Can anybody tell me what kv suits what type of aircraft and what flying style? eg

x - x kv suits slow flying scale models
y - y kv suits Sport aerobatic and fast flying scale models
z - z kv suits 3D models and ducted fans

etc

Please help as i do not know what kv to use for my scale mustang. But also interseted in knowing what kv to use for any future planes.

Thanks

In general you want the lowest Kv you can get to turn the rpm you want without using a voltage higher than your ESC can handle.

Nothing is in electric power is as simple as a=b=c except for Om's Law. In general the higher he KV the smaller the prop and the faster the plane; the lower the KV the larger the prop and the slower the plane. Waaaay too simplified, but maybe it will help.
Walt

In very broad terms...
Low kV motors are good for spinning a large prop at relatively low RPM, making them best suited for applications where thrust is more important than speed. This includes slow flyers and 3D planes.

High kV motors are good for spinning a small prop at relatively high RPM, making them best suited for applications where speed is more important than thrust. This includes fast-flying planes of all kinds. At the extreme end, it includes EDFs which need very high RPM. It also includes gearbox applications and helicopters in which the motor is geared down.

Perhaps you already know all of this, but that is about as much as one can say in general terms. If you want specifics, describe your plane in detail, and someone will likely have a good recommendation for a power system.

- Jeff

My mustang is about 6.4 pounds. Im looking for about 700 watts and 55 amps. Im using my 4s LiPo.

What Kv?

Does the prop effect this?

Any prop recomendations?

Thanks again

Try this on for size: 360Kv, 9s1p 2100mAh, 13x6 APC sport prop, 30 Amp ESC, 900 Watts peak, 300-400 Watts in flight.

where can i get a 9s lipo?

The least expensive way is to get three identical 3S packs and connect them in series.

- Jeff

Yes, 3S packs are $44 from Hobby People. I have 12.

Manufacturers use different wire winds to produce different KV results. KV stands for thousands ( K ) of rpms per volt.

So, a 1000KV motor will turn 1000 rpms when 1 volt is applied. It will turn 7000 rpms if 7 volts are applied.

Lower KV motors typically produce more torque so they are typically used with large propellers that will be turned slower. These are very popular on gliders, for example, where climb angle and climb rate is much more important than top speed.

Higher KV motors are typically used with smaller props for higher top speeds. Or they can be used with gear boxes to handle those big props.

You also match based on what battery you plan to use.

If you look here you will see that a given motor is offered in several KV ratings. They make suggestions as to which motor is best matched with which prop and which pattery packs.
http://www.maxxprod.com/mpi/mpi-262.html

Hope that helps.

WHAT DO THE KV RATINGS ON MOTORS MEAN?

Manufacturers use different wire winds to produce different KV results. KV stands for thousands ( K ) of rpms per volt. So, a 1000KV motor will turn 1000 rpms when 1 volt is applied. It will turn 7000 rpms if 7 volts are applied.

Lower KV motors typically produce more torque so they are typically used with large propellers that will be turned slower. These are very popular on gliders, for example, where climb angle and climb rate is much more important than top speed.

Higher KV motors are typically used with smaller props for higher top speeds. Or they can be used with gear boxes to handle those big props, providing a similar result to low KV motors. Sometimes a gear box works better in the installation.

You would also take KV into consideration based on what battery you plan to use.

If you look here you will see that a given motor is offered in several KV ratings. They make suggestions as to which motor is best matched with which prop and which battery packs. If you click on a given motor you can see what kinds of power is drawn based on which pack and which prop. If you click on each of the motors within a model you can see the very different power curves produced by the different battery/prop combos. Here you see the same motor with a different wind producing a different KV result, each optimized for a different purpose.
http://www.maxxprod.com/mpi/mpi-262.html

So, how does this add to other information about motors?

I first set a watts/pound target for my plane depending on the performance I want. I typically target between 70 and 100 watts per pound for sport planes and e-gliders.

Then I consider whether I am looking for high speed or high climb rate. A glider or a 3D plane would be optimized more toward the climb rate side of this dicussion. A pylon racer would be optimized more for speed. A pattern plane might be somewhere in the middle.

Now I get down to prop and battery. Wider prop for better climb, narrower deeper prop for higher speed. Now look at the motor character based on either battery target or prop target and choose the motor/battery/prop combo that meets your objectives.

That is kind of high level but I hope you get the thinking that goes into a motor/battery/prop choice.

> EVERYTHING YOU WANTED TO KNOW ABOUT ELECTRIC FLIGHT
> http://www.rcuniverse.com/forum/m_7100376/tm.htm

Excellent thanks for the replies guys!

Mind you, a motor with Kv=1000 on 5cells is will give the same results the same motor wound for Kv=500 on 10cells.

@aeajr
Nitpicking:
Kv is a parameter, not a unit, therefore Kv=1000rpm/Volt, not 1000Kv.

Vriendelijke groeten Ron

Only when comparing two identical motors wound for different Kv's. Just to be sure, Kv says nothing about power or efficiency. A 10Megawatt motor and a 100Watt motor can have the same Kv.

I see what you are saying. Kv= 830 really should be Kv = .83, but that is not how it is usually used.

Likewise it would be appropriate to write .83 Kv to indicate 830 rpm/v. But again, that is not how it is normally seen.

But I see your point. The notation should be Rv not Kv. Would you agree?

In principle yes, but in practice no! Doubling the number of cells from 5s to 10s reduces the current to half and thus all losses in the motor, speed controller and cables are reduced by a factor 4! The losses in the battery due to its internal resistance is reduced by a factor 2. Also, because of the lower current demand less strain is put on the battery, thus increasing its lifespan.

The correct notation is k_subscript_V where k denotes the constant and V that it has to do with voltage. k has nothing to do with the kilo prefix commonly used in the SI system. Thus, in the example above kV = 830 rpm/V or kV = 0.83 krpm/V are both correct, but the latter notation is seldom used.
Note that the kilo prefix is always written k not K.

Nope, Kv it is. And correct, the K is not kilo. Kt is the torque-constant in torque/Ampère.

Red, to get half the Kv, the number of winds is increased by factor two -> wire resistance increases by factor 2. And the cross-sectional area of the wires is reduced by a factor 2 too, to make rome for the extra winds. -> wire resistance again increased by factor 2. All in all, resistance now has increased by factor four. On ten cells, current is half the original current. And since P.loss = I²R, nothing has changed i.e. as far as the motor is concerned.
Losses the battery-leads are reduced by factor four, not 2. Asssuming we use batteries with half the capacity to keep the original amount of available energy, battery losses are halved because battery resistance doubles and battery current halves.

Vriendelijke groeten Ron

You learn something new every day. Thanks guys.

On the losses in the battery leads and in the battery itself we seem to agree. I stand corrected on the losses in the motor!

The old textbook that I used as reference for the motor constants seems to have made a mistake on wheter k or K should be used to denote these constants. I should have looked looked it up in some more references.