Liquid Cooled Aircraft Engine

poadeleted21

poadeleted21

Touchdown! Greaser!
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Aug 18, 2011
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I stumbled on this

http://www.liquidcooledairpower.com/news-pass_arrow.shtml

I'm wondering if it's a joke.... I'm certainly not buying what they're shoveling. The site looks old and dated but I'd never seen it before.

Aside from having to haul water around and the necessary components to circulate and cool it (which I would assume suck some power too) is there any truth in their claims?
 
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bartmc said:
I stumbled on this

http://www.liquidcooledairpower.com/news-pass_arrow.shtml

I'm wondering if it's a joke.... I'm certainly not buying what they're shoveling. The site looks old and dated but I'd never seen it before.

Aside from having to haul water around and the necessary components to circulate and cool it (which I would assume suck some power too) is there any truth in their claims?
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Not a new concept. Practical? I have my reservations. You can squeeze more horsepower out of a liquid cooled engine yes. I'm not convinced that is the best way to go for an airplane engine though.
 
How much HP does cooling drag steal?
 
bartmc said:
I stumbled on this

http://www.liquidcooledairpower.com/news-pass_arrow.shtml

I'm wondering if it's a joke.... I'm certainly not buying what they're shoveling. The site looks old and dated but I'd never seen it before.

Aside from having to haul water around and the necessary components to circulate and cool it (which I would assume suck some power too) is there any truth in their claims?
Click to expand...

P-51 Mustang did pretty good for itself being liquid cooled.
 
kgruber said:
P-51 Mustang did pretty good for itself being liquid cooled.
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Yeah but a 180 HP cherokee out running a 200 HP Turbo Arrow? They claim an experimental cowl and three blade prop too, and the Cherokee cowl is infamous for it's fight against aerodynamics. But still...
 
bartmc said:
Yeah but a 180 HP cherokee out running a 200 HP Turbo Arrow? They claim an experimental cowl and three blade prop too, and the Cherokee cowl is infamous for it's fight against aerodynamics. But still...
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Seriously, due to design efficiencies allowed for by water cooling using a tank-tube on a longitudinal axis radiator in a well designed scoop, the P-51 managed to gain a positive 'thrust' in cooling the engine. In comparison an air cooled engine is nothing but drag possible.

The efficiencies of CNC machines makes it possible to make the tubes venturi tubes with expansion/compression chambers and nozzle ends.;)
Cooling is a lot of form drag on a LyCosaur.
 
Henning said:
Seriously, due to design efficiencies allowed for by water cooling using a tank-tube on a longitudinal axis radiator in a well designed scoop, the P-51 managed to gain a positive 'thrust' in cooling the engine. In comparison an air cooled engine is nothing but drag possible.

The efficiencies of CNC machines makes it possible to make the tubes venturi tubes with expansion/compression chambers and nozzle ends.;)
Cooling is a lot of form drag on a LyCosaur.
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OK given the water cooled engine increases horsepower (I have a basic to intermediate understanding of engines but don't understand why water cooled increases HP, but I'll buy it) Speed on a plane is a function of the cube root of the HP...i.e. HP doesn't increase speed that much on the same airframe. Given the scenario they laid out, their water cooled cylinders gave performance superior to a much aerodynamically cleaner retract, with 20 more horsepower and a turbo charger. Given apples to apples in an apples to oranges comparison and to make the math easier, the radiator has to increase HP by 20 HP AND the redesigned cowl has to overcome the inefficient cherokee cowling and the drag from the fixed gear? It has to do all this while lugging around a radiator, water and suck power from the engine to circulate it. Not sold yet. If it's true why isn't the STC approved and pretty much every old Cherokee being converted.. (I know, money)
 
I don't believe water cooling directly boosts HP. A water-cooled engine can have tighter clearances, but that wouldn't seem to make more than maybe a 2%-5% difference. The water cooling might let you push the engine harder without it overheating, but without a ground-up redesign, I think that doing that would have some serious long-term reliability issues.
 
