2 blade fan or 4 blade fan? That is the question!

[old skool]

Hello,

Here is a good question. The last car I built I used a 4 blade fan on my engine. I was told and read that it would do a better job cooling the engine. I just read another "test study" and it said that the 4 blade fan isn't any better at cooling the engine than the original 2 blade. I am starting another build and I am making my check list.

I have both, so I can go either way.

So whats the scoop? Your thoughts out there?

Thanks,
Marty

[ldj1002]

I am not a aeronautical engineer and can't explain it but I am a pilot and can tell you. I have operated same airplane with a 2 blade prop and switched to 3 blade. The 2 blade prop has much better performance. I have done the same with several types planes and was the same for all. Seems logical that the 2 blade Model A fan would pull more air than one with more blades.

[glenn in camino]

Buy an aluminum two blade fan and paint it black. They work great, don't break, and look almost original.

[Mitch//pa]

the two blade aluminum comes powder coated so no need to paint. looks more authentic than a 4 and works as good or better....

[Louis]

If your driving your "A" model above 20 thousand feet elev. most of the time, go with the four or six blade fan.
If you drive most of the time under 20 thousand feet elev. stick with the two bladed fan.

[old skool]

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Good ideas and interesting. Anyone else?

Marty

[hardtimes]

Originally Posted by old skool

Good ideas and interesting. Anyone else?

Marty

OMG..not again
Did you see/read the lengthy thread last week on this same subject?
Get a belly full of info..read it
Discussion of OIL/FANS is fun and everyone has an opinion! Some say buy this one, "it won't break" never/promise! Read the entire thread about breaking comments. Hmm, 'fly low' use a 2 blade vs 'fly high' use four blade..hey at least that's a new one. Have fun.

[BRENT in 10-uh-C]

Originally Posted by hardtimes

OMG..not again
Did you see/read the lengthy thread last week on this same subject?
Get a belly full of info..read it
Discussion of OIL/FANS is fun and everyone has an opinion! Some say buy this one, "it won't break" never/promise! Read the entire thread about breaking comments. Hmm, 'fly low' use a 2 blade vs 'fly high' use four blade..hey at least that's a new one. Have fun.

Ummmm, ...I believe he either said (--or implied) he did in his initial post. I believe his quote was "I just read another "test study" and it said that the 4 blade fan isn't any better at cooling the engine than the original 2 blade." Maybe he should bring that particular thread back up for more discussion? Marty, help us out, after you read that, are you really still confused??

.

[RcT]

This isn't doing a bit to answer the question, but in 1968 I was in college and wanted a Model A for fun. I found a pickup made from a sedan, original engine, but unrestored. Got it very cheap and at the time, it suited me for my "A" fix. I had it out for a drive one weekend and was coming down a hill in third gear, probably approaching 50 mph when I heard an explosion like a shotgun and the engine just died. I came to a stop, popped the hood to find a fan blade had broken off the original fan. The belt was still good, but off the pulley. I grabbed the other blade and wiggled it back and forth until it broke off, put the belt back on and limped home, about 30 miles, stopping when it heated up, to let her cool down. The original fan had rusted from the inside out. When the blade came off, it hit the side of the hood with such force, it left a dent about like a half tennis ball and the paint that was popped off the bare metal looked to be in the shape of an angel. I was an art major in college and had all I needed to detail out the angel, about a 10" wingspan, and she graced my hood until the day I sold the truck to some guy who was shipping it to Hawaii. Wonder if it's still there...

[Patrick L.]

Not that I want to hi-jack this thread ,but , do these new fans need to be balanced ??

[BRENT in 10-uh-C]

Originally Posted by Patrick L.

Not that I want to hi-jack this thread ,but , do these new fans need to be balanced ??

I have found the new ones are close "as-is", ....but you can balance them if you would like them to be any better. I bought a balancer from Tom W and it does a decent job of balancing them.

[Mitch//pa]

Originally Posted by Patrick L.

