annular radiator - advantages?

[kennethklee]

What are the advantages and reasons for applying an annular radiator (Focke-Wulf Fw 190D-9, Focke-Wulf Ta 152, inlined-engined Junkers Ju 88, some versions of Hawker Tempest) instead of standard discrete radiator units (Messerschmitt Bf 109, Supermarine Spitfire, North American P-51, Kawasaki Ki-61) to inline liquid-cooled piston aircraft engines? I am curious because visually the annular radiator seems to negate some of the advantages of a liquid-cooled engine, such as drag reduction, decrease of cross-sectional target area, and a streamlined graceful appearance.

Thanks,
Kenneth

[Pilot]

Design is not the matter of wishes but result of mathematical calculation and industrial and technological background. This type of cooler shape have less option of drag as well it is streamlined into the general shape. If you place some other external you will have extra drag. To reduce extra drag you need to put it backward where is airstrean more turbulent and cause less drag. When you place in that rear position you have problem that turbulent stream does not have uniform cooling property and also it could be shadoved in some flight envelope. To match this you need a little larger radiator and this give penalty in extra weight. Another problem is the maintenance as well you have long line from engine back to the radiator and then return to engine. This require more access panels and result is weaknes in structure. To avoid weaknes you need extra framing and this again need more wotrk hours in factory and this mean more pay, this meam expencive plane and also this mean again penalty weight.

In combat you have cooling lines dispersed all arround the plane and bullet have chance to make demage of this system on wings, on fuselage and arround engine. This also make problem wit armor and this system is imposible to protect. Placing al in one pack on nose with anular coolant give option to introduce some kind of armor. Penalty is that many pipe lines are crowded in smal place so work is much harder for ground crew. Good thing is that oil can be place close to engine while in the other disposition it is usually placed in fuselage and in fuselage is also placed oxigen bottles. This is dead risk to hold close oil tanks and oxigen bottles- give more davastation then any ammunition shell [except of teh rockets]

As you see- choosing of the position and method of cooling is everything but easy and in any case it is gambling.

Hope this help

[Graham Boak]

The annular radiator is not necessarily draggier, as the drag of every radiator has to be considered into the total drag of the aircraft. This can indeed differ depending upon the installation position: note how the Typhoon's radiator is mounted further forward than that of the Hurricane.

Aircraft such as the 109 and the Spitfire made use of internal ducting to reduce the drag of the radiator installations: the Mustang being perhaps the finest example of this. In allied nations this was known as the Meredith effect, after the RAE engineer who suggested it in a 1930s report.

This was not possible with "flat fronted" installations such as the Ju 88, which was known as a "ring" installation". Later annular radiators - Ta 152 - used similar ducting with radiators angled away from the flight direction, this was known as a "drum" installation. See Hoerner's Fluid Dynamic Drag (and I hope I haven't got the two names reversed! It has been many years since I was using the reference.)

[kennethklee]

Thanks much for the responses, they have been helpful in my understanding both annular radiators and radiators in general. I also found used copies of Hoerner's Fluid Dynamic Drag on Amazon.com, but I must admit they seem very pricey to me; I'll keep them in mind for future consideration.

Kenneth

[Tony Kambic]

Below is a photograph I found on the Web of the restored DB engine from the HE-219 at NASM. You can clearly see the drum type radiator.

[Graham Boak]

Yes, I'm sure Hoerner is expensive! It really is a technical textbook for the use of active engineers in the 50s and later, but it is full of practical examples taken from German WW2 aircraft. One to ask a library to obtain, rather than buy for your own collection - I admit rather wish I had one when answering comments like this.

[kennethklee]

Originally Posted by Tony Kambic

Below is a photograph I found on the Web of the restored DB engine from the HE-219 at NASM. You can clearly see the drum type radiator.

Tony-

Thanks for the excellent photo of the DB engine, almost looks hi-def. For lack of a better phrase, it's neat to be able to see the annular radiator so clearly.

Kenneth

[kennethklee]

Originally Posted by Graham Boak

Yes, I'm sure Hoerner is expensive! It really is a technical textbook for the use of active engineers in the 50s and later, but it is full of practical examples taken from German WW2 aircraft. One to ask a library to obtain, rather than buy for your own collection - I admit rather wish I had one when answering comments like this.

Thanks Graham. I tried looking for this venerable book in my public library system to no avail. Asking the library to obtain this book crossed my mind and I might do that. I have both a college degree and a doctorate, but even having experienced--or endured--the inflated costs of numerous textbooks, I was still taken aback by prices I saw for used copies of this book. The book seems to be highly sought after--or simply scarce due to its out of print status. Anyway, I'll keep this book in mind.

Kenneth

[Snautzer]

would this help?
Fluid-Dynamic Drag
Hoerner

[George Hopp]

Great stuff, Snautzer! Any chance of getting a scan of the 2nd page of those 3 pages?
All the best,
George