Building molds for CF props?
10-23-2004, 07:19 AM
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Building molds for CF props?
To anyone with experience building CF props.
I am building a mold for prop blades. I have the prototype prop and I'm going to pour the molds around it. I am looking for recommendations for inserting the epoxy and venting air to avoid voids in the finished prop. Do I just lay the tow in, close the mold and pour in the epoxy? Do I wet the tow and close the mold to squeeze out the excess?
I can alter the mold in the construction phase easier than after completion.
I am building a mold for prop blades. I have the prototype prop and I'm going to pour the molds around it. I am looking for recommendations for inserting the epoxy and venting air to avoid voids in the finished prop. Do I just lay the tow in, close the mold and pour in the epoxy? Do I wet the tow and close the mold to squeeze out the excess?
I can alter the mold in the construction phase easier than after completion.
10-23-2004, 12:24 PM
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RE: Building molds for CF props?
[link=http://www.rcuniverse.com/forum/m_1758546/anchors_1758546/mpage_1/key_/anchor/tm.htm#1758546]Pics of scale carbon blades[/link]
Have you seen this thread? SCALECRAFT might know how to answer your questions.
Juice
Have you seen this thread? SCALECRAFT might know how to answer your questions.
Juice
10-24-2004, 09:49 AM
#5
RE: Building molds for CF props?
Hi, my 2 cents
I will assume you know how to mold a basic fuse.
The molds are basically the same as a two piece female glass reinforced mold.
The trick is configuring composites to keep the blades from flying apart in flight. Also to have effective airfoil design,....... and for your application of RPM, engine size, power, ect. In my case, I am looking for smooth scale flight. The prop shaft mount is solid.
Balance will also be an issue. Layup as equal in materials as possible.
I shall post pics of what I have so far. The blades you will see are hollow scale 9" Me 109F/G blades for a 3 blade gear down system. All hand made with basic low tech practice. The full arc of the blades are 22". The pitch can be varied manually.
These are the weakest set made to see what stress the basic material can take. I can always make solid ones as offered out there .
I will try to post pics of my engine starting idea later today. Hopefully.
Hope this helps and good luck
Steve
I will assume you know how to mold a basic fuse.
The molds are basically the same as a two piece female glass reinforced mold.
The trick is configuring composites to keep the blades from flying apart in flight. Also to have effective airfoil design,....... and for your application of RPM, engine size, power, ect. In my case, I am looking for smooth scale flight. The prop shaft mount is solid.
Balance will also be an issue. Layup as equal in materials as possible.
I shall post pics of what I have so far. The blades you will see are hollow scale 9" Me 109F/G blades for a 3 blade gear down system. All hand made with basic low tech practice. The full arc of the blades are 22". The pitch can be varied manually.
These are the weakest set made to see what stress the basic material can take. I can always make solid ones as offered out there .
I will try to post pics of my engine starting idea later today. Hopefully.
Hope this helps and good luck
Steve
10-24-2004, 10:14 AM
#6
RE: Building molds for CF props?
By the way to answer your layup question.
Unidirectional tow will not work well. Use a weave. I think used 5.8 oz plain weave in two layers to the tip and four layers extending up from the porp shaft to aprox 25% of the full length of the blade. at the base of the shaft I have a plastic straw placed in the mold before closing to allow drops of CA to reach the tips for balancing and adding minimal weight and no external evidence of balancing.
Now these are hollow, i may be wasting my time but I know solid works.
In a solid configuration, you layup your material "packed in" and saturated with resin and clamp the molds together to remove resin not needed.
Your mold must have exits for the resin to escape and must be relativly strong (thick).
On my blades, If hollow doesn't work, I have light weight urethane resin (similar to alumilite) I will pour in to keep the blade sided from colapsing inward and failing.
I have not made a solid blade yet, This is info from a gentleman that makes his own solid carbon blades.
Steve
Unidirectional tow will not work well. Use a weave. I think used 5.8 oz plain weave in two layers to the tip and four layers extending up from the porp shaft to aprox 25% of the full length of the blade. at the base of the shaft I have a plastic straw placed in the mold before closing to allow drops of CA to reach the tips for balancing and adding minimal weight and no external evidence of balancing.
Now these are hollow, i may be wasting my time but I know solid works.
In a solid configuration, you layup your material "packed in" and saturated with resin and clamp the molds together to remove resin not needed.
Your mold must have exits for the resin to escape and must be relativly strong (thick).
On my blades, If hollow doesn't work, I have light weight urethane resin (similar to alumilite) I will pour in to keep the blade sided from colapsing inward and failing.
I have not made a solid blade yet, This is info from a gentleman that makes his own solid carbon blades.
Steve
10-24-2004, 11:26 PM
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RE: Building molds for CF props?
What size props are you looking to make? My website on prop molding may be of some use: http://members.cox.net/davidfee/PROPS.html Unless you plan to do vacuum-assisted resin transfusion, the carbon should be wet-out before being placed in the mold/before the mold is closed up. Details will depend on your flavor of prop.
-David
-David
10-25-2004, 09:56 AM
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RE: Building molds for CF props?
I am making single blade replacements for a variable pitch hub. The manufacturer's replacement blades are nylon and too small a diameter. I intend to use a 14" diameter plan form. Each mold is only 7"long and about an inch and a quarter wide. I am using an existing CF prop for the master but altering the center to fit. A steel stub shaft is molded into the blade to attach the hub. Because of the accuracy needed I built a fixture as part of the mold to orient the shaft to the blade pitch.
This is an engineering experiment not for general consumption. After construction the blades will have to undergo lab/destructive testing. Use will be very limited and only intended for private use.
This is an engineering experiment not for general consumption. After construction the blades will have to undergo lab/destructive testing. Use will be very limited and only intended for private use.
