Air Cooled VS. Water Cooled

[Mike S]

This thread is shaping up to generate a headache almost as bad as the torsional vibration thread

Why, oh why do I keep reading this stuff??

[rv6ejguy]

Originally Posted by Mike S

This thread is shaping up to generate a headache almost as bad as the torsional vibration thread

Why, oh why do I keep reading this stuff??

Mike, we are all going to behave ourselves.

The TV thread was great and has generated some interest on some other forums. I hope this one will give people some good ideas too. Please anyone with actual bench or flight test data/ experiences- contribute.

[the_other_dougreeves]

Originally Posted by Rotary10-RV

Conclusion: I could make an arguement for either system.

Fly a Rotax and get both.

Here's a shot of a 912S install from head-on. The small round inlet on the right of the airplane's centerline (left on the photo) is the air cooling scoop, about the size of a fist. Oil cooler and radiator are below. Note 2" HVAC foil tape across the top of the oil cooler to reduce cooling for winter temps:


Here is a detail of the air baffling. The baffle appears to be made from fiberglass and directs air down through the fins on the cylinders; you can also see the coolant jackets on the heads. The air cooling is sufficient to allow the 912 to operate at part power settings without serious overheating should you loose the coolant system in flight. (tool is point to the magnetic plug, which you need to check religiously to make sure your gearbox isn't wearing excessively).





To be honest, the coolant system is one more thing to check on pre-flight and in order to do it right, you have to remove the cowling. It's only a 60 second job in the CT, but a better cowling door would make it easier.

TODR

[TSwezey]

Originally Posted by rv6ejguy

Mike, we are all going to behave ourselves.

The TV thread was great and has generated some interest on some other forums. I hope this one will give people some good ideas too. Please anyone with actual bench or flight test data/ experiences- contribute.

Hopefully soon! I think Dan and Jan were doing a lot of experimenting with cooling on Dan's -10.

[RV8RIVETER]

Originally Posted by Rotary10-RV

I believe the best solution for either an Air or Water cooled engine is for the airframe to be designed around it. If you look at a P51 that huge fighter is about the same width at the firewall as a RV-10. Much deeper vertically, but that indicates the flexibility possible with water cooling. Then again no one can argue that an F8-F Bearcat tears through the air with it's large round fuselage. I'll see if I can post a couple of the NACA war reports on the ducting. It shows that the wide open radiator rear isn't that bad, IF and it an important if, the area behind the radiator is unobstucted for at least 4x the core thickness.
Bill Jepson

Don't forget the Jumo powered FW190D/TA-152. They used an annular radiator arrangement and were plenty fast. That type of arrangement may work well in a -10 provided the LS engines are thin enough, as they appear to be in photos.

It doesn't hurt that at a distance people will think you have a radial.

[1:1 Scale]

Originally Posted by rv6ejguy

With a diverging/ converging duct, we can also slow the air down through the rad core which results in more contact time with the fins, lower pressure drop across the tubes/ fins and can re-accelerate the air closer to free stream velocity. Despite the lower Delta T, we can use each pound of cooling air quite effectively. Is it better than air cooling? We don't know without some real world testing.

This is one of the things that keeps rattling around in my head. Another consideration that I don't think I've ever seen mentioned is the fact that a good diverging/converging duct could (should) be made with smooth internal surfaces, free of drag creating items such as pushrod tubes, spark plug wires, intake/exhaust pipes, etc. Sure, straight aircooling may be more efficient without the liquid medium from a thermal standpoint, but the whole system needs to be taken into consideration.

[Mike S]

Originally Posted by rv6ejguy

Mike, we are all going to behave ourselves.

The TV thread was great and has generated some interest on some other forums. I hope this one will give people some good ideas too. Please anyone with actual bench or flight test data/ experiences- contribute.

Ross buddy, I am not concerned about folks getting rude/off track-------it is all this technical stuff, and higher math, that is so far above the comprehension of we mere mortal men.

Ach------where is my Advil???

[gmcjetpilot]

Originally Posted by Jconard

Most of these (EGG) have gotten better and better inlets to the rad, but the outlet is just the bare back of the rad...not optimum at all, but probably the easiest way to retrofit to a design originally intended for aircooled.

