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Speed,Combat,Scale,Racing => Scale Models => Topic started by: John Rist on October 28, 2011, 10:44:48 AM
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Well I have started my 24" DO335. I plan to take it to the 2012 NATS and fly it in the unofficial 1/2A scale class.
So far I have obtained the 8" rear Cox prop shaft from Lee Machine Shop. Drawn the plans and ordered the wood. Plans for me have very little detail because I kinda build to the outline, creating parts as needed base on past kit builds. The old adage - If it looks right and feel right it should work. My biggest problem is overbuilding and my models get heavy. My last build was a BRODAK LA-5. I will look very hard at the construction of this profile because it is reasonably light and reasonable strong. This is my second DO335. The other one flew but was to small for 2 TDs. It was a fast lead sled!
Any way I will post as progress. Attached photo is new drawing and original 15" DO335 (taken before it's demise)
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Set a target weight for the model and apportion that weight out to each major piece (fuse, LG, engines, wing, etc. -- don't forget the finish and details). Then as you build, weigh everything that goes in, and when you can weigh the pieces as they get built. I find that weighing each sheet of balsa before I use it does marvelous things -- heavier sheets get put back on the shelf when it's not a load bearing part, only to get pulled off the shelf when it's a long piece that needs to carry some weight.
Your ship will still be heavy for its size because it's scale, but it'll be lighter because you were forcing yourself to think about weight throughout.
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Tim, you are so right. I went to the hobby store yesterday looking for c-grain, checking the weight on 12 pieces 1/2X4X48 there was 38 grams different. (I took the lighter 2 sheets) Just a FYI.
Blessings
Allen
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Any way I will post as progress. Attached photo is new drawing and original 15" DO335 (taken before it's demise)
John:
"Before it's demise"? What happened?
Jim Fruit
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John:
"Before it's demise"? What happened?
Jim Fruit
Almost to embarrassing to tell. It's only contest, I didn't get a two engine run and was DNF. I then placed it on the top shelf of my shop. It fell off of the shelf (some 6') and crashed to the floor. In the mean time I had worked out getting the engines to run (balloon tanks were required) and as on all original designs I wanted to make changes. It became appearant that it would be almost as easy to build a second model rather than try and get this one up to contest ready looks. 1/2A at AMA was the clintcher to go for it.
n~
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Well I have the wing rib patterns finished. Time to start cutting wood.
#^
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Have one wing ruffed in. I am happy with it. Needs leading edge shaped, add wing tips, add landing gear support blocks, skin bottom with 1/16" balsa, and skin top with 1/32" balsa.
H^^
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One step along. I now have two wing halves for my DO335.
#^
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DO 335 Fues is coming along. #^
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Oooh, dat's nice.
Keep building -- watching your "in progress" pictures is almost as nice as building one myself.
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My DO335 fuselage has the motor mounts installed, the lighting holes cut and is now ready to have 1/32 skin applied. The majority of the wood removed was at the tail end. With all of the rear engine weight along with it's prop shaft wight it will take considerable noise weight to balance. It will be plywood skin over the motor mounts and balsawood over the rest.
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Is that prop shaft a hollow tube, or solid?
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Is that prop shaft a hollow tube, or solid?
Solid. Hollow tube would be nice but it would complicate the making of the shaft It could be done by maching off the two ends of the solid shaft to fit inside a tube. You then have to make sure everything runs true. Wing loading of the new model will be lower than the my original DO335 and the original flew OK so I should be OK. All it has to do is fly fast and level on two engines and slow and level on one engine. With two TDs I am betting it will.
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Solid. Hollow tube would be nice but it would complicate the making of the shaft It could be done by maching off the two ends of the solid shaft to fit inside a tube.
Yup. Or making the the ends as "caps" to a tube. But your way wouldn't make the thing have big spots.
You'd want to make up the tube-and-cap assembly, then toss it all back on the lathe and true everything up, for sure.
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Sehr nette Deutsche engineering Hr. Rist.
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'looks nice. Are you planning any internal bracing in the lightening spaces? A couple 1/16" or 1/8" diagonals in the aft lightening hole and fin ribs would not hurt weight much, but would make a large difference in strength and resistance to twisting, helping to support the shaft. That would probably make it at least as torque resistant as solid structure. Just a thought.
SK
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'looks nice. Are you planning any internal bracing in the lightening spaces? A couple 1/16" or 1/8" diagonals in the aft lightening hole and fin ribs would not hurt weight much, but would make a large difference in strength and resistance to twisting, helping to support the shaft. That would probably make it at least as torque resistant as solid structure. Just a thought.
SK
You may be right. I probably should add some diagonals. I will considered it.
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Wing is sheeted top & bottom and has been fitted to the fuselage. Next step is to sheet the Fuselage.
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Looken real good John.
Blessings
Allen
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Start of the rear bearing mount on my DO335.
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You are doing this all wrong, John. You have the rudder on the back.
Jim Fruit
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You are doing this all wrong, John. You have the rudder on the back.
