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Electra up-grade - 8/11/2010 1:10 PM   
James c harrell



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Status: offline 		One of my friends in my club hooked me on gliders by giving me a Electra glider. She was complete, stock even a futaba radio and nicd batt. I flew and soon feel slam in love with it. Even found that there was a eagle nested at the back of my field that liked to fly with me. Not sure if it liked the company or was looking to mate but it was fun.Any-way to the point. The nicd batt soon gave up and I went to a 2s lipo which was great. 2200 gave me so much less weight and a lot better power. Every-one at the field said I was struggleing to get it up but I was happy and wasn't really looking for power. I wanted flight time, never been real good at finding thermals. Unless my friend the eagle showed them to me. After a while my motor gave up and I find my-self wanting to go brushless and may-be a 3s lipo. I'm thinking of putting a motor that actually has too much power and using the esc to tone it down to about half power. The new motor needs to be about the same weight as the brushed one that's there now. I think it is about a 540. I am a newbie to brushless and have no idea about the power Classes of these motors. I like the prices at Hobby-king and have a account there but they have not answered my questions about the subject. So I will ask you . You folks fly just like me. What would you get?

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RE: Electra up-grade - 8/11/2010 5:50 PM   
da Rock



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Status: offline 		The answers to your questions are going to require some information first.

How heavy is your glider? How much room do you have for the motor?

I tried to find the Electra online but didn't. Is it a 2 meter?

One good way to find what works for your model is to find similar ones online and see what they call for.

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RE: Electra up-grade - 8/11/2010 6:44 PM   
James c harrell



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Status: offline 		It is a 2-Meter and is the same as the Gentle Lady except it comes with a motor and folding prop. It is made by Carl Goldberg. As far as room There is plenty of room around the 540 brushed motor in it, at least 1/2 inch all the way around it, ESC and batt also has plenty of room for just about any thing I will need. I have a Futaba reciever that has the speed controller made into it, yea it's old, but when I up-grade it will have a Futaba 2.4 with a seperate ESC. Not sure about the weight as I don't have scales but it is all balsa, ribbed wing and tail. Pretty light really. I will look again but I am sure I looked it up here when I got it. I am going to have to add some weight to the nose to off-set the weight of the new batt over the lipo. Already had to when I put the 2s in there. I plan on taking that weight out and compensating with the size of the new motor. I can set my transmitter to only fly on 1/2 or 3/4 and put a mix to hit the swicth and go full power when I want to climb hard.

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RE: Electra up-grade - 8/11/2010 8:44 PM   
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Status: offline 		An E-flite 400 is a very good/better motor than the can 540 for the Electra.
A 450 or 480 is even better.
There is a structural limit with that plane. Too fast, and the wing will flutter, so be careful with adding grunt.
I prefer the pod-mounted motors, keeps the prop off the ground.

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RE: Electra up-grade - 8/11/2010 9:55 PM   
BMatthews



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Status: offline 		The Electra is well worth the conversion. But I'd suggest you lighten it up as well. The Goldberg Gentle Lady airfoil is not at its best when loaded to the wing loading that the Electra struggles with at its "normal" weight as designed with the heavy can motor and heavy original battery pack. The switch to a brushless motor on top of your switch to Lipos will do a lot to perk it up IF you take full advantage of the switchover.

So how best to do that? First off you want a motor that is about 50% more powerful than the old setup. The old setup would have run at 8.4 volts (7 cell Nicd pack) and drawn about 15 to 17 amps. Let's call it 17 amps. That's 8.4 x 17 = 143 watts. Because you want a little more OOMPH let's bump this to 200 watts max runing power for the upgrade. That's less than a 50% increase but you'll be lightening up the model shortly so you'll still have up around 70 watts per lb before we're done. And that's enough for a sporty 40 to 45 degree good speedy climb angle.

Now back to the 200 watts figure. If you' want to run a 3S pack then that's 11.1 volts. Working the wattage equation backwards we have 200/11.1 = 18 amps run current at full throttle. To ensure a nice long cool running lifespan for the motor select one that is happy with a 20 to 25 amp continuous current or about 250 watts continuous. Motors of this type will be around 2.5 to 3 oz in weight. That's a bit lighter than the old can motor at around 5 to 6 oz. But we'll deal with that in a moment.

