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May 17, 2018, 05:01 PM
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Help!

GWS - P38 Power System & Prop


I've had a GWS P-38 kit sitting around for a couple of years and now decided to build it. However, I was wondering if anyone that has built this kit in the past could pass on some advice regarding which motors and props to use . I plan on using a 3s /40c / 2200 mah battery and would like to use, if practical, a 3 blade prop . GWS had a kit at one point that included 2208/18 T / 1050 kv brushless motors ( just for FYI here's a link to an old webpage for the motors).

http://www.rcmart.com/gwblm002-outru...t-p-19389.html

I've read some reviews about this gws 2208 power system and several said the motors were "just adequate". Since my kit didn't come with a power system I'm wondering if anyone has some motor and prop power system combo tips and recommendations for me.....but staying with my 3s battery choice. I'd like to be able to have "plenty of power" so I can go vertical (don't need to have unlimited vertical) and do other rolls/maneuvers, but I don't want to build a rocket.

Also, since the kit is designed to be a belly lander I was thinking of adding some plain wire, non-retract, landing gear so I could use a 3 blade prop (but which prop?). Any tips regarding this? Or should I keep it a belly scraper and use a 2 blade (and which 2 blade? ).

Thanks for your input.
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May 18, 2018, 12:24 AM
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Corelli's Avatar
I've flown this plane a lot. I belly landed it . I used 2- 20 amp ESCs. Turnigy C2830-1060 motors with counter rotating APC 9X6 props. It flies exactly like you said with a 3s 1300-2200 mah battery. Easy hand launch and great vertical - not endless. Pretty fast but she slows down nicely. I always wanted to put some 9X8s and see how it did because the motors and ESCs could handle more.

Good Luck

C.
May 18, 2018, 09:27 AM
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Thanks C. I was thinking about a 2828 or a 2830 motor and found a couple of candidates. The PropDrive 2830 / 1100kv (sku 9192000321-0) and the HK 2830 / 1300kv (sku CL2830-1300) are my top 2 choices. Your set up sounds like what I'm looking for.
May 18, 2018, 08:36 PM
Jack
jackerbes's Avatar
A google for GWS P-38 will poduce a lot of hits, many of them here and with details like this thread:

P-38-Lightning-by-GWS - https://www.rcgroups.com/forums/showthread.php?1298156

Quote:
Power is as follows:
600watts @ 39Amps on a 2650mAh 4S 20C battery with twin 830kv motors, 9x7 3 blade Master Airscrew props, twin 20A esc's and a separate 5A UBEC.
Sounds like GWS hit the bullseye with this kit...

Jack
May 18, 2018, 08:59 PM
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Corelli's Avatar
Amazing plane. Somehow they got the moments perfect and you hit the ailerons with dual rates and the plane will roll without any corkscrew and doesn't lose a lot of altitude. Good looking plane too. Sometimes there are p38s that kind of look odd to me.

I actually bought a new one after posting here last nite I had so many flights on my last one but it hit once a little too hard.


A lot of people used that 4s set up and reported that it made it a 90mph plane

C.
Last edited by Corelli; May 18, 2018 at 09:00 PM. Reason: forgot pic
May 19, 2018, 10:25 PM
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Thanks for the link J. Lots of info. That 600 watt set up is a little more than what I'm looking for but I like that he put counter rotating props on the P38 and that he says it's a steady flyer with winds. I've got a couple of hot planes with 4s set ups and so that's why I'd like to stay with my 3s / 2200 / 40c set up for the P38.
May 19, 2018, 10:33 PM
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Thread OP
Oh bummer C. Thanks for the pic. Where did you find another kit? GWS is history so when I go on Ebay they want a fortune for one. Also, since this isn't an EPP or EPO foam kit, I'd appreciate any painting tips. As you're probably aware, regular Krylon spray paint melts this type of foam. I've built only one other plane with this type of foam and discovered it the hard way. What spray paint did you use? What precautions should I keep in mind and what technique gives the best results.

Are you going to use the same power system or beef it up a little?
May 19, 2018, 11:51 PM
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Corelli's Avatar
Aloft Hobbies had 3 bare foam kits a couple days ago and now they are gone. Was $71 with shipping. That paint I get from our local HobbyLobby crafts store. It comes in a wide variety of colors and is foam safe. The silver matches the GWS silver perfectly. Ill be using this on mine. Especially because this one isn't painted.

I would suggest not using their elevator servo/linkage set up. They want some push/pull with rods in the air between the two booms . I put the servo in the oiler cooler and have a linkage that is short and mostly hidden. You can make the cover removeable. Hope the pic shows what i mean.

Also, the oil coolers imo stick out too far. If you take 1/4" off the front of them then blend and taper that back to the end, they fit better and have way less drag.

Another thing I do, is after shes all built there are lots of gear holes and wire troughs in the foam. I clean the plane with soap and water. Wash my hands to get excess dirt and oil off. Take masking tape and make precise strips to cover these holes. Cut all the tape corners at a 45 degree. Then spray them and they usually stay put and look pretty good.

I'm going to keep my same set up mostly. I do believe Ill go with some 9x8s this time, maybe 9x9s. One of the motors has a noisy bearing, so I will look into finding a replacement. Gonna keep the ESCs in the Cowl again.

