Most Overrated aircraft of WWII.....?

[davparlr]

I'm not an aerodynamicist and it has been way too many years since I have had any aerodynamics but I may be able to make an educated guess. I do not think gs in itself has any impact to the mach number but its affect on the aircraft may have an effect of lowering the speed at which transonic airflow may occur. Since pulling g's almost always require an increase in angle of attack, this would induce an increase in airflow velocity over the top of the wing and fuselage at any constant aircraft velocity thus making that airflow closer to mach. If an aircraft was flying close to its compressability limits and tried to pull more gs, and the plane had the power or dive speed to maintain the airspeed, it is reasonable to think the aircraft could enter the transonic realm. even though the aircraft did not exceed its original compressibility limits. I hope that is not confusing.

 

[michael rauls]

I think I must have been thinking of some other comparison, maybe to Axis aircraft. At high altitude, above 25-30k , the mighty P-47 was hard to beat. At high altitude even the very potent P-51H was a weakling compared to the P-47M/N and their flat rated 2800 hp to 33k!

I'm not an aerodynamicist and it has been way too many years since I have had any aerodynamics but I may be able to make an educated guess. I do not think gs in itself has any impact to the mach number but its affect on the aircraft may have an effect of lowering the speed at which transonic airflow may occur. Since pulling g's almost always require an increase in angle of attack, this would induce an increase in airflow velocity over the top of the wing and fuselage at any constant aircraft velocity thus making that airflow closer to mach. If an aircraft was flying close to its compressability limits and tried to pull more gs, and the plane had the power or dive speed to maintain the airspeed, it is reasonable to think the aircraft could enter the transonic realm. even though the aircraft did not exceed its original compressibility limits. I hope that is not confusing.

Yes you put my thoughts more clearly than I could explain them myself most specificly transsonic airflow over control surfaces and if aircraft with a higher critical mach number( p51 for example)would necessarily have more " headroom" if you will to perform high speed maneuver i.e. could remain im better control at high speeds than an aicraft with a lower critical mach number because said transsonic air flow over control surfaces would not occur until a higher speed. Thank you sir!

 

[XBe02Drvr]

I'm not an aerodynamicist and it has been way too many years since I have had any aerodynamics but I may be able to make an educated guess. I do not think gs in itself has any impact to the mach number but its affect on the aircraft may have an effect of lowering the speed at which transonic airflow may occur. Since pulling g's almost always require an increase in angle of attack, this would induce an increase in airflow velocity over the top of the wing and fuselage at any constant aircraft velocity thus making that airflow closer to mach. If an aircraft was flying close to its compressability limits and tried to pull more gs, and the plane had the power or dive speed to maintain the airspeed, it is reasonable to think the aircraft could enter the transonic realm. even though the aircraft did not exceed its original compressibility limits. I hope that is not confusing.

Thanks for translating NACA Technical Note 1697 into everyday language! I read it and (I think) understood it, but despaired of explaining it in understandable language.
Cheers,
Wes

 

[michael rauls]

If I can try to simplify my theory now. As more Gs are pulled at high speed airflow over control surfaces may become transsonic even though the aircraft itself has not reached its mach limitations and if this is the case the more the Gs the lower the speed said transsonic airflow would occur affecting the ability to manuver in a progressive fashion with the number of Gs pulled. That is to say more Gs =transsonic airflow over control surfaces at a lower speed= less ability ro manuver in a linear progression in accordance with the number of Gs pulled. There, I think I finally got it out.

 

[michael rauls]

And if this is the case it would explain(i think) why aircraft like the p51 seemed to have better handling at higher speeds than those with a lower critical mach. Such is my theory anyway. Whether it's correct or not is a entirely different matter.

 

[fubar57]

Getting pretty warm and squishy here during the last few pages(and smilified).....kudos

 

[pbehn]

And if this is the case it would explain(i think) why aircraft like the p51 seemed to have better handling at higher speeds than those with a lower critical mach. Such is my theory anyway. Whether it's correct or not is a entirely different matter.

The critical Mach number is the speed at which airflow goes supersonic at the lower critical mach number all airflow is sub sonic, at the upper then all is supersonic. the difference between is the transonic range.

