The One Man Turbofan

[azwood]

I need to get me a 3d printer they are becoming cheap these days I did a little solidworks years ago it’s a great time to be a hobbyist.

[turboron]

azwood, I like FreeCad software. It is free and has been underdevelopment for several years. Also, it is parametric(like Unigraphics) which is what the big boys use to design their gas turbines. Parametric software makes it easy to scale or redesign drawings since a change in one dimension changes all the other dimensions automatically. Its files work directly with 3D printing and machining.

Thanks, Ron

[monty]

Jan 4, 2019 1:11:25 GMT -5 Johansson said:

Monty, I am very interested in your progress with the RPM casting! As you might know I am casting a bit myself and if there is a method for us hobbyists that produce better/easier castings than the green sand or lost PLA I am all ears!

Anders,

The absolute easiest thing I found was sodium silicate bonded silica sand. The only problem is the surface finish is a bit rough for small castings since you have to use a coarse sand so CO2 can be passed through it. I never did get around to trying silica flour over the part to improve the surface finish, but it might be worth a try. It's like magic, especially for making cores. You mix in a little bit of sodium silicate with the sand (water glass) and pass CO2 through the core. It hardens into sand stone. You can bake the core or mold to make it even more durable. You can get sodium silicate from a pottery or foundry supply. the only drawback is the sand gets thrown away.

I also have some green sand and forms. It's about the easiest way to get good quality quick castings as long as they are relatively simple. The 3D printer (aka mechanical slave) makes pattern making a breeze!

But for difficult complicated castings where die cast quality parts are the desired outcome....can't beat the RPM process for our purposes. Here is a pic of the surface finish you can get. This casting needed a bigger gate, and a riser over the pin bosses, but it shows the surface finish achievable.

Another miracle thing I discovered is using a casting filter. It prevents dross from getting into the part, and makes the gating arrangement much simpler. Here is a cross section of a big diesel piston with one of my castings inside it. Look at all the dross in the commercial piston vs my casting!!

I'll be using this process for the turbofan castings. It was actually all the things that I learned while trying to cast an aircraft quality piston that convinced me the turbofan was doable.

Monty

[monty]

Jan 4, 2019 3:55:43 GMT -5 azwood said:

I need to get me a 3d printer they are becoming cheap these days I did a little solidworks years ago it’s a great time to be a hobbyist.

Hi Azwood,

Yep....can't live without it anymore. I just bought one for my nieces and nephews. It was only about $250. I like the Creality brand for bang for the buck. Get a glass bed...

I wouldn't mess with Solidworks. I have it at work, but only use it if I absolutely must. Too expensive and the menu structure is getting to be a nightmare! The only thing Solidworks has going for it is the analysis package, but that is going to be beyond most hobby users. I use Alibre, which has an inexpensive hobby version. A lot of people like Fusion 360.

Monty

[monty]

Jan 4, 2019 8:01:56 GMT -5 turboron said:

azwood, I like FreeCad software. It is free and has been underdevelopment for several years. Also, it is parametric(like Unigraphics) which is what the big boys use to design their gas turbines. Parametric software makes it easy to scale or redesign drawings since a change in one dimension changes all the other dimensions automatically. Its files work directly with 3D printing and machining.

Thanks, Ron

Hi Ron,

I've got literately thousands of hours of time using Unigraphics (now Siemens NX). It was hands down my absolute favorite CAD package. Once they started going down the sketcher route it started getting out of hand. Still an extremely powerful package that can do almost anything. Unigraphics and Catia are the ones to use if you need to do something really big like an airliner or an automobile. But for us little guys the lower end packages are getting to be quite powerful! I use Alibre, and I'm pretty happy with it. I'm tired of learning new interfaces at this point...so they keep getting my money. Fusion 360 seems to be the up and coming thing, but I don't like working in the cloud. Guess I need to get over that.

Monty

[monty]

Jan 3, 2019 12:39:28 GMT -5 pitciblackscotland said:

Yes i did see that very large engine,good that you have some other interest. I have a couple of Sachs Wankel engines that i am playing around with and slowly working on a 12A single rotary engine.

Mark,

That little Sachs Wankel has always fascinated me. IMHO the Wankel still has some possibilities. Especially with amateurs being able to make castings the way we can now. The development will have to be done by the hobby crowd though.  I was really hoping Mazda was going to make that all aluminum 16X....oh well. I used to have a Renesis project. Sold it to a friend after I bought my biplane. He should be getting close to flying with it soon. 

Monty

[turboron]

Monty, thanks, I had not heard of Alibre before. My Google search indicated a price of $1,000.00 for the Professional version. FreeCad is free and has been greatly improved over the last few years. It runs on Windows and Linux. Like you I was "trained" on Unigraphics/Siemens NX. I never used it enough to get good at it.

