Hi all,

I can’t seem to understand why - but when I was completing Exercise 5.10 in the most recent version of the book, it asks for:
1. Max t/off fuel permitted; and
2. Ballast Fuel required in the main tanks.

For the first problem, it gives you ZFW = 2540kg, the moment as 685 and flight ETI of 63 mins.

Using the performance data for the Echo - I got 88kg as the minimum fuel required.
That is 28gph x 63mins = 29.4 gallons x 1.1 (for variable reserve) = 88kgs.

The answer on page 206 says only 80kgs is required... and I thought I was doing the right thing by adding on a variable reserve.

What am I not understanding correctly? Please help!

Cheers,

The thing to remember here is that the two questions asked - the ballast fuel required and the minimum fuel required for the trip are completely unrelated. When you check out the centre of gravity at zero fuel weight, you are out of the aft limit and you need 48kg of ballast fuel to allow you to legally fly the aeroplane. So the 48kg is purely for balance so it must be put into the main tanks before you even think about the flight.

Now the minimum fuel required for the flight is another story and that has to go into the tanks on top of the ballast fuel. The trip fuel is 63 minutes @ 28 gallons per hour = 29.4 gallons = 80kg. That's the fuel that the flight plan indicates will actually be burnt en route (no reserves). The 'beetle diagram can then be used to check your landing weight (although it wasn't part of this question).

The minimum fuel at take-off will be the 80kg plus all reserves. That's 80 x 1.1 + fixed reserve 41 (15 gallons) = 129 kg no taxi allowance because we are doing this check at take-off. ( I noticed that in your calculation you forgot to include the fixed reserve).

That 129kg has to go into the main tanks to allow you to do the flight. That's on top of the 48kg already in there for ballast.

Thanks for reinforcing this Bob, and with a comprehensive reply.

In addition to the explanation above, I recommend that everyone purchase the Performance Video - particularly on this topic - Day 4 Session 3.

It leaves no doubt and the explanation is very thorough! And always use the Beetle diagram. It's a must to put everything into perspective.

Thanks again,