New Pulse Jet Dude

[dynajetjerry]

Heli-Nubee,
I have several suggestions, even though I've never flown an RC pulse-jet: 1) Make sure the area from which you will be flying has no flammable material, in case your jet crashes while the engine is running. Bruce Tharpe usually flies his pulse-jets in Nevada where there are minimal dangers. 2) Bill's Sportjet employs an exhaust pipe that, at the rear portion, is slightly larger than the D-J. Make sure you won't have trouble changing from the D-J to the Sportjet. 3) The D-J was designed to burn auto gasoline; Bruce's fuel system works only with AMA-approved methanol-based fuels. It will be destroyed by gasoline. I believe Jim Cline's fuel controller is suitable for either fuel. 4) Bruce's latex tank holds enough for about 3-1/2 minutes of operation on AMA fuel; make sure your model won't run long enough for it to fly out of the safe flying zone. 5) The original metering jet in the D-J is too small to permit operation on AMA fuel. You will need a larger one for that; Bill or Bruce can probably tell you what sizes will work. I'm guessing they will need to be about .056 in. I. D. instead of the D-J's .039 in.
AMA rules specify the necessary safe practices for flight of models that are powered by jet engines, including pulse jets. Check with the appropriate authorities before you fly the first time. If there are non-modelers living nearby, seek their approval, also. The noise of a pulse-jet can be frightening to many people (but not to me.)
Good luck! Jerry Wiles

[Heli-NuBee]

Hi Jerry,

Thanks for your input. Our flying field is located in the country on the back part of a ranch. Nearest neigbor is probably about 1/2 mile or more away. Jets are flown at our field quite often. I don't think that flying a pulse jet should be any more of a problem than some of the larger turbine powered aircraft. I will be following AMA rules regarding the operation and flying of pulse jets. I have consulted with others that have been sucessful in flying RC pulse jets including Bob Fry, Richard Caine and Bruce Tharpe. Their input has been very helpful. There seems to be a great deal of interest at our field and in our region about this pulse jet project. I believe there are quite a few others out there that would like to fly a jet but just can't afford the cost of a gas turbine. The cost of building a pulse jet powered plane should end up close to the same as a gas powered prop plane. My plane will use methonal based fuel and will be equipped with a shut off valve for safety. We will also have at least two fire extinguishers on hand as required by AMA rules. I am very fortunate to have some expert support with this project and we plan to operate and fly the pulse jet plane in as safe and controlled manner as possible. Thanks again for your input, it is great to hear from other folks interested in pulse jets.

Heli-NuBee (Roger)

[Heli-NuBee]

Posted below is a picture of the electronics for the airplane. I am using four metal gear high torque servos for the ailerons and the elevator and four standard nylon gear high torque servos for the rudders, front wheel steering and the fuel cutoff valve. Please note that I have soldered extensions on some of the servo leads as necessary. I like to solder my leads that will not be accessible rather than use plug-in type extensions. The receiver is a Futaba 7-channel 2.4mz unit with a switch that contains a charge port and a 2000 MAH 6V battery to drive the system.

[Heli-NuBee]

OK, my new sport jet engine just arrived. The workmanship on this engine is awsome. If anyone out there is looking for a quality engine or parts, contact Jet Bill at http://jetbillproducts.com/. He is very busy and one may have to wait for a short time for his products but it is well worth it. Now I can move along with my Vortex 32 pulse jet build. Thanks JB, I appreciate your hard work and quality products.

[dynajetjerry]

Roger,
What you said about Bill's Sportjet is true but I must point out something to all "jet nuts." The last I heard, Bill was still using the tooling and designs of Earl Bailey (including the exhaust pipe assembly,) except for his Fastjet. Bill has made many small changes in his and Earl's Fastjet valve head assemblies, resulting in a record-holding design.
The Sportjet is appropriate for AMA competition in the Sportjet event as are the Dyna-Jet, OS II, Minijet, and all the others that are no larger than the D-J, so long as they are not modified from their factory-made versions. Most particularly, their valve retainers should remain as manufactured.
Good luck!
Jerry

[Mark]

So the valve retainers are altered to allow more play is it? I've seen those big foot reeds for sale, where the ports are bored out a scosh more. Do you know if those have been shown to provide more thrust Jerry? And if the valve retainer is permitting more play, do the reeds wear out faster? Seems like there would be some trade-off. I wonder if you could partially run fuel through the retainers or that region as some other pulsejet designs have employed or toyed with? Just some random questions.

