What happens when hydrogen meets oxygen?

[Lapin Dormant]

**Ahem** This is what I had meant, How Stuff Works and it does work.

 

[Danger]

I've been seeing those things for decades, but never a practical one. I still like the Captain better.

 

[Ki Man]

they don't have a practical one because you can only fly for about 30-60 seconds usually. 5 minutes would be a major breakthrough.

 

[FredGarvin]

My company developed and flew a turbine engine version of that back in the early '60's. It worked pretty well. I have seen a fair amount of video of it flying.

http://www.uncleodiescollectibles.com/img_lib/Jetpack 1 10 6-15-4.jpg

 

[Ki Man]

what was its maximum airtime and speed

 

[FredGarvin]

If I remember correctly it was about 70 mph for about 30 minutes. I do remember someone saying that it did have some controll issues over water though. I'd have to ask some of the "seasoned" folks around here for more particulars.

 

[Danger]

Thanks for the pic, Fred. I vaguely remember reading something about it a few decades back, but never saw it before. That sucker must weigh a couple of hundred pounds, though. I'm guessing that both it and the rocket type would probably be frowned upon for commuter transport based solely upon the noise involved. Such things might have to stick with helicopter rotors until someone comes up with a way to put a muffler on a jet.

 

[Ki Man]

see with jet powered cars and stuff for everyday use, there comes a bunch of problems

problem: birds and small animals like nearby cats getting sucked into engine (this problem is solved a lot in the commercial airliners and stuff with small birds, but we've never had to deal with scruffy climbing up on your back while you put on your jetpack)
problem: humans getting sucked into engine (whoa! i knew i shouldn't have worn this baggy jacket. oh well. i'll just sit and wait for the paramedics)
problem: noise level of having a jet engine in a neighborhood (keep it down over there! don't make us shoot you out of the sky)

wouldn't a modified and enlarged version of a rifle's silencer help decrease the noise level made by a jet just a little at least

 

[Danger]

wouldn't a modified and enlarged version of a rifle's silencer help decrease the noise level made by a jet just a little at least

Yeah, but it wouldn't provide any propulsion then. Also, there's no such thing as a silencer, just suppressors. Keep in mind that an effective one for a .45 auto pistol is from 2 - 4 inches in diameter and 10 -14 inches long. One for a high-power rifle is much larger. The whole point of the thing is to capture all of the expanded propellant gas and then release it slowly. You need enough internal volume, plus baffles, reversal plates, etc. to accomplish that. Think of how much gas is coming out of a turbojet.

 

[Danger]

My 'edit' button still isn't working. I meant to add that a jet engine will not continue to run when its exhaust is blocked, any more than a piston type will.

 

[sid_galt]

see with jet powered cars and stuff for everyday use, there comes a bunch of problems

problem: birds and small animals like nearby cats getting sucked into engine (this problem is solved a lot in the commercial airliners and stuff with small birds, but we've never had to deal with scruffy climbing up on your back while you put on your jetpack)
problem: humans getting sucked into engine (whoa! i knew i shouldn't have worn this baggy jacket. oh well. i'll just sit and wait for the paramedics)
problem: noise level of having a jet engine in a neighborhood (keep it down over there! don't make us shoot you out of the sky)

wouldn't a modified and enlarged version of a rifle's silencer help decrease the noise level made by a jet just a little at least

Even if you solve all the above problems, you are never going to see widespread use of jet engines in cars. They are too expensive and require much more maintainence than ordinary engines.

Some sort of a gas turbine engine might already exist in cars though. You have a turbocharger which increases air pressure and you have a turbine which runs on exhaust gas. But these are centrifugal compressors and turbines. For a good efficiency jet engine you will need axial compressors and turbines which are more expensive than their centrifugal counterparts.

Jet powered cars have been made e.g. Spirit of America but they are for specialized purposes only.

 

[FredGarvin]

Even if you solve all the above problems, you are never going to see widespread use of jet engines in cars. They are too expensive and require much more maintainence than ordinary engines.

That's true and not so true. Many turbines today are operating with thousands of hours between overhauls. The issues would then become would the average person really be willing to be more vigilant with their day to day responsibilities in general maintenance and when the repairs/overhauls do happen, they would be more extensive than, say, a v-6 would. That being said, the major gripe most people have today is that many feel engines are too complicated now and that they can't be worked on by the lay person. So I think there's a bit of a tradeoff there. However, the cost factor is what is going to be the killer. Until production numbers get very large, indeed the cost will be pretty high.

