How far do you lean while on the ground before takeoff

[photofly]

plug fowling was never a problem.

Is plug fowling where a chicken pops out of the exhaust ?

[Cat Driver]

F.O. to Capt.

Which came first, the chicken or the egg?

Capt.

Neither, it was the Rooster.

[Cat Driver]

Capt.

Why did the pervert cross the road?

F.O.

To get on the other side?

Capt.

No, he was stuck in his chicken.

[dpm]

If someone's reason for leaning on the ground is for when they forget the basics of the before takeoff checklist, that person has bigger problems to worry about than fouled plugs.

... or it's a genuinely-experienced pilot who's flown enough hours to know that safety comes from multiple layers of safeguards rather than a fantasy of personal infallibility.

[dpm]

I always preferred to have a cooler cylinder head temp on takeoff. The last thing I'd want to worry about on takeoff is an engine that is at its thermal limit (considering age of engine, students beating it up, etc.), and that thermal stress is even more pronounced at colder temperatures where shock cooling is a factor. To each their own though!

Normally-aspirated piston engines (at least) aren't capable of getting anywhere remotely close to CHT limits at idle/taxi power on the ground, regardless of where you set the mixture. You need to be at cruise power before you can generate enough heat to do them damage.

OTOH, an overly-rich mixture on the ground will generate a lot more carbon monoxide (hopefully not making its way into the cabin), leave significant lead deposits on your plugs, and cost you a couple of loonies more in fuel.

[ahramin]

I have a normally aspirated engine. If it's 25°C outside it will hit 400°F in under 10 minutes at idle.

[dpm]

I have a normally aspirated engine. If it's 25°C outside it will hit 400°F in under 10 minutes at idle.

What do you see at 75% cruise?

[ahramin]

65% is 320-360. I don't think 75% is much higher.

[photofly]

What’s the aircraft type? Ground temperatures are going to be heavily influenced by cowl and baffle design etc.

[dpm]

65% is 320-360. I don't think 75% is much higher.

On the ground, do you find that leaning has much of an impact on the idling temperature? In theory, the lowest CHTs should be when the mixture is extremely lean (just above cut-off); the next lowest should be full rich, and the hottest CHTs should be when it's only moderately leaned (e.g. 50–100°F rich of peak EGT). You should still have lower CHTs taxiing (very) lean than taxiing full rich, but as others rightly pointed out, a lot would depend on your baffling, cowl, whether you're facing into the wind, etc.

[photofly]

If you get very high cht while idling on the ground where the engine is generating maybe 5% of rated power I would be much more inclined to look at airflow issues than fiddle about with the mixture.

[ahramin]

Exactly. I have no idea what effect using a brutally lean mixture setting on the ground is having on my CHTs because they are climbing rapidly anyway.

Photofly the aircraft is a BD4. Same engine and about 1/3 the frontal cooling air intake area as a 172. Very good temps full power climb and cruise but on a hot day on the ground the options are to takeoff or shutdown. I flew a new RV6 last year with the same engine and the same problem but it also runs very hot in the air so a much bigger problem, especially considering it was 400 pounds lighter and 20 knots faster than mine.

[dpm]

Exactly. I have no idea what effect using a brutally lean mixture setting on the ground is having on my CHTs because they are climbing rapidly anyway.

Photofly the aircraft is a BD4. Same engine and about 1/3 the frontal cooling air intake area as a 172. Very good temps full power climb and cruise but on a hot day on the ground the options are to takeoff or shutdown. I flew a new RV6 last year with the same engine and the same problem but it also runs very hot in the air so a much bigger problem, especially considering it was 400 pounds lighter and 20 knots faster than mine.

Sounds rough. I don't have a CHT gauge on my Warrior II -- the O320-D3G is a simple, nearly bullet-proof engine, so I just make sure I cross-check the mechanical tach with an optical tach from time to time to make sure I'm not cruising over 75%. I also fly LOP-WOT, which the engine loves (given maintenance reports over the past past 15 years).

I do have an EGT gauge. It doesn't show absolute temperature, but it indicates far lower on the ground (the needle barely budges) than it does in cruise (typically 11:00 or 12:00 position), so CHTs should be proportionally lower. When I taxi over to the pumps without flying, my engine cranks more like a cold start than a hot start, also suggesting that it isn't heating up much on the ground.

[Kejidog]

I usually lean over and close the door, then Giv’er!

But seriously i got a bit of advice from another Continental O-300 owner was to lean on the ground extensively and if holding short run er up to 1700 like I’m doing a mag check. As long as there is nobody behind me that is what i usually do. Keeps my champions winning.