Posts: 467
Joined: 10/1/2002 From: reading,
KS, USA Status: offline
heres a couple things that you may want to concider. first you have the laminating down to a art, have you given some thought to doing a laminated outline with ribs WITHOUT the balsa core? comes out very light and still very strong. you can save a huge amount of weight. plus you wont have to worry about light shining though the lightening holes. second, if using a rubber band on the tail skid you MUST make provisions to get in there later to replace it. rubber bands wont last forever (i only get a couple years out of them here) i have much better luck with the bungee elastic (still dont last forever but longer then rubber bands)
_____________________________
I once had a drinking problem.....I divorced it, now shes someone else's problem
Posts: 4376
Joined: 4/1/2003 From: Springfield, VA, Status: online
Don, yet ANOTHER consideration. When covering your rudder you don't want the fabric sides to stick to each other while covering. There are ways around this but you just need to take precautions during the covering stage. The balsa core does prevent this problem.
Posts: 297
Joined: 7/1/2002 From: Corpus Christi,
TX, USA Status: offline
Bob, your not thinking! You will have the same problem with the covering sticking to the balsa core. So you will need to powder or wax the areas you dont want the covering to stick to. I used paste floor wax lightly brushed on the balsa core to prevent it and Don Coe use talc powder on the inside of his covering.
Posts: 5172
Joined: 2/13/2004 From: Zentsuji, JAPAN Status: online
quote:
ORIGINAL: eagledancer ...have you given some thought to doing a laminated outline with ribs WITHOUT the balsa core? comes out very light and still very strong. you can save a huge amount of weight.
Well, the 1.5mm balsa core only weighs 3g so that's not much. It's really just a thin wafer that provides a building surface. The whole unshaped rudder and fin only weighs about 15-20g. There is almost no weight difference between the balsa core with and without holes. You save maybe 1.5g with the holes. I've built rudders with laminated edges before -- and rudders with bend tubing edges. Both are light but, in my opinion, probably not as strong as this method. The balsa core idea has been used for ages and I'm doing it here largely to be following the kit's design. But who knows after I've finished this rudder (and the late production variant)...we'll see!
quote:
plus you wont have to worry about light shining though the lightening holes.
Actually this wouldn't be a problem at all if it's covered with silver solartex which is 100% opaque even right up against a light source. This would work well on the rudder but not the stab which was CDL underneath. Of course if you DO use the laminated edge with ribs instead of the balsa core method you'd better be sure to make that structure 100% scale. There's nothing more embarrassing that non-scale structure shining through!
quote:
second, if using a rubber band on the tail skid you MUST make provisions to get in there later to replace it.
Well, I don't usually think of the lifespan of my models in terms of years but it's a point well taken. Actually, I just noticed a scale detail that means I'll probably be going back to the bungee idea anyway.
Posts: 5172
Joined: 2/13/2004 From: Zentsuji, JAPAN Status: online
quote:
ORIGINAL: Reg Hinnant You will have the same problem with the covering sticking to the balsa core.
Actually, I think this is more of a problem if you have a relatively thick balsa core with just little bits of balsa to simulate ribs. Chris's design is almost the opposite. He starts with a wafer-thin core and then "layers on structure" such that you end up with a spar and nearly full ribs (3mm deep before sanding). But it's something I'll keep in mind.
In fact, I wonder whether, once the "structure" is in place on the wafer of balsa, it wouldn't be possible to entirely remove the bits of balsa in between. The stab might need the extra rigidity but the small rudder would probably be just fine without it. Still, cutting away ALL the uncovered areas of the balsa core would probably only provide a 2g reduction so I it's probably not worth the effort.
< Message edited by abufletcher -- 11/7/2006 2:08:45 AM >
Posts: 5172
Joined: 2/13/2004 From: Zentsuji, JAPAN Status: online
BTW, the photo above shows the type of hinge I might use on the rudder. It's quick, easy to remove -- if necessary -- totally strong and looks reasonable scale with a dab of paint.
Posts: 5172
Joined: 2/13/2004 From: Zentsuji, JAPAN Status: online
OK, here's the deal on the skid: I had it all WRONG! On the original the bungee wasn't attached "inside" the tail box where I had it, if fact, there WAS NO tail box! I discover this when I decided to check on the specifics of the appearance of the tail adjuster rod. It turns out the fuse was was open at the rear (not closed off with fabric as I had imagined). Chris, I think I've rediscovered that "scale reason" you used the two uprights but then forgot! Basically on the original there were just a couple of vertical metal straps on which to anchor the side fabric. Luckily I had already cut a "lightening slot" in the the rear light ply piece so I'm all set to go!
