Sturtz

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I'm gonna do it !!!
I have everything I need to power it except the matching pusher prop. (Going with counter rotating props.)
Removing everything that weighs much except the front gear servo. Plus I'm sticking with the Futaba 3004s.
Hitech555 RX, mini 740mah rx battery to save pod weight.
Two PJS1000s, two Jeti 30s, two Tanic 3s-2150s.
Weight is right around four pounds. One of these PJS1000s puts my 2LB plane vertical till out of visual sight.
Should fly ,,, will keep posting conversion plus pics as I go.

Matt Kirsch

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That's coming out impressively light. Should be a real smoker. The review P-38s I've read about in the magazines come out on the porky side, around 7lbs.

This is just another perfect example of "less is more." Many times you'll discover that the weight lost by going with a lighter power system more than compensates for the lost power.

Sturtz

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It had OS-15 LAs on it. Not much power there and it would fly. Most use 25s on this plane.
Someone suggested to me going all Hitech81s on the servos to reduce even more weight. But I don't think it would lower it by enough to matter,,,plus the control surfaces need plenty of torque on a twin.
So far stripped down without motors,ESCs and batteries she weighs in at 3-1/4LBs. I am sorta going crazy with that "Should I do this or not. feeling." Wish someone else would post a conversion on this plane. But I haven't found one.
Also I've been informed that going counter rotating on the port prop is not nessasary with the electic motors on this scale/size.
In fact the real P-38s had some questionable results from doing so I hear.

mookie1

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Sturtz, sounds like you are at the "just go for it stage". Just pick a system with more power than you think need and go for it. Good luck!

Matt Kirsch

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Well, just food for thought, but Hitec HS81 servos do weigh about 1oz less EACH than standard servos. The P-38 needs... let's see... two for ailerons, one for elevator, one throttle one for rudder... That's 5 servos, five ounces. Your 3-1/4 plane now weighs less than 3lbs.

Glacier Girl

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Matt,
I may be wrong, it's happened before, but why do you need a throttle servo on an electric?
Just kidding LOL

P.S. You go Sturtz, maybe you and Mookie can get together for a fly off.
BJ

Sturtz

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Thanks everyone. Been working and haven't gotten to the planes yet. But the servo reduction would take off some weight for me.
It's true, no need for a throttle servo anymore. But I do need one for the steering system located in the pod.
I don't see much about PJS motors in here. Mostly Mega , etc. All I know is that the PJS1000 is rated at 35oz thrust with an 11x4.7 APC prop. Thats with a 7.4volt lipo. Myself and several others at my field are running 11.1 volt lipos and ripping the wings off Mini-Funtana's and Shock 3/D ARFs. I have no doubt these motors could easily fly the P-38. I just need to make time and do it .

Sturtz

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Ok,,weather is crappy here so I got moving along with this conversion.
I managed to get the weight just below 3LBs by removing the two standard Futaba pod servos (throttle and gear) and replacing the gear servo with a Hitech81. Also I removed the rubber wheels I had on it for our paved strip and replaced them with larger foam type on the mains and a 2"Kamdax wheel in the front. These two changes dropped my weight over a 1/4LB.
I then replaced the to 12" y-harnesses with 6" Ys and installed a Hitech 555 rx.

Sturtz

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Next I had to decide what the best mounting system would be for the profile booms without adding alot of extra weight.
I had a PJS Carbon Fiber stick mount ,,, measured and cut it to fit from the starting edge of the built in thrust lines to the very front of the upper boom. This will allow the back plate of the pjs to rest along the front boom edge plus give me enough ground clearance to run a 12x6 prop if I wanted. (I'm going to start with 11x4.7s for the maiden.) I still have over an inch of clearance between the center pod and the prop tips.
I then drilled two holes directly above the two upper motor mount holes on each boom .

Sturtz

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I mixed up some 30min epoxy and brushed it on the cf rod mount and the thrust bar. While holding the mount in place I crisscrossed some aircraft safety wire through the four holes snugging the mount against the boom like a shoe lace. Making sure it was perfectly straight with the thrust line I wrapped some blue painter's tape around it till it cures out.
More to come.

Sturtz

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It cured out good and solid so I added the extra safety wire and filled the gaps with ca. A touch of olive drab paint as well.
After it all dryed I tried to break the mount off. It wouldn't budge.

