AH_Sid Posted December 18, 2015 Posted December 18, 2015 I've been running a few test comparing the before takeoff 'Emergency Fuel System Check' against what we have simulated for our F86F-35, there's few differences here. For reference here's the relevant pages from the F-86F Flight Manual. click for larger versions Emergency Fuel System Check I ran a series of test at Batumi (Altitude 37 Feet, Standard Pressure), using V1.5.2.48162.126 of DCS. With each test I changed outside temperature, starting at -50°c and worked up to +50°c in 5°c intervals, noting the max RPM achieved with both Normal and Emergency fuel selected. Then I plotted the results (red line) on to the graph from the manual. The rpm does drop with temperature, but as you can see it's way off, less than 100% RPM only being achieved once below -36°c. The manual states that the emergency fuel system is set to give 99% rpm on a 100°F (+38°c) day. and with a temperature hotter than +38°c, to be careful not to over speed the engine as higher than 100% rpm could be achieved. The manual also states I take this to mean the sudden fuel surge when the emergency system kicked in would send the exhaust temperature soaring way above limits if the engine wasn't already at a high enough rpm (or at a low enough idle rpm so the EGT would remain within limits). If you switch the Emergency Fuel on at say 70% or 75% nothing particularly abnormal happens at the moment, the EGT hardly changes. This is mentioned again in the Emergency Procedures section, if it was considered safer to ditch straight ahead, rather than try switching the Emergency Fuel switch on below 80%, the consequences of doing so must have been fairly catastrophic! Lastly, when switching back to the Normal fuel system (switching the Emergency Fuel switch Off), there should be a bigger drop in RMP initially, because the main fuel regulator took time to recover from the disabled condition. At the moment switching from Normal to Emergency and Emergency to Normal both cause same small rpm drop. Summary of differences and problems. 1) The maximum engine rpm with the Emergency Fuel system engaged needs adjusting to match the temperature graph. 2) Switching the Emergency Fuel switch On below 80% rpm (not including idle) should cause dangerous engine overheating or compressor stall. 3) Switching from Emergency Fuel to Normal Fuel should cause a bigger rpm drop than going from Normal to Emergency.
AH_Sid Posted December 21, 2015 Author Posted December 21, 2015 Perhaps it also worth noting the difference between Warnings, Cautions, and Notes, as defined in the manual.
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