Topic: will these propulsion systems work in space?

[Laminar]

yes or no. is the motor under more or less load when pushing blades thru the air? yes it is. as with any moving object, if you add resistance, it will slow down unless more power is added. if you keep the power equal and remove the resistance, the speed will increase to the driving components max speed. if a component is not capable of spinning that fast, it fails.

No, it will reach maximum speed as governed by the FREQUENCY of PULSES that are MOTIVATING it to TURN.

You are implying that in a vacuum, with frictionless bearings, the devices would reach infinite speed, assuming the thing didn't fly apart due to centripetal force.

That's not how I understood:

the speed will increase to the driving components max speed.

Not infinite speed, just the maximum speed the driving components are capable of reaching without any resistance.

[MötleyRöx]

what the hell just happened?

I think the #$%* hit one of your fans.
They do work now!   

[Markcb750]

Not infinite speed, just the maximum speed the driving components are capable of reaching without any resistance.

Back EMF, or Counter E.M.F.


http://en.wikipedia.org/wiki/Back_e.m.f.


Neither a DC (Direct Current) nor an AC (Alternating Current) motor will run much faster in a near vacuum then they do in air, a little faster, but not much.

[mlinder]

Thanks Mark.

[Industrial Cafe]

umm...
           will it propel me forward? it's sucking in "something"(space) into the intake and focusing that "something"(space) out of the outlet hole.  
 what's stopping my spaceship that has no weight only mass, from being propelled forward by the fan or vacuum motor?

[mlinder]

umm...
           will it propel me forward? it's sucking in "something"(space)

No, space is not "something". It's a vacuum. Meaning, nothing is there.

into the intake and focusing that "something"(space) out of the outlet hole.  
 what's stopping my spaceship that has no weight only mass, from being propelled forward by the fan or vacuum motor?

Again, there is nothing to 'push' or 'pull' against.

[Markcb750]

Only if you are on a treadmill...


And you are using synthetic oil...


and you are not using pods...



and make sure the coils have Hondaman's resistors...



Check the balance too.

[Industrial Cafe]

ok, well that answers the question posted. it was fun.

[Markcb750]

Agreed.


Thanks

[Retro Rocket]

what's stopping my spaceship that has no weight only mass, from being propelled forward by the fan or vacuum motor?

Money....

Mick

[Inigo Montoya]

No, it will reach maximum speed as governed by the FREQUENCY of PULSES that are MOTIVATING it to TURN.

You are implying that in a vacuum, with frictionless bearings, the devices would reach infinite speed, assuming the thing didn't fly apart due to centripetal force.

Let's use an internal combustion engine instead of an electrical motor as reference. If the engine is spinning at 7000 rpm, and is connected to a fan, or paddles, or what the #$%* ever, the fans will reach the same speed in vacuum or not. Period.

If the potential speed of an electric motor is reached, it cannot go any #$%*ing faster.

mlinder, you are making it overly complicated. NOWHERE did I say the speed would be infinite. Not in one single spot did I even imply that. Obviously industrial got it. So I must not have been speaking greek. I shall endeavor to spell it out for you though.
Say the motor is capable of hitting 30,000 rpm. Even at highest setting, it will not get that fast because it is only capable of doing that rpm UNLOADED. The fan unit itself provides SOME of the load but most of the load is caused by moving air. As such, because of the load, the fan is only going to spin so fast. You remove the load caused by moving air and the fan WILL speed up. IF the fan is not able to handle its own mass spinning faster, it will stress and fail. Simple as that.
If you need even the slightest proof the fan would spin faster, use a laser to measure the fan speed(yes you can get one, RC fliers use them to measure prop speeds), now put another fan right up to it, blowing the same direction. Computer fans work well for this cause the the flat and square frame. Doing this will simulate a vacuum to a small extent as the fan you are measuring does not have to work as word to push the air. Anyways, the fan will spin faster unless of course you rig up some governor.

Again, if this speed increase is too much for the fan components, it will fail.

Movement in space requires either catching solar winds or cosmic ray, OR reaction mass of some sort. The last is how a rocket engine works.

Notice how I can explain this without having to devalue my post with a curse.

[mlinder]

Yeah, I'm a little foul mouthed after the holidays.

Like I said, though, and you've said the same thing without meaning to, that a vacuum doesn't mean bearings or such will fail.
They COULD, but it isn't a forgone conclusion, or even likely. The top speed of an electric motor is governed by the number of oscillations in the magnetic field.
The top speed of a fan connected to said motor in an atmosphere is a combination of oscillations of the magnetic field, how much power it makes, and the resistance of the spinning object (fan, in this case) to the atmosphere it is spinning in.

It's true that, of course, a 3hp electric motor trying to spin a giant water wheel will be speed-governed by resistance and (lack of) power.

This in no way signifies a probable bearing/other-hardware failure in a vacuum, however. Possibility, sure. Probability, nah. Depends entirely on the object in question.

