P51 Radiator Design

[Panthera]

1 hour ago, Ehret said:

The Tempest is a bit heavier but not that much bigger than the Mustang, and has 500-700HP more than P51D's WEP.

 

In terms of wetted area it is most certainly bigger, and a big reason behind its impressive speed would've been down to the laminar flow airfoil cutting through the air more efficiently. 

 

It's rather simple really, a sharper leading edge more easily cuts through the air at low AoA, whilst a max camber placed further aft delays/prevents boundary layer seperation, and as a result drag in level flight is markedly reduced. 

 

 

Edited March 4, 2018 by Panthera

[Ehret]

1 hour ago, Panthera said:

 

In terms of wetted area it is most certainly bigger, and a big reason behind its impressive speed would've been down to the laminar flow airfoil cutting through the air more efficiently. 

 

It's rather simple really, a sharper leading edge more easily cuts through the air at low AoA, whilst a max camber placed further aft delays/prevents boundary layer seperation, and as a result drag in level flight is markedly reduced. 

 

 

An actual jet engine like the Jumo 004 had a small compression ratio of 3.14:1. I don't know exactly (yet) what the P51' diffuser could achieve but considering the difference in inlet area to the area of receiving radiator core, I have an idea. The point is even few percent of efficiency could results in sizable thrust, because power input is so big.

 

For the lack of new high performance piston engine planes, utilizing Meredith effect, thank incoming jet-age but there were few prototypes - I know about Martin-Baker MB 5 and CAC CA-15.

[Ehret]

1 hour ago, Panthera said:

 

In terms of wetted area it is most certainly bigger, and a big reason behind its impressive speed would've been down to the laminar flow airfoil cutting through the air more efficiently. 

 

It's rather simple really, a sharper leading edge more easily cuts through the air at low AoA, whilst a max camber placed further aft delays/prevents boundary layer seperation, and as a result drag in level flight is markedly reduced. 

 

 

 

Then one could expect more from the Tempest because with +30% HP she only matched P51D and the latter had much weaker engine.

 

[69th_chuter]

More to the OP, here's a rather readable modern report using computational fluid dynamics and comparing the Spitfire, Mustang and 190D designs.  Sketches show airflow separation points in the Spitfire and Mustang cooling systems.

 

http://www.wwiiaircraftperformance.org/mustang/Lednicer_Fighter_Aerodynamics.pdf

 

(A couple of illustrations got crossed but are all there.)

[Panthera]

1 hour ago, Ehret said:

 

Then one could expect more from the Tempest because with +30% HP she only matched P51D and the latter had much weaker engine.

 

 

No that's what I'm saying, the fact that the Tempest with its larger wetted & frontal area (the wing area was a whopping 28 m^2 alone),  could achieve the speeds it did at low altitude is largely down to the low drag of the laminar flow airfoil in level flight. It's no coincidence that this type of airfoil shape has been so popular ever since, esp. as LE devices that offset its issues at high AoA became more common place. In short the effects are well documented and also quite logical from an aerodynamic point of view, in all types of applications.

 

 

[Ehret]

Dunno... the Tempest has a very similar power-loading and wing-loading to the P51 - she's not small frame but not an elephant, either. The Sabre engine was awfully powerful - the Typhoon, for a time, was very fast in spite of very draggy thick wings. A big engine helps.

 

For post WW2 piston design utilizing Meredith principle I think the P51-H and F-82 can be included. Still Mustangs but redesigned from a scratch and more efficient.

Not sure about de Havilland Hornet - if the Mosquito would qualify, then the Hornet should too.

Edited March 4, 2018 by Ehret

[Panthera]

Well like you said the power loading is similar, whilst at the same time the Tempest is noticably larger. Thus since both used a laminar flow airfoil but just one, the P-51, used a long inlet radiator design, the similar speed would indicate that the laminar flow airfoil played a bigger part in achieving said performance, the Tempests radiator design being, from a drag point of view,  perhaps one of the least graceful employed at the time.  

 

 

[Caudron431]

Anyway imho i think the Mustang aerodynamics influenced some important Nazi-Germany aero programs. The Do335 seems to have simply copied the P51 radiator, its rear one looks very similar. (BTW, the Do 335 always makes me think about the driveshaft system and the tricycle gear of  the Cobra.)

 

Another very disgraceful type (but a very interesting prototype) was probably the Fw190 V18 (!what have you done to the sweet Dora!) which looked like an attempt to mix all the allied technologies (turbo (p47), aerodynamics using the excellent P51 radiator box as a cover for its turbo iirc. Even a four blade propeller was fitted lol, it looked like some hybrid monster, a fw190D trying to be a p-51.

 

Very interesting to see how 3rd Reich engineers were seriously studying and carefully taking lessons from the allied engineers (just as the allies were too). Interesting how they understood, unlike todays fanboys from all sides, how their ways were not the only ones and that other engineers from other countries (allied or not) and cultures were coming with very interesting and competitive designs too.

 

With engineers having this kind of mentality its not surprizing that the Luftwaffe was provided with so many excellent aircraft.

[Panthera]

There's no doubt that the P-51 featured a great radiator design, esp. in terms of the sculpting of the inlet, which no doubt helped reduce drag and increase cooling. The Germans indeed seem to have shamelessly copied the design for the Do335 as they needed an efficient way of cooling the rear engine and through testing recognized the excellence of the NA design. The Americans & British acted similarly in their copy of the German radial engine cooling designs, the Hawker Tempest II utilizing a direct copy of the Fw190's cooling system. 

