8 ms·

Almost like a modern turbo drag racing setup! I always wondered with all that duct work running the length of the fuselage sending intake air back to the turbo

Almost like a modern turbo drag racing setup! I always wondered with all that duct work running the length of the fuselage sending intake air back to the turbocharger, which then fed cooled air back to carburetors serving 18 cylinders, what enemy fire damage would do to this complex setup. Presumably this doesn't have single points of failure in a sealed compressed air system but it almost feels like race car level tuning for optimal performance, let alone for limping home with fuselage damage.

jandrese 6y ago
I was wondering the same thing. What would a few bullets through that huge air tube do to your power? I recently had a pressure leak on my turbocharged car on the air intake between the turbo and the block. It seriously wrecked the performance. The engine was close to stalling and my gas mileage dropped by half. These big radials aren't quite as picky, but I bet you'd still feel the difference.
- olivermarks 6y ago
  my thoughts exactly - the engine is relying heavily on forced air induction - must have had a 'limp home' mode built in, hard to tell carbs to do different things though, no ecm controlled fuel injection
  - hedgehog 6y ago
    I don't know about the air ducts but loss of coolant pressure was a big deal, here's a video I saw a while back where one of the designers talks about the P-51's radiator: https://www.youtube.com/watch?v=8_5kSxWO5rg https://www.youtube.com/watch?v=8_5kSxWO5rg
    - jabl 6y ago
      Liquid cooled WWII aero engines generally used pressurized cooling systems, as this allowed running the coolant (usually a 70/30 glycol/water mix) past the atmospheric pressure boiling point. This, in turn, allowed smaller radiators, reducing drag. The downside was that even a small rifle caliber hit to the cooling system caused the coolant to flash to steam and rapidly escape through the hole, giving the pilot only minutes until the engine seized.
  - sio8ohPi 6y ago
    The P-47 (like all American warplanes of this era) gave pilots a lot of control over engine performance. The P-47 pilot could adjust throttle, RPM (controlled by a governor that adjusts prop pitch), fuel-air mixture, turbocharger speed (controlled by opening exhaust wastegates), as well as control of the cowl flaps and intercooler shutters for cooling, as needed. Conversely, the German fighters of this era were much more heavily automated. A Bf 109 pilot had a throttle lever: RPM, mixture, and radiators were controlled automatically (with manual overrides available). If you ever look closely at the P-47's throttle quadrant, you'll notice one small feature that's pretty interesting. There is a one-way gate on the throttle lever that catches the RPM lever as it's advanced, precisely because without it, it was too easy for a pilot to (in the heat of combat) shove the throttle forward without adjusting RPM and blow the engine apart.
WalterBright 6y ago
A P-47's engine was fairly resistant to battle damage. My dad was a P-47 driver. One time it swallowed a valve, and the engine kept running, just a bit of vibration. For contrast, one time he was in a P-51 that swallowed a valve, and he said he was lucky he was over the airfield, as that airplane was going down promptly. The P-51 had a much more fragile engine, I wouldn't want to fly one over water.
- topspin 6y ago
  The US Navy mandated air cooled radial engines due to their robustness. The US Army Air Force adopted water cooled V type engines for performance. An air cooled radial can suffer damage such as "dropping" a valve because each cylinder and cylinder head is largely independent. There is no shared water jacket, for instance.
- pitchroll 6y ago
  Though I'm not too familiar with P-51 internals Walter's comment reminded me of this spectacular P-51 engine failure followed by a successful crash-landing (this clip includes pilot commentary explaining key moments): https://www.youtube.com/watch?v=jnODYKx5ics https://www.youtube.com/watch?v=jnODYKx5ics
  - deleted 6y ago
    [deleted]
  - redis_mlc 6y ago
    I think the P-51 pilot was a bozo and ran out of fuel in that link. The P-51 was fragile because it used liquid cooling, which meant it was unsuitable for ground attacks where somebody with a rifle could disable the engine (or flak.) The P-47 used an air-cooled engine, so was more reliable at low-level attacks. Note the P-47 was the size of a house - new pilots were literally scared just looking at it parked on the ground.
- choeger 6y ago
  If your dad should still be alive you should ask him how he managed to get his P51 shot directly above a friendly airfield. I have a hunch, there's a story behind that.
bigiain 6y ago
> Almost like a modern turbo drag racing setup! I’m guessing neither of those applications care too much about turbo lag or throttle response.
- olivermarks 6y ago
  Zero turbo lag is everything in drag racing. https://youtu.be/zPNrBuuQCnw https://youtu.be/zPNrBuuQCnw
  - sanguy 6y ago
    In a drag turbo setup they solve the lag by spooling the turbo off compressed air so at launch they are already into boost.
  - bigiain 6y ago
    I'd guess in a very different way to circuit racing's requirements for zero turbo lag though? They'd be "I need enough boost while staged on the line that I've always got traction-breaking torque available when and for as long after I launch as possible", rather than "I need to be able to smoothly get from off throttle to 30% throttle as I pass the apex, then from 30 up to 100% as I exit turn 4"... Back in the 90s (and maybe still, I've lost touch) rally cars used to do off throttle "anti-lag" by using the direct fuel injection to pump fuel into the cylinders during the exhaust stroke, so it'd burn in the exhaust manifold and keep the turbine spinning to make boost without needing the engine to be creating torque by burning the fuel in the ignition strokes... They had less hard requirements for gradual application of torque than circuit race cars though, they mostly wanted to be able to get back on the throttle exiting a corner and immediately start spinning all 4 wheels again.
usrusr 6y ago
The good news is that losing intercooler or turbo would just be a fractional performance reduction, not a countdown to an engine loss that an oil cooler hit would be. This ties in with a question I was asking myself after seeing this impressive setup: did anyone build a skin surface intercooler? I seem to remember reading about at least one plane that had its oil cooler in the skin early in development until they accepted that the added vulnerability was worse than the drag from a conventional box radiator and abandoned the idea. But with the intercooler the tradeoffs might be very different. You could even add a bypass mechanism for when the skin/cooler has become so leaky that the engine has effectively become naturally aspirated and turbo without intercooler would be an improvement.
- jabl 6y ago
  IIRC there were some late WW1, or early interwar period, liquid cooled planes that did use skin coolers. As engines got bigger, they became impractically large (covering a significant fraction of the fuselage), complicated with lots of pipes all over the place, and heavy. Don't see why the tradeoff would be that different for an intercooler vs. the main engine cooler.

