I have previously built a 3 bladed prop (E- fiberglass with a fir core)
which I have flown for 1100 hrs. A good climb prop which still is VERY fast. It
is for sale for $1000.00Page 1: Prop building using a foam core (1/20/02)
Home Previous Page Next Page FAQ Results
My prop building thoughts
I have previously built a 3 bladed prop (E- fiberglass with a fir core)
which I have flown for 1100 hrs. A good climb prop which still is VERY fast. It
is for sale for $1000.00
I decided I wanted to try building a more efficient, lighter and hopefully faster prop. I strongly believe for the average guy, building a 2 blade prop is the only way to go. The 3 blade prop was very difficult to construct, align and balance properly. I felt there had to be a better way to build your own prop. Probably, the overriding reason I am building the prop is for safety reasons. After 2 engine failures, I want a better glide ratio.
When I put my wood prop was put on the plane after my engine overhaul, I carefully balance it and found it to be quiet and very smooth. BUT, on the flip side, I am very nervous flying with any wood prop because the prop's failure mode is very destructive to itself (and you).. The prop tends to fly apart. Been there, don't like it.
What left of my wood prop when part of it decided to part company from the plane on a long cross country trip. This experience has made me wary of wood and started my quest for a fiberglass prop.
The chunk of the blade went though the right rudder tearing it completely off. This necessitated an emergency landing on a 2 lane highway due to excessive engine vibration. The plane had to be disassemble and moved across the country in a U-Haul truck.
Just think about it, outside of experimental aviation there are few planes that use wood props.... I haven't seen any new production planes with wood prop. There must be a reason. Although wood props don't fail often, they do fail. I don't ever recall a metal or composite prop ever failing.
Glass props on so strong and overbuilt I don't think anything could destroy them. After 1100 hrs on my 3 blade I have the utmost confidence in the reliability of a glass props which I don't get with a wood prop. The 3 blade has a safety factor (SF) of 5. Also, consider the failure mode. The glass fibers will try and hold the blade together giving you plenty of warning to land the plane. The only time I have ever heard of a composite prop failing, the builder did not add enough strength at the hub and the movement of the blades basically heated up the blade root causing the epoxy to bake out of the glass. He notice a vibration, landed, and the blades just flopped around still attached to the hub by the strands of glass. Lesson learned: make sure the hub area is strong so flexure is distributed throughout the entire blade and is not localized at a connection point. . For this current prop design I decided to build it out of carbon graphite with a foam core. The shell provides all the strength so the core (wood, foam, air, etc ) really doesn't do anything other than provides the shape for the carbon glass. This Prop Optimizer Advanced program reports the prop will have a safety factor of eight ( SF=8) plus I am adding some Kevlar in the lay-ups (2 layers) for added strength if carbon has a problem. I am sure the SF will be about 10 when completed and will only weigh approximately 5 lbs.
I utilized Bates Engineering Prop Optimizer Advanced program for the design of the blades. I have included the prop design output. so you can see the starting point of the design. I then took the Prop Optimizer Advanced output, converted it to AutoCAD for the blade profiles and helix templates.
When I finish the AutoCAD drawings I will post them here.
The prop pro program indicates I should get 174 mph out of this prop. It would be remarkable because my AmarDemouth prop only goes 162 mph at max throttle (7000 ft), which is outstanding given the small engine(108 hp) in my plane.
This prop will be constructed utilizing a wood hub (poplar), foam blades and a carbon graphite skin. I used 2 lb foam (the type you use in the wing so I could hot wire cut it). The skin is calculated (from Prop Pro) to be 0.1194" thick (about 12 layers of carbon per side).