# After market liquid cylinders for Lycoming engines

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#### BJC

##### Well-Known Member
HBA Supporter
Dogg:

Does anyone have experience with aftermarket, liquid cooled, cylinders from ac-aero?
Do you have anything to offer in response to my question?

BJC

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Speaking as a moderator:

The OP is objecting to the off topic posts.

#### galapoola

##### Well-Known Member
"the B-17 literally had a liquid cooled variant that greatly outperformed the air cooled in efficiency"

May be true but one well placed round or flack hitting a jug, engine may still run. Same hit on the radiator of liquid cooled, you have only a few moments before it stops. I like both cooling schemes. Air cooled appeared to be more robust for combat.

#### BJC

##### Well-Known Member
HBA Supporter
"the B-17 literally had a liquid cooled variant that greatly outperformed the air cooled in efficiency"

May be true but one well placed round or flack hitting a jug, engine may still run. Same hit on the radiator of liquid cooled, you have only a few moments before it stops. I like both cooling schemes. Air cooled appeared to be more robust for combat.
I suspect that ac-aero do not anticipate that their cylinders for the 4 and 6 cylinder Lycomings will be used in combat.

BJC

#### jedi

##### Well-Known Member
" BJC said: Does anyone have experience with aftermarket, liquid cooled, cylinders from ac-aero? "

No, but! That famous last word!

One thing I learned over the years is that fluids should be contained within the engine proper to the greatest extent possible. Eliminate external hose, tube and other connections that can crack, loosen or leak.

The ac-aero conversion is grossly lacking in this regard. Rutan showed that this can work for several days but other applications show that as a problem over several years and requires good maintenance.

Rotax requires all rubber to be replaced every two years.

