Marshall Brain Answered: This is one of those things that might be easier to buy rather than to build, because the manufacturing tolerances are demanding. A gas turbine spins at a very high RPM level so it has to be perfectly balanced, and the temperatures at the exhaust end are extreme. See How Gas Turbine Engines Work for details.

If you want to buy a small gas turbine engine, this page can be helpful: Small jet engines

But if you want to pursue the DIY option, many people get started in gas turbine creation using an old turbocharger from a car. These devices have several advantages: 1) they are already balanced for high-speed operation, 2) they have all the details for longer-term reliability worked out (in particular, the lubrication system), and 3) they are made of materials that can handle high exhaust temperatures.

A basic jet engine has three parts: a compressor, a combustion area and the turbine. With the turbocharger you get the compressor and the turbine. You then need to take the air coming out of the turbo's compressor and build a combustion section. Then you route the exhaust from combustion into the turbine side of turbo.

Here's a fairly advanced example of a turbocharger engine:

The builder says:

Heres my Cummins ST50 based gas turbine. I built this after building a couple of "traditional" turbocharger based jets. I removed the cast iron scroll and fabricated the turbine shroud, nozzle guide vanes and all the other combustor components from 321 and 304 stainless. Sorry guys, I dont have plans drawn up for it. I did one pull test with it using a furniture dolly and fish scale.. probably not the most accurate method but still managed about 60lbs. It currently runs on propane. The oil pump is a 12v Flojet 2100-869 (dultmeier.com). Next on the list of things to do is to install the oil cooler and fan kit, and finish the swap to kerosene.

The main problem with an engine like this, compared to something you might buy, is the weight. But it would get you started.