Not that I want to hi-jack this thread ,but , do these new fans need to be balanced ??

i just installed 2 and did not feel any balance problems......

[Patrick L.]

OK, thanks for the responses.. I like the looks of Tom's balancer..

[Tom Wesenberg]

Thanks Pat. As Mitch said most of the fans can be installed with no problems, even if the balance isn't as perfect as it could be. I like to check the balance and make it as perfect as I can get it. Here is a picture of the first balancer I made using a pair of parallel rails. The problem with this one is the rails must be perfectly level while using it, so I installed a bubble level to help.

I much prefer the second one I made using a piece of aluminum channel and 4 small very low friction ball bearings. After I sold this one to Brent I had to make another one for myself. As I was walking around the Goodwill store I spotted a fancy brass candlestick holder for a couple bucks, and had the brilliant idea of using that instead of making another wood pedestal for the balancer.

I keep a plastic bag over the balancer to keep dust off the rollers and if the ball bearings show and resistence I'll give them a drop of light oil and spin them against the wire wheel to limber them up, just before I balance the fan. The top picture (bottom fan) shows the aluminum fan and where I drilled and filled with lead to balance. On the top steel original fan, if after making sure the blades are straight, it still need to be balanced I can add a little solder in the curved area of the blades. This way I can smooth it out so it isn't noticed.

I stuck an old shaft and impellor into a tuna fish can and poured in melted wheel weights to make a counter weight for the fan. The shaft must be smooth without pits and of course this must be balanced first before putting it to use.

[Chris Haynes]

Originally Posted by ldj1002

I am not a aeronautical engineer and can't explain it but I am a pilot and can tell you. I have operated same airplane with a 2 blade prop and switched to 3 blade. The 2 blade prop has much better performance. I have done the same with several types planes and was the same for all. Seems logical that the 2 blade Model A fan would pull more air than one with more blades.

I am curious about one thing. The original F4U Cousair's had a four blade prop. I am told they switched to the three blade prop because the four blade grabbed too much air.

[Aerocraft]

The number of blades are a function of how much horsepower is driving the propeller. I believe the four blade came after the three blade and was a result of the installation of an engine bigger that the original P&W R2800 which was what is driving the three bladed propeller shown in the picture of "795". If you look closely, you can see much larger cowl flaps on "5" which is a clue to what could be a bigger engine, I believe in that case, a P&W R4360.

As the number of blades increase, the efficiency drops. Theoretically, a single blade, counterbalanced propeller is the most efficient.


Gar Williams

[Christoph]

And why do "they" use fans with 6 to 9 blades in modern cars ?

And if you use a 2 blade, why dont you use a shrout to make
a better air-flow and reduce aerodynamic losses?
Have a look into your modern car.

Best regards from Frankfurt
Christoph

As i installed a new HD-radiator, i (being in fear) as well switched to a
6 blade plastic (ja - its ugly) from the well known vendors. I cant understand why its so much smaller in diameter For sure this will reduce airflow (knowing this, i wouldnt have bought it).

Summary:
Using the new radiator it feels as if i wouldnt need any fan at all.

[Milton]

The original F4U's had a three blade prop with a P&W 2800-W8 engine.
The four blade prop debuted in 1944 with a P&W 2800-W18 engine.

[MrTube]

Why "they" use a 6+ blade fan on newer cars is irrelevant. They have slower rpm electric motors as well as air conditioning which increases air temperature greatly.

The "A" was designed with a 2 blade fan with a certain blade pitch and it was designed well. If its not broke stop fixing it.

Many guys on here like Tom,Brent and Mitch know the "A" inside out and say to use a 2 blade fan. That has to mean something.


Now we're comparing props on air planes which consume 1000-3000HP to the model A's fan. Whats next boat props?

[Chris Haynes]

When I got my first A in 1961 it had the Ford replacement four blade fan on it. What was Ford's reason to switch to a four blade fan?