GregP
Major
I was think it looked Dewoitine-ish, too! Go figure. Looks like a worked over D.520.
Nice drawing, though.
Nice drawing, though.
Drag of annular/drum radiator
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Going back to this thread and referring to the Fligh Archive that Tomo Pauk posted (and which unfortunately is gone now) I have questions about the De Havilland Hornet. DH wanted to have the Hornet airframe to be the most aerodynamic.
According to test the most aerodynamic radiator installation was the annular/drum configuration. Yet DH went with the leading edge type like the Mosquito had.
So why would they do that? Maybe because of the extra slim Merlin 130/131? Would that provide even less drag?
And anyone got info about the P-51 cooling drag and of other underbelly radiators?
Maybe there is data by now..
People at DH probably went with what they were good at.
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- #24
Anyone you happen to have this test report?
It doesn't exist any more. Maybe it can be found elsewhere or someone might share?
It doesn't exist any more. Maybe it can be found elsewhere or someone might share?
The Mosquito and Hornet were twin engined designs so DH took a different route on cooling drag. The wings are thicker so the radiators were buried in the wing where it is thickest. The Mosquito did have some Meredith effect, perhaps not as good as the P-51 but it also didnt have an air scoop sticking out. The two systems are mutually exclusive, there is nowhere to fit a P-51 type system on a Mosquito/ Hornet and there is nowhere to fit a Mosquito Hornet system in a P-51 the wing roots were where it carried its huge (for a S/E fighter) internal fuel load. The frontal area of the Merlin was reduced for the Hornet by moving various ancillaries around the engine, looking at the Hornet and taking into acount its actual performance its hard for me to see how an annular radiator would have made it quicker, was any twin engined prop plane quicker?
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- #26
I found the article again:
The numbers show. The annular radiator configuration beats all others by a clear margin.
On a Sabre engined Tempest it does. But the air inlet is outside the spinner and the Tempest had a big fuselage cross section. Compare to a Hornet, hard to believe it has Merlins in those nacelles.
drgondog
Major
Sorry I missed this.
Couple of thoughts: First Cooling drag for P-51B, D and H were assumed =zero at or below critcal altitude forhigh speed level flight conditions.. However as angle of attack must increase as density decreases, the parasite drag of the cooling system (intake, plenum, radiator, plenum and exit gate) must increaseas a function (CL).
Performance Calc values NA-5534 for P-51B.
CDp = 0 through 29000 ft (P-51B)
=0.0004 at 35000 ft
=0.0010 at 40000 ft
=0.0064 in climb at all altitudes
I have a P-51H paper which is hard to read, but extensively calculated and plotted, including flight test results that showed 2 things - slight thrust of system below FTH and insufficient cooling for 90"/3000 rpm of the 1650-9 at low altitudes.
More later, particularly as NAA moved away from Annular to Rectangluar Matrix for Aftercooler and Prestone radiators. Key points include early intake geometry for NA-73x through NA-91 included vanes and different placement of oil cooler through the models. The early variations were decidedly inefficient due to poor boundary layer behavior as the intake flow velocity reduced in the plenum - leading to uneven pressure distribution at front face of the radiator.
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- #29
I do not quite understand what you mean with "the air inlet is outside the spinner"?
I think if you gave the Hornet an annular radiator arrangement instead for its extra slim Merlins, this would have been the option with the lowest drag.
why?
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- #31
Napier made the tests and numbers don't lie. Total cooling drag for the annular radiator was 6.3 and for the leading edge installation it was 11.0.
That is quite a difference.
Why would the Hornet be an exception in this just because it looks cleaner/slimmer?
Just going by looks you might say that the annular configuration seemed the most draggy as it makes the biggest fuselage cross section.. But apparently looks can be deceiving.
Mossie and Hornet had their wings perpendicular to the fuselage which helped reduce drag.
The Hornet was superbly streamlined, no doubt about that.
Maybe it still could have been even faster though.
There are quite some other fighters which had an underbelly radiator but those were lacking the expansion space to generate a significant Meredith effect like only the P-51's (and the likes CA-15, MB-5) could.
That being said any radiator produced at least a little of that effect not just the leading edge ones.
I'd go with that.
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drgondog
Major
"6.3' and "11.0" what?
Total cooling drag as per table on P-91 (actually third page) of article in post #26
Deleted member 68059
Staff Sergeant
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- Dec 28, 2015
I dont think "Blanket" statements are very easy to make.
As has already been stated above, where you already have a very big fuselage, the annular system will work well because
you`re just making use of air which would have been shoved out the way of the aircraft anyway.
Something like a hornet clearly needs to have the diameter of the nacelles increased considerably to fit the
annular radiators, therefore increasing the frontal area, probably negating the benefits.
There are probably about two or three definitive layouts which will all work very well in the correct circumstances.
