RDS in the "woodie" SGP wing

[harleym]

After writing this post, I learned there was insufficient space for the RDS pockets in the 1-12" wide flaps. Jim Ealy advises he could change the kit to make the flaps wider. I'm sorting out how wide the first bay from the center has to be to accommodate the servo oriented at 45 degrees and just where it is to be located relative to the main spar, etc. When I get that done and clear it with Jim, I'll do a new post with a new drawing that gives the essential details. I'm mulling over a new idea for mounting the wing servos that allows "shifting" and "tilting" without using the HEMS. More on that later, too.

Requirements for a proper RDS installation is found in file A6 in the main website at http://www.geniebuild.com/harleys_genie.html. It is no big deal to make your own "pockets" and 3/32 stainless steel solid wire "drive shafts" for pennies as described, but Augie McKibben (See the What's Available? file)can supply them along with the needed Kimbrough couplers.

All 4 wing servos go in the center section. Orient the servos 45 degrees to the hingeline. Bend the aileron shafts 45 degrees and the flap shafts 90 degrees. The bent ends of the aileron shafts protrude 1/4" from the center section endcaps and slip into a hard slot (File 10) at the end of the ailerons.

Commercial servo mounts are not well-suited to the RDS. File 3, Part 2, page 1, explains how "HEMS" mounts can be easily made for pennies. HEMS allow shifting a servo that is particularly helpful in locating the "sweet spot" for the elbow of the bend in the drive shafts. HEMS also allow "tilting" a servo to direct the drive shafts into the opening in the "pockets" in the flaps, etc.

The HEMS mount glues to a base between ribs. This base must be high enough to fully recess the mounted servo and strong enough to firmly secure the HEMS mount to.

If necessary to accommodate your HEMS mount between 2 ribs, ribs can be repositioned. Sort it out. I suggest first making mounts for your servos and then establish where related ribs should go.

As to the actual base, for flaps I'd make it one piece from balsa to extend each way from center to extend 1/8" beyond the related ribs. See the attached drawing. I'd notch the tops of the ribs for the base and contour the base to the airfoil. I'd fit a 1/8" balsa partial rib under that 1/8" to get a good glue joint. I'd reinforce the underside of the base with 1/64" ply. Front and rear of the HEMS put a cross brace on the base to attach the Monokote, etc. to. After you get the installation finalized, you could use tacky film as a servo cover.

Const. File #10, details how to fabricate and install the "hard slots" at the end of the ailerons. If you center the drive shaft vertically where it exits the center endcap and also center the hard slot vertically in the aileron, the two will align and engage as a wing tip is attached. Just be sure that the shaft exits the endcap on a line centered 5/16" ahead of the hingeline as text details.Then with the bent end protruding 1/4", there is no binding.

I've attached a drawing to illustrate the servo base idea. The bold line represents a rectangular balsa base. Related ribs, which are notched to receive the base, are shown as dotted lines. You will have to sort out rib spacing after making your HEMS mounts to fit your servos. The base would be sanded on top to conform to the upper airfoil. For the aileron servo base, you would do similarly, extending a base from the center endcap to the next rib inboard.

[Guz]

I have been working with my RDS setup in a DLG. The whole thing is AWESOME.

But... there is one point that was never really made clear in all the documents I read. The point that needs to be made is how tight the wiper pockets should be, in relation to the wiper arm.

Two words: really tight.

That is, if you feel that you can just get the wiper rod in the pocket, without breaking the pocket, you are there.

Otherwise you will have slop, and the possibility of aileron, or flap flutter at high speeds.

I just spent the last hour trying to find the right feeler gauge to tighten up my pockets. Let me tell you 0.10 mm makes a WORLD of difference for taking out the slop.

[harleym]

I have been working with my RDS setup in a DLG. The whole thing is AWESOME.

But... there is one point that was never really made clear in all the documents I read. The point that needs to be made is how tight the wiper pockets should be, in relation to the wiper arm.

Two words: really tight.

That is, if you feel that you can just get the wiper rod in the pocket, without breaking the pocket, you are there.

Otherwise you will have slop, and the possibility of aileron, or flap flutter at high speeds.

I just spent the last hour trying to find the right feeler gauge to tighten up my pockets. Let me tell you 0.10 mm makes a WORLD of difference for taking out the slop.

When modeler-machinist Walt Dimick and I were collaborating on the fit between shafts and pockets for his line of RDS accessories, we found that quantitatively, .005" made the difference between a fine fit and a poor one.

That is, if the pocket opening was .005" less than shaft diameter, the fit was just right. Thing is, few modelers have the equipment to make such measurements or the means to make pockets to such tolerances. In practice, I found the criteria of "slightly snug" to work well without slop or bind. An opening the diameter of the wire will allow unacceptable slop. If a pocket is just tight enough to prevent the shaft from falling out of it under gravity, it will make a good installation. One of the limitations is that a given piece of wire, such as SS welding rod, will vary in diameter along its length. File A6 tells how I go about getting a good fit between pockets and shafts. It is not difficult. Years back I had visions of having pockets "adjustable" with a fine threaded machine screw, but never pursued that with anyone who could make them. They think in terms of 10,000 units to be worth the trouble. We modelers just have to make do with what we have to work with.