I'm building a Guillow's P-38 and I have a few questions about it. First the scale is 3/4" = 1'-0". In the search for parts I've found that all the scales are 1/8, 1/12, 1/2 etc. How do I convert my scale? I understand the 3/4 part, but whats the 1'-0"? I'm just getting into the build so I'll have lots of questions as I proceed. I hope you vets will help this rookie[8D] I plan to use two AP Hornet .09 engines. I'm haven a little trouble find'n 8-3/4" 3 blade props for it, know a place that has something I can work with? I'm also not sure about this pitch deal. What do you recommend for this size aircraft. All replies are greatly appreciated

3/4 inch = 1 foot (or 1/16 scale)

Here's a conversion to electric. Might be a good alternative:

http://personal.rdu.bellsouth.net/g/...ldod/p-38.html

Jesse

MinnFlyer gave you the right anwer, but he didn't tell you how. They give scale in two different units on purpose to confuse you.

3/4" = 1'

is the same as

3/4" = 12"

So divide .75 / 12 = 1/16 scale

As far as the props go, I think the .09's are too much for this plane. I would use 1/2A engines such as Norvells. Why do you want 3-blade props? Do you need shorter props for clearance or are they just for looks?

Thanks CafeenMan, whstlngdeath, Minnflyer for your responces. My plans for this aircraft are to have a very fast plane that can carry a heavy payload. Thats why I desided to use gas engines. I want to use three blade props mostly for looks but I also believe that they will provide more thrust. And I just don't think a P-38 would look right with 2 blade props. As far as the heavy payload goes, I plan to use retracks for gear and put a small desposiable camera in the fusaloge. And have all the correct lights on the aircraft work, including the instrument panel. All of this in such a small plane will be a challange. Your probley wondering why not build a larger aircraft since I want so much out of it, I just think having all this in such a small package will be pretty cool. I also have a trick I found out, that aluiminum foil tape ( you know the stuff they use to seal up the duct work under your house ) is great for covering a WW2 fighter. Its hard to work with but the results are unbeleavable. It looks just like croam, and makes for a slick and shinny fighter. I can't wait to post some pics for you guys, just a pile of shinny parts right now though. I'm still not sure about the right pitch for this plane. Should I just buy all the different props and try them out? Also I know there can be problems with twin engine aircraft, if one engine dies. Any device out there to help save a wounded bird? And how big of a battery will I need to power landing gear ,camera servo and lights? One more thing, I have a pretty good collection of books on WW2 aircraft. So if you need some pics for one of your projects let me know and I'll see what I can find. Thanks again for your responses guys.

The wingloading is what will be a challenge. Have you added up the weights on all of this?

If you are able to jam all that in there you'll have a very heavy, very fast model that wasn't designed for what you're trying to do. If you can get it off the ground the odds of being able to slow it down for a safe landing aren't real high.

How much RC experience do you have?

You do have a big problem if one of your engines cuts out. The guy that built the electric version in the link above, just informed me that he crashed his on the third flight. A motor cut out on takeoff and it went in with a spiral. Took off most of the front end. One thing about these Guillows kits is that their frames are so light. You can't over stress the frame with excess weight, and being a small size, the weight and balance thing becomes very critical. You need to use the smallest of micro gear on board and more than likely a Li-poly battery to save weight.
If you do manage to get it flying with extra weight on-board, it won't take much maneuvering to break the fuselage under load. The Guillows kits were originally meant for free-flight and were designed to be built as light as possible with silk and a minimum of glue. Just some thoughts to consider. I built the Guillows Hellcat and they are great models. I also had a link to a website of someone who built a R/C version of the Guillows Hellcat. I'll see if I can find it, because he used a glow engine on his, I just can't remember which one. Good luck and keep us posted.

Jesse

As far as retracts go, I would strongly consider sheeting the bottom of the plane in areas that will make contact with the ground, glassing those areas and leaving the gear off completely.

MikeL and WhistlingDeath are giving you very good advice here. These planes don't fly all that great as designed - even when they're light. I think what you're planning is admirable from a building standpoint, but from a flying standpoint, I think it will become toothpicks on the first flight. Just too much stuff in too small of a plane.

Hummm.... Well I don't have a lot of RC experence. Build a F4U a few years back, flew it about 10 times untill you know what happened. I have three other electric planes to practice with, including a p-38 style trainer. As far as the balsa wood construction goes, the only balsa I had planed to use is for the stringers. I basicly just bought the kit for the plans and the plastic. I know this is risky buisness but I had planed to fly it without all the extra junk first, and see how it did. And add the other stuff one at a time. I also was considering adding a inch to the wingspan, for more lift. Its just a goal I've set for my self, just really want to fly it once and retire it. Once just to say it flew. I'm gona build it, with gas engines and retracts. It will probably crash on tack off, but what the hell, it will make a cool explosion Its not the only bird in the nest. If you guys were challanged with this build, with all the stuff I want to add, what would you think you chance of a good plane would be? The chance it would fly and fly well. 10%? Let me know, and i can cut your % in half and get my %. Thanks for your responces guys.

