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Everything about Electric Twins...!

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Old 03-16-2012, 12:06 AM
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Sumeet
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Default Everything about Electric Twins...!

Hello, I have gone through most of the previous posts related to "Electric Twins" but still I have few questions.

1. How do you mount both motors? I mean What Angle? Any Right/Down Thrust? or just rotating them in opposite direction keeping the thrust line from both the motors parallel?

2. Is it possible to hook an external BEC and two ESCs to one lipo battery? I mean connecting all of them parallel to battery and disabling the built-in BEC feature of both ESC by pulling out that red wire?

3. Suppose, Using two same version ESCs of same brand having same firmware with two similar brushless motors, One still can't get the same thrust out of both? What may be the reason and what can be done in this case? Provided, Nothing can be done on Radio side to match the RPM of both the motors.

4. If the length and gauge of wires from Battery to both the ESC's and then to Motors kept same, Does it mean that the motors will receive same Voltage and Generate same thrust and same Wattage"?

5. Why do they have twin rudder setups in the orginal multi Engine planes like B25 ,B24 etc. The C-2A Greyhound has four vertical stabilizers mounted on its tail. Why is that so?

6. What kind of wing(Anhedral/ Dihedral/ Polyhedral or plain) is more suitable and acts more stable for High Winger twins?

7. Same question as above to be answerd for the Low-winger twins and Mid-Winger twins.

Thanks.
Cheers.
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Old 03-19-2012, 03:56 PM
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Default RE: Everything about Electric Twins...!

#1 Two ways to go. If both rotate the same, you should add down and right thrust to both (viewed from the rear of the plane) around 2 to 3 degrees is a good starting point.
If you have a counter rotating prop on one side, the two should cancel out the tendency of the props to pull to the left. But both will still want to pull the nose of the bird up, so you'll need to add the down thrust.

#2 Sure can, I do it that way.

#3 Well on that I'd be looking at a mismatched kv rating on the motors. It happens, you may buy identical motors, but find one has a higher/lower actual kv then the specs call for.
Also I've seen on occasion where a battery isn't up to the amp draw , one motor pulls it's full amps and the other is stuck with the left over lower power.
As mentioned, sometimes if it's a kv problem, you can somewhat get around it by putting the esc/motors on separate channels, mixing them and playing with the endpoint adjustments.

#4 In a perfect world. Not always in ours. Too many things can skew it. The old mismatched kv ratings, prop variances, poor balance of the props, bad bearings, poor solder connections, etc. etc. etc. All you can do is check each and everything to make sure you have em as close to matched as you can.

#5 You'd have to ask the engineers who designed them, but as general rule I'd say the Mitchell and Liberator only needed two, whereas the Greyhound requires 4 or 6 if you count the two outer lower ones. Flight characteristics, airframe construction/design, mission, all fall into why a plane is how it is.

#6 For most it would be dihedral.

#7 could be any of them. It would depend on the type of plane, it's planned type of flying, speed, etc. Some even have changing angles as they fly. Take a look at a B-52, pronounced anhedral on the ground and as it takes off, in the air the wing goes dihedral just as much.

Polyhedral is often used for convenience , think like an F-4 Phantom. Why? lets the engineers use a straight spar, and still get the benefit of dihedral. (self centering)



Note Kv doesn't have to be perfectly match, I have a bunch of twins and depending on the bird the kv can be off by a couple hundred and the planes don't seem to mind at all, and suffer no odd ball characteristics.
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Old 03-19-2012, 10:14 PM
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Default RE: Everything about Electric Twins...!

Oh Great. Thanks a lot Glacier Girl. Your answers made my thoughts clear about the twins but there could be few more questions later on.

Thanks.


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