Motor Mount Pads

[Dick Pacini]

What is the general consensus on the use of aluminum motor mount pads?  Should the mounts be routed to accept the pads to maintain centerline height?  How about on a profile?  An ARF with a nose ring like the P40 might have a noticeable mismatch between the spinner and the nose shape.  There are several thicknesses available, so which is the preferred?

[Ward Van Duzer]

I don't rout my mounts for the alum pads. Reason: If I put the pads on the unrouted mounts I can adjust the tank up AND down. Besides, cutting the mounts weakens the them. Likewise I can adjust the pads by using different thicknesses of pads.

On profiles I like the beveled plastic pads. They can provide an infinite range of engine offset.

Then, of course there is Windy's adjustables!

Just one mans approach!


W.

[Chuck Feldman]

Hello Dick,

I use them on both types of mounts. I do not cut down the beams to compensate for the pads thickness. I find on a profile that the 1/8th" pads work very well and I do not have to angle the engine for line tension. When I build the spinner ring to the fuselage I compensate for the pad thickness of 1/8th"

On a built up ship I also allow for the extra 1/8th" for the spinner cone ring.
I do not always use 1/8th pads sometimes it is 1/16th" this is done in the trimming process. The thinnest pad I use is the tin stock from an old fuel can. Some times I stack them to get the exact trim effect. I hope this helps you.

Chuck

[Randy Powell]

I use a removable aluminum mount that bolts into the maple bearers. The engine bolts to the aluminum and the aluminum bolt to the bearer. One of the advantages is the ability to change out mounts for different engines and also to make adjustment (down thrust, out thrust, etc.).

[Allan Perret]

I use a removable aluminum mount that bolts into the maple bearers. The engine bolts to the aluminum and the aluminum bolt to the bearer. One of the advantages is the ability to change out mounts for different engines and also to make adjustment (down thrust, out thrust, etc.).

What thickness aluminum do you use ?    Do you tap it for the engine screws, or use screws from the bottom with nuts on top.    I used to do that with coutersunk flat heads from the bottom but it created a weak spot and the mount would crack.   So I changed to button head screws and had to gring small spots on maple bearers for the heads.   I was using 1/8 aluminum and didnt think that was thick enough to tap ??

[Randy Powell]

Allan,

With regular PA planes, I use 1/2" square bearers and 3/8" square aluminum engine mounts (extra material is usually machined away). Helps to radius the corners where they bolt to the bearer. They are tapped for (usually) 5-40 or 6-40 screws, depending on the engine. This leaves plenty of "meat" on the bearer, particularly if it's secured to the fuse side doubler well. Helps to have a mill to machine out the parts; mount and bearer both.

[W.D. Roland]

I cut then mill my pads out of .01 t4 or 6 aluminum.

They are C shaped , one piece with the engine bolt holes threaded and the other holes to mount to the bearers are all but one slotted for side thrust adjustment. The pad is longer than engine lugs.

Like Ward I planed on using the pad to also allow for more tank adjustment range.
On the Chip I still had to cut on the bearers to raise the tank and it is not quite enough!

On the Shark thingie The pad made the tank height close to perfect, more test flying need to make sure.

So far this has come in handy for changing engines from ST.35s to OS.35s. I made a new pad to fit the OS lugs/holes and used the old pad to locate the holes in the new pad for mounting to the bearers in airplane.
Now if needed I can swap back and forth from ST to OS.

David

[MrSteve09]

Dick,....

I am in no means an expert at this, in fact this is the first motor crutch I've ever built.  This is how I installed the motor pads.

I used #5 X 1/2 Flat Head Wood Screws to secure the motor pads to the maple engine rails.  I also used a 17/64" dia. drill bit (the diameter to the screw head) to counter sink the screw heads flush with the top of the aluminum motor pads.  Then I positioned the motor pad on the crutch marked the maple rails and drilled a 3/32" dia hole for the #5 screws.

Sounds like you're questioning the used of motor pad on a profile?  I don't think it would hurt, in fact it would spread the load over a bit more surface area.  In fact I'm putting together a Sig Primary Force for my son and I'm planning on installing aluminum motor pads this very same way.

Your question about nose ring being offset due to the motor pads is valid on a profile ARF with a nose ring already built in, however any kit built profile can have the nose ring offset to match where ever the spinner is located (due to motor pads or thrust wedges).  In fact I used a 1 degree thrust wedge on my Brodak Cardinal and did indeed take in count the location of the spinner backplate before building the fuselage nose ring.

Hope this helps.

Steve T.
Monson, Massachusetts

[W.D. Roland]

While I had the cowl off to adjust the side thrust took some pics of the adjustable pad.
In the front veiw the Bolt hole closest and on the right in pic is drilled to the shank od of bolt.( call this one 1st)
The other 3 are slotted to follow an arc measured off the 1st bolt hole.
Camera is not good at close up....

David