Author Topic: Aluminum Motor pads (Read 4221 times)

TroyMartin · « **on:** March 15, 2017, 03:22:04 PM »

I have never used aluminum pads on any of my previous CL wood beamed airplanes and plan on trying them on my current project because I have noticed alot of people using them. I have certain assumptions about them but wanted others explanations about why they are being used

? Thanks!!

Steve Helmick · « **Reply #1 on:** March 15, 2017, 03:55:01 PM »

If you bolt the engine direct to good hard maple bearers, that's not too bad. If you're bolting it to a profile with the typical kit plywood doublers, that's not good at all, because the mounting lugs will gradually mash into the plywood and loosen up. Using 5-ply Birch plywood helps, but it will still mash some over time. Spreading the load over a bigger area is a big help, and helps stiffen the nose and reduces potential for fuel foaming problems.

And then again, you can bolt the engine to aluminum plates (flathead screw heads on the bottom, flat washers and elastic lock nuts on the top of the engine lugs), and then bolt the combo to the wooden mounts. This is desireable because it cures the above problem, plus it allows one to change to engines with different bolt patterns, by just making another set of plates. It's the bee's knees....

Steve

Tim Wescott · « **Reply #2 on:** March 15, 2017, 04:52:19 PM »

What Steve said, plus if you're still crashing a lot, the aluminum plates spread the impact out on the maple bearers, making it less likely for the engine to dig holes in them.

I drill and tap the aluminum bearers for the engine bolts, making sure that there's at least five threads of engagement. This method (A) follows the guidelines I got a long time ago from an aerospace designer for aluminum structure, (B) has been criticized as being not good enough by folks here, and (C) works well for me so far -- but my test plane currently only has about 50 flights, so I can't attest to it working over the long term. My personal gut feel is that as long as the screws are kept tight it'll work just fine, but wait for another 450 flights before I positively assert that's true.

Steve Helmick · « **Reply #3 on:** March 15, 2017, 06:18:45 PM »

Well, if you tap into the 1/8" soft aluminum strip (like that which Tim buys at Ace Hardware), if you crash, either the threads will rip loose, or the strips will bend a bunch. Either of which will help save both the engine and airframe.

That's cool, but having the engine come flying out of the plane during flight is definitely NOT cool, so I'd personally prefer solidly bolting the engine to the aluminum, and then solidly bolting the aluminum slabs/engine to the plane. OR just bolting the engine to the plane (use DuBro T-nuts) with the aluminum (or phenolic) pads between the two. There are some options, so choose one that suits you and proceed as you wish...but please keep safety in mind.

Steve

RknRusty · « **Reply #4 on:** March 16, 2017, 11:11:30 PM »

Quote from: Tim Wescott on March 15, 2017, 04:52:19 PM

What Steve said, plus if you're still crashing a lot, the aluminum plates spread the impact out on the maple bearers, making it less likely for the engine to dig holes in them.

I drill and tap the aluminum bearers for the engine bolts, making sure that there's at least five threads of engagement. This method (A) follows the guidelines I got a long time ago from an aerospace designer for aluminum structure, (B) has been criticized as being not good enough by folks here, and (C) works well for me so far...

The engine in my Magnum was bolted to aluminum but I heli-coiled it.

pmackenzie · « **Reply #5 on:** March 17, 2017, 04:56:40 AM »

Another advantage of using pads is that it gives you the extra 1/8" to shim the tank up if you need to.

Pat MacKenzie

Steve Helmick · « **Reply #6 on:** March 17, 2017, 12:14:17 PM »

Quote from: RknRusty on March 16, 2017, 11:11:30 PM

The engine in my Magnum was bolted to aluminum but I heli-coiled it.

Good thought, Rusty. Not being a heli-coil enthusiast, I would have considered Keen-Serts, but last time I bought some, they were about $6 each, and that was a LONG time ago.

Meanwhile, I'll wait for Tim to have a stripped thread in his cheese plates and see if his fix is something other than installing flathead screws, countersunk into the bottom of same plates, with flat washers and elastic lock nuts on top of the engine lugs.

Steve

Russell Shaffer · « **Reply #7 on:** March 17, 2017, 01:33:33 PM »

This one has no plywood under the engine at all. I used 4-40 bolts with nylock nuts to hold the engine to the 6061 aluminum plate and 6-32 with lock washers and t-nuts to hold the aluminum to the nose. Not the most attractive mount maybe, but it sure is stout. I could have painted it but getting paint to stick well to aluminum can be a problem and after all it is just a profile. The whole nose section is a solid piece of pine - there are no separate engine mounts under the ply. The 40 FSR runs well with no excess vibration.

