When all else fails.......get the calculator out. (Bear in mind I've never flown a Robbo so all figures from the report and the Robbo website) From the report, 185 ltrs gives 3 hours endurance = 1 ltr per min. Therefore, fuel req'd for 7hrs 30 mins = 450ltrs. 450 ltrs - wherever you put it - is going to weigh 720ish pounds.
Average empty R44 weighs 1450lbs, add std & Aux fuel of 290 lbs, 2 pilots wearing lifejackets, survival suits, ELT and Sat phone etc @250lbs each, and 1 dinghy at 30 lbs. Comes to 2270lbs. This leaves only 130 lbs for extra fuel to max T/off weight of 2400 lbs. Some 300 lbs short of the fuel req'd for 7hrs 30mins endurance.
(I know some R44's are rated at 2500lbs MTOW but, according to the website, have an empty weight just over 1500 lbs, still 250lbs adrift).
All of which would lead me to conclude that either a). the 7hrs 30mins endurance figure was wrong or b). the aircraft departed well over weight.
However, 290lbs + 130lbs does give an endurance of about 4hrs 20mins. Time of flight was 4hrs 11 minutes.
I could have got this completely wrong and, if I have, no doubt I will be very quickly put right by the Robbo community.
Helmet and Flak Jacket on and awaiting incoming.