Engine question for pilots

[scottcolbath]

I flew in a Cessna 182 this week. It was a pretty nicely set up aircraft (N918RR). My friend who took me up is a pilot with Continental/American/whatevertheyarecalledthisweek. He is actually retiring at the end of this month. He hit the 65 year old mandatory retirement.

I noticed when prepping for takeoff, he had to adjust the fuel trim. Bring the engine up to 1,800 RPM, then futz with the knob until engine RPM went higher, then when RPM dropped, back off a tiny bit and set it.

So, upon further poking around on my part, I learned that the engine is a IO-540 SER    made by Lycoming. This engine is fuel injected.

Someone explain to me why setting fuel trim is needed on a fuel injected engine. Is this not smart injection, such as a closed loop system? Or, is it purely old school mechanical injection, which could explain the need to set fuel trim.

Also, let's say you set the trim at 2,500 Ft. which is about the altitude at Wickenburg. Does that setting sort of adjust as altitude/air density changes?

S.C.

[Chris Janes]

Scott,
What was happening during the engine run up is the correct fuel to air mixture ratio was being set. If the fuel is set too rich during takeoff then essentially performance from the engine is being robbed, especially when departing out of a high elevation airport with warm temperatures. By having too lean of a mixture then you run the risk of torching the cylinders because there is not enough fuel to cool them. When the fuel mixture is rolled back and you get a slight rise in RPM the engine has  more air  then fuel in the mixture equation so the engine has "peaked", the pilot will typically give the mixture a couple of extra turns back in with fuel to get the approximate best fuel/air mixture ratio this getting maximum efficiency and performance from the engine. The procedure applies to most single engine piston aircraft regardless if it's injected or carbureted..
Hope that helps.
Chris

[scottcolbath]

Scott,
What was happening during the engine run up is the correct fuel to air mixture ratio was being set. If the fuel is set too rich during takeoff then essentially performance from the engine is being robbed, especially when departing out of a high elevation airport with warm temperatures. By having too lean of a mixture then you run the risk of torching the cylinders because there is not enough fuel to cool them. When the fuel mixture is rolled back and you get a slight rise in RPM the engine has  more air  then fuel in the mixture equation so the engine has "peaked", the pilot will typically give the mixture a couple of extra turns back in with fuel to get the approximate best fuel/air mixture ratio this getting maximum efficiency and performance from the engine. The procedure applies to most single engine piston aircraft regardless if it's injected or carbureted..
Hope that helps.
Chris

That's all stuff I sort of assumed. I understand engine operating principles and the effects of air density, temprature and other factors. My issue is how can you set something on the ground, and expect it to work at altitude? Once it's set on the ground, is this baseline then compensated as altitude and air density change? If so, how does it work with this particular engine/FI setup?

Does this engine have any sort of electronic engine management, or is it all mechanical, like old school fuel injection?

S.C.

[Dave S.]

Scott,

I believe you're in the realm of 'old school fuel injection'.  Aircraft engine manufacturers (and most other aviation oriented manufacturing) tends to stick to a very conservative path.  It's sort of problematic if something goes wrong when you're at altitude.  If you leave the mixture adjustment to the pilot (i.e. old school mechanical), he can't (nor his family) come back and file a lawsuit if there's a bug in the non-existent software that results in a tragedy (i.e. the recent A400M incident).

Depending on what you guys did on your flight, I'm guessing your friend also adjusted the mixture ratio as you climbed in altitude.  If you didn't climb too high, just playing around in the weeds, then he may not have adjusted it at all.  Of course, if he adjusted on the way up, he should have reciprocated during the decent and as he prepped for landing.

[Chris Janes]

Many high performance engines have digital engine monitoring systems installed so the pilot is getting information on each engine cylinder head temperature(cht), exhaust gas temperatures(egt), fuel flows, and depending if the engine is turbocharged or not, turbo inlet temps(tits). The pilot can take  information from performance charts and set fuel flows to get a certain egt temp based on the pressure altitude the aircraft is at, thus getting the best fuel burn while keeping all the temperatures within the parameters of the performance charts. On the Cessna-340 I fly, at 16,000' I set fuel flows to about 19 gallons an hour per side and that typically keeps the CHT's at 390(c) degrees and  the egt's at 1500 all with in safe operating zones. I use the digital read outs and set everything according to the charts as opposed to getting a drop in rpm to determine fuel mixture.

[scottcolbath]

Very interesting. Thanks guys.

Interesting that nobody has tried full blown electronic engine management with hardware/software redundancy built in. I'd think there's lots of fuel to be saved when the fuel/air mixture can be precicely adjusted several hundred times a second.

S.C.

[Chris Janes]

If I'm not mistaken I believe the Diamond Twinstar has computer driven fuel management on its diesel engines. It has incredible range and burns a total of 7 gallons an hour.

[scottcolbath]

If I'm not mistaken I believe the Diamond Twinstar has computer driven fuel management on its diesel engines. It has incredible range and burns a total of 7 gallons an hour.

That's the kind of thing I'm talking about. It seems like something like this would have proliferated its way through the aviation industry a long time ago, when this sort of technology was established as reliable and efficient.

S.C.