Summer temperatures and cooling

[NWade]

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

[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.

[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.

[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.

[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

[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.

[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 7814 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 7814 times

[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.

[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!

[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.