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Why Did Boeing Overpower The 757 To Such A Degree?  
User currently offlineSkystar From Australia, joined Jan 2000, 1363 posts, RR: 2
Posted (14 years 4 weeks 22 hours ago) and read 7153 times:

We always seem to love the 757, because it gives you a great kick in the back on takeoff, and climbs like a home sick angel. Unfortunately, I can only experience that through words (never have actually been on a 757).

My question is, why did Boeing overpower the 752 to such a degree? The 753 is a bit more normal (still good), in regards to its power loading (weight over thrust)

RRs (757). All figures are for standard weights.

752: 2.74
753: 3.13
319: 3.21
320: 3.24
321: 3.05
CRJ-200: 2.57
733: 3.11
734: 3.15 (22k engines)
735: 3.12 (18.5k derate)
343: 4.33
744: 3.77 (58k RRs, 875k lbs MTOW)
763: 3.33 (60k CF6s, 400k lbs MTOW)

Source, Janes AWA. Out of interest, I've included a select range. None of the 330 figures were exact enough, so I haven't included them (roughly 3.5)

On another note, does anyone notice the difference in takeoff/climb performance between an A319 and an A321, or a 735/736 vs a 734/738? (in similar circumstances naturally).



14 replies: All unread, jump to last
User currently offlineGKirk From UK - Scotland, joined Jun 2000, 24964 posts, RR: 56
Reply 1, posted (14 years 4 weeks 19 hours ago) and read 7027 times:

Don't know but taking off in a 757 is great fun!!!  

When you hear the noise of the Tartan Army Boys, we'll be coming down the road!
User currently offlineWidebodyphotog From United States of America, joined Jun 1999, 917 posts, RR: 67
Reply 2, posted (14 years 4 weeks 18 hours ago) and read 7026 times:

Some revisions and one answer to your question.

752: 3.06/3.18 w/PW4040 41.7klbt/RR535E4 40.1klbt @255klb MTOW

753: 3.08/3.13 w/PW4043 43.8klbt/RR535E4B 43.1klbt @270klb MTOW

319: 3.21
320: 3.24
321: 3.05
CRJ-200: 2.57
733: 3.11
734: 3.15 (22k engines)
735: 3.12 (18.5k derate)

343: 4.47 w/CFM56-5C2 34klbt @606.3klb MTOW

744: 3.63/3.57/3.53 w/RR-524G-H/T 60.6klbt/GE CF6-80C2A2B1F3 61.5klbt/PW4062 62klbt @ 875klb MTOW

763: 3.42/3.35/3.32 w/RR-524G-H/T 60.3klbt/GE CF6-80C2A2B1F3 61.5klbt/PW4062 62klbt @ 412klb MTOW

My sources are Boeing and excerpts from Airline ops manuals. Figures are highest allowable MTOW/Max Thust combinations used by some airlines. I am not sure about the rest as I don't have the numbers handy.

To answer one of your questions, Boeing wanted exceptional short field performance w/ good ROC for medium range flights. With a given L/D there is only one way to accomplish this. More Power! So the 757 series developed into the big fan narrow body design you have today.

I have always been a fan of the 75. I rode on my first one about 15 years ago out of MSY on Delta. It truly is a rocket ride on T-O!


If you know what's really going on then you'll know what to do
User currently offlineTEDSKI From , joined Dec 1969, posts, RR:
Reply 3, posted (14 years 4 weeks 18 hours ago) and read 7000 times:

I flew on a P&W powered Northwest 757 in Sep 93 from Detroit to MCO and the takeoff was terrific! I am again flying on a P&W powered 757 with Delta from MCO to CVG.

User currently offlineSkystar From Australia, joined Jan 2000, 1363 posts, RR: 2
Reply 4, posted (14 years 4 weeks 18 hours ago) and read 6980 times:

I've used Janes All The World's Aircraft for my figures.

I calculated the 340, 744 and 763 figures. Admittedly, I feel most confident with the 340.

For the 340, I think my number is fairer =)
The A340-300E option (used by SQ. Are they the only ones?), at 275,000kgs does use the CFM56-5C4 at 34,000lbs, but on their -300E a 5% thrust bump is available, which would mean a 35,700 output for 5mins.

So for 5mins, your power loading is 4.25. But at the standard 34,000lbs thrust, that goes to 4.39

But, the normal A340-300E (aka, -313X IIRC), has a MTOW of 271,000kgs, which is the figure I arrived for (4.33).

The CFM56-5C2 is only used on the -200/-300 (-311), which has a MTOW of 257,000kgs. If there's a good thing about Airbus, it's that their specifications are more standard, as opposed to Boeing's ones. Airbus has very consistent specs.

So, I suppose the anti A340 stalwarts can feel good about the A340s figures. But remember one thing, if you lose an engine on an A340, you actually have a better power loading than if you did so on a Boeing 777.

Thanks for your response, I'm closer to getting a good explanation. One day I will fly on a 757. Unfortunately, the closest thing I can get to a 757 in terms of power loading is the CRJ, but derate thrust and the fact its thrust is certified at only 0°C means that in real life, it's not as great. So for me, the A320 is still good fun.



User currently offlineTravelin man From United States of America, joined Mar 2000, 3556 posts, RR: 0
Reply 5, posted (14 years 4 weeks 16 hours ago) and read 6944 times:

The 777 take-off was amazingly quick and powerful. What are the numbers for that? My guess would be that they are similar to the 757!

