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Old 05-12-2013, 05:43 PM   #1
Scottyd
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Default P-38 Power

I recently purchased the RichModel P-38, and am looking for some help selecting a motor. I don’t require hover performance, but I would like almost vertical clime outs.

Specs: WS = 51.6”, Weight around 60 oz to 64 oz, wing area = 333 sq”

I believe the plane was sold at one time with a 450 sized motor, but some people critiqued it as being under powered. Some suggested a 480. A thread from 2005 gave very detailed setup info where they used a Turnigy D3536/C. The newer Turnigy motor with approx.. the same KV is the D3536/8, which I purchased.

Now I am having second thoughts. I am a newbie to brushless and the more I read, the more concerned I am about motor quality, power, weight and efficiency.

Question: should I have used a 480 like the EFlite Park 480? It weighs almost 20 grams less than the Turnigy 3536/8, but according to the specs has less power potential.

Thanks in advance. Scott
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Old 05-12-2013, 05:49 PM   #2
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No you should be fine - what is the weight and kV of the motors you purchased? (or link).
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Old 05-12-2013, 06:40 PM   #3
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go to headsuprc.com

buy either the heads up 450 sport or the 480 plus.

the 450 sport is good for 30+ ounces of thrust on a 10x5. should be able to get a 9 or 10" 3 bladed prop for scale looks that will work well on 3 cells.

the 480 plus is capable of 50+ ounces of thrust on 4 cells and still have lots of room for prop clearance. however, its a 5 mm shaft, so you will have to reams even a apc prop out to fit the prop adapter.
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Old 05-12-2013, 07:35 PM   #4
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Is this the motor you have?
http://www.hobbyking.com/hobbyking/s...ner_Motor.html

If so as rcers said, it should be fine.
I have the Richmodels P-38 and I have two E Flite 480's for power.
Good power, not extraordinary.

That Turnigy motor looks like it can swing a slightly larger prop than the E Flite 480. Should have a good steep climb, but don't expect vertical, not for any distance.
The wing on the P-38 is not real large, you have to watch the weight. Use smaller batteries and it should be fine.
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Old 05-12-2013, 08:16 PM   #5
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I have had nothing but flawless performance from my HobbyKing motors. I know some people will talk them down, but I wonder if they have had real experience, or just talking.

I would not worry much about your motors, until you have flown them for a while. You may decide you want more or less power.

I would highly recommend using counter rotating props. I have a GWS P-38 that I had not finished until about 2 months ago. On it's maiden flight I had it in a high alpha attitude about 2 feet above ground. I have not had a single engine plane feel that solid. It was not trying to drop off or turn at all. And take off was as straight as a string. I will build more twins and they all will have counter rotating props.

Dave R, Proud PGR rider.
When you have flying skills like mine,
You become a master at repair.
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Old 05-12-2013, 09:13 PM   #6
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Originally Posted by Scottyd View Post
[SIZE=3]I recently purchased the RichModel P-38, and am looking for some help selecting a motor. I don’t require hover performance, but I would like almost vertical clime outs.
Vertical climb outs?

This will call for a few $$$$ for your power system. Be aware of the wing loading on your model, it's going to be on the high side for this size model with only 333 square inches of wing.

In order to get vertical climb outs, you'll need something around 150 watts per pound of airplane. That would be 600 watts for a 4 pound model.

Running the numbers through www.motocalc.com (Free for 30 days, then $39) indicates that one good choice for the motors up front is the $$$$ Hacker A30-12L, with a 3500 Mah 3 cell LiPo battery and a two blade 10X8 prop. Motocalc predicts this combination will be pulling about 71 Amps for the two motors, and about 730 watts, again for both motors. Prop RPM on the 10X8 will be around 8500 RPM, and the rate of climb is 3500 feet per minute, straight up. The power loading will be around 180 watts per pound.

Motocalc predicts your wing loading will be around 27 ounces per square foot, and stalling speed is around 26 MPH.

These motors are not cheap, they go for about $70 each. But they will do what their specs say, and they do last a long time. I've got 8 of them, still am using every one of them, some are going on 6 years old now.

