Making aluminum engine bearers

Rusty, I can hook you up. I just need to know the size(s) you need. We commonly use .040", .060" and .080" aluminum sheet at work.. and I can cut plates for you with elongated slots.. or a precise hole spacing. Give me your screw sizes and I'll cut plates for you. I'm thinking that slightly elongated slots might be a better way to go for being able to use the plates "universally" between engines. I am unsure of the hardness of the stock.. but I can't see it being too much of an issue. Look through your kits and note the sizes of your hardwood engine bearers.. (3/8", 7/16", 1/2" etc.) and we'll design the plates you need together.

If you need thicker material than what I've listed as "on hand".. I can get some. It will more than likely be 6061-T6 grade.

Here's a link for what a 12" x 12" square sheet of .125" thick 7075-T6 aircraft grade aluminum (hard) sheet would cost from this supplier. It's almost twice the cost of 6061-T6.

http://www.onlinemetals.com/merchant.cfm?pid=12663&step=4&showunits=inches&id=916&top_cat=0

Here's some samples that I ran yesterday out of .040" sheet. They measure 1/2" wide by 4" long. Too thin for .25+ two-strokes.. but tomorrow I have a job set up for .080"... and I will run some strips along side of the work stuff. We also have some very interesting material that is 1/8" thick.. which has .020" aluminum facers, and a core of .085" dense plastic. I'll see if I can get the exact specs on it.. but it might be "trick" for plates.

RknRusty wrote:Hey Roddie. The maple beam on the Skyray is 3/8" on the mounting face. I thought the bolt pattern would be in my spec sheets, but I'll have to go back and look at the engine to estimate it. The holes would accommodate #4 screws.
Rusty

Rusty's OS .25FP-S was determined to have a .550" hole-spacing (on center) for drilling-out hardwood mount-beams and bearer-plates. An OS .40FP-S is .690". This also applies to the same size "LA" engines. I need to double-check the case clearance.

Here's a set of .080" aluminum plates I made today for my Fox .29/.35 Stunt engines. Their hole-spacing is .625" (5/8") with .093" (3/32") case-clearance. The hole diameter in my plates is .125" (1/8"). I "think" that's OEM spec.. but both my .29 and .35 have some enlarged holes in the mounts.   (I didn't do it..)

This is my Fox .29 Stunt. Virtually the same as the .35... only slightly heavier, due to the smaller bore in the cylinder sleeve.




These plates measure; 1.25" long by .311" wide. The width was determined by .093" clearance either side of the .125" hole diameter.

I have some 1/2" thickness cast acrylic sheet that might make interesting plates for the Foxes on profile airplanes.. because of that protruding "lobe" on the bottom of the case. If you're installing threaded-inserts in your hardwood beams for a tidier appearance.. you could face the inboard side of them "flush" with sheeting.. without worry about that case protrusion. Anybody know what I mean?

A "universal" anything, is usually not as good as a purpose-designed article. For engines with the same case-width and side to side hole spacing.. to fit between the hardwood beams in a particular model.. I suppose they would work. Different plates (like those shown in Lieven's photo) could also be made with alternate fore/aft spacing for a given engine, to help adjust the center of gravity slightly.. without having to drill different holes in your beams (and weakening them). I just have to wonder if that type of "universal" plate would be prone to inducing vibration, because the engine is not rigidly mounted directly below it's cylinder; where it's "case" mounts are generally located. I guess it would depend on the thickness of the plate and it's spacing-spread where it mounts to the beams. I'm curious about the $35 Brodak plates.

Here's some experimental beam-mount plates. This is an exterior sign panel product that we have at work. It is 3mil thickness (approx. .117") and has a core (I believe) of rigid plastic PVC or ABS.. faced both sides with .010" sheet aluminum. This particular sample is high gloss red on both sides.. but we have white too.

I'm holding a plate sized for a Fox .35 Stunt's mount. The holes are drilled .125" diameter, .625" on center with .093" side-clearance for the crankcase. Overall width is .311" and length is 1.250". The "blank" plates are .375" wide x 1.5" long and .500" wide x 1.5" long. The other 4 "pairs" of sets are for Rusty to try; which are sized for his OS .25FP-S and OS .40 FP-S engines, with .55" and .69" hole-spacing (respectively).. and are both 1.375" in length.

I am also making .060" and .080" thickness "solid" aluminum plates. A pair of the .080" Fox .35 size plates weighs 2 grams. The "same" 3mil composite pair won't yield a scale reading.. so they're quite lightweight.

EDIT: I can't seem to upload photos tonight.. and no "smileys" either.... ?   

RknRusty wrote:Those look great Roddie. That will keep us from crushing our beams by spreading out the load and providing a solid boss for any thrust wedges or washers. It's nice when you preflight your plane and don't find you need to tighten the engine bolts. For those that use bolts all the way through the fuselage it keeps the nuts from sinking into the back side too. I like the polymer sandwich idea.
Thanks for taking the time to make them.
Rusty

I really enjoy this side of the hobby (if nothing else, it' educational..) Rusty mentioned the "back-side" (or under-side) of the beams.. where conventionally; there would be nuts/washers. An .040" thick plate would work well there.. and would be very lightweight.

The "composite" plates shown in my last post.. I'm not sure how the alum. skins are bonded to the core. They'd be "purely" experimental. The .010" alum "skins" are pretty thin.. and I'm not sure how much tightening torque the core would take, before it starts to crush. I can't bend those plates with my fingers... which is somewhat of an indicator as to their rigidity. The "red" coating should "sand-off" to bare aluminum; if there's a cosmetic concern. If they work-out.. they're a very lightweight option; rather than using "solid" aluminum plates for this application.