Engine Cooling

[crabandy]

I'm just like so many other RV drivers trying to lower my CHT's. Since installing new Lycoming Cylinders. I currently have 14 hours on the new cylinders and oil consumption seems to have stabilized 5 ish hours ago. I flew it full power drinking 16 GPH for 5 hours than I alternated between 24-26 inches of MP for the remaining 9 hours with minimal taxi/ground runs.

I did some plenum pressures and temps of the old cylinders last year, meaningful data starts at post #55.
http://www.vansairforce.com/communit...ng+bump&page=6

I'm consistently 20-30 degrees hotter on all CHT's in all realms of flight with the new cylinders. The standard baffle material is the same as the old cylinders, the RTV sealing around the metal baffling is slightly better due to easier access with exhaust and intake tubes removed. I did add silicone baffle wraps similar to DanH in this thread starting post 307.
http://www.vansairforce.com/communit...=94648&page=31

Since I'm thinking the biggest change I made to my cooling system was the baffle wraps, I decided to modify them and check for changes. I thought I might have wrapped my cylinders too much, restricting the flow through the fins too much. Here's what they looked like previously between the cylinders.


I used a 1 inch dia hardware aluminum tube between #1/3 cylinders, I pulled the baffle material (it really does stick pretty darn good) and wrapped it around the tube and super glued it. I then dressed the edges with RTV to make sure it stuck. I also trimmed up the upper rear edges of #3/4 baffle wraps and cut it flush with the metal baffling. In addition I trimmed up the lower baffles, I had some portions where the wraps were sticking 1/4-3/8 past the metal baffling.

[crabandy]

I made and installed new upper and lower Piccolo tubes, again Thank You DanH! My upper piccolo tubes are very similar in placement, my lower ones are about 1 inch lower than last time.



I also added an exit piccolo tube, it's about 1/2 in front and 1/2 behind the firewall. It's neighbor is a temp sensor, the v shaped wings were my "heat shield." The mount/heat shield is larger than I envisioned while making it, perhaps its affecting the piccolo tube's pressures.Tthe temp readings on the other hand seem very realistic, And.... This temp prob doo-dad is really cool----I alligator clamped it to my volt meter in the cockpit and just clicked it on when I wanted a temp reading. It told me my hangar was a balmy 88 before I rolled the airplane out, no wonder I was sweating through my shirt and on my 2nd iced tea before brunch!



Long story short, CHT's remained the same from previous flights. I think my trimming up etc let the OAT's rise 15 degrees while keeping the same CHT's. No difference from the baffle wrapped aluminum tube between cylinders 1/3 vs 2/4, everything mostly between 15 degrees CHT just like before.

I did gather some pressure and temp data from three different airspeeds, I seemed to have gained upper plenum pressure, and lost pressure just below the cylinders. I'm not sure if my exit pressures are valid, placement or bracket error my affect them. My exit air temps do seem to be valid, cold in the hangar, hot in the hanger and taxiing all had reasonable values. I have the GPS ground speeds and tracks but not sure they're relevant (about 173 knts TAS at full throttle) . Tests were in the afternoon at 3500 pressure altitude, 93-98 OAT's on the ground yielded about 79 degrees at 3500 PA thank goodness. Hot temps made things bumpy, I had an autopilot this time but still give or take a few knots. (shouldn't have much affect on pressures but they were jumping around on the manometer so it's a guess at the avg)
Pressures in In H2O, temps in F

100KIAS

Upper Press: 6
Under the Cyl: .5
Exit: 1
Exit Temp: 172
CHT's: 338-355
OAT: 78
Oil Temp: 195

140KIAS

Upper Press: 11
Under the Cyl: .85
Exit: 3
Exit Temp: 168
CHT's:386-401
OAT: 79
Oil Temp: 202

160KIAS

Upper Press: 15
Under the Cyl: 1
Exit: 4
Exit Temp: 168
CHT's: 393-411
OAT: 78
Oil Temp: 210

I seemed to have gained some upper plenum pressure and lost pressure just underneath the cylinders. I'm not sure what my exit area temp should be but 170ish degrees seems pretty low for the CHT's I'm seeing.

I Really appreciate everyone's guidance and help.

[Kent Ashton]

I see that most RV guys don't use wraps on the top sides of the cylinders relying, I suppose on pressure and turbulence to force air between the fins, however, I believe wraps help on the bottom. See some in this post
http://www.vansairforce.com/communit...9&postcount=44

As soon as the air has an opportunity after it has passed the midpoint of the cylinders, it will spill out of the fins and leave the lower fins of the cylinders uncooled. Wraps keep the air between the fins longer.