The controllability of an aircraft depends on many things, one is aileron reversal, this is a calculated speed, based on things like size of ailerons and the wing rigidity. from wiki

Due to the unusually high speeds at which the Supermarine Spitfire could dive, this problem of aileron reversal became apparent when it was wished to increase the lateral maneuverability (rate of roll) by increasing the aileron area. The aircraft had a wing designed originally for an aileron reversal airspeed of 580 mph, and any attempt to increase the aileron area would have resulted in the wing twisting when the larger ailerons were applied at high speed, the aircraft then rolling in the opposite direction to that intended by the pilot. The problem of increasing the rate of roll was temporarily alleviated with the introduction of "clipped" wing tips (to reduce the aerodynamic load on the tip area, allowing larger ailerons to be used) until a new, stiffer wing could be incorporated. This new wing was introduced in the Mk 21 and had a theoretical aileron reversal speed of 825 mph (1,328 km/h).[2]

There are many other things which can affect high speed handling, for example the mosquito prototype experienced tail buffeting at speed, this was rectified by extending the engine nacelles backwards to smooth airflow. However in combat "high speed handling" is a relative term, if you can pull out of a dive by using trim tabs or other "dodge" and your enemy cant then you have better handling than he does. In WW2 in some cases this depended on such things as the actual build and strength of the pilot.

 

[michael rauls]

The critical Mach number is the speed at which airflow goes supersonic at the lower critical mach number all airflow is sub sonic, at the upper then all is supersonic. the difference between is the transonic range.

The controllability of an aircraft depends on many things, one is aileron reversal, this is a calculated speed, based on things like size of ailerons and the wing rigidity. from wiki

Due to the unusually high speeds at which the Supermarine Spitfire could dive, this problem of aileron reversal became apparent when it was wished to increase the lateral maneuverability (rate of roll) by increasing the aileron area. The aircraft had a wing designed originally for an aileron reversal airspeed of 580 mph, and any attempt to increase the aileron area would have resulted in the wing twisting when the larger ailerons were applied at high speed, the aircraft then rolling in the opposite direction to that intended by the pilot. The problem of increasing the rate of roll was temporarily alleviated with the introduction of "clipped" wing tips (to reduce the aerodynamic load on the tip area, allowing larger ailerons to be used) until a new, stiffer wing could be incorporated. This new wing was introduced in the Mk 21 and had a theoretical aileron reversal speed of 825 mph (1,328 km/h).[2]

There are many other things which can affect high speed handling, for example the mosquito prototype experienced tail buffeting at speed, this was rectified by extending the engine nacelles backwards to smooth airflow. However in combat "high speed handling" is a relative term, if you can pull out of a dive by using trim tabs or other "dodge" and your enemy cant then you have better handling than he does. In WW2 in some cases this depended on such things as the actual build and strength of the pilot.

Ok sounds like my theory was one of those things that sounds like it might hold water( at least to me) but in reality is all wet. I was aware that there are many factors that contribute to higher speed maneuverability/ handling but thought this could have been a major contributing factor of which I was previously unaware.Guess I should have been more clear on that. Anyway thanks for explaining some of thpse things and at least my desire to know if this theory was correct or not( sounds like not) is satisfied.

 

[pbehn]

Ok sounds like my theory was one of those things that sounds like it might hold water( at least to me) but in reality is all wet. I was aware that there are many factors that contribute to higher speed maneuverability/ handling but thought this could have been a major contributing factor of which I was previously unaware.Guess I should have been more clear on that. Anyway thanks for explaining some of thpse things and at least my desire to know if this theory was correct or not( sounds like not) is satisfied.

The critical mach number can be calculated on an airframe made of lead or wood like a wind tunnel model. It is theoretical. There is no guarantee that the aircraft can reach that speed, let alone pull out of a dive at that speed. The Spitfire famously lost its propeller testing out the limits of dive speed. The P-51 and Spitfire had different wings both designed for speed, the Spitfires is thin, the P-51s is a "laminar flow" type. The P-51 has less drag most of the time because turbulent flow over the wing sets in further back. This means at almost all operating speeds the P-51 has less drag than the Spitfire it is only when approaching the critical mach number that the Spitfire has an advantage, The Spitfire would have a higher critical mach number if it had a different cockpit canopy, the front panel produces a shock first. As I said these are theoretical but useful numbers, the Spitfire may have had an "aileron reversal" speed of 580MPH, it experience handling problems like roll rate at much slower speeds.

