Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov
The principal here is that weight is taken mostly in (stiff) compression and torsionals are transmitted in (soft) shear. There have been many odd arrangements of engine mounts over the years, at least in cars, up until about 40 years ago it was a bit of a black art. Here's a moderately well informed discussion
The rings themselves are available from Aircraft Spruce & Specialty, ready to weld to whatever frame you like.
Here's a little bit; not enough I'm afraid, but maybe pointing the way. Maybe find dimensions for the O-320-A and O-320-B with dynafocal mounts and work backwards?
The 150-160-180 hp Lycoming Engines
We will confine our discussion to the 150 hp and 160 hp 320 series and the 180 hp 360 series. These engines are assembled largely from the same parts, and the differences are much more subtle than you might think. All of these engines use the same crankcase casting. The basic casting is machined for three different type of engine mounts. The conical engine mount was the first. This engine mounting system uses small rubber cones. The O-320-A and O-320-B engines use this mounting.
Next came the Dynafocal engine mount—now called the Type 1 Dynafocal mount. In this design the larger rubber isolators are positioned at an angle of 30°. The intent was to “focus” the mounts just ahead of the center of gravity of the engine/propeller combination. This mount proved to be very successful since it afforded a smoother ride. This Dynafocal mounting system is the most commonly used system.
When Piper introduced the Twin Comanche, the aircraft had long extensions to the propeller hubs. This gave an exceptionally clean cowling, but the center of gravity of the engine/propeller was moved ahead of the focal point of the Type 1 Dynafocal mounts, so the angle was changed to 18° to compensate. This is known as the Type 2 Dynafocal and is used on the IO-320-B1A engines. At the same time, larger “three inch” Lord isolators were developed.
So the crankcases are machined for one of the types of engine mounts—conical, Type 1 Dynafocal or Type 2 Dynafocal—and they cannot be converted to any other type.
"The hard axis of the mounts points at the cg of the engine, and are inclined at 30 degrees... if you had bothered to read the link."
...that's about as useful as telling me a rubber duck is yellow. Don't mean to be rude... but hey. There is a rectangular base pyramid that forms the basic geometry. Need to know the lengths of the rectangle, and the height of the pyramid.
Those depend on the airplane and where you want to mount the engine relative to it. The base isn't part of the mount specification. The maker of the engine with the dynafocal mount should have the information, though I keep running into dead links from Lycoming, for example. This one is for the
"There are two different dynafocal mount types. Type I and Type II. Type I mounts are angled in at 30 degrees. Dimensions Type I are 13.290" width center to center. and 10.637" height center to center. "
