Spitfire Radiator.

It must be remembered that any thrust achieved from an efficient radiator design first has to overcome the drag of the cooling system itself, if you can do that then your on a winner and i’me not sure any design has actually done that. The French Morane MS.406, as an example, had a retractable radiator(as do Hawker biplanes) which needed to be fully wound out into the airstream when high power was being used, consequently in a climb or during combat you had the highest possible drag situation. So just when you needed maximum performance your aircraft was handicapped by its cooling system design.

Richard

The other problem with the Spitfire cooling on the ground and even in the air, is the main undercarriage leg, in the down position, is directly in front of the radiator inlet. This does, to a certain extent, interfere with efficient airflow into the radiator. I did read somewhere that one cannot fly the Spitfire with the undercarriage down for extended periods without running into cooling problems.

Mark 12 has put his finger on it; the face of the matrix is broader, in square area, than the radiator’s intake; this has the effect of slowing the air (but increasing the pressure,) as it expands to fill the available space (you see the same effect on jet intakes, like the Lightning and Concorde.) The slowed-down air works more efficiently at removing the heat, then speeds up again as it goes through the narrower exit. There are unending arguments about whether the Spitfire matched the Mustang in its efficiency (the latter is said to have achieved a certain amount of thrust from its layout.) Unless some way could have been found to bury the radiator in the fuselage, as with the Mustang, there would have been far too little ground clearance.
In 1935, as well as his theories on ducted radiators, Meredith came up with the basic idea of jet propulsion, but never took out a patent on it, probably because the authorities took so long discussing its merits, other countries had got in on the act, as well.

On the first designs there were tubular honeycomb oil coolers positioned forward under the engine. Perhaps that influenced where the radiator was placed and having gone down that route the were not minded to start all over again. Also the radiator would need to have a specific cross sectional area. Perhaps it was just too big.

Meredith effect. I believe you can actually put up a case for the Spitfire Main Radiators producing substantial thrust.

There is sufficient room in the Spitfire wings to bury 6-8 inches of radiator. Mounted under the Spitfire fuselage, like a Hurricane, it would have to be 6-8 inches lower because of the control runs and structure. A Griffon radiator would be even nearer the ground. Then there is the intercooler radiator and large oil cooler radiator on later variants. If installed it would have to be well back behind the cockpit like a Mustang. C of G implications…start again.

Mark

I think overheating was worsened when the flaps were down, blocking the radiator outlets.
The assymetry disappeared when the extra radiators were added on the port wing. Actually some assymetry remains, because the same assymetric fairing is used on both sides.
It reduces the loads in the wing roots if some loads are slung under the wings, where the lift is made. I guess this might be some of the reason the rads were placed there. The downside is that it increases vulnerability to unsustainable powerplant damage when compared with air cooled powerplants.

Thank you all for your comments. I had never thought of ground clearance and fit issues in relation to my query. It just always seemed odd to have an asymmetric cooling system.

I seem to remember that Mitchell chose the position because it was low drag; there was a huge effort made to reduce the drag even further, the design (pioneered by Meredith at the RAE) produced thrust by squeezing the hot air with the rad flaps.

It has been discussed before, but an aeroplane is designed to fly, therefore priority is given to its handling characteristics in the air, and not on the ground; if overheating occurred on the ground , that was as a result of poor management i.e starting the machines and holding them too long.

The radiator is within the arc of the propellor and so benefits from prop wash, but being much more compact, doesn’t have the surface area exposed (to that wash) that the Hurricane has.

If you look at a Spitfire 3 view head on you will see that the oil cooler and radiator are both actually within the arc of the propeller so should be getting some prop wash airflow. Perhaps the issue is that the Spitfire radiator was sized smaller for performance reasons making it more critical.

Richard

The original plan was that the Merlin (PV12 as it was then) would use evaporative cooling with steam condensers in the wing leading edges. The change to ethylene glycol came quite late in the design and hence I guess the space and plumbing was more suited to radiators fitted in the wings. The Type 312 cannon fighter project, which was based on the Spitfire, did have a central radiator so presumably it was considered to be relatively simple to relocate.

I suspect that (and I may be wrong) it was a matter of ground clearance combined with the lower placing of the pilot’s seat compared with a Hurricane. This may have resulted in there being insufficient space under the cockpit to take the required plumbing.

Possibly because they were designed to carry centreline slipper tanks?

Exactly Beermat, i`ve always wondered why myself. I have thought about this often, and wondered if any Spitfires were modified to see if a centreline radiator would be beneficial, even if it only got to a mock up stage.

Interesting.. for me the question becomes why an asymmetric design was chosen to begin with.