A different way to mount an engine!

[Robert Zambelli]

This is the engine mount system I will use for my new plane.
I made a square plate of 3/16 6061-T6 aluminum and then tapped a ¼-28 thread in the middle of the plate, in line with the crankshaft.
Using the backplate as a pattern, I drilled and countersunk four holes for the backplate mounting bolts.
It was then bolted to the engine using the four backplate bolts.
The backplate was captured between the plate and the backplate mounting surface.
The firewall was made from 3/16 Z-Ply.
A ¼ inch hole was drilled in the firewall to accept the single mounting bolt.
Assembled with the mounting bolt and a large flat washer.
Light, clean and simple.
The tank compartment is completely uncluttered and will accept a variety of different tanks.
Comments?

Bob Z.

[Mike Haverly]

Kinda like mounting an electric motor, without the messy fuel tank!  Just kidding, looks like a good idea and should work fine.

[Tim Wescott]

You may want to put features on the front of the firewall to keep the engine from rotating.  Just a little bit of 1/32" plywood, with a hole cut out to match your engine backplate, should do.

[Gerald Arana]

You may want to put features on the front of the firewall to keep the engine from rotating.  Just a little bit of 1/32" plywood, with a hole cut out to match your engine backplate, should do.

That was my first thought too. However, if you use cap head bolts and don't counter sink them in the aluminum mount but sink them into the plywood fire wall, that should prevent rotation of the engine too. (and lighter)

Jerry

[Phil Spillman]

Hi Bob, Pretty slick trick! Let us know how it all worked out once the plane has been flown!

Phil Spillman

[Mike Alimov]

Bob...  a 2-stroke?!....

[goozgog]

Hello Bob!

   I guess that the advantage of this
mount is that you have room for any
tank in any position.
  I'll be interested in how it works for you.
Keep us posted !

Cheers! - K.

[Peter in Fairfax, VA]

Mounting via the backplate was popular early, like 1950s, and has had some resurgence (K&B Sportster 20, SuperTigre 3000.)  Looks like it will be convenient.

However, in addition to the rotation concern already mentioned, another concern is vibration based on where the engine is being held.  e.g. If it is held by the back, can the front flex?  Some high performance engines, especially pylon racers, even add a forward set of beam mounting holes/lugs to hold the engine tight.

Let us know how it works.

thanks,

Peter

[peabody]

Bob Hunt mounted an engine using backing plate screws many years ago.

[Dane Martin]

Where'd you find that modern engine!?!?

Looks cool brother

[FLOYD CARTER]

Of course.  As early as 1948, I mounted my O&R 23 and O&R 29 using the three crankcase bolts, replaced with longer bolts.  The same scheme was used with the K&B 29.  I still use the crankcase bolts to mount my Orwick 64 (it was made to do that).  This scheme eliminates hardwood rails, and opens up lots of room for the fuel tank.

[bob whitney]

Bob ,one of my Free Flight Buddy's has been mounting a Nelson 65 on  1000 sq in unlimited for years and has never had any problems with it

[Istvan Travnik]

I need to say, this is a classic solution from R/C world...

[TDM]

I want to add two things here.
One you can get rid of the aluminium plate and not use it at all. Drill the 4 bolt holes that hold the firewall in place using the back plate as template. Figure out what screws they use for the back plate (most likely candidates 4-40 or M3) and use longer screws with a washer to spread the load on the plywood. put the screws through the washer the plywood and through back plate then in to the motor and tighten. This eliminates the spin the aluminium plate and the possible rotation.
Second keep in mind cooling of the motor. If you have bad cooling you have bad cooling you have crappy motor run. When I see that vertical wall behind the motor it screams at me poor cooling.

Great idea you have come up with here.

[Jim Mynes]

I want to watch that run. With binoculars...
But seriously, aside from the possibility of unwanted engine rotation, and the 1/4-28 bolt pulling out of the backplate which have already even mentioned, I would be concerned about pressure leaks around the mounting bolt. Straight bolt threads aren’t designed to seal like a tapered (pipe) thread. Judicious use of a little bit of pipe dope might do the trick.

[kenneth cook]

            Bob, that looks like a Mars which used similar mounting. Is that what the plane is? I think it will work just fine. Ken

[Gerald Arana]

 I would be concerned about pressure leaks around the mounting bolt. Straight bolt threads aren’t designed to seal like a tapered (pipe) thread. Judicious use of a little bit of pipe dope might do the trick.
[/quote]

It doesn't go through the back plate. How is it going to leak? 

Jerry

[Steve Helmick]

Looks like a Mars to me also...and I am happy to see the engine is mounted inverted instead of sidewinder. That would be my choice also. I'm not at all concerned about the mounting system, since Bob Z. is about 3,000 miles away.