[MANOLO]

hello would like to know what thickness is the plate of the chamber of pulsejet ....
my pulses are manufactured in 0.5 mm sheet as it is the pulse??

[dynajetjerry]

Mark,
I'm reluctant to refer to the increased lifting of the reed valves as "allowing more play." I prefer to call it "reed lift" because "play" implies the reeds can move about on their mountings. Rather, they are tightly secured but must flex, only, to allow passage of air and fuel into the combustion chamber.
In my mind, the AMA Sportjet rules seem to leave a loophole: the retainer and other components must be left as manufactured, regardless of when and by whom they were produced. This can allow mfrs. to alter their retainers enough to improve static thrust so long as all such p-js from that mfr. are similarly shaped. This limitation handicaps users of older designs (such as the Dyna-Jet,) because they were designed before any such requirements were formulated. I don't have the rules in front of me but I think the intent of the Sportjet category was to allow Dyna-Jet users to be competitive in that event. As manufactured for 60+ years, D-Js are not the equal of Earl's and JetBill's (and other) speed designs. I believe that, to be fair and obey the intent of Sportjet competition, all p-js that are used in that event should utilize almost-identical and interchangeable valve head assemblies including reeds, ports, retainers, fuel injectors (with enlarged metering jets that permit the use of AMA fuel,) and combustion chamber/tailpipe assemblies. This would ban the use of any pipe assembly that employs an expanded exhaust pipe in any part of its length.
And yes, increasing the lift clearance of a retainer can increase thrust but with a markedly reduced useful life of the reeds. So-called "bigfoot" reeds and ports are allowed in regular Jet Speed only, not Sportjet.
Jerry

[Mark]

Thanks for that information Jerry. It's a lot of apples and oranges when it comes to leveling the playing field I suppose. I think my Sportjet for example weighs a couple ounces less than a Dynajet, has ten metering fuel spray holes instead of two, and it's more volume than a Dynajet, but almost all the pieces are interchangeable/screw-connect if you wanted to mix and match Sportjet/Dynajet parts as you know. The Bailey Sportjet uses a smaller spark plug of course.

[Heli-NuBee]

I received a couple of more items necessary to complete the Vortex 32 build yesterday. The lead fishing weights will be used in the nose as necessary to set the CG of the plane and the heat insulating foil tape will be used to protect the underside of the stab, the tail booms and the inside of the rudders from the heat of the engine. I hope to begin making much faster progress on this build now that I have most if not all materials and products necessary to complete the build.

[Heli-NuBee]

Making a little progress now. I am still struggling with finding time to work on this project. Servos are installed and connections made for rudders and ailerons. Please note that the tail boons are designed to use mini servos but I elected to use standard servos. Using standard servos required modifying the servo mounts in the tail boons for both the rudder and elevator servos.

[Heli-NuBee]

Applied heat shield reflective tape to the inside of the tail booms and the rudder surfaces. I ran out of reflective tape and had to order more to cover the underside of the stab and elevator. Also installed the elevator servos.

[Heli-NuBee]

The plane is beginning to take shape now. The tail booms have been installed on the wings and the wings installed on the fuselage per the mfg. instructions.

[Heli-NuBee]

The next steps will be to install the fuel system and engine. First, it will be necessary to modify one or more of the fuselage bulkheads to accomodate the 48 oz fuel bladder containment bottle. Here is a picture of one of the bulkheads to be modified.

[dynajetjerry]

Heli-Nubee,

Thanks for the update. Your plane looks good and will probably fly good, also, especially if it is balanced properly and is sufficiently strong.

I'm sure you know that the fuel system will need to be pressurized and will require a regulator. As you also probably know, Bruce Tharpe has flown many RC pulsejets and can lead you to sources for the items you will need. Jim Cline developed appropriate regulators (he called them "controllers,") but he passed away last year. I think his company is still in business near Dayton, OH, and is on the Internet, if you don't already have one.

Good luck!

Jerry Wiles