P-51 info

[davidpt40]

Theres been lots of threads on the P51s radiator.  What it all boiled down to is that the P-51 only used about 2% of its engine power on cooling, while other aircraft were using 10-15%.

But the P-51s radiator did produce 350 pounds of thrust at 400mph.  Designers later figured that they could have even increased this if they had pumped the engine exhaust into the radiator scoop.

[meddog]

I think I would have to see the radiator system diagrams or an explination on how it works.  on todays turbojet engines, as much as 60% or more of the engines total thrust output comes from bypass air  which is nothing more than a duct around the engine with a big ducted fan in the front.  But I don't see how a radiator can produce any real significant thrust.  As for propellers, They produce one of the 4 forces of flight=thrust which is used to counter act drag but it is not measered as thrust but as horsepower.  Turboprops which is a jet engine that drives a prop is measered as shaft horsepower.  Only jet engines are measured in pounds of thrust.

[davidpt40]

The radiator heated the cold air coming into the scoop.  The cold air heats up, expands, and is forced out of the back of the scoop.

... the full power propeller thrust was about 1,000 pounds and the radiator drag (gross) was about 400 pounds, but the momentum recovery was some 350 pounds of compensating thrust--for a net cooling drag of only some 3% of the thrust of the propeller.

http://www.airandspacemagazine.com/ASM/mag/supp/jj99/mustang.html

Scroll down the page a bit and there is some very interesting stuff about the meredith effect.

[joeblogs]

If you trace the lineage of the really great aeronautical scientists, you'll find many of them practiced in Germany, more than a few knew how to build a wind tunnel, and they knew what the Reynolds number was.  Some of those scientists came to the U.S. and spent many years using time at the Cal Tech wind tunnel...

Rolls Royce had perhaps the best engineer trained in fluid dynamics on its staff.  He redesigned the induction system of the Merlin as well as designing its two stage supercharger.  Rolls was one of the first engine makers to study the effects of radiator efficiency, and they started that work in the mid 1930s.  It's highly unlikely they did not understand how the P-51 radiator worked.

Source: Schlaifer and Heron, 1950

-Blogs

Originally posted by Widewing
Quoting Lee Atwood of North American Aviation:

"During World War II, everyone was trying to figure out how the P-51 Mustang was out-performing German fighters as well as the British Spitfire, which had more horsepower and was 1,000 pounds lighter. The German aircraft manufacturer, Messerschmitt, was also researching the Mustang's performance to no avail.
 
Atwood explained, "Both the British and German engineers at the time thought you could test a scale model in a wind tunnel. But the wind tunnel models didn't generate the engine-heat factor, which we successfully controlled within the air scoop to create positive thrust. They were all looking at Mustang's laminar flow wing, which was noted for reducing air friction over the surface of aircraft wings."

Pointing to several mathematical equations, Atwood continued, "The laminar flow wing is great for jet airplanes or in a high-speed dive but had little effect on the P-51's overall performance envelope. You have to attribute the speed increase to the radiator energy recovery (positive thrust), not the characteristic of the wing itself. The wing did help in a dive -- not in level flight. I never mentioned this to anyone during the war."

Atwood credited F.W. Meredith of the RAE Farnborough, U.K., whose August 1935 report known as the Meredith Effect greatly influenced his work on the P-51 cooling radiator."


There is no other explanation for the P-51s speed on the same or less power than its WWII brethren while having greater flat-plate area.

My regards,

Widewing