Cooling your AeroVee Heads

[Kai]

The Sonex at MTOW could use some more HP to improve takeoff and climb. Sonex acknowledged that and came up with the turbo. I'm seriously looking at another engine. Adding the turbo or swapping for a (used)Rotax ULS cost the same here in Europe.

[/quote]

Alex,

I- with by now quite a few others, have been through the same deliberations.

Originally my Sonex Legacy #0525 SG DS had a 85HP Jab up front: a t/o on a grass field with two in the cockpit was an exercise only for the brave. So I put on a turbo (Aerocharger): the results were smashing! But the swap was very hard on pistons and cylinders, and when Jab more or less ceased production of specific gen 1, -2, and-3 spares, I had two choices: quit flying or install a R912ULS.

There is a lot written about this in ‘Actual Flying Rotax Installs’. A chap Down Under made a sort of square tube ring mount to mate his VW engine support to the Rotax: very nice!. As luck would have it I got hold of a surplus Jab 33A engine support (the Jab 22A mount would move the 912 too far forward), and to this I mated the Rotax ring mount. A chap in Sweden has a Sonex in the air with a mount he designed himself (which is beyond me!). And of course you have the beautiful Sonex ‘fit and forget’ solution- clearly less work if you want to spend the shipping costs for the new mount to Europe, fit to cause a cardiac arrest.

Indeed- a lot to think about! Feel free to PM me should you have some questions. And when all is said and done, and you are once more sitting there looking down the runway with an entity that has not yet been in the air, remember: the thing pulls to the left- HARD right rudder!!

Thanks
Kai

[AlexZ]

Since a few don't want to understand what I'm trying to explain about cooling capacity I'll just let it go.

So back to my first reaction in this topic. - Don't do break-in on the ground.
That's what Sonex advises and I fully stand behind that. Also read this https://www.kitplanes.com/the-most-reliable-engine/ especially the chapter 'Engine Break-in or Engine Breaking?'. Note the text under picture with the shroud on an Aerovee.

[phenry]

I agree that all the Aerovee needs is good airflow to keep the heads from overheating. I suffered with overheating issues for some time before I finally worked it out.
To get maximum air flow over the heads and thus optimum cooling the pressure differential between above and below the plenum must be at its greatest. To make this happen we create a vacuum using the shape of the cowl exit, we make the cowl exit sufficiently large to handle the expanded/heated air and we block any places we do not want air to flow at the plenum including where the plenum intersects with the cowl.
Having addressed all the above issues and still having heating issues that I had to manage carefully when flying, I finally concluded that the bottom mount oil cooler arrangement is a major problem in the air-cooling system.
If you have an extra hole in the front of the cowl below the plenum that is used to cool engine oil, then this airflow adds extra pressure below the plenum and the differential pressure is reduced.
The bottom mount cooler is more complicated requiring a special oil pump, additional plumbing, and expensive hardware. It can be way to efficient at cooling the oil, meaning oil temperatures are kept to cool and people must block up the cooler airflow to get good operational oil temperatures specially in the winter.
The moment I replace the bottom cooler with a top mount cooler everything came good. I permanently blocked the bottom cooler air hole and binned all that extra plumbing and the full flow pump. Now my heads are cooler, my oil temperature gets up to the correct values. Even here in Australia with our very hot summers oil temperatures are not an issue. In fact, I have about one third of my top mount cooler blocked off all year round.
So my advise is: Ditch the bottom mount cooler.

[Scott Todd]

I found it interesting the Onex evolved to the top mount oil cooler and larger inlets. They also revised the lip on the bottom for more effectiveness. And now the B models have even more exit area on the sides. There are all good lessons here for Sonex owners, especially in warmer climates.

[karmarepair]

So back to my first reaction in this topic. - Don't do break-in on the ground.
That's what Sonex advises and I fully stand behind that. Also read this https://www.kitplanes.com/the-most-reliable-engine/ especially the chapter 'Engine Break-in or Engine Breaking?'. Note the text under picture with the shroud on an Aerovee.

That's the sort the setup I'll be using. I'll post pictures when I'm done with it.

