wuzak
Captain
The Spiteful used a similar system to the Bf 109's.
Experiments were done to see if alternative methods were any better.
Experiments were done to see if alternative methods were any better.
High-Drag Areas on the Supermarine Spitfire
- Thread starter Zipper730
- Start date
Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
The tunnel for boundary layer was discarded with Bf 109G, that also got bigger (taller) radiators to take up the slack and offer improved cooling capacity.
Advantage of 109F-style radiators vs. 109E-style was that the former were wider, thus leavinng smaller percentage of radiator itself 'hanging' under the wing and within the slipstream. All Bf 109s from E onwards have 3 radiators sticking out (2 for coolant + one for oil) - it will kill the speed very much.
This is where fuselage-installed cooling system shows it's advantage - one can install a very big radiator (or a combination of two, or three), without the shortcoming of 'dipping' too much of it into the slipstream.
Did the P-51 system have some advantages compared to the Spitfire (apart from previously discussed) in that although much bigger and further out in the slipstream being further back it didn't increase the maximum cross sectional area. Also since the fuselage curves towards the rear only the intake is visible from the front, the splitter doesn't increase the frontal area.
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
Frontal area, per se, isn't that important. Separation is, and the boundary layer splitter reduces the likelihood of separation inside the diffuser before the radiator and permits a better velocity distribution for the air flow to the radiator, which permits a smaller radiator as more of it is working effectively.
Designing a cooling system for piston-engined fighters was hard, and expediency would frequently dictate design choices that were sub-optimal, such as the British power egg. Sometimes there simply wasn't the analytical tools or skills available to do the best job. Sometimes there simply wasn't the room.
I think some people thought that cooling those sexy V-12s was easy, forgetting that the radiator would need to get rid of about the same amount of heat (slightly less, as cooling the V-12's engine compartment had to be managed separately) as a radial, to the same ambient conditions, probably with the radiator at a lower temperature than a radial's finning, so the radiator is going to have about the same amount or more wetted area than the finning on a radial, as the liquid coolant just adds a step to the transfer of heat from engine to air.
Designing a cooling system for piston-engined fighters was hard, and expediency would frequently dictate design choices that were sub-optimal, such as the British power egg. Sometimes there simply wasn't the analytical tools or skills available to do the best job. Sometimes there simply wasn't the room.
I think some people thought that cooling those sexy V-12s was easy, forgetting that the radiator would need to get rid of about the same amount of heat (slightly less, as cooling the V-12's engine compartment had to be managed separately) as a radial, to the same ambient conditions, probably with the radiator at a lower temperature than a radial's finning, so the radiator is going to have about the same amount or more wetted area than the finning on a radial, as the liquid coolant just adds a step to the transfer of heat from engine to air.
Shortround6
Major General
Frontal area was thought to be important at time, let's remember that full size wind tunnels were rare, America had one, Germany had one, I don't know about Russia. Nobody else had one at all. The American one had a speed of 80mph (?) Before WW II.
All the rest of the tunnels required models or small sections of aircraft.
Liquid cooling had also gone through several Changes in short period of time. Plain water was used up until the very early 30s. Prestone/glycol offered the use of much higher temperatures and smaller radiators but introduced some problems of it's own. They were just starting to go to a water/glycol mix at the start of WW II so they were still working on the exact size of the radiator per hp and size needed at different altitudes and even the type of radiator construction.
Getting all the different requirements to come together at the same time was not as easy at it seems today.
All the rest of the tunnels required models or small sections of aircraft.
Liquid cooling had also gone through several Changes in short period of time. Plain water was used up until the very early 30s. Prestone/glycol offered the use of much higher temperatures and smaller radiators but introduced some problems of it's own. They were just starting to go to a water/glycol mix at the start of WW II so they were still working on the exact size of the radiator per hp and size needed at different altitudes and even the type of radiator construction.
Getting all the different requirements to come together at the same time was not as easy at it seems today.
Notice the date on this communique.
Then there was a constant barrage of advice and instruction issued by the RAF to Fighter Command and its squadrons about MAINTAINING the finish on service aircraft. Generally, even in the UK, this was not done very well.
Cheers
Steve
Which is why the 'Type S' finish was adopted. It was considered not to compromise the camouflage of the aircraft as a gloss finish would.
Notice point 4 on this the second page of a circular to all Resident Technical Officers about the introduction of Type S paints.
The letter dates to early 1940 and model makers might also notice the acceptance of hard, masked, demarcations between camouflage colours on British aircraft.
Cheers
Steve
AMCKen
Senior Airman
"Ram air intake was also probably a source of drag (was changed with late Seafires). "
But it also added more horsepower than needed to overcome the drag it generated.
But it also added more horsepower than needed to overcome the drag it generated.
P-39 Expert
Non-Expert
Mainly one cleaner radiator scoop design on the P-51 vs. two on the Spitfire. Less drag. Also the Meredith Effect which said the heated radiator exhaust was actually contributing thrust, but like the laminar flow wing many experts doubt the effect was actually achieved operationally. Still the P-51 was the cleanest design in WWII.
P-39 Expert
Non-Expert
The radiator and coolant also added upwards of 400# to the weight of the plane.
P-39 Expert
Non-Expert
We had an evaporative cooler in our first house when I was 5. Everybody called them swamp coolers. Got a refrigerated window unit when I was 13. I can remember no air conditioning in Fort Worth Texas when it routinely hit 100 degrees in summer.
