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There are jetliners with 2, 3 or 4 engines and they all probably have the same top speed. And then there is the B-52 with 8 engines. I shouldn't be putting the B-52 in the same category but you get the point. Where does the horsepower go?
There are jetliners with 2, 3 or 4 engines and they all probably have the same top speed. And then there is the B-52 with 8 engines. I shouldn't be putting the B-52 in the same category but you get the point. Where does the horsepower go?
I guess I can say as an understatement that all jet engines are not created equal. The number of engines is just one design parameter. Concorde has 4 engines, so does B-747 - but the engines are as different as the rest of the airplane.
All jetliners and jetliner-like bombers operate at something like .95 Mach, because that is as fast as you can go without doing all the considerable stuff you have to do to go supersonic.
I'm kind of surprised the B-52 has not been refitted with 4 bigger high-bypass engines, as it is, I think it's quite a fuel hog. 1950's design.
There are jetliners with 2, 3 or 4 engines and they all probably have the same top speed. And then there is the B-52 with 8 engines. I shouldn't be putting the B-52 in the same category but you get the point. Where does the horsepower go?
What horsepower?
The B52 engines produce 17,000 lbs for a total thrust of 136,000 lbs.
A Boeing 777 can have two Trent 800 engines producing 93,400lbf for a total thrust of 186,800 lbs. (Can have because there are a couple of variants, by different manufacturers, but ballpark similar thrust)
You're kind of asking the aviation equivalent why a 2.0L Camry isn't as fast as a 4.0L twin turbocharged Ferrari, because they both have engines.
Thrust to weight ratio and aerodynamic factors determine the speed performance of an aircraft, not the number of engines it has. 4 engine airliners actually have lower thrust to weight ratios than 2 engine ones, because the two engine plane must be capable of meeting minimum climb gradient requirements on 50% of its total thrust if one engine fails, vs. 75% for a quad if one engine fails.
Yep, more engine are generally going to weigh more and require a larger fuel supply. A wing creating lift produces what's known as induced drag.
More weight requires more lift which produces more induced drag.
In aerodynamics like with most things, there ain't no free lunch.
That's one of the first things I learned as an aero major.
The cycle: OK, I want to haul X number of passengers (or bombs or cargo) Y distance at Z speed. So the aircraft and wing have a certain size and shape. But that wing is too big, too much drag. Make it smaller, the aircraft has less form drag. Oh, but induced drag goes up a bit, maybe a lot. Or the takeoff and landing speeds and distances go way up. Shed some weight (passengers or bombs) and the design loses money for the airlines and is a lousy bomber and doesn't meet parameter X. Or reduce fuel load, add larger engines, but now you can't fly Y distance. Use smaller engines or a larger wing and you won't achieve Z speed. The iterative process goes around and around, so almost every aircraft is a compromise. Every once in a while a "revolutionary" aircraft comes along which seems to change the rules, but it doesn't, it just exploits aerodynamic truths that no one else was able to at the time. The F-16 is an excellent example; its relaxed stability and blended shape actually reduces the amount of work the wings do, which is efficient at cruise and in combat. So now nearly all Gen 4 and Gen 5 fighters use the same techniques.
They can fly a lot faster than they do. The normal flight from Philadelphia to Bangor Maine takes about 2 hours. The last flight I was on, the pilot apologized for being late and said we were going to boogie and make up some time. They did the flight in about half the time in 65 minutes.
We never leveled out, we went up at about 30 degrees angle for about 30 minutes and then down at about 30 angle for about 30 minutes. The flight was full.
The same reason that two horses pulling a wagon aren't faster than Secretariat, and an Iowa-class battleship (four turbines) ins't faster than a speedboat (one outboard) on a lake.
We never leveled out, we went up at about 30 degrees angle for about 30 minutes and then down at about 30 angle for about 30 minutes. The flight was full.
How did you feel when you re-entered the earth's atmosphere?
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