I'm curious how many people still use the old hardwood rail method shown on plans for engine mounts. Is there any reason why it shouldn't still work?

I have been known to still use both methods. It is difficult to get two separate wooden beams on the same plane so that there is no twist applied to the crankcase when it is bolted down. My preference is for nylon engine mounts (glass filled, actually). Metal mounts are okay, but I'd rather break a nylon mount in a crash than a crankcase when bolted into a metal engine mount. Fortunately, crashing is a rare thing for me, but it does happen on rare occasion.

Wooden beam mounts are cool in that if you want to change engines with different bolting patterns, all you have to do is to fill the existing holes with small hardwood sections of dowel that has been epoxied in place with lots of epoxy. Once cured, sand smooth and begin all over again. Of course, it helps to have fuel proofed the original beam mounts with epoxy.


Ed Cregger

the hardwood rails dampen vibration better.

Because it is directly built into the framing, do they tend to wear on the fuse sides and wear out the glue joints on bulkheads?

Brian

Could you bolt the beams to the engine first, then glue them in place? Maybe make an aluminum "placeholder" with holes spaced the same as the engine mounting holes? Haven't had my coffee yet, so this may not work. . .
.
I'm a soft mount fan myself. Why beat up the airframe that you put so many hours work into?
.

I guess I was thinking along these lines. But if the hardwood rails dampen the engine vibration, would the soft mount have much over hardwood rails?

I would like to try this method if it is useful. Plus the plans have all the thinking worked out for you.

Brian

Brian,

The Top Flite Taurus normally has hardwood rails
My Taurus already has many hundreds of flights in the logbook, the bolts are glued in the rails. Even the Taurus is “overpowered�, I have no technical problems with this method.

My replica of the first Contest Taurus, as many planes of that era, does have a mount plate.
This plate is bolted on the rails. The engine bolted on the plate.
With this method it is possible to mount different engines in the plane or easy change side and down thrust.

Now I am redesigning the Simla I am thinking of use a mount plate again.
A study plan of that method see picture 3

Cees

Cees,

Thanks for the reply, and thank you for showing this to me. I may need to buy the tools I need to cut that. It looks very convienient. I like the fact it is so versitile and won't destroy the nose everytime one needs to pull things apart to perform maintenance or modifications.

Hmmm... (That's the sound of ideas churning in my brain. Scary, isn't it.)

Brian.

Brian.

This is the saw I use to cut this 6 mm, ¼ inch aluminum. (How do you call this saw, a “fretsaw�?)
Saw blades I use, “piercing saw blades for metal�, brand “Eberle� number 0.

After cutting of course the normally used files and drilling- and thread tools.

Very important is, using cooling liquid, “spiritus� (Dutch), spirit is maybe the right translation. Keep the cutting area of the material continuous wet by dripping a little bit of this liquid (drops!) on it. (sawing, drilling, making thread)
Without this liquid it’s not possible to saw the aluminum or make a good thread in it!!!!

You also can use less thick aluminum but you cannot use threaded holes I think.
I also do use this saw to saw all the wood of my planes, it allready has hundreds of feet on the counter.


Cees

Is there a scroll saw blade that will accomplish the same thing? I am not familiar with the "cooling liquid." I think I could purchase some cutting oils. Would that be the same thing?

Brian

Brian,

Someone has to help us with "spiritus" and the right translation. Cutting oils I use for steel.
Spiritus is a normal "household liquid" (my coal English!!) to clean windows, it's a kind of (95%) alcohol.
In the Netherlands "spiritus" is also used in little burners for (cheese) fondue.

The saw blad is only 0.0135 inch wide (0,34 mm) so it cost me nearly no power to saw, only time, one quarter of an hour for this piece of material.
Of course you also can use or try other tools/saws, whatever you can handle.
With my saw I can make curves.

Cees

In the original plans for many models that were featured in the magazines back in the late 50's and 60's, the plate being referred to was known as a shear plate and it was made from plywood. The idea being that the plate would fail first in an impact, reducing the damage to the engine or model. These were the days of reed and single channel R/C systems, so even the experts would have a minor crash occasionally. Folks today just coming into the hobby won't have any idea of the years of agony and frustration experienced to bring us to the level we are at today, as far as reliability is concerned. Of course, I know there are many folks reading this forum that know this much better than I.


Ed Cregger

Greetings,

The "spiritus" is probably what's known as surgical alcohol or medicinal alcohol or rubbing alcohol, and often sold as "pure alcohol". It's basically a pure form of ethanol, which is the alcohol you get in alcoholic drinks. It's fairly expensive because if it was any cheaper people would buy it to drink instead of alcoholic drinks... Besides cleaning glass, or as a smokeless fuel (fondue warmer fuel...), you can use it as an antiseptic, for wound dressing, or for a good rub down when you have a cold.

There is also methylated spirits. It's basically the same thing (ethanol) but with a bit of methanol (as used for glow fuel) mixed in to stop you drinking it. Drinking methanol will blind you, destroy your kidneys and do other horrible things to you. Methylated spirits is usually dyed blue to warn you not to drink it. I suppose in the application we're discussing, and also for use as a fuel in your fondue burner, methylated spirits would work just as well as surgical alcohol, and should cost less, but do keep it away from your skin and eyes. I suspect it would not be as good as pure ethanol for cleaning windows but I haven't tried.

Best regards,

George

George,

Thanks for explanation, the bolt is the liquid I use. Color is light blue!!
I knew it was too complicated fot me to explain, thanks again.

Cees

You are right George, what we call Spiritus is simply denatured alcohol (ethanol) used for portable hearth, teapot warmer, and also for cleaning purposes. It's tax free and that's why it's denatured so you don't have a cheap drink.

Ed,

I did not see examples of a shear plate made from plywood. Maybe these are used for small engines
I show the Smog Hog of Howard Bonner, a Tufnol plate is used (known by me as brand "Novotex") and an example of a later plane, the Crusader of Ralph Brooke, 1/4 " aluminum.
Another method to reduce crash damage is using brass bolts/screws to mount the engine on the plate or rails (Ed Kazmirski)

Cees

You make an excellent point and I hadn't thought about the plywood being used for some smaller engines.

The Goldberg Senior Falcon flew with .35 to .45 sized engines originally and the kit did utilize a plywood shear plate. When I built mine in 1969, I didn't use the plate, but bolted directly to the original bearers with my over sized OS Max .58 R/C engine.


Ed Cregger

I make a "crutch" when using rock maple motor mounts. I first drill the mounts for the engine and then bolt them to the engine. I then build the cross members and prep it for epoxy to the fuselage sides, usually using internal ply doublers though I have used balsa doublers too. The longer the maple motor mounts, the more vibration dampening.
When I used to build one piece C/L models I would actually glue the end of the motor mount to the wing sheeting when gluing the wing into the fuse by sliding hard balsa shims between them until it was pretty tight. This allowed the vibration to spread out over more structure. Typical model life was 1500 flights or so, most hang in my garage at 20 to 30 years old! It's pretty effective.

So far all of my R/C models except the King Cobra have nylon or aluminum mounts on vertical firewalls.

Chris...