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Apr 16, 2017, 07:21 PM
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spektre57's Avatar
Good luck with this build. We have a guy in our club who flies pulse jets on a fairly regular basis, they certainly are something different and not the sort of thing that can be done on your own. Pulse jets are simple in principle to operate, it's just a hollow tube, but from what I've seen and been involved with everything has to be done right or the results can be catastrophic. This isn't meant to deter you from flying, just be careful and enjoy it for the unique experience that it is. You'll certainly have everyone's attention when you start it up.
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Apr 23, 2017, 03:53 PM
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Well here are a few pics to wet your appetite.

It sure does not look a lot different from when I started, but there is a lot of time wrapped up in it already, most was filling and sanding and the early parts of paint prep.

The pulse jet is just temporarily mounted to get a rough idea on where the CG is headed. It looks like everything needs to be as far forward as it can go and I will still need a lot of lead in the nose. This also means that there is no reason to skimp on any structure up front.
Apr 24, 2017, 08:38 AM
SLCPilot still sucks!
That is super cool!
Apr 27, 2017, 10:26 AM
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I have decided to add in an extra safety feature. I am going to add a heat sensor that will cut power to the fuel pump in the event of a flame out. Pulse Jets are very sensitive to air bubbles. An unexpected flame out low and at 250 MPH could have my fingers busy and not be able to stop the fuel flow. My plan is to have a K Type thermocouple (same type as most turbines) about half way down the thrust tube of the PJ, if that cools then there was a flame out and it will open a relay to cut power to the pump.
We will see how this works out on the test bench.
In reading the PJ manual again I noted that it can be run on either straight Kero with 5% oil or a 60% kero / 40% gasoline mix with 5% oil added to that mix.. The oil is only to lubricate the gears in the fuel pump.
May 08, 2017, 11:46 AM
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Glue or screws????
I am close to the point of attaching the vertical fins. The instructions say to epoxy them to the airframe.
My concern is that the elevon linkage runs thru the inside of the fins. If I epoxy them on then there is zero access to inspect or service the linkages. The other option is to drill holes thru the wing to epoxy in some hardwood dowels that can be drilled for some screws that will go into the bottom of the fins. I am not sure just how I would get a strong thread into the fin for this attachment. But I do really like the option of access to the control linkages.
The bottom of the fin is 3/8 to 1/2 thick balsa, sanded to match the airfoil of the wing.
For the front screw it will be fairly easy to add some structure and a ply plate with a metal T nut to the inside of the fin. for a rear screw the pushrod runs straight across the balsa fin bottom that is carved out for clearance, a centered screw would hit the pushrod and not really any room to add structure.

Any other ideas?
May 30, 2017, 12:31 PM
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I seem to have run into a bit of a snag in the building process, the snow all melted, weather got nice, and I been outside playing.................
Oct 12, 2018, 12:41 PM
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Well it has been a while since I even looked at this thing. Medical issues and the associated bills got in the way of everything. I am starting to fiddle with this again. I think I have everything I need to build the actual aircraft. I am now acquiring odds and ends that will be needed to for the support stuff. I am so far astounded at the pile of stuff and cost for the necessary support equipment.

First is the ignition system for starting, I need something that will have a quick release from the spark plug that will fire the plug with a continuous spark. I got an automotive ignition coil and condenser like the old points systems used. Remember those days? I will use a DPDT relay wired as a buzzer to cycle the power to the ignition coil to generate the sparks. That output will be thru 2 long high voltage wires with alligator clips to the plug and ground. I will use a small gel cell 12V battery to power the whole mess with some fuses and switches as required and then find a box to hold it all. I had thought of building a small PC board with a square wave generator to provide the pulses to the coil, but for now that is to much like work. I have this part all designed and have everything but the box to build it in.

The next special piece of support equipment is the air supply for starting.
The pulse jet instructions say I need a mix of air and propane to be blown in to initiate ignition.
I have done a lot of head scratching on this one and watching YouTube videos. What I came up with is to use an 11 gallon air tank that will be filled to 125 PSI with air. from there I will have the airline to a blow gun with a long nozzle. Next to the trigger of the blow gun I will have a start valve for a propane burner. the kind if valve that has a thermocouple to turn off the gas if the fire goes out. these have an override button you push to keep the gas flowing while the thermocouple heats up. Well I will leave off the thermocouple to use it as a push button propane valve. Then I need a hose to a regulator that will allow me to control the flow rate of the propane and a 1 lb propane bottle. I will also need a small air compressor to fill the air tank. I should be able to run the air compressor off of the 2000/4000W inverter in my truck. The cost of this mess of parts is adding up quick.

And in the midsts of these 2 parts of the project, I have been working on the plane little by little. I have got the radio tray all built and installed, and am still forever finding and filling imperfections in the surface of the plane. At some point I will just call enough enough, and just paint it flaws and all. At 250MPH no one will see the flaws. I am terrible at painting anyhow. I am debating hiring a pro to do flames with bright colors on the top and just some contrasting bars on the bottom and then clear the whole thing.

