I am new to electrics. I bought MotoClac to help me figure out what motor battery esc combo to use and it is helpful, but.. When I measure current draw and rpm on the groundthe numbersare always lower than those MotoCalc predicted. I am not sure how far beyond these I can push the motor. I was hoping somebody can help me take the ground numbers and understand what i might expect in the air.

Motocalc is usually very accurate, so I don't understand the difference between their prediction and your measurements. More info would be helpful: name and numbers for motor, name and numbers for ESC, same for the prop and the battery pack.

With decent quality components the numbers you get from the manufacturer usually leave a little "headroom" for heavy-handed modelers - but not always.

Your current draw will drop in the air, but not as much as some claim.

Do you have the throttle pane on Motocalc wide open? Does your TX stick match the setting?
Walt

For comparison, it might be interesting to try DriveCalc and see how the predicted numbers compare to your measurements. The calculators can provide very close estimates of what to expect, but the actual measurements provide the best guide to setting up your power system. If you're running conservatively during static testing, you will have no trouble in flight.

Thanks guys, I pull some of my numbers together and post them, got to go out with the grandkids tonight though, Fathers day after all.

The power calculators will give you an estimate for your initial setup and prop size selection, but you still need to use a Wattmeter to get more accurate measurements of your actual setup.

I've seen a few guys compare static vs. in flight current numbers, and all the comparisons I've seen differed only by only a few percent.

Given this, I wouldn't let the static Wattmeter readings exceed the limits of your components.

<div style="margin: 0in 0in 0pt">Ok, here is some data. My measured numbers are lower, comparing static to static, and of course I can&rsquo;t really compare in-flight since I don&rsquo;t have an onboard data logger. I&rsquo;ve done some other motors and the results are typical. I am no so concerned with the absolute difference; they aren&rsquo;t actually that large, at least for the static case. But if you look at what happens as the airspeed goes up there is a big difference in current draw according to MotoCalc. If there is a significant current drop in the air I could prop up to increase performance. I would expect a RPM increase as the motor unloads as glow engines do.</div>Or maybe a couple of amps is not significant, Like I said I am new to electrics

By the way I am using a Astro Wattmeter and an optical tach to make the measurements

I would not recommend doing that. It would be better to use a larger motor to improve performance while safely running below the maxium rating. The in-flight drop in load is not a constant percentage and depends on the kind of flying you're doing at any particular instant. Use the static current draw at full throttle to set your maximum safe current level. You could match that while flying, but you can't exceed it.

Tim's advice is right on.

In most cases your numbers are within 5% of each other. Since Motocalc deals with an ideal system and you are testing a production system manufacturing tolerances could account for the difference.

I notice tha you are using MA props. Try switching to APC; you'll most likely see a performance increase and a decrease in amp draw.
Walt

Thanks for the advice guys, I was trying to make things to close to the max values. Tim's comment made me realize that I have always set my glow engines on he rich side and this can apply to electrics also. And Walt was right on pointing that the differences are small. I really like the electrics. I have done 4 planes so far, all converted from glow, and I probalbly will go all electric in the future