Ill keep you updated here.

C.

PS no biggy about the crash. I had so many flights on that one
May 20, 2018, 12:33 AM
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Thread OP
Thanks so much for all these tips C ! Geez I hope you find another kit. The Pic of the elevator control rod came out fine. I'll use the same set up b/c I've heard from another guy at the park that GWS has used funky servo/control rod setups on other models. He cited the DC3 and their aileron setup as an example. I've ordered the motors from HK but they're coming from the international warehouse unfortunately so I won't have the plane done for a couple weeks b/c of the shipping delay. Will post a Pic when she's done. Regarding the masking tape, a guy at the park turned me on to a super lightweight spackle from HomeDepot. They keep right next to the regular stuff and unfortunately I don't have some to send you a Pic. This stuff feels like they whipped the product in a blender b/c its sooo fluffy light. It weighs next to nothing and sands and paints easily. Have you heard about it? I've used it on several planes and it's great.
May 20, 2018, 12:38 AM
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Forgot to ask about the CG. When you built your plane C, was the CG in the instruction sheet correct or did you use a different measurement?
May 20, 2018, 09:46 AM
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Corelli's Avatar
Quote:
Originally Posted by windmill200
Thanks so much for all these tips C ! Geez I hope you find another kit. The Pic of the elevator control rod came out fine. I'll use the same set up b/c I've heard from another guy at the park that GWS has used funky servo/control rod setups on other models. He cited the DC3 and their aileron setup as an example. I've ordered the motors from HK but they're coming from the international warehouse unfortunately so I won't have the plane done for a couple weeks b/c of the shipping delay. Will post a Pic when she's done. Regarding the masking tape, a guy at the park turned me on to a super lightweight spackle from HomeDepot. They keep right next to the regular stuff and unfortunately I don't have some to send you a Pic. This stuff feels like they whipped the product in a blender b/c its sooo fluffy light. It weighs next to nothing and sands and paints easily. Have you heard about it? I've used it on several planes and it's great.
I did find the kit. I went back to look and they are down to 0 left. When I bought mine they had 3.

Yeah I use it for repairing dings and building filler. It is a must have tool for foam builds. Just be careful with large chunks, over time it shrinks and wants to fall out. Seeing how were talking I'll give you a tip using it. After I apply it, ill wet my finger and then you can smooth it out even more.

I don't remember the CG. I did put a spacer in the front of the battery bay to keep the batteries back. I flew this plane with 3 packs. A 1300, 1800 and 2250. They all sat in roughly the same place and I never had to change trim or fly any different between the packs. When I get mine together I'll let you know where it is

C.
May 24, 2018, 12:23 AM
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Thread OP
Quote:
Originally Posted by Corelli
I did find the kit. I went back to look and they are down to 0 left. When I bought mine they had 3.

I don't remember the CG. I did put a spacer in the front of the battery bay to keep the batteries back. I flew this plane with 3 packs. A 1300, 1800 and 2250. They all sat in roughly the same place and I never had to change trim or fly any different between the packs. When I get mine together I'll let you know where it is

C.
If you have the time, send a pic when she's done.
Aug 04, 2018, 05:37 PM
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Thread OP
Hey C, you got your P38 together yet? If you do, would you send a pic? I'll have mine done next week. I've to to find a tough scrap piece of plastic that I use for a skid plate. Mine is a belly lander. FYI, I took your advice and put a single servo in the right tail boom for the elevator. Also, I trimmed the side oil cooler scoops per your suggestion. Man they were HUGE! Another mod I did was put a carbon rod across the elevator control surface AND the stationary elevator surface. I remembered one of the threads from way back suggested this. Last, I'm using counter rotating props.
Aug 31, 2018, 01:54 AM
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Thread OP
Well here she is. I flew her maiden flight this morning and it went great. Plenty of power, great flight characteristics, and great to look at in the sky. She has the Prop Drive 2830 1200kv motors with counter rotating 8x4.5 props. The motors are rated at upto 200 watts. I measured 160 - 175 watts/ 14-15 amps 90% throttle. I'm using an 18 amp bec on each motor and nothing gets hot after a 5 min flight.

One notice one thing that I need to check out. It seemed that one motor iseems to be rinning at running at a higher rpm (the one where I pulled off the red wire out of the esc servo wire . On take off she pulled to the right a lot. I noticed that after reaching cruising speed it seemed the other motor's rpm peed was closer matched to the other.......but I know that's not true. I don't have the tools to chedk a motor's rpm. 1) Is there a smartphone app for that? Is there an inexpensive tool I can get to check a motor / prop's rpm? 2) Do I need to chg the slow motor's esc programming? And how do I do this? Is there a thread or threads about this in RCG?
Aug 31, 2018, 06:22 AM
Jack
jackerbes's Avatar
If you have a typical handheld optical tachometer you can do a static test (aircraft fastened against movement) and compare the readings.

When I do that sometimes I hold a flashlight behind the prop and project it into the tach with the prop blade turning between the light and the tach so that florescent lighting does not confuse the readings.

And if you can swap the ESCs to see if the readings move with the ESC change you'll know if the problem is in the ESCs or the motors.

And the manual for the plane is the GWS38 manual here:

https://gwsus.com/gws_com_tw_www/eng...ane_manual.htm

Jack


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