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Old 08-18-2019, 02:07 PM
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murphyaa murphyaa is offline
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Random Thoughts

As I get older, I often find myself having random thoughts about aviation related subjects.

For instance: Today I saw an article where a test flight for the new 777-9X had to be aborted due to a problem with the engines.

This got me thinking to the design of airliners and the airline industries fascination with only using two engines, no matter how big they have to make them. The GE9X engines are supposed to produce 105,000 lbs of thrust each at takeoff. What happens when you're on taking off, and lose an engine? Suddenly you've got 105,000 pounds trying to push the plane to one side.

I realize they use the rudder to counteract a thrust imbalance, but that only works if there's enough speed for the rudder to work. Also, as the engines get more powerful, the rudder has to get bigger to be effective. As engines get bigger and more powerful, we're gonna end up with planes that look like the Lippisch DM-1, all tail fin.

I wonder if designers will start to think that it might be better to not concentrate all the thrust of the engines into only two engines, but instead go back to 4 engines.
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Old 08-19-2019, 06:29 AM
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I would think moment goes by force times distance, so I guess, you could put the same tail fin further back, does the same job as a bigger fin. (Not counting how this affects the transverse aerodynamic modes.) The fact this had not happened probably meant the designers doesn't need it, and there is already enough torque available at v1 should anything go wrong...
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Old 08-19-2019, 08:34 AM
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Efficiency is the name of the game... also I am sure or let's say I hope the engineers pondered on the same questions you have Murph during their brainstorming sessions before starting to work on any new designs.
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Old 08-19-2019, 08:47 AM
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Murphy

Being in the jet engine and aviation business for 40 years, i can explain.
Every commercial twin engined jet is certified to continue take off after V1 (nose gear rotation), on a single engine. So in the event you lose trust on any engine after V1, you continue take off, get to safe altitude and depends on conditions, dump fuel, or burn fuel until safe landing weight is achieved.

We tested a Boeing 777 with GE90 by shutting one engine over the Pacific for over 5 hours on a flight to Australia. No issues.

Hope this helps.

Twin engines must be significantly more reliable than 4 engine configuration

Isaac
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Old 08-19-2019, 09:07 AM
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Then again they can often overthink things. Look at the amazing contraptions that were built and failed before the Wright brothers succeeded ... then consider the simplicity of a hang-glider. When they first issued us with the experimental Irvin Delta Parawing, even the designer never dreamt that we could get them to go back up ... using thermals.
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Old 08-19-2019, 09:27 AM
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Murph, you remind me of an airline pilot more than 40 years ago, who said that the three-engine configuration of the 727 made it a dream to fly. We know that every configuration has both advantages and disadvantages, so that economics and technological improvements determine which configuration makes sense at any point in time. Suppose these considerations could bring back three engines again?
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Old 08-20-2019, 07:39 AM
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The next phase is hybrid electric power. At that point, the number of engines will be meaningless. You can have hundreds of motors if needed.


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Old 01-21-2020, 10:37 PM
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So I saw this on one of my Facebook groups:

I know it's just an A-10 in primer before the camo is applied, but two thoughts occurred to me. First: Stealth A-10. Second: Night Fighter A-10. I might have to think about another repaint of the two-seater version.
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Old 02-08-2020, 12:06 PM
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Here's something you don't see every day:
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Old 02-08-2020, 09:05 PM
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That thing can sure hang on its props.

Don
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