Hi guys,

I was working through a question regarding how much ballast you can
add to the main tanks and I became stuck on a couple of things.....

QUESTION

Refer Loading System ECHO (page 18-21 Work Booklet).
An ECHO aeroplane has an operating weight and moment of 1973 kg and 488 index units respectively.
Given the following data:
Row 1 = pilot and passenger
Row 2 = 2 passenger
Row 3 = 2 passengers
Nose compartment = 20 kg
Rear compartment = 125 kg
Ballast = 5 kg sand bags available
Minimum fuel required for the flight stage is 120 kg
(assume each person on board weighs 77 kg)

If the passengers and cargo load distribution is not changed, the minimum weight of fuel required in the main tanks, as ballast is closest to: -


I became confused as to whether you split the minimum fuel into the auxiliary tanks and main tanks when adding up the total weight or just dump the minimum fuel straight into the main tanks.
Also, it states that the ballast that can be used is 5kg sand bags. When I find how much weight I need to bring the aircraft back into balance I become stuck on when and how to use this.

My calculation stated that I need 17.1kg to be added to the main tanks but the answers say otherwise (this is where I get confused on using the ballast).


Cheers

When you calculate the ballast fuel required, you base the calculation on the main tanks. With an arm of 1780mm, the main tanks are well forward of the auxiliary tanks at 2800mm.

The rule is that you always fill the mains before putting any fuel into the auxiliary tanks. That means that the CofG will have moved well forward before you load any fuel into the auxiliary tanks.

So put all of the calculated ballast fuel into the mains. Then put the all of the rest of the fuel you are carrying into the mains and if it won't fit, then whatever remains goes into the auxiliary tanks. That will ensure that the CofG remains within limits.

Thanks Bob, definitely makes sense now.