Summer temperatures and cooling
Posted: Tue Jun 06, 2023 9:37 am
by Bryan Cotton
As the calendar rolls around to summer in my first year of flying, I’m starting to have issues. Pattern work with 2 people above 80F isn’t working out. Oil temps are getting to around 230F and I got CHTs approaching 400F for the first time. Plus it’s so hot under the cowl that the burps on the ground are ugly.
I’ve just ordered a set of B model outlets and are going to add them to what I already have.
Re: Summer temperatures and cooling
Posted: Tue Jun 06, 2023 3:43 pm
by GordonTurner
Hi Brian
Looking forward to your cowling exhaust mods documentation. I’m planning to start with only these vents, hoping the lower pressure at the fuselage sides will lead to more airflow with less drag.
Gordon
Re: Summer temperatures and cooling
Posted: Tue Jun 06, 2023 6:20 pm
by daleandee
GordonTurner wrote:Hi Brian
Looking forward to your cowling exhaust mods documentation. I’m planning to start with only these vents, hoping the lower pressure at the fuselage sides will lead to more airflow with less drag.
Gordon
Hi Gordon,
Just a heads up with the Corvair in a Sonex airframe as they tend to cool very well. My summer CHTs (under the plugs) read about 225ºF. Oil temp (with stock GM 12 plate cooler) runs 200-210 in the summer months. I did get it close to 230ºF in a steady climb with two on board. I use Rotella 15W40 and have seen evidence that it is not harmed at those temps at all.
I asked Dan Weseman about the cool temps with my Cleanex and he asked what problem I was trying to solve. 8~) He reported his Cleanex was the same way with the cool CHTs.
Re: Summer temperatures and cooling
Posted: Tue Jun 06, 2023 11:10 pm
by Rick524
Hi Bryan, I made side vents for my ‘A’ Sonex on my cnc router. I can send you the Vcarve files if you are interested.
Rick
Sonex 524
Re: Summer temperatures and cooling
Posted: Tue Jun 06, 2023 11:25 pm
by Bryan Cotton
Rick524 wrote:Hi Bryan, I made side vents for my ‘A’ Sonex on my cnc router. I can send you the Vcarve files if you are interested.
Rick
Sonex 524
Rick, sounds good thanks.
Re: Summer temperatures and cooling
Posted: Wed Jun 07, 2023 12:40 am
by Rick524
i guess the best way to send the files would be via email, if you want to pm me your address.
Rick
Sonex 524
Re: Summer temperatures and cooling
Posted: Wed Jun 07, 2023 12:44 am
by Rick524
Got it, should have checked the pm before I answered…duh.
Re: Summer temperatures and cooling
Posted: Wed Jun 07, 2023 2:05 am
by AlexZ
Above 80F the Aerovee powered Sonex is basically a one seater. Flying with 2 onboard is possible, but only with a shallow climb out. Don’t do pattern work. Temps will built up and ruin your cylinder heads.
I designed side vents as sheet metal.
Side-vent-Sheetmetal-4.jpg (40.29 KiB) Viewed 12033 times
Side-vent-Sheetmetal-5.jpg (75.08 KiB) Viewed 12033 times
Can send drawings.
Re: Summer temperatures and cooling
Posted: Wed Jun 07, 2023 9:18 am
by Bryan Cotton
Got the files, thanks Rick!
Alex, looks great, I’ll pm you my email address.
Re: Summer temperatures and cooling
Posted: Sat Jun 10, 2023 6:07 pm
by Bryan Cotton
Had some email exchange with Mark Schiable. He did not recommend running both A and B model outlets together. I bought a set of B outlets from Sonex but am holding off.
One other thing, my oil pressures have always been high - like 90-100 psi at startup depending on temp. Cruise was 70 psi on my long Tennessee trip. The Aerovee manual says 40-50 in cruise. My understanding of the VW oil system is that low pressure allows oil to go through the cooler, and maybe I’ve not been getting that. So I took out and polished both plungers, then cut a half loop off the pressure regulation spring. That is the short one near the back of the engine, away from the oil pump. On the last flight I saw 60-65 psi and ~220F. I’m going to cut off another half loop.
Re: Summer temperatures and cooling
Posted: Sun Jun 11, 2023 1:16 am
by NWade
Bryan Cotton wrote:Had some email exchange with Mark Schiable. He did not recommend running both A and B model outlets together. I bought a set of B outlets from Sonex but am holding off.
