twinjet vs trijet
03-02-2010, 05:53 AM
#31
Gets Weekends Off
Joined APC: Apr 2008
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Posts: 791
If 3 engines is better than 2, then they should make a commercial version of the B-52.
As for ETOPs concerns, when you spend some time away from a divert field (ETOPs is not just about water) you soon realize you should fear a cabin fire way more than an engine failure.
As for ETOPs concerns, when you spend some time away from a divert field (ETOPs is not just about water) you soon realize you should fear a cabin fire way more than an engine failure.
03-02-2010, 06:17 AM
#32
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Joined APC: Mar 2010
Posts: 36
Originally Posted by tsquare
There is no such thing as an overpowered airplane. It's like having too much gas.. the only time there is too much is when you are on fire.
03-02-2010, 08:33 AM
#34
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Joined APC: Jul 2008
Position: 747 Captain (Ret,)
Posts: 804
Originally Posted by tuna hp
Yeah thats exactly where I'm saying that any possible efficiency benefits would come from. Say you have a twinjet with 2x5,000lb engines that has a certain runway requirement. Holding everything else constant, maybe the trijet would have 3x2,900lb engines. So it would have 5,800lb thrust with an engine out and should be able to have a shorter runway requirement.
What I was asking is, say the trijet has 3x2,500lb so it has the exact same runway requirement as the twinjet, how would performance and efficiency compare to the twinjet? It uses 3 engines, but they are much smaller and closer in power capability to what the actual cruise requirements are.
What I was asking is, say the trijet has 3x2,500lb so it has the exact same runway requirement as the twinjet, how would performance and efficiency compare to the twinjet? It uses 3 engines, but they are much smaller and closer in power capability to what the actual cruise requirements are.
It is true that after the engine failure both aircraft would have the same total power remaining and would use the same amount of runway to continue the takeoff. However, since the twin has more total thrust with all engines operating, the twin gets to V1 (engine failure speed) in much less runway. Therefore the twin uses less total runway for takeoff.
Another minor point is that the regulatory requirement for climb gradient after an engine failure is slightly lower for a two engine aircraft than for a three or four engine aircraft.
Joe
03-02-2010, 10:24 AM
#35
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Originally Posted by joepilot
I see a conceptual error here.
It is true that after the engine failure both aircraft would have the same total power remaining and would use the same amount of runway to continue the takeoff. However, since the twin has more total thrust with all engines operating, the twin gets to V1 (engine failure speed) in much less runway. Therefore the twin uses less total runway for takeoff.
Another minor point is that the regulatory requirement for climb gradient after an engine failure is slightly lower for a two engine aircraft than for a three or four engine aircraft.
Joe
It is true that after the engine failure both aircraft would have the same total power remaining and would use the same amount of runway to continue the takeoff. However, since the twin has more total thrust with all engines operating, the twin gets to V1 (engine failure speed) in much less runway. Therefore the twin uses less total runway for takeoff.
Another minor point is that the regulatory requirement for climb gradient after an engine failure is slightly lower for a two engine aircraft than for a three or four engine aircraft.
Joe
As to the second point, yeah thats definitely another factor. Is it only the minimum climb gradients required that are higher for trijets, or will every airport (even the ones that have higher than normal climb requirements already) have higher requirements for trijets?
03-02-2010, 12:34 PM
#37
Snakes & Nape
Joined APC: Nov 2006
Position: B-767 Captain
Posts: 775
I Hate to Disagree
Originally Posted by tsquare
There is no such thing as an overpowered airplane. It's like having too much gas.. the only time there is too much is when you are on fire.
G'Day Mates....and check those mach speeds (low and high) for FL390.
03-02-2010, 01:04 PM
#38
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Joined APC: Oct 2007
Position: single pilot cargo, turboprop
Posts: 484
Originally Posted by tuna hp
Also, I can't imagine why a trijet would necessarily hold more fuel in the fuselage.
I've never been given an official explanation, but my best guess is that it is to give the number two engine it's own independent fuel source and prevent an imbalance situation that might result if it drew fuel from the wings. Someone correct me if I'm wrong.
03-02-2010, 03:45 PM
#39
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Joined APC: Aug 2006
Posts: 1,091
Originally Posted by Phantom Flyer
Talk to any of the UPS pilots on the forum that flew the DC-8-73 series with the CFM-56 engines. In their configuration, you ran out of wing a long time before you ran out of engine and one had to be very careful at the higher altitudes. Definitely an example of an "overpowered" aircraft. Due to well trained crews it didn't present significant problems but nonetheless, it was overpowered.
And then there was the Hawker Sea Fury... knew a guy who flew them and he said that if you went to full power (above 50-55in) the airplane would be skipping across the runway with full left rudder (engine operates the other way). and more than a few of the big pistons have been torqued over on botched go-arounds.
03-02-2010, 03:53 PM
#40
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Originally Posted by III Corps
and more than a few of the big pistons have been torqued over on botched go-arounds.
Lost a P-51 in Camarillo, California 3 years ago with a low speed, high power go-around. Plane rolled inverted and struck the earth at about 45 degrees, upside down. Totaled and dead. First solo in the plane.
