Boost - WWII Fighter engines

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Been watching some YouTube videos about these engines and the amount of boost they ran . I figure all of you know , the more boost you run , potentially , the more hp , all things being equal . Untill something comes apart . The main comparison was between the Merlin engine in the P51 Mustangs , and various British planes . And the engines used in the BF-109 . I guess the bottom ends were mostly strong enough not to be the limiting factor . Apparently the biggest limiting factor was detonation . Apparently , the generally Allies had higher octane fuel . This allowed them to run higher boost , resulting in higher HP . The supercharger design played a part too . And they could be optimized for a specific altitude range . Some engines used 2 speed superchargers , also . Then I watched a video about water / methanol injection . Apparently , this was used in some models of German engines / planes . The net result was the ability to run higher boost , before the onset of detonation . Can not remember if any Allied planes use WM injection ? On a slightly different subject , I read some early jets used water injection , on take off , I think . I found all this interesting .
 
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Some planes were smarter than others about boost. The P-47's had intercoolers in the tail with adjustable flaps. Really helped to prevent detonation. The P-47 also had water injection. IIRC, it was something around 24 gallons, located in front of the pilot.
 
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I know with the original engines, KC-135 tankers used water injection. Also, The F-105 Wild Weasels required water injection to be able to leave the ground on a runway that wasn't longer than the average marathon course. Sitting in "Mobile" at the end of the runway, you had to confirm the correct color of the afterburner plume to verify the water injection was working, otherwise you had to call for an abort to the takeoff. I did read the Germans used nitrous injection for a short term boost for some of their WWII fighters. I believe that is where the practice used by drag racers came from.
 

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But, did they have LSPI issues??? ;^) I remember reading something decades ago about the Israelis developing some kind of water injection for their F4 Phantoms to allow them to go significantly above their usual top speed for a short time. This was in response to having a MiG-25 streak over their entire country north to south at something like Mach 3 without the Israelis having any shot at intercepting it. Western intelligence learned years later that this was so stressful to the MiG that it was barely able to land and the aircraft was unusable afterwards. The stunt was never repeated, but it sure made an impression. The SR71 did similar things on the borders of the USSR and was never intercepted even by a MiG-25, but they were also able to return home easily...
 
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Most of that aircraft engine technology (and airframe technology, for that matter) was developed in the 1930's air racers. Some of those aircraft entered WWII little unchanged as fighters on both sides of the conflict. Those hemi-combustion chamber motors were fairly low static compression by today's standards, supercharging was to compensate for the low air density as altitude increased rather than as power boosters as we know them now. Due to the weight penalties supercharging an engine involved, not just added engine weight, and castings were heavy then, but added fuel load as well, it was only employed when high altitude operation was desirable to cruise above bomber fleets for ideal attack or fighter escort, while bombers themselves sometimes used it to fly above AA ranges. The dual-speed superchargers were "military power" enhancements but their use was limited to a few minutes operation, mostly due to the fuel consumption which went even higher than high altitude operation conditions. Water / Methanol injection to avoid detonation with the low quality fuels available at the time also carried corresponding weight penalties so a true need must have existed or they were not employed. The Germans, not surprisingly, adopted it to compensate for their coal-based synthetic fuel characteristics. The engine tech of the 1930's persisted in air engines right up to the present day where the common Lycoming and Continental small air engines continued to use a Hemi chamber. Porsche persisted longer than Harley-Davidson but both continued to use essentially aircraft designs well up to the threshold of this century. With modern quality fuels which allowed firstly the leaded high compression ratios of the 1960's and now modern unleaded formulas in automotive use (aircraft still use leaded fuels with these types of chambers even today) the emphasis on high compression enhanced by boost is really a much more modern evolution of the older technologies. Other tech of the 30's air engines now being employed in automotive and motorcycle use where Hemi chambers persist include dual spark plugs (used for performance today, mostly used as an extension of redundant safety then). Chrylser's modern "Hemi" is not a true Hemispherical Combustion chamber motor so does not apply here. Chrysler calls it a "Hemi" based on a side effect of a Hemi chamber design whereby valves are situated differently into the chamber than pentaroof and other modified chamber shapes more commonly used in terrestrial vehicles. More marketing than chamber shape based. All in all, none of the above is surprising, since technology rarely fully develops to it's full potential prior to new replacement tech rendering the old obsolescent, rather than truly obsolete. RE: Russian fighter designs: virtually all contemporary (as in contemporary to corresponding era) Soviet fighters are faster than their Western counterparts. The Russians have virtually unlimited fuel and are never afraid to put an engine that is "too big" by standards in the West and compensate with big fuel loads where the weight penalty is easily overcome by the engine thrust. In normal operation they are not stressed beyond operational requirements, so the Israeli story might be true but sounds a little "urban myth" to me.
 
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The early P-3A Orions ran water injection in the T56-10's until the higher output T56-14's came on line.
 

