Why no Fw 190H but the Ta 152H?

[z42]

I wonder by how much was the radial configuration more draggy than the axial one. Advantage was that, because the former had better heat dissipation, its gills did not have to open as much when the engine runs hot, thus producing less drag.

I don't know. I suspect the change in layout came about due to a higher power engine needing bigger radiators, and thus angling the radiator matrix was the way to do it without having to increase the fuselage diameter. Also not sure of the layout of the intercooler system on the Ta 152H, if those used a glycol circuit in the main radiators that would push up the size requirements further.

I'd also be a bit surprised if the angle of the gill openings were the dominant issue in the different radiator drags for these two layouts. Perhaps the radial layout would allow a little bit better pressure & velocity behavior with a diffusor + nozzle plenum reducing drag through the entire radiator (see P-51).

But as often with aerodynamics, intuition can be highly misleading, at least to a lay person like yours truly, so I think you'd need somewhat detailed CFD simulations to really settle the issue.

 

[tomo pauk]

Using this I get for the D-12 = 0.475 sq ft = 0.441 m^2.

0.411 m^2 = 4.423967 sq ft, or roughly 4.43 sq ft.

Interestingly they call the Dora radiator an axial (annular) type and the Ta 152 a radial type (drum).
The frontal area is 49;135 to 76;85.

I'm not sure that I follow the numbers you've posted.

Could you elaborate what does Cd swet mean exactly?

Paging Aeroweanie

And do you know what everything in detail in this chart means and how these things add up?

I can translate most of the details, just give me some short time to do it properly.

I hope you don't mind the many questions.

No worries

 

[spicmart]

I don't know. I suspect the change in layout came about due to a higher power engine needing bigger radiators, and thus angling the radiator matrix was the way to do it without having to increase the fuselage diameter. Also not sure of the layout of the intercooler system on the Ta 152H, if those used a glycol circuit in the main radiators that would push up the size requirements further.

I'd also be a bit surprised if the angle of the gill openings were the dominant issue in the different radiator drags for these two layouts. Perhaps the radial layout would allow a little bit better pressure & velocity behavior with a diffusor + nozzle plenum reducing drag through the entire radiator (see P-51).

But as often with aerodynamics, intuition can be highly misleading, at least to a lay person like yours truly, so I think you'd need somewhat detailed CFD simulations to really settle the issue.

The axial/radial config proved to be quite aerodynamic contrary to intuition. Adolf Galland (IIRC) described the Ta 154 as having bad aerodynamics because of that arrangement when the opposite was the case.

Napier company conducted tests with various radiator types. They even came up with a (radial or axial?) type which had no gills. Instead the whole matrix with cowling and propeller could be pushed forward or backward to control airflow through the gap between radiator and fuselage without increasing the diameter like the gills did.
Such an arrangement would have been too complex to integrate into production I assume.

 

[spicmart]

0.411 m^2 = 4.423967 sq ft, or roughly 4.43 sq ft.

It's 0.441 actually. There is also a 1.16 figure.

I'm not sure that I follow the numbers you've posted.

See "Kühlerstirnfläche" meaning "radiator frontal area" about in the middle.

 

[z42]

Napier company conducted tests with various radiator types. They even came up with a (radial or axial?) type which had no gills. Instead the whole matrix with cowling and propeller could be pushed forward or backward to control airflow through the gap between radiator and fuselage without increasing the diameter like the gills did.
Such an arrangement would have been too complex to integrate into production I assume.

Yes, I've seen the article in Flight about the Tempest with the annular radiator, and some RAE report. I'm quite sure it's just the cowling that moves forward/back, the engine, prop, and radiators are all bolted together.

 

[spicmart]

Yes, I've seen the article in Flight about the Tempest with the annular radiator, and some RAE report. I'm quite sure it's just the cowling that moves forward/back, the engine, prop, and radiators are all bolted together.

Yes. More feasible.

 

[tomo pauk]

It's 0.441 actually. There is also a 1.16 figure.

