Mass problem.. help!

[rpetersson]

Question: Given an aeroplane with: Maximum Structural Landing Mass: 68000 kg Maximum Zero Fuel Mass: 70200 kg Maximum Structural Take-off Mass: 78200 kg Dry Operating Mass : 48000 kg Scheduled trip fuel is 7000 kg and the reserve fuel is 2800 kg, Assuming performance limitations are not restricting, the maximum permitted take-off mass and maximum traffic load are respectively:


Answer: 75000 kg and 17200 kg
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Can anyone give me an explenation on this? Struggeling to find any info....
Thanks in advance..

[lasseb]

This is actually quite trivial, and almost the prototype on a typical M&B question. Just wondering why you struggle with this?

Anyhow:
Always set it up like this:

DOM
TL
ZFM (=TL+DOM)
Fuel
TOM (=ZFM + Fuel)
TripFuel
LM (= TOM - TripFuel)




DOM : 48.000
TL : (maxzfm - DOM) 22.200
(max) ZFM : 70.200
Fuel 9.800
Takeoff mass (ZFM + fuel) = 80.000. (overload 1.800)
Trip fuel 7.000
Landing mass (Takoff mass - trip fuel) = 73.000 (Overload 5.000)

So max Traffic load must be 22.200 - 5.000 = 17.200.
Man takeoffmass = 80.000 - 5.000 = 75.000

[rpetersson]

First of all a big thanks for your help!

I didn't have a good system to solve this kinds of Q but now I do!

[rpetersson]

follow-up

What is the best way to see what is the most limiting of PLTOM PLLM MZFM? Is there a good way to see this?

[Groundloop]

Calculate three values:-

A = Maximum Zero Fuel Mass + Take-off Fuel = 70200 + 9800 = 80000 kg

B = Maximum Take-off Mass = 78200 kg

C = Maximum Landing Mass + Trip Fuel = 68000 + 7000 = 75000 kg

Lowest value of A, B or C gives the limiting factor - in this case Maximum Allowable Landing Mass.