Closed Cowl Flaps for Quicker Warm Up

[201er]

I've been wondering if it's ok to leave the cowl flaps closed to experdite engine/oil warm up while idling on the ground on cold days. Someone told me not to do that because closed cowl flaps lead to uneven cooling of the engine. What do you guys think? Any tips for improving warm up when it's cold and you actually need the heat?

[scottfromiowa]

I do it.

[Gone]

Me too.  Its cold up here in the winter.

[M016576]

Me 3

[GeorgePerry]

it't unanimous!

[201er]

Ok. Anyone disagree or know a reason not to?

[PTK]

I guess it depends on how cold is cold.  Normally I preheat, start and perform ground ops as per POH, meaning cowl flaps open. Once it is preheated and started I don't think it will cool down at that point. I take-off half open.

[jetdriven]

The only disadvantage is it might cause uneven airflow and hot spots on the cylinders.  However I have no data to base it on and I have forgotten to open them them after starting up a couple times, so perhaps it's no big deal after all.

 

I do takeoff with them in trail however.   

[garytex]

As a newb, I've been reading the operators manual for the Lycoming 0 and IO 360 family, it says to warm up with cowl flaps open, 1000 - 1400 RPM, Prop in fine pitch, full rich, (which advise I'm going to ignore) for the above stated reason, hot spots.

Happy thanksgiving, 

Gary

[PTK]

You should get into the habit of leaning very aggresively for ground operations. 

[Seth]

The Missile has no cowl flaps.  The F Model did, and on cold days I would keep them closed to help the engine warm up.  Once in the green however, I'd open them into trail for takeoff and climb.  As full power produces a lot more heat (and the sheer volume of cool air passing over the engine at flying airspeeds does indeed act as a coolling agent).

I also always used to open the cowl flaps after landing for the taxi to the ramp/tiedown/hanger, and then close them after shutdown.

-Seth

[rbridges]

what about the opposite?  Is opening the cowl flaps on shutdown to help cool the engine?  I've caught myself forgetting to open them when I land.

[jlunseth]

Quote: garytex

As a newb, I've been reading the operators manual for the Lycoming 0 and IO 360 family, it says to warm up with cowl flaps open, 1000 - 1400 RPM, Prop in fine pitch, full rich, (which advise I'm going to ignore) for the above stated reason, hot spots.

Happy thanksgiving, 

Gary

[RJBrown]

Overcooling is as bad as over heatingin its own way. I  don't drop the cowl flaps until I see oil temp. On a "cold" day in Kerville things may be different but if you need preheat you need to keep the flaps closed initially. The longer an engine is below temp the more wear you get. A good preheat and closed flaps are best. Leaning aggressivly during warm up is good advice.

[201er]

I'm curious if I've been leaning too aggressively to get the best warm up possible. I run the engine at 1000RPM and pull the mixture out as far as it will go before there is an RPM drop. I wouldn't be surprised if this is well LOP (although I've never actually checked). Would it in fact be better to be 50ROP to gain the maximum heating possible during warm up? Or is this all different at such a low idling power setting?

[Jeff_S]

Quote: 201er

I'm curious if I've been leaning too aggressively to get the best warm up possible. I run the engine at 1000RPM and pull the mixture out as far as it will go before there is an RPM drop. I wouldn't be surprised if this is well LOP (although I've never actually checked). Would it in fact be better to be 50ROP to gain the maximum heating possible during warm up? Or is this all different at such a low idling power setting?

[Shadrach]

I do not warm up with cowl flaps closed based on the POH and recommendations from the APS guys. While I've not taken the APS course, the guys teaching it have all stated that their data has shown that it does in fact increase the potential for uneven heating.  It's SOP for me to conduct all ground ops with cowl flaps open.  I typically open my cowl flaps when I drop the gear; the engine is already cool at that point (CHTs ~300 or less).

Randy, I appreciate what you're saying, but I've been told that CHT can vary as much as 200 degrees on the same cylinder dependent on conditions and where the measurement is taken. I think that uneven heating would be far more detrimental than the extra 5 mins of cooler operations required to warm the engine with cowl flaps open... 

[mooneym20d]

In Massachusetts, on 25 degree f days and below, I lean, lean, and then lean some more. I keep the cowl flaps closed until the run up. By then, (about four minutes) I can see the oil temp begin to rise. I open them during the run up. The oil temp is in the green by the time I reach the hold line. The cowl flaps remain open until I reach 120MPH on the climb and reduce power to 25mp, 2500 rpm. I have a GEM 602 and everything stays on an even keel. I have an M20E that was converted to a J firewall forward. Hope that helps.

[rbridges]

Quote: mooneym20d

I have an M20E that was converted to a J firewall forward. Hope that helps.

[jetdriven]

I have  friend with a 1966 E and a real 201 cowl and it is every bit as fast as our J, I'd say a couple knots faster even.  It handily outclimbs ours as well.

[rbridges]

Quote: jetdriven

I have  friend with a 1966 E and a real 201 cowl and it is every bit as fast as our J, I'd say a couple knots faster even.  It handily outclimbs ours as well.

[mooneym20d]

The other day, I did a five mile circuit N-S-E-W a few times. I was at 6,500 with 24 inches and 2500 rpm. I leaned aggressively and got an average ground speed 166 kts via the gps. I have a LASAR smooth belly, 201 windshield and every other speed mod known to Mooneys. The initial climb is 1100 fpm at 90 mph indicated. The plane is very light and very fast for a four banger.

[jlunseth]

To lean for taxi, lean for peak idle rise, don't worry about ROP or LOP.  To do this, set your throttle to, say, 1200.  Then lean out and watch the RPM's increase.  When they stop increasing you have reached peak idle rise, and that should be your idle setting.  If the engine falters after awhile, just enrich the mixture a little.  Your idle rise should be around 75 rpm's from full rich.

[Parker_Woodruff]

Lean as far as you can on the ground to keep the engine from stumbling.  Max RPM is a good reference.

[201er]

Max RPM is the equivalent of best power then?