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Thread OP
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Making a protoype nose cone
C-MIC, thanks for the suggestions. I will take a look at the Kontronic and geared brushless motors. I got one for my Renny (hacker B20L 4:1 I think) and the inline gearboxes have come a long way in the last few years. It is really small and appears to be built well. I know from past experience that gear drive = higher efficiency, and longer run time for the same battery. But I had hoped not to spend much more money on this plane.
Mike - I really appreciate your structural suggestions. Some kind of splice for the nose is necessary because the stock plywood I got wasn't quite long enough to make the whole fuse out of one piece. I didn't want to put splices in the rear where it is thinner so I picked the nose. If long diagonal splices reinforced with doublers aren't good, is there a better way? Seems like this is how my old Spirit 100 did it. I'm thinking of what letters and numbers to give this plane. It will always be named Raven, but Im thinking the registration letters will be NOCA because I am not using any CA in building it. I am allergic to the odors, even for odorless CA and cannot use it any more. And, on that 30-year old Aquila I have, the CA joints have come loose but the epoxy is strong as ever. And I think it will be black, with gold wingtips jsut like in Mike's photo. I may put a dark red cross on it because I have had one trip to the hospital in building this so far. That cost $1000 but I was fortunate that insurance covered it. That's a story for my next post. After Mike's suggestion to put the motor behind a bulkhead and not firewall mount it, I spent an evening thinking about the motor mount again. I came up with these requirements: -Spinner covers diameter of the nose cone for seamless streamlining -Nose cone is circular so folding prop will lay flat and not stick out into the airflow. I've tried on that Thermic plane you see in my hangar to make a square fuselage round enough so the blades will fold flat. It is difficult and doesn't look good. -Adequate cooling. The prop mount/spinner I have is an MP Jet super cool from NSP. it has a hole in the spinner that lets air into the motor right behind the spinner. With all this in mind, and thnking of how the old Guillows kits had stringers between circular bulkheads in their noses I came up with what you see in the pictures. That is a prototype to see if it will be strong enough. I wish I could make a drawing for here but I don't know how. The fore bulkhead is circular, 1.75 inch diameter. Six inches behind it the second bulkhead is circular 2.25 inches diameter. I picked 1.75 inches because that is just larger than the spinner and inline with where the blades will fold. I picked 2.25 inches aft diameter because that is inline with the taper of the hatch area and should preserve the nice lines of the fuselage and fair together well. And a 6 inch length so that up to 12 inch blades will fold flatly against the nose cone. These bulkheads are made out of 1/16 ply but I will use 3/16 for the fore one to give me more gluing surface and I also found with this motor it is necessary so the spinner will be only 1/8 inch in front of the bulkhead. Otherwise it would be 1/4 inch and that would look bad. You can see I used a 4-40 rod between them to hold while I glued on the stringers, then I removed it. There are 8 stringers made from 1/4 by 1/8 balsa although I may use spruce in the real one. I plan to put 4 layers of 1/16 sheet around the whole thing for strength and so I can sand it down to fair it in to the square fuselage part. The aft bulkhead will be epoxied to the F-1 bulkhead in the fuselage, thus attaching the whole nosecone to the fuse. I will experiment with having the stringers go beyond the 2.25 bulkhead into the fuse as well. Lastly I plan to add 2 small air scoops near the front on the sides for more cooling. Today I made the prototype and tomorrow I will drill out the motor holes in the front bulkhead and trial-fit the motor. There should be about 1/8 clearance on all sides increasing to about 3/16 at the back of the motor. Christmas for me is a day of working on my Raven and my Renny. What do you think? ImagesView all Images in thread
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Tim,
If you are using a doubler, it should be OK. If I had to use a splice, I would have spliced it in the middle of the wing root ribs. I think you are over-complicating the motor/cowling issue, if you mount behind the nose former and use a large enough spinner/prop bar, the blades will lay flat against the fuselage sides. BTW the original Raven was black all over, no gold tips. Mike |
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Thread OP
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Decided to build traditional nose for the motor mount
C-MIC and Mike, you win. I will build the tradtional way with a front bulkhead for the motor mount.
I'll build for and try to use the motor I have - an E-flight power 15 outrunner. If that doesn't work I'll get a gear drive inrunner but the numbers work out. It should have about 75 watts poer pund if my estimate of 5 punds AUW is right. I still think that is about where it will come out. By comparison, I have an AXI 2820-12 in my 88 Oz Barracuda. It has only flown once but it made an acceptable climb rate. These two motors are comparable. I have spent most of the last 2 days trying to figure out the right side length for the square bulkhead. Finally decided on 1.5 inches - the spinner on the folding prop I have is 1.4 inches in diamter. This will allow about 2mm clearance around the outrunner motor minimum on all sides, and more in the corners. I think the mount cooling holes will probably let in enough air for cooling. From trial fitting the prop I have, I think I will have to chop off diagonally the corners of the square bulkhead. But I'll do that after it is all assembled. Starting to think about the tail bell crank and pushrods. See the photo of the plans. I want to try using carbon fiber pushrods and making the bell crank out of printed circuit board material. I made my own front bulkhead out of 5/32 ply. You can see it in the photo. I surprised myself in being able to make these parts to tight tolerance but it turned out well. |
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Thread OP
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Joined the fuselage halves today
Made great progress today and passed a major milestone.
