Just This Once,
The MK1 Merlin is 6.6 metres to the top of the tail rotor disc.
The MK3 Merlin is lower (a few cm) but I can’t remember exactly and it really doesn’t matter in this case.
The undercarriage components are interchangeable between MK1 and MK3 Merlins, the differences are:
1/ Removable stub axle to allow another main wheel (MK3)
2/ No sprag lock (MK3)
3/ “High flotation” front tyres (MK3)
4/ Inboard tie down fitting (MK1)
There are a few part number differences etc but the point is the gear is the same in height and stroke.
When I taught jacking to the baby mechanics I’m sure we briefed that the hangars at Culdrose had a minimum clearance of at least 8 metres to the metal trusses, that is at the sides as some hangars have the apex interior construction which is higher.
Culdrose has had some new builds lately but even in the old hangars it wasn’t a problem for the Merlin unless you jacked under a light pendant. The Seaking hangars at Yeovilton are the same as the MDMF hangars at Culdrose and the aircraft fit lovely in there.
So to summarise, a spread Merlin at 6.6 metres is 1.4 metres below the metal trusses (assuming 8 metres from floor to trusses) at its highest point. The main oleos have a stroke of 406mm, which gives a total gap of 994 mm as the wheels leave the ground. Add a random 194mm for clearance and you still have 800mm clearance. If you want to reclaim top clearance turn the tail rotor so two blades sit at 45 degrees to vertical and apply the rotor brake, or position the aircraft so that the tail rotor is between roof trusses and of course always jack in the middle of the apex if you are able to. Piece of cake for people used to jacking at sea.
I’m too old to go clambering around with a tape measure so if you want an accurate roof truss height I’m afraid you have to ask someone else and I’ll concede the point if I’m wrong.
Cheers