 

[michael rauls]

The critical mach number can be calculated on an airframe made of lead or wood like a wind tunnel model. It is theoretical. There is no guarantee that the aircraft can reach that speed, let alone pull out of a dive at that speed. The Spitfire famously lost its propeller testing out the limits of dive speed. The P-51 and Spitfire had different wings both designed for speed, the Spitfires is thin, the P-51s is a "laminar flow" type. The P-51 has less drag most of the time because turbulent flow over the wing sets in further back. This means at almost all operating speeds the P-51 has less drag than the Spitfire it is only when approaching the critical mach number that the Spitfire has an advantage, The Spitfire would have a higher critical mach number if it had a different cockpit canopy, the front panel produces a shock first. As I said these are theoretical but useful numbers, the Spitfire may have had an "aileron reversal" speed of 580MPH, it experience handling problems like roll rate at much slower speeds.

Sounds like a drag to lift ratio ( thats probably way simplistic but the limit of my understanding at the moment) had alot to do with it. Also it's quite impressive that the Spitfire would have had an even higher critical mach if not for the canopy design. As it was I think it had one of if not the highest of any prop job at .83 I think( just going from memory here). Especially when one considers the timeframe of its development that is quite impressive.

 

[pbehn]

Sounds like a drag to lift ratio ( thats probably way simplistic but the limit of my understanding at the moment) had alot to do with it. Also it's quite impressive that the Spitfire would have had an even higher critical mach if not for the canopy design. As it was I think it had one of if not the highest of any prop job at .83 I think( just going from memory here). Especially when one considers the timeframe of its development that is quite impressive.

It may have had a higher critical mach number but the view for the pilot probably wouldn't be as good, so it would possibly be a worse plane in service. A Spitfire achieved achieved mach 0.891 in a 45 degree dive with a fully feathered prop, but this aircraft had been modified to do so and the question of how accurate the instruments are will always linger (0.001 of mach1 is?). I believe it is around 0.83 for a service aircraft, in another dive the plane lost its prop the pilot blacked out and came to at 40,000ft, these are very dangerous things to do, in a bog standard service aircraft the pilot has a good chance of killing himself.

 

[michael rauls]

It may have had a higher critical mach number but the view for the pilot probably wouldn't be as good, so it would possibly be a worse plane in service. A Spitfire achieved achieved mach 0.891 in a 45 degree dive with a fully feathered prop, but this aircraft had been modified to do so and the question of how accurate the instruments are will always linger (0.001 of mach1 is?). I believe it is around 0.83 for a service aircraft, in another dive the plane lost its prop the pilot blacked out and came to at 40,000ft, these are very dangerous things to do, in a bog standard service aircraft the pilot has a good chance of killing himself.

Yes certainly pushing an aicraft right up to it's critical mach speed intentionally was not the safest thing to do but I was more using the .83 number as a yardstick for comparison to other types.

 

[pbehn]

Yes certainly pushing an aicraft right up to it's critical mach speed intentionally was not the safest thing to do but I was more using the .83 number as a yardstick for comparison to other types.

The planes that were stated as 0,83 didn't have fully feathering props (and some other mods), they were more likely to get into trouble. Since conventional instruments don't work, the pilot hasn't a clue how fast he is going. Setting the record the plane was in a 45 degree dive doing 600mph, that is going down to earth at circa 400 MPH.....not a time to evaluate "control issues".

 

[swampyankee]

Post-war, as transonic wind tunnels were still new tech, a P-51 was modified for high-Mach number research.

The NACA engineers and technicians carefully cleaned up the aircraft, including removing the propeller, packed it with instrumentation, and towed as high as possible behind a lightly-loaded B-29 or B-50. See http://naca.central.cranfield.ac.uk/reports/1948/naca-report-916.pdf

Mr Nissen then dived towards the ground.