Again, not to toot our horn, but my company, among others, developed and tested a vehicle with a turbine driven alternator. This was the initial vault into the hybrid technology. The turbine drove a alternator that kept the batteries charged. It worked well because the turbine could operate at constant speed at or near it BEP. The batteries did the actual vehicle moving.
The noise was not terribly bad, but it was noticeable. Personally, I think this configuration would hold the most hope for vehicles with turbines in them. I also think that they would be today's best bet at an almost zero emissions vehicle.

 

[FredGarvin]

wouldn't a modified and enlarged version of a rifle's silencer help decrease the noise level made by a jet just a little at least

Not really. Turbines are usually pretty sensitive to back pressure. We do tests where we intentionally do that and the increase in back pressure has the most notable side effect of an increase in turbine temps which now throws your cycle off and puts more stress on the turbines. The most notable method of silencing today is the mixing assemblies at the rear of the engine. The idea is that mixing the colder bypass flow with the exhausted core flow does help to decrease the noise.

 

[Lapin Dormant]

If you would want to silence it, use a Counteracting sound wave as to annul the emiting wave.

Means use a microphone and computer to pick up on the sound emitted, generate a Counterwave to it, broadcast it back at the originating sound wave, the Two cancel each other, and the noise, disappears.

Practical solution.

 

[FredGarvin]

If you would want to silence it, use a Counteracting sound wave as to annul the emiting wave.

Means use a microphone and computer to pick up on the sound emitted, generate a Counterwave to it, broadcast it back at the originating sound wave, the Two cancel each other, and the noise, disappears.

Practical solution.

Not so practical. The noise being emitted is a broadband frequncy, it's not a nice, simple single frequency. That means whatever is doing it has to have the computing power, plus the output power to be able to mimic what is coming out in real time.

 

[Lapin Dormant]

Not so practical. The noise being emitted is a broadband frequncy, it's not a nice, simple single frequency. That means whatever is doing it has to have the computing power, plus the output power to be able to mimic what is coming out in real time.

Yes, and the time differntials must be met between pickup, re-creation as inversion, re-emission towards the target.

I have seen it presented on television and it is Capable of Silencing a Helicopters' rotor noise, so I would suspect that even if it sounds (pardon the Pun) complicated, it still can be done, and much more efficiently then some of the other suggestions, less power draining too, much less.

If I recall it properly the lead proponent(?) researcher(?) was from Mc Gill University, in Montreal, Canada.

 

[Danger]

Helicopter rotors, while loud and somewhat variable, still produce a pretty small-spectrum sound compared to turbines. In my experience, at least, turbines are also one hell of a lot louder to start with. In case you're basing your thoughts upon the difference in sound of a jet plane or a helicopter flying overhead rather than being close-up to one, remember that 1) the plane is probably flying a lot higher than the chopper, and 2) the sound of rotors is primarily 'focused' downward whereas the jet exits the back and has far more dispersal before reaching you.

 

[Lapin Dormant]

O.K. but I had seen that it's applicability has range to it, perhaps further study would help, better yet referencing some of the studies, just that I have no time for it, now, so perhaps later, perhaps not.

I seem to recall that It had been stated that it would-could stop the noise from one of those Compressors used to compress air for the air hammers used in construction, also able to supress the Air hammers' noise as well, is that broad enough?

 

[Danger]

is that broad enough?

I've never seen a frequency analysis of a jack hammer/compressor set, but I doubt it very much. Also, they don't have nearly the volume of a decent sized jet. (Note that in the case of a turbine-driven ground vehicle, it's mechanical power from a PTO that drives the wheels. Lots of ducting and expansion chambers and whatnot can be incorporated in the exhaust path because the thing doesn't rely on thrust. That's why the experimental gas turbine buses in Germany and similar are alright for street use.)

 

[Lapin Dormant]

Seen turbines somewhat silenced simply by covering them, so what else is new.

As for the outflow of a jet, it is the noise component that is suppressed, not the outflow component, but you could be qutie right as I have no test facility to experiment upon any of it.

 

[sid_galt]

If you would want to silence it, use a Counteracting sound wave as to annul the emiting wave.

Means use a microphone and computer to pick up on the sound emitted, generate a Counterwave to it, broadcast it back at the originating sound wave, the Two cancel each other, and the noise, disappears.

Practical solution.

Aside from the practicality factor, I don't think this will work at all. The two sound waves will cancel each other only in the region where they interact.

Say if the turbine is at point A and the counteracting sound source at point B, then you would again have noise behind point B. Not to mention that you'll have additional noise beyond point A.