I mean on the Spitfire lol. The leading edge tanks on later Spitfires were originally to be part of an evaporative cooling system.
Deleted member 68059
Staff Sergeant
- 1,058
- Dec 28, 2015
I`ve got a really nice report on special "aero Spitfire canopy" (not the speed-spitfire but wartime report, Sept 1943) which wasnt putting the armour inside but a total redesign (wasnt a bubble canopy though). Sadly I cant post the pics as its copyright infringement.
I can quote from it though !
It raised top speed from 410 to 415mph (in level flight in a Spitfire IX reg "EN 498"), when dived at 550mph it put +12mph on top speed.
It was called the "Conical Screen", the sliding bit was identical but the front bit was totally rounded off.
You can get it at Kew Archives in London ref "AVIA-6-10404"
I also have another report on Spitfire aero, which stated that basically the fit of the panels was awful and resulted in (they reckoned) 7.5mph differences production models depending on how well it was fitted together at that particular factory.
Also from Kew, ref "AVIA-6-10367" and was also 1943
There were also larger studies conducted when the Mustang arrived as the air ministry was incredulous about where the speed difference had come from, but I dont have time to go trawling through those tonight. I seem to remember that it was a big mix of panel gaps, radiator installation, wings, paint and so on.
I can quote from it though !
It raised top speed from 410 to 415mph (in level flight in a Spitfire IX reg "EN 498"), when dived at 550mph it put +12mph on top speed.
It was called the "Conical Screen", the sliding bit was identical but the front bit was totally rounded off.
You can get it at Kew Archives in London ref "AVIA-6-10404"
I also have another report on Spitfire aero, which stated that basically the fit of the panels was awful and resulted in (they reckoned) 7.5mph differences production models depending on how well it was fitted together at that particular factory.
Also from Kew, ref "AVIA-6-10367" and was also 1943
There were also larger studies conducted when the Mustang arrived as the air ministry was incredulous about where the speed difference had come from, but I dont have time to go trawling through those tonight. I seem to remember that it was a big mix of panel gaps, radiator installation, wings, paint and so on.
Last edited:
Shortround6
Major General
Some people estimate that the Wing on the P-51 could maintain laminar flow up to about 40% of the cord. It is not all or nothing, that is either you have laminar flow from leading edge to trailing edge or laminar flow nowhere on the wing. Most conventional airfoils could maintain laminar flow for 5-15% of the cord for example so the P-51 wing, even if it didn't achieve what was hoped for ( estimated from lab results?) still offered lower drag than a conventional wing. I would note that the Davis wing used on the B-24 actually fell somewhere in between. They weren't trying for laminar flow but wound up getting it to somewhere between 15-25% cord.
I think the Meredith effect was sort of the same. People knew what the theoretical goal was, achieving it in practice was a lot harder. Especially trying to get more thrust than the cooling drag. However if your installation allows the engine to cool properly and the thrust you are getting cancels out 75% of the drag of another type installation maybe you aren't doing to bad???
Everything was a trade off. RR figured that the intake drag on a Merlin XX in a Hurricane in high supercharger gear was any where between 14 and 32.8 hp depending on altitude.
The air actually rose in temperature 8.9 to 11.6 degrees C in the intake duct before it reached the carb due to the compression taking place in the intake duct.
They figured the extra several thousand feet of critical altitude in level flight was worth it.
P-39 Expert
Non-Expert
Oh. Well, it was still mighty hot in Fort Worth.
"Ram air intake was also probably a source of drag (was changed with late Seafires). "
But it also added more horsepower than needed to overcome the drag it generated.
You can have extra HP even with a blended ram air intake, but not pay as much of price in drag that will come with an intake that is protruding away from airframe.
Seafire 47 vs. Seafire 45
wuzak
Captain
The Spitfire radiator was designed to use the Meredith effect, but in practice it wasn't that well done.
The P-51's duct was also not ideal, with the expansion from the intake being uneven from top to bottom, with the roof of the duct changing directions quite sharply.
That said, Supermarine did propose a similar radiator system for the Spitfire, but the Air Ministry rejected it in favour of production. Because in WW2 production was king!
Edit: There were a lot of small areas that the Spitfire was in deficit to the P-51, drag wise. While the radiator and the wing were the most significant factors, they weren't as big a difference as is often thought. Just a lot of small bits of extra drag adding up.
Deleted member 68059
Staff Sergeant
- 1,058
- Dec 28, 2015
Spit rad ducts with boundary layer bypass (but in same overall position) were trialled for MkIII, some pics in the old faithful "SPIFIRE THE HISTORY" by Morgan and Shacklady pg127. Performance benefits unclear. I have an R.A.E. paper on it which concludes:
"With the limited length of the cowl the fitting of a bypass duct restricts the radiator duct entry area; thus the full advantages of the bypass are not realised. Owing to this the Spitfire III cowl shows little improvement on the standard cowl which allows for the fitment of a more deeply recessed radiator" (page 8 "DSIR-23-11196", July 1941)
"With the limited length of the cowl the fitting of a bypass duct restricts the radiator duct entry area; thus the full advantages of the bypass are not realised. Owing to this the Spitfire III cowl shows little improvement on the standard cowl which allows for the fitment of a more deeply recessed radiator" (page 8 "DSIR-23-11196", July 1941)
Last edited:
