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Liquid cooling

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wnorth(at)sdccd.edu
Guest

Posted: Mon Mar 10, 2008 6:15 pm Post subject: Liquid cooling

Hmmpf,



Seems like the laws of thermal dynamics are pretty clear about heat

rejection, it takes what it takes regardless of medium used.



The only advantage liquid cooling has is the capacity to provide a heat

reservoir, to absorb it when too much is being generated, and to retain it

when not enough is being generated.1



The rejection of heat off of aluminum radiator fins versus cylinder cooling

fins is the same if the delta T between the fins and air is the same. Typical

coolant based radiators need to be a bit larger per HP because the engine

designers are shooting for lower temps (220deg vs 350deg) But a radiator that

was designed for aircraft use, or a coolant medium that allowed for higher

operating tempertures would solve all the proscribed complaints.



Unfortunately there is no real science to the claims made in this argument

because the P51 is the only one mentioned that was designed completely to be

both liquid cooled and aircraft. The auto conversions are not using radiators

or coolant designed to be in an aircraft, nor is the aircraft discussed

designed to be using a liquid cooled engine.



If you put a bullet in the sump or oil tank of a radial it will stop

producing power relatively quickly, just like the P-51. And it is a mistake

to say that the 51 will drop dead if they loose their coolant. That is not

true. They will need overhaul after landing but they will produce power when

decidedly overheated particularly if one backs off the power. Of note here is

that while I have tagged a few birds I've yet to take in any lead so the

stray sniper arguement is a bit of a reach.



The fact that one design wins a race over another means nothing to this

discussion without a discussion about mean time between overhauls and rate of

catastrophic failures, which data likely shows happening more often as a

function of more HP being produced (along with winning) versus type of

cooling system used.



The down side of liquid cooling is sophistication and the inherent cost. But

something exotic like micro ducting of a high temp coolant in the cowl or

wing skins would provide all the surface cooling one would ever need with no

extra drag, and viola, eliminate the cooling inlet/outlets all together while

also having a huge thermal reservoir for extra long straight up climbouts.



So it is time for someone to invent a low cost high strength lightweight

smooth cooling blanket that can be worked like 2024, and then use oil cooling

systems off the main oil pump. I think the point of the original poster is

that there are ways to get to a better design if we are willing to be a

little open about it.

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gcomfo(at)tc3net.com
Guest

Posted: Mon Mar 10, 2008 7:32 pm Post subject: Liquid cooling

--

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rv7(at)b4.ca
Guest

Posted: Mon Mar 10, 2008 9:17 pm Post subject: Liquid cooling

On 19:12 2008-03-10 "Wheeler North" <wnorth(at)sdccd.edu> wrote:

 	  Quote: 	
		   And it is a

 mistake to say that the 51 will drop dead if they loose their

 coolant. That is not true. They will need overhaul after landing but

 they will produce power when decidedly overheated particularly if one

 backs off the power.


	


Coincidentally, this is one of the arguments in favour of a rotary

conversion... Mazda rotaries are known for running dry and not failing.  In

the event of an oil leak, your power will drop off a bit, but you won't

have to shut down.  Might make the difference between an off-airport

landing risking life, limb, and airframe, and a safe landing followed by an

overhaul.



Not saying that's the only thing you should consider in an engine choice,

but it's something to consider anyway.



 	  Quote: 	
		   So it is time for someone to invent a low cost high strength

 lightweight smooth cooling blanket that can be worked like 2024, and

 then use oil cooling systems off the main oil pump.


	


I think you'd find that the problem with such a system is the drag

internally, on the oil being pumped around.  You'd need a pump almost as

big as your lycoming just to get the pressure necessary to push the oil

around.  



-Rob

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skylor4(at)yahoo.com
Guest

Posted: Tue Mar 11, 2008 6:48 am Post subject: Liquid cooling

--- Rob Prior <rv7(at)b4.ca> wrote:



 	  Quote: 	
		   

 <rv7(at)b4.ca>

 

 On 19:12 2008-03-10 "Wheeler North"

 <wnorth(at)sdccd.edu> wrote:

 > And it is a

 > mistake to say that the 51 will drop dead if they

 loose their

 > coolant. That is not true. They will need overhaul

 after landing but

 > they will produce power when decidedly overheated

 particularly if one

 > backs off the power.

