Hello and welcome to the part where I skip the part at the beginning because I can’t be bothered.
Did you hear about the time the hotel hosted an architecture convention?
They put up a bunch of ceiling fans.
And speaking of ceiling fans,
I don’t know about you but whenever I’m looking at a ceiling fan,
this is all I can think of.
And if an airplane propeller can push air backwards so hard that it generates enough thrust to make the airplane it’s attached to fly,
well then surely a ceiling fan is producing at least a bit of thrust, right?
Mmmmaybe an airplane wasn’t the best comparison,
what about this?
I mean what is a helicopter but a big ceiling fan with a little cabin hanging off the bottom of it that you can go inside of?
And somehow that ceiling fan is blowing enough air down at the ground to make the thing fly!
And then it’s got that little fan on the back, too - fun fact,
the reason that’s there is because a single-rotor helicopter has a big spinny thing on top of it which is constantly producing a twisting torque which,
since the thing just floats in the air and isn’t attached to anything else,
would spin the body of the helicopter around real fast and that would make it very difficult to fly,
so the tail rotor is just a second sideways fan blowing in the opposite direction that the big rotor is trying to twist the cabin
to keep the helicopter from spinning out of control which makes it much easier to fly.
Dual-rotor helicopters don’t need that so long as the rotors are spinning in opposite directions to cancel each other’s twisting torque out.
But anyway this video is about ceiling fans and I wanted to find out how much thrust a typical ceiling fan produces.
Because it’s got to be more than zero - it’s the same thing as a helicopter rotor or an airplane propeller
but hanging from a ceiling to keep you cool rather than power human flight.
So I bought this cheap ceiling fan from Menards and set about finding a way to weigh it while it’s in operation.
And when I floated this idea to my friend Dan “Spiffy” Neuman, who happens to be the world’s premier source of ceiling fan knowledge,
I was immediately chastised for not having something better to run this test with.
I brought this idea up to Dan because, initially, I was struggling to figure out a way to safely test this.
I was envisioning using rope or chain and hanging the fan from some kind of scale
but I couldn’t see how the fan wouldn’t get wildly out of control without some sort of sturdier solution.
And luckily, during a visit to my office where Dan delivered several fans for testing and more,
we cobbled together various stuffs lying around the warehouse and assembled this completely safe and not at all sketchy test rig,
complete with a crane scale which can measure the weight with fairly high precision.
The filing cabinets are just to get the fan a little higher off the ground.
Now, when a ceiling fan is operating and blowing air downward, that should mean the fan itself gets at least a little lighter.
Some scientist guy said something about every action causing an equal and opposite reaction and,
well, if it’s pushing air down, then the air must be pushing the fan up.
But does it?
Well, the cheap Menards fan weighs, according to the scale, 11.5 pounds.
That’s a different number in kilograms.
And, once it’s up to speed the scale reads…
11.2 pounds.
So it got three tenths of a pound lighter, or 136 grams.
But not so fast!
Keen-eyed viewers may have noticed that the scale jumped up slightly once the fan started.
The twisting force it was creating on the scale did skew the number a bit and if we take that into account,
well things change a bit.
When first switched on the fan appeared to gain 0.14 pounds.
And when I unplugged it and the twisting force from the motor was alleviated,
the scale briefly read 11.02 pounds so the fan appeared to lose 0.18.
If we split the difference and add 0.16 pounds of thrust, then the fan actually got .46 pounds lighter, or 209 grams.
But remember, this is a cheap fan from Menards which is weak and cheap.
This is an Envirofan Gold Line and I’ve been assured that this is a good fan.
It’s certainly a lot heftier coming in at some 20.32 pounds
which is a different number in kilograms.
And how much does it weigh once it’s up to speed?
Well we have the same torque issue happening which appears to increase the weight but once it’s up to its rather terrifying top speed
the scale stabilized at 19.35 pounds, almost an even pound of thrust.
Upon power removal the scale briefly read 19.22 pounds so if I split the difference in noise between the added weight at start-up and the added thrust at power-down
the fan lost 1.035 pounds of weight, about 470 grams.
And that’s 4.6 newtons of thrust for those who prefer figures expressed in fig cookie bars.
But many ceiling fans are reversible.
The general idea there is that if you have the fan running backwards it’s blowing up into the ceiling which produces less of a noticeable draft
but still moves air around the room to reduce temperature gradients,
particularly useful in the winter when the effect of warmer air rising can get heat stuck up against the ceiling where it’s not helpful.
Would a fan running in reverse get heavier, then?