1.16 is the value of the coefficient 'K', that is calculated by this:
K =S/(π*b^2 *e), where:
S = wing area
b = wing span
e = Oswald's effciency
(K is given in the table, so there is no need to calculate it)

K is used in this equation, to calculate the total drag:
Cd = Cd0 + K(Cl)^2
With Cl (lift coefficient) = zero, the Cd = Cd0.
All this is courtesy HoHun, per this post: link

In the Fw table, 'Cl' is noted as 'ca'. However, for the 'schnellflug' case, the value of K is still stated, that begs the question of 'why'?

See "Kühlerstirnfläche" meaning "radiator frontal area" about in the middle.

Okay.
At 0.49 m^2 for the D-9, it would've been greater than the F of the whole A/C, so I'd say that actually means surface area of the whole cooler matrix.
I'm not sure what the second number means.

 

[spicmart]

I'd also be a bit surprised if the angle of the gill openings were the dominant issue in the different radiator drags for these two layouts. Perhaps the radial layout would allow a little bit better pressure & velocity behavior with a diffusor + nozzle plenum reducing drag through the entire radiator (see P-51).

It was specifically mentioned that the axial radiator could not provide enough cooling capacity so that the gills had to be opened by a few degrees which brought a penalty in speed. Thus the introduction of the drum matrix.

 

[z42]

It was specifically mentioned that the axial radiator could not provide enough cooling capacity so that the gills had to be opened by a few degrees which brought a penalty in speed. Thus the introduction of the drum matrix.

Makes sense, if you look at it that way. I was considering a case where everything would otherwise be identical, in particular the cooling capacity of the radiator.

 

[z42]

The axial/radial config proved to be quite aerodynamic contrary to intuition.

Well, intuitively I think an annular radiator should be quite good, as it doesn't increase the frontal area of the aircraft!

While I'm no aerodynamicist, I've spent some time thinking about different radiator layouts over the years in search of some general takeaway. And beyond A) The Mustang radiator is really, really good, and B) It's complicated, and details matter, I have largely failed to come up with some simple Grand Unified Theory of radiator layout.

Some general principles can of course be derived from basic fluid dynamics which sort-of leads to the Meredith effect. Namely you want a diffusing plenum to reduce the velocity of the air so that the drag through the radiator matrix is reduced. And the opening angle of the plenum shouldn't be too high lest turbulent flow is formed. And similarly after the radiator matrix you want a constricting nozzle, ideally producing some thrust. And then you have considerations like you want to minimize the surface area of the ducting to reduce skin friction, which implies you want as close to a circular cross section as possible. And the size of the radiator also depends on the speed regime you're targeting. For a higher speed design you probably want a big radiator with equally big ducting to get the velocity of the air stream down, whereas a lower speed design can make do with a smaller radiator + ducting and save a bit of weight and skin drag. And finally there are of course non-drag related considerations like having the radiator and engine close by makes it harder to score a critical hit, and potentially allows power egg style approaches, as well as reducing the length of coolant piping between the radiator and engine.

So in light of the above, what can we say about a few radiator designs:

• The Mustang belly radiator is pretty much the gold standard. But it doesn't follow that any belly radiator in general is a good design. E.g. the belly radiator for the Tornado prototype was so bad they switched to a lower drag chin radiator for the production Typhoon and Tempest V, hardly paragons of low drag radiator designs? Again, details matter, and just by eyeballing it the Tornado belly radiator looks more like an enlarged Hurricane radiator than something that would remind one of the Mustang.
• Leading edge radiators were evidently considered a success on the Mosquito. But then they apparently also tested a power egg style installation (basically to the Lancaster engine nacelles with chin radiators), which resulted in a pretty small performance penalty.
• For annular radiators, the Napier tests with the Tempest prototype were quite favorable, with the annular having less drag than LE radiators as well as the Tempest V style chin radiator. But if one compares an annular design with, say, the Mustang radiator it seems there's not much room for a big diffusor plenum and nozzle, as well as the exhaust not being directed straight back but rather must be directed at an angle, reducing the thrust effect somewhat. And somewhat confusingly for the post-war Tempest follow-up designs (that never left the paper stage), Hawker studied both LE and belly radiators (P. 1027 and 1030), but not annular ones. So what gives, wasn't the annular design as good as the Napier reports suggested?
• Wing radiators not on the leading edge like the Bf 109 or Spitfire. Maybe not as good as (well implemented) above approaches?

