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In my son's bedroom I currently have a standard five-blade ceiling fan. We are currently changing the decorating motif in his room to "airplanes". I thought it would be really cool to change the ceiling fan to look like a propeller. I have found a vintage three-blade imitation propeller that will fit on the current brackets.

The new blades will be roughly the same length and weight as the old ones, and I will mount them equally spaced (not just using three of the five original mounts), so I do not expect any issue there. So, my only concern would come from having "not factory standard".

Will it be safe to only mount the 3 blades on the 5 blade system?

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    Do you just have the propeller blades, or do you have the hub/spinner too? – ThreePhaseEel Sep 30 '16 at 21:49
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    Are you going to have the 3 blades be equally spaced (hint: good), or were you going to mount the 3 blades in 3 of the 5 mounting points for the original blades, leaving 2 free (hint: bad)? – Daniel Griscom Oct 1 '16 at 3:20
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    @Dan: Asker said in another comment that they will be equally spaced. I'm not sure why anybody would even think they weren't: not only is it obvious to anybody with a brain that it would be unbalanced (and hence they wouldn't even consider it), it wouldn't even look anything like an airplane prop. – user48010 Oct 1 '16 at 4:48
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    @FighterJet Yes, but other answerers were assuming the reverse, and I couldn't edit the question at the moment (there was a review in progress). I've now edited the question to make it clear. – Daniel Griscom Oct 1 '16 at 13:16
  • The original question indicated the imitation propeller blades would fit on the original brackets, which implies (to me, at least), that they wouldn't be equally spaced. Without clarification from the OP, or a picture of the new blades, bib's answer is correct – mmathis Oct 1 '16 at 15:57
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No, it will not be OK.

A fan blade system is meant to be balanced. Even when all of the original equipment blades are in place, minor imbalances can occur and need to be corrected with weights from a balance kit. Failure to have a balanced fan causes wobble. If the wobble is bad enough, it can damage the motor, loosen the fan in its mounting and even cause mounting failure.

The five existing blades are evenly spaced. You can get replacement blades, but they have to be the same number as the originals. If you mount on only three of the five brackets, two blades will be next to each other and one will be opposite. This is a very significant imbalance and could lead to catastrophe.

If there were a way to mount the blades evenly around the perimeter, it might work, but that would require a whole new and custom crafted bracket system.

SUPPLEMENT: The Questioner has added information, now indicating he intends to mount the blades evenly spaced. If that is achieved, balance should not be an issue. Care must be taken to ensure that the adapter used to mount is also balanced around the perimeter (an added bracket on only one side would still create imbalance).

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    Ceiling fans are deliberately mounted elastically so they can handle small amounts of wobble without fatiguing the mounting hardware. That said, if the OP was planning to mount the three blades on the original brackets, leaving two empty, then all bets are off. – Daniel Griscom Oct 1 '16 at 3:22
  • You missed the part where the OP said specifically that he'd mount the three new blades at 2/3*pi spacing. If the blades are identical, the system will be balanced. – Carl Witthoft Oct 1 '16 at 16:41
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    @CarlWitthoft That was not included in the original question and was edited in after my answer. – bib Oct 1 '16 at 17:03
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No, it's not safe, but consider that the Supermarine Spitfire XIV had a 5-blade propellor. I'd recommend getting some paint out and making the exising blades look like a five-blade prop.

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The blades of a three-blade propeller, assuming it's actually an airplane propeller, will have a significantly greater angle of attack than the blades of a normal ceiling fan. This will create more drag than normal ceiling fan blades. OTOH, there will only be three blades rather than five, so it should balance out. I would not attempt to use a four-blade propeller.

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    Thanks for the answer. I don't they are "real" based on length and price, just made to imitate. I will check the angle to make sure it not too severe. I went with the 3 blade as they will still be equally spaced around the shaft. – Skooba Sep 30 '16 at 20:08
  • @Skooba, I assumed in my answer that you were accounting for balance in your retrofit, but I should have spelled that out as bib did. But if this is a kit, then it should be balanced. – BillDOe Sep 30 '16 at 20:13
  • @Skooba well then you should write "imitation propeller" – smci Sep 30 '16 at 22:26
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Yes, it should be safe but just to make sure, I would call a contractor to come ant take a look at it as you would void the warranty and could potentially mess up/strain the motor as a result of your new blades not moving as much air as the old ones.

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    It isn't safe for the reasons stated in the answer by @bib. The fan is balanced for 5 equal blades. 3 will bring it out of balance. – element11 Sep 30 '16 at 23:40
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    Skooba said, 4 hours before @element11 posted, that the 3 blades will be equally spaced around the shaft. So the switch from 5 to three blades won't bring it out of balance. In my experience, a normal ceiling fan doesn't come with, require or mention in its documentation, a "balance kit". Most votes are going to bib though. Looks like most folks here would hate the idea of kids being allowed to play with hammers, nails or saws too and/or don't understand basic Newtonian physics. – Matthew Elvey Oct 1 '16 at 2:21
  • (If you simply removed the five blades and put propeller-like blades in where three of the 5 were, the fan would be out of balance and that would be a bad idea!) – Matthew Elvey Oct 1 '16 at 2:26
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    @MatthewElvey - every ceiling fan I have ever installed (more than I can count) has come with a balancing kit and instructions on how to balance if necessary. That said, I have never needed to use it. None of the answers here look correct to me - why don't you write one? – Mark Oct 1 '16 at 13:18
  • Why not? Answered in the last half of my first (:21) comment. – Matthew Elvey Oct 5 '16 at 17:49
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Try it!

If it looks like spinning wheel of doom, put the original 5 back on.

Don't have your kid underneath it when you try it. Watch it the first time you turn it on and if it starts wobbling too bad, turn it off. If you react somewhat quick, you probably won't damage the mounting or your ceiling. Try it on all three different speeds and reversed). If it is wobbling a lot, something is wrong. If it is only wobbling a little, go out, pick up a fan balancing kit, and pat yourself on the back for being a great dad!

In the future, maybe occasionally wiggle the blades to make sure your bolts are holding. Vibration tends to slowly work things loose.

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