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RFields5421

cruising speed/maximum range questions

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I am flying from Boston to Denver and I have a few questions. First off I am flying a 737-800 and I am cruising at 18500 feet (FL185). That's the cruising altitude I was assigned. Why does the plane only go up to 330 KIAS and anything higher is overspeeding when it says that the cruising speed is 531mph which is much greater then 330kias???? Also why does it look like I might run out of fuel (I am at 25% left and I am flying over Des Moines right now when it says that I should have a maximum range of 2,970 miles??I am really confused. Maybe I should be flying at higher altitude where the air is thinner?? Please help a newbie here thanx!!

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The cruising altitude for a 737-800 is normally at FL380 at mach 0.79 to 0.82 with 0.80 as the normal speed, so you should definitely be higher. When you create a flight plan, you can select a desired cruising altitude...

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cool thanx for the reply!!Only problem is I went to put cruising altitude at .79 mach and it started overspeeding. Which leads me to my next question: What is overspeeding and is it avoidable at higher altitudes?? If I was flying at FL380 would the overspeed warning come on?? Also what is the red dotted lines in the air speed indicator?? Is that only to go in at a certain altitude???? Thank you in advance.

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When you climb to FL380 (or wherever ATC puts you) you will notice that you can go faster the higher you get since the air is thinner. I'm not entirely sure about the right procedure, but you should only hit mach 0.80 once you level out at your assigned cruise altitude.Look at your kneeboard for information about various speeds, I'm not certain, but I think the line you're talking about might be Vne (never exceed) or equivalent. Unless you're talking about the magenta line which is the speed set for the AP.I've only been simming seriously for a couple of months, and mainly focus on helicopters, so I'm by no means an authority on the subject.

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Davewins-I'd suggest you read here on the different types of airspeeds:http://en.wikipedia.org/wiki/Airspeed1) indicated airspeed (IAS)2) calibrated airspeed (CAS)3) True airspeed (TAS)4) Ground speed (GS)5)Equivalent airspeed (EAS)I'll only talk about the 1st four that I am familiar with flying Ga aircraft- in my realm which is below 13,000 ft.Indicated airspeed is what you see on your airspeed indicator. Calibrated airspeed is your indicated airspeed corrected for instrument and position error (e.g. where the pitot tube is,instrument errors etc.). On Ga aircraft the difference is pretty minimal between indicated and calibrated.True airspeed is the speed you are going in the air around you-ground speed is the speed you are going over the ground.In my Baron at 6000 ft. I will see on the airspeed indicate about 166 knots at my cruise settings. However the true airspeed-the speed I am going thru the air is actually 186 knots. A good way to figure what this is, is you get about a 2% airspeed increase for every thousand feet you go up-so at 6000 ft. I will get about a 12% (2x6)increase. Add 12 % of 166 to 166 and you get the true airspeed of 185.92-pretty darn close to the book 186! So even though I only indicated 166-I am going quite a bit faster...What you really care about though ( at least I do) is your groundspeed-cause no matter how fast you are going thru the air-how the winds are going behind you(tailwind), ahead of you(headwind) , changes how fast you move over the ground-as once in the air you become part of the airmass. That is what really decides what time you are going to get where you are going and how much fuel you will need. Now that we have figured out that I move 186 knots in the air with an indicated airspeed 166-if at 6000 ft. is blowing directly behind me with a force of 30 knots-I'll actually have a ground speed of 216 knots (186+30)! My airspeed indicator will still show 166-I'll still be making a true airpspeed of 186-but my speed over the ground will be 216. This is why pilots carry all kinds of fancy calculators and whiz wheels-but in truth gps's now do all that work and calculations very nicely.On my blog site I have a shot of the best groundspeed I have ever seen 245 knts! It is a kinda murphys law though that more often than not you usually have a headwind...Hope this helps a little-the big jet guys will have to step in on the mach stuff.http://mywebpages.comcast.net/geofa/pages/rxp-pilot.jpgForum Moderatorhttp://geofageofa.spaces.live.com/