Old Geek said:
I don't believe water cooling directly boosts HP. A water-cooled engine can have tighter clearances, but that wouldn't seem to make more than maybe a 2%-5% difference. The water cooling might let you push the engine harder without it overheating, but without a ground-up redesign, I think that doing that would have some serious long-term reliability issues.
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In my 'not really based on facts assumption' I was assuming water cooling would increase reliability,even without a redesign due to the freedom to fine tune cooling.
 
bartmc said:
OK given the water cooled engine increases horsepower (I have a basic to intermediate understanding of engines but don't understand why water cooled increases HP, but I'll buy it) Speed on a plane is a function of the cube root of the HP...i.e. HP doesn't increase speed that much on the same airframe. Given the scenario they laid out, their water cooled cylinders gave performance superior to a much aerodynamically cleaner retract, with 20 more horsepower and a turbo charger. Given apples to apples in an apples to oranges comparison and to make the math easier, the radiator has to increase HP by 20 HP AND the redesigned cowl has to overcome the inefficient cherokee cowling and the drag from the fixed gear? It has to do all this while lugging around a radiator, water and suck power from the engine to circulate it. Not sold yet. If it's true why isn't the STC approved and pretty much every old Cherokee being converted.. (I know, money)
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Water cooled does not increase HP. Fuel increases horse power. Water cooling allows you to control and remove a greater amount of waste heat safely for the same package size and more efficiently allowing for a reduction in drag as well.
 
The Rutan Voyager had water cooled Continental IO-240 engines.
 
We have a water cooled single on the field. Owner calls it the 'Ford'. (HB)
Got a ride in it, too.
 
Color me ignorant, but water doesn't cool anything. It can transfer heat away efficiently, but that heat still has to be dumped off on the airstream eventually.
 
steingar said:
Color me ignorant, but water doesn't cool anything. It can transfer heat away efficiently, but that heat still has to be dumped off on the airstream eventually.
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Ummm... the water cools the engine by transferring engine heat to the water. Then something has to cool the water by transferring the heat somewhere else, in this case a water-to-air heat exchanger that dumps that heat to the surrounding air. We can get pedantic all day long, but in the end most people do understand how that thing we have commonly referred to as a "water-cooled engine" for the past century or so works.

(edit: Or did I completely miss your point? It's early, I'm still on my second cup of coffee. I may just be a little dull.)
 
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steingar said:
Color me ignorant, but water doesn't cool anything. It can transfer heat away efficiently, but that heat still has to be dumped off on the airstream eventually.
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Except that you can build a fluid/air heat exchanger with lower drag than the shape constraints of an air-cooled internal combustion engine create.
 
DaleB said:
Ummm... the water cools the engine by transferring engine heat to the water. Then something has to cool the water by transferring the heat somewhere else, in this case a water-to-air heat exchanger that dumps that heat to the surrounding air. We can get pedantic all day long, but in the end most people do understand how that thing we have commonly referred to as a "water-cooled engine" for the past century or so works.
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The point is you need a air interchange to dump the heat either way. I'm not bing pedantic, I honestly don't understand how the same amount of energy can be transferred aerodynamically in one case and non-aerodyanmically in the other. Energy is energy, doesn't matter what medium it's in.
 
steingar said:
The point is you need a air interchange to dump the heat either way. I'm not bing pedantic, I honestly don't understand how the same amount of energy can be transferred aerodynamically in one case and non-aerodyanmically in the other. Energy is energy, doesn't matter what medium it's in.
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Ah, OK. So I did miss your point. I think you could come up with a far more aerodynamic way of moving air through a radiator -- which could be mounted anywhere -- than you can through an air-cooled engine, which pretty much needs to be in one place unless it's a pusher design.
 
