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Feb 03, 2012, 11:56 AM
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Woody_99's Avatar
I've got the CG on the spar. Do you like if further back?
If I need to move it, may have to put a lighter motor. The one in there now is 140g, 1000kv.
I also have a plastic spinner which is adding front weight too. Figured nose heavy is a better way to start.
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Feb 03, 2012, 03:52 PM
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ATC Chilli's Avatar
I also maidened my Gemini over the last week. I tried a APC 12x6 and wattage was down 100 watts over the similar sized MAS electric prop. The plane flew great but the landing made me look like a chump novice on the asphalt with the springy gear. But on lumpy grass it was a different story. The stock gear soaked up the bumps nicely. She would nose over gently at the end of the roll out but I'm used to that after flying my PZ Spifire on the grass. She was nose heavy with the Himax motor, aluminum mount and 60 amp controller. CG was about 1/4 inch fore of the Spar. I added some weight under the horizontal stabilizer and CG is now at the trailing edge of the spar. I'll take her up this weekend and see how she does.

So far a very nice plane!!

Thanks to all for their input.
Feb 03, 2012, 04:11 PM
My Co-Pilots Rock!!
wolfewinde's Avatar
I like to keep moving the CG back until the airplane does not drop the nose when she rolls and will fly pretty neutral when inverted, BUT you are far better off to start a little nose heavy and move the CG back very slowly as you get more comfortable with the airplane.

Grats on the maidens you guys

Wolfe
Feb 03, 2012, 04:39 PM
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Woody_99's Avatar
Quote:
Originally Posted by ATC Chilli
I also maidened my Gemini over the last week. I tried a APC 12x6 and wattage was down 100 watts over the similar sized MAS electric prop. The plane flew great but the landing made me look like a chump novice on the asphalt with the springy gear. But on lumpy grass it was a different story. The stock gear soaked up the bumps nicely. She would nose over gently at the end of the roll out but I'm used to that after flying my PZ Spifire on the grass. She was nose heavy with the Himax motor, aluminum mount and 60 amp controller. CG was about 1/4 inch fore of the Spar. I added some weight under the horizontal stabilizer and CG is now at the trailing edge of the spar. I'll take her up this weekend and see how she does.

So far a very nice plane!!

Thanks to all for their input.
Question for you (or anyone) on the prop. When you say the watts were down over 100 with the APC vs the MAS prop, is that a good thing?
From what little I know, if everything else is equivalent, and you can do that with less power, the better. Right?

I read so often about high watts, etc, but to me seems like goal would be to lower the watts if you could provide the same performance.

Like some other size electric vs sport props. For what ever reason, some sport props pull less current to do the same job than their counterpart electric.
Just curious.
Last edited by Woody_99; Feb 04, 2012 at 10:18 PM.
Feb 04, 2012, 09:59 PM
Fighting Gravity
bonnie9496's Avatar
Quote:
Originally Posted by ATC Chilli
The plane flew great but the landing made me look like a chump novice on the asphalt with the springy gear. But on lumpy grass it was a different story. The stock gear soaked up the bumps nicely. .
Congrats on the successful maiden.

Check out post 2558 for my landing gear mod. Springy..... but not too springy!
Feb 05, 2012, 02:49 PM
Registered User
Finally got mine finished, finally because a couple of parts missing, found the first one missing and got that replaced fast, then ran into another shortage, that took a couple of weeks to get. Balance with 2200, 20C battery between 75% and 90%. about half way, thumb balancing hard to tell. Planning on a maiden before Super Bowl. Flight report later!
Feb 05, 2012, 06:47 PM
My Co-Pilots Rock!!
wolfewinde's Avatar
Got back out this afternoon and put 6 batteries through the Gemini. I am trying to get better at my rudder turns - made some progress today. This is just a great airplane - one of my favorites for sure

Wolfe
Feb 05, 2012, 08:58 PM
Registered User
ATC Chilli's Avatar
Quote:
Originally Posted by Woody_99
Question for you (or anyone) on the prop. When you say the watts were down over 100 with the APC vs the MAS prop, is that a good thing?
From what little I know, if everything else is equivalent, and you can do that with less power, the better. Right?

I read so often about high watts, etc, but to me seems like goal would be to lower the watts if you could provide the same performance.

Like some other size electric vs sport props. For what ever reason, some sport props pull less current to do the same job than their counterpart electric.
Just curious.
If your power hungry, wattage is power. So generally more watts is a good thing. But sending too much current through a motor will creat a less efficient set up which wastes the extra power. Instead of the wattage going toward thrust, it starts heating things up. I was pulling well over 500 watts with the MAS prop. My 60 amp controller could handle it but my motor wasnt designed for delivering that kind of power. Too much time spent drawing 50 amps would quickly overheat the Himax motor and damage the magnets (among other things). I'm not the type of flyer who runs wide open throttle allot, but I still felt more comfortable with a prop that is a little closer to the design parameters of the motor I'm using.