Your work is very inspiring to us DIYers.

Thanks, Ron

[monty]

Jan 4, 2019 12:42:51 GMT -5 turboron said:

Monty, thanks, I had not heard of Alibre before. My Google search indicated a price of $1,000.00 for the Professional version. FreeCad is free and has been greatly improved over the last few years. It runs on Windows and Linux. Like you I was "trained" on Unigraphics/Siemens NX. I never used it enough to get good at it.

Your work is very inspiring to us DIYers.

Thanks, Ron

Ron,

Likewise on the inspiration. What you guys are doing on here made me think....hey...I can do that! I had given up on the turbofan as too complex a while ago, but things have gotten better in the hobby realm.

I used to do product design for a living, so the CAD package was a necessary cost of doing business. The combination of Alibre and Rhino will do literally anything you want for a total cost outlay of $2K. Solid works makes that look cheap! and I can do things with surfaces in Rhino that would make Solid works puke...

But for hobby use the professional version of Alibre is probably overkill. They have a lower cost hobby package. Not sure what the specifics are. RE FreeCad..eventually the low to no cost stuff is going to get there, or may already be there. I just don't have the energy to learn another user interface at the moment. I have so many legacy parts and designs that I need to still have access to. Plus I'm FAST in these packages because I've used them so much. I'm sort of locked in for the moment, but when the next license renewal comes around...who knows.

Monty

[monty]

The oil tank arrived in the mail today...

[monty]

Racket and Anders,

Do you guys think 2 quarts will be enough oil capacity? I can get a gallon size too. It's a bit larger than I'd like though. Planning to run an air oil separator above the tank. I'm also wondering whether I can combine the two return lines to the scavenge pump. Typical practice is to have a scavenge line for each return...but less is more in this case.

Monty

[racket]

Hi Monty

If you can increase the capacity by having bulky oil lines, cooler, separator etc etc it might be a substitute for a larger capacity tank.

I'd keep to separate lines on the scavenge .

Cheers
John

[turboron]

Monty, oil system design practice for rotating machinery oil tanks is to calculate the retention time to size the tank. Retention time is the size of the tank divided by the oil flow rate. An industrial system would have a time of 6 minutes whereas an aircraft tank would be about 1 minute. The industrial system uses an aeration plate to separate the air and oil where as the aircraft gas turbine uses a centrifugal air oil separator.

As John says, a significant amount of oil is "hidden" in the lines, separators and coolers during operation. You can include this amount in your retention time calculation.

Typical gas turbine practice is to use separate scavenge elements for each sump. A gyrator pump works well for this application because you can have the pressure element and the scavenge elements in the same compact package. Auto racing supply house may be able to provide these pumps. I think auto racers use them for dry sump setups.

Thanks, Ron

[CH3NO2]

Monty,

If you can pull this off that would really be something. Good power density with exceptionally high fuel specific impulse.
Ditto like John said, there will be lurkers viewing this thread.

Two Thumbs up.
Tony

PS

[monty]

Jan 4, 2019 18:08:48 GMT -5 turboron said:

Monty, oil system design practice for rotating machinery oil tanks is to calculate the retention time to size the tank. Retention time is the size of the tank divided by the oil flow rate. An industrial system would have a time of 6 minutes whereas an aircraft tank would be about 1 minute. The industrial system uses an aeration plate to separate the air and oil where as the aircraft gas turbine uses a centrifugal air oil separator.

As John says, a significant amount of oil is "hidden" in the lines, separators and coolers during operation. You can include this amount in your retention time calculation.

Typical gas turbine practice is to use separate scavenge elements for each sump. A gyrator pump works well for this application because you can have the pressure element and the scavenge elements in the same compact package. Auto racing supply house may be able to provide these pumps. I think auto racers use them for dry sump setups.

Thanks, Ron

Ron,

If only I knew what those numbers are!! All I know Is I've got a single sleeve bearing, two rolling element bearings, and 4  oil jets for the gear mesh. Most of the car stuff is way too big. I'll probably make my own oil pump like Andy. So far I have a -6 oil supply line to the whole engine. A -8 return from the main case, and a -6 return from the sleeve bearing in the diffuser. I can tune the oil jets to the roller bearings, and the gear meshes.

I really didn't want a 3 stage pump...but if you guys think I need it....that's what I'll do.

Monty

[monty]

Jan 4, 2019 17:51:46 GMT -5 racket said:

Hi Monty

If you can increase the capacity by having bulky oil lines, cooler, separator etc etc it might be a substitute for a larger capacity tank.

I'd keep to separate lines on the scavenge .

Cheers
John

John,

Maybe I'll order the 1 gallon size and shorten it a bit to around 3 quarts....

noted on the oil lines.

Monty