To spin a nice big prop to dig in better for pure climbing you want to go with a motor having a lower Kv value. And given that you want to go with a 3S pack you want a really low value like 1000 or less. This value will allow you to run anywhere from a 9 to 12 inch prop depending on the Kv value. Check the user comments on the Hobby King site at the bottom of each motor's info and specs page. Often there will be a number of real world examples of what prop, pack and current draws they got. Good info to aid you as well. Your best climbs will come from a 10 to 12 inch prop instead of a smaller "toothpick". And it doesn't hurt that there's some good folding prop options in those sizes.

So how to best gain from the weight loss from this switch? Remove the old can motor and cut back any balsa nose part to reach the first bulkhead of the fuselage. Glue on a new 1/8 plywood "firewall" and mount the motor to this using the mounting plate on the back of the motor so it sits ahead of the firewall. Carve up or make a curled sheet metal shroud to streamline things a bit. Don't forget to allow for some air to flow in and out of this shroud to help cool the motor. Now relocate the battery pack into the nose under the nose hatch and move the receiver back under the wing. When all this is done you may still need to add a small amount of nose weight but overall the model should be a lot lighter than before. I think Sparky Paul has written that his was just under or just over 30 oz at some point. If your Electra comes in at anything in the mid 30 oz range a motor with 200 watts at full power will pretty much be overkill. If it comes in at 40 oz it'll still be a real hotrod. If it comes out at around 30 oz then we overpowered it given that it's an Electra and not a hotliner.

I see now that I completely got carried away with my suggestion for a 200 watt solution. As part of the prep for how to power this you should remove the motor and battery pack you have now and weigh the model with radio gear only. From there use the examples above and add on various motor and pack weights to the model weight and try to come up with a combo that allows for one or two oz of trimming weight. With the combo weight figure on aiming at 70 watts per lb for power and then go motor shopping. You'll need to do a bit of back and forth to find the motor and wattage that fits and balances out.

Sparky's suggestion for the brushless 400 size is a good one but it is best on a lighter airframe. Without knowing what your particular Electra weighs and the size of the servos in it this may or may not suit your situation. If it's one of the heavier wood kits and you're running full size servos then the model will be a bit heavier than it needs to be and would need to be powered appropriately to get the climb you want. But if it has mini servos and happened to come with a lighter grade of wood in the kit you may well be able to run with a surprisingly small motor. Just extend the nose as needed to make it balance.

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RE: Electra up-grade - 8/12/2010 2:35 AM   
James c harrell



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Status: offline 		Great info!! I have removed my motor and requested a scale from my dad. Will weigh it to-nite. It has mini servos in it but it is a very old kit. I got a feeling the wood is of the heavier type cause it feels pretty hard as balsa goes. Can't thank you all for the input and will let you know what it weighs later.

< Message edited by James c harrell -- 8/12/2010 1:35 PM >

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RE: Electra up-grade - 8/12/2010 3:19 PM   
James c harrell



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Status: offline 		I must be weighing mine wrong. I took my motor off and weighed it. With the old receiver (a futaba MRC-4A, speed control intergrated), servos, and 2200 2s lipo, it weighed in at 1 lb 10 oz. I know that sounds light but the guy who I got it from and who built it is a master builder with planes at Top Gun. One of the best on the east coast IMO. Any-way, at this weight which motor would you guys suggest. Like I said I would like to have some reserve power and plan to have the trasnsmitter set to only use partial power untill wanted.

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RE: Electra up-grade - 8/13/2010 12:17 AM   
BMatthews



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Status: offline 		Nope, 26 oz for the model with no motor but with the battery pack sounds very much about right. Pure glider versions that used the old 4 x AA pack in the nose and a touch of nose weight typically came in anywhere from what you have up to the very low 30's. So you're not out to lunch on your weight at all assuming that your scale isn't out by a bunch.

Now with the weight pinned down to coming out under 32 oz very easily even with a touch of nose weight and with the motor installed easily get away with 70 x 2 = 140 watts. The 70 watts per lb will give you a spirited climb the sort of which it sounds like you're looking for. It also means that you're now looking for about a 180 to 200 watt max motor even for allowing for excess power handling to ensure a long motor life. It also means that these motors will only be in the 2 to 2.5 oz range so you'll want to plan on extending the nose about 1/2 to 3/4 inch further out than I described above. When done the nose should look like the ones in Sparky Paul's pictures but with the motor in the nose instead of up top on the pylon.

