Skystar From Australia, joined Jan 2000, 1363 posts, RR: 2 Posted (14 years 5 months 1 week 2 days 8 hours ago) and read 7652 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)
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
Skystar From Australia, joined Jan 2000, 1363 posts, RR: 2
Reply 4, posted (14 years 5 months 1 week 2 days 4 hours ago) and read 7479 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.
TrnsWrld From United States of America, joined May 1999, 1004 posts, RR: 0
Reply 6, posted (14 years 5 months 1 week 2 days ago) and read 7397 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
Panman From Trinidad and Tobago, joined Aug 1999, 790 posts, RR: 0
Reply 7, posted (14 years 5 months 1 week 1 day 20 hours ago) and read 7341 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.
DesertJets From United States of America, joined Feb 2000, 7839 posts, RR: 14
Reply 8, posted (14 years 5 months 1 week 1 day 19 hours ago) and read 7325 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
NorthStarDC4M From Canada, joined Apr 2000, 3137 posts, RR: 36
Reply 11, posted (14 years 5 months 1 week 1 day 18 hours ago) and read 7305 times:
AIRLINERS.NET CREW CHAT OPERATOR
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.
Travelin man From United States of America, joined Mar 2000, 3566 posts, RR: 0
Reply 12, posted (14 years 5 months 1 week 1 day 15 hours ago) and read 7280 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.
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).