It’s widely known that you can find just about anything on eBay. From Twinkies to the attempted sale of an aircraft carrier, you are bound to find something interesting. Before I found SparkFun, eBay was a pretty decent source for finding parts like motors, relays, power supplies, and really anything industrial. Sure, I had a surplus store near me, but they didn’t always have what I was looking for. Time went on, and I found SparkFun, along with a host of other specialty sites that started to carry the staple ingredients for Makers, but my projects almost always had a “special ingredient.” Whether it was a sheet of titanium, an electric bike motor, or nixie tubes, I could always find it on eBay. I have a personal list of items I am always on the hunt for. Laser tubes and CNC machines are typical entries, along with the more esoteric aircraft instruments and vintage gauges. However, there was one item that I thought to be too outlandish, rare, and expensive to find. Until now…
If you were watching the SFE_Engineering twitter feed, you saw this photo with the caption, “NERDS! WE HAVE A JET ENGINE!!!”
This is not your average jet engine. This is a centrifugal gas turbine. This engine does not produce very much thrust. It converts the exhaust energy into rotary motion powering an output shaft. You would find an engine like this on a turboprop plane. This particular engine came from a surplus Navy generator commonly used to help re-charge and start helicopters. It was designed to drive a 10kw 28vdc generator. In a previous life it looked more like this:
“What are you going to do with it?” That has been the number one question since we popped the crate open. Well, let’s just start with what it is. Currently, I have the engine and the original controller. The controller is what some might call dated. Also, I don’t have any of the original cables. If you have worked around aircraft or military hardware, you can see how that will get expensive quick. The connectors used on this hardware can range from $30-$200 per cable end.
One great aspect is that the manual for this engine is in the public domain. It was tricky to track down but there are military enthusiasts who scan field manuals for release. From the 300+ pages, I have been able to understand how it is wired, plumbed, and how to service every component. I am impressed by how detailed and thorough it is. There are diagrams for every subsystem. One of my favorites is the simple engine oil flow diagram.
With this information I am going to use an Arduino to monitor the speed, temperature, and oil pressure while controlling the fuel flow to the engine. The current engine controller would require quite a bit of hacking to allow it to operate without a generator attached. By using an Arduino, I can play with settings and possibly enable some speed control. That’s where things get interesting.
“But, what are you going to do with it?” This is the second most asked question. Besides getting it to start off a custom controller, I’m not quite sure. The engine has a lovely output shaft that is designed to spin at about 12k rpm (revolutions per minute). The shaft is connected to an internal 4:1 gear reduction. So, that means the turbine is spinning at about 48k rpm. That’s pretty quick considering most automobile engines “redline” between 6-9k rpm. The difficulty will be finding some way to connect to the output shaft and keep it from flying apart. There is a nice bolt pattern that can be used to hold a secondary gearbox. Adding one would require some considerable engineering to prove something built would stand up to the speed and power associated. The true output power is not documented in the manual. The engine is rated for 10kw of electrical power. There are forums that boast anywhere from 75-150hp. There are similar engines that powered a small, single seat helicopter. I think until it is running the question will remain un-answered, although ideas for go-karts, jet-boats, and hovercrafts have been tossed around.
What would you build if you had a jet engine?