Where to Get a Rolls Royce Merlin
A close family member worked at Gamston during the period Capot mentions. They confirm that the Merlins ( if extant at the time), were not part of the Budge Aviation set up. The mil stuff as well as gee gees were his 'hobby'. There was certainly storage at the southern end of the airfield, you could see the mil vehicles from the A1. There was also an engineering facility on West Carr Road where you could see all sorts of military (army) hardware, and where I saw Cheiftans/Centurions and previously mentioned Russian SAM in the yard.
The question renmains why the P-51 was so much more favourable drag-wise , than the Spitfire.
“At the outset, an airplane has to be designed in such a manner that the air can flow evenly around the body. There is one simple way of really designing smooth curves. That way is to use conic sections to produce the surfaces that are used on all parts except the wing and tail. This means primarily the fuselage, so all curves on that fuselage were designed by conic sections. Conic sections are very simple. If you take a cone and section crosswise, you get a circle. You make a section that is under an angle and you get a parabola. All these curves are smooth, which can be calculated and then precisely shaped, and the air likes that.
“This is the kind of shape the air likes to touch. The drag is at a minimum and it was the first time that a complete airplane, with the exception of the lifting surfaces, was designed with second-degree curves. I laid out the lines myself and it was a first."
“This is the kind of shape the air likes to touch. The drag is at a minimum and it was the first time that a complete airplane, with the exception of the lifting surfaces, was designed with second-degree curves. I laid out the lines myself and it was a first."
"Previously, air would go in at the bottom of the scoop and spill out on top. By providing this lip and the gap between the fuselage and the radiator lip, we actually equalized the pressure distribution in the duct and got a much better cooling system. We reduced some of the loss due to spilling, which is always detrimental and will produce a certain amount of drag. It is always a problem with any kind of a ducted radiator installation, so this all helped to reduce the spillage."'
Aerodynamicist Ed Horkey fills in the details. “The back was the greatest place in the world to put [the radiator]. However, we started out with an opening to the radiator duct, the top line of which was the bottom line of the fuselage. The problem was that being so far back in the fuselage caused the boundary layer buildup and the airflow wasn’t doing the job of furnishing enough [air] to the radiator to give efficiency or enough cooling.
“Meredith had brought forth the theory or proposal to take in air at a high velocity and slow it down, which, of course, builds up pressure. As it goes through the radiator core, the pressure helps some, but primarily you have more dwell time. Then with the increased pressure and temperature, you squeeze the air down again as it goes out the back and you actually get some thrust from this, or what can be called negative radiator drag. It was great, but with the problems we had at the inlet, we weren't achieving cooling or a drag reduction.
“Ed certainly looks at it from a different viewpoint than we in aerodynamics did at that time. Actually, with the one—quarter scale model at Cal Tech, Irving Ashkenas, who had been working with me, was doing the night shift and I was doing the day shift. He was over one night and came up with the idea of why not put a boundary bleed in. In other words, take that top line of the radiator duct and bring it down from the bottom line of the fuselage and let the turbulent boundary layer that built up under the fuselage go by the entrance and therefore you would get more efficient air into the duct. He went ahead one night and did this on the model and the results were great. Other people may have come up with that later on. I want to give full credit to Irving Ashkenas as really being the developer of the boundary-layer bleed. This is in full use yet today. For instance, one can look at the F-16 and see the tremendous boundary layer gutter that they use."
Perfection of the cooling system was an ongoing process, requiring the input of Horkey’s department, wind-tunnel model work, and, above all, continuous flight testing. And most of it would have to be redone in 1943 and 1944 when the Mustang shifted to the more powerful Merlin engine.
Writes Horkey: “The boundary-layer bleed wasn’t all that simple. If you drop the radiator inlet down far enough to get rid of all of the turbulent boundary layer, the drag would be too high; so it ended where it was a compromise of the bleed depth to get an acceptable cooling performance with minimum drag.
“It so happened that later on when we started the P-51B project, we got the boundary layer bleed a little too small. What would happen was that it caused a duct rumble. Chilton described it to us as somebody pounding on a locker. The boundary layer would build up, and airflow would go around the duct inlet, and then it would all of a sudden go inside again, and this would create a large impact load. We did two things. We got the model out again and started checking the bleed. We also took an actual P-51B up to Ames Aeronautical Lab and cut the wing span down a little and mounted in the 16 foot high-speed wind tunnel.
“l took the first ride, and when we got up to 500 mph in the tunnel, we got the rumble. lt was quite a thrill. Smith J. DeFrance of NACA at Ames, Manley Hood, and Bill Harper all worked with us. We lowered the top inlet of the radiator duct a small amount and also went to the cutback, or slanted inlet shape and solved the problem on the P-51B. Later on, on other airplanes like the P-51H, we had to make an eighth of an inch change, and again make sure we had this problem in hand.