The other good news is that the wing will now be able to fly as Carl originally intended and not like the duck with a belly full of birdshot as the Electra did in its original specification with the heavy motor and battery pack. You think you liked it before? Wait until it glides like a REAL Gentle Lady! ! ! ! The lighter weight won't be quite as good in brisk conditions but in calm or light winds that model can't be beat. And because it's not some fancy high tech airfoil the deck was stacked against it for wind or high wing loadings. So you're giving up all the bad and getting back all the good in this design by going light.

I know you talked of switching to a 3S pack before but really there's no need. And by sticking with the 2S pack you'll be able to turn the larger 10 to 12 inch props without overloading the motor. And the 2200 will give you lots of duration. The catch is that it'll now be drawing a bit more current to get the required watts. 140/7.4 = 19 amps. Hmmmmm that's still just fine. The lighter weight held down the current needed to achieve the 70 watts per lb figure. So prop it for 19 to 20 amps with a suitable size big folder and you'll be super happy.

To help you scale things a bit you must realize that the old can motor with heavy nicad pack and running a small and inefficient direct drive 7 inch prop was likely only achieving about 35 to 40 watts per lb. Your switch to the Lipo pack likely improved that to around MAYBE? 50 watts per lb? The old 550 can motor would only survive about 14 to 15 amps for any length of time. So 20 amps was right out of the question and the motor is around 5 or 6 oz to boot. With the change to a brushless design you're not only tossing away the resistance and drag of the arcing brushes but you're gaining the much better climbing efficiency of the bigger prop.

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RE: Electra up-grade - 8/13/2010 12:54 AM   
BMatthews



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Status: offline 		You got my intrest up on this so I went shopping at Hobby King.

Here's a motor that looks like it'll easily fill the bill. And it's only just a hair over 2.5 oz. Look at the performance test by the fellow in the first forum reply below the ad copy. With a 3S pack you'll achieve a 100% power to weight at only 15 amps.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5691

And a few others that look good as well
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8139
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=5499

But for the few extra grams of that first one and the power it could give if you prop for that sort of current load it seems like a winner. Just be sure to get an ESC of 30 or more amps to go with it. It's also best if the ESC have at least an open area to sit so it has some airflow around it. Don't wrap it up in foam and expect it to not overheat.

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RE: Electra up-grade - 8/13/2010 6:06 AM   
James c harrell



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Status: offline 		Well I think I have made up my mind to go with the Turnigy 2217 motor with the Turnigy TR_P30A ESC and a 2200 3s Batt. Think I will try a 11x4.7 prop as that is what is suggested. How's that sound? I am in process of doing the changes to the nose of my plane but the finalbuild will wait till the parts get here. Think I will have something that will work with the set-up described above?

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RE: Electra up-grade - 8/13/2010 6:34 AM   
BMatthews



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Status: offline 		That 11x4.7 is drawing up near the peak. And if the fellow's test results are accurate it's generating more than the weight of your model. I'd go with a 10 x 5 or even 10x4 folder and you still won't regret it. The climb with the folder would be solid and sporty even at a bit less than full RPM. And you WANT the folder both for gliding efficiency as well as a greatly reduced risk of damage to the prop(s) and motor shaft upon landing. I said PROPS since if you go with fixed props you WILL go through bags of the thin electric props that will bust upon landing with no landing gear.

Looking over their folding props I see they have a 9x5 and a couple of 10x6's. But those may be the same prop in two spots, I didn't check that far into it. But from the data shown for the motor I can safely say that the 10x6 would be too much and the 9x5 likely not enough. I'd suggest get the 9x5 and a set of 10x6 blades. Try the 9x5 first and see how it goes. If you seem to be lacking climbing power (frankly I doubt it) then try the 10x6 blades on the spinner/hub assembly. But ground run the motor for a half minute and then check the temperature by holding it for a minute after shutting off. If it gets too hot to hold then you're pulling too many amps. If it seems OK repeat the test but this time run for a full minute and then hold for a minute. Again, if it is too hot to hold at any time during that minute then it's too hot to run with that prop. At least at full throttle. Since you're happy to run at reduced throttle the power going to the motor would be less. But you'd have to avoid full power for more than a few seconds at a time if it gets too hot during that test.

