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 Fastest Commercial Jetliner. |
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 Jul 16 2006, 12:11 PM
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The Rant Master
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From: Atlanta, Georgia
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QUOTE(charliepapa @ Jul 16 2006, 07:35 AM) [snapback]94093[/snapback] All aircraft are overpowered. Even the A343...  QUOTE(tripleseven @ Jul 16 2006, 10:43 AM) [snapback]94110[/snapback] No it's not.........  QUOTE(karlhurst_380 @ Jul 16 2006, 10:48 AM) [snapback]94112[/snapback] It would take a lot longer to get airborne if they weren't... I think we need to know what was meant by "overpowered." Typically, when a term like that is used, it is used to mean "more power than is necessary." Well, to determine if something is or is not "over"powered, we have to know what power is necessary. To get an airplane into the air, you are going to need lift - and that is normally generated by pushing the wing through the air (except in some cases where the powerplant is designed to supplement that by "blowing" air over the wings even when the forward speed is not that much - Mcchord can probably tell us more about that...). When there is sufficient forward speed to generate enough lift when the wings are at the prescribed angle of attack, the airplane will become airborne. So, there has to be enough "thrust" to overcome the inertia of the airplane at rest at the end of the runway. Then the "thrust" has to be large enough to accelerate the airplane (in the conditions that exist - headwind, tailwind, uphill, downhill, long runway, short runway, hard surface, rough surface, hot day, cold day, high pressure altitude, low pressure altitude, flaps up, flaps down, a lot of wheels, only a few wheels, etc.) to that point. Additionally, once reaching that point - where there is enough airflow for the proper AoA and the airplane becomes airborne, now the thrust has to be enough to allow the airplane to at least maintain that airspeed. Remember, we've now exchanged some of those on-the-ground conditions for the in-the-air conditions we now have. So while we're not fighting coefficients of friction for runway, brakes, and wheels, and we're not fighting uphill or downhill, now we have to fight the induced drag generated whenever lift is generated ... and we'll need enough "excess" thrust to be able to climb, not only climb out of ground effect (where the drag is less) but to continue to climb after getting out of ground effect. From here, we have to be concerned that we're not going to disintegrate the engine running it at any given RPM, temperature, etc., because we may have to reduce the power level to the point designed for “maximum continuous” operation. And, before I go on, please understand that this is NOT an exhaustive list of the things that affect this. Now, there are just a couple of more considerations you have to make in order to say that an airplane is “over”powered. Remember, we said nothing about how quickly the airplane had to accelerate to get to the necessary airspeed to become airborne, and we said nothing about what kind of runway surface we were using, and we said nothing about any of the other conditions we described – only that we had to have enough power to “overcome” those conditions. So if you put our hypothetical airplane at an airport that has 6000 feet of concrete runway, the runway is uphill, it is at a high altitude, it is a relatively hot air temperature, and the airplane is quite heavy, you’re going to have to compute all the interrelated factors to be sure that the airplane can safely operate out of those conditions. Assume that it can; but it just can. Certainly, this is not an “over”powered airplane. Now, put that same airplane at an airport that has 12000 feet of concrete runway, the runway is flat and at sea level, the air temperature is relatively cool, and the airplane is substantially lighter than during our other example. Here, you might get away with saying the airplane is “over”powered. So, which is it? Is this airplane overpowerd or not overpowered? The answer is … it depends on all the circumstances that exist at the time. 
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Jul 16 2006, 12:29 PM
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Space Shuttle Member
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QUOTE(tripleseven @ Jul 16 2006, 03:43 PM) [snapback]94110[/snapback] No it's not......... Um yeah they are dumbass. Simple answer: All aircraft HAVE to be overpowered... what happens when an engine fails? If there was just enough on four engines, on three or even two engines there wouldn't be enough grunt to keep it in the skies. Why do you think there are de-rate settings...? If you aren't clever enough to work it out, it's because not all of the power available is needed at that time. AirRabbit has hit the nail on the head... all depends on circumstances... but ALL aircraft have to have the power to keep aloft if there is a 50% powerloss (not including single engined a/c of course ) So Mr. tripleseven... if you don't know what you're talking about, watch and learn... don't make unsubstantiated rubbish up cuz you'll be caught out every time. charliepapa
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Jul 16 2006, 02:08 PM
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Space Shuttle Member
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From: Denver,Colorado USA
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QUOTE(charliepapa @ Jul 16 2006, 08:29 AM) [snapback]94126[/snapback] Um yeah they are dumbass. Simple answer: All aircraft HAVE to be overpowered... what happens when an engine fails? If there was just enough on four engines, on three or even two engines there wouldn't be enough grunt to keep it in the skies. Why do you think there are de-rate settings...? If you aren't clever enough to work it out, it's because not all of the power available is needed at that time. AirRabbit has hit the nail on the head... all depends on circumstances... but ALL aircraft have to have the power to keep aloft if there is a 50% powerloss (not including single engined a/c of course ) So Mr. tripleseven... if you don't know what you're talking about, watch and learn... don't make unsubstantiated rubbish up cuz you'll be caught out every time. charliepapa Um, no they aren't If they were you moron, then it wouldn't necessitate a four engine rotation NOW WOULD IT? Oh, I forgot, the other 2 engines are there "just in case" we need 2 more to takeoff.............. Even if the engines are not at 100% at T/O it still takes all four to rotate, now what about those "de-rate" settings?......I thought so Nice try junior............................... 
