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Will This Set-Up Work

Old 03-25-2009, 07:18 PM
  #1  
Big Johnny
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Default Will This Set-Up Work


I'm thinking of buying 2 3548-09 Motors from Heads-Up RC. They will be installed on a 6 pound, twin engine flying Boat.(Kitbashed Sig Sealane) I want to use 2 A123 2300mah packs for each motor. I have plenty of room in the nacelles for the batteries. I want to use the 12 x 6 x 3 Bladed Props. Do you think I will Have enough power to fly?

Propeller test data for the 3548-09:
3-cell Lipo Data: The following data was obtained using a Power Up 11.1v 4400 mah 15C (66 amp) Lipo battery:
APC 13 x 6.5E: 70 oz thrust @ 36 amps
TP 13 x 4E: 66 oz thrust @ 32 amps
APC 13 x 8E: 64 oz thrust @ 37 amps
TP 12 x 6E: 60 oz thrust @ 30 amps
Master Airscrew 12 x 6 x 3: 61 oz thrust @ 31 amps with a pitch speed of 48 mph (3 blade prop).
APC 12 x 8E: 56 oz thrust @ 31 amps with a pitch speed of 54 mph
TP 11 x 5.5E: 50 oz thrust @ 24 amps with a pitch speed of 44 mph.
APC 11 x 7E: 52 oz thrust @ 27 amps with a pitch speed of 53 mph.

4-cell Lipo Data: The following data was obtained using a 14.8v 3200 15C ( 48 amp) Lipo battery:
TP 9 x 6E: 52 oz thrust @ 24 amps with a pitch speed of 65 mph.
TP 10 x 5E: 58 oz thrust @ 26 amps with a pitch speed of 50 mph.
APC 10 x 7E: 60 oz thrust @ 33 amps (480 watts) with a pitch speed of 67 mph.
TP 11 x 5.5E: 72 oz thrust @ 33 amps (480 watts) with a pitch speed of 49 mph.
Please be aware that the battery used can make a tremendous amount of difference in the performance of brushless motors. The above data was obtained using batteries in good condition that were fully charged. Thrust and amp draw may be less with the use of batteries rated at lower amp output, and slightly more using batteries rated for higher amp output.
3548-09 Specifications:
Weight = 5.8 ounces (165 grams)
Diameter = 1.4 inch (35 mm)
Motor length = 1.9 inch (48 mm)
Shaft = 4 mm x 0.7 inch (18 mm)
Voltage = 7.2 - 17.0 (2, 3, or 4 cell Lipo)
Current = 40 amps or 550 watts maximum for 60 seconds
KV = 900
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Old 03-25-2009, 07:28 PM
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MustangMan
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Is the 6 lb. weight estimate an all-up-weight RTF including batteries?

Are you planning to use 3 or 4 A123 cells per pack?

Assuming the 6 lb. estimate includes everything RTF, and you achieve at least 48 oz. of thust from each motor, then that would be a 1:1 thrust to weight ratio. I'd think that would be plenty of power to fly the plane.
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Old 03-25-2009, 07:42 PM
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beau0090_99
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Have you weighed your Sig Sealane? I own one that has .46 magnum engine on it and it comes in at about 7 lbs. This is stock without fuel in the tank.Have you accounted for balance of the plane? I had to add about 4 oz of lead to the nose to balance the model.
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Old 03-25-2009, 10:30 PM
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Big Johnny
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Default Sig Sealane

I was planning on useing 2 X 2 cell packs in series for 12.2 volts 2300mah each. A123 website say's there good for 30c = 12.2 volts & 69 amps, or would I better of useing a 3S1P 3250 20c Lipos = 11.1 Volts & 65 amps. This is my first foray into the electric arena. I Have a Accucel 6 charger, that I use for my Helimax CP, which I have never got a complete flight, without crashing. I don't think my thumbs & brain is in sync with each other, heli's just react faster than I can think. Tell me if I have made a error in my calculations. Thanks; Johnny
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Old 03-25-2009, 10:57 PM
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beau0090_99
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Well, I have not done a conversion and am relatively new into Electric power too. Here is what I have gleaned from my reading...

You would typically want to match the motor(s) to the airframe by type of flying and Watts. So for a Sport model, I believe that 125 watts per pound is a good suggestion(I think that is input wats). That being said, I think if you are going to make this a dual motor design, with A123 batteries (which are heavier than your standard Lipo), you will most likely increase the weight of the plane from stock. I would guess you may increase it by as much as a pound or more. That said, you would be looking for about 8 pounds at 125W/lb which would be about 1000 watts. If you are using a 3S system or roughly 11v, then you would be consuming about 90 Amps.

When you setup a system like this and you don't use Watts and you want to look at thrust, you need to counter thrust with Pitch speed. Essentially those two components comprise Watts.

What I have heard from others is that even though your Lipo is rated 20C or whatever, it may not like being taxed that much. You may want to shoot for a continuous current rating around 10-15C if you are using a 20-30C battery. That way you are at least looking for about 4-6 minutes of runtime and also not an overtaxed battery.

Good luck, I think we both can learn a lot from this endeavor.
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Old 03-26-2009, 12:22 AM
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MustangMan
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Johnny:: Are you doing a new build or is this a conversion from a flying glow model? If you're building, you have the opportunity to lighten the airframe a little. Electric setups don't create nearly as much vibration stress as glow engines. If the airframe is built what does it weigh minus any power components but with servos? Curtis' idea of starting from watts/lb. is generally reasonable. The rules of thumb run something like 30 w/lb for minimal flight, 50 w/lb to roll off the ground, 100 w/lb for sport aerobatics, 150 or more w/lb for 3D. I'd guess, and I'm only guessing, that it would take a little more than 50 w/lb to take off from water though I wouldn't think it would take 100. Working from watts and pack voltage you can get Amps as Curtis did. AVERAGE Amps times flying time gives battery capacity in Ah (multiply by 1000 to get mAh). Pack "C" rating times capacity will give you a "never exceed" current value. But a "C" rating also tells you how quickly your battery will be completely drained if you operate at that current. 20 C will mean your battery is all used up in 3 minutes. Pack capacity divided by average current gives you flying time until your battery is dead. If you fly at full throttle all the time then your maximum current becomes your average current. Running a battery at its published C rating will seriously shorten its life, especially lipo's. Battery capacity selection starts with approximate airplane weight and flight profile. More capacity means longer flights but decreased performance.
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Old 03-31-2009, 02:38 PM
  #7  
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There's no configuration of A123 cells that will give you 12.2 nominal volts. 3s is 9.9 volts and 4s is 13.2.

A123s can handle huge amp draws, so you don't have to worry too much about that the way you would for lipos.

I'm currently working on a single motor 58" edge 540 that I plan to run with 6s2p A123. I'm holding onto a hope that I can get 15 minutes of flight out of it. (Not 3d)
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