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Old Jan 11, 2011, 07:35 PM
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Brandon, Fl
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Having flown (and crashed) several of theses, I'd try to get a higher kv motor. My earlier P-38s all had TP 2409-12 (1600 kv) motors and it was FAST. My next version will be a bit tamer (and more reliable) with a pair of EMAX CF2822 (1300 kv) turning 8*4s. Each motor is lighter by an ounce, and will spin the prop well.

Jim
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Old Jan 12, 2011, 12:46 AM
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OK Jeff here is the data. This is from a Hobby Lobby SK400 motor I think is around 900 kv. On a 1320 TP 3S battery: 9x6 = 11.6 amps, 110 Watts, 8x6 = 10.4 amps, 105 Watts. Both were APC slow flyer props.

Hope this helps,
Kevin.
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Old Jan 12, 2011, 06:54 AM
2 Cor 5.21
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Tennessee
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Thanks, Kevin.

Did you pull that data with two motors turning or was that single-motor data? I was getting only slightly higher numbers from simultaneously running my motors on the 8040x3 props (and a 3S battery). Yawn.

It would definitely be nice to have 200 plus watts at work pulling this thing than the 120 or so I'm getting now.

Jeff
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Old Jan 12, 2011, 08:02 PM
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Jeff, those numbers were from a single motor. I just found the kv for my SK400 motor, it is 980KV. So your readings may change. Best to go with the 9x6 prop then.

Good luck,
Kevin.


Quote:
Originally Posted by JMAH View Post
Did you pull that data with two motors turning or was that single-motor data? I was getting only slightly higher numbers from simultaneously running my motors on the 8040x3 props (and a 3S battery).
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Old Jan 17, 2011, 07:03 PM
2 Cor 5.21
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Tennessee
Joined Jul 2009
775 Posts
I solved my motor question...

...by crashing it in a field!

I thought I noticed that one motor turned slower than the other, but ignored that as irrelevant. This afternoon, DoubleH and I tried to get in a quick flight before supper to test out my last repairs.

Turns out the motor issue wasn't irrelevant. On a fly-by it started making a nasty screeching noise, followed by the prop coming to a standstill.

My attempt to maneuver to an emergency landing resulted in a spin and ground impact. Pretty much every component on the plane is broken except the boom-tail joint I repaired last week!

Call the carbon-fiber company. We're gonna need some spars!

(Also call HeadsUpRC. The GWS motors are going away.)

Jeff
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Old Jan 17, 2011, 07:28 PM
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Exit 4, South Jersey, USA
Joined Dec 2007
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I feel your pain. I've crashed mine at least three times from one motor out syndrome. Turned out to be a bad batt that dropped voltage real sudden like. I could never believe they weren't worse than they were, cause these were flat out death diving for heck crashes from altitude.
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Old Jan 17, 2011, 10:26 PM
who has rabbit ears down
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United States, MN, Buffalo
Joined Jan 2007
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Owee Guys! are you saying the life of the included motors needs special attentions?
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Old Jan 18, 2011, 08:23 AM
Unrepentant Carnivore
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Brandon, Fl
Joined Mar 2005
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GWS motors are a real hit and miss. I've got some that are wearing like cast iron shoes, and a buddy went through a batch of similar ones in a heartbeat. I think I mentioned above, my next build of the P-38 will use eMAX 2822's - good for 1300kv and more efficient than my beloved 2409-12's.

Regarding losing a motor in the P-38, the only way to save her is to chop the throttle immediately and try to set her down straight away. Unless you are extremely skilled/lucky, applying power will result in a quick roll over and resulting crash. I have 3 examples of such inputs.

Jim
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Old Jan 18, 2011, 11:43 AM
jbc
WHO's your DADDY!!!
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Australia, SA, Adelaide
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Got a new warbird poll going here guys, so need ya help http://www.rcgroups.com/forums/showthread.php?t=1374090
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Old Jan 18, 2011, 03:41 PM
2 Cor 5.21
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Tennessee
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Quote:
Originally Posted by jamesdr View Post
...Regarding losing a motor in the P-38, the only way to save her is to chop the throttle immediately and try to set her down straight away. Unless you are extremely skilled/lucky, applying power will result in a quick roll over and resulting crash. I have 3 examples of such inputs.

Jim
I wish I could've pulled that off. I was flying away from myself and the plane was at the edge of the soccer field headed for a wilderness full of rocks, trees, and other hazards.

I chopped the power right when the motor finally seized, but she acted like she still had some induced yaw. Trying to turn her around to land on the field just wasn't in the cards, especially without proper rudder input. Just can't get the fingers to work like the feet used to!

Jeff
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Old Jan 18, 2011, 03:44 PM
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Sorry this happened.

I used the GWS motors and props for one very arthritic flight and went to 250 watts per side!

It screams, now.

I have more than 200 flights, but doubt I'd be able to recover from an engine failure.
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Old Jan 19, 2011, 12:28 AM
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Jeff, sorry to hear of your crash. Our group had 2 crashes on Monday. I wouldn't use carbon fiber to strengthen up the crash damage. Just a small amount of epoxy to get it back together. As you see it just breaks in a new spot. Poking holes in the two surfaces to be joined makes a strong joint.

Good luck,
Kevin.
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Old Jan 19, 2011, 07:18 AM
2 Cor 5.21
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Tennessee
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Quote:
Originally Posted by angelfood View Post
...I used the GWS motors and props for one very arthritic flight and went to 250 watts per side!

It screams, now...
What is the current set-up you're using? I'm vacillating between bigger motors turning bigger (more in scale appearance) props and smaller, high KV motors turning small props for speed.

Jeff
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Old Jan 19, 2011, 07:30 AM
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Jeff, I can't recall and the plane is in storage for the winter.

I bought them from Jeff at Headsuprc.com for "pennies," and gave him my feedback for use by others.

As I recall, they are the super cheap "CD ROM" tower pro jobs, of about 1300 KV.

My 38 is actually faster than my GWS 262, refitted with HK 3700 KV inrunners, and literally jumps off the ground.

In my opinion, you cannot overpower this airframe!
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Old Feb 05, 2011, 12:23 PM
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I'm in the process of finishing out another GWS P-38. I've debated whether or not to add functional rudders. I plan on hand launching my P-38, so I don't need them to assist in directional control on the ground. The only benefit I can see is having them to assist in an engine out situation, but I don't think it would be enough to compensate for the drag of a freewheeling prop on a dead motor. What's everyone else's opinion?
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