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Improving the Great Planes DC-3

Old 03-29-2004, 12:04 AM
  #1  
Jeffpro
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Default Improving the Great Planes DC-3

I need some advice on the Great Planes electric DC-3. It has two 400 motors. I built the plane and flew it with an 8-cell NiMH battery. It flew great with no wind, but it lacks the power to fly if there's any wind to speak of. I crashed it yesterday when I let the nose get up in a headwind on take-off. I struggled to keep the fuselage level as I climbed out, and when the plane was about 30 feet in the air, I lost the battle. I simply didn't have enough power (or wasn't good enough a pilot, or both) to keep it from nosing up and stalling.

When I get it flying again, I'd like to add more power. Should I:

1) Use a battery with more cells?
2) Install larger engines?
3) Change the props?

Any advice is welcome. Also, I'd eventually like to try li-poly batteries. Would love to hear from anyone that's installed li-polies in the Great Planes DC-3. For example, what battery configuration did you use, and what ESC did you install?
Old 03-29-2004, 08:09 AM
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Matt Kirsch
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Default RE: Improving the Great Planes DC-3

There are many "8 cell NiMH" batteries out there. If you used one that was too small, it would not be able to provide enough power to the motors, and performance would suck. Specifically, what battery are you using? Anything less than 1700mAh won't cut it, and then only good quality batteries (i.e. not cheap generic chinese cells).

Are these batteries brand new? After a few cycles, the power output of NiMH batteries increases dramatically. They need to be broken in.

None of the remedies you posted will necessarily help. You need to determine the problem before you can start applying solutions. For example, if your problem is a battery that can't put out enough current to run the motors at full throttle, adding a cell will only increase the current and make the problem worse. Simply swapping out for physically larger motors will also make the problem worse.

Your solution may be as simple as using a more suitable battery. An 8-cell pack of Sanyo HR4/5AUP 1700mAh NiMH cells should power this plane easily.

Another possibility is that the motors that came with the plane are 7.2V Speed 400 motors. Swapping them out for 6V Speed 400 motors will give you a significant power increase. See if you can determine what kind of 400 motor is in the plane. They should be listed in the instructions, and the motors will have a code stamped on them.
Old 03-31-2004, 04:05 PM
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Jeffpro
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Default RE: Improving the Great Planes DC-3

I used a brand new 1800 mAH battery from Tower Hobbies. I'm not sure whether the motors are of the 6.0V or 7.2V variety, but I should be able to find out.
Old 04-01-2004, 01:20 AM
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DeafOldRocker
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Default RE: Improving the Great Planes DC-3

ORIGINAL: Matt Kirsch


Another possibility is that the motors that came with the plane are 7.2V Speed 400 motors. Swapping them out for 6V Speed 400 motors will give you a significant power increase. See if you can determine what kind of 400 motor is in the plane. They should be listed in the instructions, and the motors will have a code stamped on them.
Matt
Could you explain what you mean by this? I thought the 7.2v motor would have more power then the 6v. What do these motor rating actually mean?
Old 04-10-2004, 05:49 PM
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Eddie P
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Default RE: Improving the Great Planes DC-3

Hi DeafOld Rocker-

I'll say this right out in front - the rating system of "can" motors is misleading and outdated.

The simplistic "voltage" rating the older "can" brushed motors have been given essentially represents the voltage the motor requires to operate at a fixed power level. A 6 volt motor will generate more RPM's per volt than a 7.2 volt motor. So let's say you want to set up a standard that at 10,000rpm, you need 6 volts on motor A. And for 10K rpm, you'll need 7.2 volts for motor B. Since motor B needs more voltage per RPM, it is considered more suitable for higher voltage systems. Because you are operating at 9.6 volts, you will see more RPM, amp draw and power from a 6 volt motor than you will from the relatively "cooler" running 7.2 volt motror. Sounds weird, but you'll get the hang of it.

This is better represented in modern higher performance motors by a KV rating. K means thousands of RPM and V represents per volt. So a KV of 3000 would mean 3000RPM per volt under no load, or a bare shaft.

Now I know you have to be asking "Why woulkd I use 9.6 volts on a 6 volt motor - wouldn't I burn it out? Well, yes and no. These old "can" motors are very cheap, not that efficient, and sort of heavy compared to the new brushless motors. For this reason, we generally determine that over powering a 6 volt motor will give you two very important things, while only costing you a minor item. The two great things you get are more power from increasing the voltage, and the second thing is you get to maintain the light weight of the motor without having to increase the size and weight of the motor for the higher power. The only bad thing is that you will have to buy a new $9 motor in about 100 flights. Big deal, you'll have a few years to do that if you have a few models and fly it every once in a while, or a season to go through 9 dollars of motor if you fly the pants off of it. The higher power for lower weight is worth it.

