I have some propellers that I want to copy. I would like to make them out of carbon fiber instead of the cheap plastic that they are made out of. Does anyone have any suggestions?

Thanks,

Jay

I found this link:

[link=http://www.members.cox.net/davidfee/PROPS.html]David Fee's propellor page[/link]

I have read this thing perhaps 10 times or more... It is VERY difficult to figure out what is going on because the prop and the mold are black. I then read this page:

[link=http://www.plasma.kth.se/~olsson/propmold.html]Making a propellor mold[/link]

After reading this I realized that the propellor in David's page was still IN THE MOLD after seperating from the clay. Figuring this stuf out IS going to be hard work....

Does anyone have any tips on doing folding props?

More Propellor Links

[link=http://www.icon.fi/~jtki/prop.html]Simple Method for making a composit propellor[/link]

[link=http://digilander.libero.it/mfer/molds/PMpart1.htm]Propeller Molds [/link]
VERY GOOD LINK!!!!

Jay,
Sorry you find my pictures hard to follow. The mold is that dark brown color because it is steel-filled epoxy. I realize carbon doesn't show up well against it (in photos) but the intent was to make a very strong mold (which they are).

Yes, my prop molds were made in almost exactly the same way as those on your last link, [link=http://digilander.libero.it/mfer/molds/PMpart1.htm]Propeller Molds[/link] .

One thing I have learned since I made my molds is that the steep draft angle on the "male" part of the mold is important. If nothing else, it helps to keep the "guts" in place better when you smash the halves together.

Folding props are made exactly the same way, but you must incorporate a hinge pin in the mold, rather than center hole, for the blade pivot. I've made one folder mold, but I don't have pics... but Marcus posted a great picture on page 7 of his [link=http://www.rcgroups.com/forums/showthread.php?s=&threadid=141255&perpage=15&pagen umber=7]F5B molding thread[/link].

The molds are on the upper right... two separate molds (four halves). The blade materials are on the lower left... carbon tow (probably high modulus) for the blade cores. There is bi-directional carbon for the blade skins, and Kevlar tow for a safety at the root, just in case the high-modulus carbon fractures. Between the fabric skins and the Kevlar tow can be seen the dummy hinge pins used for the molds. At the bottom right is a template for cutting the carbon fabric blade faces.

Once you have the molds, the next trick is figuring out the recipe. Too little carbon and there will be air holes. Too much carbon and the blades will be too thick because the molds won't close. I cheated and used thickened epoxy to bulk up the core... but that is not acceptable for F5B props.

After waxing and PVA'ing the prop molds, wet out the tows and blot them pretty dry. Then apply a thin layer of epoxy (thickened with cabosil) to the blade faces in the molds. Then place the pre-cut carbon fabric pieces into the molds. Finish wetting the fabric out with a bit more thin (non-filled) epoxy, then blot away excess if needed.

Get ready to start laying the tows in whatever side has the hinge pin. It is usually the bottom side. Gather all the tows together (including the Kevlar) and make a single rope. The rope should be thickest at the middle and taper out to the ends. The rope will be wrapped around the hinge pin, if you get my drift. Lay one end of the rope into the bottom half of the mold, so that the thick part is under the hole for the hinge pin. Now insert the hinge pin, making sure that the tows are all captured beneath it. Then fold the other tows over the pin and down on top of the other tows (like the bend in a hairpin). Make sure all materials are where they should be, and then close the mold halves and clamp overnight.

Ta-da!
-David

David,

It was Marcus' thread that piqued my interest in building fully molded ships. Once I realized it was just some guy building surprise 11's one at a time. And I saw the speed and ease(?) Marcus built the ship, I figured I needed to learn how to do this...

You have been of great help. I have a wrecked flash 8 that I am going to mold. But I needed something simple to get started. And I didn't want to waste the end item. So molding props seems to be the perfect solution...

There will be more threads in the "help soho" series....

jay

I understand, and I agree that starting with something relatively simple is a good idea. My first mold was for a S400 racer fuselage. The mold was fine, but it took me some trials to get a usable fuselage... working out the details of layup thickness and how to get the seam right.

