Mass & Balance Flashcards
(49 cards)
Limit load vs ultimate load
Ultimate load = 1.5 x limit load
Ultimate: G loading where structure will fail
Limit: Operating limit
Loads between these levels might not lead to structural failure, but might lead to permanent deformation.
Unit Load Device (ULD)
Cargo container, single aisle (covers entire width of fuselage) or dual aisle.
Cargo securing latch designations
YZ or XZ types
X - longitudinal axis
Y - lateral axis
Z - vertical axis
Secure cargo containers to longitudinally mounted rails
Bulk Cargo
Odd shaped items, luggage, mail or late delivery items. Randomly loaded but contained in a specific section by tie-down or cargo net.
Partition nets can be used to separate sections of the aircraft.
Securing “large and irregularly shaped cargo”
Use pallets, not containers, as large oddly shaped items can’t fit in containers.
Distribution load intensity
Amount of weight distributed over any given area.
e.g. for a single pile of suitcases or a cargo container
Just divide weight by unit area (could be any mix of units).
Floor running load
AKA linear load
Weight per unit of longitudinal length.
If not given, assume longest axis of the item is placed longitudinally (i.e. best case scenario).
[IGNORE “width” and “length” designations]
Floor load
This means load intensity, e.g. kg/ft^2, not weight. Can seem to relate to weight limit or weight intensity limit so choose the right one in exam!
Typical arrangement of CoG vs CoP
Usually have CoG ahead of CoP, thus requiring a downforce from the tail.
This creates positive longitudinal stability as a pitch up movement increases AoA, increasing lift and pitching nose back down if CoP is behind CoG.
Negative effects of forward CoG
Tail downforce requires extra lift so not efficient. More lift required so stall speed is increased (which reduces altitude ceiling). Climb performance (rate and gradient) is reduced and take off distances increase, which could limit TOM.
Optimal CoG position therefore is just in front of the CoP.
Relationship between mass and stall speed
Stall speed varies with square root of mass.
Other speeds (e.g. V(R), V(2) relate to V(S1) so have the same relationship).
[calculations in exam]
Mean aerodynamic chord
This is the chord (leading edge to trailing edge) at the aerodynamic (not geometric) centre of the wing.
Can assess CoG as a position along the MAC (rather than vs the datum), especially for swept wing.
Between 15 and 25% along MAC (back from leading edge) is usually safe.
Trim drag
The increased drag caused by required downforce from the tailplane to balance the CoP/CoG pitch.
Body stations
An alternative longitudinal position scheme to datum. Will be at a certain position relative to the datum and they can be converted back and forth.
This is usually to do with the original construction jig.
“Station 200” means 200 inches aft of the station zero position.
Performance Limited TO or L mass
(PLTOM, PLLM)
This is TOM or MLM limited by performance considerations (field length, obstacles, temperature altitude).
Regulated TOM (RTOM)
Lower of PLTOM and Structural TOM
Allowed TOM
Mass taking into consideration all restrictions including Regulated TOM and Regulated LM
Re-weighing of aircraft
- single
- fleet
- modifications
Will be weighed to determine basic mass and DOM at manufacture.
Then re-weighed every 4 years for individual aircraft or 9 years for fleet averages.
OR if modifications change DOM by 0.5% of MLM, or CG shifts by 0.5% of MAC.
Aircraft weighing method requirements
Must be in an ENCLOSED building by manufacturer or an approved maintenance organisation.
Needs at least 3 points of support.
Equipment must be checked against a list, liquids appropriate and with a clean aircraft.
Fleet weighing
- Requirement for an aircraft to be included in a fleet
Aircraft can be included together in a fleet where:
i) DOM varies by up to +/- 0.5% of MLM
ii) CoG varies by up to +/- 0.5% of MAC
[or if just (i) applies, within the fleet but with unique CoG]
Certain specific differences (e.g. seat configuration) taking aircraft out of the fleet can be dealt with as adjusting items.
Fleet weighing
- frequency
Fleet masses determined every 4 years (individual aircraft then only 9 years).
Dry operating mass
Basic Mass + Variable Load
[Doesn’t include traffic load]
Variable load items
- Crew
- Crew’s baggage
- Removable flight equipment
eg. catering eqpt, food & drinks, potable water, toilet chemicals
Variable load masses used
Actual weights or assumed ones (85kg for flight crew, 75kg for cabin crew, inc hand baggage but not hold baggage).