User currently offlineTrnsWrld From United States of America, joined May 1999, 962 posts, RR: 0
Reply 6, posted (14 years 4 weeks 14 hours ago) and read 6898 times:

I fly 757's regularly out of MCO on TWA and yes you guys are right they do really kick you back. However, I think that no plane climbs like the MD-83's. When im flying them 83's of TWA I cant believe the climb rates once they get off that runway. A few months back we were departing 30R out of STL next to a TWA 727 departing on 30L. All I know is that in a race those 72's will be looking at MD-80 jetblast 

User currently offlinePanman From Trinidad and Tobago, joined Aug 1999, 790 posts, RR: 0
Reply 7, posted (14 years 4 weeks 10 hours ago) and read 6842 times:

I must agree with you TrnsWrld having experienced an INSANE climb rate in an MD83 when I went home to Trinidad a few weeks ago. I wrote about it a while back in the Trip Reports forum, it's titled "LGW-BGI-POS-BGI-LGW (Long Post)" or something along those lines. We climbed so quickly that my ears were hurting.


User currently offlineDesertJets From United States of America, joined Feb 2000, 7811 posts, RR: 16
Reply 8, posted (14 years 4 weeks 9 hours ago) and read 6826 times:

The thrust to weight ratio in the 757 is not the only factor that makes the plane such a rocket. Boeing also designed it with a very powerful wing, with a very high wing load factor for its size. That is also why its wake vortex is unusally large for a plane of its weight/size. Throw in two engines that blow out 40,000 lbs of thrust and you have quite a performer.

Stop drop and roll will not save you in hell. --- seen on a church marque in rural Virginia
User currently offlineMD-90 From United States of America, joined Jan 2000, 8508 posts, RR: 12
Reply 9, posted (14 years 4 weeks 8 hours ago) and read 6823 times:

The heavily loaded wing would need powerful engines to climb well. A bigger wing climbs better.

User currently offlineChiawei From United States of America, joined Nov 2000, 950 posts, RR: 1
Reply 10, posted (14 years 4 weeks 8 hours ago) and read 6831 times:

757 climb out is awsome.

But I had a even more thrilling flight on a lightly loaded 744 on EVA from TPE to HKG. The aircraft used less than 50% of the runway and was climbing like maniac.

User currently offlineNorthStarDC4M From Canada, joined Apr 2000, 3077 posts, RR: 36
Reply 11, posted (14 years 4 weeks 8 hours ago) and read 6806 times:

I believe that Boeing gave the 757 such large engines to keep it T/O distance in-line witht he 727, that it was supposed to be replacing. Also the RB.211-535 series at PW2038/40 were at the top end of the powerplants available while the CFM56 (the 20000-22000lbs thrust version) was at the lower end, there wasnt anything available in the middle at the time the program was launched (the V2500 and uprated CFM56 werent even a gleam in the designers eye yet). And for some reason Boeing went with the high end, maybe because the CFM56 was still having some teething troubles at the time (it was only just coming off the production lines) and Boeing was unwilling to go the same route Lockheed did and take the risk of the engine not being available in time?

Keep those wings level and don't look back

Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety.
User currently offlineTravelin man From United States of America, joined Mar 2000, 3556 posts, RR: 0
Reply 12, posted (14 years 4 weeks 5 hours ago) and read 6781 times:

Try taking a 757 out of SNA (Orange County). Because of noise restrictions, they make the planes take off incredibly steep, and then power back suddenly. On a 757, it feels like you're going straight up, then suddenly like you are falling (the engines also become very quiet). The pilot will even warn the passengers before the take-off, so nobody gets scared.

User currently offlineMD-90 From United States of America, joined Jan 2000, 8508 posts, RR: 12
Reply 13, posted (14 years 4 weeks 5 hours ago) and read 6781 times:

Reducing power so that the engines become very quiet after a steep takeoff would scare me!  

User currently offlineSkystar From Australia, joined Jan 2000, 1363 posts, RR: 2
Reply 14, posted (14 years 4 weeks 4 hours ago) and read 6764 times:

Guys, thanks for all your responses. Interesting to note that the MD-83 is a bit of a rocket (can anyone do the numbers for the power loading on that one?).

As for wing loadings (weight/area [kg/m2]). Standard configs unless advised.

733: 535.6 (124,500lbs MTOW)
734: 595.8 (138,500lbs MTOW)
735: 496.8 (115,500lbs MTOW)
752: 538.7
753: 661.1
762: 480.2 (300,000lbs MTOW)
763ER: 640.3 (400,000lbs MTOW)
744: 733.4

319: 522.9
320: 600.5
321: 678.1
343: 746.4 (271,000kgs MTOW)
332: 633.4 (230,000kgs MTOW)

One thing I don't think any of us have talked about in regards to the A3XX is its actual performance. I've heard somet interesting things, so I thought I'd do some numbers.

Doing some math for the A3XX-200 (560ton/1,235,000lbs & 4x 70,000 lbs engines - source AI website), you get a power loading of 4.41! As for the wing loading (I don't know the area, only the wing span), I've heard that it's not very good.

A high wing loading, coupled with an "A340esque" power loading, this potentially doesn't augur for very impressive performance, slowish climb & low initial cruise altitudes. However, maybe Airbus can work some magic with the aerodynamics. Certainly there must be something like that happening, if AI claims that initial cruise altitude is FL350 (we don't know what weight this is for, but I would assume it is for MTOW).



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