Jim Fruit
LL~ LL~ LL~ LL~
Rist
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Rear end ready for rudder (the one on top). Motor mounts are drilled. Needs lots of sanding. By the way what is the best way to create fillets? I need to creat some around the wing when I mount the wing.
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Landing gear coming along. Have to add the gear doors. As always it is getting heavy! But with two TD's it has to fly and fly fast!
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Landing gear coming along. Have to add the gear doors.
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The gear doors are started. The advantage of Robart scale struts is that they give you a place to bolt the doors. The scale struts fit sloppy loose on the gear wire. I center them up and pot them in place with a little epoxy. They become rigid enough to support the gear doors. The bolts that are sticking out will get cut off. The doors will then be covered with 1/8" balsa and sanded to an oval shape per the pictures I have.
#^
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Set a target weight for the model and apportion that weight out to each major piece (fuse, LG, engines, wing, etc. -- don't forget the finish and details). Then as you build, weigh everything that goes in, and when you can weigh the pieces as they get built. I find that weighing each sheet of balsa before I use it does marvelous things -- heavier sheets get put back on the shelf when it's not a load bearing part, only to get pulled off the shelf when it's a long piece that needs to carry some weight.
Your ship will still be heavy for its size because it's scale, but it'll be lighter because you were forcing yourself to think about weight throughout.
Hi Tim,
I do like a lot of other guys do and weigh each sheet of balsa when I get it then figure the "pound" rating. This gets marked on the sheet and the heaviest goes at the bottom of the stack, etc.. Lots of "bottom feeding" sheets but those do have a use for parts where the extra weight will not cause a problem in that it is used for greater strength.
Big Bear
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Front landing gear built and ready for paint. It's not spot on but close enough for viewing at 10 to 15'. It is a mix of brass rod, brass sheet, music wire, and a Robart strut all silver soldered together.. Weighs a ton but I need weight in the noise so all is good.
H^^
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Well all the parts are built. What left is lots of sanding - filling - more sanding etc. etc. etc. This is the part of building I like the least. This will probably be the last post till next year.
MERRY CHIRSTMAS TO ALL!
H^^ H^^ H^^
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But it's looking good!
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I must say your craftsmanship is humbling, even santa is going to drool! LL~ H^^ D>K--LOUIE
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Well I am back to thinking about CG location. Perhaps 1/2 way between the thickest part of the wing tip and the thickest part at the root? WHat say youall.
n~
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Well I have setteled on a 2 part epoxy finish from Klass Kote ( http://www.klasskote.com/ ). They have the colors I needed per fed std numbers. Can I paint the epoxy over the clear Brodak dope cleare base/primer? Can I clear coat seal the decals after applying them to the epoxy painted surface?
???
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John, I have used Klass Kote over Sig nitrate dope with excellent results. I use an epoxy primer from the automotive finishing store so can't comment on the Brodak primer. If you are refering to putting Klass Kote clear over the decals, that will work.
Chuck
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Well all of the Klass Kote epoxy and Brodak finishing supplies are on order. As always the paint job is the single most expensive item of this project. To date I have spent $150 + on finishing supplies. I will have stuff left over and will use it on the next project. Anyway I will continue posting in a few weeks when the stuff comes in and I start the finishing process. I plan to add the wing fillits, base coat with dope, cover wood with silkspan and dope, prime with dope, add Klass Kote colors, install decals, and clear coat with dope. I plan to do a balsa wood test sample applying the each next step to the sample board to make sure all is good. The only step that worries me is the dope over Klass Kote. One would think epoxy can withstand dope solvent --- but that is the reason for the test board.
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The epoxy can withstand the solvents in the dope, but I'm not sure the dope will stick to the epoxy.
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The epoxy can withstand the solvents in the dope, but I'm not sure the dope will stick to the epoxy.
Good point Chuck. I may well go ahead and order clear epoxy. What I am hearing is that the dope works as a good base coat. It is also probably true that epoxy works well over decals. Dope sprayed on too heavy can eat a decal.
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Started painting today. 3 coats of clear (cut 50-50). Next more sanding!
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What is the best way to ink panel lines? What type (brand) of pin is best? I will be inking on top of a Klass Kote epoxy finish.
??? ??? #^
By the way my 2nd place finish in fun scale at FCM 2011 got mentioned in the February Model Aviation.
CLP**
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Lots of Brodak dope! Lots of sanding! And the DO335 has been covered with silkspan, clear dope, and finally white primer. Next is let it cure out for 3-4 days. I will then start applying the epoxy color paint.
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By the way this airplane now qualifies for 3 major contests - Brodak, NATS and FCM
n~
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By the way this airplane now qualifies for 3 major contests - Brodak, NATS and FCM
n~
Make that FOUR: Tucson's annual (and pioneering) 1cc multi-engine profile scale contest (October - dates 'TBA').
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The epoxy can withstand the solvents in the dope, but I'm not sure the dope will stick to the epoxy.
I have doped over epoxy without incident - yet.
SK
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I have doped over epoxy without incident - yet.
SK
That's good to know. Saves a bundle. I have clear dope. I would have to buy clear epoxy.