French coolant for the HS 12Y?

[ThomasP]

Also in response to tomo pauk post#17,

I am pretty sure that the V-1650-1 max rating was due to what I said in my post#12. AFAIK all the other V-1650-1 based engines engines that Packard produced for the UK were limited in the same way (i.e. Merlin 28 for example). I think that the reason for this was simple logistics - there was only so much production capacity for new engines and there was not sufficient reason to expend resources on modifying either the production lines or the in service engines. Even limited to a reliable 1300 BHP they were not something to laugh at.

Of the Packard produced Merlin engines, only those labeled with the prefix 2 (i.e. Merlin 224 for example) and the 2-stage V-1650-3 series were rated to use higher boosts. The engines with the 2 prefix were manufactured to the exact same interchangeable specs as the RR produced Merlins, which included any cooling mods. The 2-stage V-1650-3 and later engines along with their cooling systems were designed from the start for the use of 130 grade and 70/30 mix coolant.

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.

 

[Shortround6]

Perhaps I missed it but I think you guys are missing the other end of the cooling situation.
What happens when your 90C water radiator is exposed to 15C or colder air?
What happens when 145C ethylene glycol radiator is exposed to 15C or colder air?
What happens when 120C ethylene glycol radiator is exposed to 15C or colder air?

The greater heat difference at the radiator meant the radiator could be smaller, at least that was the theory in the early 30s.
The US Army pushed for 300F (145-149C) temperatures. However they found that at such temperatures the oil was picking up so much heat that the oil cooler/s had to be made larger.
The balance temperature was about 120C for the smallest radiator/oil cooler combination. However this was for the type of radiators and oil coolers in use at the time. But the radiator types didn't change until the middle of the war or later. This would be the change from the honeycomb of hexagonal tubes to the fin and tube more like a car radiator.

The radiator was where the largest variables came in. vastly different air temperatures and vastly different air densities (mass of cooling air flowing through the radiator).
Air at 20,000ft is a lot colder (better) but almost 1/2 the kg per minute (worse) than sea level.

UK 100 octane was what the US called 100/130 grade.

Not in the first few years of the war. Up until sometime in 1940 US 100 octane was 100/100? (yes the rich number varied a bit and was unknown) while British 100 octane was 100/112-120. the rich number was unknown at the time but that is the range in samples that were tested later, just like the US samples. I don't know if the UK ever had a specification for an intermediate step before their first 100/130 specification or not.
The US did have a specification for 100/125 fuel and at least a few batches were made and some Allisons were rated on it. I don't know if the Air cooled engines were ever rated on it or not. In any case, it never went into widespread use and was replaced with a joint US/British specification for 100/130 fuel.

 

[elbmc1969]

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.

Excellent explanation, thanks.

All I know is that the He70 ran a pure E-G coolant to help it achieve very high speed, and E-G coolants (mixes) run at higher temperatures allowed more efficient radiators, which meant smaller radiators, which meant less drag. I clearly don't understand the details, and your help is greatly appreciated.

Obviously, if you know that you're designing the engine cooling and the radiator for E-G (or a mix), you design it that way from scratch, which is a lot easier than a redesign.

 

[tomo pauk]

In response to tomo pauk post#18,

UK 100 octane was what the US called 100/130 grade.

Not in 1940.

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.

I'm not sure where the information came that P-38 used any type of liquid in it's intercoolers, since the intercoolers were air-cooled. Heat dissipation of fuel/air mixture is a function of intercooler, not of engine cooler or coolant.
Engine and turbosupercharger were not a package in the P-38, since Lockheed manufactured and USAAF used dozens of non-turbo P-38s (called P-322).
Cooling system of early P-38s were capable to handle powers beyond 1150 HP, however the carb temperature was hurting the altitude power.

 

[tomo pauk]

..., 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.

V-1650-1 used 70/30 mix, too.

...
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.

With regard to Sea Hurricane - you might be right. However, please note that +12 psi was allowed on 100% glycol cooled engine.

 

[ThomasP]

In response to Shortround6 post#22,

You are correct that we have not addressed the effects of change in ambient air temperatures due to altitude (or season. A lower air temperature either at altitude or on the ground would reduce the work (in the physics sense: ie changing the energy state of a system or object) needed to cool the engine, and hence as you said the radiator could be smaller.

On the other hand, as you also said, an increase altitude decreases the volume of air flowing over/thru the radiator which in turn increases the work needed to be done by the radiator.

If you were just running the engine on the ground the radiator cooling surface area could be smaller in approximate direct proportion to the ambient temperature decrease.

Altitude combined with supercharging, however, adds two other factors into the equation:

1. The heat added to the system caused by the work done by the turbosupercharger compression of the incoming air.

2. The heat added to the system due to resulting increase in power allowed by the denser air/fuel charge being fed into the engine

The heat added due to compression of air by the turbosupercharger system is supposed to be reduced the intercooler enough that the engine can run at a safe temperature. For this example 90ºC.

If you figure the changes due to altitude into the equation you get:

Yo + Y1 + Y2 + Y3 - Y4 = Yn

where

Yo = start heat value needing to be removed on the ground

Y1 = heat added to system by the compression of air

Y2 = heat added to system to the system due to increased fuel burn

Y3 = heat added to system due to decreased density of air

Y4 = heat taken away from the system due to lower ambient air temperature

Yn = new heat value needing to be removed

The actual Y values can be figured out if you are willing to take the time (both in terms of learning the math - if you have not already done so - and in terms of setting up a spread sheet to do the calculations). If you were to do so I assure you that Yn is greater than Yo. This may seem counter-intuitive(?) but it is how it works.

