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## CPL Echo Fuel Tanks

• JasonM
• Topic Author

### JasonM created the topic: CPL Echo Fuel Tanks

Hi all / Bob

Quick question. For performance - the e-book - exercise 5.2 question 6 (calculating max cargo) states full tanks at start up and I just cannot get the same fuel answer that was given @ 481 kg.

there is 2 main tanks, (52 us gal each 50 that is usable)
and two aux tanks (43 us gal each and 40 that is usable)

50+50+40+40 (180) x 2.72 = 489.60kg
or
52+52+43+43 (190) x 2.72 = 516.80kg

The question states full tanks.... so nothing left for reserve / taxi / whatever - I'd assume it'd also include the weight of the unusable fuel as well, seeing the tanks are full.

481 / 2.72 = 176.83 US Gal and I can't get it to add up for full tanks.

Please help! Exam on the 2nd of Dec and I want to make sure I'm doing things correctly!

In a exam would you take into consideration the unusable fuel weight in general?

Thanks

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• JasonM
• Topic Author

### JasonM replied the topic: CPL Echo Fuel Tanks

Update - I see that it is quoted max 180 us gal on exercise 5.5 question 2 (489.6kg) so I believe 481 kg might be something to do with taking in account the 8.16kg for taxi.... my bad... that would make sense. Also I think I answered my own question regarding usable and unusable fuel, I'm assuming that weight in theory is taken in account for in the empty aircraft weight quoted much like unusable oil ect.

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• John.Heddles
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• ATPL/consulting aero engineer
• Posts: 669
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### John.Heddles replied the topic: CPL Echo Fuel Tanks

I'd need the whole question to comment on your concerns there.

However, so far as unusable fuel is concerned, that has always been included in the declared empty weight for the aircraft .. see CAO 100.7.2 definition of empty weight. .. www.legislation.gov.au/Details/F2015L01127

Interestingly, empty weight used to include undrainable oil, to accommodate the often significant oil consumption of the larger radials ,, ie, oil was a consumable. Following a number of robust discussions (read arguments) back in the 70s between me and the then DCA engineering folk over my preference to include full oil in the empty weight for small aircraft, the Order definition was changed to the more sensible full oil configuration

It is worth keeping in mind that, depending on the particular aircraft fuel tank system configuration, a portion of the declared unusable fuel will/may be quite usable for normal attitudes in flight (but not available for flight planning). This is due to the way in which unusable is determined by flight test. The required tests simulate turbulence, generally by setting up a rock and roll motion with small rudder inputs. Unusable is when the engine being fed hiccups. The actual quantity is determined by switching to another tank, landing, and draining the test tank.

Engineering specialist in aircraft performance and weight control.

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