This Takes Danger To A New Level
10-27-2013, 06:40 AM
#76
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I have seen a couple of people posting here were concerned with the quality of the HK pulse jet engine.
I would think that the head would be OK and easy to copy. Just make sure that the area the petal valve sits on is flat. It also helps to cup your petal valve before installing.
Petal valve quality would also be a concern.
My main concern would be with the tail pipe welds. Even in the higher priced Dyna Jet, OS pulse jets, and Bailey Jet engines have weld failures, which was the most common point of failure with this type of engine. The weld on the tailpipe can fail and open up, making the tailpipe pretty much useless. This can be somewhat avoided by not running the engine static for more than about 10 -15 seconds at a time. This is the reason you see everyone in the starting crew moving fast after the engine gets started. It is not the noise, they just want to get it into the air where the engine will be cooled better than static running.
I plan on purchasing one of the HK pulse jet engines just to see how well it works compared to my Dyna Jet. The last time I checked a tailpipe of a better brand costs about as much as the whole engine from HK.
Greg
I would think that the head would be OK and easy to copy. Just make sure that the area the petal valve sits on is flat. It also helps to cup your petal valve before installing.
Petal valve quality would also be a concern.
My main concern would be with the tail pipe welds. Even in the higher priced Dyna Jet, OS pulse jets, and Bailey Jet engines have weld failures, which was the most common point of failure with this type of engine. The weld on the tailpipe can fail and open up, making the tailpipe pretty much useless. This can be somewhat avoided by not running the engine static for more than about 10 -15 seconds at a time. This is the reason you see everyone in the starting crew moving fast after the engine gets started. It is not the noise, they just want to get it into the air where the engine will be cooled better than static running.
I plan on purchasing one of the HK pulse jet engines just to see how well it works compared to my Dyna Jet. The last time I checked a tailpipe of a better brand costs about as much as the whole engine from HK.
Greg
Last edited by OldRookie; 10-27-2013 at 06:49 AM.
10-27-2013, 12:09 PM
#77
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Greg,
As I recall, only the US-made Dynajet had a seamless weld on the tailpipe. The OS type had a seam but this didn't affect performance very much. I ran and flew my OS many times without a seam failure. I did go through a couple petal valves though. I only lapped their seating surface a bit and never "cupped" them as you suggest. Can you provide a photo or description of this cupping?
Rgds,
Art ARRO
As I recall, only the US-made Dynajet had a seamless weld on the tailpipe. The OS type had a seam but this didn't affect performance very much. I ran and flew my OS many times without a seam failure. I did go through a couple petal valves though. I only lapped their seating surface a bit and never "cupped" them as you suggest. Can you provide a photo or description of this cupping?
Rgds,
Art ARRO
10-27-2013, 12:20 PM
#78
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everyone gets hurt a little when dyna jets first came out in the usa i got one> i got the u control plane called the . super squirt< the only hurt i got was from the ford coil > once
10-27-2013, 01:36 PM
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I fly at a public field, and we have no noise restrictions that I am aware of. I think it's possible for most any airplane to start a fire after a crash, although some may not, like the rubber -powered variety.
And yes, we have had a few of the "Hold my beer" crowd, but we generally police ourselves, telling them "That might not be real safe to do", at times. I saw pictures posted on the internet of a foamy that had the esc burn up, and eventually consume the entire airplane. And I think I've seen turbine aircraft burn as well. Nothing is completely safe, not even staying home.
I've seen videos of Bikes with huge pulsejets on them, and some rc airplanes. Loud, Hot, and COULD be dangerous. Not my cup of tea. But who am I to tell someone else not to do it. If they have their mind set on it, I just ask them to wait till I move a safe distance away...
And yes, we have had a few of the "Hold my beer" crowd, but we generally police ourselves, telling them "That might not be real safe to do", at times. I saw pictures posted on the internet of a foamy that had the esc burn up, and eventually consume the entire airplane. And I think I've seen turbine aircraft burn as well. Nothing is completely safe, not even staying home.I've seen videos of Bikes with huge pulsejets on them, and some rc airplanes. Loud, Hot, and COULD be dangerous. Not my cup of tea. But who am I to tell someone else not to do it. If they have their mind set on it, I just ask them to wait till I move a safe distance away...
