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What size propeller for a 36 V DC motor?



 
 
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  #11  
Old July 28th 10, 09:11 PM posted to rec.models.rc.air,rec.aviation.homebuilt
John Doe[_4_]
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Posts: 115
Default What size propeller for a 36 V DC motor?

"Morgans" jsmorgan charterJUNK.net wrote:

....

I seriously doubt that you are going to get more than 8 pounds
of thrust out of that motor, even with the ideal gearbox and
prop. Probably not going to do well to move a person on skates.


Right... Just depends on how easy it is to try. But maybe I can
get a feel for what sort of electric motor would do. Propeller
powered inline skating has been done with small gasoline/petrol
motors.

http://www.youtube.com/results?searc...e+jetpack&aq=f

The first clip is on topic after the cool hang gliding introduction.

But I would not want to use a noisy gasoline motor.

Thanks.
  #12  
Old July 29th 10, 10:09 PM posted to rec.models.rc.air,rec.aviation.homebuilt
John Doe[_4_]
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Posts: 115
Default What size propeller for a 36 V DC motor?

"Morgans" jsmorgancharterJUNK.net wrote:

Look in places that talk about remote control airplanes, because
that is what even the man carrying experimental airplanes are
borrowing knowledge from, on the subject of electric flight. It
is just at larger scales.


I believe that, but how come you never see a real airplane
standing on its tail? Looks like that would be a neat way to
simulate a Harrier landing, and takeoff.
  #13  
Old August 18th 10, 05:04 AM posted to rec.models.rc.air,rec.aviation.homebuilt
Ir. Hj. Othman bin Hj. Ahmad[_2_]
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Posts: 1
Default What size propeller for a 36 V DC motor?

On Jul 30, 5:09*am, John Doe wrote:
"Morgans" jsmorgancharterJUNK.net wrote:
Look in places that talk about remote control airplanes, because
that is what even the man carrying experimental airplanes are
borrowing knowledge from, on the subject of electric flight. *It
is just at larger scales.


I believe that, but how come you never see a real airplane
standing on its tail? Looks like that would be a neat way to
simulate a Harrier landing, and takeoff.


Actually you can do it. It is just too expensive and dangerous.

As for your project. The best is to experiment with it.
As a starter, you should calculate the power that you need.
Power is a function of battery, not motor.
The motor rated power is the sustained power that the motor and
windings can withstand for along time.

the motor power is defined by rpm x torgue.
rpm is proportional to voltage

How much rpm can your motor stand for a short time, mechanically.

torgue is proportional to current. How much current can your motor
stand for a short time. Current creates heat so the limit is heat.
If you can put cooling system to this motor you can operate it at high
torgue, at least for a short time.


Propeller theory. Propeller is just like a screw. How far does it go
per RPM.
At low speed, the air need not travel so fast, so low pitch is
desirable. In order to increase the thrust, you need high volume
running at low speed. Long propeller.

You don't need maths. Just a sense of balance.

So adjust the pitch and diameter of the propeller to match the voltage
and current rating of your electric motor.

You can exceed these ratings, but take special precautions, such as
cooling the coils.
In fact I like to experiment with overcurrent and its effects. Over
RPM is dangerous because it is mechanical. Over current is just heat
which we can control.

  #14  
Old August 24th 10, 04:58 PM posted to rec.models.rc.air,rec.aviation.homebuilt
Doug McLaren[_2_]
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Posts: 1
Default What size propeller for a 36 V DC motor?

["Followup-To:" header set to rec.models.rc.air.]
On 2010-07-29, John Doe wrote:
| "Morgans" jsmorgancharterJUNK.net wrote:
|
| Look in places that talk about remote control airplanes, because
| that is what even the man carrying experimental airplanes are
| borrowing knowledge from, on the subject of electric flight. It
| is just at larger scales.
|
| I believe that, but how come you never see a real airplane
| standing on its tail?

Because you don't look in the right places?

http://en.wikipedia.org/wiki/Lockheed_XFV
http://en.wikipedia.org/wiki/Convair_XFY

Ultimately, yes, for electric flight, most of the innovation is
happening with models and UAVs because that's where it's more
practical. Once you get into planes large enough to carry humans, the
cost difference between electric and internal combustion becomes huge.
For example, for a powered parachute, somebody mentioned a 30 hp
engine. You could have that engine for a few hundred dollars, perhaps
a thousand, but a comparable electric setup would cost way more, and
something that will keep you up for an hour or two will weigh way more
than the equivalent gasoline powered setup and cost even more.

Full scale electric planes do exist, and I would expect more work in
that area, but it's not going to really be practical for most uses
until battery or fuel cell technology gets a lot better (or at least
cheaper.)

And also, if your model fails, you've got a pile of sticks to fix up.
If your full scale plane fails, you might be dead.

But good ideas certainly do flow in both directions.

| Looks like that would be a neat way to
| simulate a Harrier landing, and takeoff.

Yes, though the examples I gave had massive problems. The first was
never even taken off vertically!

--
Doug McLaren,
COFFEE.EXE missing - Insert cup and press any key.
 




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