Just look at Reno Unlimited`s, thats been won by annular air cooled (effectively no different to a water cooled annular) and belly scoop systems (p51),
and planes like Sea Fury`s which have both leading edge and annular cooling systems at once.
I think the only thing you can conclude, is that stuffing a radiator out the bottom of the wing in a lump like a Spitfire is probably just about
bottom of the pack (although it can be very nicely done - see Supermarine Spiteful).
The FLIGHT articles (there are two) were comparing not just the annular radiator, but the later article in combination with a ducted spinner, and against the chin radiator version,
which is a pretty horrid looking lump at the best of times.
Certainly I have a lot of enthusiasm for the ducted spinners, although FW found them a bit difficult to get working on the 190 and ended up
with the more basic annular system we all know.
The annular installation here makes it pretty clear its making use of "dead space" in terms of fuselage diameter compare to the
approximate size of the actual engine (my blue lines added in). Very noteworthy here is the arrangement of the fins in the radiator matrix,
angled to align with the airflow. A lot of the benefits here will be down to excellent radiator matrix design too, not just where its fitted (as such).
Not dissimlar to that suggested by Kuchemann and Weber at Volkenröde. (yes, THE Joannah Weber, of Concorde fame when she ran off to
carry on doing maths for the British after the war)
As has already been stated above, where you already have a very big fuselage, the annular system will work well because
you`re just making use of air which would have been shoved out the way of the aircraft anyway.
Something like a hornet clearly needs to have the diameter of the nacelles increased considerably to fit the
annular radiators, therefore increasing the frontal area, probably negating the benefits.
There are probably about two or three definitive layouts which will all work very well in the correct circumstances.
Just look at Reno Unlimited`s, thats been won by annular air cooled (effectively no different to a water cooled annular) and belly scoop systems (p51),
and planes like Sea Fury`s which have both leading edge and annular cooling systems at once.
I think the only thing you can conclude, is that stuffing a radiator out the bottom of the wing in a lump like a Spitfire is probably just about
bottom of the pack (although it can be very nicely done - see Supermarine Spiteful).
The FLIGHT articles (there are two) were comparing not just the annular radiator, but the later article in combination with a ducted spinner, and against the chin radiator version,
which is a pretty horrid looking lump at the best of times.
Certainly I have a lot of enthusiasm for the ducted spinners, although FW found them a bit difficult to get working on the 190 and ended up
with the more basic annular system we all know.
The annular installation here makes it pretty clear its making use of "dead space" in terms of fuselage diameter compare to the
approximate size of the actual engine (my blue lines added in). Very noteworthy here is the arrangement of the fins in the radiator matrix,
angled to align with the airflow. A lot of the benefits here will be down to excellent radiator matrix design too, not just where its fitted (as such).
Not dissimlar to that suggested by Kuchemann and Weber at Volkenröde. (yes, THE Joannah Weber, of Concorde fame when she ran off to
carry on doing maths for the British after the war)
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Numbers don't lie but are frequently very economical with the actualite, especially manufacturers testing their own and other manufacturers products. The Leading edge aircooled design was P&W R 2800, did Napier get the "best of breed" cowling for it on a Tempest in 1946 because a lash up would suit Napier better, also what does "Total cooling drag (cold radiator)" mean? The cynical in me says you dont have "cooling drag" with a cold radiator, nothing is being cooled, what difference does a hot radiator make? Cooling engines is a science and above my pay grade, but the Merlin in the Hornet was a two stage intercooled engine producing more BHP per litre than the Sabre though less in actual max BHP. Is it possible @Calum that in some circumstances that the Merlin in a Hornet needed more cooling capacity than a Sabre in a Tempest.
Deleted member 68059
Staff Sergeant
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- Dec 28, 2015
Not sure I`d have to go and find the engine heat rejection figures. From memory I dont recall what they`re like in comparison.
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- #37
Thanks for the differentiated view:
drgondog
Major
Double post
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It says in pounds at 100ft/sec
Reluctant Poster
Tech Sergeant
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- Dec 6, 2006
Here's a fact in the report that should not be overlooked:
"With an annular radiator the power plant weight is 180 lb. heavier than with the underslung type,..."
That is a big difference and would have an effect on performance, negating some of the drag benefits and reducing rate of climb. It is also moved the c of g forward 2 1/4 in which might require counter balancing (think P-39 nose armor.....or maybe not). Note that the chin radiator is already well forward on the Tempest, for the Hornet moving the radiator from the leading edge to the front of the engine would result in a much greater c of g shift.
"With an annular radiator the power plant weight is 180 lb. heavier than with the underslung type,..."
That is a big difference and would have an effect on performance, negating some of the drag benefits and reducing rate of climb. It is also moved the c of g forward 2 1/4 in which might require counter balancing (think P-39 nose armor.....or maybe not). Note that the chin radiator is already well forward on the Tempest, for the Hornet moving the radiator from the leading edge to the front of the engine would result in a much greater c of g shift.
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