jandrese 6y ago

I was wondering the same thing. What would a few bullets through that huge air tube do to your power? I recently had a pressure leak on my turbocharged car on the air intake between the turbo and the block. It seriously wrecked the performance. The engine was close to stalling and my gas mileage dropped by half. These big radials aren't quite as picky, but I bet you'd still feel the difference.

olivermarks 6y ago
my thoughts exactly - the engine is relying heavily on forced air induction - must have had a 'limp home' mode built in, hard to tell carbs to do different things though, no ecm controlled fuel injection
- hedgehog 6y ago
  I don't know about the air ducts but loss of coolant pressure was a big deal, here's a video I saw a while back where one of the designers talks about the P-51's radiator: https://www.youtube.com/watch?v=8_5kSxWO5rg https://www.youtube.com/watch?v=8_5kSxWO5rg
  - jabl 6y ago
    Liquid cooled WWII aero engines generally used pressurized cooling systems, as this allowed running the coolant (usually a 70/30 glycol/water mix) past the atmospheric pressure boiling point. This, in turn, allowed smaller radiators, reducing drag. The downside was that even a small rifle caliber hit to the cooling system caused the coolant to flash to steam and rapidly escape through the hole, giving the pilot only minutes until the engine seized.
- sio8ohPi 6y ago
  The P-47 (like all American warplanes of this era) gave pilots a lot of control over engine performance. The P-47 pilot could adjust throttle, RPM (controlled by a governor that adjusts prop pitch), fuel-air mixture, turbocharger speed (controlled by opening exhaust wastegates), as well as control of the cowl flaps and intercooler shutters for cooling, as needed. Conversely, the German fighters of this era were much more heavily automated. A Bf 109 pilot had a throttle lever: RPM, mixture, and radiators were controlled automatically (with manual overrides available). If you ever look closely at the P-47's throttle quadrant, you'll notice one small feature that's pretty interesting. There is a one-way gate on the throttle lever that catches the RPM lever as it's advanced, precisely because without it, it was too easy for a pilot to (in the heat of combat) shove the throttle forward without adjusting RPM and blow the engine apart.