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First thing to do is insure that you have the Display Indicated Airspeed checkbox checked in your Realism settings under the Aircraft menu. Then be aware that there are two things that can trigger an overspeed warning:1. Indicated airspeed above approximately 330 KIAS or2. Mach number above approximately 0.80.When you are lower than approximately FL280, you will hit 330 KIAS before you hit Mack 0.80. As you fly higher, and the air thins, your airspeed drops and you will hit the mach overspeed first. Above FL300 or so, you will typically see a mack number like 0.78 and an indicated airspeed around 270 knots.> Also what is the red dotted lines in the air speed indicator?? Are you referring to the red and white stiped needle that starts out around 400K aand moves counterclockwise as you climb? If so, it is called the "barber pole" and indicates how fast you can got at any given altitude before the overspeed warning sounds.For the above examples, I quoted the numbers used previously in this thread. I'm not familiar with the 737-800 and found these numbers a little higher than I'd expect. I think a 737-400 cruises around M 0.74.R-

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The speeds were found on airliners.net after a quick google on the aircraft type. FSX details for the aircraft states cruising speed is mach 0.785 which is equivalent to the max range speed...

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Ok that clears a lot up I appreciate all the answers but I am still a little bit confused. I just flew a test flight and went up to 35000 feet and I was amazed that I could fly much faster. Why exactly is this again?? Sorry for not getting it. The air is thinner so I can travel faster but what about overspeed how come it overspeeds at a lesser speed at lower altitude?? Is this the main reason that planes fly at 35000 feet?? So they can go faster????

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Overspeed - like many things this is one area where the real world is not relevant to Flight Simulator.The overspeed warning is based upon either KIAS or the mach # - you can find it in the aircraft.cfg file of any FS aircraft - the section below is from the default B738 in FSX:[Reference Speeds]flaps_up_stall_speed = 142.0 //Knots True (KTAS)full_flaps_stall_speed = 113.0 //Knots True (KTAS)cruise_speed = 477.0 //Knots True (KTAS)max_mach = 0.82max_indicated_speed = 340 //Red line (KIAS)When that aircraft exceeds 340 KIAS or 0.82 mach by the FS instrument readings - FS considers the aircraft in overspeed.If you are flying with Crash Detection turned on - you have about 60 seconds of a slight overspeed before FS considers the aircraft overstressed and crashes. You can have as little as less than one second of overspeed if you exceed the overspeed limit by a large margin.That frequently occurs when people transition between oceanic weather boundaries in FS and the program calculates a sudden wind shift as a sudden increase in KIAS/ Mach #.That does not happen in the same way in the real world.But is a result of trying to model the real world in a computer program.Overspeed in the real world is a warning based on many factors - but it's a warning that the aircraft is probably being overstressed. Depending upon who the pilot is, what aircraft he is flying, who he is flying for - airline or company - a short time over the top of the barber pole may be ignored. Or it may call for the aircraft to be grounded and inspected.Microsoft has to try and model the limitations of real aircraft - and that is how they do so.Yes, the thinner air up high allows the aircraft to make a faster speed over the ground - while maintaining the same speed through the surrounding air.By the 2% formula:300 KIAS at 10,000 ft is about 360 kts over the ground in zero wind.300 KIAS at 20,000 ft is about 420 kts over the ground in zero wind.300 KIAS at 30,000 ft is about 480 kts over the ground in zero wind.As far as your instruments flying the plane - the KIAS stays the same - but the true air speed - the speed over the ground climbs quite a bit.Again, that is with zero wind. I once flew a turbo-prop Piaggio Avanti in FS for 840 nm in less than two hours in FS across the US. Climb, descent and landing in less than two hours - I never exceeded 310 KIAS or 0.68 mach. The Jet Stream was perfect that day.

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