10-27-2013, 01:45 PM
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Art,
The two Dyna Jet engines I own have a seam, and this seam will separate.
I haven't seen a seamless pipe. I would think that they would be more prone to splitting.
I'll check through my pulse jet stuff (about a 3" pile of paper). There is probably a lot of stuff there that would interest people operating pulse jets. I'll post it when I find it. I could give you a brief description, but a picture is worth a thousand words.
Greg
The two Dyna Jet engines I own have a seam, and this seam will separate.
I haven't seen a seamless pipe. I would think that they would be more prone to splitting.
I'll check through my pulse jet stuff (about a 3" pile of paper). There is probably a lot of stuff there that would interest people operating pulse jets. I'll post it when I find it. I could give you a brief description, but a picture is worth a thousand words.
Greg
10-27-2013, 04:02 PM
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Greg,
The "seamless" tailpipes on the Dyna Jet were overlapped as opposed to folding and joining as on the OS Tiger pulsejets. I recall that OS made 2 versions, one a close clone of the Dyna Jet and the other smaller with less thrust= about 2.5 lbs static. I owned, operated and flew the larger version. FYI, do a seach on www.beck-technogies.com for a video on the Dyna Jet including startup and running.
Rgds,
Art ARRO
The "seamless" tailpipes on the Dyna Jet were overlapped as opposed to folding and joining as on the OS Tiger pulsejets. I recall that OS made 2 versions, one a close clone of the Dyna Jet and the other smaller with less thrust= about 2.5 lbs static. I owned, operated and flew the larger version. FYI, do a seach on www.beck-technogies.com for a video on the Dyna Jet including startup and running.
Rgds,
Art ARRO
10-27-2013, 04:31 PM
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Agreed: they are neither rockets nor ramjets. The pulsejet is the simplest possible normally aspirated jet engine, and it's what powered the V-1 "buzz bomb" of World War II. The one sold for model use was called the Dyna-Jet, and there was a C/L speed event for them in AMA contests of the 40s/50s.
They can, of course, be stopped with any means of cutting off the fuel. But they're still pretty hazardous: at zero airspeed the tailpipe will glow red hot, and the forces on the engine mount can be more than a less-than-expert modeler is ready to deal with.
There's a fascinating video somewhere on the Net of a test in the V-1 program, with an engine that had a row of viewports in the tailpipe. You can see the flame repeatedly zipping down the length of the pipe.
The engine has a flapper valve in front which actually serves as a passive "compressor". A charge of fuel gets ignited in the combustion chamber, and the hot gas expands down the long pipe, gaining speed as it goes. When the combustion finishes, there's still a charge of gas moving down the tube at high speed, and its momentum pulls the chamber pressure down below atmospheric. A charge of air comes in, mixes with fuel, burns, and the cycle repeats. The chamber pressure goes up and down in huge cycles, with the average pressure above atmospheric -- which is the condition necessary to get thrust -- but at its minimum points, it's below ambient.
Of course, those repeating bursts of gas are just like a humungous loudspeaker. My high school physics teacher used to start one up once a year -- and EVERYBODY in my 3,000-student school knew when it was...;-)
BTW,it wasn't only Germany that built the buzz bomb. The US Gov paid Ford Motors to reverse engineer a captured one and make two thousand of them; they would have been used if the planned invasion of Japan had come off.
They can, of course, be stopped with any means of cutting off the fuel. But they're still pretty hazardous: at zero airspeed the tailpipe will glow red hot, and the forces on the engine mount can be more than a less-than-expert modeler is ready to deal with.
There's a fascinating video somewhere on the Net of a test in the V-1 program, with an engine that had a row of viewports in the tailpipe. You can see the flame repeatedly zipping down the length of the pipe.