 

[Lapin Dormant]

Aside from the practicality factor, I don't think this will work at all. The two sound waves will cancel each other only in the region where they interact.
Say if the turbine is at point A and the counteracting sound source at point B, then you would again have noise behind point B. Not to mention that you'll have additional noise beyond point A.

No, if you cancel the wave out, it is Gone, no more noise.

I have seen it as applied to cars to replace muffler systems, works VERY well except that, because it is an electrically powered system, it is against 'social norms' due to the nature of Humans inasmuch as they will use disconnect switches and shut the muffler off, and on, and off, and on, all the while enjoying {ignoring} the excessive noise they are making, and it's social impact.

One of the reasons why it never gained ground in that venue, but I can assure you it does work, and really well.

 

[Danger]

As for the outflow of a jet, it is the noise component that is suppressed, not the outflow component,

Sorry, man, but the noise is an integral part of the 'outflow'. This is nothing like the exhaust from a piston engine. It's a very high volume of hot, fast-moving gas coming through a tuned nozzle. There are all sorts of harmonics and mechanical vibrations to deal with. A moderately sized engine (J-34, as used in drag racers) literally shakes the ground for hundreds of feet around it. The thing in Fred's picture is much smaller, but I bet it's probably at least half as noisy.

 

[Ki Man]

seriously, i don't see what's wrong with using cars for now. maybe in the future we will take to the air but until we can put a muffler on a jet or quiet and redisgn helicopters for everyday use, were stuck to the ground. plus, if drunk drivers on the ground are bad, what happens when they have more than 2 dimensions to worry about while driving? do you want drunks crashing into your house in the middle of the night going at 250mph. even if we have virtual sky roads built where drivers don't do much driving we will still face problems like this.

airial vehicles require routine maitenance too. that's going to cost you a lot more than standard gasoline and the occasional oil change.

 

[sid_galt]

No, if you cancel the wave out, it is Gone, no more noise.

The noise will only cancel out at the point where the two waves interfere. Beyond that you'll still hear the noise.

 

[Lapin Dormant]

Silenced myself

Sorry, man, but the noise is an integral part of the 'outflow'. This is nothing like the exhaust from a piston engine. It's a very high volume of hot, fast-moving gas coming through a tuned nozzle. There are all sorts of harmonics and mechanical vibrations to deal with. A moderately sized engine (J-34, as used in drag racers) literally shakes the ground for hundreds of feet around it. The thing in Fred's picture is much smaller, but I bet it's probably at least half as noisy.

Yes I understood that point.

The noise will only cancel out at the point where the two waves interfere. Beyond that you'll still hear the noise.

Interference isn't the goal, cancellation is, then there is no more noise, but, as it is stated above, it would be diffcult, at best, I already knew that, so now, this thread seems to be getting 'hi-jacked' to this topic, so, as to discourage that, I will cease, now.
Thanks

 

[Ki Man]

hopefully testing it this weekend. it depends on how lazy my group members become

 

[Danger]

Good luck, Ki. Keep us updated.

 

[Ki Man]

hmm... before i test this i am going to ask the people something in the general physics section

if i ever become famous, my phrase that people are going to remember after i die is: it all started with a daydream

 

[sid_galt]

Yes I understood that point.
Interference isn't the goal, cancellation is, then there is no more noise, but, as it is stated above, it would be diffcult, at best, I already knew that, so now, this thread seems to be getting 'hi-jacked' to this topic, so, as to discourage that, I will cease, now.
Thanks

According to your theory if two speakers attached to a hi-fi are placed in front of each other, the sound should diminish near completely. But that is not what happens. The sound energy can't disappear into the thin air.

 

[Lapin Dormant]

.. .. ..I will cease now .. .. ..

If you would like to start a new thread, the waves need be equal and Opposite each other, in waveform.

 

[sid_galt]

If you would like to start a new thread, the waves need be equal and Opposite each other, in waveform.

https://www.physicsforums.com/showthread.php?p=787812#post787812"

 

[Ki Man]

okay, definitely testing it this weekend

 

[Danger]

Ki, it appears that the stoned bunny has been banned, so perhaps this thread can stay more or less on topic now. Again, I offer my best wishes for the success of your project.

 

[Ki Man]

me and my group members are hopefully meeting on saterday and going to home depot to buy the proper supplies hopefully unless one of them can't make it. again

ty for the suppor teven if it doesn't work. we are basically researching equalibrums in a sense, but different. if i told you my full idea, youd think i was crazy probably, but it just might work so i'll just keep it secret