Cowling exit lip

[Nev]

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?

[Battson]

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 165Ëš to 220Ëš F. If the aircraft has a winterization kit, it should be installed when operating in outside air temperatures (OAT) that are below the 40Ëš to 45Ëš 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 50Ëš 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.

[Bcone1381]

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. https://flyhusky.com/forum/index.php...ling-lip.2516/

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.

[Nev]

I've now got 95 hours on the Bearhawk in mostly warmer ambient conditions. I've been able to control the CHT's through climb speeds and mixture when necessary, but I've decided to make a larger cooling lip and continue to use the current smaller one in winter. Here in the South Island of NZ the summer temps are typically in the mid 20°c and occasionally into the low 30's. Autumn and Spring tend to be in the teens, and winter is usually below 10°c down to -5c at sea level. Obviously it's a lot lower temps at altitude.

Yesterday I removed the small cooling lip (just 5 screws) to use it as a mould and decided to do a few circuits without it to see whether it was making much of a difference. It does. During the first circuit the CHT's started to climb and got higher with each circuit until after 4 circuits I had to land. At this point the Oil temp (normally a steady 75c) was peaking too, higher than I'd ever seen it. So I'm now sold on the benefits of the cooling lip. The new one will be slightly larger and will wrap around to give more overall area.

Here's where I'm at with it and I'll report back with results once it's finished. You can see the original orange one in the background of the top photo.

F9AE26FD-33BD-4471-9B7A-C6E472A42531.jpg

76E39C1B-B0A7-4EE8-831E-F3C2C67BB4AB.jpg

[Nev]

I've now got 150 hours on the aircraft, and simply left the new cooling exit lip (pictured above) on, even during the winter. I've found that so far I can get sufficient heat/cooling by varying the mixture. With the installation of a butterfly valve on the oil cooler I have been able to significantly restrict airflow through the oil cooler for winter ops. If anything, I will change the oil cooler winter setting to be even more restrictive.

[robcaldwell]

Per Mark's advise, I also enlarged the cowl exit opening forward by about 4 inches, which helped.

[svyolo]

I managed to make a lip with .040 5052, 1" mounting surface, 1.25" lip 30 deg using a stretcher. 2" lip didn't work. I might try one more at 1.5 or 1.6 inch lip. It was pretty easy and quick to do and get it to conform.

[svyolo]

I tried a bigger one, 1.7" lip. Worked very well. My first attempt at 2" was a fail. This was very easy to do, and I am no master metalworker. I just put a 30 deg bend, and then used a HF stretcher. lip.jpg

[Bcone1381]

Very Nice. I'd love to learn to use a stretcher! Do you sand out the tooling marks or are they left?

[Nev]

Here's a photo of mine now - I ended up simply leaving the new larger cooling lip on during the winter and it's been fine. With the addition of an oil cooler butterfly valve (summer and winter setting) I'm able to vary engine temps sufficiently using mixture and airspeed.

0B8FED71-B807-441A-91DA-80D2149D5573.png

[spinningwrench]

A discussion with Bob's engine guy Mike at Oshkosh indicated that a 3" lip at 30 degrees was about right. It seems people are putting on less of a lip?

[Nev]

I guess there's quite a few variables. Engine size is one, and outlet area has a large effect. Also on mine I'm ducting air from the number 6 cylinder to the oil cooler - so the CHT's tend to run hotter due to robbing the cooling air. I've got approximately 130 inches ² of outlet area underneath, plus another 10 inches ² above the battery etc.

[Battson]

A discussion with Bob's engine guy Mike at Oshkosh indicated that a 3" lip at 30 degrees was about right. It seems people are putting on less of a lip?

I three inch lip is huge, I don't think I've seen many with that much lip

[jaredyates]

We would have to ask Mike what he meant but it would be totally plausible to make the lip out of a 3" piece of material, with half protruding and half as an attachment flange.

[svyolo]

That is what I did, but I don't know if it works yet.

[Nev]

One idea is to add nutplates so the cooling exit lip can be easily removed and resized during the test flying.