile (range) is nearly constant versus altitude. It is the velocity at which we can traverse that range that differs (a lot).
We can fly 1820 miles at low level in a DC-6B and take ten hours, or we can do it at FL220 and take seven. Entirely our choice. We use the same amount of fuel either way but should fly the DC-6B with a drag of 182 KIAS at a velocity of 258 KTAS up at operational ceiling, not down at low level ramming much thicker air with a velocity of only 182 KTAS.
WE must not apply abusive power at low level to try to get the drag up to 258 KIAS. Abusive power forces an aircraft to fly noticeably nose down. Using the fuel to increase drag (IAS) is not a substitute for using it to increase velocity (TAS). Available excess power is used to create climb power to reach the thinnest possible air.
The tail becomes stressed if we add too much drag. DC-6B Vno is 251 KIAS. If we push the drag on the tail beyond 251 KIAS it may suffer structural failure if we encounter turbulence. We should target a drag below 251 KIAS even in descent.
The only way to fly fast is to fly high. Sure we can fly lower than the operational ceiling, but we are wasting huge amounts of time. It will take many extra hours to complete even a medium haul.
Air molecules exert great drag on aeroplanes. We must keep the IAS down and the TAS high by flying as high as possible in the thinnest possible air.
Most FS9 users never quite grasp the difference between drag (IAS) and velocity (TAS). Consequently they end up trying to increase the wrong one
ACCELERATION and DECELERATION in aircraft.
Most MSFS users have never flown an aircraft, but have operated terrestrial vehicles. Everything they have ever learned about terrestrial vehicles leads them to believe that any vehicle is easier to accelerate going downhill than going uphill. The whole point about aircraft, and the only reason airliners exist, is that aircraft are incredibly easy to accelerate when going uphill and almost impossible to accelerate when going downhill.
If that sounds unlikely then you are bound to be flying unrealistically.
It takes FS9 users, (and many real pilots), a long time to understand that if a fighter pilot power dives his fighter from 250 KIAS at 40,000 feet to 400 KIAS at low level he has decelerated from about 500 KTAS to about 400 KTAS. As the fighter pilot dives hard and watches the ASI needle proceed from 250 to 400 he is watching the drag rise, he hears the wind noise screaming ever louder as he decelerates a hundred knots in no time at all.
A drag of 400 KIAS at low level ensures that the fighter is much slower than it is with a drag of 250 KIAS at high level. It's just a lot more drag, so we hear much more wind noise. Wind noise isn't an indicator of velocity, it's just an indicator of drag. IAS isn't an indicator of velocity, it's just an indicator of drag.
In a DC-6B we must take care that the drag does not rise above 165 KIAS until we have finished accelerating the aircraft, which will be at least 30 minutes after take off. We must keep the drag low and point it up hill or it will not accelerate. So long as we keep going up hill it will accelerate so fast that we can reduce MAP from 45 inches in the stage 1 climb to just 37 inches in stage 3 climb during the final stage of the acceleration. We start the acceleration burning 600 gallons per hour and finish it burning only 480 gallons per hour. We cannot accelerate a DC-6B by applying 37 inches and burning only 480 USG/hr at low level. We can only do it at the top of a long, long hill climb. In an aeroplane climbing enables acceleration and diving promotes deceleration. When climbing we need less and less power to go faster and faster. The aeroplane is the exact opposite of a terrestrial vehicle. That's the whole point.
Airliners cannot fly fast at low level. They do not have enough power. To fly fast an airliner must accelerate for as long as possible, and the only way to accelerate an aircraft, for more than a couple of minutes, is to point it uphill and keep on going uphill into thinner and thinner air for as long as possible.
At sea level a drag of 160 KIAS delivers a velocity of 160 KTAS, but after going up hill in a DC-6B at a drag of about 160 KIAS for 30 minutes we will have reached about FL160 and we will have accelerated to a velocity of 205 KTAS. If we departed at max gross in a DC-6B we will be around our current operational ceiling by then so we will reduce power further to 31 inches and allow the drag to rise to just over 180 KIAS allowing the aircraft to accelerate further to a velocity of 231 KTAS.
To go faster (accelerate) we must step climb again and again as weight reduces hour by hour. Many hours later we can cruise at 258 KTAS up at FL220, still with only 182 KIAS of drag. We will have turned a ten hour flight into a seven hour flight by climbing and sustaining operational ceiling as weight reduces.
End of extract.
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The dynamic drag of passing air molecules (measured by pilots in KIAS) slows aircraft down and prevents them from achieving high velocity (measured by pilots in KTAS). Transonic drag (measured by pilots in Mach) also slows aircraft down and prevents them from achieving high velocity. Both exist together. One does not become the other. They don't 'convert'. The limits that depend on temperature have no dependency at all on the limits that don't.