Dennis Toth · « **Reply #8 on:** March 29, 2017, 11:38:37 AM »

Before using the aluminum pads make sure your engine mount lugs are machined flat not just out of the mold. This is particularly true for Fox 35's. You can use the pads with un-machined lugs but you need to put a 1/64" plywood crush pad between the pad and lug. If you don't use the crush pad on these older engines you can distort the crankcase when you tighten down on the mounts and cause the engine to bid and lose lots of power.

Best, DennisT

Target · « **Reply #9 on:** March 29, 2017, 01:05:16 PM »

What about using aluminum beams in place of the maple? The ply doubler could be relieved where the engine mounts? Then the beams could be either drilled and tapped, or drilled and through bolted.
Thoughts?

Allan Perret · « **Reply #10 on:** April 07, 2017, 02:25:14 PM »

Quote from: Chris Behm on March 29, 2017, 01:05:16 PM

What about using aluminum beams in place of the maple? The ply doubler could be relieved where the engine mounts? Then the beams could be either drilled and tapped, or drilled and through bolted.
Thoughts?

Sounds like overkill, but if you have a mill to groove out the aluminum aft of the engine it should work. I would check out the weight on this vs maple first..

ray copeland · « **Reply #11 on:** April 07, 2017, 07:16:37 PM »

Chris, I like the way you think with the aluminum beams !! May try that one sometime.

Target · « **Reply #12 on:** April 07, 2017, 08:46:55 PM »

Well Ray, I'm glad that someone does, LOL!

RknRusty · « **Reply #13 on:** April 08, 2017, 08:31:10 PM »

Quote from: ray copeland on April 07, 2017, 07:16:37 PM

Chris, I like the way you think with the aluminum beams !! May try that one sometime.

Yeah, I like that too.I might try it on the Sterling Mustang, next on my list. I don't know much about choosing aluminum types. Any Ideas on that? I've bought some aluminum from Lowes, but I see nothing about grade or composition, or whatever else you should know when using it.
Rusty

Dennis Moritz · « **Reply #14 on:** April 09, 2017, 11:50:10 AM »

Try whatever aluminum. A friend went to steel pads to quiet down a Fox 35 run. It helped.

Sent from my iPhone using Tapatalk

Brett Buck · « **Reply #15 on:** April 09, 2017, 12:46:50 PM »

Quote from: RknRusty on April 08, 2017, 08:31:10 PM

Yeah, I like that too.I might try it on the Sterling Mustang, next on my list. I don't know much about choosing aluminum types. Any Ideas on that? I've bought some aluminum from Lowes, but I see nothing about grade or composition, or whatever else you should know when using it.
Rusty

Most of what you get at hardware stores is dead soft and very weak. I have no idea what grade it is. I would suggest 6061-t6, it's pretty tough and also inexpensive. I think this is used for highway road signs because it's inexpensive and won't corrode easily, and will stand up to high winds. For landing gear, I would suggest 2024-t3 or t351. After trying to figure it out for years, this is the closest thing to "dural" or "duralumin" as referenced in old British Model Magazines. If it was good enough for the Hindenburg, it's good enough for you.

Get it at McMaster. Going out and removing, say, a roadside mile marker and cutting that up to use as a motor mount pad would be wrong - you didn't pay for that, the government did. So never do that.

Brett

Tim Wescott · « **Reply #16 on:** April 09, 2017, 04:36:57 PM »

Quote from: Steve Helmick on March 15, 2017, 06:18:45 PM

Well, if you tap into the 1/8" soft aluminum strip (like that which Tim buys at Ace Hardware)

Actually, I use either 2024 or 6061 from Metal Supermarket. No 3003 or Mystery Metal or whatever. (I know there's a big difference between 2024 and 6061 -- it would have been 2024 if I could get it, 6061 otherwise).

Tim Wescott · « **Reply #17 on:** April 09, 2017, 04:39:14 PM »

Quote from: Brett Buck on April 09, 2017, 12:46:50 PM

Get it at McMaster.

Get it at McMaster if you want superior service at the highest prices around. There's other mail-order metal places that don't stock a billion-and-one different (really nice) tools, but will sell metal for two or three times less than McMaster does. (I do buy stuff from McMaster -- just not much metal stock).

RknRusty · « **Reply #18 on:** April 09, 2017, 10:24:38 PM »

I've been cutting engine mounting pads from a broken set of Brodak Shoestring bent aluminum landing gear, and it's okay for that. Besides the 1/2" beams, I also want to make universal engine mounts with a thick aluminum clamp bar that won't bend when I tighten it. If I can't find what I need locally, I'll mail order some.

