MakerGear Forum

Hello all,
I was recently contacted with a request to print scale turbofan engines for a radio controlled Boeing 737! I have been flying rc for 20 years and I love 3D printing so I couldn't turn down the chance!

Basically will be printing an 18 bladed fan that has a 150 mm diameter that will be spinning in excess of 50,000rpms!
The problem some people are having is the fan coming apart at high speeds (of course!).

Can anyone suggest a super high strength material to use? Are there any other ways to add strength to the finished part?

Maybe a different method of manufacturing the part is needed? Thanks in advance everyone. I am not going to take on this project if I can't do it safely!

Being into RC, I find this interesting.
I've seen only one high rpm application.
http://www.thingiverse.com/thing:76369
there may be others. that was done in pla.
though I know there's even carbon fiber materials now.

Thats alot of speed. Not sure if your going to find anything that is going to hold up but if i was doing it i would try either esuns epc or colorfabb carbon fiber filled xt

On the surface it sounds like an interesting job.

One thing to consider, with a 150mm diameter fan spinning at 50,000 rpm your blade tips will be traveling at 706,858 Km/hr or 439,221 miles/hr.

helifrek wrote:18 bladed fan that has a 150 mm diameter that will be spinning in excess of 50,000rpms

Mmmm, the centripetal acceleration at the blade tip will be on the order of 800,000 G, an environment not well-suited to plastic parts:

a = v^2/r = (0.15 x 2π x 50x10^3 / 60 )^2 / (0.15 / 2) = 8x10^6 m^2/s → 800x10^3 G

You can certainly print such a thing, but my money says it's not going to work. The design needs a lot more engineering to make it workable.

The acceleration goes up as the square of the rotational speed; if the fan doesn't rotate at the same speed as the compressor turbine, that would help a lot.

If engineers didn't absolutely have to use single-crystal supermetals in turbine blades, they wouldn't:
https://en.wikipedia.org/wiki/Turbofan# ... technology

Background math:
http://www.spaceflight.esa.int/impress/ ... lades.html

Print it out of whatever you want, balance it, then cast it in something like TASK-2.

Thanks for all the info and help everyone. The Turbofan blades Max RPMs should not exceed 50K, They will be attached to an electric motor for a scale rc airplane, not an actual turbine!!! I know there are a lot of plastic ducted fans out there but I couldn't tell you the rpms or anything on them, I will have to look it up. I have tried to contact a place that does metal 3D printing to find out how much that would cost. I was also thinking about finding someone with a Formlabs printer an try the new tough resin. I have printed a test set of blades from a file on Yeggi, the problem is the blades are so thin that it is hard to get a solid blade to come out, so they end up being a little weak, I wonder if a solid blade from tough resin would be any stronger.....

I also though about casting the turbofan, I have never casted anything but I would like to learn! Been watching youtube videos on casting aluminum and it looks pretty straightforward.

helifrek wrote:Thanks for all the info and help everyone. The Turbofan blades Max RPMs should not exceed 50K, They will be attached to an electric motor for a scale rc airplane, not an actual turbine!!! I know there are a lot of plastic ducted fans out there but I couldn't tell you the rpms or anything on them, I will have to look it up. I have tried to contact a place that does metal 3D printing to find out how much that would cost. I was also thinking about finding someone with a Formlabs printer an try the new tough resin. I have printed a test set of blades from a file on Yeggi, the problem is the blades are so thin that it is hard to get a solid blade to come out, so they end up being a little weak, I wonder if a solid blade from tough resin would be any stronger.....

I also though about casting the turbofan, I have never casted anything but I would like to learn! Been watching youtube videos on casting aluminum and it looks pretty straightforward.

Not sure about the tough resin but you might like to look into a smaller nozzle if the blades come out badly with the standard nozzle. With a .25 nozzle you will be able to squeeze more outside perims into a smaller space resulting in a tougher blade. Also printing at a very low resolution .10 etc will help increase toughness.

Can't talk to materials but it seems like this might be a good application for some of the nylons or the CF material. There was a thread floating around somewhere on here about someone printing in CF and it listed the settings used.

I was curious about using a smaller nozzle, I also have my extrusion width set to .40 so maybe lowering it to .35 could help....

I have been wanting a smaller nozzle to try some higher resolution prints anyways.

The price on the resin printer that I have been looking at dropped from $1480 to $850 so I might pull the trigger on it and order some tough resin. The price drop could also be a bad thing if you think about it though..... I guess I won't know unless I try.

ednisley wrote:a = v^2/r = (0.15 x 2π x 50x10^3 / 60 )^2 / (0.15 / 2) = 8x10^6 m^2/s → 800x10^3 G

With nothing better to do this evening, I saw this and decided to check your math, Ed.

Circumference = diameter x pi, It should be 0.15 x π etc., no? I then get a force of ~200k G.

Helifrek, you can get a bunch of printed metal parts from Shapeways for that much money. Then again, I own an M2 for no good purpose other than to play around with, so I totally understand the compulsion.

Which model are you trying to print? I've seen some 3D printed fan-type things on Thingiverse spun up with a Dremel. That's under half of your proposed rpm, though. Plus, I imagine that when it fails it would do so in a spectacular fashion; wear eye protection.