f28 flex takeoff
-
Unfortunately the documentation to do a proper Flex take-off in the JF F.28 doesn't seem to be available - it isn't included in the manual.
The tables from Piedmont you've provided, and the ones JF include in the manual, are for the 'Rated Thrust' takeoff, which sets the maximum engine thrust permitted by the temperature/pressure altitude.
You read across the top of the table to get to the pressure altitude of the airfield (what the altimeter reads when set to 1013mb/29.92inHg sat on the tarmac), then go down the column until you reach the row corresponding with the current air temperature - that number is then what you set on the Thrust Index windows. If there's just a line rather than a number, follow the line up until you reach a number (the highest Thrust Index allowed at that pressure altitude, regardless of temperature.)
So looking at your third chart (the NOV 29-85 one for the F.28 4000), if your pressure altitude is 1600ft and the OAT is 75*F, you set a Thrust Index of 150.
This means that with the throttles set to the Take Off detent, you should get 100% on the thrust indicators - the engines are making the maximum thrust they can for the temperature and atmospheric pressure while remaining in their speed and temperature limits.
A true Flexible Take-Off involves deliberately setting a lower Thrust Index by assuming a much higher temperature than there really is. The take-off run will be extended but there'll be less wear and tear on the engines. But to calculate that you need information that isn't in any of the readily-available tables, because you need something to indicate what the minimum runway required for a given combination of Thrust Index and Aircraft Weight is.
-
Happy to help!
I assume that the relevant info just isn't available. JustFlight clearly had access to a good part of the F.28 flight manual (or at least 'a' F.28 flight manual) because a lot of the diagrams and charts are reproduced in the manual for their virtual version, right down to the one to let you calculate thrust settings for noise-abatement climbs. So I can only assume that if the tables for thrust/runway length/weight were available, they'd have included them.
There is currently a complete Piedmont F.28 Pilot's Operations Manual for sale on eBay - it's over 1000 pages and priced at nearly $150. So if someone wants to do some philanthropic work for the MSFS F.28 community and buy it to see if the Flex T/O data is in there, they know where to go!
-
If you use Simbrief, I've been playing with the latest version that includes a takeoff performance calculator.
It doesn't have preset data for the F.28 but it does have it for the F.70 and can give a calculated Flex Take Off temperature.
I've been loading data for my F.28 into that, then bumping up the weight by 10 per cent or so to account for the lower power/weight ratio of the F.28.
So far it's always spat out Flex temperatures in the 40-45 deg.C range.
Using the thrust index numbers to go with those temperatures certainly seems to do a good approximation of a Flex takeoff - less of the frantic 'pocket rocket' climb that you get at full rated thrust. I feel you could bump the assumed temperature even higher but without the proper data it seems a good compromise.
