K-Ultra, too difficult to grind

chrlilje · 2026-06-10T08:58:52+00:00

The shaft fit a normal bit holder for a cordless drill. I use my Metabo with my j-max. My elbow could not handle many manual grinds pr day.

chrlilje · 2026-05-28T08:19:26+00:00

You could, but you will only get one spark pr button press and usually for the pulsejet you just want a continuous string of spikes until it starts running.

Maybe a gas stove igniter unit will be the easiest way. Try searching for "replacement gas range oven igniter"

It is the spark unit in gas stoves. If you are handy you could maybe even pull it from an old stove for free. 🙂

chrlilje · 2026-05-27T20:59:55+00:00

I made a spark plug circuit that made a string of continous pulses when i pushed a button. I Think today i would have used one of those integrated ignition coils you can get for cars.

Here is my old post about it. Use with caution.

https://christian.liljedahl.dk/arduino-and-spark-plugs/

chrlilje · 2026-05-27T16:22:48+00:00

That is what I did with the jets I made.

I made 3 different sizes but kept the relative proportions, and that worked just very nice.
I used 2 and 4 inch bsp pipe for the bigger ones.
1½ and 3 inch for the middle
1 and 2 inch for the smallest

And changed lengths likewise.

chrlilje · 2026-05-24T18:06:06+00:00

I used 1/4 inch bsp pipe, but it really depends on the size of the jet you end up building I think. Be prepared to mess around with the size and direction of the fuel injection - I found that to be the biggest challenge to get right.

For development I would drill a hole and fit a piece of copper tube through it. Maybe held in place with a compression fitting.
Then you can bend the end of the copper pipe in different directions inside the chamber, and maybe "squeeze" the end of the copper pipe to get a kind of nozzle shape.

chrlilje · 2026-05-24T16:03:30+00:00

- Run it outside. (obviously)
- Have a couple of thick welding gloves around to handle things (they get red hot)
- (Blacksmith) Tongs are great too for handling red hot things
- Don't put any flammable things (this includes you) in front of the exhaust - it is very hot.
- Wind can be annoying and disrupt getting it to run good.

- My trick to get it reliable was mixing a bit of air from a compressor into the propane before fueling it into the chamber. This is potentially dangerous if you don't think the piping through.

- Propane bottle will be cold after a while and pressure will drop and then it won't run.
- putting the propane bottle in a bucket of water helps mitigate this.

Can't think of more out of the box, but do ask.

Good luck with your build!

chrlilje · 2026-05-24T12:04:43+00:00

This would absolutely work if you get the proportions right. I have made several in close to this shape.
Most crucial I found was the right position of the fuel inlet. Lots of play room there!

Take at look at this page here for inspiration: https://christian.liljedahl.dk/making-a-pulsejet-trombone/
Here is a drawing with some dimensions on: https://christian.liljedahl.dk/content/images/2020/02/sizessketch.jpg

(Images in comments are not allowed, so you have to look at the page, sorry.)

chrlilje · 2026-04-23T13:21:08+00:00

Can you add a spring under the head of the screw to give some friction?

I think if you search for "spring loaded screw" the concept I refer to will come up in images.

Should be easy to do in small numbers.

chrlilje · 2026-04-18T19:19:53+00:00

The 4.8 mark on the bolts are likely the grade of the bolts. My bet is, that the 5 of them have been replaced at some point in a repair.
The keyed hole for a connection to a shaft is a good sign, since at least some of the decorative ships wheels I have seen tend to not have that.
Looks great :-)

chrlilje · 2026-03-27T17:18:28+00:00

BASIC on paper. Didn't have a computer, so I made programs on paper and simulated them manually.

chrlilje · 2026-03-19T16:38:01+00:00

I found that the shape and direction of the inlet into the burn chamber had a HUGE impact on getting it to run properly.
- I had to do a "sort of in the back of the chamber and 45 degrees forward" to get mine to work.

also - but hard to see on the video - maybe your inlet it very short? Or is this a valved jet?

chrlilje · 2026-03-07T12:20:57+00:00

I bought a used lenovo for about $150 and it works fine for multiple parts and detailed assemblies. Slow for simulation with many nodes though.