This is not to say that the 7.2 volt motor has no place. In fact, the 7.2 volt motor is perfect for 10 cell setups. The higher voltage, 10 cell systems run more efficiently. This is becasue for an increase in voltage, there are very little additional efficiency losses, while increases in amperage cause power losses to increase at the square root of the amp increase. To get more power, it's better in the long run to increase voltage than simply increase amps. So, if you want more power than you can realistically get out of the 6 volt motor, go up to 10 cells and use the 7.2 volt motor. The amp draw will be similar, but the voltage will be higher. Always, always, always: Total power into a system (watts) = Amps * volts. Then minus the efficiency losses to get total watts out. That's more difficult to do longhand, but the programs like motocalc will figure things like that out for you.
Old 04-11-2004, 09:55 AM
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Default RE: Improving the Great Planes DC-3

I use 2- 3 cell 1500Mah Li-poly packs. At 11.1 volts it is extremely fast and I usually fly around at half throttle. Just in case I burn up the motors(haven't after 25 flights) I purchased another set from GP for only $11!
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Old 04-11-2004, 03:30 PM
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bassmanh
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Default RE: Improving the Great Planes DC-3

apilot,

are you flying from a grass field or paved ? i have been thinking about getting this plane but was unsure if it could fly from a grass filed or not.

also are you using the ESC that came with the plane ? with the li-polys ? and also what kind of flight times are you getting with it ?

sorry for all the questions but i am very interested in this plane and have held off buying one until i know what it can do

thanks in advance.


bassman
Old 04-12-2004, 05:16 PM
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Jim Flannigan
 
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Default RE: Improving the Great Planes DC-3

Bassman,
I fly from a paved field but it does not have any problem getting off from a grass strip.
I am using the GreatPlanes ESC that came with the plane, just watch the voltage and don't let it get too low.
I have been getting three 7 min flights from one pack.
I hope this helps.
Jim
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Old 04-26-2004, 09:04 PM
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aeroastro
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Default RE: Improving the Great Planes DC-3

After trying out the kit's supplied 5x4.3 propellers, I tested various
propellers to measure static thrust, current draw, and rpm. The stock props
produce 10 oz static thrust at 11.8K rpm, 21.3 amps with the stock NiMH
1800 mah battery pack. APC 7x4s produce 18 ounces thrust at 9.2K rpm,
26.6 amps - but also note that this high power is only needed for takeoffs.
These are actual measurements, not sim values.

With the thrust available from the larger prop disc, the plane is now a delight to
fly. Try the 7x4s, you won't be sorry. This is also less expensive than motor
or battery swapouts (that can be tried later).

Pete Young
R/C Report Magazine
Old 04-28-2004, 02:25 PM
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klppnbrg
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Default RE: Improving the Great Planes DC-3

Pete - What type of APC prop are you talking about here? I presume you mean the 7X4 Slo-Flyer as I did not see this size in Tower's list of APC electric props...

Thanks, JK
Old 04-29-2004, 04:53 PM
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aeroastro
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Default RE: Improving the Great Planes DC-3

JK, the 7x4s in question are indeed APC Slow Flyer props - I checked this morning.

Pete Young
Watertown MA
Old 04-30-2004, 12:41 PM
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enrique1123
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Default RE: Improving the Great Planes DC-3

I have s DC-3 and it does need a little improvement in the power department but then most planes out there do, I wish manufacturers gave us the option of buying the plane alone or with the power package. I flew mine one weekend with the stock motor and set it up with APC 7x4 E props, it improved but it was not spectacular, now I know I am talking about a scale airplane but I still wanted some extra power and more duration so off to my LHS I go and after 2 Mega 16/15/6 with 2 CC Phoneix 25's I were put on my Amex I went back and put it all in running separate systems, each one with a TP 2100 3 cell pack, I had to rearrange things a bit for proper balance but it came out ok with APC 7x5 props. On Wednesday I took it out to my field, (this is no parkflyer) and I trimmed it and then down the runway it went, I went a little slow but still it was airborne in about 20 feet' I flew it at half throttle or less most of the time, it would climg too steeply if I gave it more power, fly by's are great and the landings were not as bad as I thought, I saved 6 oz over the original set up in weight and got at least a 40% boos in power. This airplane deserves a power upgrade, it's way better looking than the Multiplex Cargo. I wish it had retracts though, oh and I did not try to take off grass, wheels seem to small.

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