In that case, and I know noise abatement procedures and just noise for the pax can be a consideration, I'd probably follow the book procedure. If it says to leave it wide open (no limitation on takeoff power), I'd do that. If the book says there's a takeoff limitation, I'd do that.
-mini
Agreed. I have been on the sidelines of this for the last few pages, but I decided to chime in over a cup of coffee this morning.
On some piston engines there's a Power Enrichment Valve which gives more fuel flow (more cooling) at WOT. It's not a function of MP, but of throttle position. There are also installations where at full throttle the boost pump is activated (again, not a matter of MP, but of the throttle being mashed in the panel), again, giving additional cooling. In those airplanes, you better believe there is a good reason to climb at full throttle.
On the IO-550s I flew for a living up until last month, such a device does not exist. However, I experimented with many different climb profiles during my time flying these aircraft and I determined that the most efficient way to climb is at WOT. WOT climbs result in better performance and cooler CHT in the climb. You get to altitude faster, which results in a lower noise signature, and you arrive at cruise with more energy, which results in less time spent accelerating, which, in turn means that you can set up a cruise power setting sooner. FWIW, I also flew planes with IO-360 and found the same results.
As far as noise abatement, if you're flying anything but a Cirrus, you can leave it at WOT and dial the prop back to 2600 or 2500 if you wish. In a Cirrus, you're kinda stuck. I would climb at WOT anyway. That airplane has the performance to get 1000fpm or better down low; I would WOT it and get up to altitude more quickly.
For those concerned about blowing up an engine, consider this: the IO-550 is rated up to 350hp in some applications. Pulling WOT with 310hp is not even approaching what the engine is capable of producing. In the installations I'm most familiar with (Mooney) we were only pulling 280hp in most applications (a handful were 310 conversions), which was even more comforting. All those models, even the turbonormalized Acclaim, are rated to run full hp 24/7/365 with no limitations.
Occasionally, I would run in to somebody who was afraid to go full throttle in one of my planes. "Think of it like a reduced power takeoff in a turbine - it helps them extend the life of the engine!" was the idea. However, this is not a turbine airplane; it's a piston airplane and needs to be operated with the proper technique and knowledge behind it to make it last a long time.
The IO-550 is a well-designed and tough engine if you operate it correctly. I have seen them with compressions in the 50s at 500 hours and I have seen them with compressions in the 70s with over 1000 hours. Fly it as it's meant to be flown and it will get you home.
edit: TF - I would say that if you're turning only 2660 on takeoff and climb that you need to get your SMPL adjusted. I would venture that your numbers are very close because your WOT numbers are lower than they should be. We used to see this pretty regularly. Sometimes governors need to be adjusted. If it's more than 20rpm off of book, I would take it in.