What you MAY be able to do is get yourself a 9x4 one piece prop and cut the hub and reshape the stubs to produce about a 10 x 5 set of blades for the folding hub. From what I see in that guy's test results such a prop would be the way to go and a good combo for both the motor and the glider. For hotliners this would be just the starting point. But for an Electra this is hot performance stuff. Enough so that you won't want to delay shutting off the power as you push over to level flight.

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RE: Electra up-grade - 8/13/2010 8:07 AM   
James c harrell



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Status: offline 		I found out that the folding prop I have now has inter-changeable blades. I am ordering a variety of blades in the sizes you mentioned so I can try each one and go with what fits best. The turnigy ESC is back ordered so I am thinking of going with a Tower Pro. Take a look at the TP-W30A. My dad has been using the Tower Pro ESCs' for a while and has had no problems with them and he knows less about this stuff than I do. Really got to thank you for your help. I would have never figured all this stuff out with-out your help. Let me know what you think about that ESC.

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RE: Electra up-grade - 8/13/2010 8:35 AM   
BMatthews



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Status: offline 		the numbers look great. The BEC limit of 1.5 amps in particular suggests worry free usage even on models with more than your two servos. The PWM frequency of 8 kHz is good too. I'm running a couple of Towerpro ESC's and like your dad I've had zero issues and they are running fine. But like I suggested I position them either in a spot that has air flying past or in the fuselage hanging in an open volume so that it has air around it or has at least some flow past it. You won't find me ever bundling up any ESC in foam or other padding that will insulate it from venting at least some heat from it.

Be sure to let me know how it all works out in the end. And remember that tuning the prop to the motor and model is quite important. And watch for excess heat in the motor or battery pack that indicates it's drawing a lot more current than you planned on.

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RE: Electra up-grade - 11/18/2010 10:08 PM   
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Status: offline 		How can I lighten an Electra airframe before covering?

Thanks, Bob

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RE: Electra up-grade - 4/23/2012 4:24 AM   
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Status: offline 		BMatthews,

I hope you are still checking this thread.

Is this advice good for all older power gliders?

Currently my wife took an interest in gliders, so like any good hubby I am attempting to make the introduction a pleasant experience. I picked up two gems from friends, one is a Tower Hobbies Vista Sailplane, and the other is a Spectra Electric Sailplane.

Specs:

Vista: Any 7-cell (8.4 Volt) battery pack made from “sub C” class
NiMH (nickel metal hydride) or NiCd (nickel-cadmium)
rechargeable batteries
Wingspan: 78.5 in [2000mm]
Wing Area: 678 sq in [43.7dm2]
Weight: 45 – 50 oz [1275 – 1415g]
Wing Loading: 9.6 – 10.6 oz/sq ft [29 – 32g/dm2]
Length: 41 in [1035mm]
Motor: Included 550

Spectra: 601 motor with folding prop, Battery GPMP0741 (1900SCR 8.4V 7C Thrust FLT, NiCd)
Wing Span:78.5 in (1995 mm)
Wing Area: 675 in² (43.6 dm²)
Wing Loading: 10.2 oz/ft² (31 g/dm²)
Weight: 48 oz (1360 g)
Length: 41.5 in (1055 mm)

“First off you want a motor that is about 50% more powerful than the old setup. The old setup would have run at 8.4 volts (7 cell Nicd pack) and drawn about 15 to 17 amps. Let's call it 17 amps. That's 8.4 x 17 = 143 watts. Because you want a little more OOMPH let's bump this to 200 watts max runing power for the upgrade. That's less than a 50% increase but you'll be lightening up the model shortly so you'll still have up around 70 watts per lb before we're done. And that's enough for a sporty 40 to 45 degree good speedy climb angle”.

I am not looking for the best of everything, just to boost the climb to what you describe above. The Vista at best will only climb under full power if you circle and apply light rudder an elevator in a very shallow turn, otherwise it just keeps stalling and dropping the nose. Have not flown the Spectra yet.


