fourball

Hello, I am trying to come up with an electric motor/battery combination for a Kadet LT 25 conversion. I know this has been discussed before and have read the extensive threads on ezone. The problem I am having is trying to equate Motocalcs calculations with real world performance. I seem to recall that someone suggested the AXI 2820/10 on 10 cells and a 12x8 prop, plugging this into Motocalc, it seems to be that this combo may be a little anemic. What I would like to do is have the same performance as the glow powered version of this plane, speed, maneuvers etc. Using Motocalc it seems to me that the AXI 4120/14 with 16 cells and a 12x8 prop would be a better choice, but it also looks like it may be extreme overkill. I guess the biggest confusion comes from not knowing what the glow powered version does, other than what I have seen at the field, the thing I do know is that it seems to fly circles around my PT electric with a 12x8 prop, Magnetic Mayhem, 3:1 gear and 8 cells. The LT's seem to be considerably faster and more aerobatic than my PT electric, and when I compare what Motocalc says about my PT electric compared to the LT 25 with the 2820/10 the numbers look like the performance will be identical to my PT electric, and not anywhere close to the glow powered version. Am I just way out in left field here? I just don't want to show up at the field with another "electric" that looks like it has problems getting out of it's own way.

Any advice would be greatly appreciated.

Paul

Matt Kirsch

My Feedback: (21)

I can tell you from experience that the 4120/14 setup would be more appropriate in a Sig LT40. I've got the exact same setup in a .40-size Corsair, and it pulls it around beautifully.

Be warned that the numbers that Motocalc gives for the outrunners aren't always accurate. Running a 12x8 prop on a 2820/10 and 10 cells is pushing the motor beyond its recommended limits. Motocalc won't accurately show that, instead telling you that the current remains roughly steady as you increase propeller size.

For accurate numbers regarding AXI outrunners, try http://www.modelmotors.cz.

For sure, the AXi will put more ponies to the pavement than the Magnetic Mayhem. You know, I think you might be pleasantly surprised if you simply swapped out your MM/gearbox for an AXi 2820/10, leaving everything else the same. It sure would be less work and cheaper than buying the LT-25.

fourball

would you still use the 12x8 prop and 8 cells? I appreciate your answer, eventually I am going to need a new plane, and it seemed to me that the LT 25 would be a good second choice, since it adds ailerons, and steering on the taxi-way. I may consider the LT 40, with the 4120/14, I did think this was too much for the LT 25, just trying not to make any expensive mistakes.

Thanks again

Paul

Greg Covey

Hi Paul,

I agree that the AXI motor will have plenty of power to keep you happy.

Look what I fly with an AXI motor.

[link=http://www.rcuniverse.com/magazine/article_display.cfm?article_id=114&CFID=631098&CFT OKEN=6f8044-b11ce06d-6df4-4e9c-83b0-d9b2263f957c]10lb Monocoupe[/link]

fourball

Thanks Matt and Greg,

Sounds like I will take your advice and go for the LT 40 with the AXI 4120 when I can no longer put the PT electric back together.

Paul

pikebishop

I have an lt 25 with a magnetic mayhem on a belt drive apc 11/7 e prop and ten cells and at wide open it is pretty fast. plenty of takeoff power also 30 feet off of grass. the lt has a clark y airfoil compared to a flat bottom and helps the speed a little I think.

BEC

Go back to the Ezone, and go to the article archives and look at the review I did of the LT-25.

Today I have a Hacker B50-13L on an MEC Superbox and 14 CP1700s in my LT and it will go straight up. Not what you need.....

But, I am also flying a larger, heavier airplane (JK Aerotech Big T) with an AXI 2820/10 on 10 cells and a 12X6 APC-E and it is plenty of power for anything any self-respecting foamie trainer (that weighs 5 1/4 lbs.) should be able to do and then some. The LT-25 is smaller and lighter - the 2820/10 will be plenty.

For some reason Motocalc makes the AXIs look much worse than the really perform.

If you would rather just liven up your PT-E, you could use an AXI 2814/12 and maybe an 11X7 APC-E prop - and a 40A controller of your choice (Phoenix 45, Jeti Advance 40-3P would be two worth considering) and hang on!

fourball

Thanks BEC,

I am still trying to figure all this out, I post on here because EZONE is blocked from work, not that I would be on here instead of working. One of the things that I am still confused about, is the watts/lb, I know that some say 75 watts/lb and others 100 watts/lb to perform like the glow plane, I guess that's subjective, but do you look at the watts into the motor? Or the watts at the prop?

For example looking at my PT electric, right now it's pretty close to 56 oz. which is 3.5 lbs.

So from the model motors website I get the following information on the AXI 2814/12 and 11x7 prop

1. Volts are 8.4, (says 8 cells, so I am assuming there is a 1.2 volt loss for the motor?) and current 36.6 amps, that gives us 8.4x36.6 close to 307 watts.
So 307 watts/3.5 lbs is 87 watts/lb, greater than the 75 watts/lb thing. That's watts into the motor.

2. With a motor efficiency of 70%, the watts out of the motor are 215, which gives us 61 watts/lb.

So if we look for 75 watts/lb then for watts in we are fine, but watts out we are not, do you see the confusion?

I am not in any way implying that you don't know what you are saying, I am just a still a little confused.

Thanks
Paul

fourball

Also, your option is much higher watts/lb than what I am using right now, and I am sure that it would be much, much better than what I am flying now.

Thanks again
Paul

Matt Kirsch

My Feedback: (21)

When you're working with Watts/lb, just pay attention to Watts in. Don't worry about Watts out, especially with any sort of brushless motor. The Watts/lb rules are based on Astro Cobalt motors, which peak out at around 60% efficiency, AND they were based on INPUT Watts only.

fourball

Thanks Matt, that clears things up. I still haven't decided what I am going to do, as I just had to practically rebuild the entire fuse on the PT this past week, still thinking it may be time for a new plane, but will probably be a while, at least after the holidays.

But thanks to everyones help, I believe I can now go in the right direction without too much worry about doing the wrong thing.

Thanks
Paul