231 cowl flaps

[Vlakvark]

Would flying with the cowls open hurt the engine. I went flying on the weekend. Cowls close and EGT up to 400 on the #6. Lean the mixture, still increased in CHT. Open cowls to cool down. Temps down to 320 or so but #1 down to 240. 

Any help/advise

JT

Edited May 23, 2018 by Vlakvark

[carusoam]

Typically, trailing the cowl flaps open a small amount adds additional airflow...

The cost is slowing airspeed a minimal amount...

I know a guy with a K and good instrumentation experience... @kortopates

Lets include him in the conversation... 

All the extra airflow, may not be as well guided as when flaps are closed...?

Do you have the electric, or manual flaps?

Can you set them open an inch, or two...?

PP thoughts by an O pilot...

Best regards,

-a-

[Vlakvark]

Please do. Thank you!

[gsxrpilot]

Nothing wrong with keeping the cowl flaps open. But you might want to look into why the engine is running so hot. I fly a 252 and it runs pretty cool. But when I'm up in the high flight levels above 20K ft. I usually have to open them a bit to maintain proper temps in the cool air.

[LANCECASPER]

8 hours ago, Vlakvark said:

Would flying with the cowls open hurt the engine. I went flying on the weekend. Cowls close and EGT up to 400 on the #6. Lean the mixture, still increased in CHT. Open cowls to cool down. Temps down to 320 or so but #1 down to 240. 

Any help/advise

JT

From 1993-96 I flew an '83 231 in Texas and in the summer it was just a given that most of the time cowl flaps would be at least partially open. The TSIO-360GB ran well but definitely ran hot. Where you are in Saskatchewan I wouldn't think you'd have to very often. I would definitely check your baffles. The Gee Bee baffle kit is so much better than what was ever used at the factory up until later years. The rear baffle material that they used back then gets lazy and folds back instead of forward letting air go past it instead of forcing it down over the cylinders.

(this was on an M20K Encore that I bought and the first thing I did was re-do all the baffle seals)

 

On Continentals your #6 is in the front though so you might need some cylinder work or a new cylinder. This engine very rarely ever made it past 1/2 TBO without a top end overhaul.

I hear that the -LB engine is a Little Better, the -MB engine is Much Better and have personal experience that the -SB engine is So Much Better. The 231 did not come from the factory with a intercooler but can be added which will help with the temps also.  Whatever you need to do to keep the cylinder head temps under 400, preferably under 380, do it. That might mean more fuel, not leaning quite as much, or cowl flaps open..

As far as the one cylinder at 240 - either that's a dead cylinder or your probe is bad. There's no way on that engine, if it is making power, that it's running at 240.

[AH-1 Cobra Pilot]

At my first annual, my mechanic suggested I replace the baffling as it was loose and floppy.  I did not pay super close attention to the CHT before that, but as I recall, it seemed to drop at least 10^o afterwards.

[jlunseth]

 The simple answer is no, opening the cowl flaps to help cool the engine does not hurt the engine.  It may reduce your airspeed a little.  But that’s what the cowl flaps are for.  Higher CHT’s can be any number of factors.  Whether the cylinders are getting properly cooled is one.  What mixture and power setting you are running the engine at is another? There is a half open setting on the 231 that works pretty well at cruise, you only lose a couple of knots. I have my A & P adjust the cowl flaps to trail (stay slightly open) during the summer, and to fully close during the winter.  What was your MP, RPM and fuel flow?

[DonMuncy]

It is common practice in 231s to adjust the cowl flaps about 1/2 inch or so open (when in the "closed" position), especially in the summer and especially in Texas. For this very reason.

[skydvrboy]

Is there any risk of damaging the cowl flaps if they are open over a certain speed?  My F has a placard that says not to open cowl flaps over 150 mph, but I'll admit, I've forgotten to close them in the past and exceeded that speed.  I have inspected them and not noticed any damage.

[kortopates]

A couple of things to consider:

1) Engine Monitor - Do you have a TSO'd primary engine monitor giving you CHT's like an EDM 900 or an advisory unit like an EDM 730 or 830? If the former, then one cyl will have a non-standard CHT probe that could be running cooler or hotter but off 30-60 degrees depending on the actual probe type. You need to take this into account and what cyl the non-standard probe is installed as it likely its installed in your #1 cyl since that is a common cyl for installing the OEM CHT probe preventing a standard probe from being installed. 