#### Dan Thomas

##### Well-Known Member
Maybe initial cost but operating costs and operating weights for a given range are lower. Just compare the range of the B-17 to the Lancaster. 25% difference in range with the same power and 65,000lb takeoff weight.
That applies to the SMA diesel engines, too. Much better BSFC. But the conversion for a 182 costs around $100K, negating the fuel savings. It has other drawbacks, too, such as a limited cold-weather capability. These liquid-cooled cylinders could easily sell well if the conversion costs were reasonable and the loss of useful load wasn't too bad. And even more so if the price of avgas goes way up again. But keeping costs within reason is difficult, as we've seen in so many instances in aviation. #### TFF ##### Well-Known Member I believe Burt was looking for free engines and Continental saw the potential for some advertising and testing if it got pulled off. No one else could have pulled it off. If he had not been graced with free engines, would he have gone with Continental? The avionics were borrowed too. If I remember some of the composites were some odd cast off stuff he got cheap and then he had to convince the manufacturer to make some more to finish it. It was a scrounging project that worked. Hopefully the AC installation is not as complex as the Continental. As with most aviation stuff stuff can be over done. The cooling system is pretty complex with not a lot of excess capacity on the Continental. Had some on ground overheating problems on the one I have messed with. I just pulled a Rotax head but it’s just a head. The cylinders are air cooled. It’s an in between engine. The radiator on the Rotax a VW car radiator is as big as the 520 Continental. More power starts pushing the case and crank past what it’s designed for. If you watercool a Lycoming, what are you going to do with the new potential? The rest of parts are designed to aircooled levels. If you just water cool it but run it at the same power, there might be modest efficiency increase but it all weighs more so it is mostly a wash. Use the performance potential, now you are over stressing the case and crank; that’s not good. You can’t easily shrink the engine to get the weight advantage to the better performance. Scabbing on something is not really fixing anything. BJC #### Mcmark ##### Well-Known Member From the bit I've read mostly on their website, this site and the BPF are that these are for the people that want to maximize power output. High Compression/High Horsepower. Airshow, Unlimited Competition Aerobatics and Racing engines. Generally they are selling 4 banger engines at 409ci and the 6's are ~615. Longer strokes and Bigger bores. Not saying they are not worth it, but must have a large purse to purchase. #### mcrae0104 ##### Well-Known Member HBA Supporter Log Member ...it would be completely obvious to anyone who wasn’t paralyzed with arrogance. I want to respect the OP's & Billski's request that we stay on topic so I will not respond in kind to this comment that is uncalled for, Doggzilla. Direct your spite elsewhere please. #### Dan Thomas ##### Well-Known Member From the bit I've read mostly on their website, this site and the BPF are that these are for the people that want to maximize power output. High Compression/High Horsepower. Airshow, Unlimited Competition Aerobatics and Racing engines. Generally they are selling 4 banger engines at 409ci and the 6's are ~615. Longer strokes and Bigger bores. Not saying they are not worth it, but must have a large purse to purchase. One of the limiting factors in aircraft engines is the onset of detonation. Large-bore, slow-turning engines are prone to it, as it takes time for the complex fuel molecules to break down into simpler, autoignitable molecules. Higher compression ratios increase the risk, and air-cooling takes it further. A liquid-cooled head is going to stay a lot cooler than an aircooled one, so I'd bet that liquid cooling would permit increasing compression or turbo pressures, producing more power. And if the oil was also cooled better, the piston itself could be kept cooler, though a liquid-cooled cylinder wall would be a big help. And leaner mixtures could be used, as the website stated. Getting the mixture leaned to best power for takeoff would save fuel over the typical full-rich techniques in aircooled engines. Rich mixtures don't just aid cooling; they inhibit detonation. #### Andy_RR ##### Well-Known Member ...but knock occurs in the coolest part of the combustion chamber! Having a cool head is less important than having an even temperature across the combustion chamber face. There's nothing about liquid cooling that makes an engine intrinsically more efficient than an air cooled engine. What you might gain is a shorter crankshaft (weight) by placing the cylinders closer together, except this is moot for a radial engine. You can probably increase the power density which might work slightly in your favour from an efficiency point of view but such a gain is easily lost elsewhere. The real problem with cooling aero engines is getting the waste heat efficiently into the airstream without creating too much drag. Liquid cooling helps make this task more flexible from a design and packaging perspective but air cooling can reduce the amount of air actually needing to be heated by increasing the temperature gradient. Most air cooled engines waste power by badly ducted airflow around the fins and leaks which decrease the pressure gradient across the engine reducing cooling capacity whilst increasing cooling drag. Converting an air-cooled engine to liquid cooling seems like a pointless exercise to me. Increased weight, complexity and packaging complications with very little to no gain in performance #### Riggerrob ##### Well-Known Member Dear Andy RR, Air-cooled cylinders can never be built to tolerances as tight as liquid-cooled. Part of the problem is un-even cooling at high speeds. Fins on the front and sides remove plenty of heat, but the backside always runs hotter. Cylinder walls heat to egg-shape while pistons remain round. This limits you to running your engine by limiting power to the best that can be produced before over-heating the worst-cooled cylinder .. usually rear. Air-cooled engines must be built to the worst combination of hot piston and cold, egg-shaped cylinder walls. The primary advantage of liquid-cooled engines is that they cool more evenly and can be built to much tighter tolerances. No egg-shaped cylinders here. Tighter tolerances between pistons and cylinder walls mean less leakage in to the crankcase, cleaner oil, less frequent oil changes, etc. Tighter