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Old Nov 06, 2010, 05:04 AM
Registered User
United States, CT, Stamford
Joined Jan 2007
827 Posts
Feedback and a few questions on my first WattsUp meter readings.

Hello all

After three years of flying a TRex 450, I decided to take a stab at the planes so I bought a Hobbico Cessna 182 and am pretty much done with the build.

Via a thread on this board, it was recommended to me that a good motor upgrade was the TowerPro here:

combined with a MasterScrew G/F 9x5 prop here:

I am feeding this with a Turnigy 2200mAh 25C pack via a Castle Creation 40amp Phoenix ESC. (I know 40amps is high, but I had it for three years an figured why not use it.)

So to check things over myself, I just bought a WattsUp meter and hooked it up and ran it.

So to test it, one person recommended that I just runup the plane to full throttle for about 5 sec while holding it on the ground and when I did this I got the following peak readings:

465.8 Wp
40.4 Ap

To say that I was surprised and very concerned was an understatement as just to state this motor is rated at 200W and 25Amps.

So then I took the plane out on the tall grass with the meter attached and taxied it around doing several, from a dead stop applying a good amount of power to get it roll things, and got readings of like:

172.8 Wp
14.6 Ap

So is this kinda a normal thing, are most power setups for a plane that are as powerful as need to be for good flying always going to run high watts & amps if held like this and that to really see what the proper Motor/Prop combo is, you need to test it in flight?

As well if this is the case, should I and for how long, should I run it at full throttle while in the air?

If I did happen to get a result of over 200 at full throttle, should I really be worried about this?

If I did, should I do something like test it at 70-80% throttle, or what ever my normal throttle use is, and see what that is and then consider that over 200 at FT acceptable as I rarely and only for a few seconds will ever use that?

Another question I have is, I have gotten several sizes of Props, but would say going with a 9x4 or 8x6 really bring that 465.8W down to below 200 for the static test?

I'm guessing it wouldn't.

So if anyone has any feed back on any of this, I would appreciate it.

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Old Nov 06, 2010, 11:20 PM
JOHN 3:16
Sammy70's Avatar
Central Ohio
Joined Feb 2008
6,905 Posts
A 9x5 prop on that little motor with it's 1600Kv is WAY too much prop in my opinion. It would be much happier (and live longer) on an 8x4 prop (non-sloflyer type).

Have fun!
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Old Nov 07, 2010, 03:33 AM
Registered User
United States, CT, Stamford
Joined Jan 2007
827 Posts
Yeah after doing some more research, it seems the by the manufacturer, they recommend a APC 8x4 or 8x5.

Think I'll give a MasterScrew 8x5 a shot.
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Old Nov 07, 2010, 05:58 AM
Shelter Kitty "Orange Death"
bartricky's Avatar
United States, FL, Monroe
Joined Jan 2008
3,165 Posts
Now that you have a great new tool you can make many observations and adjustments. You will find you can use a larger prop with a 2S batt. than a 3S and sometimes it's necessary to get the plane to fly on 2S.

Now the fun begins..
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Old Nov 07, 2010, 07:11 AM
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Chattanooga, Tennessee, United States
Joined May 2003
27,208 Posts
I simply cannot believe that 40A/465W reading... there is no way that motor could draw that with a 9x5! Despite that, as others have said 9x5 is too big.... read the reviews in your HK link and you'll see that guys are using 7"-8" props.

GWS9050HD 2-blade 17A,7V,123W,25oz,203oz/Kw
GWS9050HD 2-blade 18.35A,7.5V,139w,26.8oz,193oz/kw
GWS8040 3-blade 14.57A,7.48V,105W,21.1oz,201oz/kw
GWS8040 3-blade 15.24A,10.5v,160w,163oz/kw
GWS8040 3-blade 14.57A,7.48V,105W,21.1oz, 201oz/kw
GWS8040HD 2-blade 11.67A,7.41V,84w,18.3oz,218oz/kw

I use a BM2409 motor, 7x6 APC prop, 35Amp speed control and United hobbies 3S1P 2200mah 20C Lipoly battery. 190 watts in a 20oz plane.

Gives 30oz thrust with 7x5 APC drawing 20A/220W on a 3S2100 15C.
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Last edited by Dr Kiwi; Nov 07, 2010 at 07:17 AM.
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