TiptoTail

Hello everyone. I'm new to this forum, so please excuse me if I'm posting this in the wrong location. Each year, my university participates in the SAE Aerodesign competition, and this year, I'm a member of the university's team. The competition requires us to design, build, test, and fly a remote-controlled airplane which carries as much weight as possible using an engine which is chosen by the SAE. We have other design constraints as well, but to keep this post short, I won't go into detail here. However, I have a question regarding propellers. One of my university's grad students developed a computer program that designs an optimized propeller given certain inputs, but while we now have the ability to design propellers, getting them manufactured is another matter. Sure, we have CNC mills and other machines that can make a propeller, but we haven't found a suitable source of material. So my question is: where can I purchase lightweight material for making propellers, such as glass-filled nylon (I'm no propeller expert, but I've been told that glass-filled nylon is what is often used to make propellersplease forgive me if I am mistaken). Or, are there any companies that will make custom propellers to my specifications?

R8893

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wood: maple

I was the pilot for a local university team several years ago. In my opinion some 1930's technology will yield a significant performance improvement: a constant speed propeller. It seemed to me the models were limited by their ability to accelerate their mass to takeoff speed in the alloted distance. A prop that would let the engine run closer to its horsepower peak should show much improved performance.

SeamusG

Our club works with the Univ. of CO Boulder's aeronautic program. Great stuff!

You might also check in the Aerodynamics sub-forum of RC Airplanes.

Have fun!

speedracerntrixie

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You should CNC a set of aluminum molds and mold the prop out of CF

j.duncker

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See [link=http://k0lee.com/propfab.html]CLICKY[/link]

TiptoTail

Thanks for the replies. I think our engine is too small for a constant speed prop. But if we were to machine a prop from wood, how would you recommend going about it? What bit should be used to machine the prop, and once the prop is machined, how should it be finished (sanded, sealed, etc)? Iask because my university's machinists don't have a great deal of experience machining wood.

TiptoTail

Since our airplane moves so painfully slow, much slower than any other heavy-lift airplane on the market, we have decided to try and machine our own propeller. Since the propeller is already fully designed, we are trying to machine the propeller in the next couple of weeks, and even if our propeller is no better than a commercially available one, we will have learned something new and we will not have wasted too much time. However, I need to ask: Can the propeller be machined out of a solid piece of hard maple, or do we have to laminate several pieces of maple to make the propeller? The propeller will only be about 14 inches in diameter, so I'm not talking about making a huge propeller here. If the propeller must be machined out of laminated wood, how should the wood be laminated?

TiptoTail

 

R8893

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commercial props that size are one piece.

da Rock

Swing by a hobby shop and pick up a couple of wood props. Take a close look at the wood grain. Visualize what the blank they carved that prop out of must have looked like. Your questions will be answered a lot quicker that way.

Another reason to look at those props closely would be to compare the pitch of those successful props. It varies from hub to tip. It's worth noting what has evolved in the real world.

It's also worth testing what has evolved in the real world. It will provide you a basis of performance to compare your own design against.

acdii

The wood should be of a tight grain, usually maple or hickory. The grain should be as straight as possible with no knots.  You want to avoid having gain run cross wise on the prop and should run the entire length. 

Too bad you cant use a variable pitch prop, so you can increase thrust on take off, and trim it for best flight.

jester_s1

My club's field hosts the SAE contest usually, but not this year due to a relocation. FWIW, I see lots of over engineered planes that have very elegant ideas that simply couldn't be implemented right in time for the contest. With that in mind I have to ask: have you tried all of the commercially made props that you can? APC, Master Airscrew, Zinger, and a few others put a lot of time and effort tweaking every aspect of their designs trying to put out a slightly better product than their competitors. By the prop size you're talking about I imagine you're in the class that uses the OS .61? Before spending time reinventing the wheel and putting a prop on your engine that may not even be safe, I'd go spend $20 or so trying every suitable prop that your hobby shop has to see which of those is best. Then if you still want to make your own, you at least have a baseline to compare your work to.

Tarasdad

Already gave you my answer on TRF.

TiptoTail

I thought I recognized the name "Tarasdad" (I have this thread set up so that Iget e-mail alerts when someone responds, so when Ichecked my e-mail this morning, Isaw your name and thought to myself, "Wait a minute, that sounds familiar . . ."). It's kinda neat that you recognized me.