It wouldn't be difficult to use a thinner aluminum plate and put a flanged & threaded brass or steel insert in from the front side (inside the backplate cavity), if there is a problem with it as-is. The one thing that might be worth considering is that to remove the engine, you'd have to remove the hatch, tank and then engine to do a repair or modification that could be easier with a conventional mount. Plus, I've never been a fan of radial mounting, since the firewall fell off of my Ramrod 600 when I was about 17. Fiberglass is good.  Steve

[Dave Hull]

Not a fan. The loadpath is not distributed and not optimal. For those making that comparison, it is not equivalent to the Quickie 500 mounts that I have seen, which are bolted to the fuse at four corners. That said, if you use Loctite and don't have vibration problems, you may get away with it if the firewall does not soften up. Were it mine, I'd mock up the mount and run the engine on the bench repeatedly before I finished the airplane that way. Then you would know better what to expect. Of course, that takes the adventure out of it, which may be the whole purpose....

Using one fastener in a bolted joint to hold anything important onto a full-sized airplane is very rare. For good reasons....

Dave

[Dwayne]

Bob Hunt mounted an engine using backing plate screws many years ago.

Yup a few used TruVibe soft mounts to mount a side exhaust engine so the pipe would run down the middle of the fuse. 

[Jim Mynes]

I would be concerned about pressure leaks around the mounting bolt. Straight bolt threads aren’t designed to seal like a tapered (pipe) thread. Judicious use of a little bit of pipe dope might do the trick.


It doesn't go through the back plate. How is it going to leak? 

Jerry

I didn’t look close enough. There IS a backplate there.
Disregard my leakage concern, as it is a non-issue.

[Jim Kraft]

Back in my early R/C Pattern days, there were guys that made an aluminum plate with ears to bolt to the firewall. The plate mounted to the back plate of the engine, and had 3 or four tabs that were larger than the case to bolt to the firewall. I like Floyd have only mounted Orwicks  by the case bolts. That works fine, but I had to also reinforce the firewall as all the stress is now on the firewall itself.

[john e. holliday]

Just reading this again and it hit me.  Didn't Don Hutchenson do this a few years ago.   I think he also eliminate the engine mounting lugs.   Also Bob Palmer Mars had this type of mount.  I have thought of trying it but haven't done so yet.  Thanks reminding me of the idea.

[Paul Wescott]

Didn't Don Hutchenson do this a few years ago.   I think he also eliminate the engine mounting lugs...

Doc - Eliminated the mounting lugs?  You mean like ground or machined right off the case?!?!
What sorcery is this!!!!
Pictures or it didn’t happen...

Paul W.

[john e. holliday]

I can't remember which design it was.  I think was in Model Aviation and his reasoning was it made more room for fuel tank and no hardwood bearers to contend with.   Yes a good hack saw will eliminate the mounting lugs and reduce the weight of the engine a few grams.

[Ken Culbertson]

Mounting via the backplate was popular early, like 1950s, and has had some resurgence (K&B Sportster 20, SuperTigre 3000.)  Looks like it will be convenient.

However, in addition to the rotation concern already mentioned, another concern is vibration based on where the engine is being held.  e.g. If it is held by the back, can the front flex?  Some high performance engines, especially pylon racers, even add a forward set of beam mounting holes/lugs to hold the engine tight.

Let us know how it works.

thanks,

Peter

You beat me to it so this is like a "What He Said"...

Been there, done that, threw away the T-Shirt.  Vibrated like crazy but it was with a McCoy .35 and they vibrate anyway.  Maybe it will work for you.  The reason you can get away with no beams and thin sides on electrics is the lack of vibration.  Your nose looks like it was designed for electric.

Maybe a mini mount under the forward lugs - just a thought

Good luck - I hope it works!

ken

[Ara Dedekian]

Doc - Eliminated the mounting lugs?  You mean like ground or machined right off the case?!?!
What sorcery is this!!!!
Pictures or it didn’t happen...

Paul W.

      Now I know why!!

      Here's a C.I.E. (compression ignition engine) engine from the late 1940's that came out of Dave Slagles box 'o' engines. I couldn't imagine a reason for doing this. He couldn't remember why but it makes sense, I guess. The Orwick ignition and Elphin diesel buried in the box are radial mounts without lugs. The missing drive washer hole is hex shaped which prevented my starting it but MECOA shows a reproduction C.I.E. on it's website, maybe they'll come through.

     Ara

[Robert Zambelli]

Hi, Gents – sorry for the delay in responding but some other aspects of “life” got in the way. 

Putting my ALFA Romeo back together, designing and building some new type window latches for my Swift, doing the annual inspection on my Cessna 120, landscaping, new model airplane work and ------------ well, you get the picture. 

Anyhow, thanks for the many kind and inquisitive comments about my engine mount system.

Allow me to address a few.

Keeping the engine from rotating: Although I’m positive that the friction will prevent this from happening, there will be four pointed pins protruding from the rear of the plate. They will sink into the firewall.

I know that backplate mounting has been done before (using the backplate mounting bolts) but with my method, it will be very easy to swap engines should it become necessary.

