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  1. #1

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    Guillow's P-38 R/C Conversion

    I bought a Guillow's P-38 kit, and I just started building it. At first, I thought I was just going to use it for display, but then I thought about an R/C conversion. So now I don't know if I want it electric or glow-powered. What do you think about it?
    I would like to use 4 channels, rudder, ailerons, throttle and elevator.
    I would need 2 engines or motors.
    I think I need to have really in mind the altitude of where I live. I live in Mexico City that is about 1600 meters high, and I fly 600 meters above it, so that would be about 7200 ft.
    So what do you think, should I use engines or motors? and what size?
    I don't have the weight, because It is not built yet, but it has a 40" wingspan.
    I believe motors would be a better idea, mostly because of using 2, and I wouldn't need to adjust the needles.

    Thanks in advance ,
    Eduardo

  2. #2
    Half-A-Hec's Avatar
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    RE: Guillow's P-38 R/C Conversion

    Keep us posted on your progress. Check out this guys website. He did what you are doing.

    Hec

    http://personal.rdu.bellsouth.net/g/...modelhome.html
    Creating Beautiful Balsa Fountains for over 30 years!

  3. #3

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    RE: Guillow's P-38 R/C Conversion

    Lithium:

    The P-38 is not a good subject for a flying model, and definitely not a good first twin.

    You can improve its probability of survival if you go with electric, most model P-38s are destroyed when one engine quits, the electric motors should at least remove that danger.

    Suggest you continue with your original plan, make it a display model and build something else to fly.

    Bill.
    Real Airplanes have Two Engines
    AMA 25139 - More than 40 years.

  4. #4
    colmo-RCU's Avatar
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    RE: Guillow's P-38 R/C Conversion

    Sorry to disagree, everybody said that exact same thing about my zero, which is 27 in span. And it flyes like many big planes would dream of. I use a norvel 061 and it is way overpowered so I use a very rich mixture and a large prop (7/3) which looks great for scale purposes. I weighs 350 grams all together. Dont worry about altitude, I live in bogota at 8350 ft (2600 mts) and I have al the fun in the world. I posted all the items I modifyes, it must be around there someplace. The thread is called Gillows zero success story. Check it out. By the way, last Sunday I won a !st place in a scale fun fly here, as nobody could believe something so tiny could do so well.

    Colmo

    PS do you speak spanish?? any questions, just pm me. Good luck
    Modify, personalize, upgrade

  5. #5

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    RE: Guillow's P-38 R/C Conversion

    Colmo:

    It is not that it cannot be done, I would not discourage him from building another Zero like yours, a Corsair, or whatever. But Eduardo is talking about a P-38. and a P-38 of any size is a bear to fly. Any engine problem will almost guarantee a crash. That is why I suggested he not try to make it into a flying model.

    Bill.
    Real Airplanes have Two Engines
    AMA 25139 - More than 40 years.

  6. #6

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    RE: Guillow's P-38 R/C Conversion

    Hi!, thanks to the 3 people for their help.
    Bill, but if I do it electric.. you think I'll still have the same problem? or it will fly fine?
    In electrics I have an IFO, and that is the only thing I have flown electric.
    If I do it, I would use as in the page provided by Half-A-HEC:
    http://personal.rdu.bellsouth.net/g/...modelhome.html
    2 Hacker brushless motors B20S and 4:1 gearboxes.
    Li-Po battery packs and micro servos, the only thing I not sure is the retracts the guy is using, because I dont think those microservos wont resist the weight of the whole airplane.
    Colmo, por supuesto que hablo espaΓ±ol, tu vives en Florida o en BogotΓ‘?


    Thanks,
    Eduardo

  7. #7

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    RE: Guillow's P-38 R/C Conversion

    Lithium:

    Brushless with Li-Poly batteries could make it into a very nice airplane. And you shouldn't have any engine out worries unless you try to stay up too long and kill the battery charge.

    So, going electric will give you a nice plane. Enjoy it.

    Bill.
    Real Airplanes have Two Engines
    AMA 25139 - More than 40 years.

  8. #8
    colmo-RCU's Avatar
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    RE: Guillow's P-38 R/C Conversion

    I totally agree with that, no engine trouble will make it a lot easier. ThatΒ΄s for sure. On the retracts I have no idea.

    Vivo en Bogota, preo soy piloto en la vida real y paso mucho tiempo pernoctando en Miami, asi que puse esa direccion para facilitarles el entendimiento a todos.

    Good luck
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  9. #9

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    RE: Guillow's P-38 R/C Conversion

    Ever since I saw the kit about a 100 or so years ago I wanted to build it. Actually I wanted to fly the real thing and the model is just a stop gap... I stopped short of buying and building every time I ran the numbers... over 30 oz and the wing loading goes out of sight. 20 - 22 Oz/sq ft is too much for me I need something a bit more forgiving. In addition using a 1/2a glow is just asking for a major crash. Too undependable and messy. But the electric opens new opportunities as well as the miniature electronics.

