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  #11  
Old December 6th 03, 02:34 AM
Chuck
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Default Pulse Jets

A week or so ago I saw a rather neat Junkyard Wars episode on
pulse-jets. I'm also rather intrigued that it was felt to be a safe
enough gadget to build for the TV show.

It was an amazingly simple contraption, a jet with no moving parts. I
was wondering where I could find out more about the history of these
devices, and perhaps some information as to why they are apparently
outdated and no longer in use. I believe they were used in the V2
rockets in WWII (?).


One of the big reasons they are out-dated, is the noise. They are
incredibly loud, even compaired to other types of jet engines. Not to
mention that the sound is a much lower bass sound, so it travels
further than the higher pitched sound of a turbo jet.

for some info on them try these pages.

http://www.aardvark.co.nz/pjet/

http://home.earthlink.net/~famcaine/...s/PulseJet.htm

The first one is a page by the expert from the Junkyard Wars show you
mention.

-Chuck. (www.wormspeaker.com)
__________________________________________________ ___
Spread love and understanding...
but don't be afraid to bloody your knuckles doing it.
-Alex Ross
  #12  
Old December 6th 03, 02:49 AM
Bruce Simpson
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Default Pulse Jets

On 06 Dec 2003 02:36:54 GMT, (MattWriter) wrote:

A week or so ago I saw a rather neat Junkyard Wars episode on
pulse-jets. BRBR


I'm curious why the pulse-jet keeps cropping up in discussions of possible or
alleged advanced high-speed aircraft. Isn't the thing inefficient as heck?


Yes, conventional pulsejets are as inefficient as heck -- maybe even
less efficient than heck :-)

What pulsejets do have going for them however are the attributes of
cost and simplicity. You can build a pulsejet that produces around
200lbs of thrust for under $200 -- there's no other engine on the
planet that will produce more thrust per dollar (that I can think of).

What's more, you can make that engine out of plain old sheets of
stainless steel -- with out the need for CNC machining, expensive
bearing assemblies/balancing, etc.

Obviously therefore, on short-range "disposable" craft, the pulsejet
is a very cost-effective option.

The other reason pulsejets are experiencing something of renaissance
is the huge mount of money and effort being invested into PDEs (Pulse
Detonation Engines).

PDEs offer the promise of very efficient propulsion for supersonic
craft but are currently still, based on all the examples I've seen and
the research I've read -- quite a few years away from being actually
viable for such applications.

There's more info on PDEs and pulsejets on the website I mentioned in
my last posting.

--
you can contact me via
http://aardvark.co.nz/contact/
  #13  
Old December 6th 03, 02:49 AM
Bruce Simpson
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Posts: n/a
Default Pulse Jets

On 06 Dec 2003 02:36:54 GMT, (MattWriter) wrote:

A week or so ago I saw a rather neat Junkyard Wars episode on
pulse-jets. BRBR


I'm curious why the pulse-jet keeps cropping up in discussions of possible or
alleged advanced high-speed aircraft. Isn't the thing inefficient as heck?


Yes, conventional pulsejets are as inefficient as heck -- maybe even
less efficient than heck :-)

What pulsejets do have going for them however are the attributes of
cost and simplicity. You can build a pulsejet that produces around
200lbs of thrust for under $200 -- there's no other engine on the
planet that will produce more thrust per dollar (that I can think of).

What's more, you can make that engine out of plain old sheets of
stainless steel -- with out the need for CNC machining, expensive
bearing assemblies/balancing, etc.

Obviously therefore, on short-range "disposable" craft, the pulsejet
is a very cost-effective option.

The other reason pulsejets are experiencing something of renaissance
is the huge mount of money and effort being invested into PDEs (Pulse
Detonation Engines).

PDEs offer the promise of very efficient propulsion for supersonic
craft but are currently still, based on all the examples I've seen and
the research I've read -- quite a few years away from being actually
viable for such applications.

There's more info on PDEs and pulsejets on the website I mentioned in
my last posting.

--
you can contact me via
http://aardvark.co.nz/contact/
  #14  
Old December 6th 03, 03:36 AM
MattWriter
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Posts: n/a
Default Pulse Jets

A week or so ago I saw a rather neat Junkyard Wars episode on
pulse-jets. BRBR


I'm curious why the pulse-jet keeps cropping up in discussions of possible or
alleged advanced high-speed aircraft. Isn't the thing inefficient as heck?


Matt Bille
)
OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR
  #15  
Old December 6th 03, 03:36 AM
MattWriter
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Posts: n/a
Default Pulse Jets

A week or so ago I saw a rather neat Junkyard Wars episode on
pulse-jets. BRBR


I'm curious why the pulse-jet keeps cropping up in discussions of possible or
alleged advanced high-speed aircraft. Isn't the thing inefficient as heck?


Matt Bille
)
OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR
  #16  
Old December 6th 03, 04:38 AM
Henry Spencer
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Default Pulse Jets

In article ,
pervect wrote:
It was an amazingly simple contraption, a jet with no moving parts. I
was wondering where I could find out more about the history of these
devices, and perhaps some information as to why they are apparently
outdated and no longer in use. I believe they were used in the V2
rockets in WWII (?).


