I heard about this from Sun’n’Fun – may not be entirely new, but quite a radical concept to me.
A search didn’t find it mentioned anywhere on the forum already.
Adaptor kits are available to convert your Lycoming IO-360 or IO-540 into a liquid cooled engine.
AC Aero offer products called Gladiator and Centurion.
The result claims to be:
- lighter
- higher power output (eg IO540 increased from 250hp to 350hp)
- longer engine life (no problems with shock cooling)
- easier to lean properly (cylinders are manufactured to tighter tolerances, less spread)
- Improved fuel and oil consumption (Can run on lower octane fuels, and I believe I heard even MoGAS, but this might not deliver the higher power option)
- lower emissions
The conversion kit costs around $25,000 and includes replacement cylinders. I guess you’d fit this when overhauling an engine, so there would be additional costs involved compared to a conventional one.
Has anyone else knowledge of this concept?
What approvals are required? I’d guess this could only be fitted today to an N-reg aircraft, and maybe then only an “experimental” such as an RV.
Would it be worth it?
What are any increased risks (eg overheating or sudden loss of the liquid coolant)?
Addressing the stated advantages one at a time:
Increased power output: Their cylinders are increased in displacement, so it’s likely on that basis. Fuel burn in cruise will be proportionately higher if you use the power unless there is a significantly higher compression ratio.
Lightweight design: The cast aluminum cylinders are lighter, but this is offset by the added weight of coolant, radiator etc. Unless the system weight is lower, its not lighter, so that needs to made clear in PR material otherwise its meaningless.
No airflow cooling difficulties: Actually more cooling airflow difficulties because the radiator runs cooler than air cooled cylinders, and is proportionately larger and harder to package. Look at Diamonds efforts.
Uniform cooling, no shock loading: Shock cooling is not a significant issue for Lycoming engines.
Reduced oil consumption: Could be but who cares? Is oil consumption a significant issue on air cooled engines?
Lower emissions: Not something that will influence the the buyer, and likely only true for the first few minutes of initial climb.
Lower fuel consumption: This takes higher compression ratio, and is not at first order attributable to liquid cooling. Eight minutes of climb with an extra 1.5 gph for cooling is about $1 of fuel.
Increase in detonation margin: Maybe but unless you’re holding the same compression ratio and updating the cylinder design to use low octane auto fuel its a non-issue. I’m surprised that low octane fuel isn’t a major objective of this design, because to me that might make sense for some engines.
Better and lower wear: Maybe, but for sure offset by more maintenance in the cooling system.
Longer Service life: Maybe, but for sure offset by more maintenance in the cooling system.
My prediction – not many people are going to pay $25K to convert their Experimental category engine and aircraft to liquid cooling. I think all aluminum air-cooled replacement cylinders might make more sense as a replacement for current bi-metal cylinders.
@Silvaire Thanks for the detailed analysis. It’s helpful to form a more balanced view and it will be interesting to see if this gets much take-up.
I had to think twice about why it was a problem that the radiator runs cooler than air cooled cylinders – of course this means a lower differential between the outside air temperature and the radiator, resulting in a slower transfer/release of excess heat which is why it needs to be bigger/have more surface area.
Radiators are a big problem. Wasn’t it the case with the liquid-cooled WW2 fighters that one needed to get into the air and get some flow over the radiator within X minutes of startup otherwise the system boiled over?
One could raise the operating temperature by raising the system pressure, but that would probably negate the intended advantage of running cooler to allow tighter clearances.
An interesting idea is pumping the hot coolant around a ‘wet leading edge’, potentially gaining de-ice capability. I bet there are a million reasons why this wouldn’t work, not least the amount of coolant required.
One could raise the operating temperature by raising the system pressure, but that would probably negate the intended advantage of running cooler to allow tighter clearances.
Modern diesels do this e.g. my VW runs at +90C.
An interesting idea is pumping the hot coolant around a ‘wet leading edge’, potentially gaining de-ice capability. I bet there are a million reasons why this wouldn’t work, not least the amount of coolant required.
It was tried in WW2. I posted a pic here somewhere, from the Kbely museum in Prague, showing wing leading edges used for engine coolant, and doing some ice protection at the same time.
Peter wrote:
Modern diesels do this e.g. my VW runs at +90C.
I think 90C is normal for automotive cooling systems and has been for a while? I meant hotter than that – say 120C or something, closer to the ~300F CHT you see with an air cooled engine.
Graham wrote:
Radiators are a big problem. Wasn’t it the case with the liquid-cooled WW2 fighters that one needed to get into the air and get some flow over the radiator within X minutes of startup otherwise the system boiled over?
Yes, but that was by design. They were built to scramble quickly (there isn’t time for ten-minute pre-take off checks at the hold in a war), so they put in the smallest radiator they could get away with. The water cooled engines these days have enough cooling capability, at the expense of larger radiators.
Silvaire wrote:
not many people are going to pay $25K to convert their Experimental category engine and aircraft to liquid cooling
But maybe a few will pay $25k to convert a 250hp engine to 350hp engine – provided radiators don’t add more drag than the increased power is worth…
