10 ms·

Aviation’s Largest Piston Engine (2016)

36 points by PretzelFisch 8y ago

nimbius 8y ago
>At full power, the XR-7755 generated a tremendous amount of heat. Speaking as a full time engine mechanic for a small chain of midwestern repair stores, this is the death-knell of every heavily customized car. Heck, 3/4ths of the engineering for a Dodge Hellcat or Mustang cobra is just to keep the thing cool enough that the driver isnt chased out of the cockpit. You cant idle them the same way you idle a Toyota...they'll burn up. the Dodge Viper is another perfect example of engine displacement gone wild. The intercooler and radiator are massive, but the additional cylinders and their size means the V-10 motor has 10 cylinders firing onto a 90-degree crankshaft, which means it has an uneven firing interval for two of the ten cylinders. it makes the idle rougher than a garbage truck, and very prone to overheat with a 220 degree camshaft.
- dsfyu404ed 8y ago
  I'm not seeing how crank and cam specs significantly affect cooling at idle all else being equal. Any cooling system that can work under load will be fine at idle. Edit: For something like a race-car that's trying to minimize weight/power loss by running the minimum radiator/fan necessary and depending on airflow from movement (or rely on the fact that you're only running 1/4mi at a time) I can understand. Still, that's a cooling system sizing issue, not a cam or crank issue. A street going vehicle isn't going to have a cooling system that's sized within a hair of inadequate like that. Power output (and heat generated) at/near idle should be fairly constant regardless of cam and if it's not the higher power output cam profiles will probably have lower power output at/near idle (this depends a lot on the engine, some engines force you to choose where you want your power, some are hard to throw "too much cam" at). No matter how you cut it only so much air can get passed a closed throttle and that amount of air only corresponds to a certain amount of fuel, that puts an upper bound on heat generated at idle. I can see how adding forced induction could significantly affect heat generated at idle but even then, if everything is sized properly it shouldn't be much of an issue. This place is really turning into Reddit where you get down-voted for questioning anyone who sounds knowledgeable.
  - maxxxxx 8y ago
    Cars depend on air moving through the cooling system under load which means it's at speed. Cooling at idle can be a big problem for high performance cars. Going to the extreme, F1 cars have to be super careful not to overheat when stopped.
    - justin66 8y ago
      > Cooling at idle can be a big problem for high performance cars. Or any air cooled car ever made. But the reality is that in a lot of designs, idling will test the effectiveness of the cooling system more than driving the car at speed. (Adding power only exacerbates such a problem. The OP completely fails to understand this) It's much less of a problem than it used to be, with lots of cars including electric fans to help out the radiator, but it used to be standard to see a warning in the owner's manual about temperatures increasing in slow traffic or at idle.
      - maxxxxx 8y ago
        "Or any air cooled car ever made." Are there still any being built? I thought the 911 was the last holdout until they also switched to water cooling. "with lots of cars including electric fans to help out the radiator," I had that fan breaking once in my Miata and temperatures went into the red really quickly in LA rush hour.
        justin66 8y ago
        They switched the 911 over to water-cooled in the late nineties, yes. Prior to that, Porsche got the idle temp problem somewhat under control using powerful electric fans positioned in front of some of the oil coolers, but there's essentially no reliable way to cool four-valve cylinder heads with a purely air-cooled engine (the 959 used separate water cooling just for the heads), so they decided the whole thing was a performance dead end. The air-cooled 911 Turbo did get up above 400hp with two-valve heads before the change, though. > I had that fan breaking once in my Miata and temperatures went into the red really quickly in LA rush hour. No doubt. Once you train yourself to hear that fan, you realize how much the car depends on it.
- fhood 8y ago
  Take the hood off, bring a cooler of ice water, don't get stuck in traffic, stop every 10-15 minutes to cool off. Problem solved.
  - maxxxxx 8y ago
    I had to do this with my first car which had a leaky cooler :-). Always had a bottle of water with me.
- eecc 8y ago
  Used to have an Alfa Romeo 180 boxer engine. Made a weird ratchety noise but it was quite fun to ride. Besides the obvious overhead of multiple cam shafts, synchronization and so on, what do you think of this engine?
dsfyu404ed 8y ago
>What was truly unique about the cams was that there were two sets of lobes for each cylinder. One set of lobes optimized the operation of the engine valves at high power settings VTEC, yo. In in the 1940s no less. There's tons of tech that was well understood for WW2 aviation that finds its way back into land transportation given enough time. Adding water and alcohol blends to the intake charge to reduce temperature and prevent detonation, ABS, Fuel injection, probably other stuff as well.
- mkarr 8y ago
  A large part of these technologies making their way into consumer automobile engines was advances in material science, lubrication, manufacturing, etc, that allowed for them to exist economically and reliably. Those WW2 era piston engines were horrifically expensive, and required dozens to hundreds of hours of maintenance per hour of flight time.
