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Cowling exit lip

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  • #31
    You will have insufficient cooling to:
    - operate rich of peak for extended periods
    - break in a new engine
    - climb at Vy for more than a couple of minutes
    - cruise on very hot days
    Thanks Jon. In your opinion do you think if I add a cooling lip to the current cutout, is it likely to then provide sufficient cooling to break in the engine? Any other suggestions?
    Nev Bailey
    Christchurch, NZ


    • #32
      Originally posted by Nev View Post

      Thanks Jon. In your opinion do you think if I add a cooling lip to the current cutout, is it likely to then provide sufficient cooling to break in the engine? Any other suggestions?
      The community's experience shows that a lip is sufficient in most cases, to manage overheating issues. I haven't got personal experience with a lip.
      As you have seen, many aircraft in hotter drier climates with the -540 engine have ended up installing additional ventilation because the lip was not sufficient on very hot days. There are many ways to do this, some more elegant than others.

      Conversely, on very cold days, the lip and additional vents are all adding unnecessary drag, and the engine will run very cold with all that extra ventilation. Shock cooling is also a greater risk. Many ignore this issue, as overheating has more immediate consequences. Lycoming urges caution.

      This from the Lycoming website: Operating in Cold Weather | Lycoming

      Engine operating temperature is another item that is not usually given enough consideration in cold weather. We usually are very cautious about high oil temperature which we know is detrimental to good engine health, while a low oil temperature is easier to accept. The desired oil temperature range for Lycoming engines is from 165˚ to 220˚ F. If the aircraft has a winterization kit, it should be installed when operating in outside air temperatures (OAT) that are below the 40˚ to 45˚ F range. If no winterization kit is supplied and the engine is not equipped with a thermostatic bypass valve, it may be necessary to improvise a means of blocking off a portion of the airflow to the oil cooler. Keeping the oil temperature above the minimum recommended temperature is a factor in engine longevity. Low operating temperatures do not vaporize the moisture that collects in the oil as the engine breathes damp air for normal combustion. When minimum recommended oil temperatures are not maintained, oil should be changed more frequently than the normally recommended 50-hour change cycle. This is necessary in order to eliminate the moisture that collects and contaminates the oil.

      And finally, power-off letdowns should be avoided. This is especially applicable to cold-weather operations when shock-cooling of the cylinder heads is likely. It is recommended that cylinder head temperature change not exceed 50˚ F per minute. Plan ahead, reduce power gradually and maintain some power throughout the descent. Also keep the fuel/air mixture leaned out during the descent. If an exhaust gas temperature gauge is installed with a normally aspirated engine, keep it peaked to ensure the greatest possible engine heat for the power setting selected
      We considered a variable oil cooler control to address these issues. I have heard others mention this before.
      In the end, I felt that variable cowl flaps were more useful than a variable oil cooler inlet / outlet. Cowl flaps help manage shock cooling, CHTs in climb, and oil temp all at once. Blanking off the oil cooler only helps with one of these issues.


      • #33
        The Husky crowd has done some experimenting with the Cowl Exit lip. This thread shows they seem to like a "long exit ramp" shaped lip compared to the factory "Exit Dam" shaped lip.

        I can visualize organized airflow over a ramp compared to a dam.....I'm thinking of Evel Knievel right now. (motor cycle stunt guy in the 1970's) Water flow in a river might be more applicable though.
        Brooks Cone
        Southeast Michigan
        Patrol #303, Kit build