Vinny wrote:
Marin wrote: I believe in the case of the PT6A-135 turbine I was talking about earlier, the only things that were changed to derate this 750 shp engine to 600 shp were the power settings used, N1, N2, etc.* (I think that's the correct term for the shaft rpms in a turbine--- I haven't flown one for a long time).
Marin
So then in affect the change in*the power settings is like*putting a governor in place thus chopping 150shp.* Now the maintenance schedule can be changed due to the lower RPM's.
Ken,
That was what I was talking about.* Three different injectors three different*HP ratings.* But something mechanical or electrical (new engines) has to be changed.
Thanks guys, I didn't see that in Johns post but I felt that was the case.
Vinny, in many aircraft there is a guage that measures the "work" or load of an engine.* In recips with variable pitch propellors, that would be the manifold pressure guage.* In turboprops, that would be the torque guage(with respect to temps). In pure jet, it would be %RPM(again with respect to temps).* In most of these, you can "overboost" an engine simply by advancing the power lever.* What determines "overboosting" is what is in the manual and/or placarded on the guage.* SO the FAA may say your maintenance interval is "this" if you run the aircraft in this manner.* There are operators of the same exact airframe and powerplant that have maintenance plans and intervals that are totally different.* ANyway, I am oversimplifying it a bit.* In a turbine engine, generally they are capable of doing A LOT more work than they are rated for and many times some of that power can be recognized/recovered with paperwork.
How does this apply to diesels and boats.* In reality, it doesn't really.* In theory a simple placard(colored arcs...ala "red line") at 3200RPMs on a 3600RPM motor....or maybe a restriction that you are allowed to operate from 3200-3600 for no more than one hour.....just things like that.* Pleasure boats are different in that once you own it, it is the owner that is responsible for maintaining it or not.* IN aircraft, you are required by law to maintain it.
My boat's max continuous rating is
190hp@3100rpms*with an alllowance to run at
240hp@3300rpms for no more than an hour.* So do I have a 190hp engine uprated to 240 with restrictions or do I have a 240hp engine derated to 190hp???* The manufacturer expects me to adhere to those numbers and produces maintaenance intervals based on those numbers.* My boat is also underpropped and it will make close to 3600RPMs when everything is clean.* SO most likely, it is making even more power at that RPM even though Yanmar does not recognize that(fuel cutoff is at 3800) nor would they "support" that type of operation.
Aircraft operators have a very close relationship with the FAA and the manufacturer of the plane.* Many times, all it takes is trends/history to apply to the FAA and ask for a longer interval or more power and if the operator has a good case backed up by good engineering, then it may be granted.* And yes, these days it may require plugging a laptop into the engine management computer to tell it to allow more fuel,etc.* In the old days, if you firewalled the power levers in a jet it would give you WAY more than rated power and this is where the term "overboost" comes from.* Newer computer controlled engines do not allow this.
-- Edited by Baker at 22:41, 2008-10-14