Brett,
Thanks for your comment.
I doubt that David's model has the same structural characteristics as the Score:)
Also, I suspect that the side mounted engine on this particular Score isn't helping the problem.
I would not jump to that conclusion. The airplane has a firewall mount and the rest of the front end was built assuming there was a soft mount, i.e. not very sturdy by stunt standards. The solution - replace the rubber with solid metal spools - led to several other issues, in particular, he started with 3/32 6061-T6 backplate mount, and it worked for 6-ish months with that. When he hard-mounted the engine, this plate started cracking almost immediately, a few flights. He replaced it with 1/8" aluminum, it broke in a week or two, then 3/32 mild steel, that broke after 40-50 flights, then 1/8 mild steel. That made it last long enough to get through a few contests, but still had to be replaced multiple times. At that point, he was concerned about the rest of the front end coming apart due to the light construction, and the airplane was retired in relatively short order.
I can think of multiple solutions to this issue that don't involve soft mounts. I cannot emphasize how much trouble various people have had with soft mounts on stunt engines. The *only* time I have seen them work in competitive airplanes was with the OPS40 which are remarkably smooth to begin with and probably didn't need it. And had issues with the custom built "flex header" cracking.
In all other cases, it didn't even give a *hint* of working. That includes some very capable individuals, including experts on soft mounts in other events and full-scale aerospace applications.
Before anyone points it out, the B-17 was a different issue, where the engines were interacting through common graphite/epoxy structure, and in that case, the "isolation" consisted of mounting the engine to a 1/8 aircraft ply firewall with an RC mount. That was a funny series of phone calls, with Howard calling me up at work, trying to beat Paul to the phone - to try to get me to talk him out of it when he did call. Howard explained the issue to me, and how Paul wanted to cut the carbon mounts off, and how bad it was. I said "I don't know, that seems like a pretty good idea to me", and, it was very clear that this was not the answer Howard was looking for!
Brett