The skid should properly be attached to the top of the tail post. That seems so obvious now! So the bungee can be seen crossing the top of the open space with the tailplane adjuster -- thus the rubber band idea is out. Speaking of this tail adjustment gear there is a small but, I think, significant little detail missing here. This tube was not some kind of "shock absorber" dealy but rather there was a horizontal lever the end of which attached to the tail post as a pivot. Then as the adjustment control was moved this the forward end of this lever it would transfer this movement to raise or lower the tailplane adjustment rod. So I need to include this lever (or at least the visible portion of it).
My rough "new" plan for the skid is to go back to a (black) bungee of about twice the length. I'm going to solder a very small "ring" to the inside top of the brass tail post and use small black cable ties to attached the bungee on both ends. And of course I'll need to remove the old eyebolt. This new arrangement should be only slightly heavier than my previous "minimal" setup.
< Message edited by abufletcher -- 11/6/2006 11:24:47 PM >
Posts: 5172
Joined: 2/13/2004 From: Zentsuji, JAPAN Status: online
OK. Here are the basic skid mechanics in the flesh! After looking at a number of possibilites, I finally settled on this rather simple arrangement. It took some time playing "Goldielocks and the Three Bungee Cords" to find the tension that was "just right" but once that was settled it all went pretty fast. The bungee attaches at the tail post to a medium cotter pin via a small black cable tie. I also put in a small cottor pin in the bottom of the tail post (inside the lite ply) to lock the tube into position and to give the epoxy something to hold on to. The tension on the bungee can be finalized by how tight it's cinched to the skid (with another small cable tie).
There's still some scale detailing to do on the "tailplane adjuster" but the piece of metal tape I've got here now shows the position. Also I'll wrap the curved part of the skid with thread and soak it with CA (the original appears to have been wrapped in this location). Also my gut tells me that this open slot is just a tad too wide so I think I'll add a couple of vertical strips of 2mm balsa just aft of the rear ply support. This will also give a nice grip for the covering. Eventually, all of this assembly will be finsihed in a grimy, oily sort of black.
In the end (pardon the pun), the weight of all of the parts of my slimmed down skid assembly (minus the tailplane adjuster) is 8.5 grams (0.3oz).
< Message edited by abufletcher -- 11/7/2006 2:02:15 PM >
Posts: 5172
Joined: 2/13/2004 From: Zentsuji, JAPAN Status: online
Now that I've finished up the tail post, I can get on with hinging the rudder. On that topic, I thought I'd post a link to a very informative thread on scale WWI hinges:
Posts: 5172
Joined: 2/13/2004 From: Zentsuji, JAPAN Status: online
I added one minor modification to the forward side formers. Since I'm planning on using thin 1/64 ply for the side panel I was concerned about having to span large open areas so I added three 3mm square strigners across F3 to F5. And sure enough when I went back and looked at the datafile I found a couple photos showing stringers in just those locations!
You might wonder why I didn't do them all the way forward. Well, I've decided to do the panels in a scale manner so I'll only be using the ply sheeting from F3 to F5. There's actually a good reason to do this. Several in fact. First there's actually a bit of a compound curve on the forward fuse and I found the ply would fight me in places. I suspect the original builders noticed a similar thing because the panels almost perfectly reflect the problem areas. The area forward of F3 with be done of 1mm aluminum sheet in two panels. There is a smaller triangular shaped panel towards the bottom and the larger trapazoidal one. These should be very easy to make and I've already figured out how to to the tongue in groove flanges.
Another reason not to sheet all the way to the front, is to avoid problems with matching the cowl diameters. At present, I have 0.7mm "edge" to the cowl. If I put 1mm aluminum sheet on top of 1/64" ply it would stick out. And of course not doubling up saves a bit of weight (mostly in terms of the epoxy I'd have to be using to glue the metal panals to the ply).
Oh, and I'm throwing in here an interesting materials test of 3mm bamboo doweling. After soaking in hot water for a while I was able to tie this stuff in a pretty tight knot. It wouldn't make the very tight curves on the rudder but with some small slits on the interior of the curve it would probably make a great rim.
< Message edited by abufletcher -- 11/8/2006 12:33:22 AM >
Posts: 5172
Joined: 2/13/2004 From: Zentsuji, JAPAN Status: online
Time to mobilize all of the parts for the elevator. This is not quite as intuitively obvious as the rudder and I'm very thankful to have Chris's explanations from his Pup build (which are similar).
Note: It's worth making a photocopy of the elevator part of the plan for reference, since (of course) once you lay down the balsa core you can't actually see much of the plan details! Actually, there's no real need to build the stab over the plans at all -- guess this is just a habit left over from "the old days."
Note2: I beleive Chris has now translated all of his Pup instructions into English -- so never fear.
< Message edited by abufletcher -- 11/8/2006 10:54:26 AM >
Printable Version
All Forums >> RC Airplanes >> RC Scale Aircraft >> RE: CD ScaleDesigns Sopwith Snipe build 
RE: CD ScaleDesigns Sopwith Snipe build - 
Bob, your not thinking! 
Actually, I just noticed a scale detail that means I'll probably be going back to the bungee idea anyway. 