 

[pbehn]

Post-war, as transonic wind tunnels were still new tech, a P-51 was modified for high-Mach number research.

The NACA engineers and technicians carefully cleaned up the aircraft, including removing the propeller, packed it with instrumentation, and towed as high as possible behind a lightly-loaded B-29 or B-50. See http://naca.central.cranfield.ac.uk/reports/1948/naca-report-916.pdf

Mr Nissen then dived towards the ground.

As did many brave test pilots.

 

[Reluctant Poster]

It was more to do with RPMs and running in "Auto-lean"

"Lindbergh talked with MacDonald. The colonel then asked the group's pilots to assemble at the recreation hall that evening. The hall was that in name only, packed dirt floors staring up at a palm thatched roof, one ping pong table and some decks of cards completing the decor. Under the glare of unshaded bulbs, MacDonald got down to business. "Mr. Lindbergh" wanted to explain how to gain more range from the P-38s. In a pleasant manner Lindbergh explained cruise control techniques he had worked out for the Lightnings: reduce the standard 2,200 rpm to 1,600, set fuel mixtures to "auto-lean," and slightly increase manifold pressures. This, Lindbergh predicted, would stretch the Lightning's radius by 400 hundred miles, a nine-hour flight. When he concluded his talk half an hour later, the room was silent."
Charles Lindbergh and the 475th Fighter Group

I can't find the other website but I believe they were also told down to 160Kts from 180(?). Lindbergh said that the Pilot's Notes were wrong

Low revs, higher boost and auto lean is the recipe for maximum range for any engine and was in the pilot notes for the P-38D, well before Lindbergh shows up in the pacific. The attached file is an excerpt from the Lancaster Pilots and Flight Engineers Notes showing similar advice.

 

[fastmongrel]

Low revs, higher boost and auto lean is the recipe for maximum range for any engine and was in the pilot notes for the P-38D, well before Lindbergh shows up in the pacific. The attached file is an excerpt from the Lancaster Pilots and Flight Engineers Notes showing similar advice.

Low revs, low speed, low altitude is a good way to increase range over water. It's also a good way to die if you do it over defended territory.

 

[XBe02Drvr]

Low revs, higher boost and auto lean is the recipe for maximum range for any engine and was in the pilot notes for the P-38D, well before Lindbergh shows up in the pacific.

And pilots disregarded that aspect of the pilot notes reflecting their instructor's ingrained prejudice against oversquare engine operation, which was in itself a throwback to less robust engines of the twenties and thirties.
Adding to this was the caution against operating in a condition that impeded rapid acceleration to combat speed in case of a surprise bounce.
In addition to stretching the Lightnings' legs, I believe Lindberg surreptitiously shot down a couple of Japanese planes in one.
Cheers,
Wes

 

[Navalwarrior]

And pilots disregarded that aspect of the pilot notes reflecting their instructor's ingrained prejudice against oversquare engine operation, which was in itself a throwback to less robust engines of the twenties and thirties.
Adding to this was the caution against operating in a condition that impeded rapid acceleration to combat speed in case of a surprise bounce.
In addition to stretching the Lightnings' legs, I believe Lindberg surreptitiously shot down a couple of Japanese planes in one.
Cheers,
Wes

Resp:
Don't forget that Lindbergh also helped the US Marines in getting the most performance from the F4U Corsair.
PS. Lindbergh also sent a very detailed letter to Maj McGuire's wife after his death, outlining their close relationship, his leadership ability and how much he contributed to the war effort.

 

[XBe02Drvr]

Don't forget that Lindbergh also helped the US Marines in getting the most performance from the F4U Corsair.

Doubled the bombload they could get off "your basic fighter strip" with, didn't he, in addition to preaching his signature fuel economy mantra?

PS. Lindbergh also sent a very detailed letter to Maj McGuire's wife after his death, outlining their close relationship, his leadership ability and how much he contributed to the war effort.

Never cease to marvel at the tidbits you pick up around here! I think "Major Tom" was an undersung hero, not so much for those he shot, as for those he taught, and the kills he gave away. An "ace multiplier". Thanks, shipmate.
Cheers,
Wes