High CHT's resolved and what worked.

[N520TX]

Originally Posted by aerhed

No biggie. The manufacturers have used that trick for years. "What do you mean the temps too high to certify? Oh well, put a blast tube on it. "

Gumman solved the hi oil temp problem for my AA1A in the same manner - instead of an oil cooler (too heavy), the just put a bast tube onto the oil temp probe itself !

[Titan-Xpert]

About twenty years ago, Airmotive Engineering was hired to resolve some cooling problems with a modified Mooney. It had high CHT?s in the climb and poor oil consumption. We heavily instrumented this aircraft and preformed extensive flight testing. One of the things we learned was there was a 100 F+ temperature difference between the top and bottom of all the cylinders on this aircraft. The exact same engine in our test cells showed a 0 F difference. With a large temperature difference the cylinders were not round any more. This can cause poor ring seal, blow-by, oil consumption and high CHT?s. When we corrected the cooling problems this engine showed a 5 F temperature difference, vastly improved oil consumption and normal temp control during the climb.

Also there are very hot areas of the head (around the exhaust) and relatively cool areas (around the intakes).This cool area around the intake does not need a large amount of air flow. That?s why there are smaller and fewer fins on the intake side of the head and a small regulated airflow. Heat always flows from the hot areas toward the cool areas, inside the head. The idea is to have a head that is as even in temperature as possible to help control internal thermal stresses.

Just because you haven?t observed or measured the changes in the heat flow path does not mean that no changes were made, good or bad. If this modification of a very well proven design with hundreds of thousands of successful operational hours, works so well don?t you think it would have been incorporated in all cooling systems before now.
I do not want to discourage anyone from trying new ideas. But it?s best when you can prove beyond a doubt, that you have accomplished what you think you have

[DanH]

Originally Posted by Titan-Xpert

When we corrected the cooling problems this engine showed a 5 F temperature difference...

Fascinating. What changes did you make?

Also there are very hot areas of the head (around the exhaust) and relatively cool areas (around the intakes).This cool area around the intake does not need a large amount of air flow. That’s why there are smaller and fewer fins on the intake side of the head and a small regulated airflow.

Again, cylinders 1 and 4 have unrestricted airflow to the same fins which are largely blocked on cylinders 2 and 3. Can you explain the difference?

[dwrichey]

"When we corrected the cooling problems this engine showed a 5 F temperature difference, vastly improved oil consumption and normal temp control ......"

Mr. Looper,

Could you please expand on this statement and share how you corrected the cooling problem?

Thank you

[Titan-Xpert]

The engine was a Lycoming O-360A1A. Temperatures were measured on the barrel and head, top and bottom of all cylinders. This airframe had a custom made baffle system to go with a completely new cowling.
It had some poorly fitted lose fitting baffles in the area around the heads on all four corners and poor cooling pressure differential of 4?water. (It takes about 6-7?water to cool properly). One square inch of total leaking area in the baffling is equal to about 1?water cooling pressure.
When we corrected the cooling problems this engine showed a 5 F temperature difference. Between the top and bottom of the cylinders. Not between individual cylinders.

[alpinelakespilot2000]

Originally Posted by Titan-Xpert

poor cooling pressure differential of 4?water. (It takes about 6-7?water to cool properly). One square inch of total leaking area in the baffling is equal to about 1?water cooling pressure.

Can anyone point me to a simple, preferably quick, means to check the pressure differential between top and bottom?

[MarkW]

DanH explains in detail on this thread.
http://www.vansairforce.com/communit...=112941&page=4
Maybe not the easiest but great for repeat-ability.

[DanH]

Originally Posted by alpinelakespilot2000

Can anyone point me to a simple, preferably quick, means to check the pressure differential between top and bottom?

You want quick and dirty? Pick up two aquarium bubble rocks, about 20 feet of 1/8 vinyl tubing, and 4 feet of 1/4" vinyl tubing. Ziptie one rock (with connecting tubing) to the top center seam of the engine case. Ziptie the other rock to the engine mount somewhere behind the engine. Neither should be positioned in a stream of high velocity air.

Run the pair of tubes back to the cockpit any way you can. Some have gone through the heater box. You could also run it out the cowl exit and up around the fuselage, and under a canopy edge. Duct tape it to the fuselage skin.

Fasten the 1/4" tubing to a 24" x 4" board so it forms a "U" with straight sides. Mark the board with lines straight across every half inch. Mix some food coloring and a bit of dish soap into a few ounces of water. Pour the water into the U-tube until it fills the bottom 10 inches. Now connect the engine compartment tubes to the ends of the U-tube.

Go fly. If the water jumps up and down too much, install restrictors in the lines....plugs with a 0.040" hole bored through them.

Pressure differential is the difference between the two water levels. Pressure varies with both altitude and airspeed. Email me for a Lycoming cooling air demand chart.

[Toobuilder]

Originally Posted by Titan-Xpert

... If this modification of a very well proven design with hundreds of thousands of successful operational hours, works so well don?t you think it would have been incorporated in all cooling systems before now...

"This modification" addresses the significantly restricted/zero airflow at the point of zero fin depth on some Lycoming cylinders. Yes, there are hundreds of thousands of hours flying with restricted or zero airflow to the bottom fins, but are you suggesting this is an acceptable practice? Why go through the trouble of adding the wrap around baffle if there is no airflow?

[Titan-Xpert]