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[Motorman]

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[Brett Buck]

Seems the maple engine bearers are the first thing to go on my planes. How do you keep the mounting bolts from crushing the wood? I've tried a few different things but I wanted to see what others have worked out.

   Aluminum pads glued to the mating surface. I use 2.5 mm 2024 T4 aluminum, about and inch and a half long. Curiously, 2.5mm 2024 is the same thing they make stop signs out of, at least around here. It has a thick vinyl sticker for the sign part that is really tough to remove.

     Brett

[Scott Richlen]

Motorman:

Try lower pull-outs 

Our stuntships deserve a chance to go out in glory - (before their motormounts turn to mush)

[Robert Schroeder]

Blind mounting nuts.

[Brett Buck]

What do you do for the other side?

    Blind nuts, at least so far. If those start compressing the wood, then it's being over-tightened. If you need to tighten them really hard to keep the engine from coming loose, then the likely cause is that you aren't spreading the load enough, and allowing the wood to compress.
 
      I am tempted to go back to nut plates the next time, but hitting them when shaping the nose is a significant problem.

     Brett

[Steve Fitton]

  ... It has a thick vinyl sticker for the sign part that is really tough to remove.

     Brett

Pray tell how you learned that little factoid....!

[Steve Helmick]

Up here, highway signs are 6061T6. Our last CL/FF Contest Coordinator used to work for the WA DOT and got some old/damaged signs from the scrap for LG's. It's more corrosion resistant than 2024 and a lot cheaper. If they're using 2024 in California, you know they're wasting your tax dollars. Oh, wait, that's a given.  Steve

[Brett Buck]

Pray tell how you learned that little factoid....!

   Someone told me, of course.

     Brett

[Peter Grabenstein]

I use between Aluminum pads and Blind nuts + epoxied brass bushing tubes.
This way, crushing maple mounts is no issue for me.
Should mention, I use metric M3 stainless free screws and 4mm outer/3mm inner dia brass tubes.

   Peter

[Douglas Ames]

 

  Aluminum pads glued to the mating surface. I use 2.5 mm 2024 T4 aluminum, about and inch and a half long. Curiously, 2.5mm 2024 is the same thing they make stop signs out of, at least around here. It has a thick vinyl sticker for the sign part that is really tough to remove.

     Brett

"I'm tellin' ya, there was a Stop sign here yesterday!" 

[Steve Helmick]

I use between Aluminum pads and selflocking nuts, epoxied brass bushing tubes.
This way, crushing maple mounts is no issue for me.
Should mention, I use metric M3 stainless free screws and 4mm outer/3mm inner dia brass tubes.

Peter

Is there any evidence of galvanic reaction with aluminum/stainless/brass? Do you assemble with any sort of anti-seize compound to reduce that problem?  Steve

[Peter Grabenstein]

Is there any evidence of galvanic reaction with aluminum/stainless/brass? Do you assemble with any sort of anti-seize compound to reduce that problem?   Steve

If I get you right,
never had galvanic reaction with this combo but a thin layer WD 40 on to screws can
prevent this I guess.
Soon or later (after a few flight sessions) small amounts of Castor oil will find its way.
The hard stainless screws I use, never seize with the sort of Blind nuts I use too.
I allways replace screws and nuts from China (ARF/ARC) into stainless free screws (DIN Norm 9.8 or 10.3)
(which is an indacator for hard and stiffness) because much harder/better Quality.
Small amounts of grease Spray from a Bicycle Shop could be an Overkill.
The brass tube bushings just prevents crushing the maple mounts.
1/8 Epoxy sheet pads can do the same instead of Aluminum.
  Peter

[Peter Grabenstein]

 

"I'm tellin' ya, there was a Stop sign here yesterday!" 

 

[Peter Grabenstein]

  Aluminum pads glued to the mating surface. I use 2.5 mm 2024 T4 aluminum, about and inch and a half long. Curiously, 2.5mm 2024 is the same thing they make stop signs out of, at least around here. It has a thick vinyl sticker for the sign part that is really tough to remove.

     Brett

A heatgun and a sharp spatula could solve this prob. removing the sticker.

Peter

[Brett Buck]

A heatgun and a sharp spatula could solve this prob. removing the sticker.

   You would think so, but no.

      Brett

[John Stiles]

Seems the maple engine bearers are the first thing to go on my planes. How do you keep the mounting bolts from crushing the wood? I've tried a few different things but I wanted to see what others have worked out.

Thanks,
MM

I give up.....a miniature torque wrench?

[Gerald Arana]

I used to work for the County and "ALL" signs were available to me so.........
The glue surface has to be scraped off or just left on. It is put on with heat/vacuum and is VERY difficult to remove (That's why they do it!)

I use the 4-40 bronze inserts with aluminum pads and I can tighten the 'L out my mounting bolts with NO crushing of the mounts.

Jerry

[Scott Richlen]

Who do you purchase the bronze inserts from?
thanks!
 

[Brad Smith]

Scott microfasterners.com has the bronze inserts .

[Brett Buck]

When I consider brass tubing or threaded inserts they always seem to take out too much wood and are too close to the edge of the wood. I guess my experience comes from racing where even the aluminum pads work there way in and blind nuts crush in very quickly. I've pressed blind nuts into aluminum plates but eventually nothing seems to save the wood from the pulse of the greasy engine.

      I have a 25-year-old airplane that has only a tiny bit of compression, after thousands of flights.

    I also do not use inserts. If you have a hard insert, you have to count on stretching the bolt to create all the preload and clamping pressure. The spring of the wood help keep some preload without stretching the bolts. I can tighten mine with a ball driver, which is not a lot of torque, and not have it come loose.

     Brett

[Trostle]

I use 1/16" aluminum cut in the shape of a yoke with the cross piece sitting behind the firewall forming the forward portion of the tank compartment floor with the two members extending forward through the firewall to cover the entire motor mounts inside the engine compartment.  My 14 year old Bearcat, 90 gallons of fuel, Aldrich-Jett .50, well over 1,000 flights and the motor mounts are completely intact as if they were new.

The single piece of aluminum forming that yoke helps simplify the assembly and alignment of the motor mounts, firewall, and doublers.

Keith