All -
For those not on the Facebook page, I performed the first flight of my Legacy Sonex with an AeroVee Turbo & “B-model” side exits (on a Universal cowling with no exhaust tunnels) back in mid-May. I found that the engine did not cool AT ALL with just the side exits once I went to takeoff power. I have since added a 13" x 5" opening in the bottom cowling at the rear with a ~1.5" deflector (angled downward from horizontal by 30 degrees). I hate the idea of the extra drag of the deflector, but this bottom exit has taken my CHTs from ~450 down to ~380-390 as long as I keep the MAP below 31" after about 90 seconds of takeoff power (40" MAP). This is still not ideal, but way better! And that comes after I tried redoing my baffle seals and other tweaks to ensure I was getting good air to the upper plenum.
Per suggestions from Sonex I’m going to try taping over the side exits on an upcoming flight to see how that changes lower cowling airflow. I may also temporarily mount deflectors to the front of the side exits to see how that changes drag & cooling.
I am still dealing with some pretty insane temps in the rear of the engine bay. Its causing some vapor-lock issues on landing & taxi after flight (even with firesleeved fuel line and aluminized fiberglass heat shielding over the fuel flow sensor). The AeroInjector itself is skin-blisteringly hot after flight and I’m worried the heat is going to kill the firewall-mounted items like my engine monitor RDAC, voltage regulator, etc. I am debating whether to mount a NACA scoop on the side of the lower cowling with a blast tube generally directing air along the firewall; or whether I should punch a small hole in the rear engine baffle and use a short bit of SCAT/SCEET tubing to achieve the same effect. Either one potentially disrupts the pressure differential between the upper plenum and lower plenum; but I don’t see a better way to get more airflow to the firewall-mounted items and keep that area cooler. The engine bay with the Turbo is just tight and that area experiences low airflow plus a lot of radiant heat due to the turbo (even with the SS shield looped around it).
Bryan - Regarding oil pressures: If you look through my older posts you’ll find an epic one about my oil cooler blowing out during early ground runs. A lot of the oil pressure sensors top out at 80-100 psi so if you see those readings beware that you could actually be way higher than that!! When mine blew out (probably around 150 psi even though it only read 90 on the gauge), the pressure-relief plunger had gotten stuck at the very top of its travel. During assembly I could slide it smoothly in its bore on the bench, and thought it was hitting the end of its travel. But in running conditions it was able to push up a little further and get wedged.
So make absolutely certain when you polish the plunger that it really is making it to the end of its travel in the bore without any impediment. I polished the plunger and then also wrapped some fine-grit sandpaper around an appropriately-sized dowel and did a light bit of polishing/sanding to the bore (and then carefully rinsed it out thoroughly with 90% isopropyl alcohol to ensure I wasn’t putting a bunch of metal grit into the oil system). Now with Penngrade 15W-40 I see ~45-55psi in flight and ~10-20 psi on the ground.
Hope this info helps,
–Noel
Sonex #1339
Re: Summer temperatures and cooling
Posted: Sun Jun 11, 2023 2:25 pm
by Bryan Cotton
Thanks Noel! I did take another shot at polishing the plunger. To do this, I found that a 1/2" metal rod was a slip fit inside the plunger. With a little blue tape on the end it stuck pretty good. I chocked up the rod in the drill press and polished with scotch brite. Then I chocked it up in a hand drill and worked the plunger up and down in the case. Seems pretty free to me. I also shortened the spring by another half turn. I’ll see what happens next. I did do a ground run and the pressures seemed a little lower. Need to get out and fly it again.
Re: Summer temperatures and cooling
Posted: Mon Jun 12, 2023 9:34 am
by bvolcko38
Until I cut a NACA scoop in front of the air cleaner, my engine never ran well at all. With the MGL efis I put thermocouples all around in the engine bay and temps were 150 in the carb throat. Now my carb temps are a little over ambient…depends on climb angle.
Re: Summer temperatures and cooling
Posted: Mon Jun 12, 2023 10:06 am
by Bryan Cotton
Thanks Bill, great picture. I am planning on some fresh air for the induction system as well. I will not pressurize the system as that messes with the aerocarb mixture.
