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Since I am unable to change the pitch of the blades on my ceiling fan, I am considering buying a larger one. The current one is certainly efficient enough as that is why I bought it in the first place (CFM/watt); however, I need more airflow.

Altering the pitch would have been ideal but that is not an option. This ceiling fan has hidden blade connections. How can I modify the fan blades to increase the airflow produced by the fan?

For example, does the idea of winglets have merit? What would be the effect of winglets on a ceiling fan vs an airfoil? Or, would notching the trailing edge as suggested in this answer help increase airflow?

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    $\begingroup$ Hi Imaginetivelywild, welcome to Engineering SE. I see that you added some direct messages for myself and another user to your question. I will read your message in a moment but first, I have to roll back your edits for the following reason: Questions on Stack Exchange are dedicated specifically to defining and explaining a problem statement. Communicating directly with a user is something you could do in a comment or in our chat room, using the @username reply feature. $\endgroup$ – Air Jul 1 '15 at 18:27
  • $\begingroup$ Regarding your general objection to my edit, please be sure to review our Help Center article about how to approach editing on Stack Exchange. My intent was to help you communicate your problem in a way that is likely to attract answers that will both solve your specific problem and be useful to future readers with the same or similar problem. As the original author of the post, you are within your rights to alter or revert a third-party edit, and if you feel my edit misrepresents your problem I would encourage you to do so. $\endgroup$ – Air Jul 1 '15 at 18:42
  • $\begingroup$ If you would like a more long-form response to your specific points about the edit, I would be happy to give one, but the appropriate venue for that discussion would be on Meta Engineering (see also: What is "meta"? How does it work?) $\endgroup$ – Air Jul 1 '15 at 18:46
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Ceiling fan blades are usually rather crude airfoils - you won't find one in a NACA catalog :-). In many cases a certain amount of violence may be wrought on them without too much fear of disaster. Whether this is so with your one depends on the design.

As I write this I'm visualising some blades which are probably findable in my dungeon. If any of this sounded useful but unclear a photo or few may be able to eventuate.

In some the blade to hub transition consists of a flat sheet steel section and a degree of "pitch" (or even ALL the pitch) may have been imparted at this point by the simple expedient of "twisting" the transition piece. If so, you may be able to introduce some more twist by the same means. A long jawed vice grip, or a builders clamp or some similar tool with a say 3" / 75 mm or longer jaw can be slipped over the blade close to the hub and twisted (add handle extension to taste to allow less force and smoother action). If doing this (or anything else in life), decide the worst case result and whether you are prepared to accept it if it happens, and don't start if not. If it does look possible then breakage odds should be low. Snapped blade is possible and damaged hub shouldn't be. Bending off-hub with blade mount in a vice removes hub damage risk but, hey, where's the fun? :-). Balance will be impaired and tuning will be needed. (I could have said " ... may be ..." but Murphy seldom deals in "may" if worse is possible.)

If the blade does not seem amenable to pitch shifting but the mount angle at the blade-mount join affects pitch, you may be able to shim the mount closest to the forward edge so that it becomes more forward. Longer bolt with washers may work. Nuts (correct size or larger) can act as fat washers if you need significant thickness and are not embarrassed or scornful of bush engineering.

I'd think there was a moderate chance that adding leading edge extensions - initially at least with say cardboard and "sellotape", would have a chance of working usefully well. You'd probably find that these only needed to be on the outer half of each blade length but longer is OK if desired. This has the advantage of potentially looking really terrible even if it works well - although this can be altered with enough work. Thin aluminum sheet is liable to last longer.

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The motor is likely an induction type, which by design, "slips." So the more load placed on it, the slower it will spin. Which means, if you increase the blade pitch angle, this will produce more load for the motor, resulting in lower RPM, and probably a very similar amount of airflow overall. Of course, if you could install a more powerful motor, more air would flow.

One interesting thing about page 10 of that link. If you were to essentially put the motor on a dynamometer and produce a curve of it's torque vs. RPM, then you could calculate at what RPM the maximum power is produced, and adjust the blade shape, size, and pitch to suit. But if the engineer that designed the fan already did this, any improvement would be minor. And loading a small motor too heavily will cause it to reach a higher temperature and likely fail sooner. There is only so much power available from this motor to move air, and no "weird trick" will make it produce remarkably more airflow. Yes, you could "airfoil" the leading edges, plane-down the trailing edges, notch it, add "tips" or all sorts of other things, but these will not produce any remarkable difference as the motor is the limiting factor.

As a practical solution, could a second fan be added? Or this fan upgraded to a more powerful model? A squirrel-cage fan moves lots more air (and use a lot more power), but that topology doesn't lend itself well to ceiling use.

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I wish our fan would expel more air? I have considered changing the pitch of the blades by bending them but each blade, the pitch must be exact or else the blades will not rotate properly and could shake itself apart. I'm going to try adding washers to one side of the blade which holds the blades in place to the rotating motor. In theory, this should work as the weight and tilt of each blade should be exact at minimal effort.

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  • $\begingroup$ This does not seem to answer the question at the top of the page. It might be time to take the Tour to learn how StackExchange works. $\endgroup$ – Transistor Apr 28 '19 at 13:13

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