Centrifugal Turbojet

[william]

Hello all,

Some background on me.
I'm currently a mechanical engineering student, married, and recently separated from the Air Force where I worked as an Avionics Technician. Currently working as an autopilot integration "engineer" for smallish UAVs. My interests are, UAVs obviously, and aircraft propulsion. So it's no wonder that I'm combining the two into my next project.

So, I've recently begun this fun little big project. I'm going to be building a centrifugal turbojet. Looking at using an 4" exducer for the compressor and trying to get 35-40lbs of thrust. I'll be focusing on optimizing the fuel efficiency. I currently have a SolidWorks assembly made, but it's really only meant to give me an idea of how everything is going to be designed. Before I do a redesign (which will really only be tweaking what I currently have) I'll be doing math to find out what exactly I need, to get the thrust I want. This is the step I'm on now. Also, the only components, beside hardware, I'll be buying is the impeller and the turbine. Everything else is going to be designed by me and machined on a fancy schmancy cnc. Then it'll be on to the 3D printer so I can make sure everything fits and works like I meant it to. After all that I can take it to the the machine shop.

I'm building this to put on an RC plane (that I am also designing and will be autonomous at some point). So I'll end up posting all that stuff too, if it's allowed here. Because of this, the goal is to make the engine as light as possible with the best fuel efficiency possible.

Thoughts?? You guys know better than me. Ask me questions! I don't know what I don't know, so I need some guides to make sure I've at least thought of everything.


P.S. I'll post some SolidWorks screenshots later today.

[racket]

Hi William

35-40 lbs of thrust is getting down to model levels where we don't have a great deal of experience .

The main thing for good fuel efficiency/thrust is the comp wheel/stage efficiency , so much energy is required during compression that has to be provided by the turbine that theres more left over if the comp works even a tad more efficiently .

May I suggest you join the GTBA www.gtba.co.uk there is a massive amount of information available on Site and some very experienced builders to help out , I've been a member on and off for many years , well worth the small membershp fee

Also have you got Thomas Kamps excellent book au.trapletshop.com/model-jet-engines-3rd-edition-by-thomas-kamps

Cheers
John

[william]

racket

Aw, that's unfortunate. However, I'm sure you guys will still be a ton of help.

That association looks great! Too bad I have to pay but I can't get quality without paying and $30 for the first year isn't much compared to what the total cost of the project will be. Glad you showed me them!

I don't have the book yet but I do plan on getting it. I saw some others on here recommend it and its cheap enough that it's fine even if it doesn't teach me much (Though I'm sure it will).

Thanks!

[racket]

Hi William

We'll still be able to give you "constructive criticism" on anything that doesn't feel right , but the GTBA is more into aero type engines rather than our larger more "heavy duty" ground based ones , they both have the same theory , but slightly different construction methods , you'll get the best of both worlds :-)

Thomas' book has some good basics for a project like yours , but there are a few shortcomings for us guys who use higher pressure ratios as well as radial turbines , but we can't have too much information, theres little snippets found in the most unlikely places that can be invaluable .

There are other jet engine construction books at the Traplet online shop as well , I think I have 4 different ones , Schreckling is the author of some of them

Cheers
John

[smithy1]

Hi William,
As John mentions....40lbs is getting down to model aircraft size....strangely enough I have a 40lb turbine fitted in a 1/4 scale miniature jet dragster...John has seen this thing run a few times..! It's full after-burning/reheat too but I doubt you'd need that...They can be bought for ~$4000USD ready to run.....but I suspect you're wanting to build one yourself...

A 4" exducer will be more than ample for your requirements...

Cheers,
Smithy.

[william]

racket
Reading the book now. It's exactly what I needed. It's no wonder its so recommended in this community.

smithy1
You are correct. The point of the project is for me to design, build, and test it. I'm sure after all is said and done I will have spent nearly that amount, without even considering the time spent but I think its worth it. Also, good to know that it's plenty big. Doing the math right now, so I'll scale it down as needed.

[racket]

Hi William

Yep , its a good book to get the basics from .............LOL, then it more complicated ;-)

Cheers
John