Planko/Nigel: I 'get' the blade flapping phenomenon and I think most manufacturers have had to deal with it at some point in the development of their rotorcraft. Its the blade 'stretching' that I find amazing .. as in your 76 incident!
We had a driver come into the crew room one day telling us that the main rotor struck the boom on the D model 500 he was flying after he had shut down. Apparently a 'freak' gust of wind! It just glanced off the boom and evidently there was no significant damage done but, it was disconcerting to listen to the ease with which this happened.
When they stretched the Gazelle (just a couple of inches) they had to all but remove the vertical stabilisers, mind you the Gazelle blades are so 'bendy' one would think you could make animal shapes with them!
I once shut down a 206 and was unable to stop the main rotor (no rotor brake). They just kept on and on milling round (the wind was approx. 25-30kts and there was a slight updraft). After nearly 15mins (thinking the wind would drop at some point) I had to re-start and fly away telling the engineers (post and telecommunications working on repeaters) that I would be back for them later. I found a village green surrounded by trees .. a bumpy approach with the wind as it was but .. once below the tree line the worst of it was gone and I was finally able shut down.
To answer your question on the Salvesen Whirlwinds .. I'm not a 100% sure what the 'bump' is but .. I have a feeling it was an ADF antenna because the Salvesen whaling ships were fitted with NDB towers. I know the 'Whaling Whirlwinds' had a small amount a 'special' avionics (I think a marine band as well as the standard VHF radio) and then, as mentioned, the ADF.
I've only ever seen this tail-mounted housing on Antarctic Whirlwinds, as per the photos below:
Originally Posted by
Senior Pilot
Royal Navy HAR1 XA868 from the Ice Patrol Ship HMS Protector over Speedwell Island on the Falklands in December 1963 (Photo: Joe Barr)
And shown below with the cover removed:
Originally Posted by
Savoia
Oh and yes .. I would agree with you and say that the antenna (or whatever it was) probably came pretty close to the main rotor on occasion!