Alright, I need someone's help. We're doing a renewable energy project for one of my classes in which we have to design a new way to capture energy. We decided to put turbines at the end of a runway so that as large jets throttle up to full power prior to takeoff, the wind generated can be captured for energy. Thing is though, I can't for the life of me find any facts online about the speed of the exhaust say 25, 50 or 100 feet behind a jet. If anyone can find or knows this info, it would really help us out with our project! Thanks!
Jet Blast
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Jet Blast
You'd have to do a small CFD experienment to be sure, but I'd guess that the flow would be so turbulent it would be pretty unuseable. You might be able to condition the flow somehow, but at the expense of flow rate... again, experiemental data would be needed.
25 feet behind it would be quite hot and fast.
50 feet a bit less so
100 feet warm and breezy. All depending on the engine, plane and prevailing conditions. Speak to Boeing or Airbus for more information.
Any energy harnessing device (I'd guess an array of ducted fans on mini-generators would be most efficient) would need to be removable when something lands (or crashes).
Reading a few books about aircraft jet engines might be of some help - better than the internet anyway.
25 feet behind it would be quite hot and fast.
50 feet a bit less so
100 feet warm and breezy. All depending on the engine, plane and prevailing conditions. Speak to Boeing or Airbus for more information.
Any energy harnessing device (I'd guess an array of ducted fans on mini-generators would be most efficient) would need to be removable when something lands (or crashes).
Reading a few books about aircraft jet engines might be of some help - better than the internet anyway.
Yea, we're thinking of a very low profile scoop (much like the hood scoop on a car) to catch some of the air closer to the ground and just channel it to a row of small turbines, that way it would be out of the way of landing aircraft...
...it's just a theoretical mini-project. It doesn't really matter if it would work in real life. I'd just like to be able to say "positioned 50 feet behind the runway, the airspeed would be in excess of ____ mph..."
...it's just a theoretical mini-project. It doesn't really matter if it would work in real life. I'd just like to be able to say "positioned 50 feet behind the runway, the airspeed would be in excess of ____ mph..."
At ground level there will be a considerable boundary layer, which would severely limit efficiency. You would NEED to get it up in the air, at least a couple of feet, which could make it a problem for landing aircraft
Well, a single 747 jet engine produces over 50,000lbs of thrust at full throttle. times that by 4, and your looking at 200mph+ winds a couple of hundred feet behind the plane. Then factor in wake turbulance, exhaust heat and a certain amount of ground effect, then your talking about a lot of energy going on in a very short space of time. I know of an airport somewhere in South America with a road running right along the end of the runway, and several cars have been thrown hundreds of feet when a jet was taking off as they were driving past.
Will have a look for some info..
Will have a look for some info..
Thanks.
Well, we're not talking about necessarily putting it RIGHT behind the aircraft. It could, for example, be placed where the landing lights are just off the end of the runway. The landing lights would be placed on it and it wouldn't be much taller, so I don't think landing aircraft would have to worry much about it. And yea, against the ground wouldn't work because of turbulence, but if you get CLOSE to the ground, you still would get decent airflow without too much ground effect. Still though, regardless of whether or not it would work in reality, I still wanna find some basic wind speed numbers.
Well, we're not talking about necessarily putting it RIGHT behind the aircraft. It could, for example, be placed where the landing lights are just off the end of the runway. The landing lights would be placed on it and it wouldn't be much taller, so I don't think landing aircraft would have to worry much about it. And yea, against the ground wouldn't work because of turbulence, but if you get CLOSE to the ground, you still would get decent airflow without too much ground effect. Still though, regardless of whether or not it would work in reality, I still wanna find some basic wind speed numbers.
Sounds like a nice idea but completely unfeasible. There are a couple of practicalities that should probably be taken into account (regardless of whether you could usefully harness the energy). Firstly jet airliners, where the runway length is comfortably long enough normally either roll from taxi speed or stationary onto full power, they don't hold it on the brakes, so the maximum thrust isn't produced at the start of the runway.
More importantly remember most airliners are too big to turn on the runway and therefore just turn from the first taxiway (which means they're never pointing straight and ready to take off for at least the first 100 feet). You've also got to remember that there's an assumption that the grass immediately before the runway should be relatively flat and free of unnecessary obstacles in case a plane lands short. This would mean you'd be looking at a long distance behind a plane (maybe 200 feet) before you could place even a low level device.