The engine has a flapper valve in front which actually serves as a passive "compressor". A charge of fuel gets ignited in the combustion chamber, and the hot gas expands down the long pipe, gaining speed as it goes. When the combustion finishes, there's still a charge of gas moving down the tube at high speed, and its momentum pulls the chamber pressure down below atmospheric. A charge of air comes in, mixes with fuel, burns, and the cycle repeats. The chamber pressure goes up and down in huge cycles, with the average pressure above atmospheric -- which is the condition necessary to get thrust -- but at its minimum points, it's below ambient.
Of course, those repeating bursts of gas are just like a humungous loudspeaker. My high school physics teacher used to start one up once a year -- and EVERYBODY in my 3,000-student school knew when it was...;-)
BTW,it wasn't only Germany that built the buzz bomb. The US Gov paid Ford Motors to reverse engineer a captured one and make two thousand of them; they would have been used if the planned invasion of Japan had come off.
10-27-2013, 06:48 PM
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Agreed: they are neither rockets nor ramjets. The pulsejet is the simplest possible normally aspirated jet engine, and it's what powered the V-1 "buzz bomb" of World War II. The one sold for model use was called the Dyna-Jet, and there was a C/L speed event for them in AMA contests of the 40s/50s.
They can, of course, be stopped with any means of cutting off the fuel. But they're still pretty hazardous: at zero airspeed the tailpipe will glow red hot, and the forces on the engine mount can be more than a less-than-expert modeler is ready to deal with.
There's a fascinating video somewhere on the Net of a test in the V-1 program, with an engine that had a row of viewports in the tailpipe. You can see the flame repeatedly zipping down the length of the pipe.
The engine has a flapper valve in front which actually serves as a passive "compressor". A charge of fuel gets ignited in the combustion chamber, and the hot gas expands down the long pipe, gaining speed as it goes. When the combustion finishes, there's still a charge of gas moving down the tube at high speed, and its momentum pulls the chamber pressure down below atmospheric. A charge of air comes in, mixes with fuel, burns, and the cycle repeats. The chamber pressure goes up and down in huge cycles, with the average pressure above atmospheric -- which is the condition necessary to get thrust -- but at its minimum points, it's below ambient.
Of course, those repeating bursts of gas are just like a humungous loudspeaker. My high school physics teacher used to start one up once a year -- and EVERYBODY in my 3,000-student school knew when it was...;-)
BTW,it wasn't only Germany that built the buzz bomb. The US Gov paid Ford Motors to reverse engineer a captured one and make two thousand of them; they would have been used if the planned invasion of Japan had come off.
They can, of course, be stopped with any means of cutting off the fuel. But they're still pretty hazardous: at zero airspeed the tailpipe will glow red hot, and the forces on the engine mount can be more than a less-than-expert modeler is ready to deal with.
There's a fascinating video somewhere on the Net of a test in the V-1 program, with an engine that had a row of viewports in the tailpipe. You can see the flame repeatedly zipping down the length of the pipe.
The engine has a flapper valve in front which actually serves as a passive "compressor". A charge of fuel gets ignited in the combustion chamber, and the hot gas expands down the long pipe, gaining speed as it goes. When the combustion finishes, there's still a charge of gas moving down the tube at high speed, and its momentum pulls the chamber pressure down below atmospheric. A charge of air comes in, mixes with fuel, burns, and the cycle repeats. The chamber pressure goes up and down in huge cycles, with the average pressure above atmospheric -- which is the condition necessary to get thrust -- but at its minimum points, it's below ambient.
Of course, those repeating bursts of gas are just like a humungous loudspeaker. My high school physics teacher used to start one up once a year -- and EVERYBODY in my 3,000-student school knew when it was...;-)
BTW,it wasn't only Germany that built the buzz bomb. The US Gov paid Ford Motors to reverse engineer a captured one and make two thousand of them; they would have been used if the planned invasion of Japan had come off.
By the way, the length of the exhaust tube is somewhat critical and determines the the frequency of the negative pressure wave and consequently the pulse rate of the engine. There is a minimum critical length determined by the volume of the combustion chamber and the cyclic rate of detonation that produces the greatest efficiency. In a pure rocket engine the exhaust nozzel is also tuned for maximum thrust but is not resonant in the way that the pulse jet nozzel is since a backpressure wave in a rocket engine is unwanted.
