Jump to content

Rapid decompression and fuel-flow


Recommended Posts

Posted

Hi,please imagine the following scenario :Polar flight from Europe to PANC and the plane encounters a rapid decompression and has to dive down to FL 140 ( at least ) for atmospheric oxygen . . . next suitable airport for diversion is about 1000 nm away. Is the remaining fuel sufficient to reach this airport due to extreme higher fuel-flow at lower level ?I simulated this and my findings are as follows ( PMDG 747-400 ) :Max speed at FL 140 was M 0.68 and now the surprise : the fuel-flow went DOWN from roughly 2.9 Ktons/engine at FL 340 to 2.5 to 2.6 at FL 140.Is this realistic ? I thought always that the lower you fly the higher the fuel consumption - I checked the abnormal proc in the manual but I could not find any solution.Any expert advice ?Karl-Heinz - EDDI/THF " Tempelhof "" The mother of all airports " - Sir Norman Foster

Guest ColdBear
Posted

Karl-heinz,It might be normal depending on your weight, but you haven't taking into account that you'll have a considerably less TAS at FL140 than at FL360. In ISA conditions at FL340 the TAS/FF(pr eng. pr hour) is 511/2400kg(280tonnes and .86mach) and with the same weight at FL150(almost same as FL140), TAS/FF is 439/2100(approx)btw, you should descend to 10.000feet or MSA which ever is higher. Martin

Posted

Hi Martin,Thanks for the answer - butI have an old manual of the Grand Old Dame " DC10 " and there it says that the specific range at lower altitudes will be reduced by around 30 % ! Per 1000 kgs of fuel from the sixties to the forties of NM ! Or is this only on account of reduced speed ? But the difference between 511 and 439 is only 14 % !?!Are your figures from a real world manual 747-400 or other sources ?Karl-Heinz - EDDI/THF " Tempelhof "" The mother of all airports " - Sir Norman Foster

Posted

Karl,let s assume your infos.FL340 at LRC with 4 engines at 340t for 2903 kg/eng/hr mach.859 tas 497 knots all in ISA datas.now about 14000' not pretty sure that s good or you ll carry oxy in huge quantities but i ll write down both infos for you.14000'340 t TAS 434 mach.690 3084 kg/eng/hr10000'340 t TAS 413 mach.647 3080 kg/eng/hrso in this case you need extra fuel and time to make it ...if you give me more infos on your flight then i can generate some scenarios for yousee you

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
×
×
  • Create New...