ERfly
Well-Known Member
I have never seen a jet perform like the MD! She was a beast...all the time! I miss her!
Off-topic performance discussion (from ATR 72 Crash thread)
- Thread starter Ian_J
- Start date
Ecl!pse
Well-Known Member
-100 or -300? The -300 is built more like a 737-800, not quite like a 757
| A22-300 | 737-800 | 757-200 |
| Thrust - lbs | 46,000 | 52,600 | 80,740 |
| MTOW - lbs | 156,000 | 174,200 | 255,030 |
| Wing area - ft^2 | 1,209 | 1,396 | 2,045 |
| Thrust:Weight ratio | 0.29 | 0.30 | 0.32 |
| Wingload lbs/ft^2 @ MTOW (lower = better T/O performance) | 129 | 125 | 125 |
| Effective Aspect Ratio (w/ winglets) | 10.9 | 10.4 | 8.6 |
-100 or -300? The -300 is built more like a 737-800, not quite like a 757
Thrust - lbs MTOW - lbs Wing area - ft^2 Thrust:Weight ratio Wingload lbs/ft^2 @ MTOW
(lower = better T/O performance)Effective Aspect Ratio (w/ winglets)
You made me curious about my old ride, which I thought was a pretty good performer.
I see thrust:weights of 0.29, 0.30, and 0.32 for the planes listed above.
The Learjet 75 has 3,850 lbs thrust per side, with max take-off weight of 21,500 pounds for a ratio of 0.36 - substantially higher than even the 757!
The more I thought about it I realized that the ratio probably changes to a big advantage for the 757 at less than max weights. The thrust-to-weight for a “lightly loaded” Lear (16,500#?) would be in the area of 0.47, and I suspect it could be much higher for a 757…(?).
I still vividly remember one night taking an empty charter 757 out of HPN on a quick hop back to BOS. Empty airplane, light fuel load. The Westchester 8 departure has a top altitude of 3,000 feet. The thing went into ALT CAP pretty much as soon as the gear came up. I had to override the autothrottles and yank a bunch of power back just to avoid it overspeeding the flaps and ballooning through it. Also had to anticipate the flight director significantly. Good thing I was hand flying because I don't think the automation could have kept up. The rest of the flight was a rocket ride, including a hilariously low approach speed.
SrFnFly227
Well-Known Member
Most of my legs in the 45 are less than 2 hours with only 3-5 people in the back. 1 flight we do often is only an hour and half with one passenger. There's just something about climbing through FL180 at 4000fpm while accelerating well above profile speed.
I recently flew on a Delta 757 from STT to ATL. The runway at STT is about 7,000 feet long. The flight was completely full. We were off the runway maybe a little past halfway point with what felt like almost no effort. I'm sure being at sea level helped, but it was over 90 degrees. It was damn impressive.
roundout
VNAV monitor
That's not very 737 of you
Ecl!pse
Well-Known Member
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…
CoffeeIcePapers
Well-Hung Member
Yeah, my first time in the 737 jumpseat out of DFW, it took something like 8000 feet to takeoff. I was wondering WTF was going on, but asked in cruise and they explained how they derate it for T/O.
And now I did that math for the NearJet 3+. 294 sq ft of (straight) wing and .41 at max gross from the two Tomahawk cruise missile engines it flies in close formation with. When we’re super light it can get a little north of .50. It goes fast straight up and down at least
Apophis
Resident Iconoclast
Flew to STT a few weeks ago, there was maybe like 2-3 knots of tailwind landing on 10. Did an an autobrakes MAX landing.
Anyways, it was definitely longer than 4 hours after that experience and no, I didn’t see a doctor.
Autothrust Blue
”…trusting ze process…”
Meanwhile in Toulouse.
Autothrust Blue
”…trusting ze process…”
Derated *and* assumed temperature!
And now I did that math for the NearJet 3+. 294 sq ft of (straight) wing and .41 at max gross from the two Tomahawk cruise missile engines it flies in close formation with. When we’re super light it can get a little north of .50. It goes fast straight up and down at least
121 guys - what’s the take-off weight of a “lightly loaded” 757?
roundout
VNAV monitor
Some Air Lines do this.
Besides, it's the only narrowbody with engines which don't suck, we have to keep em flying.
STT is one of my favorite departures. Full thrust, PACKs off, and bank right after takeoff to fly between the two hills. It's one of the few times where you really feel the power of the 757
I've done it in the 140k range off the top of my head. Lowest chart I see is for 120k but I don't think I've ever actually been that light
Autothrust Blue
”…trusting ze process…”
The E-jets do both as well (T/O-1 and -2 fixed thrust modes, plus flexible/AT). But I never thought that airplane short on thrust except in Denver on a hot day going farther, etc.