More importantly remember most airliners are too big to turn on the runway and therefore just turn from the first taxiway (which means they're never pointing straight and ready to take off for at least the first 100 feet). You've also got to remember that there's an assumption that the grass immediately before the runway should be relatively flat and free of unnecessary obstacles in case a plane lands short. This would mean you'd be looking at a long distance behind a plane (maybe 200 feet) before you could place even a low level device.
Hmmm, you're right Stang it is difficult to find this kind of info on the net. But i did find this http://gizmodo.com/gadgets/gad ... couple-of-cars-251332.php
Also, the engines used in the new 777 set the WR for power output at 127,000lbs of thrust
nice
As Tristan said it's probably best to checkout Boeing etc, maybe even NASA would be a good place to look, but it might be best to phone their R&D departments and explain why you need the info.
Best of luck with this, sounds like a fun project, shame i never did this kind of thing at school.
{edit} same link as poster above me, too slow again
Also, the engines used in the new 777 set the WR for power output at 127,000lbs of thrust
niceAs Tristan said it's probably best to checkout Boeing etc, maybe even NASA would be a good place to look, but it might be best to phone their R&D departments and explain why you need the info.
Best of luck with this, sounds like a fun project, shame i never did this kind of thing at school.
{edit} same link as poster above me, too slow again
Does it count as a renewable energy source if it depends on a large airliner burning masses of aviation fuel? 
Interesting, though. Definitely a lot of energy, albeit in brief chunks rather than a steady stream. It's hard to imagine that a generator used in this way could produce more power than a normal wind-farm wind-mill does on an average day. Unless it was at a very busy airport and somehow very close to the aircraft, but that gives problems in itself.
Interesting, though. Definitely a lot of energy, albeit in brief chunks rather than a steady stream. It's hard to imagine that a generator used in this way could produce more power than a normal wind-farm wind-mill does on an average day. Unless it was at a very busy airport and somehow very close to the aircraft, but that gives problems in itself.
Well, it counts 'cause you're not using the turbine TO create energy. It would otherwise be wasted but used anyway...
Regardless of wind speed, internal energy, and distance behind the plane, having the generators on the ground (under landing lights or on their own) will massively reduce the effectiveness due to the boundary layer (a layer of air that is 'stuck' to the ground and barely moves at all).
If you want to see how big a problem that is, on a windy day note how much wind is hitting your face (facing into the wind). Now lie down with your chin on the floor - you'll see you can barely feel and wind at all.
The boundary layer will be thicker with more flow (from an exhaust). Hence you will need the generator matrix AT LEAST 2 ft from the ground, probably closer to 6ft. Which is when it starts becoming a hazard.
If you want to see how big a problem that is, on a windy day note how much wind is hitting your face (facing into the wind). Now lie down with your chin on the floor - you'll see you can barely feel and wind at all.
The boundary layer will be thicker with more flow (from an exhaust). Hence you will need the generator matrix AT LEAST 2 ft from the ground, probably closer to 6ft. Which is when it starts becoming a hazard.
Well in theory it could either fold down or sink into the ground when a plane is landing. If it's just hood scoop style it could flatten into the runway, then come back up when there's a plane holding for take-off permission.
The real problem would be the length of time the engines are actually producing that much wind. Most of the time they're sitting there spinning up, they only really kick the power on when the plane starts moving, so you'd get a massive amount of wind but only for a couple of seconds.
You'd probably only end up with enough stored energy to power the rise and fall of the scoops
The real problem would be the length of time the engines are actually producing that much wind. Most of the time they're sitting there spinning up, they only really kick the power on when the plane starts moving, so you'd get a massive amount of wind but only for a couple of seconds.
You'd probably only end up with enough stored energy to power the rise and fall of the scoops
Or if you're lucky, enough to boil a cup of water for the man who comes to repair it every couple of days. Would be nice for him to get a cup of tea. And if it's borked he get's no tea, which is his incentive to fix it.
Well i'm not even going to try to argue with a guy with a masters degree in engineering or whatever it is you've got, but, that Hammond vid clip does suggest there's quite a bit of energy going on out the back end of a 747. Granted, harnessing that energy is another matter, but you cant knock the kid for trying.
Masters my arse - I'm far too stupid to get a Masters. I didn't even manage a first at Bachelor! Besides, this thread is more about common sense than practical/theoretical engineering knowledge (apart from perhaps the bit about boundary layers, but that's not rocket science).
Yes, there is a lot of energy, but it 1) is for short durations 2) only happens now and again depending on traffic 3) really difficult to harness effectively. If you do get some fans in the air stream, stopping them from melting might be difficult, but I don't know what sort of temperatures you'd actually get.