 

 Coincidentally, this is one of the arguments in

 favour of a rotary

 conversion... Mazda rotaries are known for running

 dry and not failing.  In

 the event of an oil leak, your power will drop off a

 bit, but you won't

 have to shut down.  Might make the difference

 between an off-airport

 landing risking life, limb, and airframe, and a safe

 landing followed by an

 overhaul.


	


Well, I know of one rotary powered RV-6 that had an

off-airport landing due to cooling system failure, and

subsequent engine failure.  His engine did not run for

very long at all after the coolant leaked out and

boiled over.  Fortunately, he was able to make a safe

landing on a highway.



Skylor

RV-8 QB

Under Construction

Never miss a thing.  Make Yahoo your home page. 

http://www.yahoo.com/r/hs

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Ed Anderson

Joined: 10 Jan 2006
Posts: 475

Posted: Tue Mar 11, 2008 7:26 am Post subject: Liquid cooling

> Well, I know of one rotary powered RV-6 that had an

 	  Quote: 	
		   off-airport landing due to cooling system failure, and

 subsequent engine failure.  His engine did not run for

 very long at all after the coolant leaked out and

 boiled over.  Fortunately, he was able to make a safe

 landing on a highway.



 Skylor

 RV-8 QB

 Under Construction




	




 I know about the one rotary powered RV-6 with a blown radiator hose where 

the pilot elected to make an emergency landing on a dirt road due to the 

smoke and steam (and probably fear of fire) - who can blame him. Since both 

he and the aircraft flew again - he clearly made a good decision.  Could he 

have made it to an airport - we will never know for certain and I certainly 

would not fault him for the good decision he made.



I do  know of two other rotary powered aircraft that lost coolant and 

although the engine was fried got both aircraft back to a safe airport 

landing.  One was a LongEZ and the second was another RV-6.  The pilot in 

the Rv-6 even had to make a go-a-round due to conflicting traffic.  He 

stated that when he returned the next day to examine the engine and poured 

liquid into the engine - it leaked like a sieve - all the rubber seals had 

been destroyed.  $600 for another core and $1800 for new parts and he was 

flying again for less than $3000.



The rotor engine is a bit different than piston engines in one significant 

way that prolongs the engines ability to operate while overheated.  In a 

piston engine the overheated aluminum pistons will expand more  than the 

iron cylinder until the engine seizes.  The rotary engine on the other hand 

has an iron rotor inside an aluminum housing - the housing expands greater 

than the rotor so you do lose some compression but the engine will not seize 

due to loss of coolant alone.



The rotary can also operate on very low oil pressure due to its large 

bearing surface and low inertia loads on  the eccentric shaft (crankshaft) - 

however, it like any other engine, it will eventually seize without oil to 

the bearings.



The mechanical configuration of the rotary also does a good job of isolating 

one rotor from what happens to the second rotor.  I lost all the power to 

one rotor on my way to Sun & Fun one year, my fully loaded RV-6A.  I 

managed to maintain 6500 MSL on the one remaining good rotor by cranking the 

mixture to full rich and getting 14 gph fuel flow.  It was just blowing 

through the bad rotor but was enabling the good rotor to make max power 

which was sufficient to get me to a 6000 foot runway 60 miles away.



 Yes, I will admit after 400 hours behind my rotor I am a "bit" biased 

toward the rotary, but, I like to think its because it has proven its 

suitability as a viable aircraft engine.  But, like with any engine - 

failures can happen and the one thing all engine failures have in common is 

that they rarely  happen at a good time {:>).



Ed

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_________________
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com

billsettle(at)bellsouth.n
Guest

Posted: Wed Mar 12, 2008 1:12 am Post subject: Liquid cooling

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tracy(at)rotaryaviation.c
Guest

Posted: Wed Mar 12, 2008 8:21 am Post subject: Liquid cooling

The rotary will run for an amazing amount of time after coolant loss but loss of oil pressure is a different matter.  Main bearings will sieze just like in a piston engine.  Backing off the power does help with oil pressure loss but the allowed power will not sustain level flight. 

