Help converting 12 year old Bi Plane - RC Groups
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Oct 30, 2010, 07:36 PM
Registered User

Help converting 12 year old Bi Plane

I've recently returned to flying again after a 12 year hiatus, and all this electric stuff is very new to me!
I would like to resurrect my old stunt bipe and convert it to electric power. I'd like enough power to be somewhere in-between the sport/3D range. Any suggestions would be greatly appreciated!


Wingspan: 39.5"
Wing Area: 671.5 Sq. Inches
Flying Weight: 6-7 lbs.
Fuse Length: 39"


2-stroke .45
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Oct 31, 2010, 10:17 AM
Crash Test Dummy
bsumpter's Avatar
I just converted an UltraStick 40 using an E-Flite Power 46, CC 60 ESC, CC BEC Pro, and 5S-5000mAh lipos. It pulls 58A static WOT with an APC-e 12x8, and generates about 1100 watts of power.
Oct 31, 2010, 12:43 PM
Registered User
Doug Bartley's Avatar
Boy, she's a heavy old girl!! I use Scorpion Motors and love the power!
Before I could make a recommendation,
I need to know the largest propeller it will turn with say, 1" ground clearance with the plane level to the ground. Sport/ 3D will take 700-1000watts!
Prop size and motor match will determine battery size as well. Flighttime will be determined by the needs of the motor and room available for a battery!

What was the plane originally powered with, did you like the way it flew? Did it do all you wanted it to do flying?

That will be important in getting enough/ right motor behind it at that weight. Most bipes at 39-40" now only weigh 2 1/2 to 4 lbs. My 44" Stearman is considered heavy at 4lbs3ozs!!

This will be a tough little bird to convert, but it can be done.
Let me know, and I'll try to help. Doug Bartley
Oct 31, 2010, 11:49 PM
Registered User

Thanks for your help.

It looks like the biggest prop she could handle while still maintaining a 1" clearance would be an 11x?. I was previously running a 10x6 prop on the glow engine. I think it was a .45 OS engine but I can't recall for sure. I'd like a little more power than what it gave me.

As for the weight, I am just estimating an all-up weight of 6-7 lbs. The current weight, with no motor, and 4 big/ancient HiTech servos is just under 3 lbs.

I don't anticipate having a problem finding room for batteries. There is a decent amount of space in front of the servo bay, and even more in front of that when I remove the gas tank.
Oct 31, 2010, 11:52 PM
Registered User

Thank you for the suggestion.

About how long is an average flight with this configuration?
Nov 01, 2010, 06:00 PM
Registered User
Doug Bartley's Avatar
OK, the Scorpion I would suggest is the 3020-1110, on 3S with an 11/5.5 prop, should do 500-600 watts, The bigger prop on the electric results in more thrust, efficiency. Lighten the plane if you can, make sure the motor/ esc get plenty of air, and provide and air exit at least twice the entrance size, you should be golden. Doug Bartley
Nov 05, 2010, 11:16 PM
Balsa Flies Better!
I'm sorry, but I'm going to disagree with Doug. You're going to be undergunned with short flights.

I'm flying a Hot Kanary which is about the same size as your airplane- maybe a smidge larger- with a 6s setup pulling 50 amps for a bit over 1000 watts swinging an 11 x 8.5E prop at 6 lbs. The Kanary is a bit faster, so the prop recommendation of 11 x 5.5 is probably OK, but this airplane won't fly slowly- so 3D is out. I might be happier with an 11 x 7, but that's me.

My suggestion- look for 5s at about 40 amps which should come in at 850 watts. A 5s 3700 pack should be OK in terms of weight and give you 5 min. at full bore. It'll also be more efficient than the 3s high amp setup. I've never owned a Scorpion motor, but they have a decent rep. Call up the mfg and see what fits the bill. A Phoenix 45 ESC or perhaps an ICE 50 should work.

Last edited by Megowcoupe; Nov 05, 2010 at 11:38 PM.
Nov 06, 2010, 03:19 PM
Registered User
Thanks for everyones advice.

How do I learn how to calculate all of this stuff for myself?
Nov 06, 2010, 05:14 PM
Balsa Flies Better!
Good question. I use S-calc which has been developed over 50 airplanes and a decade or so. Folks used to use e-calc and motocalc which are commercially available software programs. However, I S-calc uses a few simple rules of thumb (S-calc is Sam calc by the way)-

1) Using a wattmeter- (and you should get one of these- its the single most indispensable tool in e-flight and will quickly pay for itself)- the easiest way to figure performance is watts/lb. For glow conversions (not e-designed aircraft which are often a bit lighter and slower)- comparable performance as glow starts at around 150 watts/lb. Somewhere around 175 watts/lb- you're getting into good glow performance- at at 200 watts/lb you're beginning to do better. Some of the really extreme F5B ships are north of 500 watts/lb- I think they're pushing a 1000 watts/lb and the performance is breathtaking.

2) Glow engine performance was always prop limited- the damn engines were advertised in terms of horsepower which often occurred at uselessly high rpms. Four strokes capitalized on this- less horsepower, but more efficient props. Electrics go even further- e-props are more efficient than glow props and can be sized to the airframe- rather than the engine.

3) In terms of calculating duration- it's very complicated. If you have a 4000 mAH (or 4 amp hrs) battery and you run it at 40 amps-i.e. 10C- that's 1/10th of an hour or 6 minutes.

N.B. be careful in listening to the advice of e-only fliers who have never flown glow. The airplanes are much lighter built and have lower wing and power loadings. The old advice was that you could have very good performance at 100 watts/lb- but it's not the same as glow. Follow my recommendations for glow equivalence. You can't take a glow ship that was intended to fly fast and get it to 3D- you need to start with a different airplane. Often 3D setups are a disaster on a converted glow ship.

Does this help?

Nov 07, 2010, 02:39 PM
Registered User

Yes. That helps. I'm slowly starting to understand this stuff.

Do you know of any calc programs that will run on a Mac? Both E-Calc and Motocalc only run with windows.
Nov 07, 2010, 05:28 PM
Balsa Flies Better!
Believe it or not- I never bought a calc program. (I'm on a mac these days too.) Used to be folks round here would love to plug in variables into motocalc for you. If you nose around this site- there's probably a 10 year old tutorial with problems to solve on some basic electrical theory- you learn why watts aren't exactly watts (high V, low A watts are more efficient than low V, high A) that might prove helpful.

One other point- with electrics we design power systems correctly. In contrast to glow- where you start with the engine- with electrics- start with the prop. Figure out how big it is and how fast it has to turn to get the airplane to fly the way you want. Then figure out the number of watts needed to turn the prop. That generally sets up the battery requirements- and finally you pick a motor. Then check and make sure that your wing loading hasn't gone through the roof.

These days with lipolys, the need for calc programs isn't as critical. Like glow, electrics have power to burn. When I set up a glow conversion- I often figure out what size prop and what pitch speed I want- or I just use watts/lb and make sure the prop is about an inch or two larger than a two stroke prop- often it's much higher pitch. I used to fly the Kanary on a 10 x 7- it's faster and has better vertical pull on a 12 x 10. Make sure that your fueled weight is what you use and you'll find that an electric bird should set up at the same weight as a glow ship. And remember, the airplane doesn't know what's turning the prop.

Nov 07, 2010, 05:40 PM
Registered User
Ken Myers's Avatar
Originally Posted by bassistheplace

Do you know of any calc programs that will run on a Mac? Both E-Calc and Motocalc only run with windows.
Yes, my favorite runs on the Mac, Windows and Linux. You'll find Drive Calculator at

I pretty much only use a Mac.

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