Also, consider that gap between the cylinder heads. It will pass lots of air that does not go through the fins--wasted cooling air. Same for any other gaps in the baffles.

Think like a lazy air molecule: "I do not like going through fins and tight places. Please don't make me; I get hot. I want to take the easy way through the engine."

Subject those pesky molecules to your will. :-)

I like aluminum colored silicone sealant from the home stores for filling the odd gaps. Sticks well and blends with most engines.

[crabandy]

Originally Posted by Kent Ashton

I see that most RV guys don't use wraps on the top sides of the cylinders relying, I suppose on pressure and turbulence to force air between the fins, however, I believe wraps help on the bottom. See some in this post
http://www.vansairforce.com/communit...9&postcount=44

As soon as the air has an opportunity after it has passed the midpoint of the cylinders, it will spill out of the fins and leave the lower fins of the cylinders uncooled. Wraps keep the air between the fins longer.

Also, consider that gap between the cylinder heads. It will pass lots of air that does not go through the fins--wasted cooling air. Same for any other gaps in the baffles.

Think like a lazy air molecule: "I do not like going through fins and tight places. Please don't make me; I get hot. I want to take the easy way through the engine."

Subject those pesky molecules to your will. :-)

I like aluminum colored silicone sealant from the home stores for filling the odd gaps. Sticks well and blends with most engines.

The wraps I made started about 10 o'clock and 2 o'clock on the cylinder and continued to the bottom of the lower baffle theoretically keeping the cooling air in contact with the fins longer. On my old cylinders I had RTV'd Van's baffle material to the lower aluminum baffle wraps to keep the fins from eating the aluminum.

Large gaps/small gaps filled. I assume you mean between the cylinder barrels, my inner lower inner cylinder baffling are sealed with a large bead of RTV. They also sit on the baffling wrapped cylinder.

I do like the aluminum colored silicone idea!

[DanH]

Originally Posted by crabandy

My upper piccolo tubes are very similar in placement, my lower ones are about 1 inch lower than last time.

Shouldn't make any difference for measurement of upper/lower delta pressure.

I also added an exit piccolo tube, it's about 1/2 in front and 1/2 behind the firewall.

Probably useless. As a very qualified aero guy explained exit pressure transition to me, given a "hole" type exit, the pressure drops almost instantly when the air passes through the hole. Here the piccolo would just average the static pressure inside the cowl, in the exit, and outside the exit.

It's neighbor is a temp sensor, the v shaped wings were my "heat shield." The mount/heat shield is larger than I envisioned while making it, perhaps its affecting the piccolo tube's pressures.Tthe temp readings on the other hand seem very realistic

The heat shield is pretty good, and probably needs to be that large. The aluminum will re-radiate some energy, so adding an insulator layer might be a good idea for best accuracy. A little sheet of fiberfrax felt on the wings, under some aluminum tape, will do it.

I did gather some pressure and temp data from three different airspeeds, I seemed to have gained upper plenum pressure, and lost pressure just below the cylinders.

Compared to the baffles on your previous engine? Generally speaking, that's good. Means you eliminated some leaks that were bypassing a trip through the fins.

Overall, the numbers suggest that the baffles are a bit restrictive.

I'm not sure if my exit pressures are valid...

Upper-lower delta values are valid for your installation, and quite useful. We can't accurately compare those pressure values to other installations without true airspeeds, as velocity is the basis of dynamic pressure.

Ditch the exit piccolo, move the exit temp probe forward, a few inches inside the cowl, and add some insulation to the heat shield.

What mixture and ignition timing for these tests?

[crabandy]

Quote:
Originally Posted by crabandy View Post
My upper piccolo tubes are very similar in placement, my lower ones are about 1 inch lower than last time.
Shouldn't make any difference for measurement of upper/lower delta pressure.

Quote:
I also added an exit piccolo tube, it's about 1/2 in front and 1/2 behind the firewall.
Probably useless. As a very qualified aero guy explained exit pressure transition to me, given a "hole" type exit, the pressure drops almost instantly when the air passes through the hole. Here the piccolo would just average the static pressure inside the cowl, in the exit, and outside the exit.

Quote:
It's neighbor is a temp sensor, the v shaped wings were my "heat shield." The mount/heat shield is larger than I envisioned while making it, perhaps its affecting the piccolo tube's pressures.Tthe temp readings on the other hand seem very realistic
The heat shield is pretty good, and probably needs to be that large. The aluminum will re-radiate some energy, so adding an insulator layer might be a good idea for best accuracy. A little sheet of fiberfrax felt on the wings, under some aluminum tape, will do it.