DaleB said:
Ah, OK. So I did miss your point. I think you could come up with a far more aerodynamic way of moving air through a radiator -- which could be mounted anywhere -- than you can through an air-cooled engine, which pretty much needs to be in one place unless it's a pusher design.
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That's the idea. That, and with a much more efficient cooling system you can make more power.

Rotax has definitely been successful. Would love to see a higher HP motor from them.
 
bartmc said:
I stumbled on this

http://www.liquidcooledairpower.com/news-pass_arrow.shtml

I'm wondering if it's a joke.... I'm certainly not buying what they're shoveling. The site looks old and dated but I'd never seen it before.

Aside from having to haul water around and the necessary components to circulate and cool it (which I would assume suck some power too) is there any truth in their claims?
Click to expand...


They are the same folks who operate http://www.planeparts.com
While I was ordering interior plastic piper parts from them, the owner described the Liquid cooled project referenced above. He was very passionate about it.
 
Depending on what altitude they did the test at (as well as which power settings for each plane), the test is possible. The main gain will be in making the plane slicker. I wouldn't be surprised if losing the drag from the engine cooling were enough to give a significant speed increase.

As far as power increase, you won't see much. It's more that you won't see a power decrease caused by high CHTs if you have poor cooling (and can thus remove more BTUs with water cooling, which depends completely on the system). Reliability will improve if you can keep the CHTs more optimal.

Weight will increase. Whether or not this matters will depend on the airframe.
 
steingar said:
Color me ignorant, but water doesn't cool anything. It can transfer heat away efficiently, but that heat still has to be dumped off on the airstream eventually.
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You are very right. And thats why cars have a big fan to cool the radiator. And if your fan belt fails you have no water pump, no fan but a very hot engine. Glad I don't have to worry with my air cooled I0-360.

Jose
 
steingar said:
Color me ignorant, but water doesn't cool anything. It can transfer heat away efficiently, but that heat still has to be dumped off on the airstream eventually.
Click to expand...

Yes, but using water to collect the heat from the engine and taking it to a radiator made specifically for the transfer of heat rather than blowing air directly across the engine, the thermal exchange can be accomplished with considerably less drag due to increased efficiency.
 
Piloto said:
You are very right. And thats why cars have a big fan to cool the radiator. And if your fan belt fails you have no water pump, no fan but a very hot engine. Glad I don't have to worry with my air cooled I0-360.

Jose
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I maintain half a dozen water cooled engines right now, not a fan or fan belt among them.
 
Henning said:
I maintain half a dozen water cooled engines right now, not a fan or fan belt among them.
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Well boats have no radiator neither fan but plenty of ocean water to dissipate heat. But have other problems. Unless the engine has a heat exchanger salt water is going to corrode your engine very quickly. And you still need the water pump.

Jose
 
Piloto said:
Well boats have no radiator neither fan but plenty of ocean water to dissipate heat. But have other problems. Unless the engine has a heat exchanger salt water is going to corrode your engine very quickly. And you still need the water pump.

Jose
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All of them are fresh water (antifreeze) single loop system with no radiators or heat exchangers. An airplane doesn't need a radiator as you know it either to get rid of the heat.
 
Henning said:
I maintain half a dozen water cooled engines right now, not a fan or fan belt among them.
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My airplane does have a fan up front - that's what makes it go. But there is no fan belt.

Liquid cooled heads seem to be working for me...

Water can do a better job of getting the excess heat out of the cylinder heads which can let you run the cylinders at higher power levels. And, you can do a better job getting heat from a radiator to the air than from cylinders to air. But it's not magic.
 
Far more than not, installing liquid cooled auto engines in "experimental" airplanes has been a disaster. Too much radiator exposure is required, which adds to the drag. The cowls end up with inlets and vents all over the place. More than not, the plane ends up with less performance than a Lycoming or Continental...........even though the HP rating is suppose to be more. The pilot ends up "step climbing" to keep the coolent from boiling over. There have been some successes, but they are few. For GA, the air-cooled engine hasn't changed much, because it was a simpler & lighter design, back then..........and still is today.

