Hi Sid
Don't forget that watts are corresponding to the product of two factors
depending of rpm and the prop
** Static thrust
** Pitch speed
For the same power you could increase one and decrease the other
For acro flight increase the static thrust against the pitch speed
For a racer do the contrary.
Your choice (flight mission)
These two factors are clearly showed in "Scorpion Calc Wizard - generic"
http://www.rcgroups.com/forums/showp...&postcount=368
Down-list "user basic ratios" in the field "User/pilot"
Louis

I've got S.C. 3.53 and the Wizard doesn't work.!??

Originally Posted by jollyroger

I've got S.C. 3.53 and the Wizard doesn't work.!??

The wizard is not enabled on the v3.53 SC
nor on the last v3.55 SC
The wizard is only on the "preliminary-beta 4" SC, indicated
Inversely the SC beta 4 is not updated with the recent motors.(> feb 2011)
Louis

sidless,

The amount of power you need depends a lot on the exact model and the desired flight performance. Real full size airplanes fly well on around 40-50 watts per pound. You have to go a couple thousand feet on a take-off roll and you climb at a 4-5 degree angle with respect to the ground. Most people want way better performance than this in their RC model airplanes. If you are flying a Pitts S12 or an Ultimate Bipe, that has Gobs of power in real life, then you would want your model to have anywhere from 150 to 200 watts per pound. Something like a JN-4 Jenny or a Stearman can be flown quite well on about 75 watts per pound.

As you said, if you need to swing a big prop, you need to use a lower Kv motor, and the S-4035-250 is a good option in cases like this. I confirm your numbers that you calculated for operation on 7 cells with the 20x11 prop. This will give you good take-off performance, and the ability to climb out briskly if you ever need to do a "go-around" on a landing approach. This higher pitch of the prop will still give decent cruise speeds, even when throttled back to 50 to 60% throttle, which is all you will really need to maintain very scale level flight.

A lot of time people forget that different models can do very well with lower power levels. If you only wanted to spin a 16 or 17 inch prop, then the S-4035-250 motor would perform very well on 10 Li-Po cells, but for the larger 20-21 inch props, you would need a motor with a Kv closer to 200 to be able to spin a prop that big.

Lucien

The full size Piper J 3 Cub flies just under 50 watts/Lb.
Continental 65HP engine.

which scorpion motor on 3s would be good for a crash test hobby hercules pusher wing that comes in at 8.5lbs loaded with fpv gear (includes 2 3s 8000mah lipos). I need something that will give me decent vertical.

Thanks Lucien I thought it would be ok but my large model experience is limitedas I like to keep between 2 and 4 pounds. Now just gotta get all the stuff fitted and up and flying.
Sidless

Hi Sid I purchased a scorpion 2503 for my F3p airplane it has the prop saver machined in a cone it is giving me fits trying to run a gws style prop. It just wobles around on the cone and will not let the prop turn true. When I bought the motor it specified gws style props is there a trick to this I am missing ?

Originally Posted by RandyQman

Hi Sid I purchased a scorpion 2503 for my F3p airplane it has the prop saver machined in a cone it is giving me fits trying to run a gws style prop. It just wobles around on the cone and will not let the prop turn true. When I bought the motor it specified gws style props is there a trick to this I am missing ?

..have you tried it both ways...usually one way or the other fits GWS props..

Bill

Both ways??? Im just putting the prop on and the o ring to hold it although I do like to use a few small rubber bands instead of the o ring. It works fine on my AXI motor.

Originally Posted by RandyQman

Both ways??? Im just putting the prop on and the o ring to hold it although I do like to use a few small rubber bands instead of the o ring. It works fine on my AXI motor.

Yes, by "both ways" I mean you can generally install the prop saver unit TWO ways....and the outside hub is made in two different sizes to fit different diameter holes in different props.
Also there are times that I have fitted one of those small plastic spacer rings into the prop hole to size it properly for the prop saver. (they come with APC props)
Take a closer look at the hub and you may have to remove it, flip it over, and reinstall it for the GWS prop to fit properly.
If it is the same size on both sides....then a spacer is the way to go.

In the picture you can see that the "hub" size is different on each side....one side fits the GWS props better than the other side.

Bill

Thanks for the reply but the prop saver on the 2503 is machined in with the rotor on the motor. With just a few millimeters of the shaft sticking out .

Ok...that's a nice motor from Scorpion and they will stand behind it...

The Scorpion S-2503-1610 F3P Special motor is designed to be the ultimate competition motor for the indoor F3P planes. This motor is designed to run on a 2-cell Li-Po battery pack, and when teamed up with a Scorpion 11 amp ESC, provides a potent power system for your indoor model. The S-2503-1610 motor features a Titanium Main shaft, and tips the scales at a scant 20 grams (0.69 ounces). This motor was optimized to work with props such as the GWS 8x4DD and 8x4.3SF, which are so popular with the indoor fliers.

If your having a problem with the recommended GWS prop not fitting securely....contact Lucien Miller at Innova8tive Designs.com for a replacement. He's a great guy..!

Bill

Isn't there a metal thingy that looks like an aluminum washer with a piece of tube attached that fits inside the pro hole to adjust to the other common size. I have one in my GWS 8x4 for my H****r A10.

Thanks for the help Bill & DavidN I did find a previous post where Sid suggested putting a nut in the GWS prop. I found a nut that fit and opened the hole up to 3 mm . Seems to work good now I will find out when I madin this SU-29 in the Gym this morning. Thanks again Randy