Fan blade

[Tom T]

I need to build a fan blade for my air cooled engine. I don't know how many blades and the angle they need to be set at to give me max air flow .

Here is what I have to work with. 200 to 300 rpm 10 dia. 1inch thick.
Thank You Tom

 

[Powder keg]

I don't know much about this but I think Odd numbers will run better as far as balance goes. Also I think on lower speed applications the fewer blades the more efficient? I think there is less turbulence created.

Wes

 

[Tom T]

Wes that's interresting because its just the opposite of what I was thinking.My hillbilly engineering tells me the more blades and the steeper the pitch the better.I think your right about the number of blades being a odd number.After Reading your post I looked at the fans in the house and sure enough the ceiling fan had 5 blades and the fan by the bed has 3 blades.thank you Tom

 

[Rog02]

Tom,

You might consider looking around the model airplane sites for a propellor tutorial. The rubber band powered free flight aircraft use hand carved props at low RPM.

Not to sound like an expert on propellor design (because I am not), but the rotor/prop guy at the helicopter company worked with me (powerplant/gearbox guy) from day one. Operating RPM and available torque had to be balanced between the two systems. Everything was a compromise and any single change would require reconsideration of the entire system.

Oddly enough the major difficulty was not in designing the main rotor system and tail rotor, but the engine/radiator cooling fan. That little project almost sunk the entire project and absorbed a HUGE percentage of the developement budget and postponed the delivery date more than once.

As mentioned before, odd number blade arrangements simplify balancing problems.

A properly designed cooling fan will make for an interesting project and the research is available out there.

 

[Powder keg]

Here is a favorite of mine. I have one nearly done.

One Bladed Prop

Would make a great conversation piece on your model:O)

Wes

 

[shred]

You might look into computer cooling fan designs. Lots of research there on moving the most air for the least power and noise at a set RPM. Typically that RPM range is higher, but there might be something out there already.

 

[Tom T]

Thank you guys for the imfo. Wes I like the monoblade but I don't have enough room.Poor planing on my part. I just kept it simple and built a 5 blade fan.I ran the engine for 20 minutes with out the fan and the hotest spot was 230fh.I will check it later with the fan and see if it helps

 

[Powder keg]

I really like the way this has turned out. Would it be to much trouble to post another video?


Later, Wes

 

[Tom T]

Wes its no trouble I will up date my post .

 

[Powder keg]

Thanks) I can't wait to see how your tractor turns out.

Wes

 

[Don Huseman]

I am working with a group engineers that is building a 1903 wright flyer kind of look alike. Because the original engine was just barley able to get the plane off the ground when the air was very dense, about 35 and it had a massive head wind of 25 knts the wright were able to get the plane of the ground. We are flying at Flaybob air port in Riverside calif and will never have those conditions. We are using a revmaster Volkswagen aircraft engine. The engine get to hot an about 5 minutes of running. Normally you have a big propeller blowing all kinds of wind on the fins of the engine cooling it. The Wright plane has two 8 ft propellers about 6ft away form the engine pushing the plane. There is very little air on the engine. I am thinking of putting a fan on the shaft that comes out of the engine to try and cool it down. Weight is a problem . One idea was to put an electric fan from a car blowing on the bottom of the engine. This requires a alternator which adds weight. Weight is no good.
give me some Ideas on how to cool the engine

signed I DON'T WANT TO DIE

 

[Tom T]

Don if your engine is built from a beetle engine you could get the cool sheet metal of a pancake engine or just run it on alcohol ;D Tom

 

[AllThumbs]

To just move the most amount of air 2 blades is the most efficient. Multiblades are used where max diameter (space) is a concern (space is almost always a concern). Also multi blades are used to direct a lot of air onto a small area (like for cooling a computer CPU or an engine). Notice that most electric windmills use 2 blades, some 3. This is because less blades is more efficient. Higher pitches will move more air at the cost of the required power to turn the fan for a given diameter. Generally the smaller the diameter, the higher the pitch to move the same air as a large diameter, low pitch.

E

 

[bigsteve]

The number of fan blades has little to do with the mechanical efficiency of a fan. With larger fans, it has a lot to do with economic payoff. A 3 blade fan will move 50% more air than a 2 blade fan with the same pitch and rotational speed, with the tradeoff that it will use 50% more energy to do so. A 4 blade fan will move 33% more than 3 blades, 5 will move 25% more than 4, etc. The reason that wind generators have 2 or 3 blades is because the blades are huge, and cost a lot of money, but adding them does little to increase the performance.

Virtually any fan will have turbulent flow.

As they say on MythBusters - "Warning, science content!"

To demonstrate that, the Reynolds number (used to measure turbulence) of an impeller is Re = D^2*n*rho/mu
For air, rho is 1.205 kg/m^3 and mu is 0.0000188 N-s/m^2. D is the diameter of the impeller (in meters) and n is the number of rotations per second. For a 10 inch (0.25 m) fan, Re = 4006 seconds * n. Turbulent flow begins at a Reynolds value around 3000, so anything faster than 44 RPM will be turbulent. Turbulent flow has less drag than laminar flow, so you want turbulence.