For a prop mold, you really need a filled epoxy of some kind. The surface needs to be hard and smooth... so use a "surface coat" or cabosil-thickened laminating epoxy. The bulk of the mold can be filled with anything from steel/aluminum powder to sand to sawdust. You cannot pour that volume of epoxy without filling it with something. It will be weak first of all, but more significantly it will exotherm and boil over... leaving you with a very disgusting mess.

So I don't know which is easier... the prop mold or the fuselage. I have seen some fiberglass prop molds, but they also had very large blocks of aluminum bonded to them... for strength purposes. You need to clamp prop molds together very firmly.

My advice would be to pick something and make a mold from it. Then build some parts. Once you have initiated yourself this way with first-hand experience, each different type of mold you'll see will be a lot more intuitive to you. You will be able to look at something and see exactly how they did it. This takes time...

-David

I understand the inherent danger in building a prop that could potentially expolode or fall a part in flight.

What do I need to look out for?

What portions are likely to fail?

Any other advice?

Thanks,

Jay

When making props it is essential to get the mold fully packed with material. Any cavities in the prop will cause failure. Cavities will sometimes not be visible.

Some suggestions. I always lay up the tow in one side of the mold only. This will ensure that every layer is down on the previous. If you lay up in both halves when the two are put together a big cavity can be created right down the centre of the blade. It is impossible to see what is happening when closing the mold.

I never wrap tow round and round the centre pin. This creates cavities in the hub area. I lay tow from one end of the mold to the other, decreasing in length. I pack the hub with chopped fibres. Again it is easy to see what is going on as you pack more and more material in.

Ity is not easy to estimate the correct amount of material to pack into the mold. The only way to tell is make the first one. If nothing squeezes out you did not have enough material in there. If a lot squeezes out there was too much. It is trial and error. A rough guide can be had by measuring the closed empty mold. It should measure close to the same when fulll and clamped. I lay out the tow on a piece of paper and make notes of how many strands and their lengths, go in to the mold. That way it is easy to adjust up or down for future moldings.

Ed S

Ed,

Excellent. That's what I wanted to read. So the goal is to:

1. Leave no gaps, pores on the inside of the prop.
2. Make sure there is enough material to fill in the mold.

I love this forum... Thanks again...

I just had another thought. When making the prop/plug try and produce a draft angle on the hub either side of the intended split line. My prop molds have square sides to the hub. Very often the prop is difficult to get out of the mold. It is not stuck in, it is wedged in at the hub.

Ed S

Thanks I had every intention of making an angular side to the clay mount...

To be clear, I meant the hub of the actual propeller, before you get to the clay stage.

Ed S

Years ago I published a web page on the topic of molding props. I intended to add pictures as time went on but started too many other projects along the way. The above replies are correct in my opinion but there are many things to watch out for when molding props. The web page listed here is full of text and not enough pictures but might answer some questions.

http://winshipmodels.tripod.com/hi-temp_prop_mold.htm

Dan Winship

Hey guys,

I haven't done props before, and have only read about it in one of the Harry Higley books, so this is interesting. Excellent work, by some guys who are thinking.

Thanks for sharing all the info with us.

For clarity, Jay is talking specifically about a folding F5B propeller. The tow MUST wrap around the pin, or the prop will shed its blades and disintegrate the nose of your airplane in short order. They could maybe hit a person in the process. The pivot/hub area is the most likely area to fail because of the very large stresses.

-David

This is only to inform you that ALL German made model propellers are hollow.
They make the two thin halves, and close the mold with a few rovings in the middle to act as a spar.

Regards

Roberto
www.modelcompositi.com

Roberto,
Many of the large 1-piece props are hollow, but the small ones are not. And the F5B folding propellers are definitely NOT hollow. The hubs are very small, so they need to be solid carbon.

-David

Ok, David, thanks

Roberto
www.modelcompositi.com