Hempy
Be careful listening to Trent.
‘Endurance’ is indeed about ‘how long the donks will keep turning’.
But there are many variables that affect when the donks will ‘stop turning’ and how far down track the aircraft to which they are fitted will be when they do.
The donk in question in this thread is one fitted to a Warrior.
Let’s assume 25 knots headwind
Lowest drag IAS in a Warrior at MTOW is about 80 knots.
Apply a headwind of 25 knots and assume our adjusted-for-headwind best range IAS is 85, for a ground speed of 60kts. (Trent (correctly) says that the adjusted speed should be around 92, but let’s not complicate things at this point by making assumptions in my theory’s favour. We could complicate things more by taking into account changing weights and climb fuel consumption etc, but let’s not, at this point.)
500 nms at 60 knots is a very long way. At a constant 60 knots GS it would take 500 minutes or 8 hours and 20 minutes.
With 180 litres usable on board, you’d have to burn less than 22 litres an hour to make it.
And how much do you have to burn to maintain an IAS of 85 knots in a Warrior?
Well jigger me with a bargepole if it’s not: “Less than 22 litres an hour”! You wouldn’t land with much more than fumes - those operations are called “W8”.
Let’s assume no headwind
Given that the actual aircraft appears to have had a slight tailwind in real life, let’s assume it didn’t (because otherwise the assumption would be in my theory’s favour).
Best long range speed is the lowest drag speed for nil wind: That’s 80 knots.
500 nms (on the same assumptions) is 6 hours and 15 minutes.
With 180 litres on board, you’d have to burn less than 28 litres per hour to land with fuel.
To maintain 80 kts IAS in a Warrior, you don’t have to burn anywhere near 28 litres per hour.
Trent will hopefully help us out by explaining where and why my calculations are wrong, rather than merely asserting they are “wrong”.