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Jul 16 2006, 02:33 PM
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Space Shuttle Member
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Expounding a little on what AirRabbit wrote:
I would say, in this context, the definition of "overpowered" would be: Having more power than you need under any conditions for which the aircraft is designed to operate (pretty much what he said). With this definition it is the rare aircraft that is overpowered. An F-15 Eagle, which can accelerate going straight up, is very powerful, but not overpowered. It has the power it needs for what it's designed to do.
"Overpowered" is at least an insinuation that the aircraft is overcome by that power, by having too much and under at least some flight conditions for which it is designed, and is uncontrollable as a result. Obviously, this is not the way to design an aircraft. Otherwise, if power is a good thing, why not simply bolt on the most powerful engine(s) you can fit to the airframe? Because too much power can be a bad thing. And not just for economic (fuel burn) reasons.
Take a twin, such as the Boeing 737, for example. If it has an engine failure the asymetrical thrust coming from a too-powerful engine can make the plane uncontrollable. At full power from the remaining engine the airplane must still be controllable (through the flight controls) or it would not get certified. This needs to be balanced by having sufficient remaining thrust available for the aircraft to continue flying, and with a required minimum performance remaining (ability to climb). If THAT required power is too much to handle (pun intended) then other design changes must be made, such as increasing the size of the vertical stabilizer and rudder. With more power comes design accomodations to handle it. So you don't put more power on the plane than needed.
When an airplane is designed and certified it must, as written above, meet minimum climb performance criteria in the event that it loses ONE engine at the worst possible time. This would be in the take-off roll at V1 (the decision speed, after which you continue the take-off and fly regardless of what may happen - such as an engine suddenly failing). A 4-engine plane would lose 1/4 of it's overall power. A 2-engine plane would lose 1/2 of it's overall power. A much bigger loss for the twin. For this reason twin-engine jets have a better power-to-weight ratio than planes with more engines. So, if any plane can be said to be "overpowered" compared to another, it is twin-engine planes compared to those with 3 or more engines. For its weight a 737 is more powerful than a 747, but it is not overpowered.
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Jul 16 2006, 02:42 PM
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Space Shuttle Member
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QUOTE(tripleseven @ Jul 16 2006, 07:08 PM) [snapback]94136[/snapback] Um, no they aren't If they were you moron, then it wouldn't necessitate a four engine rotation NOW WOULD IT? Oh, I forgot, the other 2 engines are there "just in case" we need 2 more to takeoff.............. Even if the engines are not at 100% at T/O it still takes all four to rotate, now what about those "de-rate" settings?......I thought so Nice try junior............................... Yay! I love this game... A four engine rotation? Erm yeah.... that's more made up than pixie porno movies. All engines are used... they are de-rated in preparation for a flight via the FMC. This chops the EPR/Flex (depending on whether you're a Boeing or Airbus sorta guy) down a few percent. This saves engine wear and tear. If the aircraft had just enough power to get off the ground, then it would be using all the energy available... wouldn't they? Nice try junior
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Jul 16 2006, 02:43 PM
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Cessna 152 Member
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From: EGXC, UK
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Don't forget the mighty VC-10. We still have them in the RAF and are used extensively all over the world. I know strictly speaking they are not civil passenger aircraft anymore, but they are still used to carry our troops and for air to air refueling our fighter and bomber aircraft. And the aircrew certianly know how to throw the VC-10 around!!!! I have been sat in the cockpit of a VC-10 whilst refueling from another VC-10. Absolutly remarkable!!!!! VC-10VC-10 in FormationVC-10 Take Off
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Jul 16 2006, 04:32 PM
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Space Shuttle Member
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QUOTE(tripleseven @ Jul 16 2006, 09:20 PM) [snapback]94152[/snapback] So then....using your logic...... It can rotate on JUST ONE ENGINE right?....... Yay....I love this game  Rotate? You mean take off? Yes.. it can. It is a requirement of all jets... what happens when there is an enginefailure after V1? The plane crashes and burns? Nope... it takes off and goes around ;) Yay...
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Jul 16 2006, 05:37 PM
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Airbus 380 Member
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QUOTE(Mcchord_AFB_Airman @ Jul 15 2006, 05:07 PM) [snapback]94028[/snapback] What are you talking about? Carry the plane? Im sure im not the only one confused here, and the 747 isnt overpowered, its got just the right amount. I clearly never stated that the 747 was over powerd. I believe I should of rephrased myself and sorry for that. Carry the plane as in bring it up to that altitude. Can someone correct me so I dont have any bad information please if needed. Lets not get rude. Guys Im sure we can handle this in a more adult way. Cheers, Ap
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Jul 17 2006, 03:35 AM
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Space Shuttle Member
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1: B727/DC-10
2:B747
3: B757
4: B767
5:B777/MD-11
7: MD-80
8: A340
9: DC-9
10: A300/310
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) So I think that they know what they are doing.