I think anything and everything is worth trying. Where would we be today if nobody took the chance. Maybe you'll hit the right combination and it will fly great. Take plenty of pictures of it before the first flight, though, just in case!

Jesse

Yeah, I'll defiantly take some pics As soon as i get the fuselage done I'll post it for you guys to check out. Don't forget to try out that foil tape, it looks pretty good.

Sounds like a cool project.

Btw, my understanding is that the P-38, done scale (ie, with out altering the dimentions, enlarging bits here and there and such) is a real monster in the air, and pretty much a gonner on engine out. There are a lot of other twins that handle engine-out a lot better than the P-38.

Back to your prop question, it's going to be a trial-and-error thing. 3 bladed props are actually less efficient than 2 bladed. The main (but not only) reason for using 3- and 4- bladed props is ground clearance or in other situations where a longer 2-bladed prop isn't possible.

Well, you're not going to like my answer, but you asked. I'd say 10% chance of even surviving the first flight (with an experienced RC pilot) would be on the high side.

I think it's a noble goal, and you'll learn a lot by building it, but it's on the very edge of possibility in my opinion. There have been a few successful conversions of Guillows kits to RC. They are usually predicated on keeping the aircraft as light as physically possible by replacing Guillows' notoriously hard, heavy balsa with contest grade, then using the very latest in light weight RC equipment, AND by limiting the plane to three channels, throttle, elevator and either rudder or ailerons.

By adding retracts, a lighting system and a camera, I doubt that the plane will be capable of flight.

Try this. Figure out what your wing loading will be by getting the wing area in square feet and the weight in ounces. (You want the loading in ounces per square foot.) For a plane that small, you don't want the wing loading to be much over 15 to 18 ounces per square foot. I'm guessing your's will come in closer to 30 (or more).

You might get it to fly by skipping the retracts (maybe landing gear all together), skipping the lights and camera, keeping it to three channels, and using the absolute lightest RC gear around. I'd suggest something like a GWS RS-4 receiver, and their Pico servos.

Using a couple of geared electric speed 400 motors will also let you use a small Lithium pack for power and radio, and eliminate one servo by using a speed control for throttle.

Just my thoughts.
Dennis-

Thanks DBCherry, Montague. The only reason I thought I could add all that crap to it is because its a twin engine plane. Just thought the two engines would be able to carry it all. After reading all of you guy's replies, I'm defiantly considering the electric engines instead of gas power. But I still believe gas will give me the best performance( If it flies[X(]) I figure if I can achieve a power to weight ratio of 2 to 1 or may be 3 to 1 it might make up for the lift issue and weight issue. I am a rookie so this is just my hypotheses. The main reason I choose the P-38 is that it has always been my favorite plane. whstlngdeath gave me a link that shows the exact plane I'm building done with re-tracks and electric engines, check out the link at top of page. I can't thank you guys enough for your help, without your responses the % of succes would be negative%

The problem is that as the wing-loading goes up flying qualities diminish quite quickly. The airplane has to fly faster for the wing to generate sufficient lift necessary because of the higher weight. The stall speed of the airplane rises, and it becomes downright unmanageable at a certain point. If all you need it to do is go straight up then power-to-weight becomes an issue, but that's not realistic.

Have you thought about starting with a more conventional trainer? It'd give you valuable experience and insight that would increase your chances for success with your P-38.

I have another question. I'm not liking the idea of using wood for the frame of the plane. I'm a welder by trade so wood just offends me. I've been thinking about building it out of fiber glass. Using one thin layer of cloth and hardener. I just don't know how much heaver it will be. I'm pretty sure it will be stronger and it will complicate the build 10 fold. But I'm building a machine, and most machines are'nt built out of wood. I know its a small plane and balsa is as about as lite as you can get. But if I build it out of glass 20 parts becomes 1 part. Know what I mean. One shell for the fuselage. What do you think? should I build both? one of wood and the other of glass. And then weight them. Or should I just stick to the balsa? Or am I just trying to take a simple plane just too far?

Making a fiberglass fuse that's both lighter than a balsa structure and stronger will be a task. You'll need at least a few formers in the fuse to maintain the shape and rigidity, and it will likely have to be thicker than you might think. (I don't think one layer of 1/2 ounce glass would support the wing and tail structures for example.)

Common thought is that a glass fuselage can be built to about the same weight as balsa, but lighter is tough.
Dennis-

Well, I figured I'd use the wooden frame and lay the glass on it one half at a time. Then stick them together, add a few braces, and a small shelf for the re- track bace and servo bace. The wing on my P-38 will travel trough the fuselage, it will be its own structure. As you know the P-38 wing is its main stucture, the tail is supported by the booms that connect to the wing. From my understanding the wing needs to be the strongest part. I'm a green horn though, so give me some feed back on this[8D]