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Making a 3 blade prop? Possible?

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Old 12-13-2006, 03:13 PM
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wc524
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Default Making a 3 blade prop? Possible?

I am thinking about taking some NX props that have been given to me and broken by me and making one 3 blade prop from three halves. I know that rigidity structure to eliminate failure is a must. The center hub is all intact on every half, so it is a matter of lining them up.

First I would need to make some sort of interlocking between the three halves that would set the spacing at 120 degrees.

I like making things, even if it just hangs on my wall I would like some input as to how you would do it. Much appreciated.
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Old 12-13-2006, 04:00 PM
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Gremlin Castle
 
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Default RE: Making a 3 blade prop? Possible?

Yes it is possible to make them into a single three blade unit. The biggest question is whether you have the skill and the materials to make anything other than a display prop. We have a local builder that has made a lot of 6 blade props for a special application on blimps that use 75 to 150 cc motors. They use aircraft grade plywood hubs and pin as well as epoxy the blades into a sandwich between the hub discs. I have seen one of their props with broken blades but nothing was broken free at the hub area.
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Old 12-13-2006, 05:00 PM
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dennis
 
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Default RE: Making a 3 blade prop? Possible?

A friend of mine made the first DC3 from Ziroli pre production plans years ago, like in the 80's. he even got to be in a Hot Stuff glue add in the magazine. Now to the point. The plane needed 3 bladed props and at that time there simply wasn't any for Quadra 35 sized motors.
I helped him with them but basically it involved cutting 3 blades at the hub to fit into a triangle pattern, this must be done precisely so that when they join the prop hole is exactly like the hole on an unmodified prop. Next they had a slot milled into the centers of each blade and in effect an epoxy impregnated hardwood biskit was used with copious amounts of very slow drying epoxy to join the three blades. Please do not use modelling glues to assemble one of these things, failure is a real option if you do. These were clamped in a fixture to maximize compression to the joints.Next the props had front and back discs glued under pressure and when dry the 3 blabes were pinned throught the front, center, and back discs.
Finally the blades were really balanced well. I need to add that before this started you have to really pick out your blades for weight and composition, in other words weigh each one before you even consider using it.
The plane flew really well, the props worked perfectly, RPM was never over 6400, it flew realistically at half throttle and the planes weight was enormous due to a heavy hand on the finish. The plane was sold for a movie project and that was the last I ever heard of it. Oh what size prop was it, as I remember it was made from Zinger 16inch blades
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Old 12-13-2006, 06:04 PM
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wc524
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Default RE: Making a 3 blade prop? Possible?

I am going to try three NX 23x8 prop halves, but after looking at many prop recommendations there is no such thing as a 23x8 three blade. I wonder how it would perform on my DA-50. I'm going to keep coming up with designs of interlocking and go from there. I would be using West Systems Epoxy by the way and the front and rear disc idea is wonderful thanks Dennis!!!
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Old 12-14-2006, 06:39 AM
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Pelle Gris
 
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Default RE: Making a 3 blade prop? Possible?

As far as I know, the multiblade props from Zinger is only held together between to aluminium discs by 2 bolts each? No glue, pins or anything?
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Old 12-16-2006, 07:49 AM
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Default RE: Making a 3 blade prop? Possible?

Here is a link to a site that has all of the info you'll need to build a full scale prop. The section on joining the blades at the hub should be helpful.

http://www.canardzone.com/members/Ph..._propeller.htm

Regards,
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