A host of questions not deserving of their own individual posts.

[AspiringHowardHughes]

I thought of the exhaust gas issue - I have been hoping that the exhaust gas would remain contained within the boundary layer. I imagine that if anything, a larger boundary layer diverter could resolve this problem. In case this changes things, my planned aircraft would exhaust through a turbocharger, rather than directly from the headers. The turbocharger would still be directly in line with the radiator, albeit located further forward in the aircraft of course. Perhaps some sort of turbocharger shielding would ensure that the exhaust does not project so far out the side of the aircraft?

How far back behind the wing would the radiator installation have to be before the pressure difference becomes negligible? I had not considered this drawback.
I agree that the example presented on that website is poorly executed. If I were to use this design it would be done with more grace, like the Mustang installation.
I may have the opportunity to simulate things like this later in my school career, these sorts of questions would make for a good project.

 

[don4331]

Drgondog, thanks for your commentary on the thought process of the designer.
Hopefully the radiator system would not be anything of an afterthought, but if designers of years past are at all like me I can see how the need to fit a cooling mechanism could be dismissed until the general aircraft layout has already been established - especially in an age of "slap evaporative cooling on it and call it a day".

In an attempt to avoid mounting anything under the wings or fuselage (to allow for ideal wing performance and centreline payload) I have thought of mounting mustang-style radiators on the flanks of the rear fuselage, exhausting on either side of the rudder. From the internal layouts of aircraft I have seen, there tends to be a good deal of free space back there - probably because it is far from the centre of gravity....
This radiator location could be justified by a need to restore the balance of the aircraft after a heavier engine is installed, but is probably not advisable as an initial decision.
After having this idea myself, I came across it online in the form of this hypothetical WW2 aircraft.

Focke Wulf Fw 190 mit DB 609

The Focke-Wulf Fw 190 mit DB 609 was a 1942 design venture to provide the Luftwaffe with a successor to the Fw 190 and its troublesome BMW 801 radial engine. Intended, to mount the envisioned exper…

plane-encyclopedia.com

It is interesting to hear that idle and taxi conditions might be considered. Knowing the desperate drive for increased performance that was the second world war, it would not have surprised me to hear that some external solution was used to solve those problem areas (a leaf-blower into the radiator inlet during idle and taxi, perhaps!).

Was the Mustang radiator being behind the "turbulent point" of the wing of any significance?

Additionally, what would the penalties be for a radiator design which ingested the boundary layer separately rather than divert it around the intake, as the Mustang does? Think of the Bf 109 arrangement, but for a Mustang. I imagine this would consume more internal space, but probably improve the drag characteristics of the radiator by not demanding that the boundary layer be redirected so forcefully.

It is interesting to hear that the lightweight Mustangs modified the radiator arrangement within the duct. Any idea what drove the initial decision?

Thank you for your two cents!

The "beauty" of the Mustang is the whole design: The NAA team looked at the airflow from the spinner to the rudder. They worked to have smooth increase in area to mid-wing, then constant taper aft. So, you have to be looking at the resistance the air is experiencing. The position of the enlarged fuselage for the radiator corresponds with the reduced resistance of the wing. The taper aft is mathematical calculated; when you add area for the horizontal stabilizer, it is offset by the reduction in area of the fuselage.

As you have to consider the whole design, not just the high speed airfoil, not just the radiator install with its Meredith effect (or lack there of) , etc to come up with something truly exceptional.

 

[z42]

The "beauty" of the Mustang is the whole design: The NAA team looked at the airflow from the spinner to the rudder. They worked to have smooth increase in area to mid-wing, then constant taper aft. So, you have to be looking at the resistance the air is experiencing. The position of the enlarged fuselage for the radiator corresponds with the reduced resistance of the wing. The taper aft is mathematical calculated; when you add area for the horizontal stabilizer, it is offset by the reduction in area of the fuselage.

This sounds like the area rule, which is mostly a post-WWII thing, and important for transsonic drag reduction. German aerodynamicists had discovered it in the early 1940'ies but Germany never managed to get an area ruled aircraft into service during the war.

AFAIU the area rule was rediscovered and realized to be important in the West only in the 1950'ies. Area rule - Wikipedia

Are you saying the P-51 was explicitly designed with the area rule in mind, and not just sort of accidentally due to the radiator placement?