I still think these things pose a much greater fire risk than any glow or electric power system. I have never seen a a glow or gasoline engine catch fire in a crash. I have only seen one electric plane go down in flames, bad ESC. OTOH pulse jets are hotter than hades and even an otherwise uneventful landing in tall dry grass off the edge of the field could start a fire in a second.
Last edited by topspin; 10-27-2013 at 06:53 PM.
10-27-2013, 08:28 PM
#87
By the way Art Arro excellent outline on the engine operation. First two photos gives a close up on the fuel syphon with the schrader valve threads on top for the air pump.
Ironically although I am sure it was not the OP's intent this thread has probably given pulse jets for responsible use in both controlline and RC the biggest shot in the arm they have enjoyed in years.
John
Last edited by JohnBuckner; 10-27-2013 at 08:41 PM.
10-28-2013, 05:02 AM
#88
10-28-2013, 05:11 AM
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John,
The photos of your OS pulse jet looks exactly like mine- which I unfortunately sold at a previous Toledo RC Expo swap shop. I've ordered the HK version and will comment on it upon receipt. Note that pulse jet interest has really piqued with this thread-and another in the RC Jets Forum. Maybe the OP is really a shill for HK.
Long live pulse jets!!
Rgds,
Art ARRO
The photos of your OS pulse jet looks exactly like mine- which I unfortunately sold at a previous Toledo RC Expo swap shop. I've ordered the HK version and will comment on it upon receipt. Note that pulse jet interest has really piqued with this thread-and another in the RC Jets Forum. Maybe the OP is really a shill for HK.
Long live pulse jets!!
Rgds,
Art ARRO
10-28-2013, 05:54 AM
#90
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I remember my uncle back in 1965 built a shark looking control line model and put one of these engines in it. When he flew it his brother stood behind him and held on to his waist. He only flew it a couple of times then the plane and the engine hung in his basement untill he died last year. His brother has it now
10-28-2013, 07:22 AM
#91
By the way Art Arro excellent outline on the engine operation. First two photos gives a close up on the fuel syphon with the schrader valve threads on top for the air pump.
Ironically although I am sure it was not the OP's intent this thread has probably given pulse jets for responsible use in both controlline and RC the biggest shot in the arm they have enjoyed in years.
John
Thank You for these latest pictures , seeing the inner workings of the valve , especially , has been very interesting . To be honest , My mind had pictured some kind of big single flapper valve (which would never work upon further thinking cause it'd never cycle fast enough) and the view of the "fingers" explains that aspect of the engine perfectly . I am happy to see you mention responsible use , and since the AMA has spelled out responsible use then we know everybody has a nice easy roadmap to pulse jet happiness . As you well know , we all as fellow lifelong RC aircraft modelers would never do anything to jeopardize either our public image nor our insurance coverage , so we know we will all "play by the book" . I think what the OP was worried about was not his fellow modelers , but more the "hey look at me" bozos like the guy on the bicycle ,going out and buying a couple of em , strapping them on a skateboard or something , and ending up as another headline on the 6:00 news "MODEL PLANE JETS USED IN KILLER SKATEBOARD ACCIDENT !!" or other stupid such . My friendly answer to his concerns would be to reassure him that the hobby as a whole stands behind safe , fun use as defined by AMA , and that is the difference between us and the jerks who will hurt themselves , we will use them for their intended uses , rather than the foolishness of a possible few miscreants .
PS , I realize "bicycle Bozo" was using a home made engine , and not anything sourced from the model airplane worlds , I used him as an example of the "watch this" crowd only .
Long live responsibly used pulsejets ! (and every other power source we can fly these things with as well) !!
10-28-2013, 08:46 AM
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A couple of comments:
-All jet and rocket engines are reaction engines. If it makes thrust by flinging gas out the back end, it's a reaction engine.
