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axi 5330/f3a or axi5330/18

Old 03-24-2006, 03:57 AM
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Default axi 5330/f3a or axi5330/18

Hi all,

I know the physical difference between these two motors, but want to ask - of people who have used them both which would they prefer? My experiences with experimenting with larger diameter/lower pitch props on my i/c setups generally didn't succeed as the slower flying speed tended to make the planes less precise - they didn't lock in as well. My feeling is that the 18 would give this slightly higher flying speed leading to more precise flying, whereas the f3a would tend to fly more slowly leading to the lack of precision in comparison.

I have also heard people say that the 18 is not suitable for fai class, only for the lower classes? Why is this? I would have thought that the overall performance would be similar, just with a different style of power delivery as described above.

If I have got the wrong end of the stick here then please do correct me, I just want to be sure of picking the right one!

thanks guys,

Old 03-24-2006, 03:45 PM
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Default RE: axi 5330/f3a or axi5330/18

I built a Focus 2 and powered it with an /F3A (RIP), flew great had more power than I needed. My father built a Focus 2 and powered it with an /18... RIDICULOUS power! Seriously way too much.

To compare them we had the same prop, an APC 20-13. With the F3A this resulted in a nice manageable power band, verticals generally needed no more than 60-70% throttle to get over the top at good speed. The /18 on the other hand was a handful. Any throttle over half stick (even with the curve set at 40% power) the plane would accelerate like mad in the vertical. Seriously, anything over half was just showing off. I ended up bringing down the curve to where it looked like a bunny ski slope just so you could fly it! Way too much power.

The difference between the two props is that the /F3A allows you to use a larger prop without a high current when compared to /18. You can use either motor for F3A, but if you want to have the larger prop for downline braking and overall speed management, the /18 isn't for you.

At sea level an /18 will pull close to 100 amps with a 22x12. I have never tried it, but I do know at 5000' it's about 89 amps, and I have tried that!.

At sea level a /F3A will pull with that same prop somewhere around 80-85 amps. I have flown that combination in three airplanes and the speed is very constant and the vertical pull is something to behold.

With my Dad's plane, he has ordered an /F3A so he'll have a more usable power band. The /18 could be used successfully, but the props would have to be in the 18-19 inch range, for his plane anyway.

Tom Messer
Old 03-24-2006, 05:15 PM
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Default RE: axi 5330/f3a or axi5330/18


that's a great response, many thanks. It tells me what I want to know - essentially, that I want an F3a motor, not an 18!! Sounds like they'll both have more than enough power, but with the F3a version, that power will be more manageable and I am likely to get more life from my batteries too as I will be using fewer amps.

thanks!! Not long now before I join you guys on the dark side!!!

Old 03-24-2006, 09:30 PM
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Default RE: axi 5330/f3a or axi5330/18

Ditto to what Tom is saying and I can verify as I fly with him that he's not lying or stretching the truth. Plus I have an F3A and it's awesome. I'm running the 22x12 and it's great. I'm going to try other props still, but I like it the way it is...
Great, great, great motor. I cannot say enough about it.

Old 03-25-2006, 01:32 PM
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Default RE: axi 5330/f3a or axi5330/18

hello james

everything said is of course true, but...but if your airplane is as light and aerodynamic as my obsession (see pics on my profile), then the /18 will serve you well. that said, it's difficult to get a plane down to 10 lbs, and in windy conditions, it's not even an advantage. but with a APC/E 19 x 12, cut down slightly to 18,5 x 12, you get the 18 to draw not much more than 78A, you have a nice singing prop (yeah, some of the old "zing" remains), good tracking with less torque influence because of the smaller prop, and also with the brake on the Castle Creations Phoenix 110HV set between 20 and 25%, really smooth braking action on your downward legs. with the F3A on the large apc, the transition between braking and not braking is sometimes causing the plane to rock to the torque changes. so yes, i agree with everything said, but if you use the motor like i do, it beautifully does the trick. and i fly P05 two times in calm air with 10S1P3700's...hard to beat, that!


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