Anti-Detonation-Injection; a system whereby either pure water or a water/methyl alcohol mix is injected into the engine. The German MW 50 (50% water 50% Methanol) was one such system; Pratt Whitney R-2800s with ADI used the suffix W; eg: R-2800-16W.
With the P-38K, was the P-51 and F4U even necessary?
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Anti-Detonation-Injection; a system whereby either pure water or a water/methyl alcohol mix is injected into the engine. The German MW 50 (50% water 50% Methanol) was one such system; Pratt Whitney R-2800s with ADI used the suffix W; eg: R-2800-16W.
OldSkeptic
Senior Airman
- 509
- May 17, 2010
Not quite, the BMW system was actually a C3 feed before the supercharger. Yes it richened the mixture but also charge cooled the air in the supercharger (ah lah the Merlin).
The combination of the richer mixture and the cooler supercharger outlet meant you could run higher boost without detonation.
Basically, in their complex way they copied the RR system, but only for emergencies. And in their complex way they still maintained all the individual feeds to each piston ????
The correct way was fuel injection into the supercharger inlet, as per the Merlin 100 series (late 44), which the Germans could have done very successfully in 1939.....
Funny design attitude.
The combination of the richer mixture and the cooler supercharger outlet meant you could run higher boost without detonation.
Basically, in their complex way they copied the RR system, but only for emergencies. And in their complex way they still maintained all the individual feeds to each piston ????
The correct way was fuel injection into the supercharger inlet, as per the Merlin 100 series (late 44), which the Germans could have done very successfully in 1939.....
Funny design attitude.
Shortround6
Major General
Once a company or country starts down a design path it is hard to change. Germans believed the fuel injection gave better economy for power produced and given the Germans fuel situation they may have been right. The high compression used in German engines was also good for economy but limited ( in some cases severely) the max amount of boost that could be used.
The Allison is often considered to have lost about 10% of it's max boost/power capability due to it's higher compression and it was nowhere near as high as the later German engines. The Allison did have better spc than the Merlin.
The Allison is often considered to have lost about 10% of it's max boost/power capability due to it's higher compression and it was nowhere near as high as the later German engines. The Allison did have better spc than the Merlin.
I'd like to see exactly where BMW copied RR? Being single stage engine, that never used intercooler, but used C3 as ADI?
Some people still consider sleeve valves as funny design attitude, as well as 'their complex way'.
C3 feed before the supercharger still counts as ADI, no?
Shortround6
Major General
Maybe yes, maybe no 
A lot of American ( and some others) ran really,really rich at max power settings, so rich than when water injection was introduced and used, fuel consumption was cut back using a "de-enrichment circuit" in the carburetor.
The extra fuel ( way more than could be burned in the available quantity of air) acted as a charge coolant and internal coolant to the engine. Even if supplied by the "normal" carburetor would the excess fuel be considered "ADI".
Pictures or videos of these planes taking off and trailing black exhaust plumes show the extra fuel being used even at take-off power.
A lot of American ( and some others) ran really,really rich at max power settings, so rich than when water injection was introduced and used, fuel consumption was cut back using a "de-enrichment circuit" in the carburetor.
The extra fuel ( way more than could be burned in the available quantity of air) acted as a charge coolant and internal coolant to the engine. Even if supplied by the "normal" carburetor would the excess fuel be considered "ADI".
Pictures or videos of these planes taking off and trailing black exhaust plumes show the extra fuel being used even at take-off power.
swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
Water injection was used in the jet engines on a number of airliners and multi-engined military jets. Oddly enough, it was frequently called ADI, even though gas turbines don't have anything akin to engine knock. They'd mix water and alcohol to get the lowest freezing point. Thankfully, especially for people who live within a few miles of an airport, high-bypass fans don't tend to need water injection.
silence
Senior Airman
Thanks!