I didnt measure the thrust difference between the two props and not do I know much about prop efficiency or design. Hopefully someone else will chime in on the difference between the two.
Last edited by ATC Chilli; Feb 05, 2012 at 09:22 PM.
Feb 05, 2012, 11:37 PM
chuck
Quote:
Originally Posted by ATC Chilli
If your power hungry, wattage is power. So generally more watts is a good thing. But sending too much current through a motor will creat a less efficient set up which wastes the extra power. Instead of the wattage going toward thrust, it starts heating things up. I was pulling well over 500 watts with the MAS prop. My 60 amp controller could handle it but my motor wasnt designed for delivering that kind of power. Too much time spent drawing 50 amps would quickly overheat the Himax motor and damage the magnets (among other things). I'm not the type of flyer who runs wide open throttle allot, but I still felt more comfortable with a prop that is a little closer to the design parameters of the motor I'm using.

I didnt measure the thrust difference between the two props and not do I know much about prop efficiency or design. Hopefully someone else will chime in on the difference between the two.
well this sums the whole prop thing very well, and few understand it this well. as far as the difference in type goes , my guess is both are to much prop and the small difference in loading is magnified at these current levels . these props have shown to be close in power vs rpm . unless u need absolute power to weight as in racing or full blown 3d ,propping down and using more throttle has huge benefits.

power in vs power out is greatly affected by any heat produced by the motor , a watt is a watt , some turn the prop some make heat. as the motor heats the resistance in the copper windings goes up and makes even more heat for a given current flow . vicious circle.

the upper end of the throttle is the most efficient settings in the esc also , as the switching at lower settings causes heating , this of course is given the esc is rated for the load.
i shoot for 2 1/2 to 3 1/2 static watts per gram of motor weight depending on how efficient i want to be then check the heating from there , any thing over warm and i prop down.

most gas props are made to run at higher rpm and to put up w/ the pulsing power of the ic motor, that being said i have used some w/ great success.

chuck.
Feb 06, 2012, 08:57 AM
Registered User
Woody_99's Avatar
Thanks guys for the feedback on the watts question. I know this probably wasn't the right place to ask it, but some of the post prompted the thought. Basically more power is good if it is performing work, and not turning to heat. I also tend to like to run the lower side of the amp limits too.

I've used "sport" props on a couple of different electric planes, and been happy with the results. Seems like less current to do the job. Might be that curl at the root of the electric props that I don't see on the sport props.
Feb 06, 2012, 04:54 PM
Fill'er Up!
mattyhawk's Avatar
Quote:
Originally Posted by ATC Chilli
...
I didnt measure the thrust difference between the two props and not do I know much about prop efficiency or design. Hopefully someone else will chime in on the difference between the two.
Thrust is better with the MAS than APC in most of the throttle range except full throttle. MAS make really bad speed props, APC are better. Since the MAS blade cord is wider overall as the prop goes from the hub to tip, it promotes lots of thrust at lower RPM with the issue of more load as RPM goes up. I believe I saw a test that showed APC is more efficient than MAS, but I can't remember where, so it may be moot to even mention it. APC's are generally lighter than MAS, so changes in direction and acceleration make the APC easier on amp draw than MAS. APC's are also more responsive due to less weight. Also, I suspect MAS are better than APC with regards to static prop stall resistance.

Quote:
Originally Posted by Woody_99
Thanks guys for the feedback on the watts question. I know this probably wasn't the right place to ask it, but some of the post prompted the thought. Basically more power is good if it is performing work, and not turning to heat. I also tend to like to run the lower side of the amp limits too.

I've used "sport" props on a couple of different electric planes, and been happy with the results. Seems like less current to do the job. Might be that curl at the root of the electric props that I don't see on the sport props.
I really like what was said by ATC Chilli and chas650r. Just remember, RPM's are everything and to sum it up, "Basically more power is good if it is performing work...". Just remember what your goal is. 3D and Ultra speed tend to eek out every bit the motor can handle. The key to look for is to find the point the motor is stalling for a given load and stay under that, indicated by a significant loss in RPM and significant increase in heat out.. You can suck all the heat out of a motor you want, but a motor cannot do work if stalled. And remember, your statemement "...and not turning to heat" is only applicable IF your goal is to maximize flying time with your highest efficiency.
Feb 11, 2012, 10:04 AM
Registered User
Woody_99's Avatar
Far too quiet here in the Gemini thread, and too cold outside to fly here, so I thought I would post a couple of pictures of my build.
Nothing too unique (other than my odd sense of humor) about it. Modded the LG, rubber tires and a plastic spinner.
The wire tie in the battery compartment is just a little insurance against wires bouncing up and toward the motor. I put the battery in, connector end first and up against the right hand wall.
Anyway, just wanted to share.
Last edited by Woody_99; Feb 11, 2012 at 10:23 AM.
Feb 11, 2012, 10:19 AM
PSALM 14:1
Sammy70's Avatar
Looks good Woody.

Too cold/nasty here to fly as well...
Feb 11, 2012, 10:29 AM
My Co-Pilots Rock!!
wolfewinde's Avatar
Good looking plane, Woody.

Have had my Gemini out a few times this week. She is still one of my favorites. It has been pretty windy here n Florida but temps have been good as usual. 20 mph this weekend, though, so no flying for me until it calms back down.


Wolfe
Feb 11, 2012, 01:03 PM
Registered User
14 degrees in mid Michigan right now!!!!!


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