tolerances (liquid-cooled) allow you to lean the fuel air mixture much closer to optimum, halving fuel consumption. As the cost of gasoline increases, fuel consumption becomes more and more expensive. Fuel consumption becomes increasingly important with long flights. For example, when you install a liquid-cooled Corvette engine in a Seabee, you increase horsepower by 50 percent (300 versus the original 195 hp.), while dropping fuel consumption by half. Air-cooled engines made sense when gasoline was cheap, but now expensive fuel makes liquid-cooled cheaper to run. #### Andreas K ##### Member I was flying my RV-10 with a GM LS-7 engine for 33 hrs. before the gearbox blew up (older BW-350 unit). The engine ran at 4725 RPM (2700 prop RPM) WOT thus creating roughly 400+ hp. At 8500' max speed was 199 TAS @ 17.5 gal/hr. I could cruise 180 on 12.5 gal/hr and 170 on 10 gal/hr. Now I have an IO-540 D4B5. All stock but cold air, AFM 300 and tuned exhaust. I estimate 280 to 290 hp. The cowling looks significantly different too. Top speed now is 188 TAS @ 8500'. I cruise 180 at 15.5 gal/hr ROP and 170 at 11.5 gal/hr LOP @10500'. I loved the LS-7 engine but it was significantly more complex with 2 radiators and all the hoses connecting them. The airplane lost a whooping 140 lbs. installing the Lycoming. So, for a family hauler I should have gone with the Lycoming right away. The GM engine is unsupported (1 year extra built time), more complex, heavier but saves some fuel and is easier to operate. Blue skies Andi #### BJC ##### Well-Known Member HBA Supporter Thanks for sharing, Andi. What is an AFM 300? Do you have electronic ignition? Thanks, BJC #### harrisonaero ##### Well-Known Member Someone needs to take the historically empirical goodness of a Lycoming and upgrade it by copying what Rotax did with the incredibly efficient 912is. Liquid cooled heads, air cooled cylinders, dry sump oil cooled block, fuel injection with dual electronic ignition. #### Riggerrob ##### Well-Known Member The primary reason that Rotax built the 912is was to increase endurance/loiter time of surveillance drones. #### BJC ##### Well-Known Member HBA Supporter Someone needs to take the historically empirical goodness of a Lycoming and upgrade it by copying what Rotax did with the incredibly efficient 912is. Liquid cooled heads, air cooled cylinders, dry sump oil cooled block, fuel injection with dual electronic ignition. Some years ago, I was optimistic that Henry Bouley’s “improved” engine would be a winner. Read about it here: Bacon QUESTAIR-VENTURE crash in Iowa (N4QV) | PlaneCrashMap.com BJC #### Andy_RR ##### Well-Known Member Dear Andy RR, Air-cooled cylinders can never be built to tolerances as tight as liquid-cooled. I think you mean clearances, not tolerances... Part of the problem is un-even cooling at high speeds. Fins on the front and sides remove plenty of heat, but the backside always runs hotter. Cylinder walls heat to egg-shape while pistons remain round. This limits you to running your engine by limiting power to the best that can be produced before over-heating the worst-cooled cylinder .. usually rear. Air-cooled engines must be built to the worst combination of hot piston and cold, egg-shaped cylinder walls. Cylinders bores don't really reject so much heat compared to the cylinder heads. The temperature that they operate is huge compared to the temperature differential radially around the cooling flow path. Most of the thermal gradient is axially also so the thermal expansion is largely diameter rather than ovalization which is why the bore on the cylinder barrels is (intentionally) not actually parallel. They also have lots of ribs which keeps them pretty stiff. Pistons, on the other hand, don't stay round at all, despite your claim! - they grow round from their cold ovality and they suffer most from lack of cooling - the majority of heat they absorb is rejected through the ring pack to the bore walls. The rings are also flexible enough to cope with any remaining bore ovality, but, in any case, the largest area of leakage of the ring pack is at the ring gap which is larger on an air-cooled engine to allow for worst-case cooling scenario. The primary advantage of liquid-cooled engines is that they cool more evenly and can be built to much tighter tolerances. No egg-shaped cylinders here. Tighter tolerances between pistons and cylinder walls mean less leakage in to the crankcase, cleaner oil, less frequent oil changes, etc. No! Not tolerances here either - clearances! Liquid cooled engines operate at more stable temperatures because of thermostatic control of the cooling system. However, unless you compare apples and apples, you'll mislead yourself. Much of what you propose here is heavily influenced by bore diameter so comparing a 4.125" Chevy with a 5.125" Lycoming will lead you to an erroneous conclusion. Tighter tolerances (liquid-cooled) allow you to lean the fuel air mixture much closer to optimum, halving fuel consumption. Again, I think you mean clearances, but even so, there is no halving fuel consumption to be had at all! The lowest BSFC of a LS compared with a Lycon is closely comparable! Also the lean limit is more influenced by chamber charge motion and overall surface/volume ratio rather than the cooling method. The Lycons are terrible in regards to surface/volume with a bore/stroke ratio of 1.17 compared with 1.03 for Andi's LS7. The higher the CR the worse this gets too! A proper modern design with a focus on fuel consumption will be undersquare at around 0.9 For example, when you install a liquid-cooled Corvette engine in a Seabee, you increase horsepower by 50 percent (300 versus the original 195 hp.), while dropping fuel consumption by half. No, again, there is no half to be had anywhere here! Andi's numbers above demonstrate that! #### Chetontheprairies ##### Member Does anyone have experience with aftermarket, liquid cooled, cylinders from ac-aero? See http://www.ac-aero.com/gladiator/# No, I ant not considering them, just curious. Thanks. BJ I have no experience but I do think that they look promising, at least with the brief look that I had at their website. The concept does make sense and they claim that it offers weight savings although offer no specifics. Outside of the high performance world it could also be a beneficial conversion for someone who wants to run mogas, pair it with efi and it would be a proper modern engine. The price listed on their website is under$19000 it looks like that's complete (you provide a core and radiator) if that's the case the price is even in line with a conventional rebuild.

In short I guess I would like to know more as well!