Startup idle rpm

[susang777]

At the risk of stirring up controversy, I'd like some opinions on startup engine procedures.

I noticed that on the last day of the 170 convention this year, when many beautiful 170s were hightailing it out of there to catch a break in the weather, that there was a distinct difference in the startup procedures.

Some pilots very carefully and thoroughly went through pre-flight procedures and let the engine idle at low speed, then went off toward the runway.

But others did quick pre-flights and then revved up the engines and off they went, without much idle time. I have noticed other pilots where we tie down revving engines obviously over minimums also, then taxiing off.

I read in the owners manual that the engine should be idled for a period of time first before taxiing. I read the same thing in owners manuals and textbooks on car maintenance. (I have a car with 230,000 miles on the engine, still going strong. We hope to retire it soon for use only as an airport taxi/car at a nearby airport we fly into regularly.)

So am I wrong about this, or will the engine last longer and be in better shape if the idle times before and after flying are properly observed? This isn't just an idle question, as I'm going back into flight training again soon.

[N1478D]

Your cylinders are a larger diameter at one end than the other, like the choke on a shotgun. With different metals expanding at different rates, cramming a cold piston up in a choked cylinder will induce unnecessary wear. If the parts are allowed to warm up to an even temperature, it is much easier on the parts. You can idle at too low of a speed and not sling enough oil around, and a person could sit and idle so long that things like plug fouling could be a possibiltiy, so like every thing else - just right works best.

That's great that you noticed the differences and wondered about the possible results. Flight schools usually get more than TBO on their engines in my opinion because they are flown many hours every day, even though students get in there on 20 degree days and start off at 1900 RPM, etc. On aircraft that are flown less, rust and other problems make start up procedures, etc, even more important. Sounds like you are going to have an engine that is well taken care of.

[GAHorn]

While some engines have "choked" cylinders, our C-145/O-300's do not. But Joe's comments are nonetheless valid. (Lyc's have choked cylinders.)
Pistons are always smaller diameter than even the tightest choked cylinders...it's the rings that must slightly,...ever so slightly,...compress to a smaller diameter during the travel to the top of the stroke. Those rings only get lubrication by oil-sling from the crankshaft journals.
Accordingly, the engine (all engines in my opinion) should be started at it's lowest practical rpm setting and allowed to idle there until oil pressure is indicated. (Our oil pressure sensing and relief valves are located at the end of the oil gallery system, so by the time oil pressure is indicated the galleries are full of oil and air has been expunged. The Operator's Handbook, by Continental suggests 800 rpm for a starting rpm. This should be in the vicinity of 1/4" open throttle.)
When oil pressure is indicated (within 30 seconds min.), the rpm should be increased to 1200 rpm for the warm-up. This speed also allows the generator to come online for recharging the battery, and for proper voltage for turning on the radios. It also allows oil-sling to lubricate the upper cylinders, rings, and cool pistons. Avoid idling for long periods (more than 1 minute) below 800 rpm due to lack of cylinder/piston lubrication. Contrary to popular thought, this is even more important when oil is cold and doesn't wish to "sling". By bringing rpm up and slinging oil up onto the lower surfaces of the piston, the oil is warmed up more quickly. (Like the Apostle said, "All things in moderation." I wouldn't operate an engine with starting temps below freezing without pre-heat of the engine or at least without pre-heating the oil and pouring it back in. I would never use an oil dilution system but that's an operating luxury I can afford down here in the South.)
I use this time to obtain local ATIS, clearance-delivery, and organize my cockpit for the flight. It can also be used for taxi purposes, but I avoid high rpm (more than 1700) break-away from a tie-down until I have an indication of oil temperature. (My oil temp, like most, begins at 100 F.)
By the way, notice that the Operators Handbook indicates that mag checks should occur at full throttle, not the 1700-1800 that most folks use. (100 rpm max drop of any mag.)
The Operators Handbook (C-series 6-cylinder engines)is available from Spruce 877/477-7823.

[Bruce Fenstermacher]

Susan, you complimented me in a private email on my preflight procedures which I though was odd cause this is one area which I usually don't spend enough time. Only because I was on vacation and relaxed and in a strange place did I do what seemed like a good preflight/engine warmup. When in strange places I like to think through my taxi and departure which sometimes helps kept me from looking like an idiot.

As George has discribed there is a good discription in the Aircraft Operators Manual of the start and warmup procedures. I try to follow this pretty close except for the lenght of times given. At home after idling at about 800 for 30 seconds or so and seeing oil pressure I usually start my taxi. About 2 minutes later I'm at the end of the runway and do a mag check at 1600 which is what the Aircraft Operators Manual says George.
I rarely if ever wait for a rise in oil temp on the ground.

In general when operating on the ground I operate the engine at the least amount of power I can to get the job done. No need to go blasting all over the place. Always be mindfull where your prop blast is going and be considerate of others planes.

[susang777]

Thank you! That was most instructive and helpful.

Since the engine is so costly to rebuild/replace and I do not wish to have engine failure in flight, I think it is important to learn how to treat it right. N3440D thanks you, too!

[GAHorn]

Susan, you complimented me in a private email on my preflight procedures which I though was odd cause this is one area which I usually don't spend enough time. Only because I was on vacation and relaxed and in a strange place did I do what seemed like a good preflight/engine warmup. When in strange places I like to think through my taxi and departure which sometimes helps kept me from looking like an idiot.