  - Gravityloss 8y ago
    Sleeve valves could enable higher compression ratios without detonation, for higher efficiency? I guess there is the NOx to consider nowadays though.
  - Blackthorn 8y ago
    They were also ridiculously unreliable and had the tendency to just catch on fire. Acceptable losses in wartime. Not so much elsewhere.
funAtParties 8y ago
Sometimes I think about aerial bombardment, and what that really meant during that period of conflict. When you think about the effort to concoct the compounds for the air war, and drop them on cities, with no guidance like lasers or anything, and then you look at the sheer tonnage dropped, and how indiscriminate it really was, you wonder how aerial bombardment is at all distinguishable from chemical weapons. It really is chemical warfare by another name. The only real difference being the explosive burning. Clean up was still a similar problem, since, as with shells, munitions would hit but not detonate. Couple this with such indiscriminate bombings that cities were engulfed in fire storms, and I think it's splitting hairs, for the most part.
- ElDji 8y ago
  Yeah now we do really better using surgical strikes on afghan weddings. God bless america.
- mc32 8y ago
  It’s all well and good to examine these things while we have tjr benefit of having vanquished an enemy or enemies. Twiddling about this and whether we should bomb Hitler or Hirohito would either result in more total deaths or our defeats, neither would have been better alternatives. It’s not as if we’d go to Hitler and Hitohito and say stop killing indiscriminately in your conqured areas and we’ll stop bombing you and while you're listening, be good and surrender to us.
  - funAtParties 8y ago
    There's another aspect to the sheer insanity of the period that probably would be worth exploring, if only it were possible. People were so mentally numbed and damaged by the carnage of the first world war, that the second world war was put on track by the leadership that had survived the carnage. But looking at engines like this, and knowing that they ran on leaded AvGas, and knowing that leaded mechanization was the norm, you wonder if the psychotic leadership was actually an expression of lead poisoning from environmental factors. Just like all those crime curves that trend according to leaded gasoline bans, what if front line WWI veterans were driven psychotic by frontline exposure to heavy metals through exhaust fumes?
deleted 8y ago
[deleted]
Gravityloss 8y ago
120 liter displacement. 4x9 = 36 cylinders and many valves and sparks plugs in each. As comparison an early generation single spool turbojet has pretty much one moving part. Nowadays there might be two or three spools and moving vanes and a thrust reverser. But aviation would never have been possible for the masses with piston engines.
- NeedMoreTea 8y ago
  Avro Lancaster, one of the two most successful heavy bombers of WW2 had 4 27litre V12 merlins, with proven reliability. The Avro Lancastrian was a passenger variant of the Lanc and developed into the large bodied Avro York that had the range to replace a few of the old flying boat routes. Some lasted into the 60s on commercial routes. The Lockheed Constellation had four 18 cyl radials, and being pressurised survived in commercial service even longer. Neither had a turboprop variant. Mass aviation was going to happen anyway whether the DH Comet arrived or not. It would have looked rather different, and perhaps not quite as endemic as now, but definitely mass aviation as we know it. Jets just hastened the process, and came at just the right time.
  - dingaling 8y ago
    Mass aviation could not have happened without the turbine. The big propliners of the 50s were notorious for having engines fail in flight and had insufficient power reserves to do anything but struggle to the crash site, even with the tiny payloads they carried. 64 years ago today a KLM Constellation crashed at Shannon in Ireland, it was carrying 56 people. That's miniscule and was only sustainable with fares that the 1%ers of the era could afford. A Norwegian 737Max on a thin Atlantic route today carries 186 and that is considered borderline small. Incidentally the Constellation did have a turboprop variant but Lockheed and GE had a disagreement and it went ahead with pistons instead as the Starliner. Few people even remember that aircraft now because of the 707.
    - NeedMoreTea 8y ago
      I disagree. The desire for aviation came in thanks in part to the war, and was there with or without jets in amongst post-war growth. Jets certainly helped the growth in size, and grew the market faster than it could have without. The market was already there and growing. Prop aircraft would have grown too had there been no jet engines, though I doubt we'd have got to 300+ capacity - but who knows? On seating. The DH Comet had a smaller passenger capacity than the Super Constellation, which was upto 110 depending on seating configuration, though usually a bit less. The 707 had 140 when first introduced. For the 1.5% - 2%ers then? A turboprop constellation variant was prototyped but never produced commercially. The were none in service. I think the US Navy might have ended up with a couple for trials too.
nabla9 8y ago
Even if you ignore the heat and the power/weight ratio, reliability starts to become a problem. Adding more smaller piston engines improves reliability and safety in long flights. The number of moving parts and the complexity of the piston engine compared to a gas turbine is significant.

