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UK 100 octane was what the US called 100/130 grade.
Excellent explanation, thanks.Sorry this is so long winded but I do not know how to explain what is actually a very complex problem in a compact manner. Hope this helps clarify what I said in post#14.
In response to tomo pauk post#18,
UK 100 octane was what the US called 100/130 grade.
In response to tomo pauk post#17,
The early P-38 models used 2/98 mix in both the intercooler and engine (until they redesigned the intercooler and engine radiator systems to use 70/30 mix in the P-38x model). The reason the air/fuel charge entering the carburetor/intake manifold was too hot was that they did not build enough extra heat dissipation ability into the cooling systems. As I am sure you know, the P-38 was designed as a complete package, and the engine and turbosupercharger were part of the package. The cooling systems were designed for 1000/1150 BHP sustained/maximum and no more. The early turbosupercharger system was at/beyond its limits at 1150 BHP at high altitudes. When the P-38 became active in the pacific the problems were less apparent because most missions were at relatively low altitude where the systems could handle the heat.
I may be wrong about what I am about to say, but I think the higher ratings for the 1-stage V-1710s did not occur until the switch was made to 70/30 coolant mix, and the US switched from their early-war 125 grade fuel to 130 grade fuel. This took place at about the same time as the new models of the P-38 entered service also.
..., and why the V-1650-1 engine charts for the P-40F&L were never rated at more than 1300 HP). AFAIK The US did not switch to a 70/30 mix until the adoption of the Merlin 60/V-1650-3 engines in the P-51B Mustang.
...
As for the Merlin III in the SeaHurricane, I am pretty sure that those ratings were not available until after the required modifications for increased cooling were made (late-1941) as well as some mods for the use of 100 octane (130 grade). There were many detail mods for strengthening the engines also.
You are I believe correct when you say 70/30 mix was used in the V-1650-1, but not by original design of the cooling system. The UK simply switched to 70/30 mix in the V-1650-1 based engines when they received them. Without a cooling system redesign they could not achieve the higher power outputs of the RR Merlins, but the slight increase in cooling effect allowed a greater safety margin and they were happy that.
You may be right about the +12 lbs boost being used by the Merlin III with the pure glycol mix, but I do not think it was actually rated at that power level. From what I have read, it was kind of iffy to use +12 lbs boost without the mods, and was only done if really-really-really....needed.
In response to tomo pauk post#24,
I apologize if I got it wrong about the P-38s using liquid coolant in the intercooler (Did they maybe switch to liquid cooled in the revised system that came into service in the mid-war period? I do not have any authoritative references on the subject). I thought I remembered that they operated in a similar manner to the V-1650-3 intercooler system but with the radiators built inside the wing leading edges. If they used air cooling only (i.e. the compressed air was pumped through the radiator tubes as if it was liquid) then the system would have been less efficient than a liquid cooled system. Do you know how the heat was transferred to the ambient air?
In response to tomo pauk post#28,
I am sorry, but I do not have any handy references as to the use of pure ethylene-clycol in the V-1650-1. I read about it some years in an old industry technical study on the subject. If I can find it again I will let you know.
As to the subject of Merlin IIIs modified to use 70/30. If I remember correctly the switch to 70/30 began during the BoB (Spitfire II with Merlin XII used 70/30 mix off the production line). Many earlier aircraft never received any mods due to time constraints and a lack of perceived need, and the tendency of the airframes being used up or retired. I do not know what all the mods actually were, but if you can find a copy of the Merlin III powered Hurricane I or Spitfire I manual with the complete list of engine mods, you will see a series of mods to the aircraft concerning the cooling system.
also see: http://www.wwiiaircraftperformance.org/ap1590b.
In response to tomo pauk post#24 re my post#20,
My apologies, when I used the term package I meant that the overall design of the P-38 was intended to fulfill a set of parameters that were very capable, unusually so for the time. The designers were required by the USAAC (USAAF?) to incorporate the turbosupercharger in the design. Lockheed did so, but it resulted in a very tight design particularly where the intercoolers were concerned. In order to significantly increase the intercooler capabilities a major redesign of the installation was required, with the result that the intercooler radiators were moved from inside the leading edge of the wings to the engine nacelles/tail booms.