 

 

[Holtzauge]

With the benefit hindsight engineers today know that it is advantageous to divert the boundary layer before letting a flow into a diffusor since otherwize the flow separates and you get a lower pressure recovery than what is possible. Unfortunately a lot of early designs like the Yak, LaGG, Spitfire and Me-109 (F being an exception) did not incorporate this. The P-51 was AFAIK the first and then other designers followed suit (e.g. La-7). Another problem in the Spitfire and Me-109 was that the diffusor opened up to fast which also lead to flow separation. The so-called Meredith effect is nothing new really since a well designed radiator is in principle an engine work cycle: compression, add heat and then expand. However, the compression is small so the area enclosed in the work cycle is also small. In addition, a lot of designs had serious leakage issues (like the Me-109) which of course did nothing to bolster the work cycle.

 

Another trick developed during the war was to have as short a diffusor as possible to avoid boundary layer buildup and then a reasonable diffusor ratio like on the annular radiator installations on the Fw-109D and Tempest II which had about the same radiator efficiency as the Mustang.

 

Regarding copying others designs, there is in sensible engineering circles the saying "steal with pride" while some go with the "not invented here" way of looking at things. Seeing how the Germans used NACA input for both the Me-109, Fw-190 and Me-262 wings it looks like they went with the former in those cases anyway.

[Holtzauge]

22 minutes ago, Panthera said:

There's no doubt that the P-51 featured a great radiator design, esp. in terms of the sculpting of the inlet, which no doubt helped reduce drag and increase cooling. The Germans indeed seem to have shamelessly copied the design for the Do335 as they needed an efficient way of cooling the rear engine and through testing recognized the excellence of the NA design. The Americans & British acted similarly in their copy of the German radial engine cooling designs, the Hawker Tempest II utilizing a direct copy of the Fw190's cooling system. 

 

 

 

Beat me to it: I was typing away when you posted this. Yup, the Fw-109D radiator design was also very efficient so well worth copying.

[Ehret]

2 hours ago, Caudron431Micha said:

Another very disgraceful type (but a very interesting prototype) was probably the Fw190 V18 (!what have you done to the sweet Dora!) which looked like an attempt to mix all the allied technologies (turbo (p47), aerodynamics using the excellent P51 radiator box as a cover for its turbo iirc. Even a four blade propeller was fitted lol, it looked like some hybrid monster, a fw190D trying to be a p-51.

 

Looked at the schematics - they put a turbo-charger and an inter-cooler radiator in under the fuselage scoop. There are two more - one for the oil under nose, then the circular one on the front. It is interesting that the turbo unit is small - very unlike the huge one in the P47.

 

It's clear the needs of V18 outgrown 190(D) frame... Sometimes optimizing too much at a beginning results in problems later.

[AndyJWest]

3 hours ago, Caudron431Micha said:

Anyway imho i think the Mustang aerodynamics influenced some important Nazi-Germany aero programs. The Do335 seems to have simply copied the P51 radiator, its rear one looks very similar. (BTW, the Do 335 always makes me think about the driveshaft system and the tricycle gear of  the Cobra.)

 

Another very disgraceful type (but a very interesting prototype) was probably the Fw190 V18 (!what have you done to the sweet Dora!) which looked like an attempt to mix all the allied technologies (turbo (p47), aerodynamics using the excellent P51 radiator box as a cover for its turbo iirc. Even a four blade propeller was fitted lol, it looked like some hybrid monster, a fw190D trying to be a p-51.

 

Very interesting to see how 3rd Reich engineers were seriously studying and carefully taking lessons from the allied engineers (just as the allies were too). Interesting how they understood, unlike todays fanboys from all sides, how their ways were not the only ones and that other engineers from other countries (allied or not) and cultures were coming with very interesting and competitive designs too.

 

With engineers having this kind of mentality its not surprizing that the Luftwaffe was provided with so many excellent aircraft.

 

I very much doubt that the P-39 had much influence on the Do 335:

 

 

[Panthera]

Both sides certainly copied each other a lot during the war, however even more fascinating is how often all these seperate industries came up with the same/similar ideas and designs despite being isolated from each other. 

[D3adCZE]

It is simple. There is only one optimal solution. Engineers strive for optimal performance.

[senseispcc]

The Tempest is a low to medium level fighter and 426 mph at 18.500 ft.

The Spitfire IXc 404 mph at 21.000 ft.

The Spitfire XIV (Griffon) 417 mph at 12.000 ft.

The P51B 427 mph at 20.000 ft. 430 at 25.000 ft.

The P51D 424 mph at 20.000 ft. 437 mph at 25.000 ft this is a High escort fighter ! 

[BlitzPig_EL]

P 51, Allison engine, 390mph @ 13,000 ft.  Still pretty respectable for it's time period.

[senseispcc]

The A-20 and the P51B where nice planes but the late production models of the P51D where long range high altitude escort fighters that could only be equaled by the P47N in range.

[BlitzPig_EL]

The B and C (same aircraft, just assembled at different plants)  got the long range rear tanks installed in the field, so they had the same range as the D.

[Gambit21]

On 3/9/2018 at 4:39 AM, senseispcc said:

The A-20 and the P51B where nice planes but the late production models of the P51D where long range high altitude escort fighters that could only be equaled by the P47N in range.

 

Ask George Preddy, Bill Whisner, Don Bryan and company if the D model was only a high altitude escort. I think you'd get your ears boxed.

 

As is so often the case, reality is quite different than what is parroted on the internet.