-The combustion in a pulse jet (or any other reaction engine, or a piston engine for that matter) is deflagration, not detonation. Deflagration gives a smooth surge in pressure that's essentially a controlled shove; detonation causes a short, massive pulse of pressure that makes things come apart.
-All jet and rocket engines are reaction engines. If it makes thrust by flinging gas out the back end, it's a reaction engine.
-The combustion in a pulse jet (or any other reaction engine, or a piston engine for that matter) is deflagration, not detonation. Deflagration gives a smooth surge in pressure that's essentially a controlled shove; detonation causes a short, massive pulse of pressure that makes things come apart.
10-28-2013, 10:26 AM
#93
My friendly answer to his concerns would be to reassure him that the hobby as a whole stands behind safe , fun use as defined by AMA , and that is the difference between us and the jerks who will hurt themselves , we will use them for their intended uses , rather than the foolishness of a possible few miscreants .
Long live responsibly used pulsejets ! (and every other power source we can fly these things with as well) !!
Long live responsibly used pulsejets ! (and every other power source we can fly these things with as well) !!
Yes Indeed
John
10-28-2013, 12:28 PM
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This whole post is so funny.
1) They are nothing new if you go to any control line event and you will see them flying.
2) Know one is asking you or anyone if we should be able to buy one. SO BE QUITE!!!
If one shows up at your local field that has noise restrictions tell them they can'y fly.
1) They are nothing new if you go to any control line event and you will see them flying.
2) Know one is asking you or anyone if we should be able to buy one. SO BE QUITE!!!
If one shows up at your local field that has noise restrictions tell them they can'y fly.
10-28-2013, 03:04 PM
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Art,
Here is the picture of the cupping procedure,
You don't want to over do it. I did this to one valve that had a petal that wasn't sitting flat. I put about 1/32" bend in it, and it worked well. This seemed to work better than using a second cut down petal valve over the main valve.
I was going through all my pulse jet stuff, and most of it is based on performance increases. If you have any interest in this type of stuff I can start posting it.
Most of the information I have is either from Bruce Tharp, or Mike Hazel. Mike use to sell what he called a jet pack that was about 1" of reprints of pulse jet articles. Lot of good information there.
Greg
Here is the picture of the cupping procedure,
You don't want to over do it. I did this to one valve that had a petal that wasn't sitting flat. I put about 1/32" bend in it, and it worked well. This seemed to work better than using a second cut down petal valve over the main valve.
I was going through all my pulse jet stuff, and most of it is based on performance increases. If you have any interest in this type of stuff I can start posting it.
Most of the information I have is either from Bruce Tharp, or Mike Hazel. Mike use to sell what he called a jet pack that was about 1" of reprints of pulse jet articles. Lot of good information there.
Greg
10-28-2013, 04:01 PM
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My dad, brothers and I have been flying Dynajet powered R/C models for almost 20 years. We fly at an old WW II training base out in the country because of the racket these things generate. The airplanes we fly are draggy enough that they're no faster than the average .60 sport model. We've never managed to burn anyone or anything, and we do it just because it's fun!
10-28-2013, 04:46 PM
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Greg,
Thanks for the info on the "cupping" of the petal valves. I never had a valve that would not sit flat but will try your procedure if I do.
I'd like to purchase a copy of the "jet pack" articles for my own edifiication. Kindly point me in the direction of Mike or I can pay for a copy of your material. Much has transpired since I flew controline Jet Speed as a teenager many years ago. You can PM me or respond on this forum.
PS: Hop over to the Control Line forum here on RCU and open the thread on Jet Stunt.
Rgds,
Art ARRO
Thanks for the info on the "cupping" of the petal valves. I never had a valve that would not sit flat but will try your procedure if I do.
I'd like to purchase a copy of the "jet pack" articles for my own edifiication. Kindly point me in the direction of Mike or I can pay for a copy of your material. Much has transpired since I flew controline Jet Speed as a teenager many years ago. You can PM me or respond on this forum.
PS: Hop over to the Control Line forum here on RCU and open the thread on Jet Stunt.
Rgds,
Art ARRO