Well, I reversed the Gold Line fan to find out and the answer is…
yes!
The fan went from an initial 21.07 pounds to 21.86 pounds.
The different initial number has to do with the taring weirdness of this particular scale.
This time I didn’t see any weird weight changes from torque so I’ll just go ahead and say that the fan got 0.79 pounds heavier when running at full-speed in reverse.
That’s 358 grams.
Oh, and speaking of heat recovery, here’s another fan to test!
This is an Emerson Heat Fan - a commercial fan designed for buildings with high ceilings to push the warm air collecting against the ceiling back down
so people on the floor can feel all that warmth and the heat doesn’t have to run so much.
This was a product of the energy crisis of the seventies, and someone at Emerson realized
“hey, we make motors.
Why not take one of our washing machine motor housings, stick some fan blades on there, and sell it as a heat recovery fan?”
and, well, that’s what this is.
And because it’s got a big ol’ motor powering the thing, it can move a lot of air.
So how much thrust does it generate?
Well, we had an initial reading of 24.24 pounds, and this time the torque generated by the motor didn’t seem to matter.
and by the time the fan had hit top speed the lightest reading seen was 22.88 pounds.
Ah, except when the fan had come to a stop the scale now read 23.85 pounds.
I tried my best here to make sure the power supply cord wasn’t pulling on the fan
but there was some wobbling around so it’s possible the cord did influence the scale by half a pound or so,
but it’s also possible that the scale was just being wonky.
It has some internal logic which makes the reading a little weird:
I would have loved to have tared it at zero and then done the test but it would just stay at zero even once the fan was at full speed
so the only way to get any sort of reading was to do subtraction.
Regardless, this fan either produced a similar 1 pound of thrust or, if we’re feeling generous, it produced 1.36 pounds of thrust.
But speaking of heat fans, here's a very weird home ceiling fan from the ‘80s with a built in electric heater.
I will probably make a video about this fan specifically one day -
it’s an interesting concept but runs up against some rather fundamental problems and was also executed…
strangely but for now I just want to see how much thrust it produces.
I didn’t have a great way to hang this guy - its mounting hardware didn’t quite work with a standard hook, at least not easily, so I just hung it from some rope which…
worked.
But, Dan, look away for a moment.
This sucker’s heavy, coming in at 32.62 pounds,
which is a different number in kilograms.
And…
once that disaster was over the scale stabilized at 31.91 pounds.
I even checked the wiring this time to make sure it wasn’t taught.
The scale read the same 32.62 pounds once it had come to a stop so this fan apparently generates about 7/10ths of a pound of thrust,
which is 322 grams of weight reduction or 3.16 fig Newtons of force.
So, there we have it.
Ceiling fans apparently produce somewhere between half a pound and a full pound of thrust depending on how good of a fan it is.
Surely some fans produce more and some produce less - those big high-velocity low-speed fans which are starting to spread all over the place
undoubtedly generate more thrust than these, and I’m sure there are crappier fans than this one out there which produce even less.
But to be honest, the reason I was curious about this is because
I’ve always been a little concerned with the forces that a typical ceiling fan produces on the electrical box it’s mounted to
and I wanted to have a better understanding of those forces.
Clearly these tests show that the reduction or addition of weight caused by thrust generated by the fan is pretty insignificant -
the torque the fan produces on the box as the motor spins is undoubtedly much more noteworthy,
especially when we consider the jerk force at startup.
But I am glad to know that there is actually a measurable decrease in weight when you run a ceiling fan on high… at least forward.
Was there really any reason to know that?
No, but now we do, and at least I got a video out of it.
And I don’t want to hear anything about the effort involved here -
I did zero research other than double check what HVLS stood for and relied on Dan for all the fantastic fun fan facts which were peppered in here and there
and also for three of the fans.
And thanks to Dan the Fan Man, oh boy is the next video gonna be great.
Christmas time this year’s gonna be better than ever.
Kay bye.
♫ propulsively smooth jazz ♫
Hello and welcome… zzhhzh what the why does that keep happening?
…doubtedly much more noteworthy, especially when you con—
I dunno what happened there.
I mean what is a helicopter but a big ceiling fan with a little hh…
eughhh
…every action causing an equal and opposhit re -- oof.
Well, lost that one.
And if we take that into account there’s a lot of road noise so I will back up and restart.
But not so fast!
But once it’s up to speed…
ahhhhh,
ahhhhh!!! [an octave higher]
♫ over the rainbow ♫
I relied on Dan for all the fantastic fun fan facts which were peppered in here and there
and for ff ff f f f f ff f