SonexBuilders.net

Hi,

I am presently considering rebuilding my standard vertical split Sonex cowling. Seal off the previous original bottom cooling air outlets and open up the cowling sides for the cooling air outlets as per Sonex plans.

Has anybody tried this relocation?

Do the side outlets work as adverised? Any negative experiences? Any comments?

I believe I saw a picture of a Sonex (Australian?) with side outlets, which also had extra lips added as recommended by Sonex for the bottom outlets. Any significant improvements?

Thanks
Kai

My current and highly experimental opinion is that exit area/extraction is crucial for cooling. Whether side-vents or bottom-vents are better for airflow I do not know. I have a vertically split cowling with the bottom vent, and I may soon add side vents to increase cooling.

How the cowling is split is irrelevant for cooling, what matters is the airflow (intake area, exit area, and baffling). I'd rather have discharge air on the less-sightly bottom of my fuselage then on the sides, but I'm willing to play with other options if it means better cooling.

Ryan, Where do you have your CHT probes mounted? My engine seems to be running hotter than expected at 25hrs, but I'm wondering if it might only SEEM to be running warm because my probes are under the spark plugs and not screwed to the cooling fins as suggested by Sonex.

To test that theory, I've purchased another probe that I intend to attach to the fins to compare any temperature differential between the two locations.

I've already enlarged the cooling exit twice (3/4in each time) with no noticeable change in head temps.

I've been thinking of installing one of these Antisplat "E-Z COOL FLAPS"
check out the youtube video...
https://youtu.be/RnwkRsQxIQE

Are you running hot all the time or just in climb and other full power settings?

Area 51% wrote:Ryan, Where do you have your CHT probes mounted? My engine seems to be running hotter than expected at 25hrs, but I'm wondering if it might only SEEM to be running warm because my probes are under the spark plugs and not screwed to the cooling fins as suggested by Sonex.

To test that theory, I've purchased another probe that I intend to attach to the fins to compare any temperature differential between the two locations.

I've already enlarged the cooling exit twice (3/4in each time) with no noticeable change in head temps.

Mine are installed per the Aerovee installation in this PDF:

http://www.aeroconversions.com/support/ ... nstall.pdf

They're about 1/4" outside the cutout for the top spark plugs, at either the 2 o'clock (pictured) or 10 o'clock position depending on forward/aft cylinder spark plug. The hole is into the meat of the cylinder head, not into a fin.

Rynoth wrote:My current and highly experimental opinion is that exit area/extraction is crucial for cooling. Whether side-vents or bottom-vents are better for airflow I do not know. I have a vertically split cowling with the bottom vent, and I may soon add side vents to increase cooling.

How the cowling is split is irrelevant for cooling, what matters is the airflow (intake area, exit area, and baffling). I'd rather have discharge air on the less-sightly bottom of my fuselage then on the sides, but I'm willing to play with other options if it means better cooling.

Ryan,

Of course you are right.

Too many cowlings on homebuilts are configured with large cooling air inlets, while the outlets are added more or less as an afterthought, followed by grey hairs when trying to figure out why the engine is running so hot.

Tony Bingelis specifies cooling air inlet size area as a function of engine power, and the outlet size as 1.5 to 3 times that: located in a low pressure area. If there is no low pressure area, the needs for cowl flaps, outlet lips etc become mandatory. Slow planes should aim for the higher value; the pocket rockets for the lower, as airspeed is a factor in creating suction.

About the combo ‘bottom plus side’ outlets: I intensely hope you may have a point!

So I specifically raised this topic with Kerry Fores a while back: both bottom and side outlets. He was less than enthousiastic.

His point was that if one of the two was more effective than the other, the outside air could be drawn from the outlet with the smaller pressure drop to the one with the larger drop. Thus the total cooling airflow through the cowling could be reduced.

But- to be fair- he specifically pointed out that he could not be sure: this double configuration had simply never been tested on any of the factory prototypes.

Personally, I am very much in doubt what to do. I recently decided to cut the openings for the side outlets: should I seal off the bottom ones?

Thanks
Kai

If you already cut the cowl for new side vents it gives you the perfect opportunity to test the theory. Fly the plane with the new vents taped closed, record the temps, then fly again with the vents open. You should do several runs which include taping the bottom vents closed while running with the side vents open.
Post what you find out.

Yeah,

Well- I was hoping that someone already might have the answer. Jason Kroetje at Jab US once mentioned that a number of Jab engines under a Sonex cowling with scoops were not exactly overcooled, and I am not risking yet another cooked head or out of round jug.

As you put it, it seems that nobody has a clue yet: remarkable!

Thanks
Kai

Hi there,
Here is my two cents worth. Where I live it is generally just hot or bloody hot most of the time. A Onex had a major overheating issue while I was building, so I made the decision to enlarge the outlet on my horizontal split cowling by 50% over what was stated on the plans. With my Aerovee my CHT's have always been excellent, normally hovering around the 220-240 F in the cruise. I had to mess around with cooling airflow over my sump as I initially had high oil temps that scared me. I don't regret the decision to make the outlet bigger at all. I'm not sure whether side outlets would work better than a similar sized bottom one, however hiding any mess under the aircraft is much neater. I find it very rude if a bystander wants to bend over and look at my bottom. I am however in the middle of fitting a Jabiru 3300 to mine now as I really want the extra oomph. My CHT sensors are mounted as close to the spark plugs as I could get so are probably reading a few degrees cooler. Good luck.

Richard,

Just hot or bloody hot, you say?

A few days ago my wife’s uncle told me they were having +29C on the Gold Coast: wonderful! As soon as this Corona thing is solved I am going back there as right now we are fighting -11C and a snow blizzard up here: I am too old for this :-( And in my shop my 3kW propane heater is going full blast to keep things (me) alive. Adelaide can’t be that bad!

I found proper cooling of a Jab- and especially the longer six, to be a frustrating exercise- even with our summer temps seldom going much higher than +25C. I went all the way with both the original Jab scoops, and later the Sonex version. Things (temps) did not come down to a satisfactory level before I did the following:

- get rid of the scoops and make a cooling air plenum baffle like is common on LyCon engines (and as Sonex does on the Aerovees)
- make the cooling air outlet on the cowling underside as wide and long as possible; preferably the whole width of the cowling.
- make a good solid, wide lip in front of the outlet gap.

With the Jab 6 the Sonex becomes quite lively, and if you are located on a short grass strip you will notice that your glutinus maximus muscles will start to relax, so you are not going to regret the change once in the air. But with a plenum you need a very rigid horizontal split top cowling to avoid cooling air leaks/spillage: sitting in the cockpit at 130 kts watching the top cowling bulge upwards (view not possible on a Sonex), is a fascinating experience. So a cooling plenum with the top half cowling as the ‘lid’ also requires sturdy, wide baffle seals.

Since prop rotation has a marked influence on cooling air supply- the blade going upwards helps, but the downward one is a pain causing uneven air distribution. The idea of a longer prop flange neck on the Jab therefore has some merit, just to get the prop further away from the air intakes. The backside is that this also requires substantial cowling rework. Not to mention the crankshaft out of center once you have the slightest propstrike.

Have fun!
Rgds
Kai