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1/4 scale Dormoy Bathtub

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Old 09-13-2013, 06:37 AM
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33willys
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Default 1/4 scale Dormoy Bathtub

I'm about to start a build of the Dormoy and, looking at the plans, the main (only) longeron appears weak. Thought about using a dowel but there is a high possibility of it warping. How about a fibergrass arrow or aluminum arrow? Attaching things to either would be a chalenge. Suggestions?
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Old 09-15-2013, 02:25 AM
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Never heard of this machine, before today. A little Googling exposes a really interesting airframe ... I love the minimalism of the design.

WRT to the longerons. If it were me, I'd build the fuselage structure from thin-walled tubing, if you can source some. Wooden dowel would be fine, though. Use Ash or Spruce or Hickory. Once it's braced, it'll be strong as an ox. You need to keep that slender look of the prototype, imo.


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Old 09-15-2013, 05:32 AM
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I found a piece of thick wall 1/2" aluminum tubing for the backbone. Because everything is attached to that longeron I worried about getting a kink in something thin wall. Looking into using knitting needles for some of the rigging. If I overbuild enough I'll need a small block Chevy for power!
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Old 09-16-2013, 03:01 AM
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Where did you get the plans for this plane?

Bill
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Old 09-16-2013, 06:10 AM
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I got the plans from Cleveland Model and Supply. They are blown up from much smaler plans and a little fuzzy. Not sure what I'm going to use for power yet (electric or glow). Plans require SOME modifications and I would like to lean toward function over form. Maybe modify the wing a bit and lower the power plant a little also.
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Old 09-30-2013, 10:31 AM
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Are you aware of the 1/3 scale version by Frank Iltzsch in March 1981 "Model Builder"? 96" span, OS FS-60 engine. His is a model of Mike Kimbrel's VW-powered replica. He made booms for his 1/3 scale model from 5/16" fiberglass tubing with 1/4" dowel inserted & CA'd. He did a really nice job and it might give you some ideas. He also suggests getting a copy of Sept. 1978 "Sport Aviation".

This has approached the top of my to-build list several times, but not quite made it all the way to the top. I'd likely go for 1/4 scale like you.

-Dave Plumpe

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Old 09-30-2013, 10:44 AM
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I found reference to the build article of the 1/3 scale but was unable to pull it up. Also PMed about another reference and no answer. I looked at fiberglass arrows ffor the "backbone" but they had too much flex to my liking. Major problem I have now is attaching the plywood sides to the aluminum tube. Intend to make the nose and back of the "bathtub" out of fiberglass, nose will be removable but the back will be blended into the sides. Also found two sizes of aluminum tube, one slides inside the other, for the landing gear shocks. Found a compression spring that would drop inside so the whole assembly does not look out of place. Outside diameter of the larger tube is 5/16".
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Old 09-30-2013, 12:42 PM
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How will you create the joints between the longerons and the "other bits" ? ... I don't know what term to use.

On the full-size, it was a welded joint, presumably. Do you have the facility to weld thin aluminium?

I've puzzled over this, but can't think of a really clean way of doing the job, short of replicating the original constructional techniques. I don't like the idea of penetrating the walls of the longerons, so as to insert the upright "other bits".
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Old 09-30-2013, 01:29 PM
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The backbone or longeron is a fairly thick but light 1/2" aluminum tube (or pipe). I chose the pipe over other things because everything depends on that one piece. If that longeron bent, broke or warped it would render the entire craft useless and almost impossible to replace. I do have the ability to TIG weld but I doubt the original was welded (1924 remember). Right now I'm machining three small aluminum slugs to fit inside the longeron. The front one will be drilled and tapped for the axle pivot as well as strut mounting. The other two will be inserted in the longeron to mounting points for struts. Each will have one smal bolt thru it and mounting the "ears" for struts.
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Old 10-01-2013, 06:42 AM
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Above is a quick pic of the landing gear shock. Inner tube, outer tube and spring without the roll pin for a limiter and mounting ends. They will come after I get the bathtub built and mounted on the backbone.
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Old 10-01-2013, 07:24 AM
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Good idea. I never thought of making reinforcements which are internal to the tubing.
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Old 10-01-2013, 10:14 AM
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Sorry if I misled you but the inner tube slides and the spring acts like a shock. This setup is for the landing gear which will provide a little give during landings.
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Old 10-01-2013, 10:17 AM
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No, I meant the reinforcements within the longeron. You said that you are turning some plugs from ali.
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Old 10-01-2013, 11:25 AM
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Sorry, missed your point. Yes, wanted to put plugs where the bolts would be going thru so that there could not be a question of bowing or crushing the longeron. What would you say is the best method of glueing wood to aluminum?
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