I still have not made up my mind on the vertical fin attachment, I can make a strong case for either option. At this point I am leaning toward gluing them on permanently with a small access hole that will allow me to see and reach the screw that holds the pushrod to the servo arm. This will not be an everyday flyer. A dozen flights a year will be a lot, mostly to not abuse anyone (other pilots or neighbors) with the noise it will make.

I have not even started looking at what to do for a launching system.......$$$$
Oct 16, 2018, 10:50 AM
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For the heat reflector below the PJ I got hold of some of the gold foil that NASA uses on satellites to reflect heat. Not cheap but will look really cool, and should get the job done. The aluminum tape would have been a lot cheaper but would not look as pretty.

The propane regulator and gas valve are on the way, I already have a selection of blow guns on hand to pick one from. Once I get these parts I can measure to see what threads the fittings are and then try to find the hoses I will need to make the connections.
Oct 22, 2018, 10:05 AM
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The propane parts are here and I am now trying to find the fittings to connect them up.
Started to mount electronics and stuff to the radio tray. I have the bubble trap, fuel pump and the ESC for the fuel pup mounted. Those pretty much dictated where the RX will have to go. Then the switch and BEC will go where ever there is room. The battery will be stuffed way up in the nose. The battery will be a 5S NiMh. I will still need the BEC because the factory installed servos are 4.8V and are permanently built into the wing. If I ever have a servo issue I will have to do major surgery to get new servos in there.

I have decided that the fins will be glued on, I added a plywood plate to the inside and cut an inspection hole for the servo linkage. The inspection hole is just big enough to get in and remove the linkage or tighten the screw, should I ever have to. I will add a generous fillet of something to help spread the load out and give a bigger effective glue joint. Was thinking of a mix of epoxy and milled glass and/or micro balloons to make the fillets. I also thought of using 1/4 inch triangle stock for the fillets.

It is in that phase where you work like mad and at the end of the day you step back and see no change.
Nov 05, 2018, 09:36 PM
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Well I have the release mechanism for the launcher all built. Of course it took longer and more work than I expected.
Dec 19, 2018, 11:11 AM
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Well I took a detour back to the ignition box. I now have the actual circuit all bread boarded up and have started to assemble it into a waterproof case. Of course as I always seem to do I added complexity as I progressed. I have 4 red flashing LEDs to warn that it is powered up. I have added an interlock so that if the case is open the power shuts off. For now I have gone with the original plan of the relay and ignition coil. this setup is giving me about a 3/4 inch long very bright blue nearly continuous spark. when connected to the spark plug I have opened the gap way up and still have a very hot spark that will ignite paper instantly. I am getting close to having it all installed into its water proof case. I will post pics when I finish it. Just waiting for the big brown truck to bring some more parts to mount everything in the case..

I do not know how long the relay will last with this abuse, so I have a spot in the case for a couple of spares.

I have also designed a solid state spark generator and have gotten as far as drawing up the schematic and the printed circuit board layout. I have neither acquired any parts for this version nor done any actual building of it. So far this version just lives on paper.
Dec 28, 2018, 12:26 PM
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OK as promised her are some pics of the ignition box.

I have now completed the ignition system for the engine. I need a continuous spark to get the fuel to ignite. once the pulse jet is running the flame is self sustaining. this box will stay on the ground and is just for starting. It produces a spark about 3/4 inch long, and has a really hot fire across the electrodes of the spark plug. It is really pretty simple electrically. A 12V battery, A relay wired as a buzzer, which also acts as the points in an old bike, a condenser to try to save the relay contacts a bit, and an automotive ignition coil to step the voltage way up. I also added 4 random flashing LEDs to show that the power is on. I have some "DANGER HIGH VOLTAGE" stickers coming to put by the switch and the output terminals.

Next on the list is the Air supply for starting. This will need a source of compressed air and that will need to be mixed with the correct amount of propane to make a nice combustible mixture to blow into the front of the engine. Once this mix ignites inside of the engine I can then turn on the main fuel flow and it should keep running at that point. As soon as I get all of this ground support stuff designed and built I can do the first test fire of the Pulse Jet engine on a test stand.

There is still a lot of work to do on the aircraft itself, but that is also coming along little by little.

Warning Lights (0 min 8 sec)

Spark generator for pulse jet ignition (0 min 7 sec)
Jan 19, 2019, 03:12 PM
coriolan's Avatar
That will make an interesting video!
Jan 21, 2019, 12:08 PM
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I do expect there will be some video of the mile stones. Like first engine start and maiden flight.
Feb 12, 2019, 11:43 AM
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It was foamed into the box, It took me a couple of hours just to get it out of the box.
Sure is bigger that I envisioned.
Will post some pics tomorrow.

Bluestacks Kodi Lucky Patcher
Last edited by amzoun95; Feb 14, 2019 at 12:49 PM.

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