Sonex-A purchase - What to look for

[Hambone]

Lots to read! Thanks to everyone.

Now I assume there are scores, perhaps even hundreds of AeroVees flying successfully without melting valves and warping heads. Why does temperature management seem to be so much more critical in an AeroVee than in a similarly configured ‘traditional’ air-cooled aircraft engine, and is it a foregone conclusion that stock AeroVees are always going to be problematic?

[Kai]

I was under the impression that this would have been made clear in the previous postings.

To start with the latest- IMHO it is a foregone conclusion that sooner or later all these small high output air cooled engines that depend on differential cooling will come up with some cooling/heat related issue- I don´t think it is confined to only one make. I would certainly not be surprised if someone could come up with exeptions- but generally: yes.

Presently the only heads in use by converters are the DP ones, as these are presently the only ones commercially available as new, although the single ports are better for our use. As Hoover wrote in his blog 20 years ago, this dp design is flawed for aeroderivative application. Sooner or later something will give- there is just not enough cooling surface for exhaust seats, valve heads, stems and guides. Exactly when depends on the builders attention to detail in head preparation for high output operation without a massive cooling fan, the design and construction of a proper no air leak cooling plenum, the installation and testing of air fences and tins under the head to take advantage of the available cooling air, sufficient pressure differential between cooling plenum and cowling outlet, hamfisted engine operation during climb- the list goes on and on. All are issues the builder will have to deal with before the installation may be considered operational- it is tedious work.

It is this individuality that makes it so hard to offer to the point comments. Not two installations are exactly alike- something is always different.

LyCons on the other hand, are designed from start for pressure differential cooling. Great attention has been given to large cooling areas around the exhaust side of the heads, as well as the cowlings- though it must be admitted that nothing in this world is perfect: last season a Warrior plonked down on our airstrip with an engine that had swallowed an exhaust valve. But there are thousands and thousands of them, all running just fine under very strict operational directions, with only a small percentage of issues. Compare that to the relatively few VW-1´s in operation and the high quantity of issues they experience.

[Bryan Cotton]

Fortunately my AeroVee has never read the Hoover blog. 265 hours and counting. I'd like to catch up to the high time AeroVee guys, but some of them set a high bar to reach. I do agree that the cooling is not as good as the Lycoming series. I also strongly suspect that the burned valves Kevin experienced happened before he got the airplane. One of his concerns was it didn't seem like there was much compression when turning the prop by hand, when he initially flew out to check it out. That's a hard thing to quantify via email. But yeah, it was a lot less than mine when he arrived here. With 60 hours in the logbook, it would be interesting to see if all the break-in valve adjustment and head torque schedule was carried out. We set the valves when he was here and some of them were on the tight side.

[Kai]

Great Plains once offered liquid cooled heads for the VW-1. It´s probably like cussing in church, but I was sorely tempted to try them on a friends engine which was also on the hungry side for valves and heads. However, not the lightest by design, the VW engine got even heavier with these on, so Steve Benett told me it had not been a marketing success. Friend refrfained from this project and took his business elsewhere.

I, on the other hand, was so sick of the neverending head battle with my aircooled Jab, that I went Down Under with my pennies and got a set of LCH´s. The result was like magic, and I immediately became a convert. Gone were the burnt and broken valves, cracked heads, detonation, and loose seats. Although the engine itself became a little lighter with these heads, coolant, radiator and pump increased installed weight somewhat- nothing the Sonex could not handle. Since my need for speed later forced me to remove this engine from the airframe, as far as I know it is still putt-putting around up there with its new owner. When I ask him for any issues, all I get back is a puzzled look.

Like I said- like cussing in church…………

[Arjay]

Bryan had stated:
"hambone had mentioned that in a climb he got over 400, and then cooled to 330 or so. On my Aerovee I rarely get over 300 and I typically cruise with the hot cylinders in the mid 200s. One major difference we noticed was the baffles. They sealed ok against the cowl, but there were a lot of gaps where the sheetmetal met the engine. Not sure if that was as built by Derrick or as redone by the second owner, but the tabs that form the back corners were loose or hacked up. The back right side had a huge gap - you could drive a truck through it. Also the rear baffles were not tucked into the cooling tins. Up front there was a large gap forward of the heads. I think all the time I spent to seal that stuff, either with sheetmetal or a gallon of red RTV, was worth it."

I bought my legacy Sonex, with Aerovee, from the second owner. Originally, I had no particular cooling issues, but they started when I replaced the CHT probes (one failed and I replaced both). Now, I can never keep the CHT under 400 F on climb out. Even step climbing at 70 mph, 2800 or so RPM, it always goes over 400. I will level off and richen the mixture and get it down into the 390's, then climb some more, while it goes over 400 during the climb. Ususally, after about 30-40 minutes into the flight, the CHT will come down a little so and I can keep it under 400, then.

We have tried several things to help this: opened up the air inlet and outlets in the cowl, partially closed off the inlet to the bottom oil cooler, and taped off the side NACA opening in the cowl that was only feeding air into the bottom area under the engine, checked the baffles around the engine, etc. These changes have helped a little, but the problem, although improved, is still evident. Not having built the plane, myself, I don't have the knowledge and/or building skills to know what to do to solve this. I NEED SOME HELP. (And I suspect I'm not alone).

