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Guest mikeernie

747

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Had a question about the 747...it seems to take off like a rocket down the runway....I'm reaching 80 knots in just a few seconds, maybe 3 or 4....that doesn't seem right, it feels like it's entirely too quick...has anyone else been experiencing this? I have it fully loaded by the way...thanksRick Ryan

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Do yourself a favour, look up Pound of Thrust on the internet. Note that the 744 has about 200,000 pounds of thrust. Then get out your calculator( or open the computer's calculator) and do some equations.

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Well, that answered my question...do you mean "equations"?

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Hi Rick,You'll need to look at a thrust derate if she's leaving you behind on the runway on takeoff. search the forum and manual using the term 'derate' and you should get an idea. If you still have questions then come back to this thread and I'll help you out.Andy, try being nice to people who ask questions mate. If you didn't know what the term derate meant this would be a hard problem to find an answer to.

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I gave my answer to help give a better understanding of how fast a 747 can go with 200,000 pounds of thrust pushing it. That way he might get a better understanding of how well the airplane can accell. Sorry to be rude or anything.and mark, "search the forum and manual using the term 'derate'"In a way we're asking for someone to do something, YOu ask him to search the manual and forum and i ask him to google thrust. Please don't accuse me of being rude.Here's some key points i've found on the internet:"At approximately 400 mph, one pound of thrust equals one horsepower, but at higher speeds this ratio increases and a pound of thrust is greater than one horsepower. At speeds of less than 400 mph, this ratio decreases. " or how about this "A "pound of thrust" is equal to a force able to accelerate 1 pound of material 32 feet per second per second (32 feet per second per second happens to be equivalent to the acceleration provided by gravity). Therefore, if you have a jet engine capable of producing 1 pound of thrust, it could hold 1 pound of material suspended in the air if the jet were pointed straight down. Likewise, a jet engine producing 5,000 pounds of thrust could hold 5,000 pounds of material suspended in the air. And if a rocket engine produced 5,000 pounds of thrust applied to a 5,000-pound object floating in space, the 5,000-pound object would accelerate at a rate of 32 feet per second per second. "

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To put it all another way, there is enough thrust in the B747-400 to accelerate a 400 Tonne aircraft to flying speed (close to 200 miles per hour) in only two miles.If you have the aircraft at fairly light weight (min fuel and no pax you could be a mere half of max gross weight) and utilise full thrust it will obviously accelerate like a rocket.Try more pax or more fuel and/or try derate thrust on the appropriate page of the FMC and see how the acceleration changes.

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>Do yourself a favour, look up Pound of Thrust on the>internet. Note that the 744 has about 200,000 pounds of>thrust. Then get out your calculator( or open the computer's>calculator) and do some equations.Hi,The 747 DOSE NOT accelerate to 80 knots in 3 or 4 seconds at the weight Rick's referring to. At near gross weights, it takes about 15 to 20 seconds to reach 80 knots.Rick, you are correct. There is something wrong here. Let's make sure we have everything correct. You said you were at gross weight. Are you using pounds or kilograms? Make sure you didn't use the wrong units, pounds and kilograms. What is the gross weight of your airplane? What is the elevation of the runway? If you are at gross weight, it should take much longer than 3 or 4 seconds at any weight. Ken.

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I wasn't accusing you of being rude Andy, I just felt that your response wasn't exactly going to help a new guy with an emerging understanding of the aircraft. (He obviously thought so too).Your point is well made, there are some interesting things to learn on the subject. But the derate thrust option is what this guy is looking for I expect.I wasn't trying to be inflammatory and I apologise if it came across that way.

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i've been reading a lot of the forums, and this andy aude seems to get very snippy with many of his replies. i am, alas fulfillng his need to continue to rant and rave with this remark.psychic, i am. i bet we will get another snippy one from him.But, yes. I agree that with a full load, acclerating to 80 knots in 3-4 seconds seems odd. low pressure, dry situation? Tomm

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I really don't want this thread to get locked because of a fight without the original poster getting his problem solved.So just to close off the matter: I wasn't trying to be rude to Andy, nor was I implying that Andy was being rude himself. I've apologised to him if that's how he took it.I think we should keep the focus on helping this guy out with his takeoff issues. Yes, 3 to 4 seconds is mighty fast even empty and without derated thrust.What was the thrust indication on the EICAS? TO? TO1? TO2?

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>i've been reading a lot of the forums, and this andy aude>seems to get very snippy with many of his replies. i am, alas>fulfillng his need to continue to rant and rave with this>remark.>>psychic, i am. i bet we will get another snippy one from him.>Tomm, You're right, now this time it's toward you, grow up.I hope you have better things to do than search the forum for a member's posts so you can critisize them. "Rant and Rave." Ha. Not quite. You aren't seeing the big picture. Also, your message highjacks this thread. What's your point for it? Do you want a prize or something? People like you make me snippy. Not new people.Mark i accept your apology. I also apologize to you.

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According to the load manager my actual TO weight was 717,079 lbs. the eleveation was around 600 ft....unfortunately I have not been able to reproduce the original problem...I'm not sure how it happened or why it happened, but it did happen....I was not doing anything differently than I have done 30 or 40 times before...the plane just took off like a rocket and I was airborne in less than 1/3 of a fairly short runway....I thought maybe it was some kind of bug emerging and my original intent was to find out if anyone else had experienced this...apparently not....it appears that I also started a small amount of trouble between some folks....certainly not my intent, I was asking what I thought was as simple question...

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well. no i haven't been trolling the archives to search for your insipid little remarks. i just don't forget. that's all lil' chap.the ranting and raving was in reference to your past posts, wee man.maybe your head is full of cheese.

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Do you like the Single Slices or the the blocks of cheese?

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No trouble at all, believe me it wouldn't be the first time disharmony has popped up and like always it's due to misunderstandings mostly.Besides, you'll notice that it has now mutated into a discussion about cheese so that's how serious it was.Back to your problem: Suffice to say if it happens again, capture as much info as you are able to and bring us up to date.Good luck!

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