|Aug 03, 2001, 02:41 PM|
Anbody know how to build a prop?
For some reason Atlanta is deprived of decent hobby stores. most of them carry a ton of nascar garbage, a few carry some plane kits, but hardly any carry props or other accessories. My question is whether there is an accepted way to build props that are safe and light. I have a pretty complete set of building materials, so welding, soldering, and machining are not out of the question.
|Aug 03, 2001, 02:47 PM|
If you go back through the articles form Wayne Hadkins, he covered it a few times.
Some were from pop bottles and soem from CF.
Plus there are some ideas in RCMicroflight, but you have to subscribe. They included hubs and I believe making CF&FG props layed over a PVC pipe.
For slowfly building your own prop is just fine.
|Aug 03, 2001, 04:02 PM|
Joined Jul 2001
I don't know if this qualifies as "build your own prop" but I've copied props before using the following method:
[This explanation will produce two props - the first one is your unreinforced prototype. The second one is the one you'll actually utilize.]
Take some modelling clay and knead it like you're making an oblong pastry; then lay it out flat. Next, spray some Pam on the front (text) side of the subject prop, and push it into the clay far enough for the hub to appear flush with the clay. Let it sit this way until the clay just seems hard enough for you to remove the prop without deforming the impression. This is the hard part; but when you get familiar enough with the characteristics of the clay you're using, it gets easier. Don't worry about the bit of clay that comes off with the hole in the hub. But note where the hole is, and mark a small depression into the clay there - this will become your drilling reference for the finished part.
Now you need to fire the clay the same way kids at summercamp used to make ashtrays for their parents before they all stopped smoking. For this, follow the instructions on the package of clay.
Now you have a tough ceramic mold capable of manufacturing an arbitrary number of prop copies. Wax the inside of your mold with some mold release compound. Pour some catalyzed casting resin into the mold. It will cure fairly quickly. It will also get pretty hot, which is why we're doing this in ceramic. Attempting to approximate where the hole in the hub will be, push one end of a length of dacron flyfishing backing into the surface of the casting resin; this is what you're going to tug on to get the finished part out of the mold.
In two hours, start pulling. The part won't come out real easy, but it can be coaxed. If necessary, use the tip of a knife and gently pry the part away from the mold.
Using rough sandpaper, shape everything the way you want it, frontside and back. Then go to successively finer paper until you acquire the finish you're looking for. Drill out the center hole using the little reference nub where the original hole was.
You now have a prop capable of being used on a static display piece. Mandatory additional work is now required to make this piece reliable. (I practiced the following steps on those Guillow rubberband props that I would normally toss in a drawer and never see again; as bizarre as this is going to sound, the process actually works, and produces good results as well as a safer propeller.)
You now require a modest amount of lightweight fiberglass cloth. Cut four strips of it, each a little smaller than each of the blades. Now attach the cloth to each blade, front and back, using very small amounts of sanding sealer as glue. Do the "tacking" sparingly and in tiny deposits of sealer, as if you were using CA; the purpose here is to attach the cloth enough to seat each piece without wrinkles against the faces of the plastic. When all four sides are done, go on to the hub itself, front and back, with dime sized round pieces of cloth. After the sealer dries, brush catalyzed resin (it can be the same resin you casted with) over and into the cloth until the cloth weaving disappears under the layer of resin. If it's not thick enough, you can put another coat on later.
In about two hours, go through the same finishing process with sandpaper as was done originally.
Now balance the prop and try it out. I would do this with ample eye protection and make it a point to stay well behind the plane of the spinning prop.
There are some obvious limitations to using your new propeller. In fact, the one you just created shouldn't be used at all once you have established that the process is viable. Having just practiced on this one, we repeat the entire process for a second propeller. Only this time, now that you're familiar with the casting process, embed some of your fiberglass cloth into the cast while you're pouring it. Alternatively, you can embed loose carbon fibers or even a combination of the two.
Now finish the reinforced prop the same way you did the first one. This becomes your first viable prop.
Again, I have only done this to replicate scale props for display purposes with modest electrical power. If you opt to place this prop on something more than "modest", exercise appropriate caution and realize that there are dangers here in addition to the limitations...
I've done some electrified freeflight Guillow conversions using these homemade props, essentially copies (with minor mods) of the rubberband props provided in the kits. The electric motors utilized spin the props at about the same rpm as good rubber and have access to very modest amounts of electricity. The purpose is to mimic the performance of rubber but extend the effect...
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