I have read numerous books and researches, but I couldn’t find any formulae that actually work for how to calculate the following (for commercial aircrafts):
1- Drag coefficient for a retractable landing gear.
I tried the following equations:
CD,gear = WingLoading * FlapDeflection * (( AircraftMass(TO,LD))^-0.215)
CD0,gear = SUM i=1 > n [CD,gear(AreaLG / WingArea)]
The results were ASTRONOMICAL
2- Weight of main and nose landing gears.
LG weights are calculated as a percentage of the MTOW, but different sources had different percentages (Normally between 3.8% and 6%). That doesn’t really seem to be the case; For example, a Boeing 747–400BCF’s MTOW is 410 tonnes. Based on my research, the wing-mounted gears (2) are 2952 kg EACH, body-mounted gears (2) are 2924 kg EACH, and the nose gear is 1432 kg. In total, main landing gears weigh 11752 kgs, which is, roughly, 2.9%. If the nose landing gear weight is added to the calculation that’d be 13184, which is 3.2% for ALL landing gears combined!
If anyone knows how to calculate the CD or weights, please help. Very much appreciated!