Unfortunately the intercooler system in the early P-38s could not reliably reduce the heat added to the overall system when more power was demanded. It was not that the engine/turbocharger cooling system was a poor design so much as it was a very tight design, with no room for growth. I suspect that it was also over rated by Lockheed, but I may be wrong about that.

 

[ThomasP]

In response to tomo pauk post#24 and Shortround6 post#22,

The UK switched to the 100 octane (130 grade mix) of 100 in mid-1941, just in time for use in the 2-stage Merlin 60 series.

The US adopted 125 grade just prior to the war. It was produced in and issued in very large volume, and remained the standard avgas mix until sometime in early-1943 when institutional inertia was overcome and the switch to 130 grade took place. The 125 grade stock was then used for training only in the US, while the remaining stock in the PTO, MTO, ETO was used up or remixed with incoming 130 grade and additional additives.


In response to tomo pauk post#25,

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.

 

[tomo pauk]

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.

Do you have any reference that can confirm that V-1650-1 ever used 100% glycol in service?

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.

The mods didn't include change to 70/30 coolant mix.
The short duration of +12 psi is no wonder, engines were much more stressed when in combat/WER mode than it would be some continuous or 'military power'.

 

[ThomasP]

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.

 

[ThomasP]

addition to my post#29,

also see: http://www.wwiiaircraftperformance.org/hurricane/pilots-notes-merlin3-pg6.jpg

 

[ThomasP]

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??

 

[ThomasP]

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.

 

[tomo pauk]

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.

No need to apologize that much, I myself was wrong many times
I still don't think that +12 psi boost required switch to 70/30 coolant mix. FWIW, the manual for the Merlin X specifically allowed +10 psi boost whether the coolant was 70/30 mix or pure glycol.
With regard to early P-38 intercoolers - the compressed air was not pumped by any other means but the compressors themselves. Coming from turbocharger, the compressed air was directed into the pipe-in-pipe system located in the leading edge, then it was fed to the carburetor, and imediately after into the engine-stage supercharger. The outer pipe of the pipe-in-pipe system radiated and convected heat into the ambient air.
The easily obtainable manuals (from this site, for example) for the V-1710 show different engine installations on American fighters that used that engine.

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.

The redesign was probably not that major, when they switched from LE intercoolers to 'chin' intercoolers. And yes, the later P-38s still used air-to-air intercooler.

 

[elbmc1969]

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??

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 ...

 

[rinkol]

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.

Before coolant systems were pressurized, the use of water or water-based mixtures had the problem that the boiling point of water falls with increasing altitude, thus requiring further reductions in operating temperature. I'm not sure about E-G, but suspect that the difference in boiling points became greater with increasing altitude.

An additional drawback of pure E-G concerns its propensity to leak through anything short of a perfect joint.

I think Sam Heron said something to the effect that water would be more respected as a coolant if it cost $10/gallon. Of course he was referring to the hat capacity.

 

[ThomasP]

Good point Rinkol.

When coolant flows through the cooling channels it encounters hot spots, causing some of the coolant to vaporize creating a bubble. If the cooling channels are designed properly the force/pressure of the coolant flow will cause the bubble of vapor to continually collapse and the vapor to be dispersed back into the coolant. If the cooling channels are not designed properly there can be problems. If the spots are hot enough they can create a bubble of vapor that effectively is self-sustaining causing the hot spot to get worse. The lack of cooling in the area of the hot spot can result in various problems such as overheating of cylinders (causing detonation) or possibly overheating of the oil (due to a similar process to that of the coolant).

Even in pressurized systems the type of coolant has a significant impact on the design. Ideally, systems are designed for the different coolants - with appropriate cooling channel sizes, condenser volumes, and flow rates, sometimes materials, etc. A system designed for one type/mix of coolant may not function effectively when another type/mix of coolant is used.

 

[elbmc1969]

1936 article on evaporative cooling in the "Revue du Ministère de l'air" Revue du Ministère de l'air : organe de l'armée de l'air et de ses réserves

 

[jmcalli2]

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.

Your reply makes me remeber something I read from a Russian P-39 pilot about the Americans being too concerned with engine overheating in their manuals (a holdover from the low-budget 1930s perhaps?). 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? I would add the P-51 as having less intake area considering it included the intercooler, but your glycol ratio answer shed light on that I think.
It seems to me the P-38 particularly would have benefited from reduced radiator drag, and certainly could have had the coolant radiators designed for a Meredith effect.
Just curious.
Thanks, Jim

 

[Shortround6]

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

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.

 

[jmcalli2]

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.

I'd agree totally with your P-38 comments except the P-51 had a similar engine but only half the intake size.
The P-40 they increases the radiator size for a plane with the same critical altitude in later models but not on the P-39. Just seems strange.
P-39 cooling intakes should be easy to calculate if you can find a good scale drawing since they'r rectangles. P-38's are basicallt two half-circles per engine, and P-51 is an oval/almost a rectangle. But I haven't found reasonable scale drawings with measurements on them; I was hoping some one knew the answers.
You could be 100% spot on.