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Guest cfm56

Thrust for Altitude

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Hello all, Im looking for information on how to tweak the .AIR file to allow the aircraft to descend with thrust as opposed to pitch. Im many of you have heard the saying "pitch for airspeed, power for altitude" in ref to slow flight......Can any one help me set this up in the sim.Gideon

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To be honest, based on your post... this has nothing to do with an .air file at all.However, I have to admit I'm still uncertain what you're wanting to accomplish.

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OK, what im aiming to accomplish is to control an aircrafts Rate of descent on the vsi using thrust imputs so that when i power down to say 60 percent n1 the aircraft descends by xxxx on the vsi for example.... and likewise when power is increased the aircraft vertical speed increases...Gideon

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Well, it doesn't work quite like that in the real world. Pitch and thrust are inter-related during climbs and descents.Theoretically, you could climb (poorly) by simply increasing power and, therefore, airspeed. When the aircraft accelerated, the wing would provide more lift at the same angle of attack. To maintain that same exact AoA, you'd have to trim against it, which would mean you were climbing (clumsily) and trimming down at the same time.Climb and descent rates are controlled using both pitch and power.Btw, that "pitch for speed; power for altitude" is only a mantra for beginners. At best, it indicates only which element you introduce FIRST in SOME scenarios. In reality, because pitch adjustments are fast-acting and precise, pitch is used to maintain whichever element (speed or altitude) is most critical in the applicable flight regime at that time. Consider an ILS approach. Staying on the glideslope is more important than a few knots more or less. You get high, let's say, so you lower the nose slightly. That causes the speed to increase slightly, so you also back off the power a fraction. Note: you don't chase the glideslope with pitch; you just adjust the pitch by a degree or two, then hold that new pitch angle until you see how it works.A tight short-field landing is just the opposite. You want that speed nailed close to, but above, stall. Pitch adjustments keep the airspeed correct and power is used to adjust the descent rate.Either way, pitch OR power may be the very first corrective control input, but the other adjustment will probably be needed also.(Boy, oh boy, is this gonna bring the 300-hour instructor pilots out of the woodwork!)Sorry about the long post, but I hope it helps explain why what you want to do is neither practical nor realistic.Good luck,Glenn

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Thanks for your post Glenn but I must differ... just a bit"I hope it helps explain why what you want to do is neither practical nor realistic." I am well aware of the inputs required to maintain proper altitude and airspeed on appr. THe reason why I must differ though is because I was on a few 737winglet flights just a few weeks ago and the entire way down to "flare" and landing I listening and watching for the inputs the pilot was making to get the aircraft down (yes i know its not the ideal vantage point to see what pitch changes was made seat5F but the ears and stomach can tell no lie as to what was going on.) On all four legs of the trip with 4 different sets of crews the pilots made significant power changes to control the aircraft in the way that i described and every single one of them where followed by the sensation that the aircraft was "falling" at a rate greater than what it was b4. Similarly, when power was increased you could literally feel the vsi changes.The second reason Y i have to disagree is that, the PMDG 747 in its default Airfile settings(said to have been tested by real pilots), Pitch for airspeed, power for altitude principle applies on final just cut power on final and hold 4-5 deg pitch up. If by the time u say ROCK, the aircraft doesnt hit the ground just change my name to aunt sally. (CALLING ALL QUEEN DRIVERS FOR BACK UP) lolNonetheless, Ill survive on flying the queen on short hops for now.