 Tracy Crook

 On Tue, Mar 11, 2008 at 1:16 AM, Rob Prior <rv7(at)b4.ca (rv7(at)b4.ca)> wrote:

 [quote]--> RV-List message posted by: "Rob Prior" <rv7(at)b4.ca (rv7(at)b4.ca)>

On 19:12 2008-03-10 "Wheeler North" <wnorth(at)sdccd.edu (wnorth(at)sdccd.edu)> wrote:

 	  Quote: 	
		   And it is a

 mistake to say that the 51 will drop dead if they loose their

 coolant. That is not true. They will need overhaul after landing but

 > they will produce power when decidedly overheated particularly if one

 	  Quote: 	
		   backs off the power.

Coincidentally, this is one of the arguments in favour of a rotary

conversion... Mazda rotaries are known for running dry and not failing.  In

 the event of an oil leak, your power will drop off a bit, but you won't

have to shut down.  Might make the difference between an off-airport

landing risking life, limb, and airframe, and a safe landing followed by an

 overhaul.

Not saying that's the only thing you should consider in an engine choice,

but it's something to consider anyway.

 	  Quote: 	
		   So it is time for someone to invent a low cost high strength

 lightweight smooth cooling blanket that can be worked like 2024, and

 > then use oil cooling systems off the main oil pump.

I think you'd find that the problem with such a system is the drag

internally, on the oil being pumped around.  You'd need a pump almost as

big as your lycoming just to get the pressure necessary to push the oil

  [quote][b]

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tedd(at)vansairforce.org
Guest

Posted: Fri Mar 21, 2008 9:47 am Post subject: Liquid cooling

 	  Quote: 	
		   The only advantage liquid cooling has is the capacity to provide a heat

 reservoir, to absorb it when too much is being generated, and to retain it

 when not enough is being generated.1


	


I'm quite surprised nobody challenged this yet!  Liquid cooling provides many

more benefits than just transient heat absorption.



Perhaps the biggest is reduced hot spots in the combustion chamber.  That

allows either a higher compression ratio or a more efficient combustion chamber

shape, or some combination of both.  Combustion chamber shapes that have high

detonation resistance (such as wedge) typically produce poorer flame fronts,

less complete combustion, and greater head loss than othe shapes, but have the

advantage of high detonation resistance.  By reducing hot spots, liquid cooling

allows a better trade off of these factors to produce more efficient

combustion.



Another huge advantage of liquid cooling is that, by limiting thermal

expansion, it allows tighter tolerances.  Compare the piston-to-cylinder

clearance on a Lycoming to a typical, modern auto engine.  These tighter

clearances greatly reduce wear, and can be exploited to also reduce internal

friction (by, for example, reducing piston ring tension).  Limiting thermal

expansion also allows greater freedom in selecting materials.



There are numerous other advantages.  For example, liquid cooling allows

smaller valve stems, resulting in lower intake and exhaust restriction.  The

resulting lower valve mass allows the rest of the valvetrain to be lightened,

resulting in further savings in engine weight and internal friction.  The

coolant can also be used for various ancillary functions, such as heating the

cockpit (without risk of CO poisening), and provides a handy mechanism for

pre-heating the engine in cold climates.



Finally, liquid cooling has the potential to reduce cooling drag, as

demonstrated in airplanes like the P-51 and the Mosquito.  But that's difficult

to achieve if the airframe wasn't designed for liquid cooling from the start.



So the advantages of liquid cooling are legion.  Of course, air cooling has

certain advantages, too, but those are already well known to most people on

this listserver.



Tedd McHenry

Surrey, BC

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tedd(at)vansairforce.org
Guest

Posted: Fri Mar 21, 2008 11:04 am Post subject: Liquid cooling

 	  Quote: 	
		   less complete combustion, and greater head loss than othe shapes,


	


Sorry, that's "heat loss," not "head loss."



Tedd

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