I have just returned from a packed out (above MTOW) APS class this weekend. Boy am I wrecked! Owners, commercial operators and everything from a Jabiru powered U/L to a C421 owner, Chieftan and Airvans……what a great mix!
I am most pleased to see this thread and some good advice in it. I have a few thoughts, first of all to anyone reading it,PM me your details and I will keep you informed when the next class will be.
First of all a little mind game. A previous student reports that after the class and learning the "really old way" of operating his C182 (IO540) he was able to do the following things. Burn way less fuel, have more range, cooler CHT's and actually have a higher IAS/TAS. How is this possible when WOT/2400 and ROP produces more HP than when he was WOT/2400 and
appropriately LOP?
The simple answer is he could now contain CHT to a reasonable level with the cowl flaps closed and they remained lower. A win / win I would say.
The secret to all this lies in the following. First of all you need to get your Fuel/Air ratios sorted out. This then balances up the heat IN part of the equation. Then you can work on a level playing field at getting the baffles etc sorted and thus the heat out part of the equation fixed. What is left is the cruise CHT, and if you have the first two sorted the cowl flaps can be closed.
DO NOT go monkeying around with the injectors unless you work for GAMI or your last name is Denyer and you have a flow bench.
SLIGHT CORRECTION FOR A STATEMENT ABOVE
It is a commonly held belief that the higher the power higher the CHT. this is not true. In fact at 500 feet running WOT/2500 and 80dF LOP generating 82-84% power my CHT's are 30 or so degrees cooler than FL130 WOT/2400 and appropriately LOP. Someone above (not radar identified) mentions the air density.
It is also true that even generating the SAME horsepower at the same altitude but using two different methods of doing so will result in different CHT's. This is all to do with the effective timing of the engine controlled by mixture, resulting in a different placement of ThetaPP, which results in a higher or lower peak pressure. It is the magnitude of the peak pressure that determines the heat into the cylinder head, and not the HP or fuel flow. This is not what we are taught in flying schools.
In the photo on the front cover of the APS class manual you can see if you look closely some interesting data. Besides weather, look at the engine instruments. Both engines were generating the same HP, the pilots feet were flat on the floor and the skid ball in the middle
Any questions drop me a line!