Ceiling fans with just one large winglet? I am from India and in India ceiling fans have generally three wings.
Today while laying on my bed a question came in my mind.
First of all, I know that if we use just a single wing at a time of same dimensions as each wings of a three winged fans have then it will reduce the amount of air being pushed down.
But what if we just weld the edges of the three wings to make a single wing ? Will we get the same amount of air as we get generally from a three winged fan ? Which factors determine the amount of air being pushed down ?
I think by this technique the amount of air being pushed downward due to the curvature of the three wings (as a whole) will not be affected. And we can get exactly the same amount of air.
 A: This is actually something that I saw models of! I worked for one summer at the Delft University of Technology’s aerospace faculty in the Wind Energy Project Group. Wind turbines are basically just ceiling fans in reverse.
So, it is apparently folklore in wind energy that you never want an even number of blades. The problem is that usually wind speeds increase the further from land you go, so the top most blade is getting pushed most: but if it is mounted on a skinny tower, the tower slows down any wind going past it due to friction, and so if blades are opposite you have a stronger periodic torque setting up some unusually large loads and stresses and so your wind turbine breaks a bit more often. On the other hand, each blade gets a certain amount of your manufacturing budget, so typically people prefer 3 blades to 5 because it allows you to spend 67% more per blade, and fewer blades can be built out a little wider because the total perpendicular surface area is a design constraint. (If you are curious why, it has to do with hurricanes or other anomalous wind events. The total surface area is determined by whether the tower falls down in unusually high wind conditions.) So this is where you see the difference with ceiling fans, where the blades are not particularly complex and so aesthetics are more important than raw performance.
So the models that I saw were trying to see if the logic continued down to just one blade. A massive lump called a “counterweight” sits on the opposite side to balance out the blade, which can be even wider and made of even more expensive materials because you have 3x the budget. If my memory serves me correctly, it was not economical at that time, but just barely. So there was the possibility that maybe in 50 years or so as the landscape of available materials changed, maybe single-bladed designs would become more efficient.
So yes, a single bladed ceiling fan would move air, but you would want a counterweight on the other side to protect the bearing. Stacking the three blades on top of each other the way that you are suggesting probably moves more air than one blade but not as much as three blades separately would.
There were a couple of other interesting designs I saw that you might want to try with your ceiling fan, one of them had no net angular momentum, because one fan spun clockwise while the other above it spun counterclockwise. For reasons I don't remember, one of the two should be smaller than the other and therefore you only get 50% more energy, not 100% more—but the research had to do with, maybe this will have fewer failures and less repair cost. I don't think that the Delft WEPG was working on that, I think it was just a paper on someone's desk I was reading.
A: A fan blade is just a wing. At the tip, air spills round creating a vortex in its wake. This wastes energy and reduces the efficiency of the wing.
A long, thin wing has a smaller tip, and hence smaller losses, than a short, fat wing of the same area. So the long, thin wing is more efficient. In other words, you need a smaller area to do the same job.
A ceiling fan would be a little more efficient if it had one long, thin blade. But the blade would be very long. Many smaller blades are more practical.
But if blades are close to each other they interfere, reducing efficiency again.
For a ceiling fan, three blades is the best compromise between small size and high efficiency.
A: @trula comment is correct. The fewer the blades the more unbalanced the air load on the fan putting more stress on the bearings. It is similar to what happens to a top loading washing machine in the spin cycle if the clothes are concentrated on one side of the tub as opposed to being distributed around the center of rotation. The machine can shake violently.

what about the amount of air being pushed down ? You didn't mention
anything about that

Sure it will increase the amount of air being pushed down. But @Justjohan pointed out that increasing the number or size of the blades will result in more air drag as well as weight. Although air drag can be compensated for by using a bigger motor, the additional weight may exceed the max load capability of the ceiling structure.
Bottom line, you can add blades or use a bigger blade, and you can use a bigger motor, but the cost benefit ratio may be too high considering that the common 3 to 5 blade fans provide more than enough air flow. And then there are the safety concerns associated with excessive weight and an unbalanced load that also need to be considered.
Hope this helps.