Phone:
Boeing
Airbus
BAe
NASA
Rolls Royce
Pratt&Whitney
General Electric
Yes, there is a lot of energy, but it 1) is for short durations 2) only happens now and again depending on traffic 3) really difficult to harness effectively. If you do get some fans in the air stream, stopping them from melting might be difficult, but I don't know what sort of temperatures you'd actually get.
Phone:
Boeing
Airbus
BAe
NASA
Rolls Royce
Pratt&Whitney
General Electric
I was under the impression renewable energy got the tag not because you are re-using some energy from a wasteful process but because you aren't relying upon a 'dirty' process involving fossil fuels or nuclear power.
What I'm saying is that harnessing some small percentage of a jet's wasted energy is no more a renewable source of energy than the 3rd cylinder in a triple-expansion steam engine.
The concept outlined, to me at least, is more akin to some sort of recycling of energy than renewable energy - so I'd be running this by the lecturer to ensure you aren't on to a bad project from the outset. If they are OK with the concept being a renewable energy source then go and do the maths.
What I'm saying is that harnessing some small percentage of a jet's wasted energy is no more a renewable source of energy than the 3rd cylinder in a triple-expansion steam engine.
The concept outlined, to me at least, is more akin to some sort of recycling of energy than renewable energy - so I'd be running this by the lecturer to ensure you aren't on to a bad project from the outset. If they are OK with the concept being a renewable energy source then go and do the maths.
I'd rather not thanks all the same
1) Even a 5 second blast of a 200mph gust of wind should be able to keep a turbine spinning for quite some time.
2) Not got the official figures, but at somewhere like Heathrow with it's 5, soon to be 6 runways, We could be taking 40-60 flights an hour. Even light aircraft produce a sizable amount of turbulance/wash and propulsion.
3) Maybe using some sort of venturi system on the edge of the runway ? Not a clue about the heat aspect, but i doubt it'd be enough to melt or even distort steel blades for e.g, just think of the forces and heat going on in the engine itself, if it's possible to produce those to build the engine in the first place surely it's possible to build a similar device strong enough to withstand the energy they produce.
For all three points, bear in mind the turbines/fans won't be freely spinning - they will be having to turn a generator at useful speeds. The amount of drag caused when turning a generator is quite large - even a car alternator takes about 4hp (average engine speeds), which is 3KW - a fairly significant amount of 'drag'.
Yeah, thats a point 
In laymens (i.e thicko's) terms its the magnetic drag from within the generator itself and not the friction from the bearings ? Interesting stuff....
Even if it is an impractical solution i still think it's great that this kind of thing is being taught/investigated in schools and collage's these days. In my day all we got was a strip of litmus paper and an egg cup half full of vinegar
, is it any wonder i chose to do geography.
However, if someone can come up with a surefire way of harnessing our waisted energy, then you're talking riches beyond your wildest dreams, oh, and perhaps saving the planet, but who really cares about that kinda stuff anyway ?.
Stangbuckwheat (or whatever your name is, i found this site about wind energy which might come in handy, have a look, see if it helps. http://www.windpower.org/en/tour/wres/index.htm
Also found this http://www.sfgate.com/cgi-bin/ ... 007/05/07/MNGNEPMD801.DTL it's not related to your experiment Stang, but it's quite interesting nontheless
In laymens (i.e thicko's) terms its the magnetic drag from within the generator itself and not the friction from the bearings ? Interesting stuff....Even if it is an impractical solution i still think it's great that this kind of thing is being taught/investigated in schools and collage's these days. In my day all we got was a strip of litmus paper and an egg cup half full of vinegar
, is it any wonder i chose to do geography.However, if someone can come up with a surefire way of harnessing our waisted energy, then you're talking riches beyond your wildest dreams, oh, and perhaps saving the planet, but who really cares about that kinda stuff anyway ?.
Stangbuckwheat (or whatever your name is, i found this site about wind energy which might come in handy, have a look, see if it helps. http://www.windpower.org/en/tour/wres/index.htm
Also found this http://www.sfgate.com/cgi-bin/ ... 007/05/07/MNGNEPMD801.DTL it's not related to your experiment Stang, but it's quite interesting nontheless
The Hammond video had a 747 with brakes on and the engines going at full - this uses a lot of fuel doing very little, and as such is only done at a short runway to get better acceleration.
no its simple conservation of energy
if you want to produce power its got to come from somewhere ... ie from slowing the engine down
half actually ... only the centre engines were running
Jet Blast
(22 posts, started )
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