Me 109 F vs Spitfire coolant radiator installations
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I think the main selling point was that you could just bolt on and off an entire powerplant in the field with little effort. You also keep ducting to a minimum, saving weight. Hard to tell how it compares in the drag department but iirc vsaero models of the Fw 190 D showed that plane to to be a bit better than the spitfire so the annular radiator can't be all that bad. BUT the way it works, I expect it to be less and less favourable as it opens. I also doubt it utilizes the meredith effect well. On the plus again it does not offer an additional weak spot from behind or below. The only really vulnerable angle is form the front where any bullet would hit the engine otherwise anyways.
wuzak
Captain
This report shows Napier claims less cooling drag for an annular radiator than for a radial, or for chin and leading edge radiators.
http://pdingle214687.home.comcast.n...iles/Napier_Flight_Test_Developments_1946.pdf
The core is oriented differently than this used by Germany during WW2, and used a sliding ring rather than gills.
http://pdingle214687.home.comcast.n...iles/Napier_Flight_Test_Developments_1946.pdf
The core is oriented differently than this used by Germany during WW2, and used a sliding ring rather than gills.
What they are saying is that the increased frontal area allows less pressure loss through the radiator than in wing or chin type raditors and this, overall, produces less drag than a smaller frontal area radiator that must be both long and dense to transfer sufficient heat. They are also claiming more energy recovery than a chin type radiator.
It seems they found the same or similar cooling system as that of the Republic XF-12 Rainbow. Wonder why the Germans would not go with this solution whereas the flaps they were using increased drag when they had to open up..
Thanks, Tante Ju!
Unfortunately I don't have more accurate info on the effects of the radiator flaps of 109G on climb than that their opening reduced climb markedly, as they wrote in the FAF test report.
Juha
wuzak
Captain
That is also my understanding.
IIRC correctly, I don't have now time to check that, Meredith proposed 2 or 3 ways to improve Spitfire's radiator and one of them was annular radiator a la 190D,
Juha
I doubt this is the case, the cowl flaps probably wouldn't have more drag or disturbance to the airflow than the air spilling out of a flush sleave. Furthermore there is no suction drag behined these cowl flaps and as there is heated and expanded air ejecting out one would instead expect to find some thrust. At high speed the cowls would tend to be closed. Think of it this way, it would be harder to keep the cowl flaps closed, I think they would be trying to open themselves.
There seem to be precious few photograhs of Dora's in flight.
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wuzak
Captain
From memory, since I haven't read it in a while, it says that the annular radiator allows for much better expansion ratios between inlet, radiator face, and also for the converging duct than for the leading edge radiator.
wuzak
Captain
I'm sure that at speed the closing force is greater than the opening force of teh cooling air. Remember that even when closed there is a gap for teh air to escape.
The jet thrust of the sliding ring system would not be disimilar to the cowl flaps, if different at all. But it would reduce the drag measurably, if not significantly.
A sliding door could have been used for the Mustang's radiator exit instead of a flap, if so desired. Flaps in that situation are easier. The cowl flaps on radial engine/annular radiator installations required many actuators, or flexible drive systems. A sliding ring woul dbe simpler to operate.
I still don't think cowl flaps would produce any drag. Consider that if the cowl flaps were just free hinged they would be open anyway as the dynamic pressure 'ram effect' from air entering the nose would push it open as it sought a way out. The pressure on either side of the cowl flap would be equal. There would be some tension on the hinge but that would be from skin friction drag and relatively small. If there was no free hinged cowl flap the air would simply spill out of the anular slot in much the same streamline or flow pattern.
The air however has been heated by the radiator, by forcing the cowl flaps closed the heated air is accelerated effectively turning the cowl flaps into nozzles.
The drag comes from the intake, not the cowl flaps. I don't see them changing the airflow much at all.
However opening the cowl flap beyond its 'free floating angle' would create suction behined the flap, this would cause drag but also reduce backpressure, effetively it would suck more cooling flow through the engine.
wuzak
Captain
Suction on the underside of the flaps would tend to try to close them too.
Also, usually in radial engined aircraft it was desireable to close the cowl flaps for takeoff - because of drag.
There are likely to be more than two settings.
Open would be to maxiumise cooling especially at low speeds and high power levels, partially closed to maximise jet thrust
No, it's not better than aluminum if heat is to be transferred to air, as experience from today's CPU cooling shows.
There were some pure copper coolers that transferred heat from CPU into the heatsink rather quick but with all sorts of problems to transfer it further into the cooling air. It required lots of very thin cooling fins (large surface area) to ensure proper heat transfer to cooling air. Aluminum was not that capable to transfer heat from CPU to heatsink but did not require such a large surface area to transfer heat to cooling air. That's the primary reason most of today's CPU coolers are a hybrid copper/alu construction - copper for fast transfer into the heatsink unit with alu for the surface areas and heatsink->air transfers.
