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Propellers

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Old 09-10-2012, 12:19 PM
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TiptoTail
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Default Propellers

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 SAEAerodesign 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 airplanewhich 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, Iwon'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 beentold that glass-filled nylon is what is often used to make propellersplease forgive me if Iam mistaken). Or, are there any companies that will make custom propellers to my specifications?
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Old 09-10-2012, 01:40 PM
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Default RE: Propellers

Not sure where you can get them made, but your crew needs to be very careful around any prop on any RC engine. They will and can cause a person some serious hurt and damage. Good Luck on your mission, Dave
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Old 09-10-2012, 01:40 PM
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Default RE: Propellers

Beechwood and Maple are often used. One manufacturer of wooden props is http://www.zingerpropeller.com I do not know if they will make a custom prop
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Old 09-10-2012, 02:26 PM
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Default RE: Propellers

I would make it out of wood also. Carbon Fibre might be lighter and stronger, but a nice wood prop will be safer and you could CNC it yourself. Do you know the engine that will be used? If so there are many guys here that have flown that engine and can steer you in the right direction. It is also possible on a wood prop to buy one that is bigger than you need and custom cut the tips to your specs. The hardest way would be to CNC a plug , use it to make a mold , than make your own CF version. This would also be the most dangerous way!!! It's no fun when a prop comes apart.

David
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Old 09-10-2012, 03:27 PM
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Default RE: Propellers

First question I would have is , what size aircraft are you planning to build or what size is typically built and what engine sizes are typically used in this competition? That way we will have an idea what size props you will be dealing with.
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Old 09-10-2012, 03:54 PM
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Default RE: Propellers

You might try to contact Robert Vess.
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Old 09-11-2012, 04:31 AM
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Default RE: Propellers

Since you say, you have a propellar program and access to CNC machines, make yourself some molds and lay-up your own. Try a post or 2 here to gather additional info from the Giant Scale Racer's website,,, they mostly make their own stuff as well as props from composite materials. www.usrainfo.org/index.asp

Another source of info might be Robert over at www.apcprop.com


Goodluck


BV
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Old 09-11-2012, 06:46 AM
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Default RE: Propellers

I have been piloting at the SAE competitions in Fort Worth Texas since 2007.... In the past the common engine was the OS 61 FX, so one would have to presume it will be the OS 65 in the future. One team I flew for was using a Bolly 13x4 if I remember right, and gave it to me in appreciation. (did not work real well on my 60 size stick though [:'(]) It was carbon fiber, though most teams use the apc.
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Old 09-11-2012, 02:54 PM
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Default RE: Propellers

The SAE hasn't released the official rules for this year, so I can't guarantee which engine will be used. But I'm guessing that an OS 65, or something close, will be used. Also, several people mention machining the propeller out of wood; does anyone have instructions for doing that? For instance, if we were to make our propeller out of Maple, what kind of bit would we use on our CNCmachine to cut it? Currently, Ithink all of our tooling is made for machining metal instead of wood, so we don't have a great deal of experience with wood. Also, once the propeller is machined, how should it be finished? As in, what kind of sanding, sealing, etc needs to be done?
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Old 09-11-2012, 03:45 PM
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Default RE: Propellers

Is it a requirement to MAKE the prop ? There are boatloads of different types of props for a 60 size engine out there. Instead of making a new prop try taking a prop and reworking it (cutting it down, etc...) to make it work better.
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Old 09-11-2012, 03:51 PM
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Default RE: Propellers

It isn't a requirement to make the prop, but last year, we built our own prop and it gave about 15% more thrust for a given rpmthan the commercially available props we have used in years past. The biggest problem with our custom propeller was that it was made out of Baltic Birch, and it was so heavythat the engine couldn't swing the prop at its design rpm. Therefore, we think that a lighter prop would give us a substantial performance increase. I just want to make sure that we understand the best materials and best construction methods before we begin, because due to our lack of wood-machining knowledge, the process of making the propeller last year took too long and had too many imperfections. Additionally, the shape of our custom prop is very different from the shapes of commercially available props, at least the ones that I've seen, so Idon't think that we can triman existing propeller to match our custom prop.
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Old 09-11-2012, 06:54 PM
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Default RE: Propellers

buy one from these guys [link]http://masterairscrew.com/propellers.aspx[/link] and hit it with some flat black and move onto a keg party
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Old 09-12-2012, 02:21 AM
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Default RE: Propellers

Just seems to me that you are trying to reinvent the wheel here. A lot of work for little gain. Could put that effort into building a better airframe and reworking/tuning the engine for better output.
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Old 09-12-2012, 06:00 AM
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Default RE: Propellers



They make tooling to cut wood on metal cutting machines, just contact some tool suppliers. When you doask about the turning speedsas thiswould be different for wood as well. You will need to sand, and finish with nitro proof varnish. I would simply spray withepoxy varnish. Weight shouldn't slow down the eingine other than taking a little longer to rev up. If the prop was 15% more efficeint that alone would slow the engine down. you would need to change the diameter or pitch (or both)of that design to bring the rev back up.

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Old 09-13-2012, 06:10 AM
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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 tomachine the propellerin 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?

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Old 09-13-2012, 06:47 AM
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Default RE: Propellers

Quote:
ORIGINAL: 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?


I don't know how much stress is on the prop or what RPM it is expected to turn at. Laminated wood provides higher structural integrity than a single piece of wood and less probability of changing shape. Unless you can find a solid piece of wood that is without any defects below the visible surface prior to machining, which is unlikely, a laminated stock would be appropriate. The best way to laminate an appropriate piece of working stock would be to use several pieces of wood that when laminated equal your design working stock dimensions, be sure to cross the grain in at least one laminate. Use any of the high bond strength weather proof wood glues available at any hardware store. The key is presure so the wood must be very tightly clamped for 24 to 48 hours. It would then be a good idea to kiln dry it at about 200 degrees prior to machining it to avoid any warping. Once you are done a thin coat of urethane will not add significant weight and will prevent the finished prop from absorbing any moisture and changing dimensions as a result. Sounds like an interesting project and I wish you the best of luck with it.
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Old 09-13-2012, 07:01 AM
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Default RE: Propellers



[8D] Topspin has given you great advise . The only thing I'd add here is ,

If possible , Make more than 1 propeller . Of all the laws of Aerodynamics you'll encounter , Murphy's law is the one that'll make or break ya
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