 

[Bretoal2]

This sounds like the area rule, which is mostly a post-WWII thing, and important for transsonic drag reduction. German aerodynamicists had discovered it in the early 1940'ies but Germany never managed to get an area ruled aircraft into service during the war.

AFAIU the area rule was rediscovered and realized to be important in the West only in the 1950'ies. Area rule - Wikipedia

Are you saying the P-51 was explicitly designed with the area rule in mind, and not just sort of accidentally due to the radiator placement?

It seems that the aera rule was known, or at least anticipated, by many European aerodynamicists as early as the 1930s, notably by Marcel Riffard, the designer of the Caudron-Renault aircrafts that won the Deutsch de la Meurthe Cup several times.

See note 2 of the French version of the Wikipedia entry :

Loi des aires (aérodynamique) — Wikipédia

fr.wikipedia.org

This reduction in drag at subsonic speeds is, of course, only an approximation of Whitcomb's true rule, which produces its effects primarily in transonic flight.

 

[Jugman]

Jugman, do you have diagrams of the two nozzleboxes, or the installations as a whole?
I am interested to see how the problem of control was solved (or mitigated).

In a nutshell a PRT doesn't need controlled.

NACA-TR-786

View: https://youtu.be/1j9164wb6TE?si=biqR-3OzZ4veU95P

Tom calls it a reaction turbine by mistake. He also says It has an 8.25in cooling impeller while the tech brochure says 7in. I don't know if they changed it or if one is in error.

 

[Tom Fey]

In a nutshell a PRT doesn't need controlled.

NACA-TR-786

View: https://youtu.be/1j9164wb6TE?si=biqR-3OzZ4veU95P

Tom calls it a reaction turbine by mistake. He also says It has an 8.25in cooling impeller while the tech brochure says 7in. I don't know if they changed it or if one is in error.

Yep, I stepped in it by calling the PRT a reaction turbine. The Wriight PRT is indeed an impulse-type turbine. As for the diameter of the cooling impeller, I never completely disassembled my PRT, but based on the assembly photographs and the diameter of the cooling annulus on the top of the turbine disc (17:21 to 17:41 in the video), I estimated the diameter of the impeller to be 8.25 inches. TF

 

[Jugman]

T Tom Fey For what it's worth, I make the same mistake all the time. Measuring the cutaway drawing from the brochure I get a ratio of 33.5cm to 23.5cm turbine to impeller radius. Zoomed in of course. At a turbine maximum diameter of 11.45in = 8.03in. I have a hunch that 7in is measured from the top of the impeller vanes.

 

[F119doctor]

Regarding the optimum method of introducing fuel, no one has mentioned the P&W method used on the R2800, and probably others

They used a pressure carburetor to meter the fuel, but instead of introducing it directly into the eye of the supercharger, it was sprayed into the inner bore of the supercharger rotor, where it was centrifugally distributed around the bore. From there, radial passages moved the fuel outward between every other rotor blade, exiting into the air flow path approximately 1/2 way out to the tip. This ensured even distribution of the fuel to all of the individual intake manifolds coming off the outer edge of the supercharger, and aided in the vaporization of the fuel with its cooling effect. The R2800 was relatively unaffected by the uneven mixture distribution that caused all sorts of problems on the R3350 before they incorporated direct fuel injection.

FYI - P&W still uses a similar system to introduce lubrication oil into modern jet engine bearing compartments to lubricate the bearings and cool the compartment seals, with oil jets spraying into rotating scoops that use centrifugal force to distribute the oil thru rotating passages to where it is needed.

 

[drgondog]

This sounds like the area rule, which is mostly a post-WWII thing, and important for transsonic drag reduction. German aerodynamicists had discovered it in the early 1940'ies but Germany never managed to get an area ruled aircraft into service during the war.

AFAIU the area rule was rediscovered and realized to be important in the West only in the 1950'ies. Area rule - Wikipedia

Are you saying the P-51 was explicitly designed with the area rule in mind, and not just sort of accidentally due to the radiator placement?

No. In fact the lines were composed using projective geometry in which the fuselage was composed of increasing conic sections by applyingProjective geometry. This technique was applied to extent possible through the cockpit and lower intake scoop but there was no preconceived application of 'whitcomb area rule' type geometry at the wing region.

The purpose was to achieve an even velocity gradiant along the fuselage to reduce drag. Horkey had zero knowledge of 'area rule as applied to supersonic airfcraft fuselage design.