The One Man Turbofan

[monty]

Jan 4, 2019 22:50:34 GMT -5 CH3NO2 said:

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

Tony,

Well that all remains to be seen....and I'm not so sure about the fuel specific impulse part..It's better than a straight turbojet for sure, but nowhere near a proper two shaft solution, or a recuperated turboprop like Mdot makes. But I appreciate the sentiment

Monty

[azwood]

Jan 4, 2019 11:07:39 GMT -5 monty said:

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

I need one I’m sick of makeing things and remakes a few times when I could print them

[monty]

I ran some quick numbers on oil flow and I'm getting closer to .8-1 gal/min. I don't expect there to be that much capacity in the lines and cooler, so looks like I'll be ordering the larger tank. I'm sure I can find a use for the other one!

On a positive note I think I figured out how to incorporate the scavenge for the bushing into the main engine scavenge. I will probably have to re-make the compressor seal bushing into an oil slinger to make it work. This will really simplify the oiling system. I won't need a scavenge stage on the oil pump at all. The ring gear will be the main scavenge pump. That will feed into an air/oil separator and then to the tank. From there to the pump/filter unit, a fuel/oil cooler, and back to the engine.

[monty]

Jan 5, 2019 4:57:07 GMT -5 azwood said:

I need one I’m sick of makeing things and remakes a few times when I could print them

Indeed! If I had to make the patterns for this thing by hand...there is no way I'd be doing this!

CAD, CNC, and 3D printing are what makes this even possible.

Monty

[turboron]

Monty, if you are using the ring gear as a scavenge pump you should consider a tangential offtake to get the oil out of the housing.

Thanks, Ron

[monty]

Jan 5, 2019 10:32:07 GMT -5 turboron said:

Monty, if you are using the ring gear as a scavenge pump you should consider a tangential offtake to get the oil out of the housing.

Thanks, Ron

Ron,

I would love to make that happen, it was my original intent. Unfortunately that is incredibly valuable real estate. everything is vying for it. Airflow, gear-train and structures won out. If needed I'll add a scavenge stage to the oil pump. That's my back-up plan.

Monty.

[turboron]

Monty, I have been in this corner many times. Somehow we always find a compromise that works. Can you fit a baffle to help the cause?

Thanks, Ron

[Johansson]

Jan 4, 2019 10:51:07 GMT -5 monty said:

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

Thanks a lot Monty for this, my electric furnace has burned out its heating coils at the moment but I have ordered replacements so hopefully I will have my casting shop up and running again soon.

I´ve tried the core sand stuff when I made the first version of the shaft tunnel but I ended up casting a solid chunk of alloy instead since it was easy enough to drill it out.

I will absolutely try the RPM method out some day, for those more challenging castings it seems like a good choise.

/Anders

[monty]

Jan 6, 2019 14:57:27 GMT -5 turboron said:

Monty, I have been in this corner many times. Somehow we always find a compromise that works. Can you fit a baffle to help the cause?

Thanks, Ron

Ron,

Here is the pickup for the oil return. I'm going to add an extension to the rib behind the gear that gets machined to a close tolerance. This will form a baffle that strips the oil off at the outlet. I'll also clean up and contour the inlet to the return with a die grinder to be as close to tangential as I can get. Hopefully this will be sufficient to push the oil out.

Worst case, I'll add a scavenge stage to the main oil pump.

Monty

[monty]

Jan 6, 2019 15:13:16 GMT -5 Johansson said:

Thanks a lot Monty for this, my electric furnace has burned out its heating coils at the moment but I have ordered replacements so hopefully I will have my casting shop up and running again soon.

I´ve tried the core sand stuff when I made the first version of the shaft tunnel but I ended up casting a solid chunk of alloy instead since it was easy enough to drill it out.

I will absolutely try the RPM method out some day, for those more challenging castings it seems like a good choise.

/Anders

Anders,

I'll post more on it when I get to making the forms and molds. I'm jealous of your electric furnace. I need one. It would be really nice to just set the temperature and get the molds set up once the metal gets close. I could also put an argon blanket on it so I didn't have to worry about hydrogen being absorbed by the melt. Plus I can pour in my shop so the weather isn't a factor. Right now I feel like a one armed paper hanger trying to get everything to arrive at the right temperature at the same moment in time..

Monty

[turboron]

Monty, your design should work okay if the oil flow is limited. Aircraft gas turbine practice is to squirt limited oil into the mesh under pressure. Industrial is just to have a lot of oil fall onto the mesh. If you could provide for an changeable oil supply orifice it would allow you to strike the best comprise.

Also, it looks like you have the room to design a small udder around the top of the drain to help the cause and create a small gravity head.

Thanks, Ron

[monty]

Jan 6, 2019 18:13:47 GMT -5 turboron said:

Monty, your design should work okay if the oil flow is limited. Aircraft gas turbine practice is to squirt limited oil into the mesh under pressure. Industrial is just to have a lot of oil fall onto the mesh. If you could provide for an changeable oil supply orifice it would allow you to strike the best comprise.

Also, it looks like you have the room to design a small udder around the top of the drain to help the cause and create a small gravity head.

Thanks, Ron

Ron,

Like this??

All of my oil feed galleries have these little stainless grub screws so I can calibrate the oil flow to each.

I can orient the housing so that it forms an udder.

Monty

[turboron]

Monty, yes that is what I was suggesting on the udder. It needs to be on the bottom for gravity drain. I suggest you start with the lowest oil flow that you are comfortable with and increase the size in steps until you see signs that you have achieved your maximum feasible flow then back off one step. Oil systems are very tricky as you probably know. The individual grub screws are an excellent idea that will allow you to dial in the system.

Thanks, Ron

[monty]

Jan 6, 2019 21:11:05 GMT -5 turboron said:

Monty, yes that is what I was suggesting on the udder. It needs to be on the bottom for gravity drain. I suggest you start with the lowest oil flow that you are comfortable with and increase the size in steps until you see signs that you have achieved your maximum feasible flow then back off one step. Oil systems are very tricky as you probably know. The individual grub screws are an excellent idea that will allow you to dial in the system.

Thanks, Ron

Ron,

The only way I know to calculate the oil flows is as follows:

The journal bearing is relatively straight forward using typical formulas. Assuming you know the loads...which I don't.

The gear mesh I will calculate the oil flow based on carrying away the heat load from an assumed efficiency.

The rolling element bearings....I have no idea, except it doesn't need to be much.

Of course I need to decide which viscosity oil and pressure to use....

Monty

[monty]

Made a little progress today. I started on some gear blanks for the ring gear. I've managed to take some weight and diameter out of the gear by optimizing hoop stress, bending stress, and heat treat. I did some serious pencil sharpening on the gears. I didn't have to shift the pinion addendum. I have room in the design to increase the factor of safety if needed....but that can wait for version 1.1. The gears currently should have about a 99.5% chance of lasting 1000 hrs....so I'm not going to spend any more time on THAT!

The new 1 gallon oil tank showed up today:

I'm getting close on the castings. Can't wait to start making the forms.

Monty