Polyurethane For Dynafocal Isloators?

[Toobuilder]

The general comments of caution are appreciated and I may even instrument the engine, mount and airframe to see how much vibration is passing through the isolators. That said, there is a wide variety of "stiffer" engine isolators available for aerobatic aircraft - and in some cases, the very stiff "compression" side of the Lord isolators are recomended by Lord in all 8 locations for the hard core acro airplanes. And finally, solid polyurethane isolators are available from Spruce today for conical engines, so I'm not going too far off the reservation with this experiment.

[grubbat]

I had poly conical in my -3 and you could feel every engine quirk. It wasnt bad but there was a difference. I did notice more vibration on the panel.

I wonder if you could machine out a 1" core and use a softer rubber material there and poly on the rest?

Originally Posted by Toobuilder

The general comments of caution are appreciated and I may even instrument the engine, mount and airframe to see how much vibration is passing through the isolators. That said, there is a wide variety of "stiffer" engine isolators available for aerobatic aircraft - and in some cases, the very stiff "compression" side of the Lord isolators are recomended by Lord in all 8 locations for the hard core acro airplanes. And finally, solid polyurethane isolators are available from Spruce today for conical engines, so I'm not going too far off the reservation with this experiment.

[rv6ejguy]

Of course it works and sag is much reduced. With everything, there are usually tradeoffs and it depends what's most important to you. Only time will tell if the avionics or airframe suffers more problems or not. Engine sag is annoying and ugly for sure.

[Toobuilder]

Originally Posted by grubbat

...I wonder if you could machine out a 1" core and use a softer rubber material there and poly on the rest?

I am contemplating machining an air gap between the spacer and the body of the poly to try emulate the action of the Lord mounts, but I have to balance that with the shear loads on the remaining material. It will be an iterative process, for sure.

[Radioflyer]

Why not switch to hard rubber. More compliant. If you can't source a "rod" to cut the shape from, maybe laminated sheet circles would work? Just an idea.

[Toobuilder]

Laminated sheet might work if we were only dealing with compression loads, but the mounts have to deal with shear as well. Anyway, rubber is more compliant, but has a memory. Poly can handle billions of cycles and will retain original shape. That's the theory, anyway.

Flew it yesterday and hardly notice the vibration anymore. It's really not that bad unless you jump from rubber directly to poly and have the opportunity to compare the two.

[spark68]

There are different density polyurethane springs available too. We use them in the metal stamping industry for springs. They are large cylinder shapes, look like they could work for your raw material size. Maybe I can find someone at work to give me a source. Mitsumi comes to mind.

[Larry DeCamp]

Urethane can be cast from liqued components just like epoxy. The durometer can be varied similar to to selecting slow and fast catalyst. Since tool builder has a lathe, simple molds can be formed for the task.

I did this for a Cont A40 mount to avoid the crude rubber sheet stock used in 1936. Just another option if you want to tinker.

[rv6ejguy]

Originally Posted by Larry DeCamp

Urethane can be cast from liqued components just like epoxy. The durometer can be varied similar to to selecting slow and fast catalyst. Since tool builder has a lathe, simple molds can be formed for the task.

I did this for a Cont A40 mount to avoid the crude rubber sheet stock used in 1936. Just another option if you want to tinker.

This is what I did on mine. I machined the molds allowing for contraction, specified the durometer and they turned out great.

[Toobuilder]

Ross (and Larry)

You poured the mounts yourself, or had them cast? I'm aware that they can be built to spec, but the idea of building a mold and pouring them at home is intriguing. How dimensionally accurate are they (contracion)?