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The Israeli story is absolutely true. But it was the Tumansky engines that were toast after the flight, as they were deliberately overtemped to maintain that mach number... The airframe was fine. The Russians don't just put in "big" engines, they have a whole different philosophy. Their pilots fly much less than ours, so airplanes don't get the number of flight hours that ours do, and while we might expect to get 4,000 hours service life from an engine, they expect to get 400, and thus can push the metallurgy much harder. They change engines far more often than we do. Labor (building and changing out engines) is cheap. Further, airplanes like the MiG-29 are designed as point defense fighters. They don't hold as much fuel (as a percentage of total weight, which includes, structure, engines, weapons system, pilot & environmentals and yes, fuel) because range was never intended as a design criterion. So, without the structural weight or room for tanks, and without the weight of the fuel itself, you see higher thrust/weight because the weight is lower. It's not that the engines are bigger, it's that the weight is lower...
 
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Originally Posted By: Johnny2Bad
operation, mostly due to the fuel consumption which went even higher than high altitude operation conditions. Water / Methanol injection to avoid detonation with the low quality fuels available at the time also carried corresponding weight penalties so a true need must have existed or they were not employed. The Germans, not surprisingly, adopted it to compensate for their coal-based synthetic fuel characteristics.
I thought that they synthetic gasoline they made was better than plain old dino juice. Cool!
Originally Posted By: Johnny2Bad
Other tech of the 30's air engines now being employed in automotive and motorcycle use where Hemi chambers persist include dual spark plugs (used for performance today, mostly used as an extension of redundant safety then). Chrylser's modern "Hemi" is not a true Hemispherical Combustion chamber motor so does not apply here. Chrysler calls it a "Hemi" based on a side effect of a Hemi chamber design whereby valves are situated differently into the chamber than pentaroof and other modified chamber shapes more commonly used in terrestrial vehicles. More marketing than chamber shape based.
I had a 1971 Honda CT-70 and when I took the head off I was surprised to see that it was an actual hemispherical chamber. I think wedge designs exist because that was how they looked on the first OHV engines and they just kept them.
Originally Posted By: Astro14
The Israeli story is absolutely true. But it was the Tumansky engines that were toast after the flight, as they were deliberately overtemped to maintain that mach number... The airframe was fine.
I love this story! I also read that the plane just smoked the mills. I also read that they designed the F-15 according to those specs and it was revolutionary because they actually achieved them.
 
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Originally Posted By: ArrestMeRedZ
I did read the Germans used nitrous injection for a short term boost for some of their WWII fighters. I believe that is where the practice used by drag racers came from.
https://en.econologie.com/Water-injection-motor-Daimler-benz-aircraft-messerschmitt/
Quote:
About the MW-50 MW-50 (water / methanol 50 / 50) was injected through the air intake and served as an anti-explosive, allowing more below the ideal altitude thrust. The evaporation of water also cooling the supply air, thus increasing the weight of food. Limited by over-supply system, the MW-induced 50 as maximum yield began to decline in 1.5 - 2 km below the ideal altitude, becoming inactive above this altitude (compare eg DB 605A -1 and AM). Maximum usage time: 5 10 in minutes. Constraints shortening endurance flying and life of candles, the additional weight of MW-50 tank and pipes. The majority of sub-categories of Me 109 1944 / 45 was equipped for the use of MW-50. About GM-1. Another way to increase the performance was the GM-1 (Göring Mischung 1). It consisted in injecting nitrogen dioxide (nitro) in the on-feeder above the ideal engine altitude. Nitrogen was used as "carrier" oxide oxygen to increase the high-altitude performance (using pure oxygen being too volatile). The effect was phenomenal, instantly increasing the power of 25 - 30%. GM-1 was used by the flight of groups specialized in high altitudes from 1941. Volume and excess weight were the main constraints of this system and the additional over-feeding was generally seen as more efficient.
https://en.wikipedia.org/wiki/MW_50 https://en.wikipedia.org/wiki/GM-1
 

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Originally Posted By: Virtus_Probi
But, did they have LSPI issues??? I remember reading something decades ago about the Israelis developing some kind of water injection for their F4 Phantoms to allow them to go significantly above their usual top speed for a short time. This was in response to having a MiG-25 streak over their entire country north to south at something like Mach 3 without the Israelis having any shot at intercepting it. Western intelligence learned years later that this was so stressful to the MiG that it was barely able to land and the aircraft was unusable afterwards. The stunt was never repeated, but it sure made an impression. The SR71 did similar things on the borders of the USSR and was never intercepted even by a MiG-25, but they were also able to return home easily...
I also read the MIG-25 burned out the engines . The SR-71 was designed to go Mach 3 . Every time it went out . Above a certain speed , the engine took on some of the characteristics of a ram jet . As first introduced , it had a boat load of bleeding edge technologies . That came with a very high cost .
 