Re: Summer temperatures and cooling
Posted: Mon Jun 12, 2023 10:27 am
by tom.corso
Bryan / All,
As I have done my “tinkering” on my 80HP Aerovee, I have gotten to know some folks with considerable expertise on air cooled VW engines. One of these guys is Prescott Phillips and he actually “wrote the book” on rebuilding these engines. He and others convinced me that 40 - 60 psi oil pressure is perfect. On the low end, an idling engine with hot oil will do just fine with 5psi or less oil pressure. The VW Bugs low oil pressure light came on at 2psi. Running really high oil pressures might contribute to more leaking. For those running external oil filters, an excellent idea, 100psi puts stress on the lines and could even burst the lines or the oil filter. The recommendation is to run the stock parts originally supplied by VW. That is what is in my engine. With warm oil and rpms of 1700 or above I have 40 to 60 psi. Saturday after flying in 85 degree air temp and 80% humidity, I had 15 to 17psi at idle with an oil temp of 165 degrees.
While I am up here on my soapbox, given that running 80 or 100 hp in these engines produces a lot of heat, and that the oil circulation is an important part of cooling “air cooled engines”, does anyone really think that an oil capacity of less than 3 quarts is a good idea? Adding high capacity oil sumps and external oil filters adds weight and complexity, but it might help with cooling and longevity. Anyone have thoughts on this? I tried to paste a scan of the back cover of the book in this message, but I don’t think it worked.
Tom
Re: Summer temperatures and cooling
Posted: Mon Jun 12, 2023 10:38 am
by DCASonex
Not sure how to post photos on this site, but while my CAMit cylinders were off to the UK to be fitted with forged pistons, I made a modification to the cooling air outlets on my A series Sonex. Cut the openings about 5" forward and inserted ramps that slope down to about 2 + " below the cowl at exit. seems to have greatly increased cooling. Have photo showing one side original and one side converted. I thought the small lip that Sonex called for at forward end of the openings looked like turbulence generators that would reduce to ability of air moving past the outlets to help draw air from within the cowl. The modification seems to have helped a lot, may even have to install part of my winter baffle kit for all but hot summer days.
David A.
Re: Summer temperatures and cooling
Posted: Sat Jun 17, 2023 7:27 pm
by Bryan Cotton
I have dropped my cruise oil pressure to about 60-64 but no big change in oil temperature yet.
Next thing to try is to open up the exits from my oil cooler plenum. Before:
oil cooler plenum exit before.png (915.79 KiB) Viewed 9137 times
The openings were pretty small before. Now I’m more than double, by my eyeball estimate.
oil cooler plenum exit after.png (727.94 KiB) Viewed 9137 times
Re: Summer temperatures and cooling
Posted: Mon Jun 19, 2023 8:03 am
by Bryan Cotton
So I have now flown three times with my improved exits - and the temperature is 10F warmer. Any thoughts? I am going to tape it back up to original or maybe slightly less and see what happens.
Re: Summer temperatures and cooling
Posted: Mon Jun 19, 2023 9:12 pm
by n502pd
The lower lip on the bottom cowling is called a ‘seaplane lip’, and is indeed used for enhanced engine cooling. I put one on my plane after opening the overall size of the opening by 25% on all dimentions. I am using a bottom cooler that is, probably, 100% bigger than the top cooler, or maybe a bit more. Its hot here at times and I have not seen oil temps higher than 210 deg durring break in, and less than that after.
A small thing to consider, and I say this with sinserity, " its easier to control over cooling, than under cooling’. In winter, to get temps off the peg, I made cowl opening restrictors to limit the overcooling on cold days. Just a thought!
Re: Summer temperatures and cooling
Posted: Mon Jun 19, 2023 11:07 pm
by Bryan Cotton
Thanks for the thoughts Joe and guys.
One of my former Sikorsky coworkers has a Mooney. Much different animal, I know. But they found that the airflow through the cooler was backwards from expected, so apparently the area they thought was low pressure was actually higher pressure. They tufted it and put a camera on it. I have a hard time understanding how the pressure behind the engine could be higher than over the engine, but if that was the case I could be heating my oil from the hot air in the bottom.
Re: Summer temperatures and cooling
Posted: Tue Jun 20, 2023 12:29 am
by 13brv3
Do you have a manifold pressure gauge, or at least an option to connect a MAP sensor to your engine monitor? If so, that makes a dandy cowl pressure sensor.
Re: Summer temperatures and cooling
Posted: Tue Jun 20, 2023 9:29 am
by Bryan Cotton
13brv3 wrote:Do you have a manifold pressure gauge, or at least an option to connect a MAP sensor to your engine monitor? If so, that makes a dandy cowl pressure sensor.
I don’t. I do have some old Motorola pressure sensors and a raspberry pi, but I’m not sure I have the ambition.
