Cooling your AeroVee Heads

[Area 51%]

The heads run hot because the original design was only 45HP and forced cooling

Not sure where people keep coming up with this number. In 1965, the 1200cc engine developed 40hp. In "66" the 1300 was producing 50. The 1971 version spat out a whopping 60hp with pretty much the same heads we are using. Over-worked and under-paid to be sure, but 35% over is more realistic than 90%.

[Scott Todd]

We've had this discussion before. It doesn't matter what they were 'designed' for. These 'original HP' discussion and ones like "don't have enough cooling capacity at full power" are just urban myths. As Alex eludes to, its just simple Thermodynamics. You can pump as much heat into them as you want as long as you have sufficient cooling on the other side. This has been proven OVER and OVER and OVER...Tiny inlets, not enough exit area, too much blockage from fin cast flashing, improper baffles, etc are the real problems.

People like John Monett and thousands of car enthusiasts have been racing these little engines and making much more than our 80 HP for decades. Make sure you have enough cooling air moving across the fins, and you can run them quite hard, for a long time.

My brand new AeroVee powered Onex can climb at full power until I decide to level off. My max CHT has been 384F. None of the other 3 Sonex airplanes I have test flown had cooling issues either. I made sure of that before they ever ran for the first time :)

Scott

[AlexZ]

People like John Monett and thousands of car enthusiasts have been racing these little engines and making much more than our 80 HP for decades. Make sure you have enough cooling air moving across the fins, and you can run them quite hard, for a long time.

In cars forced cooling does that. In the air it's airspeed.

My brand new AeroVee powered Onex can climb at full power until I decide to level off. My max CHT has been 384F. None of the other 3 Sonex airplanes I have test flown had cooling issues either. I made sure of that before they ever ran for the first time :)

Flying a Onex and single in a Sonex hardly ever gives cooling issues. A Sonex at MTOW does. Too long at a too low airspeed will kill your heads. No matter how perfect everything is under the cowl. High power and low airspeed. Pumping in heat and unable to get it out. A Sonex at MTOW is a bad climber, so climb out takes a wile.

[Scott Todd]

You keep missing the point. It just needs to be cooled. Airspeed IS forced cooling. There are lots of Sonex's that cool just fine at MTOW. The ones I tested did just fine at MTOW, in Phoenix! If its perfect under the cowl, and out of the cowl, its perfect!

High power and low airspeed. Whats does that even mean in numbers? Is 50 too slow? How about 60? Maybe 70 is the magic number. 90 seems to ring a bell. Its still about cooling air flow and cooling (fin) efficiency. Of course each airplane will present slightly different but Sonex's can be made to work.

Clearly you are convinced a VW will NEVER cool properly in a Sonex. Perhaps you should try a different engine. Maybe we should tell Sonex their design is flawed.

"unable to get it out" says it all. Look at the people that have added the side outlets and their cooling problems were solved. Maybe they are on to something...

[XenosN42]

I have been following this thread with some interest. I have flown behind an AeroVee in a XENOS and now a OneX. I have had some cooling issues, but never had CHTs above the upper limit of 420°F. I’ve always been able to keep it below 405°F.

I’d like to present some real world numbers from my OneX. I picked an arbitrary recent flight with an initial climb of approx. 4,600 feet. I’ve stacked the graphs showing different flight and engine parameters.
https://jasflyer.com/OneX/AeroVee%20Performance.aspx

I’m not saying these engine numbers are perfect or achievable in all flight situations. They are just offered up as an example of the performance I’m seeing. Performance that I’m very happy with.

[Scott Todd]

Looks great Michael! I had my first flight today collecting data. Finally figured out the MGL protocol and format. Here is a quick screen grab. It had 3.1 hours at the start of the flight and has always been at full throttle for the entire first few flights. Today was the first time I pulled it back other than for landing. I was monkeying with the throttle and different air speeds until about 10 minutes. I was at full throttle from the 10-15 minute mark and then 3200 until I started my descent for landing. These are CHT's. OAT was 69F. Stock Onex. Sonex recommended position for TC's. Exit area using lip per latest Onex plans.

The Flight Data Viewer is awesome!

[AlexZ]

You keep missing the point. It just needs to be cooled. Airspeed IS forced cooling. There are lots of Sonex's that cool just fine at MTOW. The ones I tested did just fine at MTOW, in Phoenix! If its perfect under the cowl, and out of the cowl, its perfect!

High power and low airspeed. Whats does that even mean in numbers? Is 50 too slow? How about 60? Maybe 70 is the magic number. 90 seems to ring a bell. Its still about cooling air flow and cooling (fin) efficiency. Of course each airplane will present slightly different but Sonex's can be made to work.

Clearly you are convinced a VW will NEVER cool properly in a Sonex. Perhaps you should try a different engine. Maybe we should tell Sonex their design is flawed.

"unable to get it out" says it all. Look at the people that have added the side outlets and their cooling problems were solved. Maybe they are on to something...

I'm not missing the point. I know it needs to be cooled. With forced cooling I meant pressurized with a fan. Climbing out at MTOW with 60 to get some climb performance builds up heat in the heads, because of lack of cooling. The cooling efficiency of the fins is not enough in that situation. So in climb watch the temps and act accordingly. That keeps the engine happy. 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.

[Area 51%]

I have been following this thread with some interest. I have flown behind an AeroVee in a XENOS and now a OneX. I have had some cooling issues, but never had CHTs above the upper limit of 420°F. I’ve always been able to keep it below 405°F.

My ""Error-V" assembly manual has the absolute upper limit at 450deg. It allows 420 for five minutes.

[GraemeSmith]

Further to my comments about CHT's tracking EGT's and so my belief that getting mixture evened out is a factor:

Note that temps are in CELCIUS.. Scales are set exaggerated to show small differences.

This is pretty typical of a climb out

[mike.smith]

With forced cooling I meant pressurized with a fan. Climbing out at MTOW with 60 to get some climb performance builds up heat in the heads, because of lack of cooling. The cooling efficiency of the fins is not enough in that situation. So in climb watch the temps and act accordingly. That keeps the engine happy. 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.

With all the AeroVees/VWs flying, this is just completely untrue. The AeroVee/VW has plenty of cooling capacity with normal air flow through the cowl, and no need for tricks like fans. That is a fact, because it's how all the AeroVees/VWs have flown, and continue to fly, successfully. It's not conjecture; it's proven. I have 500 hours behind mine, so I do know of what I speak.