What might be more impressive is the size of the Learjet 75's wing relative to its MTOW: 312 sq ft vs. 21,500 lbs of MTOW = wingloading of 69 lbs/ sqft. Compare that to the 125 of the 752 and the 738. Massive wing on the Lear75 relative to the capability of the airplane - great for takeoff performance, especially from challenging airports (e.g., hot/high), but bad for fuel burn - when cruise drag is > 50% determined by wetted area of the airplane, that extra wing area comes at a significant penalty (granted, it can help with service ceiling). This is ultimately why 752s have been replaced by 739s and A321s in short/medium haul markets, especially when takeoff performance isn't need - they just burn so much less gas for the same passenger count.
I’ve got a couple of questions/speculations on the Lear 45/75 wing and performance…
First is that while the wing is (according to your calculations) fairly “large” relatively, my question (to you guys with real aero engineering knowledge) - does wing shape/sweep etc. have a major effect on that “wetted area / cruise drag” calculation? The Lear always felt pretty slippery to me, and fuel burn at cruise seemed really reasonable for the plane’s size, even at airline cruise altitudes (mid-30’s).
[Your comment re large wing / service ceiling may also come into play, I guess, as we routinely cruised at FL400 - FL450 and saw
really nice fuel burns up there.]
Secondly the comment about a “large” wing giving good take-off performance made me pause too, as I really didn’t think of the plane as especially good in that regime. It was a plane that you could very easily end up taking in to a short runway airport with room to spare, but not be able to get back out of due to long(er) t/o numbers. One side of that equation is that the plane is an awesome stopper with carbon brakes. The flip side is, I
think, other factor(s) that affect take-off numbers - in this case a relatively small rudder area requiring higher V1 speeds for single-engine directional control.
Anecdotally I came to understand the rudder/take-off limitation relationship due primarily to our experience with one of our aircraft owners. This owner had a Lear 40 that we operated. They had a summer place in northern Wisconsin near a pretty short runway airport, and conditions had to be fully favorable to be able to take-off from there (dry, reasonable temps, light pax load, short first leg). When Bombardier announced the upgrade from the Lear 40/45 to the 70/75, one of the changes was increasing thrust from 3500 pounds per side to 3850 per. This owner was one of the first to upgrade from the 40 to the 70, and had a reasonable expectation that the increased power meant that they would be able to use their preferred airport more often as they knew that take-off performance, not landing, were limiting. I was either Chief Pilot or D.O. at the time, so I was the one that got to run the numbers after we received the plane and pass on the fact that the take-off numbers, in many scenarios, was actually
worse with the more powerful engines. Awkward conversations ensued…