There are a lot of other quality motors out there at much lower prices. And also a lot of other not so quality motors out there at lower prices. Last week, a club member just had the magnets come loose on the cheap motor in his electric model, and had a dead stick landing. It also fried his ESC.

Just ran the numbers on the Hobby King motor. This motor has lower efficiency than the Hacker, and it shows up in the amount of watts actually put on the prop shaft. The rest is used to heat up the motor.

The Hackers put total of 730 watts on the two prop shafts, the HK motors put a total of 620 watts on the two prop shaft. The rate of climb out for the HK motors is predicted to be about 2700 feet per minute at a 70 degree climb out. But, the HK motors are a fraction of the cost of the Hackers.

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Old 05-12-2013, 09:56 PM   #7
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Thanks for all the great info.

Yes, the HK link above are the Turnigy's I purchased.

Wildflyer: I used to live in Lacey for 10 years, about 8 years ago. Nice town! What are some of the specs on your GWS please? Flying weight, motor, batt, flight times, etc. Thanks!

Dennis: Thanks for the great motor info. The Hacker specs are pretty similar to the Turnigy (if you can believe the specs). I do see the winding resistance of the Turnigy is higher and the weight of the Hacker is greater. Larger wire AWG could account for this. It makes me wonder who's specs are accurate. Then there's all the effects such as efficiency (comes at a weigh cost) versus weight (lower wing loading).

I know I am not going to get all the answers at once; I'm bugging you experienced guys so my first trial is as close as possible.

It looks like my 3536/8 motors are in the ballpark so I'll give them a try.

The Dr. Kiwi site looks good, with him giving very detailed actual data. Unfortunately not all motors (such as the T 3536/8) are characterized. Oh well...

thanks again, Scott
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Old 05-12-2013, 10:05 PM   #8
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Oh, the battery I am going to try is 220 grams. http://www.hobbyking.com/hobbyking/s...dProduct=11946

Now, as you guys know, selecting the correct battery is another bag of worms!

The props I selected are 9X7 3 blade Master Airscrew (CR). I'm hoping to get decent performance and flight time (5 minutes, 7 a stretch depending on the lead foot) with this combo.

Scott
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Old 05-12-2013, 11:36 PM   #9
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Originally Posted by Scottyd View Post
Oh, the battery I am going to try is 220 grams. http://www.hobbyking.com/hobbyking/s...dProduct=11946

Now, as you guys know, selecting the correct battery is another bag of worms!

The props I selected are 9X7 3 blade Master Airscrew (CR). I'm hoping to get decent performance and flight time (5 minutes, 7 a stretch depending on the lead foot) with this combo.

Scott
You will be fine with those motors. You will not however be fine with those props. The MAS are terribly inefficient.

Use two blades to start and if you have the power needed you could play with some GWS HD 3 blade props - they are a bit better.

Twins are odd beasts they tend to do much better and have gobs of thrust. Give you setup a try minus the props.

Mike


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Old 05-13-2013, 01:08 AM   #10
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Something like an APC thin electric? 10 x 7??

Dennis - what did motocalc say about prop choices for the turnigy 3536/8 motor, please?

I'll fire up motocalc myself, but i'm sure you have much more experience driving it.
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Old 05-13-2013, 02:14 AM   #11
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Originally Posted by Scottyd View Post
Something like an APC thin electric? 10 x 7??

Dennis - what did motocalc say about prop choices for the turnigy 3536/8 motor, please?

I'll fire up motocalc myself, but i'm sure you have much more experience driving it.
Best prop for the Hobby King 3536-8 1000 KV motor looks to be the same as the Hacker 1000 KV motor. For the calculations, I used an APC-E 10-8 (electric) prop.

APC doesn't have much in three bladed props, but they do have a variety of "pusher" props to allow reverse rotation on one of your motors.

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Old 03-12-2014, 12:23 AM   #12
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Here's my Richmodel P38 that I maidened today. Bought the ARF at the AMA show in Ontario, CA in January. Used HeadsupRC (Power Up) 450 sport motors turning counter rotating APC 9x6 props. 30 amp ESCs and 1500 mAh 3 cell batteries round out the package. I had to put a half ounce of weight on the tail to balance it but it flew well. No trimming was required.


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