Bryan, you have obviously worked miracles with your installation. I am so envious of what you and Adam have achieved with your low CHT's. Would you mind sharing the details of how you did it? Could you provide details, including pictures, of what you did to get such low CHT numbers? Where did you put that gallon of red RTV? What are the dimensions of your cowl air inlets and outlets? Can you show us how you sealed the air box around your engine, including baffles, seals, closed gaps, etc.?

Thank you so much. I am sure you have and will continue to help many of us with this issue.

Ron
Legacy Sonex taildragger with Aerovee, Rotec TBI, modified Anson tailwheel

[Bryan Cotton]

Bryan, you have obviously worked miracles with your installation. I am so envious of what you and Adam have achieved with your low CHT's. Would you mind sharing the details of how you did it? Could you provide details, including pictures, of what you did to get such low CHT numbers? Where did you put that gallon of red RTV? What are the dimensions of your cowl air inlets and outlets? Can you show us how you sealed the air box around your engine, including baffles, seals, closed gaps, etc.?
Ron
Legacy Sonex taildragger with Aerovee, Rotec TBI, modified Anson tailwheel

Ron, next time I have the cowl off I'll take pictures and start a new thread. I'll confess that my CHTs have never been calibrated. But I've also looked at my valves with the borescope when I was troubleshooting the lean #1 cylinder issue, and they looked great. Totally different than Hambone's. We probably had about 240 hours when I last had a look at them. Regarding the inlets and outlets - I followed the plans.

[BRS]

In my thinking, valve condition and CHT's are not directly related. Yes EGT affects CHT but really well baffling and appropriate inlet/outlet will keep CHT's happy while valves are still cooking. Fuel flows as well as fuel type (even oil type) seem to affect the valves more than CHT's Unless of course you are north of 450 or so on the heads and the seats are getting pounded into recession.

I'll get a pic of how the Revmaster CHT probes are installed, for your new thread Mark. They are considerably different from the spark-plug gasket type. No doubt they will give different results. Hotter or cooler I'm not sure.

[Kai]

I have always been thaught that the main heat generator is combustion. Combustion temperature (EGT) is a function of fuel flow: too little fuel and the EGT goes through the roof. One needs to take care that the EGT´s in all cylinders are reasonable well balanced with a delta T of say 30-40 centigrades, and a maximum not exceeding manufacturers values. I don´t know about the VW-1´s, but on the Jabs this was a daunting task. Too much fuel and everything coked down, too little and the seats were dropping out. Further complicating the situation is the fantastic fuel quality available to us these days, with these small engines none too happy about the lead in Avgas 100LL, forcing users over to Mogas with ethanol. Wonderfull!. The only asset normally available for checking the EGT, is the temp probe. Its readings are hugely affected by where in the pipe it is positioned. Manufacturers indicate 100-120 mm from the exhaust port:they seldom say anything about the inside or the outside of an exhaust pipe elbow, up- or downstream from it, or on the side. The result is that a direct comparison is of questionable value- some are even sitting smack in the middle of the cooling air stream.

Much of the heat goes out with the exhaust, but a lot remains, which needs to be dealt with, as it is soaked up by the components in the cylinder head, the piston crown and the top of the cylinder causing many issues if left unattended. The only medium available for piston crown cooling, is engine oil- and you can do little about it. The rest is handled by liberal quantities of cooling air. The final result of its work is quantified by the CHT probe. The lower its value, the better- IMHO well below 150 C/300 F as a continuous value for safe operation. A common position of this as a ring probe is under a spark plug- which unfortunately is sitting smack in the middle of the cooling air as a result of engine design. An alternative position as indicated by Brock is therefore highly interesting. Jab too tried to do something about this and stuck a probe into the head between the sparkplugs- still with liberal quantities of cooling air flowing over it. Something better needs to be found.

[WesRagle]

HI Guys,

The final result of its work is quantified by the CHT probe. The lower its value, the better- IMHO well below 150 C/300 F as a continuous value for safe operation.

Just to back up the above statement.

Back when I was first flying the Onex I ask Scott Casler or Hummel Engines this question: "Is there a temperature that is just too low for CHT *after* break in?

His reply: "The lower the CHT the better."

I've spent a lot of time thinking about fuel injection lately. One of the books I've read suggests that it is a mistake to inject fuel directly into an open intake valve. It's better to evaporate the fuel against a closed intake valve just before valve opening to ensure full evaporation. I can't help but wonder if evaporating a gallon of fuel per hour at each intake port might lower CHTs a bit.

Wes

[Kai]

Wes,

You may perhaps have a point, but I am speculating the very small quantity of heat it takes to evaporize injected fuel spray, counts for nothing compared to the great quantity of heat already stored in the head as well as residual heat in the combustion chamber.. So should you start with an efi project on you Onex engine, don´t be disapointed if you notice no change. Another misconseption is that efi will noticeably increase engine power, everything else being the same. Truth is there might be a very few ponies gain, solely because the engine no longer has to negotiate the power loss associated with the (manifold) pressure drop in the venturi.