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+--- Thread: How to caluclate cruise altitude (/showthread.php?tid=15284)
How to caluclate cruise altitude - lcrane - 01-11-2007
I remember see a while ago on a forum somewhere ( I don't remember where ) a chart to caluclate the cruise altitude based on the distance flying and
type of aircraft. For example. 250 nm for 737-400 cruise at fl300. Does anyone else know of a chart or equation that would work?
Re: How to caluclate cruise altitude - advancedcapfs04 - 01-11-2007
Er... cruising altitude depends on your aircraft's weight. It is specific to your aircraft and its current weight and performance. Optimum cruising
altitude is whereby there aircraft is at the airspeed corresponding with the most efficient angle of attack with least drag in combination with its
cruising mach number. This is why a long flight starts lower and step climbs throughout the flight. The optimum altitude gets higher as the plane gets lighter,since to maintain its most efficient angle of attack as it gets lighter, its airspeed must reduce. It climbs higher, maintaining its original mach number and the airspeed gets lower....
Sorry for a poor rushed explanation.
I think you may be thinking about only very short flights for your distance/altitude relation formula.
To work out cruise altitude on flights less than 300nm, it is simply distance x 100.
Example. 140nm x 100 = 14,000ft
To calculate your descent point the formula is cruise altitude / 1000 x 3
Apart from this - on flights which are not limited to distances of 300nm or less, initial cruising altitude will always start out fairly low and you will step climb as you get lighter, as already mentioned. To get an idea of this here is a table showing cruise altitudes for a 737 at various weights and when (what weight) you would climb to your next step altitude.
http://www.b737.org.uk/perf_altitude.gif
Optimum altitudes for a 737.
A 737-400 on a 250nm flight would likely be so lightly loaded as to have the capability to climb all the way up to its ceiling altitude (FL370) but its distance would limit this since it just doesn't have the time for the long climb/descent thus the earlier distance/altitude formula...
Post Edited ( 11-01-07 22:30 )
Re: How to caluclate cruise altitude - lcrane - 01-11-2007
I understand that. I know Cessna has a chart in their handbook for the 172 optimal cruise altitudes based on weight and air temp and I use it to
consider my cruise altitude in real world flying. I'm wondering where I can find one for other aircraft to use with FS. I've looked at avsim.com and
flightsimmers.com and couldn't find one. I also tried googling preformance manual and couldn't find what I was looking for either.
Re: How to caluclate cruise altitude - advancedcapfs04 - 01-11-2007
Are you using freeware or payware? To answer this question I would have to know which make of (not boeing or airbus, the software company who makes
it) plane it is, and they should have documentation on its optimum cruising altitudes. It certainly will if it is payware. You specifically asked for
737-400 in your first post and I've given you the answer... as for other planes, it depends what they are, if the software developers who made them do
not give any further information you may have to request such information from the actual company who designed the real plane however it still may not
be accurate because FS flight models are generally not that realistic.
Like I said... distance has little to do with it other than a plane flying further is generally carrying more fuel so will be heavier, therefore start
at a loewr height, and you clearly know that already.
I said that if you are flying very short flights in an airliner:
"To work out cruise altitude on flights less than 300nm, it is simply distance x 100.
Example. 140nm x 100 = 14,000ft"
That is the only answer relating to distance.
Say you were talking about a 747 flying a distance of 4,000nm, there is no specific "altitude" it will fly at. It could be fully loaded with fuel and
passengers or could be doing a ferry flight in which case it might be much lighter, different altitude. As I said if the software developers of
whichever aircraft these are do not have the details then try the actual company. I know that Project Opensky have performance charts for many boeing
and some airbus airliners regarding altitude. you can try them. I am a member of Delta Virtual Air Lines and have access to charts in their manuals I
could pass on through a pm if you wish
Re: How to caluclate cruise altitude - lcrane - 01-11-2007
Oh! I understand what you're thinking now. no. no. no.
I fly a cessna 172 in real life. In the back of the handbook there is a chart for the pilotto calculate optimal cruise altitude. I'll make a copy of it and show you what I mean. I'm not using any software at all. Paper and pencil and my
brain. Ok, I'm also using a flight calculator ( basicly a circular slide rule ), plotter, and charts. But that's it. Also, you don't want to start
your descent before you reach TOC so distance does need to be taken into consideration.
Back when I flew with Meridian Airlines, they posted asimilar chart for each type of aircraft they had in their operation/performance manual which included recommended cruise altitides. I'm guessing they
used a similar equation you recommended. I'm just wondering is someone has similar chart for various aircraft. I couldn't find the performance charts
on Project Opensky when I looked but I'll look again. It's been a few years sense I flew for a VA. Real world flying and work got in the way of VA
flying and I ended up not being able to keep up the hrs.
I don't know if my email is visible for you but, yes. Thank-you. I'd like a look at thosecharts from Delta.
Re: How to caluclate cruise altitude - advancedcapfs04 - 02-11-2007
No I do agree with you where distance is important, but only on shorter flights, my example of the 737-400 being that while one could reach FL370 on a
250nm flight (performance wise) you wouldn't have the time since you would be starting descent before even reaching your TOC , as you said. Well I
will try and attach those manual documents from this virtual airline, they should have all relevant data.
Re: How to caluclate cruise altitude - advancedcapfs04 - 02-11-2007
Well I have had a look through those DVA documents but it seems that since their fleet includes only airliners which have an FMC which will calculate
altitude performance etc.. on the flightdeck, they don't feel the need to publish such tables in their manuals! Sorry about that, I'd liked to have
helped more but that is all it says really. I don't know where else I might be able to find any than that resource. I could try asking some other
members of DVA if they have got more information regarding this, some of them are or know airline pilots who might have the data for airliners to hand.
If you can tell me specific aircraft models in particular I can try asking some of the people there about it or I might know the info.
Post Edited ( 11-02-07 00:28 )
Re: How to caluclate cruise altitude - lcrane - 02-11-2007
No worries. Thanks for your help. I'll build a chart based on the equation you gave me and that will give a rule of thumb that I can use. Thanks
again. When I was working on my private license years ago, I had an instructor that insisted that I do all my flight planning with pencil and paper. I
could not use any GPS devices ( they were still new then :D ) and could only use my flight computer (
http://www.sportys.com/acb/showdetl.cfm?DID=19&Product_ID=1200&CATID=171 ), a plotter, and VFR charts. I started to do the same when I flew in FS. Now
that I'm working on my IFR, I'm starting to do the same when I fly an IFR flight in FS. It adds a level of realism to it, I think.