I have just been talking to a friend who is current on Spitfire MKVIII,XVI,P40E,P40F and P51D and the Harvard/T6, Wirraway and Hudson. His day job
is an airline pilot, his Warbird flying is with the Australian Temora collection and also flies for a number of Warbird owners. Below is a summary of the conversation.
The discussion was to determine -Ve G effects and cut outs and RPM fluctuations and how they compare to what we have in COD.
COD RPM FLUCTUATIONS
On RPM Fluctions he was quite adamant that in the Spitfires which are running Hydraulic Constant Speed units the RPM is "Rock Steady" throughout a display. Now the MKI,MKII and Hurricane both have Hydraulic CSU's that are pretty much the same as those fitted to the MKVIII and XVI. The bottom line is we shouldn't be seeing ANY of the fluctuations we see at present.
Interestingly he made the comment that the Merlin powered P40F (currently the only one flying in the world) that has an Electric CSU is not so stable. In a typical display with fixed prop lever position he says the electric CSU is slow and this results in RPM fluctuations of around +-150RPM over 2-3second period. The Allison P40E he flies has an Hydraulic CSU and like the Spits is also rock steady.
COD -Ve G CUT OUT
Now obviously the Spit VIII and XVI don't have an issue with -Ve G but the Harvard he flies does. It suffers similar issues that the early Merlins do. I asked him at what G value does the engine start to cough ? The answer was 0G. As long as the G is positive he said there were no issues. Normal flying is unaffected by the cutout phenomena. This is the best level of information we have at present. This is also backed by a separate reference from a UK Harvard pilot spoken to by sternjaeger and referenced in an earlier post. It bolsters the position that what we now experience is too sensitive.
I post this here for info.
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