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03-02-2006, 02:31 PM | #1 |
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Scratch building electric park flyer
Since my GP Flat Out is basically a lost cause now, I am going to scratch build one - something real simple. I am going to make it out of balsa (yes I know that is not very durable, but what the heck!) I am taking my design from the GP Yak 55 park flyer. I want something that has a built up wing, not the flat plate. I am going to try and get this as light as I can - under 14oz is my goal. I have 9.03 oz in the electronics, so that leaves me with 4.97 oz in the airframe and hardware. Hopefully it can be done!
Ill post some pictures on here as I build. Time for a trip to the hobby store. Steve |
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03-02-2006, 05:38 PM | #2 |
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Well I spent a little more $$ than I was expecting to on the wood. I probably would be better off buying the arf version instead of trying to scratch it... but oh well I made a few changes in the size of some parts based on what was avalible at the hobby shop and how much certain pieces weighed. Since weight is the biggest factor in this airplane I wanted to make sure I wasnt adding too much in certain spots.
I was going to use a solid basswood sheet for the ailerons since basswood is stiffer than balsa, but it is MUCH heavier. So I went with a balsa sheet instead. The fuselage is going to be a profile - 1/8"x3/8" strips with 1/32" sheeting. The wing is going to be 3/32" ribs with 3/32" square spars all the way around (about 2"-3" gap between) instead of sheeting. The tail surfaces are going to be 1/8" sheet balsa with some material cut out to lower the weight. I am thinking about adding a couple inches to the wingspan to bring the wing loading down. The wood all together weighs 11oz, but I havent cut all my parts out of it yet. Any thoughts from everyone there? Steve |
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03-02-2006, 06:42 PM | #4 |
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Well this is going to be a 3D airplane, so a V-tail is out of the question. I went with 1/8" balsa because it is fairly stiff and JUST thick enough to hinge. I am going to use some CA hinges cut into real small pieces to make them work. I am going to be cutting some of the material out of the center of the tail surfaces to lighten them, as I said before.. Do you still think its going to be too heavy, j-coles?
I am in the process of laying out the design right now. I was just going by rough dimensions before. I am still calculating some of the dimensions - thickness and shape of the wing so I can fairly accurately replicate it. It will be interesting to get the taper right! I have the dimensions for the rib at the fuse and the rib at the tip, I guess it will just take some eyeballing to get the rest of them in between. Steve |
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03-02-2006, 07:41 PM | #5 |
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Heres the latest.
I am working on laying out the ribs on the balsa sheet. I am going to have a LOT of scrap, I bought 2 sheets and Ill be only cutting about 2 ribs out of the second. The way I am estimating this, consitering I will have quite a bit of scrap, is I will have between 6 and 8oz in wood on the airplane. Adding in my electronics, glue, covering, and hardware, I will be up at roughly 15-17oz . The original airplane says that the flying weight will be between 14 and 16oz. Since I am going to be over that a bit I am going to increase the wingspan to 42" and add a couple inches to the fuselage length. Thats a bit of a stretch, but it will bring the wing loading down to the original specs. I did a rough calculation at 17oz all up weight and 42" span I will have just under 7oz/ft loading. This is all just estimates right now, I did some calculations but since the weight of everything is subject to change so is the wing loading Hopefully it will go DOWN and not UP Steve |
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03-04-2006, 03:06 PM | #6 |
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I started the tail surfaces today. I am cutting the elevator and rudder out of a 6" wide sheet of 1/8" balsa. It has a tad bit of a bow in it, about 3/32" in the center, so I am putting some stress on it in the opposite direction to try and level that out. That much of a bow probably wont matter TOO much anyway, I just like things to be strait. Ill post some pictures when I get a chance.
Steve |
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03-04-2006, 06:12 PM | #7 |
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I am laying out the fuselage right now. I added an inch to the height and I stretched it 5 inches to 30". The way it was looking before it was too out of proportion. I am also going to move the location of the wing forward a bit because the review on RC universe of the GP Yak said that with the brushless conversion the airplane was REALLY nose heavy and it took a lot of weight in the tail to get it to ballance. I am still going to make the battery compartment big enough to allow fine tuning of the C.G. once complete.
Steve |
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03-04-2006, 07:52 PM | #8 |
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just out of curiosity why didn't you make your tail and fuse using sq stock?
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03-04-2006, 07:55 PM | #9 |
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I am: Gord C
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Steve:
A trick to straighten out the warp in the ails. and rudder is to, on the rudder for instance, cut a half in. off the top and bottom and glue on 1/2 in wide strips with the grain going front to back. Straightens it up and adds a lot of strength. If you have a razor plane, taper it down to 1/16 at the trailing edge. Looses a bit of weight with a little work.
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03-04-2006, 08:06 PM | #10 |
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Well I figured I could cut the exact shape of the tail surfaces out of one piece to make it easer - no gluing sticks together. I was also thinking along the lines of contruction techniques with depron and other kinds of flat foam. The balsa is heavier so I will cut some of the material out to lighten them. For the fuselage I wanted the flat profile look. I also wanted it to be sheeted to make it more rigid. The profile fuselage is going to be constructed with 3/8"x1/8" stock (or close to that, dont remember right off the top of my head what it is) sandwitched between 1/32" sheets. The fuse and tail surfaces could have been built using all kinds of methods, thats just the way I figured I would do it. I am not the best builder on the block but I figured I can get the airplane to fly. I scratch built a 1/2A float plane a while ago but I used basswood and WAY over-built the airplane so there was no way it could fly real well, if at all. I learned a lot from that and know now to pay more attention to the weight, and also construct certain areas better (wing for example) and lighten up on other areas (fuselage) while still maintaining a strong assembly. This is just one more airplane I can add to my construction history and I am sure Ill learn even more with it
Steve |
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