1 hour static thrust test run new pulse jet engine.

[Rocket Man]

I ran my new engine today. I did several test runs for a total of just over 1 hour of run time on propane. The reed valves show almost no signs of getting hot only the very tip edge of the pedal valves show signs of heat. I used the German V1 research data and 3 research papers from 3 different college students to build this engine. It is designed specifically to protect the reed valves so they will last for a minumum of 1 hour. I ran it in a test stand that I build today. It is 50% throttable and runs on 5 psi to 10 psi propane fuel pressure. The video shows it running on 8 psi. I used the Head from a Dyna Jet engine with the original reed valves just so I could compair the thrust and run time against the original Dyna Jet engine. Thrust is 4 lbs on 8 psi gas pressure. At 10 psi it does not produce any more static thrust but on an airplane at 150 or 200 mph ram air will make it produce more thrust.

http://www.youtube.com/user/Lowracerman ... kOR8IZPsFg

[Mark]

What is the volume of your jet compared to a typical Dyna-Jet? I filled my Dyna-Jet with water to see how much it held but I keep forgetting the number. It was kind of hypnotizing to watch your jet run rock steady for so long.

[Rocket Man]

I don't recall the exact volume of the engine without finding my notes or doing some math. The volume is more than double the Dyna jet engine.

The Germans learned that a properly designed engine with a compression ratio of not more than 2 to 1 the reed valves can be made to open and close at zero velocity. The reed valves should open and close by riding on the pressure wave inside the engine just like a boat riding on the waves in a lake. With the reed valves closing at zero velocity it will never hammer the reed valve to death.

I learned from 2 of the college research papers how to keep the flame in the combustion away form the reed valves. The engine will run for a very long time with no damage of any kind to the reed valves.

Notice in the video about 4" of the engine body near the head never gets red hot. A Dyna Jet engine get red hot all but about 1/2" near the head.

Another thing that needs to be calculated is the burn rate of the fuel exactly as you would for a liquid fuel rocket engine. If you blow fuel into the air inside a combustion chamber without the tail pipe it produces a long flame as it burns. If the flame is 8" long then the combustion chamber of the pulse jet engine needs to be 8" long. Each fuel has its own burn rate. Faster burning fuels have a shorter burn rate and slower burning fuels have a longer burn rate. Fast burning fuel produces a hammer effect on the engine while slow burning fuel produces more of a good steady push.

Hobby engines are designed wrong, compression ratio is too high, combustion chamber is too small, most of the fuel burns in the exhaust pipe not in the combustion chamber. The exhaust pipe diameter is too small and that restricts the flow.

All hobby engine exhaust pipes are too short. The engines will run with a short exhaust pipe but that is not what is needed to satisfy the condition of the engine.

Thrust of this engine should be 5 lbs with ram air and 10 psi gas pressure flying on a Model Airplane. The engine actually needs a speed fuel regulator exactly like the Germans had on the V1 engine. As the model airplane picks up speed the fuel pressure needs to increase as the ram air increases. At 200 mph fuel pressure needs to go up. At 16 psi gas pressure the engine will produce 8 lbs of thrust. With 8 lbs of thrust the model airplane will pick up more speed. At 250 mph the fuel pressure needs to go up more at 20 psi the engine will produce 10 lbs of thrust. The faster the engine goes the more ram air it gets and the more fuel it needs to use the extra air so the engine produces more and more thrust as it picks up speed.

If you consider the engine will run static with 5 psi gas pressure to 20 psi gas pressure with 250 mph ram air the engine is 75% throttable.

[Mark]

What is the volume of your jet compared to a typical Dyna-Jet? I filled my Dyna-Jet with water to see how much it held but I keep forgetting the number. It was kind of hypnotizing to watch your jet run rock steady for so long.