Quote:
I did gather some pressure and temp data from three different airspeeds, I seemed to have gained upper plenum pressure, and lost pressure just below the cylinders.
Compared to the baffles on your previous engine? Generally speaking, that's good. Means you eliminated some leaks that were bypassing a trip through the fins.
Yes, I used the same aluminum baffles and Van's black baffle material from the old cylinders, it was just easier to RTV the gaps with the intake/exhaust removed.

Overall, the numbers suggest that the baffles are a bit restrictive.
My thoughts as well, thats why I started trimming the baffle wraps. Trimming the aft side of Cylinders 3/4 seemed to help about 5-10 degrees. Now the cylinder head wraps are very similar size to what was on the old cylinders. The barrel portion of the cylinder is still wrapped unlike the old cylinders. Whats the best way to "open" them up a little?

Quote:
I'm not sure if my exit pressures are valid...
Upper-lower delta values are valid for your installation, and quite useful. We can't accurately compare those pressure values to other installations without true airspeeds, as velocity is the basis of dynamic pressure.
IAS and TAS (3 leg NTPS Shows TAS is about 1 knt slow at 178 knts TAS, I have the values for the other airspeeds, i still have to enter them in the spreadsheet) for pressure values:
100IAS was 112TAS
140IAS was 152TAS
160IAS was 171TAS

Ditch the exit piccolo, move the exit temp probe forward, a few inches inside the cowl, and add some insulation to the heat shield.
Roger Wilco

What mixture and ignition timing for these tests?
Mixture was full Rich 250+ ROP, with my CHT's I haven't leaned to find peak EGT at high power settings. I do have a dual EFII ignition, but I'll need to grab the data cards in order to pull RPM/MAP data.

[BillL]

Andy, how did the CHT and oil temp data balance look/change with the better "sealing"? With higher pressure, it would force more air through the oil cooler, so the (oil temp)-(OAT) delta should have dropped. If it didn't, then a change in heat rejection might be suspected. Timing will have an effect on that. One day it would be nice to know CHT vs timing on the same day - like the effect of + 2 deg.

One more thing, not directly related to your data, my new Lycoming YIO-360 had flashing in the fins between the plug and ports. It was open, but about half blocked. I am assuming your new Lycs are the same. I have not had good success in getting that out. It is hard to find a tool small enough (and productive enough) to get in there. .

[krw5927]

Originally Posted by BillL

One more thing, not directly related to your data, my new Lycoming YIO-360 had flashing in the fins between the plug and ports. It was open, but about half blocked. I am assuming your new Lycs are the same. I have not had good success in getting that out. It is hard to find a tool small enough (and productive enough) to get in there.

Try an abrasive carbide rod hacksaw blade. Snip the ends off with lineman pliers, cut it in half, and chuck it into your (least) favorite drill. As it spins, push it along with a sacrificial piece of steel hinge rod.

http://www.disstontools.com/rg-carbiderod-hks.html

[BillL]

Originally Posted by krw5927

Try an abrasive carbide rod hacksaw blade. Snip the ends off with lineman pliers, cut it in half, and chuck it into your (least) favorite drill. As it spins, push it along with a sacrificial piece of steel hinge rod.

http://www.disstontools.com/rg-carbiderod-hks.html

Thanks for the tip! I just bought one for this purpose. I tried silver soldering a broken carbide burr to a piece of piano wire and after breaking it a couple of times I gave up for the time being.

[crabandy]

Originally Posted by BillL

Andy, how did the CHT and oil temp data balance look/change with the better "sealing"? With higher pressure, it would force more air through the oil cooler, so the (oil temp)-(OAT) delta should have dropped. If it didn't, then a change in heat rejection might be suspected. Timing will have an effect on that. One day it would be nice to know CHT vs timing on the same day - like the effect of + 2 deg.

One more thing, not directly related to your data, my new Lycoming YIO-360 had flashing in the fins between the plug and ports. It was open, but about half blocked. I am assuming your new Lycs are the same. I have not had good success in getting that out. It is hard to find a tool small enough (and productive enough) to get in there. .

Bill,
The Oil Temp seems to behave exactly as it did with the old cylinders. With the old cylinders I only saw oil temps above 178 on climbs where the CHT's hit 385ish or above, with the new cylinders the oil temp is hotter following the CHT's.
I'm going to look a little closer between the fins when I can make it back to the hangar, I did clean up the shallow fins on the front of #2 and rear of #3.