Cooling a 9A

Puzzled by plate blocking the cyl fins on starboard side. Port side has drilled holes for a blocking plate, but none installed. So my question is, why are the forward side fins blocked anyway? Is it to force air up and over... And then make the turn downward and out the bottom?
Also, is a blast tube needed these days for a slick mag? Tempted to plug that hole. Thanks for any tips and data sent this way.

flightlogic said:

Puzzled by plate blocking the cyl fins on starboard side. Port side has drilled holes for a blocking plate, but none installed. So my question is, why are the forward side fins blocked anyway? Is it to force air up and over... And then make the turn downward and out the bottom?
Also, is a blast tube needed these days for a slick mag? Tempted to plug that hole. Thanks for any tips and data sent this way.

Click to expand...

Cylinder blockers are generally used to deflect air away from the coolest cylinders, hopefully redirecting at least some of that air towards the warmer cylinders. Typically #1 and #2 are the coolest cylinders and can afford to lose a little cooling air to help the hotter cylinders - typically #3 & #4.

The challenge with cylinder blockers is to find a size that results in relatively even temperatures between all cylinders in climb and in cruise. On my airplane, if I size the blockers for cruise, #1 gets hot during climb. So if I reduce that blocker's size, #1 is substantially cooler than the other cylinders. So I found a compromise where #1 is slightly warmer than the others in climb and slightly cooler in cruise.

Kyle, thank you. That makes sense. I think I will make a small collection of plates and try some temperature graphing now as summer approaches.

Buy some metal tape from the HVAC isle at your local hardware store. Use that to figure out what your air dams should look like.

If you really get ambitious, you can drill out the rivets in front of the cylinders and install some platenuts. Then you can make removable air dams.

Platenuts. Good idea. Now I know what Saturday is for.
Blasting the mags? Needed, you think?

N941WR said:

Buy some metal tape from the HVAC isle at your local hardware store. Use that to figure out what your air dams should look like.

If you really get ambitious, you can drill out the rivets in front of the cylinders and install some platenuts. Then you can make removable air dams.

Click to expand...

I just finished working with this method for my #1 cylinder. I had originally installed the air dams per Vans plans but was getting very hot temps so I removed them by grinding off the shop heads of the three rivets. I flew for a many hours, monitoring the temps. The #1 cylinder would be about 20 degrees cooler during level flight. The other three were pretty close. I added a 5/8" strip of the aluminum tape mentioned above. This brought #1 temp up but still lower by about 10 degrees. Added 1/4" more by overlapping the first piece of aluminum tape and this brought the #1 temps pretty even with the others. #4 is the coolest in level flight by about 5-8 or so degrees. #2 is still very hot on takeoffs, especially after multiple takeoffs, so I have to manage that, and, hopefully find a solution.

I installed a .040 aluminum air dam in front of #1 that matches the aluminum tape (removed) and attached it by removing three of the AN470AD4 rivets in the horizontal flange of the angle that supports the ramp and installed three #6 screws with nylock nuts. Will see how this works on the next flight.

Picture of air dam installed:
http://www.aclog.com/rv-9a/images/Firewall%20Forward/c56e9afbfc3b282b465c9a0726348ee75584_cylinderOneAirDam041414.jpg

flightlogic said:

Platenuts. Good idea. Now I know what Saturday is for.
Blasting the mags? Needed, you think?

Click to expand...

I knew I had a picture somewhere.

Mag blast tube?

You may get a lot of yes, no, and maybe answers, but I like data, so I contacted the Slick Mag guys, and got an answer in 3 hours on a Sunday afternoon!!

The Slick Mag rep told me the limit temperature of the coil housing is 185 Deg F. My plan is to glue a thermocouple there and see if the blast tube is needed. Then I take before and after (blast tube) data to see how much is really needed and post it.

YMMV

Oh - you might get some of the temperature dots to put there too, they melt and change color at a specific temp. Just stick them on the part and then look after the flight to see the results. You won't know when the temp occurs, but will know the peak temps. I don't remember the brand or part number, sorry.

Bill,
Thank you for photo and data. Climbing out of San Diego today #2 hit 400F first. Followed by #1. Lowered nose to drop them to 390F. Pulled pwr back a bit too. I can see I will be doing some step climbs as summer comes. Standard cowl and baffles so far. Appreciate the efforts of those who are responding. Always something to learn.

flightlogic said:

Bill,
Thank you for photo and data. Climbing out of San Diego today #2 hit 400F first. Followed by #1. Lowered nose to drop them to 390F. Pulled pwr back a bit too. I can see I will be doing some step climbs as summer comes. Standard cowl and baffles so far. Appreciate the efforts of those who are responding. Always something to learn.

Click to expand...

This is where things get touchy. They Lycoming Operator's Manual for O-360's states "For maximum service life, cylinder head temperatures should be maintained below 435*F (224*C) during high performance cruise operation and below 400*F (205*C) for economy cruise powers." (I think those temps might be the same for the other engines, I just don’t know.)

In other words, they expect the CHT's to go above 400 during climb but come down in cruise.

I typically climb out at Vy and then at 1000' AGL I lower the nose and establish a 500 FPM climb. This gets more air moving over the cylinders and lowers their temps.

One other thing I did was to use a flashlight and a dark hangar to find and plug any air leaks between my baffles and cylinders. This dropped my “in cruse” CHT’s almost 20 degrees.