IdahoRenegade
Airman 1st Class
I have a question about the '38K I wonder if someone can answer. Most of our top fighters were originally equipped with fairly narrow, 3-bladed props at the start of the war if I remember correctly. I'm pretty sure the P-51-A and the F4U at the least did, not so sure about the '47. Anyway, in every plane except the '38, when "high activity" paddle props were installed, they were all 4-bladed (Corsair, '47 and '51). The pictures I've seen of the '38K still show it with a 3-bladed prop, just a wider one. Any reason they didn't use a 4-bladed one? Seems like the one (with spinner) from the '51 might have been adapted.
The other oddity for me was the way the '38 was treated by the War Production Board. By late 40 to early 41 it should have been obvious that the only AAC plane in the work that was both a match for the best enemy fighters and had useful range was the '38. At that time the '51B (Merlin version) wasn't even a pipedream. It was obvious early on the '47 wasn't going to have the range to provide escorts or any kind of long range fighter sweeps. It seems odd that a 2nd source of production for the '38 was never set up until the VERY end of the war (Vultee made a very few hundred in '45). Had this been done early, significant numbers of '38s could have been in Britain (without shorting the SWPA and MTO) to start providing long range bomber escort in early '43. More planes, with time for the ground crews to get used to servicing them, and for the pilots to gain experience, would have made a huge difference in effectiveness when they were finally allowed to escort the bombers. Moreso, as it was the '38s were available as escorts only in very low numbers by late '43, they were often outnumbered 5 or even 10 to one. An extra few hundred fighters would have made a huge difference. In addition, that extra production capacity would mean that one line at a time could have been shut down and converted to K production. The Bell p-39 plant could have been converted, both enhancing production of the '38 and avoiding the "waste" of some V1710s in the under-performing P-39.
The other oddity for me was the way the '38 was treated by the War Production Board. By late 40 to early 41 it should have been obvious that the only AAC plane in the work that was both a match for the best enemy fighters and had useful range was the '38. At that time the '51B (Merlin version) wasn't even a pipedream. It was obvious early on the '47 wasn't going to have the range to provide escorts or any kind of long range fighter sweeps. It seems odd that a 2nd source of production for the '38 was never set up until the VERY end of the war (Vultee made a very few hundred in '45). Had this been done early, significant numbers of '38s could have been in Britain (without shorting the SWPA and MTO) to start providing long range bomber escort in early '43. More planes, with time for the ground crews to get used to servicing them, and for the pilots to gain experience, would have made a huge difference in effectiveness when they were finally allowed to escort the bombers. Moreso, as it was the '38s were available as escorts only in very low numbers by late '43, they were often outnumbered 5 or even 10 to one. An extra few hundred fighters would have made a huge difference. In addition, that extra production capacity would mean that one line at a time could have been shut down and converted to K production. The Bell p-39 plant could have been converted, both enhancing production of the '38 and avoiding the "waste" of some V1710s in the under-performing P-39.
IdahoRenegade
Airman 1st Class
Oh as far as the K model making the '51 and F4U unnecessary...maybe. It could certainly have provided adequate escort for the bombers had it been available in volume. And it was much more versatile than the Mustang, with a far higher bomb load (4000lbs) and it was much more "survivable", with dual engines. Don't forget the '51 was not going home with one hit anywhere in the Merlin's cooling system. In addition, the cluster of guns in the nose made it much more effective in ground attack than any fighter dealing with gun convergence of a wing-mounted gun. With regard to the Corsair, yes, it was eventually cleared for carrier ops, but not until late '44. It was primarily a land-based plane operated by the Marines. The '38K could certainly have provided similar capability, with the redundancy of twin engines, a higher weapons load and much longer range. As far as carrier ops, the Hellcat could have been used throughout the war. Though it wouldn't have been nearly as effective chasing down Kamikaze planes due to it's much lower top speed.
drgondog
Major
The P-38s in the 20th, 55th and 364th P-38s suffered much higher losses while strafing LW airfields than P-51B's (All three 8th AF P-38s converted to P-51s in July, 1944. The 479th did not have as high percentage losses to strafing as the other 3 and were closer to Mustang average loss per aircraft destroyed on the ground.
