If the total fuel required is 35.5 USGAL @ 9USG/hr, the Endurance would be 3.9 hours correct?
Incorrect!
Based on above figures, you cannot work out endurance. I'm sure it's just the way you've worded it, but 'total fuel required' is the amount of fuel you actually require for the planned leg and/or route.
Endurance is based upon the fuel you actually have in your tanks, which will be more than you actually
require.
For example, using your numbers above, you require 35.5 USGALS to complete a flight, fair enough. Add on, say, 5% contingency, and an hour reserves at 9 USG/hr (9 USGALS
), and you get 46.3. Call it 50 USGALS you have in your tanks. This is what you then use to calculate endurance. 50/9 = 5 hrs 33 mins endurance. If this is for test purposes, be sure to use the methods of adding contingency fuel/extra fuel as taught by your instructor, or in your manual. This is just my personal method to produce an absolute minimum.
Just for info, the 3.9 hours figure you came up with would be your enroute time, assuming total fuel required calculation is correct and the 9 USG/hr figure was an average. So (using the method above), deduct 3.9 from 5.55 (5 hrs 33 mins) and it leaves you with about 1 hr 40 mins of fuel above and beyond what you actually need.
I always set one hour reserve as the bare minimum.
All the best.
edit: Sorry I can't be of much help on the CRP front - I just cheat and use a calculator!