The V-1 flying bomb (essentially a primitive cruise missile), actually.

They're no longer used for a couple of reasons. They are not actually
very good jet engines, compared to more sophisticated designs (which can
be made in quite small sizes at relatively low cost, if you try hard).
And the noise and vibration are tremendous -- the Germans looked into
pulsejet fighters but the idea never went anywhere, partly because it
was very difficult to provide a livable environment for the pilot.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |
  #17  
Old December 6th 03, 04:38 AM
Henry Spencer
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Posts: n/a
Default Pulse Jets

In article ,
pervect wrote:
It was an amazingly simple contraption, a jet with no moving parts. I
was wondering where I could find out more about the history of these
devices, and perhaps some information as to why they are apparently
outdated and no longer in use. I believe they were used in the V2
rockets in WWII (?).


The V-1 flying bomb (essentially a primitive cruise missile), actually.

They're no longer used for a couple of reasons. They are not actually
very good jet engines, compared to more sophisticated designs (which can
be made in quite small sizes at relatively low cost, if you try hard).
And the noise and vibration are tremendous -- the Germans looked into
pulsejet fighters but the idea never went anywhere, partly because it
was very difficult to provide a livable environment for the pilot.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |
  #18  
Old December 6th 03, 05:23 AM
Bruce Simpson
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Posts: n/a
Default Pulse Jets

On Sat, 6 Dec 2003 03:38:17 GMT, (Henry Spencer)
wrote:

They're no longer used for a couple of reasons. They are not actually
very good jet engines, compared to more sophisticated designs (which can
be made in quite small sizes at relatively low cost, if you try hard).
And the noise and vibration are tremendous -- the Germans looked into
pulsejet fighters but the idea never went anywhere, partly because it
was very difficult to provide a livable environment for the pilot.


Indeed. My most recent engine (200lbs-thrust) has been measured at
145dB and no amount of hearing protection can stop the pressure waves
from rattling your skull -- thereby rattling the bones of the inner
ear.

However, if you think pulsejets are bad news -- wait until you've
experienced being within close proximity of a PDE.

I did build a simple yet intermittently capable pulsed detonation
chamber using acetylene and oxygen as fuel. It was very small, just
50mm diameter and 2.5 metres long. However, the shock waves that it
generated felt like someone beating on your skull with a ball peen
hammer.

By comparison,a pulsejet, even a very large one, is more like someone
beating you rapidly about the head and body with a pillow.

There is no way that a PDE will ever be used on a manned craft that
doesn't have excellent acoustic insulation. between the occupants and
the engine when travelling at sub-sonic velocities. It's also an
engine that will most definitely not be used anywhere near a populated
area. If the bitched about the Concorde and its single shockwave,
imagine what they'd say about a reasonably sized PDE spitting out
anywhere from 60-300 shockwaves a second!

--
you can contact me via
http://aardvark.co.nz/contact/
  #19  
Old December 6th 03, 05:23 AM
Bruce Simpson
external usenet poster
 
Posts: n/a
Default Pulse Jets

On Sat, 6 Dec 2003 03:38:17 GMT, (Henry Spencer)
wrote:

They're no longer used for a couple of reasons. They are not actually
very good jet engines, compared to more sophisticated designs (which can
be made in quite small sizes at relatively low cost, if you try hard).
And the noise and vibration are tremendous -- the Germans looked into
pulsejet fighters but the idea never went anywhere, partly because it
was very difficult to provide a livable environment for the pilot.


Indeed. My most recent engine (200lbs-thrust) has been measured at
145dB and no amount of hearing protection can stop the pressure waves
from rattling your skull -- thereby rattling the bones of the inner
ear.

However, if you think pulsejets are bad news -- wait until you've
experienced being within close proximity of a PDE.

I did build a simple yet intermittently capable pulsed detonation
chamber using acetylene and oxygen as fuel. It was very small, just
50mm diameter and 2.5 metres long. However, the shock waves that it
generated felt like someone beating on your skull with a ball peen
hammer.

By comparison,a pulsejet, even a very large one, is more like someone
beating you rapidly about the head and body with a pillow.

There is no way that a PDE will ever be used on a manned craft that
doesn't have excellent acoustic insulation. between the occupants and
the engine when travelling at sub-sonic velocities. It's also an
engine that will most definitely not be used anywhere near a populated
area. If the bitched about the Concorde and its single shockwave,
imagine what they'd say about a reasonably sized PDE spitting out
anywhere from 60-300 shockwaves a second!

--
you can contact me via
http://aardvark.co.nz/contact/
  #20  
Old December 6th 03, 05:57 AM
Henry Spencer
external usenet poster
 
Posts: n/a
Default Pulse Jets

In article ,
MattWriter wrote:
I'm curious why the pulse-jet keeps cropping up in discussions of possible or
alleged advanced high-speed aircraft. Isn't the thing inefficient as heck?


Pulsejets and Pulse Detonation Engines are completely different devices,
despite the similarity in name and the vague similarity in operating
principle.

(One important difference is that pulsejets went from concept to flying
hardware very quickly, while PDEs have been The Engine Of The Future for
nearly half a century now.)
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |
 




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