SolarWind From United States of America, joined Apr 2004, 66 posts, RR: 0 Posted (11 years 4 months 3 weeks 2 days 14 hours ago) and read 5114 times:
Just wondering...when they were Test Flying the big Twins..before Certification....such as the T7...When they were test flying with only one engine..do they just see if the plane can just make the airfields within ETOPS regs. or do they really push these guys to the limit....For example..(although..probably never Necessary)...Could a 777 make it fully fueled .. across the pond from say JFK to LHR..on one engine?..what about the other way...LAX to NRT..on one? I know engine Failures are extremely rare on the new Twins ..But has any plane and Crew been forced to the limits on one engine on a regularly scheduled flight?
Prebennorholm From Denmark, joined Mar 2000, 6884 posts, RR: 54
Reply 2, posted (11 years 4 months 3 weeks 2 days 10 hours ago) and read 4946 times:
All airliners must be able to take off at MTOW, cruise and land with one engine inop.
Normally the runway won't be long enough for the take off. But when one engine quits after V1 speed it must be able to accelerate to VR and V2 speed and climb out.
Of course it will climb much less steeply. And it will not cruise at high altitudes.
The latter is also because with only one engine running you will lack redundancy on air conditioning and cabin pressurization. A twin on one engine will normally cruise at around 10,000 feet for safety reason - should the aircon fail on the lone remaining engine.
At 10,000 feet any twin including the 777 will cruise brilliantly on one engine at nowhere near max power. But it will cruise somewhat slower due to the thick air, and that's the main reason why it will have considerably reduced range on one engine.
A nice and clean airliner as the 777 will with one engine windmilling have a lift to drag ratio around 16 - 18. That means for instance that if we assume an actual weight of 500,000 lbs it will need 30,000 lbs thrust for level cruise. At low altitude that is roughly half power from one engine only.
In fact it will need at much higher power setting for cruising on two engines at 40,000 feet. But that's because at such high altitude, and consequently the thin air, the available power is reduced by some 70 - 80 percent.
The 6 hours "test" on one engine tells nothing. Any 777 out there is able to cruise for 15 hours on one engine. And if it isn't, then something is seriously wrong and that particular plane should never be allowed to be moved anywhere near a runway with the intention to take off on its two engines.
Always keep your number of landings equal to your number of take-offs
Rendezvous From New Zealand, joined May 2001, 530 posts, RR: 0
Reply 3, posted (11 years 4 months 3 weeks 1 day 2 hours ago) and read 4651 times:
Prebennorholm, yes I agree with your last part about 15 hours on one engine. Planes regularly fly 15 hour flights with each engine running for those 15 hours. The engine knows little difference if the other one has failed.