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RE: Electra up-grade - 4/23/2012 5:01 PM   
da Rock



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Status: offline 		Those two are going to take the same power and give back the same climb performance. They're the same size and weight.

I've got an inrunner with a gearbox. Both came from Tower. I went with an inrunner because the Spectra was originally suggested as working best with a Multiplex Permax BL-48 brushless and it comes with a gearbox on it.

My setup gives around 280W. It works great. Look for any brushless rated about 275 and you'll have good performance.

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RE: Electra up-grade - 4/23/2012 11:17 PM   
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Status: offline 		Okay, I found the Multiplex Permax BL-48 brushless, but what speed control and prop combination do I run. Is it possible to use the current speed control and/or prop, or will the amps fry it and sling the blades?

Sorry for my limited knowledge on electric. I have only been running Glow, Gas, and Jet A. I still have a lot to learn about the electric portion of our hobby.
Thanks for your help

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RE: Electra up-grade - 4/24/2012 1:31 AM   
da Rock



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Status: offline 		OK, I wouldn't bother with the Multiplex. It's actually somewhat out of date, and the one you need to find is the BL-480/6G, which comes with a gearbox and back when it was recommended was the only 480 suggested for gliders. I put one into my Spectra because of the mfg's suggestion. It ate itself after about a half season of use. So I looked around for a replacement in-runner with a gearbox and wound up using a Tower Ammo with a gearbox. It turned out to be a major trial to match up the motor and gearbox and then work out a prop.

I'm still using the setup but would suggest looking for any outrunner that fits and has enough power.

Outrunner power is usually limited somewhat by diameter. Let me go down in the shop and check out that Spectra. brb

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RE: Electra up-grade - 4/24/2012 1:50 AM   
da Rock



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Status: offline 		OK, just for background.....

I fly my Spectra with a Tower Ammo inline 28-56-1530 with a gearbox stuck on the front. At the time, it was what Tower had in stock. I use a Castle Creations Phoenix 45A ESC. The Spectra has the two servos limiting how far back you can carry the LiPo so for better balance (still not what I'd like) the battery is usually a 3S 2200mAh. I'd prefer to use a slightly smaller 4S, but haven't found any in stock where I buy. The smallest 4S I've got right now is 2650mAh and it moves the CG forward too far. It's ok for windy days.

I've tried a number of props and checked the static readings and have a 15x10 (yeah, that's a BIG blade) on it right now. With a 4S battery I can climb with anything. Not an important detail at all, but it is what it is. Bottom line is you don't need that much power.

There is room in front for 1 1/4" width outrunner.

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RE: Electra up-grade - 4/24/2012 5:07 PM   
da Rock



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Status: offline 		This thread triggered me to search again for something like a 30-32mm wide outrunner. That'd be about the most an average size 2 meter fuselage would take and clear the cords the way most motors are installed, with the firewall forward.

It was somewhat of a shock to discover how few gliders there are available right now. The major hobby retailers have almost nothing.

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RE: Electra up-grade - 4/26/2012 9:46 PM   
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Status: offline 		My own taste is to stick with outrunners even if it means needing to do something a little "creative" at the nose. I like the idea of avoiding gear boxes for casual flying. That and even the best makes some amount of gear noise.

You MUST NOT use the old brushed motor speed control. They are not in any way compatible with the newer brushless outrunner or inrunner motors. The brushed motors are simple DC motors and the speed controls controlled them by simply switching on and off the power at varying duty cycles corresponding to minimum to maximum throttle. Brushless motors are actually 3 phase AC motors. The ESC's we use with them are DC input to 3 phase variable frequency output converters that are able to sense the EMF back voltage to determine the RPM and set the switching rate to work with the motors and props.

The prop you have now may or may not be compatible with the new setup. It simply depends on what the Kv of the motor is and the gear ratio if you go with a gear box. The prop needs to be matched with the cell count of the pack and the Kv value of the motor. Typically you'd go with whatever the motor's maker suggests. Or get a wattmeter and work up your own prop selection based on measurements.

Other than this the stuff I wrote before for the Electra would apply to your case as well. You still want to aim at around 65 to 70 watts per lb. But the models you've got will need a little more power to reach that since the basic airframes of these two models are typically a little heavier than the rather minimalist Electra airframe.

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