If a motor can reach 30,000rpm, but can only reach 15,000 in an earth-like atmosphere, if the bearings and other components can handle 45,000, then in a vacuum, the motor will still only reach 30,000. A vacuum wont allow the motor to somehow go faster than it's cap of speed. 

[Inigo Montoya]

No a vacuum does not mean bearings will fail, they usually dont anyways unless too much heat is generated. But then I consider them to be part of the drive system. As for top speed, again, I am not saying the motor would go faster itself as far as top speed is concerned. You need to stop worrying about that part. I know it can only go so fast, I am not disputing that. I am saying it will be allowed to spin faster than if it had a load.
Ducted fan engines already fail and they are not spinning faster than rated. Their mass cause them to fatigue and the blades fracture.

Also while a motor might reach 30,000 rpm, I have yet to see a fan do so. They just are not capable of spinning that fast because the spinning the blade mass that fast would overwhelm the blade construction and materials.
Again, I am NOT saying a motor will spin faster than it is capable of. If it can go 30,000, it will not go over that. Like I said, get that part of it out of your head. You are stuck on that like a car stuck in snow. I am talking about the FAN spinning faster than it is designed to.

[mlinder]

With no resistance, the fans would spin past their operational limits and kill the bearings or bushings. Possibly lose a few blades.

You said "would", not "could". Big difference. One is an absolute, the other a possibility.

[Inigo Montoya]

And how is that wrong anyways? Whos to say how fast bearings can and cannot go? Some bearings are made for low speed apps. You put them into a high speed and they will fail. Also, if you increase the rotational mass and near perfect balance is not maintained, it will place more force on the bearing surfaces and if the bearing construction cannot handle the increased forces, it will fail. It might not be right away, but it will be sooner than if kept within operational limits. Bushings are even more susceptible to this as they must rely on lubrication between itself and the moving part much more. if that lube cant keep up, you kill the bushing.
Needle bearings very reliant on lube as well.

[mlinder]

And how is that wrong anyways? Whos to say how fast bearings can and cannot go? Some bearings are made for low speed apps. You put them into a high speed and they will fail. Also, if you increase the rotational mass and near perfect balance is not maintained, it will place more force on the bearing surfaces and if the bearing construction cannot handle the increased forces, it will fail. It might not be right away, but it will be sooner than if kept within operational limits. Bushings are even more susceptible to this as they must rely on lubrication between itself and the moving part much more. if that lube cant keep up, you kill the bushing.
Needle bearings very reliant on lube as well.

"Would" is an absolute. That means that, as you said, the "fans would spin past their operational limits and kill the bearings or bushings". That means they all will, every time.

Which is wrong.

[Inigo Montoya]

So now it is down to nitpicking?

[Retro Rocket]

So now it is down to nitpicking?

I wouldn't call it "nit picking" would and could mean 2 entirely different things......a bit like maybe and definitely....

Mick

[mlinder]

So now it is down to nitpicking?

How can that be nitpicking? You used an absolute. How am I supposed to know you weren't inferring an absolute by using an absolute?

"All CB's will explode."
"All CB's can explode."

Two completely different things. Would you not call me out on the first?

[Inigo Montoya]

Why would I when I am capable of reading between the lines. After all, are we actually conducting the experiment right NOW? Unless you have too much time and a massive vacuum chamber, I doubt it. As such, it is nitpicking. After all, EVERY cb CAN explode. I could put dynamite on it and blow it up so theoretically every cb can blow up. I mean isnt it a wifes job to nitpick? 

[Gordon]

It's nitpicking when someone points out one insignificant, essentially meaningless thing that you said which happens to be incorrect, but has no real bearing on the larger issue.

It's not nitpicking when someone points out that what you said is completely, 100% wrong.

"Would" means that something will, with 100% certainty happen.
"Could" means that something may happen, but it isn't certain. 

It's a minor sounding difference, but a major difference in practice. 

[mlinder]

Why would I when I am capable of reading between the lines. After all, are we actually conducting the experiment right NOW? Unless you have too much time and a massive vacuum chamber, I doubt it. As such, it is nitpicking. After all, EVERY cb CAN explode. I could put dynamite on it and blow it up so theoretically every cb can blow up. I mean isnt it a wifes job to nitpick? 

I'm sorry dude, I don't "read between the lines" when dealing with scientific data or problems. I try not to on a personal level either, because all it leads to is misunderstandings. To top it off, reading between the lines should deal with things similar to what you are speaking about, not completely erroneous statements.

The differences between 'could' and 'would' are almost as large as 'do' and 'don't'.

[Industrial Cafe]

bla bla bla bla bla

[BLUE71TURBO]

READ IT !  LEARN FROM IT !!  LIVE IT !!  Enough said !!   

  http://www.answerbag.com/q_view/398860

[Industrial Cafe]

guys!! the thread was over several posts age.