That is a good point John. I would say look at the new (EGG) cowl with square inlets. The radiator outlets do just dump out into the cowl, but he has improved from imprevious designs. They look (don't know dimensions) larger than a Vans and certainly James cowl inlet area. I'll say by inspection the drag is higher. Why not get less cooling drag? Well easier said than done. A lot of work has been thrown into optimization of air cooling aircraft engines down to the fin spacing, height and thickness. The cowl designers have been optimized through more research.

Originally Posted by rv6ejguy

The coolant pressures used on the P51 are up to 50 psi! to raise the boiling point and Delta T................Some other tidbits include speeds with open and closed rad flaps. Typically closing the flaps at full power was worth between 10 and 24mph more speed depending on the airframe. Drag is reduced by reducing massflow through the HE (lower pressure drop).

Great post. The pressures where much greater in many aircraft coolant systems. I remember in the 80's the early V6 and V8 auto conversions (no particular) had problems with hot spots, steam pockets and cavitation. So how to get a REAL HIGH PRESSURE pump radiator system? The stock pump will not due, will it?

The "cool jug" guys (water cooled cylinder/heads for Lycs) ran a separate mechanical pump off the accessory case at very high pressures. I talked to them once and the pressures I think where 15-20 psi (typical) but the flow is very high. They don't say much on their site but this might be worth a quick read:

http://www.liquidcooledairpower.com/cj-pump.shtml



It will be great to read about you twin turbo Subaru RV-10 with a P-51 belly scoop set-up, when you get flying Ross. You have to go with a streamlined P-51 cowl to match the belly radiator. Long coolant lines are begging for higher pressures. If the radiator size, thickness and fins/tube spacing if carefully selected should cool very nicely. Will the stock water pump be up to it? Will you have redundant or supplemental electric water pump?

Coolant (what not to use)
In a related topic the General Motors Dex-cool lawsuit has been settled. The class action covers 35 million GM vehicles manufactured from 1995 to 2004. GM's "Dex-Cool" coolant allegedly caused serious car problems such as: corroded clogged radiators, eroded water pumps, rotten radiator hoses, leaky cooling system gaskets, chronic overheating and engine damage from coolant sludge, as well as head gasket and intake gasket failure possibly resulting in engine damage. GM marketed Dex-Cool coolant as good for 150,000 miles or 5 years without needing to be flushed and replaced with new coolant. GM agrees to pay up to $800 per car for repairs.

[SvingenB]

The main difference is how heat is removed from the hot parts of the engine. An air cooled engine use only conduction through metal, and this is not particulary effective regarding heat transfer rate. A liquid cooled engine transports the heat with the liiquid, and this is orders of magnitude more effective

A liquid cooled engine is simply an air cooled engine where channels for liquid flow are drilled into the fins and the core, and liquid is flowing in a loop from the core to the fins and back. For the same temperature in the core, which engine requires more coolinng air? There is noo difference, only the radiator can be made much morre effective, so the liquid cooled engine will be the better choice.

[rtry9a]

Ive been studying various water cooling systems over the last few years while building my RV, mostly in reference to the Mazda rotary engine. There seems to be two groups of thought, and both have made examples that seem to work effectively.

The Egg folks and Tracy Crook prefer the small densely packed (4-5" thick) radiators placed in front of the engine, which restrict the airflows out the back. These generally cool quite well at high speeds due to the high pressure of 200 mph air, but tend to be inefficient at slower (climb, during taxi) when the pressure is lower, and they present close-to-the-same drag profile as the air-cooled heads do.

The other school (where I'm personally leaning, btw) places a much larger, full-size aluminum automotive radiator that is less densely packed and thinner (maybe 1.5-2" thick) placed either parallel to the engine, or beneath it, or both. This arrangement is obviously more complicated and requires well designed wedge diffusers with ducting before and after the radiator. Because the radiator is thin, there is far less restriction/drag involved, and the outgoing air can be controlled with a flap; which, when closed, can substantially reduce the cooling drag when it is not needed in cruise. Because high pressures are not required for efficiency, this design cools well at high and low air speeds. The thing I like about this particular water cooling design, is that once it is proven effective in the particular application, it will work without problems from then on, with no worry about limiting power, shock cooling, or hard warm restarting.

The rotary engine is so much smaller than Lycs or Subis, either radiator orientation works quite well.