Homemade fan Jet

A few years ago I decided to build a Fan Jet Engine. I started with a stainless steel wine glass, a stainless steel chutney dish, high pressure duel stage computer fan, and a few small pieces of tubing.

S/S wine glass from thrift store.

When I purchased the S/S wine glasses (2) I had no idea what I would build. But soon after I came up with a plan. A jet engine, well a fan jet at least. I began by designing a flame tube. This is the most critical part of the build, it needs to create a cone shaped flame inside of the combustion chamber.

Flame tube mock-up.

After lots of research this is the design I came up with.
36 - 0.09375 holes = 0.24837890625 = 32%
12 - 0.125 holes =0.151875 = 19%
10 - 0.21875 holes = 0.3756347665625 = 48%
The total is 99% of the flame tubes flow.
I then proceeded to make the flame tube out of 0.875 S/S tube and capping the end. Once finished I cut the stem end off the wine glass leaving a 0.875 hole for the flame tube to be installed. And then welded the flame tube into the opening and drilled a 0.25" hole for the fuel tube in the capped end. I then began work on the fan side. Taking a S/S chutney dish from the dollar store I removed the bottom and welded the dish over the open end of the wine glass. To create a thermal break I used High Temp Copper Silicone to attach the fan mount tube inside of the chutney dish.

Finished Fan Jet

As you can see I cut and narrowed the output nozzle slightly. You can also see how the fuel tube entering the engine. What you don't see is how the tube bends 90degrees and enter the flame tube.

I have run the engine on butane and 5-12v dc and it produces enough thrust to move itself . I then made a smaller nozzle out of a vinegar dispenser lid and it increased the thrust a little. I did at that point start to make a thrust augmenter but never finished it. Maybe some day I will build something with the engine.

Pencil Gun Video

Thingiverse user Parkolay has printed two pencil guns and has sent me a video for all to see. It's hard to see the pencil.

These are his prints.

And this one is printed by Thingiverse user Linkreincarnate.

From their experiences it is clear the choice of elastics is very important. The outer two elastics can not be to strong or they will over come the trigger friction and inner elastic. You may be able to use as strong of elastic as you want but the inner elastic will have to be very strong and may make the trigger hard to pull.

Pencil Gun Trigger Detail

Close up view of my pencil guns trigger mechanism. Uses one internal elastic to return the trigger and latch to their rest positions. And two larger elastics to propel the piston forward and launch your projectile.

I designed this with the little pencils you get from Ikea and golfing in mind as the ammo. The barrel has a minimum diameter of 11mm and most pencils are 7mm's giving it lots of clearance.