engine mount plates

[Chris Belcher]

Want to make some engine mount plates. I know how the system works except for the holes for the mounting of the engine itself. If so..are these just tapped to the threads of whatever bolts i will use? How thick does the plate need to be to have enough threads to hold well? What about the excess of the bolt length...may be i don't know as much as I thought...as usual

[Tim Wescott]

You'll get lots of opinions on this.  The rule of thumb that I was given is that with good quality aluminum (2024, or 6061 if no machinists are looking) the minimum hole depth should be at least five threads deep -- so 5/32" for 6-32 fasteners, or 1/8" for 4-40.  This wasn't for model airplanes -- but it was for high-zoot imaging systems that had to hang off of helicopters, so it's a pretty high-vibration environment.

[Bill Johnson]

That's pretty close to the rule-of-thumb I was taught: 1D as an absolute minimum. 1.5D preferred.

[Motorman]

I spent allot of time in racing trying to figure better ways to marry the greasy vibrating metal thing to the soft fluffy wood thing. Came up with some interesting solutions.

If you're talking about bolting the engine to strips of metal then bolting the strips to the plane 1.5 D is not enough for a 2 stroke engine with safety any margin imho. 2.5 x Dia of the bolt would be my minimum depth of thread. I've seen allot of engines pull out or crack the plate after a few flights.

 Also, 6061-T6 is very available which is why everyone uses it but it is one of the softer alloys.  I wouldn't thread anything into 1/8th aluminum that was bigger than 1/2a engine. 3/16th up to .19, 1/4" up to 46, 5/16th up to 65 and that's with 2024-T6 or 7075-T651 and sport engines with the right size and grade bolts.

What you can do is use 1/8th plates under the engine to spread the crushing force and have the bolts go through to nuts on the other side of the maple motor sticks. You can even use plates on the nut side so they don't dig in. Sometimes I make my own blind nuts with a bigger diameter. What we really need is something light weight that is less crushable than maple.

MM

[Tim Wescott]

What we really need is something light weight that is less crushable than maple.

I have seen a few build threads on this forum that used aluminum for the engine bearers.  I'm not sure how widely accepted the practice is, how rugged it is (I can envision the entire bearer breaking off the wood, cleanly), or how well it works in a weight/work sort of way.

[Bill Johnson]

"What we really need is something light weight that is less crushable than maple."

Doesn't the T-Rex use a Dave Brown Mount? That's a "glass-filled nylon" mount.

[Geoff Goodworth]

I am currently repairing a model that I want to fit with a different engine. The mounting holes for the existing engine overlap the holes for the engine I want to try.

My solution is a 1/8" plate with the mounting holes for the new engine countersunk on the side where the plate contacts the bearers. I will be using countersunk 4-40 screws protruding through the plate and the engine will be retained by hex nuts.

The installation procedure will be to fix the engine to the plate and then attach the assembly to the aeroplane.

I can't remember for certain, but I think this is the approach Larry Cunningham used on his New Mexico Universal Mounting Plate.

[Randy Cuberly]

I am currently repairing a model that I want to fit with a different engine. The mounting holes for the existing engine overlap the holes for the engine I want to try.

My solution is a 1/8" plate with the mounting holes for the new engine countersunk on the side where the plate contacts the bearers. I will be using countersunk 4-40 screws protruding through the plate and the engine will be retained by hex nuts.

The installation procedure will be to fix the engine to the plate and then attach the assembly to the aeroplane.

I can't remember for certain, but I think this is the approach Larry Cunningham used on his New Mexico Universal Mounting Plate.

Sound...except how do you keep the screws from turning when you tighten the nuts?  Do you have screw driver access from the bottom?

Randy Cuberly

[Dan McEntee]

The installation procedure will be to fix the engine to the plate and then attach the assembly to the aeroplane.

I can't remember for certain, but I think this is the approach Larry Cunningham used on his New Mexico Universal Mounting Plate.
[/quote]

   I have done this on occasion. Tighten engine to the plates, then mount the plates to the maple mounts. I try to keep the length of the aluminum plates as short as possible, with the bolts that hold them down just clearing the engines mounts. If care is taken, you can mount different engines in a test bed airplane this way.
  Type at you later,
  Dan McEntee

[Gerald Arana]

I am currently repairing a model that I want to fit with a different engine. The mounting holes for the existing engine overlap the holes for the engine I want to try.

My solution is a 1/8" plate with the mounting holes for the new engine countersunk on the side where the plate contacts the bearers. I will be using countersunk 4-40 screws protruding through the plate and the engine will be retained by hex nuts.

The installation procedure will be to fix the engine to the plate and then attach the assembly to the aeroplane.

I can't remember for certain, but I think this is the approach Larry Cunningham used on his New Mexico Universal Mounting Plate.

That is the way I did it on my "Trivial Legacy". My analysis is: I won't be doing that again! When I counter sunk the flat head bolts, it weakened the to much. That is, the plates bent when the plane landed hard. (I won't go into that)

A much better mounting system is the "glass filled" Dave Brown RC mount.

Or a simple plate bolted through the back plate (with longer bolts of course) and then bolted to the fire wall. The best thing about this way of mounting an engine is a very narrow nose can be gained with the shearing off of the mounting lugs. That is of course if you're into that sort of thing. (Which I' not)

Good luck, Jerry

[Motorman]

You're putting big counter sink hole in a 1/8th plate?

Why don't you just plug the holes with hardwood dowel and epoxy then drill for the new engine. Because, you'll have to dig into the other side to change the blind nuts, right? Well that's what I would do.

MM

[Steve Helmick]

The only ones I've used were 6061 T6, but 3/16" thick x 3/8" wide. I countersunk the bottom side for a 4-40 sockethead flathead machine screw. Worked fine. The plates are long enough for 1.500" bolt-down center spacing, into 4-40 T-nuts. This worked real well.

I think the hardware store aluminum strips are something even weaker than 6061T6, so I'd avoid it.  Steve

[Allan Perret]

1/8" plates, 4-40 button head screws from backside, grind out small dimple in mounts for the button heads.

[Bill Johnson]

1/8" plates, 4-40 button head screws from backside, grind out small dimple in mounts for the button heads.

You could drill and tap the holes then use a 4-40 bolt with the head cut off as a stud. Then you'd have thread engagement the entire thickness of the plate. Red loctite to secure it and the'll never come out.