Darn it, tomo pauk, now you have me wondering if the later intercooler radiators were air cooled too.
That is exactly the purpose of the retractable radiator. I've just been trying to figure out why it was (apparently) so bad that it needed this sort of fiddly solution. It doesn't seem to have worked out well because at full throttle, you had to lower the radiator again, and full throttle is the only way to achieve maximum speed, so now you have the drag again, so maximum speed is restricted, so ...As to elbmc1969's original question,
I have tried to think of why the MS.406 airframe would be designed with a retractable radiator. The only plus I could come up with is less drag allowing higher speeds at higher altitudes, with the higher speeds probably including combat cruise. The rational, and this is just supposition on my part, is that if the cooling system was designed with more capability than was strictly needed then the reduced air flow through the radiator when retracted might still be sufficient at lower ambient air temperatures and higher speeds. The pilot would be able to retract the radiator when sufficient altitude and speed were reached, and the radiator could then be deployed again when descending and/or slowing down, as long as the engine temperatures stayed within safe limits. Maybe??
Ethylene glycol has a lower specific heat capacity than water. My father and I looked this up in the CRC handbook when I was curious about why the He70 would use pure E-G. I've double-checked. E-G has a slightly higher density, which makes up for this a bit. However, if the E-G system is being run well above water boiling (at 120C), the density difference is very marginal. Of course, at 120C the E-G is carrying a lot of heat, helping to make up the difference between it and pure water at 90C.
I'm not aware of that and I can't think of any reason why it would be so.
Of course, running E-G coolant at 120C makes the radiator a lot more efficient. The result was that you could have a much smaller radiator, which meant much lower drag.
I believe Aerodiol was a french commercial brand name for ethanediol, just with some additives making it more suitable for use in aero engines.
Ethanediol is in turn a contraction of ethane-1,2-diol.
Ethane-1,2-diol is in turn the IUPAC standard nomenclature for ethylene-glycol (C2H6O2).
The French automobile and aircraft industries were well aware of the cooling properties of the various blends of coolants - but like the US, UK, and Russia in the late 1930's - they had not yet settled on the later more-or-less standard universal mix of 70/30 (water/ethylene-glycol) mix for aero engines.
The US in 1939(?) had specified a 2/98 mix for all liquid cooled aero engines, including the V-1710 (this was a major part of the problem with getting rid of heat in the turbocharged V-1710 systems used in the early P-38s, why the non-turbo V-1710s had problems developing higher power ratings early war, and why the V-1650-1 engine charts for the P-40F&L were never rated at more than 1300 HP). AFAIK The US did not switch to a 70/30 mix until the adoption of the Merlin 60/V-1650-3 engines in the P-51B Mustang.
The UK was just starting to switch over from pure ethylene-glycol to the 70/30 mix in 1940 with the adoption of the Merlin X and XII engines. The earlier Merlin II-VIII powered aircraft had to continue using the earlier pure ethylene-glycol unless/until their cooling systems were modified for pressurized cooling.
I am not sure when the Russians switched to ~70/30-60/40 but from what I have seen of their engine charts and manuals I think it would have to have started in 1942.
A question about cooling airflow if I may; why were the oil and coolant radiator intakes on the P-38 and P-40 so much larger than on the P-39?
On the P-38 you were trying to get rid of the same amount of heat in thinner air. If you are trying to get rid of the heat from around 1400hp (prop HP + friction + power to supercharger) at 25,000 ft you need bigger radiators and ducts than you do at 12,000ft. where the air is much thicker. (more weigh/mass per cubic ft)
for the P-40 you would have to measure the intakes. The P-40 has them all in that one big chin intake, the P-39 has 4 intakes. They may look smaller due to location?
And one the P-40 the early ones didn't have the huge chin intake
View attachment 531444
View attachment 531445
The later ones got a new reduction gear that moved the propshaft up 6 in and eliminated the cowl guns. the radiators and oil cooler were already up against the bottom of the engine so you couldn't raise them. Apparently using the bigger opening but using an internal fairing/duct to get the air down to the radiator position didn't create much drag.