Sturtz

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Test fit a motor with and without a prop to check the thrust line. The GP Profile's port thrust is to the left and down with the starboard side just the opposite.
I went ahead and ordered another PJS1000 w/Jeti30 from Hobby Lobby plus another Tanic 3S 2220mah pack from Brian at TanicPacks. They will be in next week so I'm at a stopping point till then. I have another PJS setup but it was an older model and I wanted to keep the motors as close as possible.
This whole conversion may look cheap. But the lack of heavy brackets and rods for the motor mounts will pay off in the air.
I'm also gonna have to wait on running the controller and wires till I get the batteries in their cg balanced positions.

Krupps

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Sturtz wrote: I am sorta going crazy with that "Should I do this or not. feeling."


Don't go there Bud! If it makes you feel good, then do it. After all, it's only money! lol You're pioneering here, so you're bound to run into a few snags. I plan on trying the same thing with a Stinger .10, at least I have the benefit of someone trying it before me. You are making history! lol

Sturtz

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I think more Stingers have been converted to elec than profile P-38s. I may be wrong.
You gotta get out your glue and finish that Stinger and those 15 other kits and ARFs waiting in your garage dude.
Winter will be over soon and you can't fly my planes.

Krupps

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I found this posted in another forum abot the Stinger .10-[8D][8D] Should do fine w/PJS1000/10x7.4


I bought that little bird about 7 years ago thinking it was perfect for my .10 but it came out too heavy and flew extremely sluggish. After a couple months not enjoying it that much I did exactly what you have in mind. I sold the old airplane and ordered me a new kit. I removed practically all the foam of the wings. Using a hotwire cutter I left 1/2" ribs and a 3/4" center spar section of the original foam. Then I sheeted the whole wing. Got rid off practically all the plywood except the firewall and did some modifications to the landing gear mounting block.
It flew beautifully, lots of speed with just an OS .10 FP......not enough to hover though.
Have fun!

Sturtz

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A couple of flying buddies want me to redo my mounting idea and go with a centered mount on the booms. I admit I get in a hurry sometimes and the stick mount idea doesn't look that great. Also they think the thrust lines should be kept centered. I have to agree ,,,so I'm going to experiment with a few other ideas while I wait for the second motor.
But,,,,just to ask you fellow RC folks,,,,would the upper mount "as pictured" not work just as well ? Or is it more important to center the motor on a twim boomed a/c ?

Sturtz

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There is a lot of room for fresh ideas in the elec flight world. It's still young enough of a hobby to experiment with what you got laying around than to go out and buy or order everything. I can afford to order the parts,,,but I like to see what I can come up with first. If it doesn't work,, I jump in the car and head to the LHS or punch in the order via computer online.
I see guys like Matt Kirsch ,, elec moderator always commenting on a new idea. It's how alot of this elec and nitro gear was developed in the first place I imagine. And hearing feedback on ideas is a good thing.
Anyway,,,all that bs above was just to prepare you for my latest sloppy modeling idea.
I stepped outside for a breath of fresh cold air and happened to look down at a fence I put up to keep my dogs from roaming and tracking up the entire yard. I had put an elec fence (low amps) up for a few weeks till they learned about shock treatment and would stay put on their own. I noticed the yellow fence couplings . Nice color of yellow.
I grabbed a couple and headed back to the work table. With a Dremel tool I started shaving off the extra plastic to fit my profile booms. The yellow plastic is very tough but light because of the honeycombed design .

Sturtz

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I then mounted a PJS firewall type mount on them and sanded the areas directly around the mount. Leaving just enough to reach the top and bottom of the boom ends.

Sturtz

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I cut some balsa from an old former to use as shims and glued it all in place with medium ca when I was sure of the thrust lines.
After it cured I ran thin ca along all the lines and soaked up the balsa with it before hitting it with activator.
Then using small zip ties I ran the ties through the motor mount holes , snugged them all down and clipped the extra off.
Again like the rod mounted version I tried to physically move the plastic mounts. They don't budge and I'm a 6.3" 225lb guy. So I hope the motors will stay put during flight.
My biggest fear so far is the extreme tail heaviness of this plane. I sure hope I don't have to add a bunch of nose weight. I had to add 1/2 oz to the tail with the nitro setup before.
Will post more when new parts get here.

