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Boeing Jumbo-Jet Era Ending in US as United Retires 747 Fleet

Marc

Captain Nice
Staff member
Admin
#3
I recently saw a documentary on the design and development of the 747. Very interesting. The first flights they were using engines which kept exploding and flaming out so they had to be gentle with the engines for about a year or so until they found the problems.

These pages of a Flight International article from 1969 describes one of the early JT9D problems, where the engine case became slightly oval causing turbine blades to rub against the engine casing.

Although P&W developed a fix, it was still a problem during the initial period of 747 service. There were other problems also. Even Pan Am's inaugural 747 flight JFK-LHR in January 1970 was delayed about 3 hours when they had to substitute another aircraft for the one planned when the first one developed engine problems.

- 1) Under powered ,delivered not enough thrust for the ever increasing MTOW of the 747, to get maximum thrust HP turbine section was operated at limits.
- 2) Very sensitive for tail and X-wind, especially during starting, causing hot starts or stalls.
- 3) Ovalisation of the engine casing during T/O, causing blade rubbing and loss of efficiency.
- 4) In general very stall sensitive during power transitions, don't put the power levers suddenly to idle.
- 5) Damaged HP turbines, caused by failing rivets in blade-retaining plates in early engines.
Remedies :
- 1) Product development, slowly increased thrust from 43.500 lbs, first via addition of water injection in the dash -3A engine. Then further increase possible via improved HP turbine blades in dash 7, 7W, 7A, 7AW, 7F and finally maximum 50.000 lbs in dash 7J with single cristal HP turbine blades with improved cooling. Two improved variants (with different type certificate) with more thrust were developed to counteract the GE and RR engines offered from 1975. First the -70 and -7Q were developed, the final (at last matured) engine was the dash -7R4 series.
- 2) Small improvements made starting not so demanding, but still the engine was/is very tricky to start in tail wind conditions. (valid for all dash -7 versions up to -7J.)
- 3) Was remedied by a thrust yoke, to spread the forces applied between the pylon and engine better.
- 4) Addition of ARS (automatic recovery system) in fact extra (3.5) bleed valves dumping air, when an impending stall condition was sensed. During reverse RABS (reverse actuated bleed system) was built in to release air from the engine in case of impending stall.
- 5) Improved rivets installed.
Sources : Jet and Turbine Aero Engines by Bill Gunston.
 

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howste

Thaumaturge
Super Moderator
#4
Interesting stuff to read.

I believe Delta still has nine 747s in service, but they'll be replacing them with A350s soon. Most of the 747s still in service now are in Europe and Asia. All of the flights I've been on with 747 service were to/from Asia.

I suspect that Air Force One may be the last 747 in regular "passenger" service in the US.
 
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