As George has discribed there is a good discription in the Aircraft Operators Manual of the start and warmup procedures. I try to follow this pretty close except for the lenght of times given. At home after idling at about 800 for 30 seconds or so and seeing oil pressure I usually start my taxi. About 2 minutes later I'm at the end of the runway and do a mag check at 1600 which is what the Aircraft Operators Manual says George.
I rarely if ever wait for a rise in oil temp on the ground.

In general when operating on the ground I operate the engine at the least amount of power I can to get the job done. No need to go blasting all over the place. Always be mindfull where your prop blast is going and be considerate of others planes.

The most restrictive limits are the ones most would agree are safest. I was not quoting the Aircraft Owner's Manual (is that what you meant, Bruce, rather than the Aircraft Operators Manual? I'm unaware of any Aircraft Operators Manual for our airplanes.)
I was quoting the engine manufacturer's "Operator's Handbook" for C series, 6 cylinder, Continental "Red Seal" Aircraft Engines. It specifies the more grueling magneto check performed at full throttle.
In addition, the Overhaul Manual for our Engines, in Table XII, also specifies magneto performance must not drop more than 100 rpm at Full Throttle. I tend to believe the engine mfr has more expertise in operating their engine than Cessna would. (By the way, in this game of "tit-for-tat", I'm saying do as they say,...not do as I do!)

In a serious note, magnetos, ignition harnesses, and spark plugs are all being checked in the run-up. Many times a spark plug or harness will operate just fine at moderate rpms, but break down under the pressures of high rpm and full cylinder pressures. Continental recommends performing that check as the last item before releasing the brakes while in position on the runway.

[Alterfede]

Very interesting posts here. I learn a lot with all of you!!!
You will be amazed of the amount of checklist available in argentina, i think 1 per pilot. Of course most pilots/owners dont have the source for that kinda information, or dont want to search, as we see there a places like this with plenty of data about planes and their operation.

[N1478D]

While some engines have "choked" cylinders, our C-145/O-300's do not. But Joe's comments are nonetheless valid. (Lyc's have choked cylinders.)
Pistons are always smaller diameter than even the tightest choked cylinders...it's the ring

Most times the piston travels with the rings!

Teledyne Continental Aircraft Engine Service Information Directive SID97-4C Figures #1 & #3 both show the area of choke in the cylinder diagram. Some Continental cylinders have choke. After looking further, the piston diagram for the C Series, all O-200 and O-300, figure #7, does not show choke. Very interesting. Straight Barrel No Choke. Straight Wings - Straight Barrels!

[Bruce Fenstermacher]

George, the Aircraft Owners Manual is what I meant. Got to get up pretty early in the morning to get one over on you.

[funseventy]

Susan,

I give quite a bit of instruction to people who do not have tailwheel time. It seems they are all excited about the ability to swing the tail; this is exciting when the run up area or runway turnaround is small. But they want to use it every time they can. This means blasting people at a flyin or turning the tail towards an open hangar door to make it easier to push in. I simply teach that there is a 200' stick attached to the tail, don't hit anybody or thing with it. This helps when trying to meet people in a positive manner at a fly in, while at the same time keeping you from having to sweep the hangar out as often.

Good luck with your flying,
Kelly

[susang777]

Somehow I never thought of swinging the tail around as fun, although I have noticed some people doing that. I think they tend to be men.

I'm pretty logical and serious about flying. I'm also still a bit afraid of it, although that's getting steadily better as I learn more and gain experience with it. It's irrational, I know, but there. I think once I understand flying and can control the plane better, it'll be fine. It's not knowing what to do to avoid mistakes or accidents, and how not to cause a problem that is what scares me the most, and those are things that are standard instruction. I also read articles about other people's mistakes in the hope that I will learn from them.

Thanks for the good wishes.

[N1478D]

Susan, you do not need to worry until you stop being afraid! Just an opinon, but would believe that the pilots who are not afraid are the majority of pilots having accidents. It is a sign of intelligence and common sense that you have fears. As your experience grows, the ability to manage the risks, and skills like spot landing in to a football field during an engine out as an example, will change the fears to an almost enjoyable part of your aviation experience. The ability to control the airplane at the edge of it's envelope can only come with experience, training, and staying current. That is one of the parts of flying that prevent it from ever becoming boring and makes it a never ending very enjoyable activity. Your instructor will not allow you to hurt yourselves. When you solo it will be your fears that will keep you inside of your ability envelope, sometimes pushing out towards the edge of that so you safely expand the envelope. Fly and enjoy and don't worry about the fears, they are there for a reason.

[zero.one.victor]

This talk about a little fear being a healthy thing brings to mind a conversation I just had a couple days ago with a pilot at my airport. A few months ago,his Cherokee had a partial engine failure (broken-off valve stem) a couple minutes after takeoff.He 180-'d & chugged back to the airport without mishap. I happened to stop by the local mechanic's where his freshly-overhauled engine was being hung back on the airplane. I asked him if he'd had to have the upholstery cleaned after the incident. A fairly low-time private pilot (and an attorney!),he proceeded to tell me that his heart rate never even went up,he just went into emergency mode, and all about how he was running his emergency checklist,etc just as cool as a cucumber. I told him he was a better man than me,when mine broke a connecting rod in-flight my heart just about leaped out of my chest!
He's either the bravest,calmest man I know (doubtful) or the biggest liar in town. Like I said,he's an attorney so you can probably figure out my opinion..........

Eric

PS: any lawyers on board here (like jerry),don't get your panties in a bunch about my comments............