Sturtz

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Well,,,what do you know ?? Hobby Lobby and TanicPacks got all my stuff to me today already. They must have known I was missing a power plant for this Lightning profile. lol
Anyway,,, my good friend Mark came over with his trusty RPM meter and a CG machine and helped me finish up tonight.
THANK YOU MARK !!![sm=thumbup.gif]
After doing the RPM check we switched the motors so the one with the little bit extra rpms would power the port side.
During this test we recorded rpms at idle, mid and full throttle. We hadn't cg'd it yet but I knew it was tail heavy. At a hair over 1/4 throttle it stood right up on all three wheels while I held it by the tail section. At half throttle it wanted to fly away. And at full throttle it was trying to pull outta my hands.
After recording the rpms I held it vertical at the leading edge and had Mark throttle up from start to full. At a little over half it would rest in my hand without gripping. And at full throttle it would jump right into my open fist with plenty of thrust. I fly 3/D nitro and electrics alot and know by feel if they will hover or not. This P38 will hover easy. I'll never try it,,,but it would if ya could.

Sturtz

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After finding the right battery positions along the booms and getting it balanced we marked everything and flipped it over to start running the wires, etc. I used servo tape for the ESCs and a couple of self-adhesive cable locks to hold the wires down.
We then measured and cut the slits for the velcro battery straps . I'll add the full velcro strips to the booms and batteries tomorrow then put all the screws back in the center pod. Blue tape can hold it on till then.

Sturtz

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Mark didn't want in the pictures,,, but I tricked him on at least one.
I found that the port motor BEC switch is the best out of the two for some reason. I tried it both ways and got one faulty start using the other switch so that was easy enough. I tucked the one that will not be used around the main gear and used servo tape to apply the other in a good spot under the port boom.
The little things like some touchup paint and basic grooming can wait till tomorrow as well.
After everything else checks out ,, like servo positions , control surfaces and the nuts and bolts....... she'll be ready for a maiden.
Been too wet, cold and breezy around here lately so I can't say when I'll get to fly it. But basically it's a done deal people.
Thanks for looking in on my elec conversion of the Great Planes P-38 Lightning Profile.
Thanks to PJS motors and Max at Hobby Lobby . Thanks to Brian at TanicPacks. "Best LIPOs in the world."
And thanks to everyone else in here for your great electric know-how.

Will post after maiden. Will try to get you some video too. I don't know how to convert it so you can watch it here. But I'm sure Matt .K or someone else will know how when the time comes.

Sturtz

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After going through several props while checking the amp draw I have decided on the APC 10x4.7 slow flyer prop as the maiden screws. The 11x4.7s drew too many amps at full throttle. I will probably end up with the E-series APC later on but for now the 10 will be safe on the amps and I'll have more clearance.
Thanks goes today to Mike McMurtry of Mike's Models OKC, OK. And Greg Ward of OKC,OK. Mike is Sean McMurtry's dad and model designer. Greg works with Sean on all his tournament planes, elec included. Greg Ward is the designer of the REFLECTION . One of the best indoor class 3/D flyer that will hit the market this spring.
Great Planes has put their stamp on it and it will be available in March 2005.

Thanks again for checking out my conversion.[8D]

Sturtz

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Maiden Flight
Weather is wonderful here in Okla today. Some buddies and I decided to hit the field.
I was a bit nervous about the maiden flight on this P38 and one of my friends stepped up to the plate and offered to test fly it.
(Jim Bennet) has been flying RC for over 20 years and is asked by many people to maiden fly new planes. So I agreed.
And since I've never flown a twin and he has,,,it was even a better decision.

I got a return phone call today from L.A. Johnston of Hobby Lobby and he filled me in on a few important tips on the PJS/Jeti setups.
One thing I didn't know was the 1000 needs to run with a thicker type elec prop like the APC E-series or the Master Airscrew elec props. The APC slowfly props are too thin for this motor unless your just fly 3/D and need the thin flat low pitch for hovering, etc.
On a scale type plane or warbird these thin props hurt your performance because of all the give when under high torque.
Anyway,, on to the first flight.

It rolled out on all three wheels until elevator was introduced. It flew like it was on a track. It did want to pull up when full throttle was applied , but that is not uncommon for an elec. The decreased wing loading with the brushless motors causes this many times. Some tinkering with pitch and trim might help for the next flight. But all and all it flew very well.
The plane still has most of the same habits as the nitro powered twins. Great care is needed when making a tight banked turn and the torque is higher with two motors.
The one thing it still has that I don't like about the GP profile is the lack of extra elevator when landing. Just runs out of up on the flare.

Sorry about the lack of pictures or video but it was so nice out I was more into flying than recording video. Plus I don't own a camcorder.[&o]

mavdriver

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[8D] sturtz how was the speed ? about the same when it was power by glow , or did it seem faster ? by the way good job > Ed