For our 'flying boat' mock-up, as in the past I simulate the power-units too, invariably with tins of tuna which match the look-and-feel of U7 motors.
This has two advantages in that it avoids damage to the originals, plus you can make a sandwich with them after the shoot.
N.B. If you are mocking up your own build, note that tuna comes in spring-water, brine or oil and that any of these variations will address our needs here.