I think the "holy grail" might be something that would combine a Mustang-style diffuser + nozzle ducting along with a compact package that could be used for a power egg style installation, suitable for nacelles in multi-engine aircraft as well as single-engine planes. Say, have the air intake just under the spinner, the diffuser duct under the engine, and then the radiator matrix would be behind the engine. As an additional bonus, combine the radiator air intake duct with the supercharger air intake, thus the supercharger also gains a bit of pressure due to the diffusing duct, and by having the intake at the very front of the aircraft the chance of ingesting all kinds of crap is also reduced. Something like Figure 11 in https://www.arpnjournals.com/jeas/research_papers/rp_2015/jeas_0715_2249.pdf .

 

[SaparotRob]

"Grand Unified Theory of Radiator Layout."

 

[spicmart]

Well, intuitively I think an annular radiator should be quite good, as it doesn't increase the frontal area of the aircraft!

While I'm no aerodynamicist, I've spent some time thinking about different radiator layouts over the years in search of some general takeaway. And beyond A) The Mustang radiator is really, really good, and B) It's complicated, and details matter, I have largely failed to come up with some simple Grand Unified Theory of radiator layout.

Some general principles can of course be derived from basic fluid dynamics which sort-of leads to the Meredith effect. Namely you want a diffusing plenum to reduce the velocity of the air so that the drag through the radiator matrix is reduced. And the opening angle of the plenum shouldn't be too high lest turbulent flow is formed. And similarly after the radiator matrix you want a constricting nozzle, ideally producing some thrust. And then you have considerations like you want to minimize the surface area of the ducting to reduce skin friction, which implies you want as close to a circular cross section as possible. And the size of the radiator also depends on the speed regime you're targeting. For a higher speed design you probably want a big radiator with equally big ducting to get the velocity of the air stream down, whereas a lower speed design can make do with a smaller radiator + ducting and save a bit of weight and skin drag. And finally there are of course non-drag related considerations like having the radiator and engine close by makes it harder to score a critical hit, and potentially allows power egg style approaches, as well as reducing the length of coolant piping between the radiator and engine.

So in light of the above, what can we say about a few radiator designs:

• The Mustang belly radiator is pretty much the gold standard. But it doesn't follow that any belly radiator in general is a good design. E.g. the belly radiator for the Tornado prototype was so bad they switched to a lower drag chin radiator for the production Typhoon and Tempest V, hardly paragons of low drag radiator designs? Again, details matter, and just by eyeballing it the Tornado belly radiator looks more like an enlarged Hurricane radiator than something that would remind one of the Mustang.
• Leading edge radiators were evidently considered a success on the Mosquito. But then they apparently also tested a power egg style installation (basically to the Lancaster engine nacelles with chin radiators), which resulted in a pretty small performance penalty.
• For annular radiators, the Napier tests with the Tempest prototype were quite favorable, with the annular having less drag than LE radiators as well as the Tempest V style chin radiator. But if one compares an annular design with, say, the Mustang radiator it seems there's not much room for a big diffusor plenum and nozzle, as well as the exhaust not being directed straight back but rather must be directed at an angle, reducing the thrust effect somewhat. And somewhat confusingly for the post-war Tempest follow-up designs (that never left the paper stage), Hawker studied both LE and belly radiators (P. 1027 and 1030), but not annular ones. So what gives, wasn't the annular design as good as the Napier reports suggested?
• Wing radiators not on the leading edge like the Bf 109 or Spitfire. Maybe not as good as (well implemented) above approaches?

I think the "holy grail" might be something that would combine a Mustang-style diffuser + nozzle ducting along with a compact package that could be used for a power egg style installation, suitable for nacelles in multi-engine aircraft as well as single-engine planes. Say, have the air intake just under the spinner, the diffuser duct under the engine, and then the radiator matrix would be behind the engine. As an additional bonus, combine the radiator air intake duct with the supercharger air intake, thus the supercharger also gains a bit of pressure due to the diffusing duct, and by having the intake at the very front of the aircraft the chance of ingesting all kinds of crap is also reduced. Something like Figure 11 in https://www.arpnjournals.com/jeas/research_papers/rp_2015/jeas_0715_2249.pdf .

