Originally Posted by
XPMorten
@Mad
B734, L 36,5m, OEW 33,2T
B773, L 73,9m, OEW 167,8T
So B734 is half the length of the B773.
So 734 weight should be 1/6 th right?; 167,8 / 6 = 28T
Considering the 777 has more composites and is more modern overall
I'd say that weight does scale about L^3
L^3 is length cubed. The cube of 2 is 8. So that "rule" would predict a 734 weight of 167.8/8=about 21 tonnes. The true value is 33.2T. That's an error of about 50%, indicating that the exponent, in this case, is closer to 2.5 than 3 - a pretty significant difference (it's actually 2.33).
That;'s not really surprising - airframe loads are probably closer to being dependent on area than volume, and loads drive structural mass. Things like fuselage skin are also area-dependent if not load driven (i.e. if you assumed a constant skin thickness, a tube scaled up by 2 would have 8 times the volume but only 4 times the surface area). A ratio a bit above 2 seems quite sensible.
Sure, but what bypass ratio do their engines have compared to their
larger cuisines?
And why don't airlines use them?
xpm
Airlines don't use small business jets due to all kinds of economic factors, some of which have nothing to do with aerodynamic efficiency (salary cost spread over very few seats, cost of slot used versus total revenue, being two examples) in addition to the fact that even if certified to part 25, being designed in most cases for Part 91 type operations there are many Part 121 regulations such small aircraft do not, and often cannot, meet. For example, fitting a reinforced cockpit door to a Learjet would be somewhat challenging, yet its a Part121 mandated feature.