Need a little advice on a motor upgrade to a Green Sleeve sail plane.
08-28-2013, 12:50 AM
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Need a little advice on a motor upgrade to a Green Sleeve sail plane.
I'm modifying a older Green Sleeve for my daughter. I've removed the old brushed Speed 600 motor and installed a E-Flite Power 15 (575 watts)
on 3 cells on a 45 amp ESC with a 10x8 folding prop. The issue I have is the lack of rigidity in the nose. Anything above about 60% power the nose begins to twist.
Thinking about installing Graphite below the canopy cutout to stiffen? Have I gotten to aggressive with my prop selection or is this just to much motor?
Thanks in advance for your help.
on 3 cells on a 45 amp ESC with a 10x8 folding prop. The issue I have is the lack of rigidity in the nose. Anything above about 60% power the nose begins to twist.
Thinking about installing Graphite below the canopy cutout to stiffen? Have I gotten to aggressive with my prop selection or is this just to much motor?
Thanks in advance for your help.
08-30-2013, 12:27 PM
#2
As I recall the Green Sleeves was a 2M glider. More info would be helpful.
Is this your glider?
http://www.maxfordusa.com/greensleevessailplane.aspx
If you replace the 7 cell NiXX pack with 3 cell lipo and go to a brushless you are probably around 44 oz, about 2.75 pounds. That is over 200 watts/pound. For that glider, 575 watts is a wild amount of power. The stock setup was around 150 watts, and that was brushed, so less got to the prop.
If I were to go brushless I would probably have gone around 275 to 375 watts. At 375 it should go vertical.
Like putting a V8 in a VW Bug. No wonder you are having problems. I think you have too much motor. Either prop back or just hold back on that throttle.
Is this your glider?
http://www.maxfordusa.com/greensleevessailplane.aspx
If you replace the 7 cell NiXX pack with 3 cell lipo and go to a brushless you are probably around 44 oz, about 2.75 pounds. That is over 200 watts/pound. For that glider, 575 watts is a wild amount of power. The stock setup was around 150 watts, and that was brushed, so less got to the prop.
If I were to go brushless I would probably have gone around 275 to 375 watts. At 375 it should go vertical.
Like putting a V8 in a VW Bug. No wonder you are having problems. I think you have too much motor. Either prop back or just hold back on that throttle.
Last edited by aeajr; 08-30-2013 at 12:42 PM.
08-30-2013, 07:15 PM
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The old Speed 600 was about a 18A x 8.4V=150'ish watt power plant. You've just stuck in what is potentially 3 to 5 times as much power depending on how hard the old and new motors are being used.
Is it any wonder that the model is shuddering in fear?
Seriously though, you've upped the anty WAY beyond what the folks that designed the model could expect. So why not simply re-motor it down to something around 200 watts and call it good to go? The lighter motor and pack will lighten up the model so it'll fly in a far more dainty manner than the old Speed 600 and big NiCad pack. So you're already leagues ahead. And it would be FAR more simple than beefing up the nose only to find out that the added speed brings on other problems on this old design.
Is it any wonder that the model is shuddering in fear?
Seriously though, you've upped the anty WAY beyond what the folks that designed the model could expect. So why not simply re-motor it down to something around 200 watts and call it good to go? The lighter motor and pack will lighten up the model so it'll fly in a far more dainty manner than the old Speed 600 and big NiCad pack. So you're already leagues ahead. And it would be FAR more simple than beefing up the nose only to find out that the added speed brings on other problems on this old design.
08-30-2013, 09:30 PM
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Good point. Mind you if it's not TOO much work I'd still prefer to see a lighter motor and shift stuff around so the heavier items are up front to aid with balance. Even if a little nose lead is still required there's much to be said for lightening up these old or simpler designs as much as practical. The issue becomes what each individual considers "practical".
08-31-2013, 05:28 AM
#6
BMatthews,
I agree with you but with some of the old speed 600 designs it is hard to lose weight from the nose. I had a Dust Devil, a Cox 2M. Very short nose that was built to balance with that Speed 600. took the 600 out and put in a Rimfire brushless and 3 cell lipo. Had to add 6 oz of lead to the nose to get it to balance no matter what I did. I was not going to extend the nose.
But I got it down from 48 oz to 42 oz and it flew pretty well. .
I agree with you but with some of the old speed 600 designs it is hard to lose weight from the nose. I had a Dust Devil, a Cox 2M. Very short nose that was built to balance with that Speed 600. took the 600 out and put in a Rimfire brushless and 3 cell lipo. Had to add 6 oz of lead to the nose to get it to balance no matter what I did. I was not going to extend the nose.
But I got it down from 48 oz to 42 oz and it flew pretty well. .
09-01-2013, 08:34 PM
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Thanks guy's, I'm kind of new to the electrics. I've been a gas guy for like 25 years so pardon the ignorance!
I had just looked at the all up weight being around 50 oz for this model and check the e-flite specs and came
up with the motor selection. I see your point now and understand that I have overshot the power curve big time.
Now the question remains, what the next step in selecting the proper power for this model? I'm guessing something
like a 450 or 480 outrunner or do you have a better (cheaper) alternative?
Thanks again for the advice>
I had just looked at the all up weight being around 50 oz for this model and check the e-flite specs and came
up with the motor selection. I see your point now and understand that I have overshot the power curve big time.
Now the question remains, what the next step in selecting the proper power for this model? I'm guessing something
like a 450 or 480 outrunner or do you have a better (cheaper) alternative?