Re: Summer temperatures and cooling
Posted: Tue Jun 20, 2023 1:44 pm
by 13brv3
I bought one of these a while back to try to measure differential pressure, but I’ve had that same ambition problem. I also just don’t have a good way to run the hoses through temporarily.
https://www.amazon.com/gp/product/B099ZYCV1L
Re: Summer temperatures and cooling
Posted: Tue Jun 20, 2023 10:18 pm
by Bryan Cotton
Rusty, run your lines out an air vent and then up through the cowl outlet or inlet. Just use the good duct tape. That’s out of the Sikorsky flight test playbook.
So in the name of science, I taped over both oil cooler plenum exits inside and out. Left the plenum cover off and went flying.
Screenshot_20230620-210641-363.png (576.39 KiB) Viewed 8793 times
Screenshot_20230620-210657-554.png (638.69 KiB) Viewed 8793 times
Last Sunday we stabilized at 219-221 F in cruise. Tonight after 12 minutes of flight, including a climb to 2500’ it was 226 and slowly rising. We did a simulated engine failure as we stayed right over the airport.
So I’m calling that one a fail. Onto the next science experiment. Stand by.
Re: Summer temperatures and cooling
Posted: Wed Jun 21, 2023 10:43 pm
by Bryan Cotton
I mounted a little piece of pipe into my exit plenum and secured it for a test flight. The idea is to pull the air out to a separate external exit.
air goes in here.png (549.41 KiB) Viewed 8706 times
air comes out here.png (509.95 KiB) Viewed 8706 times
This aluminum tube is sealed to the plenum with metal tape. I used a little shop vac hose for a temporary test.
hose through bottom of cowl.png (709.7 KiB) Viewed 8706 times
I even used the hose end that plugs into the vac as my exit.
shop vac pipe.png (511.83 KiB) Viewed 8706 times
Initially it seemed like I had a winner. Temps looked really good during climb. They were slowly going up towards 200, it was 90F out, and I was at full power and 80kts. Leveled off and after a bit it seemed the rate of increase was going up even though I was at cruise power and 100kts. So I landed, and found the hose had softened, rested on the exhaust pipe, melted and sealed itself.
Based on my initial positive results I am pursuing this further. The shop vac hose, besides not handling the temperature, is only about 1" ID and corrugated. It was too long also. So I’ve got some 1.75" scat tubing on the way. I plan to do this right and try again.
Why am I messing with this approach? My CHTs are almost always under 300F. I don’t want to screw that up. The only time I went over 400 was a month ago, doing patterns in the heat. The oil got hot first.
Re: Summer temperatures and cooling
Posted: Thu Jun 22, 2023 11:46 pm
by Bryan Cotton
Ok, getting serious about this mod. I’m no longer baffled on what to do.
baffled no more.png (582.94 KiB) Viewed 8647 times
Re: Summer temperatures and cooling
Posted: Sat Jun 24, 2023 5:42 pm
by Bryan Cotton
I’ve got the rivets drilled out of my baffle. It’s all apart on the bench. I used it to make a paper pattern. The black outline is where the opening currently is. The green outline is how far I can go if I ignore the rivet line.
pattern clecoed.png (677.63 KiB) Viewed 8581 times
Here I have marked out where my 1.75" tube needs to go.
pattern for locating pipe.png (562.55 KiB) Viewed 8581 times
Re: Summer temperatures and cooling
Posted: Mon Jul 03, 2023 9:33 am
by Bryan Cotton
Here is a progress update. Tubes riveted onto the baffle:
tubes riveted to baffles.png (647.23 KiB) Viewed 8392 times
Baffle back together and clecoed to the case:
baffle with tubes in place.png (601.25 KiB) Viewed 8392 times
This is a mockup reverse scoop. It’s a box constructed in two pieces. The flanges go corner to corner and will mount inside the cowl with the ramp sticking out.
mockup reverse scoop.png (698.57 KiB) Viewed 8392 times
I am going to try one hose and outlet first, and record results. Effectively I’m just increasing outlet area by about 2.5" per scoop.
Come wintertime, I see cabin heat experiments in my future.
Re: Summer temperatures and cooling
Posted: Tue Jul 04, 2023 5:36 pm
by Bryan Cotton
Two reverse scoops.
two reverse scoops.png (638.01 KiB) Viewed 8279 times
Re: Summer temperatures and cooling
Posted: Tue Jul 04, 2023 10:22 pm
by Bryan Cotton
I still need to trim the hole before I can rivet it in.
outside view reverse scoop.png (500.02 KiB) Viewed 8254 times
inside view reverse scoop.png (507.74 KiB) Viewed 8254 times