I made the elevator bell crank out of printed circuit board material from Radio Shack. Because I worry too much I thickened it at the pivot point and at each end from what is shown on the plans. That got me into trouble – at the bottom end it touched the longeron reinforcement strips so I had to carve them out a little. To make a good pivot bearing, I sandwiched two concentric tubes of aluminum. The outer one inserts through the bell crank and acts as a spacer inside the tail, and a sleeve bearing. The inner tubing extends into the tail root ribs which will be glued to the fin, and inside all that the music wire goes between the tail halves. It made for a smooth bearing with little slop. I was quite surprised that I was able to make these parts to a tight but smooth fit. Normally my workmanship isn’t that good. I decided to use plastic flexible pushrods, that originally came with the Barracuda model. I didn’t use them there because I mounted the elevator and rudder servos in the tail on that model. I attached the plastic sleeves to the left side of the fuselage with hot-melt glue. Caution, it can melt the plastic. I had to remove the rudder sleeve and remount it because it got too hot. But if you are fast it doesn’t melt it. So then I trial fit and measured the fuse halves. After testing the fit several times, I joined them! A major milestone in the construction. And, there is no going back if soething wasn’t right. But everything came out ok. While the epoxy was still fluid I took special care to make sure the elevtor front pin was square to the fin. If it wasn’t, the tail would be lopsided. I got it practically perfect. Thanks, Mike for making that clear in the directions. It’s beginning to feel like I will actually finish this one. Can’t wait – the tail group sure is beautiful. ImagesView all Images in thread
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Looking good Tim, what size prop will the outrunner swing?
Mike |
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Thread OP
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Prop for the motor
Mike, I have an 11 x 6. And I'm going to sell the E-Flite motor and put my AXI 2820-12 in it. I bought a better motor for the Baracuda, and the AXI will come out of it and go into the Raven.
In the Baracuda 3m here is what the aXI did: AXI 2820-12 motor 11x6 prop 3s LiPo 3300 pack Phoenix 45 esc Plane AUW is 88 Oz. Full throttle measured 9000 rpm. Full throttle about 37 amps = about 370 watts. I dialed it down a few clicks to get 33 amps and it still climbed, although slowly. I am expecting the Raven AUW to be about 70 oz. I have weighed all the parts and that is about what it will come to. No progress in the last few days. But I expect to work on it a lot over this weekend. It is going to be a cold, rainy weekend here so what else is there to do? And the Renny I have been building is almost done. |
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Tim,
Obviously, we'll have to see how it goes, but I still can't help thinking that an outrunner is not right for this size sailplane. My Silent Dream at 2.8m with Kontronic Drive 502 and 18" x 12.5" prop would be virtually out of sight vertically within 1 minute. Mike |
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Thread OP
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Framing up the fuse, and a messed up wing
Today I framed up the fuse. I made formers out of 1/8 ply for the aft former, and 3/16 for the front formers. I think this is different from the plan a little.
The elevator and rudder servos are going to have to mount behind the CG by about 1.5 inches. I am using hs-81 for these, they weigh .58 oz each. Putting them forward would interfere with being able to slide the battery back and forth and the cables would most likely get in the way of the wing rod holes. As it is the battery will have room to be moved for or aft by about 4.5 inches. In the picture you can see former F2 where I cut a hole large enough to get the motor through, with a notch for the wires. Although I am planning to use the outrunner, when the new motor I ordered for the Baracuda gets here I will trial fit it into the Raven. I might bite the bullet and order one of those for the Raven too. It is a medusa 2856-1900 with 4:1 gearbox and swings an 18 inch prop. According to the medusa website, that will give about 75 ounces thrust on 3s LiPo at around 40 amps. OK, I couldn't sleep last night so I measured the wing washout with the incidence meter. On each wing I measured in 4 places - 3 inches from the root, 2 inchs inward from the anhedral break (28 inches from the root), 2 inches outward towards the tip from the anhedral break (32 inches on the wingspan), and 3 inches inward from the tip (57 inches on the span). The way I measured it, less degrees indicates washout or downward twist at the leading edge. Here's what I got: Left Wing root: 6 degrees Left Wing at 28 inches: 6.5 degrees Left Wing at 32 inches: 7.25 degrees Left wing at 57 inches: 5.25 degrees Right Wing root: 5.25 degrees Right Wing at 28 inches: 6 degrees Right Wing at 32 inches: 6 degrees Right Wing at 57 inches: 1 degree Since I was trying to build washout into the tip panels only in the last 10 inches of them, this means that the washout in degrees is Left Wing: 2 degrees Right Wing: 5 degrees Is this enough difference to worry about? This is a fully sheeted wing. I won't be able to correct the twise with the covering like you can on gasbag wings. Anybody know what to do if it needs to be corrected? Steam? Soaking and weighting? Surgery? Seems like I read somewhere that you have to cut the sheeting longitudinally to be able to make any correction. The wing is really stiff. Would really appreciate any ideas. ImagesView all Images in thread
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Tim, that certainly is enough to worry about
The way I read your incidences, that is wash-in not wash-out, which is disastrous. Mike |
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Thread OP
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Wing twist
So I've decided to finish the glider and flight-test it, at least by tossing near the ground. I'll do this before covering it.