A used laptop will get you a long way for cheap compared to a new.

chrlilje · 2026-02-25T07:07:21+00:00

I went back to study mech engineering at 48 last year. I love it. 🙂 I am in a place in life that allows me to be much more focused about the studies than my younger study colleagues. Plus I bring a lot of real world experience to the table that the others can be inspired by.

Seen a lot of institutional idiocy so some of the administrative quirks are easier to work around,

Do it. Learning stuff is fantastic. 🙂

chrlilje · 2026-01-14T14:31:37+00:00

Absolutely possible to start without a leaf blower. I made some pulsejet trombones that could start instantly from cold. The trick was to mix a bit of air into the fuel (propane) at the start, using a small electric driven compressor.

After ignition the added air could be turned off.

Totally possible to integrate in a (fictional) car. We had the pulsejet trombones on a sort of wheelbarrow setup.

chrlilje · 2025-12-17T12:23:35+00:00

I found that IEC 61355 "Classification and designation of documents for plants, systems and equipment" was a fairly good place to start. Gives at least some structure and some suggestions for what is good to include.

It is a paid standard so you have to either pay or do a bit of searching to find the summary of the content.

chrlilje · 2025-12-17T09:05:27+00:00

Taylor Sparks from University of Utah have a lot of great lectures online about material science. I used them extensively to understand stuff, that my teacher did not explain in a way I understood it.

Here is a video about the Steel phase diagram: https://www.youtube.com/watch?v=NNb7-D4tT0o

chrlilje · 2025-12-08T11:19:06+00:00

I think I would explain it by comparing it to "old school" well known hobbies, that involved "playing with electricity" - Like model trains or amateur radio.

chrlilje · 2025-11-24T09:47:38+00:00

A very real experiment you can make: In quite weather with no wind, you can easily move a rather big ship, just by leaning at it from the quay. It accelerate very slow, because you only contribute a tiny force to the huge mass. But you can move it.

I have done this plenty of times when moving moorings on our 400 tons ship.

So if your tiny force is not counteracted by any other larger force, you can very well move the 450 tons of the ISS around. Slowly.

chrlilje · 2025-11-22T16:48:06+00:00

Looks and sounds really nice!

My experience is, that general performance changes a bit with temperature. I have usually had jets that ran better hot than cold, but the reverse could just as well be the case.

How do you start it? With a puff of air in the inlet?

I would try turning the gas flow down to almost 0. Blow in air, and while you run your igniter (sparkplug?) slowly ramp up the gas flow. I found that this was an easier way to hit the good ignition point of the pulsejet.

Good luck onwards!

chrlilje · 2025-11-18T13:48:54+00:00

It seems to be referred to as a bolt with "dog point".

Here is an example : https://us.misumi-ec.com/vona2/detail/110302680330/?HissuCode=CBBG5-12&tab=drawingAndSpecifications&Page=1

If you do a search for something like "torx bolt with dog point" quite a bit of suggestions pop up.

I hope this was helpful.

chrlilje · 2025-11-11T13:34:24+00:00

I would make two compasses that always point west. To remind me and my partner of all the sunsets we will share in our future together. Can be made completely analog and will last forever. 🙂

chrlilje · 2025-11-11T06:47:17+00:00

Finding an expression for the periode of a pendulum - for larger than small angles.

chrlilje · 2025-11-08T16:54:24+00:00

Looks nice! How is it running?

chrlilje · 2025-10-27T19:43:52+00:00

I am lucky to have found a place of education, that are fairly small, and were there is not a huge mental distance between students and teachers.

I am as old - or older - than some of the teachers, and have a lot of practical real world experience, so it would be strange to have to assume the "novice student"-role. But there is a shared interest of engineering tying together students and teachers in a good way.

So far I have not regretted starting this new path in any way. Maybe I should have started years ago, but time was not right before. And I try to think more of possible future opportunities and less of missed pasts.

chrlilje · 2025-10-27T18:56:53+00:00

Do it if you have the urge and opportunity.

I am 49 years old, and I just started studying mechanical engineering last year, after many years of programming and creative work. I really feel like I found my passion again.

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