Building an RC Pulse Jet Powed Airplane.

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 am estimating it to have 20,000 volts of output. 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 and the one in use is in a socket so it will be easy to replace in the field.

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.
 
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.

Ignition 1.jpg
Ignition 2.jpg
Ignition 3.jpg
 
Well this ended up on hold for a while again with more health junk. But I am back at it again. The construction phase is pretty much done, and I just splashed on the first coat of primer. The first coat is just a light dusting of black primer. All other coats of primer will be bright white. The black is just so I can tell when almost all of the white primer has been sanded off. This is an aircraft where weight matters, so each coat of the white has to be sanded off almost entirely just leaving what is needed to fill imperfections. Right now it really looks like a stealth missile in all flat black primer. It is nearly invisible in the pics I tried to take.

I still have not decided on a paint scheme other than it will be very bright colors for visibility.

This brings you up to date as of my current progress. I will continue to post progress as it happens.
 
Looks like a cool project. I flew a Goldberg Falcon 56, Skylane 62, Midwest Mach 1 pattern plane and a Dave Keats designed "Polecat" helicopter back in the day. I recall the radio range being about 5 miles though my eyes couldn't see the planes that far away anyhow. 60 mph is a mile in a minute, so 240 is a mile in 15 seconds! Keep us updated on your progress!

I interviewed with Martin Marietta when I graduated from engineering school. They were making the MX missile. I recall the interviewer saying they had to pot their circuit boards to keep the components from shearing off during launch. What's a small resistor weigh? A lot when it's accelerating at 200+ G (F= M A). Don't think you're anywhere close to that, but your fuel pick up is probably at the back of the tank!

Bruce
 
Yup fuel pickup is at the back. It will burn 2 liters of fuel in about 4 minutes. I am only going to be launching at around 10 Gs. It will be 14lbs of airplane with 18 lbs of thrust and about 150 lbs of pull on the bungee cord.
250 MPH means it will travel a football field in .8 seconds. Not much time to decide if I want to turn right or left to get turned around and headed back.
 
Those things are so loud that it'll be heard for miles. Hope you have a really remote place to fly it.

Also, consider relearning how to fly with something slower, otherwise this will likely be a very short flight.
 
Last edited:
Very cool project!

I thought pulse jets relied on having a certain amount of incoming air pressure to operate? I.e. The pulse jet would not ignite and stay lit until it was up to a certain air speed? Basically air speed compressing air into the intake took the place of the rotary compressor? I thought the V1's were launched via retrievable reusable rocket motors to get them up to speed and a certain air pressure at the intake before the pulse jet was lit off?

I am not a pulse jet expert so please correct my ignorance?

Thank you for sharing your project!
 
Last edited:
I am not sure if the old V1s needed ram air to operate or not, But most of the modern pulse jets need a compressed air source to get them started but once running will draw their own air even bench mounted. The catch is that they need the air movement for cooling. On the bench it will be close to melting the tailpipe in about 30 seconds without a high speed airflow.

kb58 said:
Those things are so loud that it'll be heard for miles. Hope you have a really remote place to fly it.

Also, consider relearning how to fly with something slower, otherwise this will likely be a very short flight.
Click to expand...

Oh yea it will be LOUD. Picture a 30-06 going off ~200 times a second......... The equivalent exhaust note of a single cylinder 2 cycle engine turning 12,000 RPM

Yes our flying field is in the middle of a several square miles of designated flood plane and our nearest neighbor is an abandoned airfield that can not be developed because they found some protected species of weed growing there, so no one can build anything anywhere near us. The drawback is that the field is under water a few times a year from the flood plain doing what flood plains are for.

I have other jet turbine powered models that can get real close to 200 MPH so while this one will be faster, it is not that much faster than some of my other aircraft.
 
Flyinfool said:
I am not sure if the old V1s needed ram air to operate or not, But most of the modern pulse jets need a compressed air source to get them started but once running will draw their own air even bench mounted. The catch is that they need the air movement for cooling. On the bench it will be close to melting the tailpipe in about 30 seconds without a high speed airflow.
Click to expand...

Very cool! Do you know what the tail pipe of your engine is made out of? Is it some super high temp alloy? ...Just curious.
 
Amazing video, astonishing that onlookers stand out in the open with 100% confidence in the pilot and plane.
Makes bull fighters look like wimps.
Thanks for sharing, would never have imagined that level of RC.
 
You must log in or register to reply here.
Back
Top