Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: davidpt40 on September 21, 2003, 01:06:44 PM
-
(1) The P-51 could only fly inverted for 8 seconds before the oil drained out of the cylinders. When this happened, the engine would seize.
(2) Some pilots flew the P51D with only 4 guns. This allowed them to carry more ammunition.
(3) When flying at 400mph, the radiator of the P51 produced 400 pounds of thrust, compared to the 1000 pounds of thrust produced by the engine.
-
(4) we get all our info from the "childrens edition:bumper book of paper aeroplanes"
:D
post where you got this info and maybe it could be discussed for its merrits but for me this all sounds like absolute twaddle.
Much as id like to see the P51 have a few limitations in ts performance i cant believe that list,
zero G carbs but non zero G oil? why would they do that? ( i mean put zero G carbs on an engine that cant fly inverted for long, things like that would cause them to cancel a contract im sure and we would never have seen it if it had a fault like that) same engine in spitfires did the same thing i assume?
sorry i think thats nonsense
400(? sounds high) lbs thrust from the exhaust of the engines supercharger i think(underside) it was not radiator as such, dont quote me though.1000lbs from the engine? assume you mean the propellor?
4 guns extra ammo? hmm again could be true i guess but i think the limit on ammo for the guns was due to the lack of space in the ammo bays, not the weight of ammo. Again dont quote me but i was of the opinion the 4 guns on the P51D and P51B were loaded with as many bullets as the standard armoured ammo bays allowed. Maybe they made field mods to enlarge the capacity but again i cant see it myself.Plus the difference in performance between a 4 gun P51d and a 6 gun one isnt that great.still who knows :)
still I'll give you the benifit of the doubt until i see your source :)
-
Im just dying to see this radiator that creates 400lbs of thrust...I didnt think they had an afterburner on that thing:rofl
-
The p-38 has a similar inverted flight restriction, the p51d having one would be unsurprising, though 8 seconds sounds more like a reccomendation, and far from the moment the engine siezes up.
The four gun/extra ammo option is available in aces high.
And the radiator thrust is not an "Extra" 400lbs of thrust. The radiator produces approx. 400lbs of DRAG. It produces about 350lbs of thrust, greatly reducing the net cooling drag.
-
The p38 also had a similar problem with flying inverted. It could do negative-g maneuvers, but not fly inverted for more than 10 seconds or so. This is not the same as the original spitfire problem.
-
Do your own research hazed. Type "Meredith effect and P51" into google.
1) The P-51 could only fly inverted for 8 seconds before the oil drained out of the cylinders. When this happened, the engine would seize.
-Source: Airshow announcer
(2) Some pilots flew the P51D with only 4 guns. This allowed them to carry more ammunition.
Source: P51 Mustang (book)
-
I get all my ww2 aircraft info from the discovery wings channel.
-
Originally posted by ALF
Im just dying to see this radiator that creates 400lbs of thrust...I didnt think they had an afterburner on that thing:rofl
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
-
Originally posted by davidpt40
Do your own research hazed. Type "Meredith effect and P51" into google.
-Source: Airshow announcer
Source: P51 Mustang (book)
And we all know them announcers are spot on all the time. I remember one misquoting specs on multiple aircraft when I was at one. Made me laugh. And you might want to remember the 51's at the airshows are not always equipped with the stock engine ;)
-
Nope- I did some additional checking. The P-51 is not rated for sustained inverted flight.
Another interesting fact- The P51 had no provisions for wing de-icing (besides pitot heat).
-
Mustangs did get a small amount of thrust from the radiator exit duct. If you heat a gas it expands, restrict the flow of the heated gas and it has to speed up ====> thrust. The amount of thrust gained is dependant on airspeed, altitude, air temp and coolant temp (just to name a few) so be wary of any source that doesn't say "maximum" or "average" when quoting a figure.
Pitot heat prevents icing in the pitot tube which is used by the airspeed indicator but has absolutely no effect on the build up of ice on the wing.
-
I thought Pitot Heat was when you lit your umm H20 Boong
-
Not sure just how exactly the P-51 radiator worked, but I remember Hohun's post where he commented about the British test data of the P-51D which only yielded about 414mph.
Hohun comments, while other planes of Germany or Britain were typically tested with closed radiators for maximum top speed, the P-51D travelling with a state of open radiators actually yielded better results, and the quick overheating problems and slower top speed mentioned in British tests, were most probably from a P-51D tested with radiators closed.
-
On early models of the P-51, the oil scavenger pump could only pull oil for about 10 seconds if inverted or pushing negative Gs, after that the sump was dry. I'll have to look it up to see if this was modified on later models.
Removing one set of guns allowed for more ammo storage for the remaining 4 guns, however the total overall capacity (total bullets carried) was almost the same.
See Widewing's post about the thrust.
-
sounds like the 400lb drag and 350lb thrust are marketing figures.
I doubt (havn't calculated though) that the heat in the radiator gives enough energy for thrust that is 40% of what the propeller can give. If so, it means that the engine/propeller system is terribly and horribly inefficient in using the fuel energy. too much is wasted on heat.
if they lowered the colling system's drag from 400 to 50 lb, using a good ducting that takes into account the heating of the air, then they lowered the drag - not created thrust.
It's like saying that the airframe creates more thrust when I raise the gears.
400lb drag + 350lb thrust just sounds a lot sexier then 50lb of drag.
Bozon
-
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.
-
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.
-
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.
-
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