36 points by PretzelFisch 8y ago

>At full power, the XR-7755 generated a tremendous amount of heat. Speaking as a full time engine mechanic for a small chain of midwestern repair stores, this is the death-knell of every heavily customized car. Heck, 3/4ths of the engineering for a Dodge Hellcat or Mustang cobra is just to keep the thing cool enough that the driver isnt chased out of the cockpit. You cant idle them the same way you idle a Toyota...they'll burn up. the Dodge Viper is another perfect example of engine displacement gone wild. The intercooler and radiator are massive, but the additional cylinders and their size means the V-10 motor has 10 cylinders firing onto a 90-degree crankshaft, which means it has an uneven firing interval for two of the ten cylinders. it makes the idle rougher than a garbage truck, and very prone to overheat with a 220 degree camshaft.

dsfyu404ed 8y ago
I'm not seeing how crank and cam specs significantly affect cooling at idle all else being equal. Any cooling system that can work under load will be fine at idle. Edit: For something like a race-car that's trying to minimize weight/power loss by running the minimum radiator/fan necessary and depending on airflow from movement (or rely on the fact that you're only running 1/4mi at a time) I can understand. Still, that's a cooling system sizing issue, not a cam or crank issue. A street going vehicle isn't going to have a cooling system that's sized within a hair of inadequate like that. Power output (and heat generated) at/near idle should be fairly constant regardless of cam and if it's not the higher power output cam profiles will probably have lower power output at/near idle (this depends a lot on the engine, some engines force you to choose where you want your power, some are hard to throw "too much cam" at). No matter how you cut it only so much air can get passed a closed throttle and that amount of air only corresponds to a certain amount of fuel, that puts an upper bound on heat generated at idle. I can see how adding forced induction could significantly affect heat generated at idle but even then, if everything is sized properly it shouldn't be much of an issue. This place is really turning into Reddit where you get down-voted for questioning anyone who sounds knowledgeable.
- maxxxxx 8y ago
  Cars depend on air moving through the cooling system under load which means it's at speed. Cooling at idle can be a big problem for high performance cars. Going to the extreme, F1 cars have to be super careful not to overheat when stopped.
  - justin66 8y ago
    > Cooling at idle can be a big problem for high performance cars. Or any air cooled car ever made. But the reality is that in a lot of designs, idling will test the effectiveness of the cooling system more than driving the car at speed. (Adding power only exacerbates such a problem. The OP completely fails to understand this) It's much less of a problem than it used to be, with lots of cars including electric fans to help out the radiator, but it used to be standard to see a warning in the owner's manual about temperatures increasing in slow traffic or at idle.
    - maxxxxx 8y ago
      "Or any air cooled car ever made." Are there still any being built? I thought the 911 was the last holdout until they also switched to water cooling. "with lots of cars including electric fans to help out the radiator," I had that fan breaking once in my Miata and temperatures went into the red really quickly in LA rush hour.
      - justin66 8y ago
        They switched the 911 over to water-cooled in the late nineties, yes. Prior to that, Porsche got the idle temp problem somewhat under control using powerful electric fans positioned in front of some of the oil coolers, but there's essentially no reliable way to cool four-valve cylinder heads with a purely air-cooled engine (the 959 used separate water cooling just for the heads), so they decided the whole thing was a performance dead end. The air-cooled 911 Turbo did get up above 400hp with two-valve heads before the change, though. > I had that fan breaking once in my Miata and temperatures went into the red really quickly in LA rush hour. No doubt. Once you train yourself to hear that fan, you realize how much the car depends on it.
fhood 8y ago
Take the hood off, bring a cooler of ice water, don't get stuck in traffic, stop every 10-15 minutes to cool off. Problem solved.
- maxxxxx 8y ago
  I had to do this with my first car which had a leaky cooler :-). Always had a bottle of water with me.
eecc 8y ago
Used to have an Alfa Romeo 180 boxer engine. Made a weird ratchety noise but it was quite fun to ride. Besides the obvious overhead of multiple cam shafts, synchronization and so on, what do you think of this engine?

dsfyu404ed 8y ago

>What was truly unique about the cams was that there were two sets of lobes for each cylinder. One set of lobes optimized the operation of the engine valves at high power settings VTEC, yo. In in the 1940s no less. There's tons of tech that was well understood for WW2 aviation that finds its way back into land transportation given enough time. Adding water and alcohol blends to the intake charge to reduce temperature and prevent detonation, ABS, Fuel injection, probably other stuff as well.