The twin engines were a definite advantage for loss of engine in a non lethal strafing environment but consider that the F4U and P-51 losses in Korea per sortie (ALL CAS for both ships) was about the same with 51 very slightly higher - one with coolant/one without. The P-38 was a huge (and slower) target on the deck with not only greater number of vulnerable surface areas and internal components(Fuel cells of internal fuel, supercharger systems, two radiators/oil coolers, coolant lines - all vulnerable to fire from explosive 20mm flak.
But, True - that if hit in a coolant line and that engine is shut down immediately the P-38 will survive where the P-51 will not.
The P-38K does Not solve the following
1.) Has very small window between top speed in a chase from 22000+ ft to compressibility in a dive. If dive flaps are deployed, the Critical Mach increases slightly but far short of the P-51, P-47, Bf 109 and FW 190. It can't chase nor can it evade from a dive initiated at high altitude. 8th AF operations required high altitude performance envelope and the P-38 was least suited of the Big 3 for Germany. The J-15 solved many of the mechanical issues but could do nothing for the aerodynamic issues of the NACA 23018 wing near transonic.
2.) It is HUGE and easily spotted long before the P-38 driver spots the other guy - giving the other guy a tactical advantage.
3.) It P-38J/L had less Combat Radius than the P-51B/C/D/K (not by much, 675mi to 750mi) limiting target escort options for 8th AF (and 20th AF) Planners. For example no P-38J with additional 110 gallons in LE fuel cell went past the Berlin/Leipzig/Munich line when P-51s were going to Stettin and Posnan Poland and Brux, Czechoslovakia. Even if the K had been configured for a Merlin 1650 it would consume even more gas than the V-1710 and further reduce Combat Radius..
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drgondog
Major
BTW - it would be interesting to see a real flight test report on the P-38K to understand a.) what the load out looked like, b.) understand the magic of overcoming the drag rise as the Propeller tips way exceeded M=1 at 29,000 feet at the alleged 450mph, c.)understanding the math of a theoretical 10-15% range improvement due to prop selection. If true, that change would have been as easy as selecting and installing the Aero Products prop/Spinner on the P-51K.
I suspect Bodie was waxing euphoria and sunshine and unicorns - again. Seeing the Flight Tests and write ups would silence my skepticism
I suspect Bodie was waxing euphoria and sunshine and unicorns - again. Seeing the Flight Tests and write ups would silence my skepticism
Don't know the reasoning of not installing the 4-bladed prop, but the new prop was also of greater diameter than the old one - 12'6" vs. 11'6". As I understand by posts in this forum, the increased diameter of the prop will mean more than increased number of blades, efficiency-wise, so they judged that going for 4-bladed is not necessary? The choice of prop was probably undoing of the P-38K, since it required also the new reduction gear, that required change of cowling, that required halt of production line by couple of weeks - ain't going to happen when P-38 was in such a demand. Maybe it's too bad the new prop didn't retain the diameter, but went to 4 wider blades? Merlin Mustang was outfitted with the prop of 11'2" diameter, a small change from 10'9" of the Allison P-51.
Not having the second source for P-38 is surely a shame. The 'useful range' was not that a big thing for the USAF of 1940/41, since then current doctrine was that fighters are for defense. Nobody was talking much about escorting the bombers since it was expected the high flying + plenty of HMGs will mean safe bombers, and we know now that id didn't paned out that way.
Im afraid that here you are wrong - the P-47 have had the ingredients for long range work, as we know the combat range was 300 miles with small external fuel tankage, then 400 (all in 1943), 450 and then 600 (early and mid 1944), while the P-47N was managing 1000+ in mid-1945. Where the USAF made a mistake was not specifying wing pylons from P-47C at least.