If it turns to the right too much from the twist then I'll try a few things, in increasing order of severity: Adjust incidence about 1/2 degree off from equal when mounting the root ribs to the fuse to try to compensate a little Twist and heat Cut longitudinally on the right wingtip, twist and re-glue And, I'll be prepared to table-saw off the right tip panel, from 30 inches out to the tip, and re-build it. No pictures, but today I glued on the aft rear fuselage plywood. The bulkheads are in place and the fuse turned out perfectly straight and square. That's one small piece of comfort. I'm still considering if I should order a medusa geared motor. Since its mounting holes are different size than the AXI, I didn't glue on F-1 yet until I decide. |
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Thread OP
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Fixed the wing twist
After I got over wanting to feed the whole plane into the fireplace I decided to try a few things. This is why I ahven't posted for a few days, I was discouraged and didn't feel like working on it.
So, I sprayed the outer 1/2 of the tips panel soaking wet, and applied 15 pounds of weights in such a way as to twist the wingtip up at the leading edge. From my previous measurements I had 3 degrees too much washout in the tip panel. After it dried, I had about 8 degrees of washin! It moved 11 degrees. Encouraged that the wet and dry method would work, I tried it again with a little less soaking and a little less weight for only a few hours. And I twisted both wingtip panels to get them closer together. I think I got it, at least better than it was. Here is what I have now: Left Wing 3 inches from the root: 3.2 28 inches: 4.8 32 inches (just past the anhedral joint): 4.8 57 inches: 1.6 Right Wing 3 inches: 5.5 28 inches: 5.75 32 inches: 5.8 57 inches: 3.4 So what I'm reading into this is, the Rt. wingtip panel has 2.4 degrees of washout, and the left has 3.2. I wanted them within one degree and this might be good enough. The way I measured these lowere numbers mean the leading edge is turned down. Mike, I see what you mean that the left panel has some washin between stations at 3 inches and 28 inches. I',m thinking that, since these measurements are relative within each wing and we cannot compare them between the wings since I didn't fix them the same way when I took the measurements, when I mount the ply root ribs to the fuselage I'll adjust the incidence a degree or so i.e., the right wing will be mounted about a degree lower than the left. I will have to measure this while I glue it. Do you think that will compensate a little? And, I'm hoping that I can make small adjustments in the twise with the covering when I apply it. Maybe the next few days I'll get back into working on the fuselage. |
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Thread OP
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Got back to work, on the fuselage
Its been awhile since I could work on this project. But I finally got going again. I have put in the motor mount bulkhead, fuselage sides and top and mounted the tail fuse ribs. See the photos.
All that work on planning how to mount the motor paid off - it fits nice and snug, with room for airflow around it. I will be using a MP jet super-cool spinner which has holes in it to let air in through the spinner. I have decided on the paint scheme - the fuse and wings and tail will all be black, with the outer few inches of the wingtips, outer inch or so of the elevator and the whole rudder being painted sky blue. I plan to paint the fuselage since I hate covering them and cant do a good job. The wings and tail part will be covered with black Ultracote. ImagesView all Images in thread
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Thread OP
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Not much progress recently, but close to finishing
I have glued the root ribs on and done most of the finish sanding. The only part I have to fabricate yet is the canopy cover. I find this is the least interesting part for me, so I tend to drag my feet. I have another glider all done except for the canopy, and it has been that way for years.
Here is what the color scheme will be: Fuse - painted, all black Rudder - painted, sky blue Canopy - painted, sky blue Wingtips, outer 10 inches or so - painted sky blue The rest of the wings, monokote black. Tail - monokote black After painting all that is left is putting in the electronics. I would like to finish this in the next month or so. My excuses for being so slow in the lasst 6 weeks - i "had" to go to France for awhile, and the rain here in Seattle. Anybody buying those excuses? More pictures soon. |
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Electric Raven
Hi Tim,
I think you are doing a very good job building your Raven! Not an easy build for sure! I am looking forward to seeing it done, and getting your flight report !! A very unique looking Glider!! Joe Pierson Kerman Ca. USA |
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