Someone said that the 6061-T6 “will deteriorate and pull out.”
Nonsense! When I was designing linear and rotary actuators for the aerospace divisions of Northrop-Grumman and Moog, many of our customers specified the materials to use. A Swiss company in particular specified 7MM x .75MM thread x 13MM WAF nuts be made from 6061-T6 hexagonal stock. We had the stock custom-machined from 6061-T6 barstock. Minimum order two five-foot lengths. We needed a total of 14 inches, so the rest was to be scrapped. I was able to rescue one three foot length and I’ve made around twenty five prop nut of different lengths – not one has failed.
As extra insurance however, there is as steel nut in the cavity forward of the mounting plate.

A concern about cooling: I have added two large holes in the firewall since my original post, and there is a 3/8 x 2 inch slot above the firewall. Also, the outboard cheek cowl is an air scoop that ducts air in directly at the bypass. Four large holes on the cowl allow plenty of room for cooling air to exit. And, of course, the head will be exposed.

“Using one fastener in a bolted joint to hold anything important onto a full-sized airplane is very rare. For good reasons....”
Good point – both my full-scale planes have six bolts holding the propellers on BUT, all of my model airplanes have ONE bolt (or nut) holding the propeller on. Consider the amount of power being transmitted through the thrust washer/propeller interface as well as the RPMs. My mount will not be compromised.

Furthermore, my firewall is made from white birch plywood and carbon fiber/epoxy. It WILL NOT compress.
Will my firewall come loose from the fuselage? It is epoxied to the plywood doublers. Also, six small hardwood dowels pass through the doublers and around ¼ inch into the firewall edge.  And finally, two small gussets will be added to the rear of the firewall where it joins the doublers.

Why am I doing all this? It’s the only question I can’t answer but I’m sure having FUN!!!     

If anyone is interested, I’ll post some photos of the plane as it’s coming together.

Bob Z.

[Dwayne]

Hi, Gents – sorry for the delay in responding but some other aspects of “life” got in the way. 

Putting my ALFA Romeo back together,
Bob Z.

Pics???

[Robert Zambelli]

Hi, Dwayne.
Which pics would you like to see?
You highlighted the ALFA.

Bob Z.

[john e. holliday]

Hey Robert, that is the most important thing,  having fun.   Cleaning some things in the shop I found an engine I had forgot about.  It was all corroded up.   Couldn't even budge the crank.  So, into the crock pot for a while.   Pulled it from the pot and finished cleaning it.   The interior was great and the shaft I could turn by the fingers.   Started looking for parts to get it running and found two more engines of the same type and brand.  Super Tigre G-21  .35.  By the way had to crock pot the other 2 engines also.  All I'm missing is a venture for stunt work.   It is the sprinkler type system. 

I know I get to long on this but your fire wall should never come out unless the fuselage separates right behind it.   I my try that on my next build.

[FLOYD CARTER]

      The Orwick ignition and Elphin diesel buried in the box are radial mounts without lugs.

OUCH!  That's no way to treat an Orwick!  Well, maybe it's one of the factory Cunningham motors.  Still should be cleaned, restored, and saved.

p.s.  The Elfin diesel (any model) is one of the best.

[wwwarbird]

 I can't figure out why one would want to mount an engine this way. 

[john e. holliday]

Reread Roberts last post.

[Roy DeCamara]

For what it is worth, back in the 1950's K&B made radial mount plates for the 4 bolt backplate Green head motors.  Self explanatory.

Cheers,  Roy D

[Chuck_Smith]

Bob, I'm wondering if the firewall and plate is redundant. Maybe it would be possible to make the firewall the aluminum backplate and save the weight, complexity and the backplate screws become the anti-rotation.

Then thinking further - eliminate the plate completely. Install the Aluminum or CF firewall in the airframe, with a hole pattern for the backplate screws, and use the backplate screws to attach the engine to the firewall, i.e., the screws go through the firewall, through the backplate and into the the threads on the crankcase. You could even counterbore or countersink the heads into the firewall and have a super-clean install. Judicious use of blue Loctite might be a good idea too.

Shucks, I might have to try this too.

Same Alfa you've had all these years?


Chuck

[Igor Burger]

I had several models with engines mounted by backlape screws and never had any problems with them:

http://www.netax.sk/hexoft/stunt/the_max.htm

http://www.netax.sk/hexoft/stunt/the_max_ii.htm

http://www.netax.sk/hexoft/stunt/the_middle.htm

[Ara Dedekian]

OUCH!  That's no way to treat an Orwick!

p.s.  The Elfin diesel (any model) is one of the best.

       Floyd

          Not to worry, the Orwick got the proper treatment as well as the Elfin. Both engines were refurbished and run. I may have test run the Orwick on glow. After returning most of the engines in the tool box to running condition, I can't remember. The green paint on the Orwick was gone when I got it.

       Ara