Me 109 F vs Spitfire coolant radiator installations

[riacrato]

Inspired by Tomo's thread about improving the Spitfire...

I have often wondered which of the two radiator designs and installations was the better one. The Me 109 F had larger radiators than the Spit but they were partially buried inside the wings. They had a bypass (later omitted from G-type onwards) allowing air to pass over them in order to not disturb the boundary layer flow too much. I read in a report about the DB601 powered Spitfire that the (German) evaluating person (probably from the RLM, I'll dig up the report later) thought the Spitfire radiators to be more efficient since despite being smaller they provided enough cooling to for the same engine. However the Spitfire radiator was of a different material which may have been a factor. Also I doubt the "Messerfire" was pushed to the limits as much as were operational fighters, so maybe the smaller area was no problem due to the engine not coming near to overheating.

Still, since it was the only direct comparison available I tended to believe the Spits radiator installation might've been better.

However, as I learned the Spiteful used radiators similar to the Me 109, so maybe Supermarine thought otherwise? Is there any documentation available that tells us why they changed from the simple "bolt-on" radiator to the more complex buried-in-the wings design? Did the Spiteful's radiators have a bypass?

 

[davebender]

Germany had plenty of aluminum. Britain didn't but I think they had an adequate supply of copper. That might account for the difference.

Both materials work ok for automobile radiators. At least they have in various cars I have owned.

 

[tyrodtom]

Copper is a little bit better conductor of heat.

 

[tomo pauk]

Spitfire's radiators were also (visualy, but not structurally) partly within the wing.

 

[wuzak]

I don't know much about the Bf109's radiators, but I know that Supermarines weren't completely satisfied with the Spitfire's.

Spitfire's radiators were deeper, but the Bf109's wider. Anyone know the surface area/frontal area of the two designs?

Cooper is a whol lot heavier than aluminium, so I assume that the aerodynamics is the deciding factor between the two.

 

[Juha]

While speaking on radiators. Opening the radiator flap(s) fully reduced the max speed of 109G-2 50km/h and that of LaGG-3 37 km/h. Does anyone know the effect of that on the max speed of Spit? I'm mostly interested in info on Mks IX/VIII and XIV but info on Mks I - V would also be interesting to know.

TIA
Juha

 

[davebender]

My 87 Mercury Tracer came with a copper radiator. When that wore out the replacement radiator (from auto parts store) was made of aluminum.

The replacement radiator was smaller (height x width). However it was thicker which exposed more metal to air flowing through. You could probably perform the same trick with an aircraft radiator. Make it thicker while reducing the height and width so it's more compact.

 

[tyrodtom]

When you make a radiator thicker, it doesn't cool as efficently. The water tubes in the back are exposed to air that's already warmed by the tubes in front of it. Plus a longer row of water tubes is more resistant to the air flowing thru.

 

[davebender]

That might be a worthwhile trade off for a fighter aircraft because aircraft speed will insure plenty of air flow.

 

[Juha]

But one must remember that the cooling must be adequate also for climbing on a hot summer day and the optimal climbing speed was usually rather low.

Juha

 

[tyrodtom]

reIf you make it too thick it's nothing but drag, no chance of the Meridith effect. Of course if you make it too wide and broad, thats drag too. You've got to get the right balance.

But copper is a better at heat transfer than aluminum, just check any radiator website. Only disadvantages to copper/brass radiators is weight of course, and that they have to be soldiered, the soldier usually eventually breaks down ( soldier blume) and blocks passages.

If you wonder why all the manufactors are switching to aluminum, it's weight, plus check the price of aluminum verses copper.

 

[DonL]

I have a test report of a Spitfire V with the DB 605A

http://cms.klassiker-der-luftfahrt.de/sixcms/media.php/58/Spitfire_Versuchsbericht.pdf

The report is only in german, but the DB engineers are truely amazed about the water cooling system of the Spitfire V!
The report says that the water cooler of the Spit V is only 50% in diameter of the Bf 109G water cooler but had only 4% less performance.

The flow resistance of the water cooler (Spit V) is much better and the cooler is much more stable compare to the Bf 109G

 

[Siegfried]

Inspired by Tomo's thread about improving the Spitfire...

I have often wondered which of the two radiator designs and installations was the better one.

The issue caused Proffessor Messerschmitt some concern as he was very proud of the Me 109F redesigned radiators and his engineers curiosity would have driven him to want to understand. He wanted to carry out all manner of tests and radiator swaps with captured aircraft.

The Me 109F radiators were thermodynamically very sophisticated as much as the lauded P-51's radiator: they included boundary layer bypass ducts. Air was taken in beneath the wing but ejected between the split flap. In other words the split flap functioned as a radiator nozzle as well as a flap. Of course the radiator placement wasn't as optimal as the P-51's single ventral duct. Messerschmitt did try a ventral radiatior duct on the Me 309, it was partially retractable as well. This aircraft which flew in June 1942 thus had all of the ingredients of the P-51: it had an efficient ventral radiator duct, laminar flow wings, an 800+ mile range, bubble canopy. The flaw seems to have been the shortage of DB603 engines which forced the fittment and consideration of the weaker DB605 and the resultant degradation in performance. It probably also may have needed re-engineering with a bigger wing area. The aircraft was very very fast at 466 mph but it was probably better to compromise a little speed to gain manouverabillity. The effort was not considered worthwhile in the context of the hoped for Me 262 however it might have been able to enter service at the same time as the P-51B in December 1943.

It would be interesting to know of the material the Germans used for their radiators, copper was certainly in short supply, however modern Aluminium radiators seem to be plastic/aluminium composit structure? Magnesium was the only metal the Germans were autonmous in.