Aerodynamicist Ed Horkey fills in the details. “The back was the greatest place in the world to put [the radiator]. However, we started out with an opening to the radiator duct, the top line of which was the bottom line of the fuselage. The problem was that being so far back in the fuselage caused the boundary layer buildup and the airflow wasn’t doing the job of furnishing enough [air] to the radiator to give efficiency or enough cooling.
“Meredith had brought forth the theory or proposal to take in air at a high velocity and slow it down, which, of course, builds up pressure. As it goes through the radiator core, the pressure helps some, but primarily you have more dwell time. Then with the increased pressure and temperature, you squeeze the air down again as it goes out the back and you actually get some thrust from this, or what can be called negative radiator drag. It was great, but with the problems we had at the inlet, we weren't achieving cooling or a drag reduction.
“Ed certainly looks at it from a different viewpoint than we in aerodynamics did at that time. Actually, with the one—quarter scale model at Cal Tech, Irving Ashkenas, who had been working with me, was doing the night shift and I was doing the day shift. He was over one night and came up with the idea of why not put a boundary bleed in. In other words, take that top line of the radiator duct and bring it down from the bottom line of the fuselage and let the turbulent boundary layer that built up under the fuselage go by the entrance and therefore you would get more efficient air into the duct. He went ahead one night and did this on the model and the results were great. Other people may have come up with that later on. I want to give full credit to Irving Ashkenas as really being the developer of the boundary-layer bleed. This is in full use yet today. For instance, one can look at the F-16 and see the tremendous boundary layer gutter that they use."
Perfection of the cooling system was an ongoing process, requiring the input of Horkey’s department, wind-tunnel model work, and, above all, continuous flight testing. And most of it would have to be redone in 1943 and 1944 when the Mustang shifted to the more powerful Merlin engine.
Writes Horkey: “The boundary-layer bleed wasn’t all that simple. If you drop the radiator inlet down far enough to get rid of all of the turbulent boundary layer, the drag would be too high; so it ended where it was a compromise of the bleed depth to get an acceptable cooling performance with minimum drag.
“It so happened that later on when we started the P-51B project, we got the boundary layer bleed a little too small. What would happen was that it caused a duct rumble. Chilton described it to us as somebody pounding on a locker. The boundary layer would build up, and airflow would go around the duct inlet, and then it would all of a sudden go inside again, and this would create a large impact load. We did two things. We got the model out again and started checking the bleed. We also took an actual P-51B up to Ames Aeronautical Lab and cut the wing span down a little and mounted in the 16 foot high-speed wind tunnel.
“l took the first ride, and when we got up to 500 mph in the tunnel, we got the rumble. lt was quite a thrill. Smith J. DeFrance of NACA at Ames, Manley Hood, and Bill Harper all worked with us. We lowered the top inlet of the radiator duct a small amount and also went to the cutback, or slanted inlet shape and solved the problem on the P-51B. Later on, on other airplanes like the P-51H, we had to make an eighth of an inch change, and again make sure we had this problem in hand.
With the same 61 series Merlin the Spitfire IX was 32 mph slower, but part of that can be laid to the fixed tailwheel, the Mk. VIII with retractable tailwheel was 23 mph slower. Difference in cooling drag is given as being the major reason.
it would be interesting to see how a P-51 with a minimum drag in the shape of a streamlined nose w/o any cooling configuration, as a benchmark, would compare to the P-51 with the existing configuration
It also means, that designing the elliptical wing of the Spitfire for minimal induced drag as compared to the prismatic wing of the P-51 was less effective than winning drag-reduction with the cooling ducts-ex-boundary-layer. Correct?
washoutt, a little late in digging through the book shelves, but found an online copy of a paper I have. Discusses Spitfire/Mustang wing comparison.
http://aerosociety.com/Assets/Docs/P...ng-Ackroyd.pdf
http://aerosociety.com/Assets/Docs/P...ng-Ackroyd.pdf
Thanks ,Megan, brings back to memory the university years, ah, happy days.
It was a revelation to see, that the benefit of elliptical wingshape is so prominent at higher Mach numbers, hence maybe the drive to install ever greater power in the Spitfire, so as to take advantage of that effect. It seems that with a thicker wing, more fuel could have taken along, to protect the bombers all the way to the furthest targets.
Fascinating reading!
It was a revelation to see, that the benefit of elliptical wingshape is so prominent at higher Mach numbers, hence maybe the drive to install ever greater power in the Spitfire, so as to take advantage of that effect. It seems that with a thicker wing, more fuel could have taken along, to protect the bombers all the way to the furthest targets.
Fascinating reading!