mkarr 8y ago
A large part of these technologies making their way into consumer automobile engines was advances in material science, lubrication, manufacturing, etc, that allowed for them to exist economically and reliably. Those WW2 era piston engines were horrifically expensive, and required dozens to hundreds of hours of maintenance per hour of flight time.
- Gravityloss 8y ago
  Sleeve valves could enable higher compression ratios without detonation, for higher efficiency? I guess there is the NOx to consider nowadays though.
- Blackthorn 8y ago
  They were also ridiculously unreliable and had the tendency to just catch on fire. Acceptable losses in wartime. Not so much elsewhere.

funAtParties 8y ago

Sometimes I think about aerial bombardment, and what that really meant during that period of conflict. When you think about the effort to concoct the compounds for the air war, and drop them on cities, with no guidance like lasers or anything, and then you look at the sheer tonnage dropped, and how indiscriminate it really was, you wonder how aerial bombardment is at all distinguishable from chemical weapons. It really is chemical warfare by another name. The only real difference being the explosive burning. Clean up was still a similar problem, since, as with shells, munitions would hit but not detonate. Couple this with such indiscriminate bombings that cities were engulfed in fire storms, and I think it's splitting hairs, for the most part.

ElDji 8y ago
Yeah now we do really better using surgical strikes on afghan weddings. God bless america.
mc32 8y ago
It’s all well and good to examine these things while we have tjr benefit of having vanquished an enemy or enemies. Twiddling about this and whether we should bomb Hitler or Hirohito would either result in more total deaths or our defeats, neither would have been better alternatives. It’s not as if we’d go to Hitler and Hitohito and say stop killing indiscriminately in your conqured areas and we’ll stop bombing you and while you're listening, be good and surrender to us.
- funAtParties 8y ago
  There's another aspect to the sheer insanity of the period that probably would be worth exploring, if only it were possible. People were so mentally numbed and damaged by the carnage of the first world war, that the second world war was put on track by the leadership that had survived the carnage. But looking at engines like this, and knowing that they ran on leaded AvGas, and knowing that leaded mechanization was the norm, you wonder if the psychotic leadership was actually an expression of lead poisoning from environmental factors. Just like all those crime curves that trend according to leaded gasoline bans, what if front line WWI veterans were driven psychotic by frontline exposure to heavy metals through exhaust fumes?

deleted 8y ago

[deleted]

Gravityloss 8y ago

120 liter displacement. 4x9 = 36 cylinders and many valves and sparks plugs in each. As comparison an early generation single spool turbojet has pretty much one moving part. Nowadays there might be two or three spools and moving vanes and a thrust reverser. But aviation would never have been possible for the masses with piston engines.

NeedMoreTea 8y ago
Avro Lancaster, one of the two most successful heavy bombers of WW2 had 4 27litre V12 merlins, with proven reliability. The Avro Lancastrian was a passenger variant of the Lanc and developed into the large bodied Avro York that had the range to replace a few of the old flying boat routes. Some lasted into the 60s on commercial routes. The Lockheed Constellation had four 18 cyl radials, and being pressurised survived in commercial service even longer. Neither had a turboprop variant. Mass aviation was going to happen anyway whether the DH Comet arrived or not. It would have looked rather different, and perhaps not quite as endemic as now, but definitely mass aviation as we know it. Jets just hastened the process, and came at just the right time.
- dingaling 8y ago
  Mass aviation could not have happened without the turbine. The big propliners of the 50s were notorious for having engines fail in flight and had insufficient power reserves to do anything but struggle to the crash site, even with the tiny payloads they carried. 64 years ago today a KLM Constellation crashed at Shannon in Ireland, it was carrying 56 people. That's miniscule and was only sustainable with fares that the 1%ers of the era could afford. A Norwegian 737Max on a thin Atlantic route today carries 186 and that is considered borderline small. Incidentally the Constellation did have a turboprop variant but Lockheed and GE had a disagreement and it went ahead with pistons instead as the Starliner. Few people even remember that aircraft now because of the 707.
  - NeedMoreTea 8y ago
    I disagree. The desire for aviation came in thanks in part to the war, and was there with or without jets in amongst post-war growth. Jets certainly helped the growth in size, and grew the market faster than it could have without. The market was already there and growing. Prop aircraft would have grown too had there been no jet engines, though I doubt we'd have got to 300+ capacity - but who knows? On seating. The DH Comet had a smaller passenger capacity than the Super Constellation, which was upto 110 depending on seating configuration, though usually a bit less. The 707 had 140 when first introduced. For the 1.5% - 2%ers then? A turboprop constellation variant was prototyped but never produced commercially. The were none in service. I think the US Navy might have ended up with a couple for trials too.

nabla9 8y ago

Even if you ignore the heat and the power/weight ratio, reliability starts to become a problem. Adding more smaller piston engines improves reliability and safety in long flights. The number of moving parts and the complexity of the piston engine compared to a gas turbine is significant.