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Whatever floats your boat...BUT there are several factors you could not see or recognise from seat 5F.First, who knows who or what was actually flying the aircraft. Were the flaps fully deployed before you starting monitoring the power changes? Autopilot on or off? Auto throttle on or off? Autoland on or off? Second, I'm glad you used the 737 as an example. The low-slung engines on a 737 mean pitch trim changes are required whenever thrust is increased or decreased. The bird is well known for that characteristic. Accordingly, I feel safe in saying that there was a pitch change (or pitch trim change, which is essentially the same thing) with each and every power change you heard.Third, you said, "...but the ears and stomach can tell no lie as to what was going on." Sorry, but that is both incorrect and dangerous. When you can't see outside, instruments tell you the truth; stomachs (and ear canals) lie. Always. Think of the old term "graveyard spiral."As I indicated originally, there will always be hangar discussions about which comes first; pitch or power. But the fact remains that regardless of which control input leads, the other must, and will, follow closely behind to maintain a stabilized flight regime.Consider the differences between aircraft and cars. Want to turn a car? It's quite simple. Twist the steering wheel, hold it for awhile, then neutralize it when you're pointing in the right direction. In an aircraft, the same maneuver requires, in order: A roll input plus an increasing pitch input as bank increases and a yaw input to center the ball. Then the roll input is removed, but the pitch input remains and may vary if speed decreases (a bit of power might help here). To exit the turn, a roll input in the opposite direction is needed but it must be removed at the correct time. Simultaneously, pitch is reduced as the wings level while the rudder input is removed in a coordinated movement.You cannot control an aircraft by varying only one input. It may appear that an autopilot is doing that, but other control inputs are taking place simultaneously.But as I said above.... whatever floats your boat. Glenn

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air files....never been a real strong topic round here. in deferance to the last couple of posts here on this topic..stick vs throttle walking running hopping jumping.....if you are new to the air file i recomend a program 'aired'you will still need some kind of hex editor to tweek the graph entries. there is also a program out there called airwrench which while having a softer interface, is really for building an airfile from scratch, a job that will turn into an avocation if you are the slightest bit OCD! the tried and true method seems to be find an airfile that is close....and tweek it. if you want a stronger reaction from power...ie. underpowered thick ratio straight winged high drag aircraft... you will start with #1101 primary aerodynamics in the airfile. play with the CL. know that the airfile is a bowl of marbles...move one and they all move. if you tryout airwrench...you can see the aerodynamic visual model of the plane you are flying...its scarey....a lot of planes do not have the wings actually attached to the airframes, and tails that are meters above the nose section....its a wonder they behave anything remotly like an aircraft...the air file is a world of its own....having looked at hundreds i can tell you folks get one that is working and tweek a few parameters, ( i keep seeing the same strange visual aerodynamic models) your best bet is to start with a microsoft plane ( they look pretty normal aerodynamically ) or an airfile from a good payware version of the aircraft you are tweeking or as close as you can find. if you invisioned a shorter answer and a quick resolution...you know now why there were not that many respondents to your post.the good news is you can find ( world is full of OCD types) lots of aerodynamic studies on various aircraft on the web, many will get you well on the way to building a airfile from the bottom up. good luck

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I'll say it again... the contents of the .air file has absolutely nothing to do with this at all. Nothing. Zip, zilch, nada. Am I getting through yet? ;)

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How are u doing Ed, Something tells me your holding out on us... Do tell us what we are missing, pleeez.Gideon

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Gideon...You have already been advised that manipulating the .air file cannot accomplish what you want to do.You have already been advised that what you want to do would be impractical and unrealistic even if you could do it... which you can't.It seems important to you that you win. Okay, you win. Left is right; bright is dark; hot is cold; if you drop something, it will fall up. Happy now?As the old saying goes, no further correspondence will be entered into.Glenn

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>How are u doing Ed, Something tells me your holding out on>us... Do tell us what we are missing, pleeez.>>GideonWhat you are missing is what the actual pilot is doing in the cockpit. He's manipulating the throttles.I can fly any aircraft in FS and control ascent and descent to maintain a specific airspeed (which is what they do) via the throttle. The only thing that's "different" is the default FS autothrottle is not like the real-world deal. In FS, the autothrottle maintains a speed... in the real world an autothrottle would maintain a thrust level.The .air file has absolutely nothing to do with that at all.

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Glenn y are u taking such a combative posture to such a simple req for information, Mr Wilson made a statement and i simply asked him in a nice way to explain where he is coming from and by God it makes sense. All of thhat talk of which u did up there is really unnecessary. Pleease remember that this is a forum where opinions will differ.Ed thanks for your non-militant answer which makes sense and passes the logic test.

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