This document sums up all the important information concerning Mass and Balance. Mass and Balance (M&B), is one of the fourteen subjects that a student pilot needs to pass in order to continue the ATPL-training program. It is written by myself and can therefore contain faults. I tried to cover all ...
,Table of Contents
Performance & design requirements 3
Stress 3
Wing loads 3
Ultimate load 4
Conversion of units 4
Fuel and oil requirements 4
Cargo handling 5
Floor loading limits 5
Centre of Gravity 5
Balancing the forces 6
Effects of a forward CG position 6
Stall speed 6
Overloaded aircraft 7
Moment 7
Finding the CG-position 8
Changing CG while adding and removing mass 8
Mass and weight definitions 9
Frequently used terms 10
Aircraft weighing 10
Aircraft weight categories 11
Standard masses 11
Nineteen passenger seats or less 11
Twenty or more passenger seats 12
Responsibilities of the operator 12
CG-envelope 12
Documentation 12
Calculating the Maximum Permissible Traffic Load and MTOW 13
Calculating the Maximum Fuel Load 13
Load sheet 14
Last minute changes (LMC’s) 14
Load sheet presentation 14
Body stations and balance arms 15
2
,Performance & design requirements
- CS25 document for:
o All multi-engine jets
o Multi engine turboprops with more than 9 passenger seats or a maximum
take-off mass greater than 5700 kilograms.
- CS23 document for:
o All aircraft with 9 passenger seats or less, and a take-off mass less than
5700 kilograms.
o Propeller driven twins with a maximum take-off mass equal to or less than
8618 kilograms, or 19 passenger seats or less.
A combination of the above four types of stress is possible as well.
Ultimate stress: stress where the structure fails. Returning stress below the ultimate
stress may weaken the structure, so the ultimate stress ‘border’
lowers. This is called metal fatigue.
Airliners are designed to be damage tolerant, or, in other words: fail safe designed.
Wing loads
Wings must deal with bending forces (mainly tension and compression). In flight, the wings
are supported by the lift, so they bend upwards a little bit. On the ground, the wings are
supported by the landing gear. Forces on a wing are called the wing load.
The maximum bending appears at the wing root (close to the fuselage). Shear loads occur
in the centre section of the main spar.
Forces on the spar are affected by the amount of fuel in the wing. To minimize the fatigue
loads on the wing root during flight, standard fuel management procedures make sure
there stays fuel in the outboard tanks. This generates extra weight in the wings, so that
there is an opposite force to the lift. In this way, the wing does not bend too much. The
correct order to burn fuel is to first use the centre tank, and then the wing tanks.
Wing loads can be extremely high when:
- The wing suffers from aerodynamic flutter.
- The wing suffers an undamped oscillation caused by aerodynamic imbalance.
The above two situations are more likely to occur when the wing’s mass is low.
3
, Ultimate load
Ultimate load: the vertical force (g loading) where the structure of the aircraft will
fail. There are both positive and negative ultimate loads. The positive
ultimate loads are usually higher. Aircraft always fly in a so called
‘load envelope’ to ensure a safe operation. The borders of this
envelope are still a factor 1.5 away from the ultimate load. So, when
the limit would be 3.2g, the actual ultimate load would be 3.2 x 1.5 =
4.8g. Loads between the limit and ultimate load may not cause
structures to fail, but they might lead to permanent deformation.
Conversion of units
1 lb = 0.454 kg
12 in = 1 ft
3 ft = 1 yd
1 ft = 0.305 m
1 kg = 2.2 lbs
1 m = 3.28 ft
1 IG = 1.2 USG
1 USG = 0.83 IG
1 IG = 4.545 L
1 USG = 3.785 L
Fuel is lighter than water. It weighs about 70% - 80% of water.
Specific gravity (SG): measurement of the relative density (factor).
Fuel and oil requirements
To operate a flight, enough fuel must be on board to ensure a safe flight. Total fuel is
divided into multiple sections by EU-OPS:
- Taxi fuel. Fuel required to start up and taxi to the end of the runway.
- Trip fuel. Fuel required from take-off to touchdown.
- Contingency fuel. Extra fuel, most of the time a percentage of the trip fuel, to allow
for un-forecasted winds and ATC re-routes.
- Diversion fuel. Total fuel required from the point of diversion to touchdown at
alternate.
- Final reserve fuel.
o Jets: fuel to allow for 30 minutes holding at 1500 ft above the destination
alternate aerodrome.
o Reciprocating engine aeroplane: fuel to fly for 45 minutes.
- Block or ramp fuel. All the above fuel elements added. It gives the total fuel.
Other fuel types:
- Additional fuel. Fuel that caters for failure of a power unit or loss of pressurization,
when the failure occurs at the most critical point. This includes fuel to descend as
necessary, proceed to an adequate aerodrome and hold for 15 minutes at 1500 ft,
and finally make an approach and landing.
- Extra fuel. At the discretion of the commander.
4
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