Thanks for that last tip, Brett. If I were to swipe some road sign stock, I'd get it from a turkey crossing sign or something like that.
Rusty

Bill Johnson · « **Reply #19 on:** April 10, 2017, 12:57:56 PM »

6061 has about 80% of the strength of 2024 in their respective tempered forms. 2024T3 and T8 are primary structural materials in aircraft while 6061T6 is relegated to secondary structure. The biggest advantage of 6061 is it's resistance to corrosion as well as being weldable.

Brett, would you would need to use a thicker piece of 6061T6 than 2024T3 to have sufficient strength when threading it for 4-40 engine mount bolts? I'm using some 6061 .050 just for wear plates on Shoestring Stunters but am also thinking of using a mounting plate so I can flight test different motors easily.

Target · « **Reply #20 on:** April 10, 2017, 01:36:50 PM »

Quote from: Allan Perret on April 07, 2017, 02:25:14 PM

Sounds like overkill, but if you have a mill to groove out the aluminum aft of the engine it should work. I would check out the weight on this vs maple first..

3/8" x 1/2" x 12" 6061T6511 is 3.5oz before any lightening holes are cut.
https://www.onlinemetals.com/merchant.cfm?pid=1152&step=4&showunits=inches&id=997&top_cat=60
I'm not sure what Maple weighs in at, but I would assume it could vary quite a bit.

R,
Chris

Tim Wescott · « **Reply #21 on:** April 10, 2017, 01:43:35 PM »

Quote from: Chris Behm on April 10, 2017, 01:36:50 PM

3/8" x 1/2" x 12" 6061T6511 is 3.5oz before any lightening holes are cut.
https://www.onlinemetals.com/merchant.cfm?pid=1152&step=4&showunits=inches&id=997&top_cat=60
I'm not sure what Maple weighs in at, but I would assume it could vary quite a bit.

Rock maple is 0.57gm/cc. 2024 aluminum is 2.8gm/cc. So yes, aluminum motor mounts would be much heavier. You could probably machine much of the weight out of the aluminum ones until you had something that would be strong and light -- but wouldn't that kind of defeat the whole purpose of building a profile?

Target · « **Reply #22 on:** April 10, 2017, 02:21:57 PM »

Yes, and no....
It depends on what you want. Simple is great, but if it's not as durable as you want, then adding a little labor to take out that weakness makes more sense than building again, to me.

Tim Wescott · « **Reply #23 on:** April 10, 2017, 03:06:40 PM »

Quote from: Chris Behm on April 10, 2017, 02:21:57 PM

Yes, and no....
It depends on what you want. Simple is great, but if it's not as durable as you want, then adding a little labor to take out that weakness makes more sense than building again, to me.

I have yet to lose a plane to worn out motor mounts. And motor mounts can be replaced.

I see your point. I'm not entirely sure that aluminum mounts in a wooden plane would be more durable: wood mounts absorb vibration and bond really well with epoxy. I'd be concerned that a wood to aluminum glue joint, together with the extra rattling you'd get from aluminum mounts, would mean that the motor mounts might shake themselves loose over time.

Steve Helmick · « **Reply #24 on:** April 10, 2017, 03:31:16 PM »

Aluminum pads or a universal adapter plate is one thing. I wouldn't consider using solid aluminum bearers. FWIW, when PW built his 2nd B-17 stunter for the Y2K World Champs in France, he used CF beams for all 4 OS .15FP's. One engine always ran goofy, which Paul fixed by sawing off all the CF beams and replacing them with regular R/C mounts of glass/nylon construction. Apparently, vibration is one thing, but vibration damping is another. Maple should absorb vibes better.

About aluminum heat treating, if it says, for instance, 2024T351, that indicates it was heat treated at the aluminum factory. If it's a single digit after the T, then it was done afterwards. I'm not sure if it really makes a difference, but an FYI.

The SIG LG's, blanks, etc., are said to be 6061T6, because it isn't too unhappy to be bent post-HT. At least some of the Brodak gears appear to be SIG items, from squinting at the Brodak online catalog. It's possible to determine the alloy and HT spec by a combination of Rockwell and
Eddy-Current tests, without damaging the part. Another FYI, 7075 is heavier than 2024, which is heavier than 6061...more copper in the alloy. It's enough to be very noticeable.

I sure miss Boeing Surplus. The last time I went there, I looked at a bin of nice pieces of Ti, but I didn't want any. I moved on to look at other bins, and noticed a guy pick up some of the Ti, and put it in his cart, like he was going to buy it. I asked what he was intending to do with the Titanium, and he put it back like it was rotten fish.

Steve