Thanks again for the advice>
09-02-2013, 07:34 AM
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The old numerical names really don't mean much anymore other than as a very broad idea of the power range or frame size. Far better is to look at the motor's peak watts and go with that.
For sport flying I like to look at motors with enough power that I only need to use about 80% of the maximum rating to adequately power the model. If the original model was about 50 oz with the old 600 can motor and big sub C pack on board then you can expect the weight to drop by 10 oz down to 40 oz ready to fly depending on motor, pack and possible nose weight issues as related by aeajr. Even with a possible nose weight issue it would not be unreasonable to see a 10 oz reduction though.
To climb out at a good but not rocket like climb angle with a low Kv motor turning a big "climber" prop a good value is 80 watts/lb of model weight. And with 40oz being 2.5 lbs that means you want to load up the motor to around 80 x 2.5= 200 watts. So motors with a max rating of 230 to 250 watts are all you need from a simple power handling perspective. And even if you want to achieve the darn near vertical climb rate that comes from running up around 100 watts/lb you're still only looking at 250 watts of power from a 280 to 300 watt max motor.
Then there's the Kv value of the motors. For turning a bigger prop which works better for climbing performance we want to go with a fairly low Kv value.
A quick look at the budget priced motors at Hobby King suggests that ;
http://hobbyking.com/hobbyking/store...er_1100kv.html
would be one viable option. It's rated for 270 watts max so running it at between 200 to 250 watts on a glider would not stress it overly. Note that the motor with mount and all is sitting at around 2 oz. So unless the tail is light and other stuff inside can be relocated towards the nose it's likely that you'd need a little nose weight to restore the original balance point.
The odd thing is that brushless motors are such good converters of power to wind that aeajr is right about using a bigger motor than required if you need nose weight anyway. The power that the motor will draw from the pack is simply related to the prop and pack voltage. A small and a big motor will both do the job provided the power draw as determined by the prop doesn't result in the smaller motor exceeding its max power rating and burning out. This is a pretty simplistic way of looking at it and other factors DO count for something. But it's still a valid way to look at brushless motors compared to the rather narrowly focused old conventional brushed motors.
And the bigger motor might suit you better for some future design. On the other hand if you prefer smaller park size models then going with one of these 2 oz 300 watt motors and simply using extra nose weight might suit you better for some future project. Only you can provide this answer.
For sport flying I like to look at motors with enough power that I only need to use about 80% of the maximum rating to adequately power the model. If the original model was about 50 oz with the old 600 can motor and big sub C pack on board then you can expect the weight to drop by 10 oz down to 40 oz ready to fly depending on motor, pack and possible nose weight issues as related by aeajr. Even with a possible nose weight issue it would not be unreasonable to see a 10 oz reduction though.
To climb out at a good but not rocket like climb angle with a low Kv motor turning a big "climber" prop a good value is 80 watts/lb of model weight. And with 40oz being 2.5 lbs that means you want to load up the motor to around 80 x 2.5= 200 watts. So motors with a max rating of 230 to 250 watts are all you need from a simple power handling perspective. And even if you want to achieve the darn near vertical climb rate that comes from running up around 100 watts/lb you're still only looking at 250 watts of power from a 280 to 300 watt max motor.
Then there's the Kv value of the motors. For turning a bigger prop which works better for climbing performance we want to go with a fairly low Kv value.
A quick look at the budget priced motors at Hobby King suggests that ;
http://hobbyking.com/hobbyking/store...er_1100kv.html
would be one viable option. It's rated for 270 watts max so running it at between 200 to 250 watts on a glider would not stress it overly. Note that the motor with mount and all is sitting at around 2 oz. So unless the tail is light and other stuff inside can be relocated towards the nose it's likely that you'd need a little nose weight to restore the original balance point.
The odd thing is that brushless motors are such good converters of power to wind that aeajr is right about using a bigger motor than required if you need nose weight anyway. The power that the motor will draw from the pack is simply related to the prop and pack voltage. A small and a big motor will both do the job provided the power draw as determined by the prop doesn't result in the smaller motor exceeding its max power rating and burning out. This is a pretty simplistic way of looking at it and other factors DO count for something. But it's still a valid way to look at brushless motors compared to the rather narrowly focused old conventional brushed motors.
And the bigger motor might suit you better for some future design. On the other hand if you prefer smaller park size models then going with one of these 2 oz 300 watt motors and simply using extra nose weight might suit you better for some future project. Only you can provide this answer.
09-11-2013, 09:08 AM
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Ed and BMatthews,
Thanks for this information as I am about to replace a brushed Astro 05 Cobalt with a brushless setup in an plans-built "Electricus" e-sailplane. I prefer an in-runner motor, non-geared, to drive a Graupner 7.5 x 4 folder on 2 or 3S Lipo or 3S A-123 batteries. The max motor diameter is 38 mm and I should find something suitable at the NEAT Fair this coming weekend. Many thanks for all your good info-much appreciated.
Art ARRO
Thanks for this information as I am about to replace a brushed Astro 05 Cobalt with a brushless setup in an plans-built "Electricus" e-sailplane. I prefer an in-runner motor, non-geared, to drive a Graupner 7.5 x 4 folder on 2 or 3S Lipo or 3S A-123 batteries. The max motor diameter is 38 mm and I should find something suitable at the NEAT Fair this coming weekend. Many thanks for all your good info-much appreciated.
Art ARRO