Can you elaborate on how the Lancaster's power-egg style chin radiatord differed from the normal on?

I also thought that Napier's test ended in favor of an annular radiator but Tomo pointed out that the fastest planes were those with LE radiators.

One should draw and see how such a machine with your proposed arrangement would look like. I fear something akin to a Buchon.

 

[Shortround6]

"Grand Unified Theory of Radiator Layout."

Black magic

Will the slower speed (lower drag) of the diffused cooling air through the matrix make up for the increase drag in the long duct/s and any changes in direction. Will lower drag in the core make up for increased drag of larger outside surfaces of duct?

 

[SaparotRob]

Black magic


Will the slower speed (lower drag) of the diffused cooling air through the matrix make up for the increase drag in the long duct/s and any changes in direction. Will lower drag in the core make up for increased drag of larger outside surfaces of duct?

The Shadow knows.

 

[Shortround6]

The Shadow knows.

He knows what evil lurks in the hearts of men. Radiator duct design is another level of hell.

 

[SaparotRob]

Touché.

 

[z42]

Can you elaborate on how the Lancaster's power-egg style chin radiatord differed from the normal on?

I haven't seen any primary or even secondary sources on this, but I think there was a post on this forum. Oh yes, here it is: Drag of annular/drum radiator

Rolls Royce didn't think their powerplant installation was any different from a leading edge radiator in terms of drag. From "The Merlin in Perspective" by Alec Harvey-Bailey

"The same Mosquito was subsequently fitted with Rolls-Royce powerplants with chin radiators. Tests before and after conversion using the same Merlin 23 engines and propellers showed no measurable difference in performance at the same all up weight. On calibration test flights the speed was 378 mph true at 18,000 ft at a weight of 18,400 lb."

I also thought that Napier's test ended in favor of an annular radiator but Tomo pointed out that the fastest planes were those with LE radiators.

I think a problem that was pointed out in some previous threads on this topic were that the tests weren't done with the same engine so not really comparable. It is a bit strange how draggy the LE radiators are per the RAE/Flight articles about the annular radiator tests, but still that's the path forward they chose for the P. 1030. Perhaps Hawker thought there was lots of scope for improvement on the Tempest LE radiators?

Another interesting (or, another level of hell) thing with wing mounted radiators is how they affect the airflow around the wing. I've seen it claimed that LE radiators blowing air out of the underside of the wing would improve lift, but I'm not sure.

One should draw and see how such a machine with your proposed arrangement would look like. I fears something akin to a Buchon.

Heh, maybe. A problem with that layout is that the radiator would be under the legs of the pilot, so the fuselage might need to be pretty high? Or for a inwards retracting taildragger landing gear, that's about where you have the wheel wells.

 

[spicmart]

Another interesting (or, another level of hell) thing with wing mounted radiators is how they affect the airflow around the wing. I've seen it claimed that LE radiators blowing air out of the underside of the wing would improve lift, but I'm not sure.

Maybe analogue to the thought that the slanted exhaust pipes of the Merlin enhanced lift and shortened take-off run.

It was the Tempest 1 which was the fastest.
Not sure about the engine settings.

tomo pauk You once mentioned that, in a German document, it was noted that the wing profile of the Me 109 was draggier than a Fw 190's.
Where was that?

 

[tomo pauk]

tomo pauk You once mentioned that, in a German document, it was noted that the wing profile of the Me 109 was draggier than a Fw 190's.
Where was that?

I've 1st read it in the book 'Vee's for victory', the book that deals with V-1710 engine. The doc is mentioned at the pg. 338. It lists the profile drag coefficients of the wings, at lift coefficient of 0.2, like this:
- Bf 109B - 0.0101
- Fw 190 - 0.0089
- Mustang - 0.0072

(wing profile of the 109 remained the same through the 109K)

IIRC Calum Douglas posted the original table somewhere on the 'net.

 

[Aeroweanie]

> Could you elaborate what does Cd swet mean exactly?

Its CD0 (zero lift drag) nondimensionalized by the wetted area of the aircraft, instead of the wing area.