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As far as hemi heads ; Our little 2015 Chevy Sonic 1.8l 4 banger , has 4 valves per cylinder hemi heads with DOHC . All , a hot rodder's dream , at the time of my youth .
 
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Originally Posted By: Astro14
The Israeli story is absolutely true. But it was the Tumansky engines that were toast after the flight, as they were deliberately overtemped to maintain that mach number... The airframe was fine.
Interesting info, the source I read definitely mentioned that the engines were fried but I thought that the whole plane was just retired after the streak. I would guess my imagination just filled in the false idea about the airframe being shot. I believe I read this in Air International in the early '80s and then ended up selling all my defense mags when my dad told me to get my junk out of his house after I bought my own place in the early '90s. I had sort of lost interest and got a few bucks for them back at the hobby shop where I had purchased most of them...wish I had at least kept that issue! Spent a lot of hours at that shop when I was in high school, became friendly with the son of the owner and it turned out they had an informal round table discussion about modelling and general defense issues once a week when the shop stayed open late. One participant was ex-military but non-US (maybe a S American country?) and he would bring his very cute and MUCH younger sister from time to time...she was my age and I really wanted to ask her out, but I was very shy AND also very worried about what her still quite muscular brother would do to me if he didn't like me dating her. We went to a couple of Chicago lakefront air and water shows as a group and had a lot of fun, but I quit the group after the second trip because an occasional member I didn't much care for went out of his way to try to pick a fight with a black guy who brought his white girlfriend to the beach. I guess the racist guy thought the rest of us would back him up as he was about half the size of guy he was antagonizing, and I grateful when the latter gentleman just eventually walked away rather than escalating the situation. Turned out on the train ride home that I was the only one who felt that the racist abuse was totally out of line so I was done with the meetings, but I did stay friendly with the shop owner and his son until I went off to college. There was a new owner when I went to sell the mags and the place closed down not long after that.
 
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Originally Posted By: WyrTwister
Been watching some YouTube videos about these engines and the amount of boost they ran . I figure all of you know , the more boost you run , potentially , the more hp , all things being equal . Untill something comes apart . The main comparison was between the Merlin engine in the P51 Mustangs , and various British planes . And the engines used in the BF-109 . I guess the bottom ends were mostly strong enough not to be the limiting factor . Apparently the biggest limiting factor was detonation . Apparently , the generally Allies had higher octane fuel . This allowed them to run higher boost , resulting in higher HP . The supercharger design played a part too . And they could be optimized for a specific altitude range . Some engines used 2 speed superchargers , also . Then I watched a video about water / methanol injection . Apparently , this was used in some models of German engines / planes . The net result was the ability to run higher boost , before the onset of detonation . Can not remember if any Allied planes use WM injection ? On a slightly different subject , I read some early jets used water injection , on take off , I think . I found all this interesting .
Convair 880s and I think 990s in late 50s and 60s had water injection to augment takeoff thrust. TWA called them "water rwagons." Watched many a Convair smoking out of Albuquerque.
 
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This can get really complicated. This really helps explain boost and manifold pressure. Takeoff power in the P-51 always impressed me at 3,000 RPM with 61" of manifold pressure.
 

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Good video - I wouldn't agree with his statement that supercharging was added to increase sea level power - it was more a matter of adding back lost power at altitude. That's why the two stage supercharger was so important. Hence the "high" and "low" blower... I also appreciate that the placard limit is for a "Packard V-1650-7" The photos (airplanes and engines) are mostly taken in the USAF museum, in Dayton, OH. Well worth the visit.
 
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thank you i really enjoyed that. my only experience with blowers. was a friend had one on a street rod. he told me that when set up for a street rod it will not make boost with normal driving . until l you put a load on it. as the engine will eat all the air going into it. BUT the full race blower is a lot different.
 
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The P51 had a peak manifold pressure of 70-73 inches late in the war, this is over two atmospheres. The P47 was similar but usually just a few inches less partly due to being air cooled. And yes they regularly ran in excess of sealevel pressure while in steady flight. The reason for two speed compressors was that the designs of the era were mostly mechanically driven and were optimized only at fixed altitudes, the turbo-supercharger doesn't have this altitude optimization problem but was bulky and experimental at the time, the turbocharger is the reason the P47 was so large the whole tail section was filled with turb and ducts and an intercooler (a real intercooler not an after cooler) and then up front just before the engine was a mechanically driven compressor second compressor stage. So a turbo-charger fed super-charger. A true inter-cooler is used between compressor stages, most cars have an after cooler. Many planes had two stage mechanical compressors with one of the stages having a two speed gearbox to adjust for outside air density, using high speed at low altitudes just put extra parasitic load on the engine. The navy had no turbo-supercharged planes.
 

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I think the early B-52's used water injection , and as mentioned the F-105 . For take off , I think . But both were jets , not piston engines .
 
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