I was just rereading some previous posts of mine and found that the Dynajet holds roughly 600ml of water or 600cc or ~2.5 cups or 20 fluid ounces or 36 cubic inches or a pint and a half. ha
I haven't measured the volume of my Bailey Jet but the weight is 14 ounces.
The little TIgerjet I have holds 250 mls of water.
I guess your engine with the Dynajet head then would contain at least 1.2 liters of water if you were inclined to fill it.
http://www.easysurf.cc/cnver6.htm#foci4

The carbed engine you posted made me curious. The pipe looks very well made and has a pleasing shape to it. What kind of steel is it and did you have someone make it for you or was the shape an existing shape you found somewhere or did you painstakingly make the body of this jet yourself?
http://i43.photobucket.com/albums/e358/ ... 0005-1.jpg

[Rocket Man]

Total volume is 114 cu.in = 1868 ml. I always buy the exhaust pipe diameter and length I need for the thrust I want. I use a formula to calculate the preducted thrust of the engine according to the cross section area of the exhaust pipe. The combustion chamber and cone are always designed to match the exhaust pipe. I buy a piece of tubing the correct diameter and length to make the combustion chamber. The cone volume is calculated by doing some math and it is cut from a piece of 1/16" steel with a hand held jig saw then bent into a cone shape by hand and welded. The hardest part to make is the cone it usually takes me 2 or 3 hours to hand bend and form it to the perfect shape by hammering it around a piece of pipe in a vise. All the parts are welded with an old Lincoln AC stick welder using 3/32" diameter 7014 rods. All the welds are sanded smooth with a 4.5" flap disc hand sander 60 grit.

Here is a pic of the sander these are dirt cheap at Harbor Freight and those foreign tool places for $15 to $19 each.
http://cgi.ebay.com/Hitachi-G-12sr3-4-1 ... 563708fdcd

Here is a pic if the flap disc sanding pads. These are cheap on ebay 10 disc for about $10 plus postage.
http://cgi.ebay.com/4-FLAP-DISCS-FOR-4- ... 3ca770b73a

The jib saw is from Home Depot $29. They are cheaper at Harbor Freight and other places.
http://cgi.ebay.com/BLACK-AND-DECKER-JI ... 2557588f1b

[Mark]

I ran my new engine today. I did several test runs for a total of just over 1 hour of run time on propane. The reed valves show almost no signs of getting hot only the very tip edge of the pedal valves show signs of heat. I used the German V1 research data and 3 research papers from 3 different college students to build this engine. It is designed specifically to protect the reed valves so they will last for a minumum of 1 hour. I ran it in a test stand that I build today. It is 50% throttable and runs on 5 psi to 10 psi propane fuel pressure. The video shows it running on 8 psi. I used the Head from a Dyna Jet engine with the original reed valves just so I could compair the thrust and run time against the original Dyna Jet engine. Thrust is 4 lbs on 8 psi gas pressure. At 10 psi it does not produce any more static thrust but on an airplane at 150 or 200 mph ram air will make it produce more thrust.
http://www.youtube.com/user/Lowracerman ... kOR8IZPsFg

Did you use a thicker reed valve material for the above results? My Dynajet and Bailey Jet use/came with .006ths blue tempered spring steel. And for my little Tigerjet, it too uses .006ths but oddly it's really hard to even blow the least amount of air into it with your mouth over the intake, the smaller holes and shorter arm on the reeds make .006ths really "stiff." If you are using thicker material, perhaps this extra thickness, in addition to the longer combustion chamber, contribute to the longer life of the reed?
I noticed this information on eBay.

"Make your own Dyna Jet Reed valves in about 5 minutes each for about 70 cents each. Once you see how easy this is you will be wondering why you never though of this yourself. You can make reed valves for any pulse jet engine, tiger jet, bailey jet, silver jet and others.
Blue Spring Steel .010" thick is $29.23 for a 2 sheet pack. There is enough material to make 44 pedal type reed valves for a Curtis Dyna Pulse Jet Engine if you cut the metal into 2 1/4" squares. If you layout the entire 2 sheets 3 rows 10 parts per row you can make 60 reed valves for about 50 cents each. "

