Oozabooza From , joined Dec 1969, posts, RR: Posted (12 years 11 months 3 weeks 1 day 16 hours ago) and read 2040 times:
Now, I love the 727 as I have said before but as I watched one fly over me earlier today, I started thinking about what the point is of a plane that size having 3 jets. It seems to me that an MD80 would be fairly similar in size and performance to the 727, but with one less engine to operate and maintain, making it a whole lot cheaper. Wouldn't a twin jet have made more sense? What was Boeing's reasoning for a tri-jet that was so small? Thanks!
WISHIHADALIFE From , joined Dec 1969, posts, RR: Reply 1, posted (12 years 11 months 3 weeks 1 day 16 hours ago) and read 1956 times:
From what I know, Boeing needed an aircraft that was economical for short to medium haul routes. The two launch customers, Eastern and United, each wanted a different number of engines. Eastern wanted two for low costs and United wanted four for their high altitude Denver operations. They compromised on three engines and the 727 was born.
Ilyushin96M From United States of America, joined Sep 1999, 2609 posts, RR: 14 Reply 2, posted (12 years 11 months 3 weeks 1 day 16 hours ago) and read 1936 times:
The PWJT8D turbofan used on the 727 was designed back in the '60s. The 727 was designed as a medium-range aircraft, with a passenger capacity of over 130 (727-100), and therefore required three engines to power it. The original JT8D did not produce very high thrust, either. The DC-9, which appeared around the same time as the 727, was much smaller, requiring only two JT8Ds to power it on its projected short range flights.
The successor to the DC-9, the MD-80, has uprated, revamped versions of the old JT8D, the JT8D-217C, which is quieter, more powerful, and less of a polluter than its predecessor. These engines were never used on production 727s, but only retrofitted as hush kits to replace the outer two original JT8Ds.
OPNLguy From , joined Dec 1969, posts, RR: Reply 5, posted (12 years 11 months 3 weeks 1 day 16 hours ago) and read 1887 times:
As others have pointed out, there were many factors why 727 ended up as a trijet. Engines were a big one.
Simply stated, had the latest and greatest (and newest) variants of the Pratt JT8D (-15, -17, -17R, -217, and -219) actually existed when the 727 was designed (instead of the common predecessor -1, -7, and -9 variants, all with less thrust), who knows what would have happened.
Now that the 727's are long-since paid off, and the engines (most of them) upgraded to at least the -15 variant as a standard, the 727 still has a cost-effective future in most cases. Compared with a new aircraft, a well-maintained 727 still is good value, even with the 3rd engine and crewmember.
Now, if Jet-A goes to 2 or 3 bucks a gallon for airlines, that could all change in a hurry...
Prebennorholm From Denmark, joined Mar 2000, 6019 posts, RR: 55 Reply 6, posted (12 years 11 months 3 weeks 1 day 16 hours ago) and read 1883 times:
When the 727 was designed 35 years ago engines were considered less reliable. Therefore there were once tight rules telling that if you flew where there was a certain distance to an alternative airport, especially over water or oceans, then you had to have four engines. Those rules had already been relaxed to minimum three engines when the 727 was designed.
But much later they got somewhat more relaxed. You will see terms like ETOPS-120, ETOPS-180 or ETOPS-209. (ETOPS = Extended Twin OPeration Specifications). Twin engined airliners and airline companies, which comply to those specifications and have that certified, may fly their twin engined planes 120, 180, or 209 minutes flight time away from nearest alternative airport. That means that on some intercontinental flights a twin engined plane cannot fly in a straight line while a three or four engined plane can.
But back in 1965 there was really no choise but three or more engines if you flew a substantial distance over water. Therefore many three engined planes were designed in the 60'es and 70'es: 727, DC-10, L-1011, Trident, Tu-154, Yak-40.
I dont think that any new three engined airliner will ever be designed again. And if the A3XX is cancelled, then we may have seen the last new design with more than two engines.
When going into smaller technical details, then you will notice many more differences between long and short range planes. For instance the B707 and the B720 are basically the same plane except size of fuel tanks. The 707 was intercontinental range, the 720 transcontinental range. The 707 had three separate cabin airconditioning systems, but the 720 only two. The 720 could always just go down to low altitude and land at the nearest airport if one system failed and next failure otherwise would mean disaster. That was difficult in a 707 over the middle of the Atlantic Ocean.
The same goes with hydralic systems. You will see planes with two, three or even four separate hydralic systems. But mostly three on modern planes.