The handling notes specify the targets that users must pursue to allow velocity to maximise. These targets do not just differ in value from aircraft to aircraft. The type of target differs depending on what type of limits constrain performance of that particular aircraft. The B377 handling notes promulgate the combination of dynamic drag (KIAS) and transonic drag and/or shock tolerance (Mach) that allows velocity (KTAS) to maximise. During an air race (with no wind) pilots must work hard to target the promulgated combination of KIAS and Mach that maximises velocity (KTAS).
In a B377 maximum velocity is only available when having already restricted current dynamic drag to just over 190 KIAS the transonic drag is fractionally under M0.52. This condition exists only along a single thermocline of fixed temperature in the Earth's atmosphere. Its altitude varies minute by minute and mile by mile. All other conditions reduce available cruising velocity in a B377.
The maximum possible velocity of a B377 varies with weight and the weather, but regardless the variable maximum is always achieved by restricting dynamic drag to => 190 KIAS and transonic drag to <= M0.52. Our operating targets (specified in the handling notes) never change with weight or weather in FS9. It is the resulting maximum velocity (Vmax) that varies and is constrained by both weight and weather.
The real world operations manual may provide a wider range of combinations for a wide range of unusual weather conditions. However those manuals are copyright and if we want them we have to pay for them. They cannot (legally) be given away within freeware.
Either way we cannot target a KTAS or MTAS incorrectly published as a 'fact' in the 'Boys Bumper Book of Big Planes'. In real life or in FS9 we have no idea what its value will be today, in this weather, at this weight. We can only target the same dynamic drag (IAS) and transonic drag (Mach) each day and everywhere, which is precisely why our propliner cockpit has no TAS gauge. When max cruising a B377 we have two target drags. We must work hard to control all types of drag until the velocity maximises to whatever the maximum may be at this moment, at this weight, in this weather. We control and optimise all the types of drag by varying altitude
We must step climb hour by laborious hour, in accordance with the handling notes and the propliner tutorial. Our cruising velocity will be much less than that claimed as 'fact' in the 'Bumper Book of Big Planes' until we are light enough to reach the optimum thermocline. If later still we make the captaincy mistake of climbing above that optimum thermocline (maximum) cruising velocity will diminish.
Sometimesthe optimum thermocline will be above the certification ceiling of the aircraft. We cannot achieve 'book' velocity at all on those days. On other days we may encounter 'unusually' warm air just below certification ceiling. On those days we will be able to exceed a dynamic drag of 191 KIAS at FL250 without exceeding the maximum safe transonic drag of M0.52 and we will be able to exceed 'book' maximum velocity (295 KTAS) without risk of sudden structural failure. We may be able to reach 305 KTAS..... or not. It just depends on all the above.
Most post war piston propliners (including the DC-6B) have much simpler handling criteria than the B377 because they have superchargers (rather than turbo chargers). Most piston propliners (or bombers) can withstand much less transonic drag than a B377 or B-29 but their engines produce so little power that they have no possibility of reaching an unsafe transonic drag in level flight. Most must however exercise caution during early descent from high level cruise. The relevant limits are specified in their individual handling notes.
How to maximise the speed of a B377 during an air race would involve a whole different answer. The original question asked about maximising the velocity of a B377, not maximising its speed, and they are very different concepts. How to maximise the speed (KTS) of a B377 between A and B whilst using FS9 involves more complex captaincy decisions and is more complicated, but is anyway explained in later parts of the Propliner Tutorial. Part 1 only explains how to maximise cruising velocity (KTAS).
By now everyone should have grasped that aircraft dynamic drag (KIAS), aircraft speed (KTS) and aircraft velocity (KTAS) are three different things and maximising any one of them requires different captaincy decisions. Learning how to make the correct captaincy decisions to maximise a chosen performance attribute of a given aeroplane is how we learn to fly any aeroplane (better).
We all have to acquire the knowledge and develop the skill to maximise it in a different environment every time we fly. The relevant skill is the skill of captaincy. The best pilot will achieve the highest mean velocity. That is the point of air racing. If all the aircraft are identical the best pilot wins. They don't cross the line together. Maximum velocity (in any power setting) is a function of pilot (captaincy) skill.
The handling notes promulgate the targets and the propliner tutorial explains the captaincy decisions so that FS9 users can understand which set of targets to pursue to maximise a specific attribute of performance. Nobody in any forum has to guess wildly about any of the values discussed in this thread or how to achieve them by making skilful captaincy decisions whilst using the B377 within FS9. All the answers were always in the B377 download and the associated web tutorial.
Did anyone really suppose that the knowledge base and skill required to captain a Boeing Stratocruiser well was going to be minimal? Remember the skills learned in a video game are worth nothing in the real world, but the skills needed to use a flight simulator competently are worth hundreds of dollars per hour in the real world. That is what makes flight simulation more interesting and demanding than video gaming.
FSAviator.