CIAS.............
Another one for the list
Naval Aviation Museum, Royal Navy Helicopters, Aircraft, South West Bit of a long haul from Cambridge but an excellent museum.
Re: train travel, should you happen to be above 60 years for age (I am sure you are not !!), consider investing in a Senior Railcard. Cost £ 28:00 but it will give you 1/3 off virtually all rail fares in the UK. A couple of medium length journeys and it can pay for itself.
Senior Railcard - 60 or over? Save 1/3 on Standard and First Class rail fares
Planemike
PS If you are into things rotary, you could try this one:
www.helicoptermuseum.co.uk Roughly in the same direction from Cambridge as Fleet Air Arm Museum.
PPS You should be here now, we are enjoying an early spring. Sunny, temps up to 20 C, record breaking for this time of year !!!!