Mike Williams
Senior Airman
- 572
- Oct 19, 2006
The following document was referenced earlier but is interesting and gives performance data of the P-38J and the prototype P-38K obtained from flight tests carried out by Lockheed.
Additional Performance of P-38J Airplanes, 11 March 1944
Balljoint
Senior Airman
This may be redundant; I don't recall it being specifically cited other than quotes.
Whatever Happened To The P-38K ?
Whatever Happened To The P-38K ?
drgondog
Major
1.AAF testing not performed to validate Lockheed tests.
2.The values from Lockheed are derived from a 'light' P-38K at 16,200 versus fully loaded I(nternal fuel plus ammo)GW of 17,600 pounds which is an 8% reduction in Wing Loading. Would also result in a reduction to Induced Drag when compared to normal combat loaded P-38J-15 and higher dash number. Net result of lower wing loading is much faster climb and slightly more speed in the comparison than valid for equal Load Out between J and K..
3. They discuss Water Injection for the F-29 engines and the subsequent penalty in performance should the 600 extra pounds (tank, water, lines) be added to 17,600 pound Combat weight (without external fuel) as well as suggesting replacing 55 gallon fuel in each leading edge for the water, compromising range for hoped for performances.
4. The Mystery of the drag rise of the prop tips for greater diameter prop is answered with changing 2:1 to 2.36:1 ratio ------> reducing prop RPM from 1500RPM to 1271 RPM
5. The ROC for the P-38K would still be impressive, as well as increase in ceiling but look carefully at the 20000 to 30000 foot window for ROC. Both the speed and the ROC are virtually identical at MP and WEP at those altitudes for the 1475Hp and 1600Hp ratings (without WI) and close to the P-51B in climb with 1650-7 and 72" for WEP
Summary - In other words the Paddle Blade didn't do much where it counts just by looking at the data, and you have to keep in mind that the stated load out for the P-38K was 1400 pounds shy of the comparable J/L.
Next consideration - Allison finally put out a V-1710-143/-145 two speed/two stage engine for the P-82 to replace the V-1650-9 with W/I. It did not work well, never achieved the reliability of the Merlin and forever lived its existence limited to 61".. the implication is that the 1710-F29 would not have realized its design Power output predicted for WI and high octane fuel - or even improved on the 1710-89/91 on the J/L.
Bodie doesn't touch on those details for either the Flight Test by Lockheed (unseen) or the geneology of the F-29 V-1710 which IIRC was a modified V-1710-75/77.
I remain highly skeptical of either range or speed or even climb virtues (could probably get near same with P-38J-15 at same load out) as claimed by Lockheed as sufficient to proceed at that stage of the war. It was dead in the 8th AF, just waiting to convert to P-51 when the report Mike Williams just submitted was written (11 March, 1944). After 8 March, 1944 I can find no example where a P-38 Group was providing Target Escort for Munich-Regensburg-Dresden-Berlin radius.
Final thought - If the P-38K replaced the J-15 LE fuel tanks with water tanks for WI, they would have been near the existing P-47D-21 Combat Radius and relegated strictly to Penetration and Withdrawal escort in ETO and MTO.. but would have been fine in the 9th and 12th AF for CAS.
Most of the long range escort for 15th AF would be taken over by Mustangs from the P-38 Groups similar to US. Only in PTO would the twin engine safety factor be important enough to pay 1.5 X (1945 $$)more as well as CAS.
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drgondog
Major
The AAF senior leadership was curiously enough against the concept of long range fuel tanks for combat. IIRC Colonel Ben Kelsey snuck in the design mod under the guise of Ferry Tanks in 1942 but by that time the P-47C design was complete and Republic was trying for second source manufacturers. Even if Republic had the vision, AAF exhibited no interest until 1943 when it became apparent that a.) losses for deep penetrations would be prohibitive, and b.) there was a market for a P-47 with more internal fuel also as a requirement for Combat Radius extension.
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