2) Min CHT temps- Continental's CHT limitations are from 250-460F. Although your POH wants you to keep CHTs at or above 250F at all times, we've learned a lot more about engine management since the POH's were written and Its fine to operate in cruise below well 250F. But what we should pay attention to is before going to full power we should increase power slowly or moderately to get all the cylinders to at least 250F before going to full power as well as oil temperature to at least 100F (which is even more important than CHT in these engine). This is usually very easy to do. (but important to keep in mind when practicing power off landing or glides to a landing).

3) Cowl flaps settings - The factory did a lot of testing with an Engineer at Continental to establish the closed cowl flap setting, which IIRC is in the Service Manual. They found if the cowl flaps were closed entirely, that in addition to cooling problems, it caused back pressure in the top of the cowling that actually caused a forward area of turbulence in front of the air inlets that significantly increased drag and decreased prop efficiency resulting in a several knot airspeed loss (I forget detail of precise number of knots but recall in the range of 4+ kts). The lesson they learned is that fully closed should actually be ~1.5" open, but see maintenance manual as my recollection may be off a bit.

Overall though, I can't agree more with the comments above to address any baffling issues. But it also just as important to make sure your engine is getting enough fuel at takeoff or max power in climb and to do a thorough mixture analysis to make sure your mixture distribution is adequate to prevent hot cylinders from to lean a mixture at climb power when IAS is low. I see a surprising number of M20K's with inadequate max FF. Fuel set up is suppose to be checked at every annual, but because of the specialized gauges needed to do it, it is often overlooked. It shouldn't be and if the plane does have accurate FF, it really simplifies the max FF adjustment too, making it much easier.

You'll notice of course that all performance data in the POH is based on Closed Cowl flaps because opening the 231 cowl flaps has a significant penalty - this was significantly addressed in the 252 and Encore models. But even opening them in trail is a 5 kt penalty with fully open a whopping 14 knot penalty. So you really want to make sure your cowl flaps are rigged properly and your baffling is in good shape.  The crazy thing about the performance tables, with showing only data for cowl flaps closed, is that its virtually impossible to run at max cruise power up high without the cowl flaps open in trail - that is if you care about cylinder longevity since the POH only cautions you to keep CHTs within 440F - which is too high! Which is what led to so many top overhauls.

Edited May 23, 2018 by kortopates

[jrwilson]

7 minutes ago, kortopates said:

 

2) Min CHT temps- Continental's CHT limitations are from 250-460F. Although your POH wants you to keep CHTs at or above 250F at all times, we've learned a lot more about engine management since the POH's were written and Its fine to operate in cruise below well 250F. But what the limit we should respect is before going to full power you should increase power slowly/moderately to get all the cylinders to at least 250F before going to full power as well as oil temperature to at least 100F (which is even more important than CHT in these engine). This is usually very easy to do.

One of mine likes to drop below 250 degrees too in cruise with flaps partially open.  Do you have a reference source for it being ok to go below 250?  It would certainly make me more comfortable...

[jlunseth]

9 minutes ago, kortopates said:

Overall though, I can't agree more with the comments above to address any baffling issues. But it also just as important to make sure your engine is getting enough fuel at takeoff or max power in climb and to do a thorough mixture analysis to make sure your mixture distribution is adequate to prevent hot cylinders from to lean a mixture at climb power when IAS is low. I see a surprising number of M20K's with inadequate max FF. Fuel set up is suppose to be checked at every annual, but because of the specialized gauges needed to do it, it is often overlooked. It shouldn't be and if the plane does have accurate FF, it really simplifies the max FF adjustment too, making it much easier.

Couldn't agree more.  The OP commented that he "leaned the mixture" and that caused the CHT to climb more.  I am suspicious that, as Paul said, the fuel flow is set up wrong, or that the OP was already flying at a power setting and fuel flow that was not good for the engine, and then leaned it more making it hotter.  

It could be a cooling issue, yes, but it could also be an engine management issue, running a turbo at a cruise power setting with the mixture leaned to right around peak or 50 dF ROP as some of the POH settings recommend. That would sure do it.

[Vlakvark]

I will post pictures of the baffels soon. I changed them last year. Also, I have a manual cowl lever. I use the JPI 830 so I kinda agree with jlunseth about managing. I will go back to my AME and see what we can do about the fuel flow and also what we can do to open the cowls 1/2 way. 

[Eraaen]

on your "cold" cylinder .. check the probes.  On mine I noticed the same thing. (one cylinder running 50 degrees cooler than the rest)  It turned out that this cylinder has the original CHT probe for the dash.  Not sure why is wasn't swapped out.  But speculation is, that this is why that cylinder shows colder than the rest. (can't remember what # it is)