"Here is a video of a Dyna Jet Red Head valve HEAD on a custom built Engine Body. The body is custom designed from the German V1 Research Data and 3 research papers written by 3 different college students from 3 different colleges. This engine produces 5 lbs of static thrust running on propane. It will run on gasoline or alcohol too. 200 mph ram air on a model airplane increases the thrust to about 6 lbs.
5 lb Thrust Video http://www.youtube.com/user/Lowracerman ... kOR8IZPsFg
10 lb Thrust Video http://www.youtube.com/user/Lowracerman ... qxjgmelP-Q
You will receive Step by Step Instruction with photos to make your own Pedal type Reed Valves and you also get PLANS to build this custom Pulse Jet Engine. You also get information where to Buy the Blue spring steel 2 sheets per pack. Build your own pulse jet engine from scratch in only a few hours work."
http://cgi.ebay.com/44-REED-VALVES-Dyna ... 2a02f79a10

[Rocket Man]

I bought my first Dyna Jet Pulse Jet Engine in 1977 the reed valves were .010" spring steel reed valves. I have bought 3 more Dyna Jet engine since then and 2 of them have .008" reed valves. I have the factory original papers that came with 2 different engines 20 years apart one says .010" and the other say .008" reed valve thickness. I have tried both in my Dyna Jet engines and they both start and run fine. The .010" metal thickness works the best in the Dyna Jet engine. The biggest problem I have is the tip ends of the petal valve get too hot and they hammer the tips off as it runs. If you replace the reed valve retainer with a larger diameter retainer that covers the entire surface of the reed valve that helps to protect the ends from combustion chamber heat. The biggest problem is the Dyna Jet engine has a compression ratio of almost 4 to 1 that is double what the German V1 engine had 2 to 1. Also the exhaust pipe on the Dyna jet is too short to produce enough kenetic energy to suck the flame away from the valves. The extra kenetic energy from a longer exhaust pipe causes the engine to suck in a larger air fuel mixture which gives the engine more power and more thrust. The extra air fuel mixture flowing over the reed valves acts like additional cooling for the reed valves. The combustion chamber of the factory Dyna Jet is too small this forces all the fuel to try and burn is a space that is too small forcing the flame back against the reed valves. The cone of the Dyna jet is too small too. The Dyna Jet engine does run as we all know but it can be improved. It is interesting that the cone acts like it is part of the combustion chamber and it also acts like it is part of the exhaust pipe. A correctly designed cone makes a much improved engine. A pulse jet engine appears to be a very simple thing with only 1 moving part but there are 6 parts to this engine and each part effects all the other parts. If you make a change to any one of the parts it effects all the other parts.

Liquid fuel rocket engines use the fuel as the cooling system for the engine. The fuel picks up waste heat and runs it back through the engine. This added extra heat to the exhaust which is expanding gas which is more thrust. You can do the same thing to a pulse jet engine. Put the whole engine inside of a shroud that covers the entire engine out past the tip end of the exhaust pipe. The exhaust from the engine produces a vacuum that sucks air along the surface of the pulse jet engine body. This funnels all the waste heat out the end with the engine exhaust producing more expanding gas and more thrust. It also keeps the engine cool during a static run.

[Mark]

One of the constraints of a pulsejet is the low compression ratio. I mentioned that I filled my Dynajet with water and it held about 600 mls and you said your jet was more than double that at first and then you gave a specific answer of 1868 mls. What we are getting into is comparing apples and oranges.
"Also the exhaust pipe on the Dyna jet is too short to produce enough kenetic energy to suck the flame away from the valves. The extra kenetic energy from a longer exhaust pipe causes the engine to suck in a larger air fuel mixture which gives the engine more power and more thrust."
"A pulse jet engine appears to be a very simple thing with only 1 moving part but there are 6 parts to this engine and each part effects all the other parts. If you make a change to any one of the parts it effects all the other parts."
By enlarging your pulsejet you also enlarge the weight and drag somewhat. I remember in Foa's book "Elements of Flight Propulsion" he talked about shrouds and augmenters but at high speeds the extra weight and drag canceled out any benefit.
In past posts this same debate came up on thrust, weight, fuel consumption, drag, volume, fuel used, cost, effort, etc. All these factors made for some interesting rules or goals to strive for. I opted to stick with volume, constrain everyone to the same vessel volume as a starting point.
But then maybe you could make a larger engine that is more fuel efficient or if you didn't care about weight you might use this to fuel a V-1.
http://junkyardsports.com/images/piggas.jpg
There's just so many things that make comparisons very hard to judge.