Always keep your number of landings equal to your number of take-offs, Preben Norholm
N-156F From , joined Dec 1969, posts, RR: Reply 7, posted (12 years 11 months 3 weeks 1 day 15 hours ago) and read 1872 times:
I still see use for a 727 myself- startup airlines will be using the until Stage IV regulations hit, and I believe RR Tays can be hushed past Stage IV. Re-engining is an option, and there are several choices out there. Most airlines have upgraded at least to the JT8D-17A, with some choosing to further upgrade the outer two engines to JT8D-217A turbofans, and UPS upgrading to RR Tays. The BMW/Rolls Royce BR715 turbofan could also be used on the outer engines, and possibly the inner one as well, I'm not sure of the diameter.
No matter what happens we can count on seeing 727s until Stage IV at the earliest, probably in the colors of startup airlines and cargo operators. It's a great jet- as versatile as the 737 with the capacity of the A320, and a very low secondhand price.
FDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 38 Reply 8, posted (12 years 11 months 3 weeks 1 day 13 hours ago) and read 1851 times:
From accounts I've read WISHIHADALIFE is correct, Eastern wanted 2 engines and United wanted 4 due to their Denver ops. Boeing compromised on 3. Not only that but originally the 727 was supposed to be equipped with Rolls Royce engines. Eddie Rickenbacker insisted on manufacturing them in America but Rolls said no. So Boeing opted for the JT8D which at the time was being used in on military a/c, I forget the military designation.
Another compromise was wing sweepback: Eastern wanted 35 degree sweep for higher speed but United wanted 30 degrees for better T/O performance from Denver. Again compromise was struck and sweepback was pegged at 32 1/2 degrees.
L-188 From United States of America, joined Jul 1999, 29350 posts, RR: 62 Reply 10, posted (12 years 11 months 3 weeks 1 day 12 hours ago) and read 1825 times:
The 727 was originally designed for Rolls Royce Spey engines. Pratt and Whitney quickly developed the JT-8D engine as an alternative. At the time it was the first commercial engine that was designed from the start as an airline engine.
Military versions came later, I belive the first was the basicly stock JT-8D's that are used on the T-43 and the second developed was the afterburning SAAB built motor(Sorry I don't know the designation) used on the Viggen fighter.
This info comes from a sales tape made by Pratt&Whitney
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
Rikkus67 From Canada, joined Jun 2000, 1464 posts, RR: 2 Reply 12, posted (12 years 11 months 3 weeks 1 day 11 hours ago) and read 1821 times:
I do believe that when the 727 was originally conceived, the amount of thrust available for engines was lower than its newer contemporaries. Remember that the DC-9 was only a 70 - 90 seater when it was first launched...with TWO engines around the same thrust as the larger 3 engined 727. As technology advanced, so did engine thrust... The 757 (the 727's replacement) has two engines of much greater thrust than that of the original 727-200, and seats appx. the same amount of people.
Kind Regards, Rikkus67 (Rik)
Cessna 172; King Air 100; Twin Otter; SAAB 340; Dash 7; Dash 8-100,-200,-300,-400; CRJ-200,700,900; ERJ-170; F-28; DC 9-
PropilotJW From United States of America, joined Mar 2000, 585 posts, RR: 7 Reply 13, posted (12 years 11 months 3 weeks 1 day 11 hours ago) and read 1815 times:
The 727 was built to take the place of the 707. The inside of the 727 has 3 seats on each side just like the 707 and the smaller MD-80 only has 2 on one side and 3 on the other. The 727 was made to fly some trans-atlantic flights and going that way on 2 engines was unheard of at that time. Airlines love the 727 b/c of it's capability to take off on a very short runway (much like it's predecessor, the 757). You probably know that the 757 was built to take the place of the 727. The 757 also has the 3/3 seating and now people comfortably fly trans-oceanic routes on two engines. If you have been on a 757, you will know why it takes off in such a small distance...The engines have much more power then is needed.
Prebennorholm From Denmark, joined Mar 2000, 6019 posts, RR: 55 Reply 14, posted (12 years 11 months 3 weeks 1 day 5 hours ago) and read 1799 times:
L-188 wrote: "Pratt and Whitney quickly developed the JT-8D engine as an alternative. At the time it was the first commercial engine that was designed from the start as an airline engine".
That's only partially correct.
The JT-8D was a fanned version of the already old J52 military turbojet engine which was mainly used on the A-4 Skyhawk. That was the reason why P&W could respond so fast to Boeing requirements.
As its name J52 indicates this engine design is in fact older than the J57, which became the civil JT-3C and JT-3D on the Boeing 707 and DC-8.
The SAAB Viggen military version (named VOLVO RM-8) was, however, a development of the JT-8D, not the J52. Most of the "development" was fitting a VOLVO afterburner.
So the basic JT-8D design has already passed its 50th anniversary by now. That's really not bad considering that the JT-8D-2xx versions may soldier on for another 20 years.
Always keep your number of landings equal to your number of take-offs, Preben Norholm