So would I operate LOP without an EGT, sure by setting the fuel flow. If the engine runs rough, richen up until the roughness disappears and then increase the fuel flow by about a GPH. If it runs smooth or smooth enough, just operate at the LOP fuel flow. In my IO520BA, 12.5 GPH is 65% LOP. In the IO550B, I would use 13 GPH.
I think many engineers reckon that EGT temperatures are more use when leaning than CHTs because the CHTs lag on the temperature curve. In the Baron 58, the PA 44 and the Seneca 3 there were fuel flow meters and we learnt to set a particular fuel flow for each stage of flight through power and mixture settings .In the DA42 you set 100% for take off and initial climb, 90% for the rest of the climb and 70% in cruise.
On the G1000 there is a procedure for leaning but I have never used it.
As @GA_Pete wrote in the Robin 400 leaning didn’t appear to do much of anything so most club pilots didn’t bother. The worst problem we had was fouled plugs on occasions but no real engine problems right up to the overhaul at 2400 hrs.
There is another advantage of cruising LOP: there is very little CO produced, only CO2.
On a flight over the North Sea, at night in IMC, I had an exhaust tube blowout, a piece about the size of my palm fell off. I could immediately smell exhaust gases. I still had more than half an hour to fly to the nearest airfield. Checking the engine instruments, the engine was running fine but blowing exhaust out of the side gills.
I don’t know if I would have survived if not LOP.
Lastly, on my aircraft, with current fuel prices, at TBO of 2000 hr, the difference between ROP and LOP fuel flows will pay for more than half of the overhaul.
Lots of these old engine myths stem from WW2 accelerated training.
Great thread, I’ve been curious about this for a while now and have read quite a bit about it and run LOP for longer flights.
@NCYankee can you give a brief description or a link to how one determines proper fuel flow at appropriate LOP settings?
This makes perfect sense, but I’d like to walk through the workflow of it without making any assumptions in ignorance. Thanks
It’s still incumbent on manufacturers to be reasonable in considering failure modes. Just as it’s also reasonable to expect the same in methods taught in flight instruction.
We have reliable backup instrumentation to determine power output. You got ASI and your eardrums among other things. What have you got for mixture? You can certainly detect vibration.
It’s quite possible to operate these engines at or near take off power with close to peak egt or lop but everything would have to perfect, and maybe you would need some modification etc. But what would be the failure rate?
At 65% or lower if the fan spins and it sounds ok. You should not have issues as the margins are increased. You still have the issue that you must adjust mixture to safely achieve take off power, in the case of a baulked landing.
Running ROP is not being safe and LOP less safe or more difficult. That is a bit emotive. They can both have modes of failure as part of a system of operation.
IMHO as a starting point ROP is probably best from an ab inito point of view.
gallois wrote:
I think many engineers reckon that EGT temperatures are more use when leaning than CHTs because the CHTs lag on the temperature curve
The purpose of leaning is to get CHT down because for most piston engines CHT is a more relevant limitation that EGT.
One uses EGT (or in some engines/airplanes TIT) to do it because CHT is to slow to practically lean.
And as NCYankee pointed out: If you know your aircraft well you don’t care about EGT and TIT at all but just do the power and fuelflozw setting and you end up in the right spot…
AF wrote:
@NCYankee can you give a brief description or a link to how one determines proper fuel flow at appropriate LOP settings?
For engines with a compression ratio, divide HP by 14.9. So my IO520BA Maximum HP is 285. At 65% power is 185.25 HP. Divide by 14.9 = 12.43 GPH.
For an IO550 with a maximum HP of 300, 65% = 195 HP, divide by 14.9 = 13.09 GPH.
I use 12.5 and 13 GPH respectively because they are easier to remember.
You have to take into account the current density altitude. In wintertime this may well be below sealevel. Your engine will need more fuel if the air is more sense.
dirkdj wrote:
You have to take into account the current density altitude. In wintertime this may well be below sealevel. Your engine will need more fuel if the air is more sense.
I know it is an unintentional typo, but my air never makes sense. :)