WalterBright 6y ago

A P-47's engine was fairly resistant to battle damage. My dad was a P-47 driver. One time it swallowed a valve, and the engine kept running, just a bit of vibration. For contrast, one time he was in a P-51 that swallowed a valve, and he said he was lucky he was over the airfield, as that airplane was going down promptly. The P-51 had a much more fragile engine, I wouldn't want to fly one over water.

topspin 6y ago
The US Navy mandated air cooled radial engines due to their robustness. The US Army Air Force adopted water cooled V type engines for performance. An air cooled radial can suffer damage such as "dropping" a valve because each cylinder and cylinder head is largely independent. There is no shared water jacket, for instance.
pitchroll 6y ago
Though I'm not too familiar with P-51 internals Walter's comment reminded me of this spectacular P-51 engine failure followed by a successful crash-landing (this clip includes pilot commentary explaining key moments): https://www.youtube.com/watch?v=jnODYKx5ics https://www.youtube.com/watch?v=jnODYKx5ics
- deleted 6y ago
  [deleted]
- redis_mlc 6y ago
  I think the P-51 pilot was a bozo and ran out of fuel in that link. The P-51 was fragile because it used liquid cooling, which meant it was unsuitable for ground attacks where somebody with a rifle could disable the engine (or flak.) The P-47 used an air-cooled engine, so was more reliable at low-level attacks. Note the P-47 was the size of a house - new pilots were literally scared just looking at it parked on the ground.
choeger 6y ago
If your dad should still be alive you should ask him how he managed to get his P51 shot directly above a friendly airfield. I have a hunch, there's a story behind that.

bigiain 6y ago

> Almost like a modern turbo drag racing setup! I’m guessing neither of those applications care too much about turbo lag or throttle response.

olivermarks 6y ago
Zero turbo lag is everything in drag racing. https://youtu.be/zPNrBuuQCnw https://youtu.be/zPNrBuuQCnw
- sanguy 6y ago
  In a drag turbo setup they solve the lag by spooling the turbo off compressed air so at launch they are already into boost.
- bigiain 6y ago
  I'd guess in a very different way to circuit racing's requirements for zero turbo lag though? They'd be "I need enough boost while staged on the line that I've always got traction-breaking torque available when and for as long after I launch as possible", rather than "I need to be able to smoothly get from off throttle to 30% throttle as I pass the apex, then from 30 up to 100% as I exit turn 4"... Back in the 90s (and maybe still, I've lost touch) rally cars used to do off throttle "anti-lag" by using the direct fuel injection to pump fuel into the cylinders during the exhaust stroke, so it'd burn in the exhaust manifold and keep the turbine spinning to make boost without needing the engine to be creating torque by burning the fuel in the ignition strokes... They had less hard requirements for gradual application of torque than circuit race cars though, they mostly wanted to be able to get back on the throttle exiting a corner and immediately start spinning all 4 wheels again.

usrusr 6y ago

The good news is that losing intercooler or turbo would just be a fractional performance reduction, not a countdown to an engine loss that an oil cooler hit would be. This ties in with a question I was asking myself after seeing this impressive setup: did anyone build a skin surface intercooler? I seem to remember reading about at least one plane that had its oil cooler in the skin early in development until they accepted that the added vulnerability was worse than the drag from a conventional box radiator and abandoned the idea. But with the intercooler the tradeoffs might be very different. You could even add a bypass mechanism for when the skin/cooler has become so leaky that the engine has effectively become naturally aspirated and turbo without intercooler would be an improvement.

jabl 6y ago
IIRC there were some late WW1, or early interwar period, liquid cooled planes that did use skin coolers. As engines got bigger, they became impractically large (covering a significant fraction of the fuselage), complicated with lots of pipes all over the place, and heavy. Don't see why the tradeoff would be that different for an intercooler vs. the main engine cooler.