    With the advent of lighter electronics (park flyer stuff) , Li-Poly batt etc., I think I can get it ready to fly under 25 perhaps 22 oz. What would be terrific is flying weight at about 20 but I think thats a bit much to hope for... That will bring the wing loading to a more desirable 15 or so oz/sq ft. and certainly make it a more gentle and predictable model to fly.

    Any ideas on brushless as opposed to a couple speed 400 or 600 in series using a common controller? Seems like brushless will be a lot of HP and $$$ for the model? Configure it with counter rotating props? A couple of 7 x 4 APS Electric? Right offset and down thrust? CG...? Standard calculations? Retracts, why not vacuum? Weight saving... Thinking about using some carbon fiber spar caps. strong and light... Same for the two booms...

    I'd be very interested to hear from this forum to know what other builders think about the project....

    Regards,
    Ron

  10. #10
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    RE: Guillow's P-38 R/C Conversion

    I used to fly 704 combat with a guy who ran 2 CONQUEST 15s in his P38 and it was 1/12th scale. He crashed about as often as everyone else, but when he did, he always had alot of work to do. It was the most crooked and twisted looking thing you ever saw. The 704 rules allowed a slight oversizing of the wing and stab. The problem with a GUILLOWS kit is they are true to scale, so the wing area ends up being marginal to carry just a bare bones type model, forget about retracts and that sort of stuff. I think one has a much better chance of being a good flyer if the landing gear is left off. I bet you could outfit one with electric motors and make it a decent flyer at 25 ozs or less. The lifting type airfoil will require that the engines have a couple of degrees of down thrust. Test the thrust issue with the model in your hand, work the elevator up and down with the props turning full blast, you should have equal control up and down.
    WHO GUNNA FEED MAW KEEEIDS..???

  11. #11
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    RE: Guillow's P-38 R/C Conversion

    I don't believe that the Guillows P38 has very much wing area dispite the 40 inch span. So LIGHT is the watchword that you need to live by. So this means NO retract gear. In fact I would say don't put any gear on it. Just hand launch and belly land on grass.

    The P38 has a very tapered wing with a narrow tip chord. This is a large part of what the problem is. You should use a good 3 or even 4 degrees of washout to help avoid or delay tip stalling. And I agree that electric is the way to go. Brushless would be nice but you don't need that. Speed 300 motors with 5x3 direct drive should offer sufficient speed. But you can check with MotoCalc for options and better detail.

    In any event I suggest you keep the weight down as close to 20 ounces as you can manage. This means very little sheeting and a better spar system.

    Frankly, if it was me trying this I'd use the kit parts for the fuselage, nacelles and tail sections but redisign the wing with a better airfoil and spar system that uses leading edge sheeting back to about the 50% chord mark. While I was at it I'd cheat and make the tips a bit wider as a nod to at least try to improve the Reynolds numbers. Adding even a 1/2 to 3/4 inch to the tip chord would make the tip stalling much less prevalent. Something thin and simple in shape with low camber in the 9 to 10% thick and 1.5 to 2% range for good upright performance and decent inverted. The Guillow's wing section is terrible and the spar system is a joke that was never intended for serious flying.

    PS: to Ron Kay....

    Forget the twin 600's for a model of this size. It would come out way too heavy given the motor and required battery weights. And I really think it's close to being a "ditto" for two 400's but at least they would be within the range of practical. I much prefer the idea of a lighter built design using two speed 300's. Perhaps even the low gear ratio GWS EPS350's with the smaller high pitch props.
    Witty saying to be plagarized shortly.....

  12. #12

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    RE: Guillow's P-38 R/C Conversion

    Bruce,

    I agree redesign the wing, larger cord I like the 10% and a bit less on the taper with a healthy washout. All it needs it to do is be a good look-a-like P-38 on the way by....

    Reynolds numbers, ! Keep it as light as possible. F=MA! I'm not sheeting only where absolute necessary. Other surface is Mica or similar. I'm thinking of making the model scratch from the plans and choosing the materials very carefully. 20 - 25 oz is the target weight. The plastic in the kit would be nice but not a big deal. About the landing gear, I live about 100 mile N of Phoenix AZ at 5500 feet in the mountains and there is simply nothing even remotely like grass up here. I've been flying HOB 1/2's 30" P51/P47/ME109 etc and they are all hand launched. But the landings take a major toll. They are more likely to be damaged on landing then by my flying. Rocks, cactus, bushes, cows, horses ... but no grass. Light retracts that are in the electric park 's. Perhaps hand or bungee launch and a soft runway landing... Being very optimistic here..

    If the weight is right I prefer the direct drive 300's... I'll hold off on making that decision for the moment.

    I'll keep you posted on the 38..

    Ron


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