IF I had built this engine myself, I'd be much more inclined to do it the "Sonex Way". But I did not. The original engine builder did some strange things, and then the engine sat for about 15 years. The massive amounts of white lithium grease they used as "assembly lube" stuck the oil relief piston in it's bore and blew up two oil coolers before the problem was ID'd. This was AFTER an experienced VW aeroengine owner (1000 hrs in a VP-1) cracked the case to look around, and fixed a few things he saw he didn't like. What OTHER surprises does this engine have? I want to find them ON THE GROUND, and I'm prepared to do what it takes to safely run this engine ON THE GROUND. CHT limit (and I have 4 probes) is 375 deg F for ground running, PLUS I have an infrared remote reading thermometer to cross check the under plug thermocouples.

Kerry Fores, the author of the article you cite, makes a good case for NOT doing extended ground running, and that advice is sound for most builders.

[karmarepair]

I agree that all the Aerovee needs is good airflow to keep the heads from overheating. I suffered with overheating issues for some time before I finally worked it out.
Having addressed all the above issues and still having heating issues that I had to manage carefully when flying, I finally concluded that the bottom mount oil cooler arrangement is a major problem in the air-cooling system.

That's what I have, and I don't like it. My Sonerai had a top mount oil cooler.

If you have an extra hole in the front of the cowl below the plenum that is used to cool engine oil, then this airflow adds extra pressure below the plenum and the differential pressure is reduced.
The bottom mount cooler is more complicated requiring a special oil pump, additional plumbing, and expensive hardware. It can be way to efficient at cooling the oil, meaning oil temperatures are kept too cool and people must block up the cooler airflow to get good operational oil temperatures, especially in the winter.

The cast aluminum pump cover also is far less wear resistant than the stock cast iron, especially on an engine with no oil filter. That can be fixed with a better cover from Gene Berg...but I digress.

The moment I replaced the bottom cooler with a top mount cooler, everything came good. I permanently blocked the bottom cooler air hole and binned all that extra plumbing and the full flow pump.

I'm still a believer in full flow, but I'd rather have an oil filter than a cooler IF I had to choose, me.

Now my heads are cooler, my oil temperature gets up to the correct values. Even here in Australia with our very hot summers oil temperatures are not an issue. In fact, I have about one third of my top mount cooler blocked off all year round.
So my advise is: Ditch the bottom mount cooler.

I may do. I also hate how hard it is to change the oil or drop the sump with the bottom mounted oil cooler. But I want to get this airplane FLYING. I'm at roughly sea level, will rarely flow at MTOW, and it's pretty cool here pretty much all the time, so I can fiddle around later.

[AlexZ]

IF I had built this engine myself, I'd be much more inclined to do it the "Sonex Way". But I did not. The original engine builder did some strange things, and then the engine sat for about 15 years. The massive amounts of white lithium grease they used as "assembly lube" stuck the oil relief piston in it's bore and blew up two oil coolers before the problem was ID'd. This was AFTER an experienced VW aeroengine owner (1000 hrs in a VP-1) cracked the case to look around, and fixed a few things he saw he didn't like. What OTHER surprises does this engine have? I want to find them ON THE GROUND, and I'm prepared to do what it takes to safely run this engine ON THE GROUND.

There's only one way to find the OTHER surprises! If you really don't trust the engine you MUST REBUILD it. Even if it runs fine on the ground you'll never sit relaxed behind it in the air.
Tearing it down only takes half a day. Inspect all the parts closely and order new for the ones you don't like. A normal rebuild(when everything is okay) will cost you about $500 in parts. Read the manual at least twice before you start. Take your time to do it right and after 2 weekends of work you'll have an engine you build yourself and, most important, trust.
The other things that count is the learning experience and the fun doing it.

[AlexZ]

Last weekend I did a comparison between the ring TC and a screw-in TC.

TC-ring.jpg (8.96 KiB) Viewed 2505 times

TC-screw.jpg (4.53 KiB) Viewed 2505 times

I used the screw-in TC to clamp the ring TC. So they're in the same spot with the difference that one is about 1/2 " in the head and one is on top.
The scew-in gave a 85℉ higher value and was reading 480℉.

[Scott Todd]

I thought it would have been higher. 1/2" is a long way in :) But it helps to illustrate the point to other curious builders. Just put it where Sonex recommends and go from there.

[karmarepair]

Looking for something else (converting to top mount oil cooler) I found this great illustration of what I'm talking about
viewtopic.php?f=3&t=2804&hilit=casting+flash#p21394

Your heads will cool much more effectively if they look like the ones on the right of this photo.