This discussion contains 3 of my 4 pet hates in piston engine management fairy tales
- power reduction on takeoff
- LoP fallacies
- Shock cooling, and
- running down the turbo after landing.
I was as ignorant as the next sprog product of a generic training program, until I hooked up with Chuckles & spent some time reading both Pelicans Perch and the POH / engine manual for the aircraft I was flying. I flew Chucks mighty Bonza and used the JPI and the LOP procedure under his tutelage. Then when I bought an aeroplane - before I even flew it the first time - I had a JPI installed so I knew for FACT what was going on under the cowls. Then I installed GAMI-jectors. I downloaded literally REAMS of data from the system and learned how to operate the engines properly, be it LOP or ROP. I would have thought with the profusion of engine data systems on piston-props these days, a lot of these would have been laid to rest. Apparently not.
Reducing power on initial climb:
All the normally aspirated flat aero engines, be they injected or carburetted, include in the design of the fuel system an enrichment device that adds extra fuel at full throttle, to reduce CHT and thus the risk of detonation in high power settings such as take-off. As soon as you pull the throttle back a little, like when you reduce to 2500rpm / 25" MAP, you shut off this feature and make the engine run hotter, just when you want it as cool as possible. LEAVE THE BLOODY THROTTLE ALONE! Once you level off set it per the power tables, and if that's above full throttle altitude pull it back just a bit to disable the enrichment. If you have decent engine instrumentation you can experiment and see the effects this stuff has.... like watching the EGT / CHT go UP when you pull the throttle back a little.
LOP / ROP:
Both are completely valid - if you take the time to learn how to do them correctly. The worst place to run an engine is 'a little rich' of peak EGT, or 'a little lean' of peak EGT. We use EGT for power setting because it responds almost instantly to changes and most aircraft have an EGT gauge. You need to be aware that the PURPOSE of EGT is to give an indication of CHT, which is what really matters. Of CRITICAL importance to understand is that peak CHT - where you absolutely DON'T want to be - is 50 or so degrees either side of peak EGT. Once you find the peak EGT with mixture adjustment you need to get well rich of it or well lean of it. You don't shag engines by 'running too lean' (bloody Whyalla) - you shag 'em by not running lean enough for LOP, or not running rich enough for ROP. Bear in mind also that the single point EGT gauge is only looking at one point in the 4/6/8 cylinder exhaust system, and not necessarily the hottest point at that. You REALLY need a multi-function all-cylinder digital engine monitor. I would not fly a piston-prop aircraft without one - well, not one I was paying the maintenance on anyway
Shock cooling:
Bloody BOLLOCKS. If the engine is running it's producing heat; nothing shocking about that. If it ain't running it's all cooling - no big shocks there (at least, not if the engine baffles are working). There are sound reasons to not yank the throttles closed at ToD, but shock cooling isn't one of them. Reverse-loading a drivetrain like a GTSIO gearbox is a bad idea, so slapping the throttle shut on a Titan in flight will not get you any brownie points with the boss. The greatest likelihood of a successful landing is in a stabilised approach, which precludes dirty great power alterations during the descent, which is best achieved by a planned steady power reduction throughout, not by pulling the levers to the back and sticking the nose down. All valid points, but shock cooling...
.... look to the JPI once again.
Running down the turbo:
starts when you reduce power during descent and by the time you're at low power on final the turbo is as cool as its gunna get. The longer the engine runs on the ground after landing, the hotter it gets (to a point) and sitting on the apron with the pax having a sauna while you 'run down the turbo' for 3 minutes is just silly. The JPI data proves it.
The test of an OWT or just plain ignorance is whether the other party can prove their position. All these points are eminently provable.
Rant over
