Re: 757 highest thrust to weight ratio ?

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works
Date:         02 Dec 92 03:49:51 PST
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In article <airliners.1992.65@ohare.Chicago.COM> (Terrell D. Drinkard) writes:
>In article <airliners.1992.39@ohare.Chicago.COM> Bob Coggeshall <coggs@Hongkong.Cogwheel.COM> writes:
>>I've heard that the 757 has a very high thrust to weight ratio. Just
>>how high is it ? Is it the highest of any commercial jetliner ?

>My back-of-the-envelope calculations would suggest about a .38 thrust to
>weight ratio.  That is assuming the RR RB211-535E4B gives around 42,000 lb
>thrust (SLST) at a MTOW of 220,000 lb.  I'm not aware of anyone who
>actually bought that configuration, though.

The various RB.211-535 variants used on the 757 range from 37,400 lb
thrust up to 43,100; the PW2037 is rated at 38,250.  Most airlines
choose a 230,000 or 240,000 lb MGTOW, however.  The only one I could
find on a quick scan with only 220,000 was Northwest, which with the
PW2037 works out to 0.3477.

Curiosity drove me to dig out the March 16, 1992 AW&ST with the big
specifications section and look up the power/weight ratios for some
common transports.  Where a choice was available I tried to pick the
heaviest version with the highest thrust verion of a common engine
type, and tossed in a couple of other interesting cases.  Over 24
samples the power/weight ratios ranged from 0.2428 to 0.3477.  The
higher figure is the 757 in Northwest's configuration; a better
comparison point is the 240,000 MGTOW 757 which comes in at 0.3187,
trailing only the A320/A321, MD-90, and 737-500 (and of course the
lighter 757).

Not surprisingly, the top 11 were all twins.  At the other end of the
scale, the heaviest 737-200 Advanced, at 0.2488, was only ahead of the
727-200 Advanced.  Judging by these numbers it would seem the 737-200
is a rather underpowered aircraft.

Subjectively, pilots I've talked to love the 757 for its abundant
power and from the cabin once I was impressed with how quickly a 757
got us out of a wind-shear situation at O'Hare.

Another factor that may give an illusion of power is that most 757s
are used on medium-range routes, yet they've got a 4550 mile range.
Typical flights probably carry a light fuel load and thus may be well
short of MGTOW.

As for highest of any commercial airliner, even the lightest 757 is
still well short of the Concorde's 0.3725 power/weight ratio.  :-)

Karl Swartz	|INet		
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