Gents,

Waiting for the opinion of Free Bird I do show some pictures.
(He calls himself "Free Bird", so the opinion for sure will follow, nobody will stop him!)

Picture 1 the inverted 4 stroke of the Calypso, Hanno Prettner 1984 plane of the world champion and picture 2 the Orion again.
Hanno did use the 2 stroke but he did also give this advice for mounting a 4 stroke in the Calypso.
The Calypso is in the picture, se the thread of Berusty: Prettner Calypso Plans...
http://www.rcuniverse.com/forum/m_8133426/tm.htm
When you want to use this design I give you the advice to mount the “head rest” (green) I did design for the Orion to protect the engine in belly landings see picture 2.
Distance between the headrest and the engine 0,5 a 1 mm depending of the flexibility of the engine mounting and the amplitude of the engine vibrations and thrust forces.

BTW I did not see this drawing when redesigning the Orion, but look to the mounting screws of the engine cover! I call this, “This is my cup of tea!!!”, even the washers are there.

Fuel tank? look to the earlier posts!

More to come.

Cees