L.Adamson
 
L.Adamson said:
Far more than not, installing liquid cooled auto engines in "experimental" airplanes has been a disaster. Too much radiator exposure is required, which adds to the drag. The cowls end up with inlets and vents all over the place. More than not, the plane ends up with less performance than a Lycoming or Continental...........even though the HP rating is suppose to be more. The pilot ends up "step climbing" to keep the coolent from boiling over. There have been some successes, but they are few. For GA, the air-cooled engine hasn't changed much, because it was a simpler & lighter design, back then..........and still is today.

L.Adamson
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That's because the majority of people applying liquid cooled engines are doing so with little regards to the fact that the airframe was not designed with liquid cooling in consideration and it is typically applied in a hackneyed method by not the best and brightest of design and engineering methods. If you build the wings and tail from extrusions you can have a clean ice free aircraft in any conditions at a much lower performance penalty than either radiators or air cooled engines.
 
Henning said:
Seriously, due to design efficiencies allowed for by water cooling using a tank-tube on a longitudinal axis radiator in a well designed scoop, the P-51 managed to gain a positive 'thrust' in cooling the engine. In comparison an air cooled engine is nothing but drag possible.
Click to expand...

Although Wikipedia fails to mention that, the "Meredith Effect" is available on any cooling system that is properly designed, including those without any liquid. It was originally obtained at radial engines. Mustang made it famous because it used it very efficiently.

It really is no different from the works of a jet engine in a way. The highest pressure is obtained at the front and the highest velocity is at the back. Result is thrust.

P.S. Since we're on topic, cooling of most Rotax engine installations is not designed with aerodynamic efficiency in mind. Instead, it minimizes the weight by keeping the piping short. This is why airplanes that replace Rotax 912 with Lycoming IO-233 gain weight, and part of the reason why Cessna Skycatcher has unusually large dry weight for an LSA.
 
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L.Adamson said:
Far more than not, installing liquid cooled auto engines in "experimental" airplanes has been a disaster. Too much radiator exposure is required, which adds to the drag. The cowls end up with inlets and vents all over the place. More than not, the plane ends up with less performance than a Lycoming or Continental...........even though the HP rating is suppose to be more. The pilot ends up "step climbing" to keep the coolent from boiling over. There have been some successes, but they are few. For GA, the air-cooled engine hasn't changed much, because it was a simpler & lighter design, back then..........and still is today.

L.Adamson
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A Continental 85 is 180 pounds, a Rotax 912 132 not counting the radiator, but I'm pretty sure my radiator weighs less than 48 pounds. A lot less.

And I don't seem to have any of the problems listed above.
 
In a water cooled engine if you loose the water pump or the coolant you loose the engine. Something you do not need to worry about in an air cooled engine. Why would I risk my life with a water cooled engine when an air cooled system is more reliable. After all, aircraft engine reliability and safety is the #1 objective.

Jose
 
Piloto said:
In a water cooled engine if you loose the water pump or the coolant you loose the engine. Something you do not need to worry about in an air cooled engine. Why would I risk my life with a water cooled engine when an air cooled system is more reliable. After all, aircraft engine reliability and safety is the #1 objective.

Jose
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Not totally true again. You do not lose the engine, you lose the ability to run the engine at high power. The Rotax 912/914 engine I believe is designed to be operated dry at reduced power levels.
 
And besides, like on a fuel system adding a standby electric pump is cheap easy and light
 
Henning said:
Not totally true again. You do not lose the engine, you lose the ability to run the engine at high power. The Rotax 912/914 engine I believe is designed to be operated dry at reduced power levels.
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Just when you need max power on take-off and climb over mountain terrain with a fully loaded plane full of gas. Now you convinced me. Thanks for the tip.

Jose
 
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