For what it is worth, electric motors wound with aluminium instead of copper are around 10% heavier due to the greater bulk of magnetic and housing material arund the windings (which are about the same weight due to aluminiums lower desnsit though bigger due to the the lower conductivity per unit volume)

 

[Tante Ju]

While speaking on radiators. Opening the radiator flap(s) fully reduced the max speed of 109G-2 50km/h and that of LaGG-3 37 km/h. Does anyone know the effect of that on the max speed of Spit? I'm mostly interested in info on Mks IX/VIII and XIV but info on Mks I - V would also be interesting to know.

TIA
Juha

I do not know speed, but open position sure reduce performance of climb of IX... http://www.spitfireperformance.com/jl165climb.gif

 

[Shortround6]

Part of the problem with aircraft radiator design is getting the drag-cooling-size combination right. And drag is not just the size of the radiator but the pressure drop through the radiator. A radiator of twice the frontal area can have 1/4 of the pressure drop and so have less actual drag OF THE AIR GOING THROUGH the radiator. Other air frame drag may go up. Boundary layer spliters may be used to allow smaller radiator installations as the turbulent boundary layer, which is actually lower airflow, is channeled off allowing only the higher velocity but "straighter" airflow to the radiator. Good radiator installations do try to lower the speed of the air actually flowing through the radiator core because, once again, the drag goes up with the square of the speed.
Aluminium radiators were not common at the beginning of WW II or even most of the way through because fabricating the radiators was a problem. The P-40 got Aluminium radiators in the "N" model. Welding thin gauge aluminium was in it's infancy at the time. Radiators need a LOT of continuous welding/brazing not spot welding like aircraft skins.

 

[davebender]

Messerschmitt did try a ventral radiatior duct on the Me 309, it was partially retractable as well. This aircraft which flew in June 1942 thus had all of the ingredients of the P-51: it had an efficient ventral radiator duct, laminar flow wings, an 800+ mile range, bubble canopy. The flaw seems to have been the shortage of DB603 engines which forced the fittment and consideration of the weaker DB605 and the resultant degradation in performance.

Apparently Professor Messerschmitt did not share Daimler-Benz's faith in the DB605 engine. Not that I blame him as DB605 engine technical glitches required two years to solve. If the Me-309 had been designed around the lighter and more compact DB605ASM engine it might have been a great 1944 fighter aircraft.

 

[Siegfried]

I have a test report of a Spitfire V with the DB 605A

http://cms.klassiker-der-luftfahrt.de/sixcms/media.php/58/Spitfire_Versuchsbericht.pdf

The report is only in german, but the DB engineers are truely amazed about the water cooling system of the Spitfire V!
The report says that the water cooler of the Spit V is only 50% in diameter of the Bf 109G water cooler but had only 4% less performance.

The flow resistance of the water cooler (Spit V) is much better and the cooler is much more stable compare to the Bf 109G

If you have a look at the end of the report it says the Spitfire had a radiator made of "Cu" while that the the Me 109 was of "Al"

Good guess Dave Bender.

 

[Hop]

Opening the radiator flap(s) fully reduced the max speed of 109G-2 50km/h and that of LaGG-3 37 km/h. Does anyone know the effect of that on the max speed of Spit? I'm mostly interested in info on Mks IX/VIII and XIV but info on Mks I - V would also be interesting to know.

I don't know, I have the cooling report on the Spitfire IX but it only gives figures for the radiators "closed" in level flight.

However, it's unlikely that a Spitfire IX at least would have "open" radiators in high speed flight, anyway.

The Spitfire had 2 radiator positions, wide open and "minimum drag". "Minimum drag" was often called "closed", but the Spitfire radiators did not fully close. For the Spitfire IX, for example, exit area was 1.67 sq ft open for the starboard radiator, 1.47 sq ft for the port, and 0.83 sq ft each for "closed".

The report details tests for the Spitfire IX running at 25 lbs boost. It gives results as "radiator suitability" where any figure greater than 1 means the radiator can keep temperatures below limits. The equation is:

Radiator suitability = (Maximum permissible coolant temp - summer standard air temp) / (observed coolant temp - actual air temp)

Maximum permissible coolant temp was 125 c for the purposes of the test, but 135 c in service.
Summer standard air temperature was 27 c at sea level for temperate, 41 c tropical
Radiator suitability was 1.36 temperate, 1.17 tropical, both at 3,000 ft, achieved after engine temps had stabilised in cruising flight, then 5 minutes at 25 lbs, 3,000 rpm. Those figures are for "closed" radiators.

The radiator flaps would open automatically above 115 c.

If you consider the Spitfire only used 25 lbs boost in Europe, then the figures for temperature summer conditions:

1.36 = (125 - 21) / (x - 21)

That means coolant would reach a maximum of 97c at 3,000 ft, 25 lbs boost, after an indefinite time at maximum cruise and 5 minutes at full power.

At 13,500 ft:

1.32 = (125 - 0) / (x - 0)

Coolant would reach 95c at 13,500ft.

These 2 altitudes were chosen because they were the full throttle heights. At other altitudes temperatures should be lower.

 

[wuzak]

I believe Joe Smith said that the exit to the radiator could have been smaller. It's in one of my books, but it is in storage.

 

[jim]

Speaking of radiators
How Bf 109F&G actual radiators would compare, from drug point of view, to an installation similar to Fw 190D9 ? On planned later version of Me 410 Messerschmitt was planning to replace the under wing radiators with annular radiators. If that choise had advantages could have been appleid to 109 as well?
Fw 190 V18 used an under belly fairing to house the intercooler and turbo supercharger air intake. Would be possible to use a smaller version of the fairing to house the coolant and oil radiators like p 51, g55 , re 2005 did instead of an annular radiator? I know it would be more expensive to produce but would cause less drug?