Recurring Theme in WW2 Aviation

[stona]

It is not a straightforward answer.

Again, we will agree to differ.
Cheers
Steve

 

[pbehn]

A negative on one hand, versus a very strong positive relative to portability, weight and performance on the other hand. Most pilots would prefer the latter

2,500 LW pilots who made 5 kills or more would agree I am sure.

Swept wings were discovered to suffer from "pitch up" causing the "sabre dance". Were planes re designed without swept wings or were training and flying procedures changed to allow swept wings to be flown safely?

 

[BLine22]

Not if it made the 109 a more compact lighter faster machine. No 109 pilot would trade the undercarriage for a fixed one that took away its advantage in speed and handling. Of all the planes in the war the 109 was the most dangerous to the opposition from 1939 to 45. The Spitfire was much easier to fly in 1940 than it was in 1945, no pilot would want to get rid of the weight and power unless they were having a pleasure flight post war.

pbehn, I agree with you, every design is the outcome of give and take. I don't think LW pilots would want to give away any of their power to weight ratio for beefier wide track landing gear.

I think a good comparison is Hellcat and Corsair. Hellcat was very easy to fly and had a great combat record. Corsair had much better performance but was a hand full for less experienced pilots. After the war, the Corsair remained operational while the Hellcat was relegated to the Reserves or for use as drones.

 

[pbehn]

Corsair had much better performance but was a hand full for less experienced pilots. After the war, the Corsair remained operational while the Hellcat was relegated to the Reserves or for use as drones.

The Corsair was such a handful that it took the British to teach the Americans how to land it on a carrier!












He He He I know its a myth, I dont really know where it came from, but it still runs.

 

[Shortround6]

I had in mind a previous post explaining why thin wings could not be fixed to the Hurricane, It was explained with photos how big the box structure was to contain the undercart mechanism. I believe the Spitfire needed a new type of tyre to fit its wing.

In the design stage when most things are "rubber" or at least just pencil lines on paper you can do quite a bit of changing. Once you have an established structure in production changes are a LOT harder to make. Like trying to make thinner wings to stick on the existing center structure. IF the undercart mechanism (legs and piston/s and linkages) was designed for the thick wing space you could certainly design a new mechanism to fit a thinner wing. But that is just more work (man hours) added to the conversion scheme and means that many fewer interchangeable parts/spares with the old airframe.

While you can't really move the bottom of the wing up you might have been able to move the top of the wing down to make it thinner. I would note that the pilots feet and rudder pedals are on top of the wheel wells so I am not sure how much you can squish things there.


Depending on the the load on the tire they could sometimes just use a higher load range tire of the same size. Usually meant increasing the number of ply's. Like going from a 4 ply to a 6 ply. The tire would be heavier but pretty much the same size. Down side is that the contact patch (area where the rubber meets the road/grass/dirt) stays the same size and the tire sinks further into the dirt. Other choice is use a larger size tire that is wider and slightly larger in diameter even if it fits on the same rim. Tire still weighs more but spreads the weight out over a larger area preventing (or lessening) the tires sinking into soft ground.
I don't know what they used on the Spitfire but apparently on the 109 they fitted the bigger tires.

 

[pbehn]

Here is a table of US losses in training 1942-45
United States World War II Aircraft Loss Statistics during Flight Training

Fatalities
Primary trainers =439
Basic trainers =1,175
Advanced trainers =1.888
P40 =350
P47 =455
P51 =137


The A36 had the highest rate with 274 crashes per 100,000 flying hours while the P51 was 105.
Are there any figures for the Bf109

 

[XBe02Drvr]

Swept wings were discovered to suffer from "pitch up" causing the "sabre dance". Were planes re designed without swept wings or were training and flying procedures changed to allow swept wings to be flown safely?

Procedures, man! The "Sabre dance" resulted from pilots using take-off techniques learned in straight wing aircraft that were inappropriate in the Sabre. Early jets were REALLY slow accelerators on the runway, consequently designed with minimal pitch attitude when sitting on the wheels, to keep drag to a minimum and ram effect maximum. This could lead to a situation where the near-symmetrical airfoil would produce enough NEGATIVE lift to pin the aircraft to the ground and make rotation and liftoff impossible. By this time there's not much runway left, and the ejection seat doesn't have zero altitude capability.
So at some point well before take-off speed the stick goes back to full up elevator, then as the nose gets "light" and starts to rise, the stick goes forward some to prevent an over-rotation. Elevator effectiveness is increasing rapidly at this point, so timing is critical. A little delay or not enough forward stick pressure, and the pitch-up takes over. This whole song-and-dance was not an issue with straight wing aircraft as their center of lift didn't migrate so much with pitch attitude in ground effect. M.A.C.murphy strikes again!
Later jets with afterburners and positive AOAs on the ground were less susceptible. (Except McDonnell products!)

 

[pbehn]

Procedures, man! !)

Exactly my point, no one suggested doing away with swept wings, they identified the problem, found a solution and changed procedures and training.

 

[stona]

Exactly my point, no one suggested doing away with swept wings,.

No, because they were a huge aerodynamic advantage, all subsequent high performance aircraft adopted swept wings.

There was no advantage to attaching the Bf 109 chassis to the fuselage, other than to met a transport specification. No subsequent German aircraft (or other nationality off the top of my head) adopted this system and its inherently dodgy geometry. There were some other chassis attached in a somewhat similar way, but they used some very complicated construction to overcome the geometric problem (think F-4F, which despite better geometry still had less than ideal ground handling characteristics, described variously as 'tricky' and 'terrible' and everything between.)

Cheers

Steve

 

[BLine22]

The advantage of attached the landing gear to the fuselage is that the landing forces are transmitted from the landing gear directly to the fuselage and therefore the wing structure doesn't have to be reinforce as much. The further outboard on the wing that landing gear are mounted equals a longer lever arm between the landing gear and fuselage and the wing must be designed to withstand.

 

[pbehn]

No, because they were a huge aerodynamic advantage, all subsequent high performance aircraft adopted swept wings.

There was no advantage to attaching the Bf 109 chassis to the fuselage, other than to met a transport specification. No subsequent German aircraft (or other nationality off the top of my head) adopted this system and its inherently dodgy geometry. There were some other chassis attached in a somewhat similar way, but they used some very complicated construction to overcome the geometric problem (think F-4F, which despite better geometry still had less than ideal ground handling characteristics, described variously as 'tricky' and 'terrible' and everything between.)
QUOTE]




No subsequent aircraft used the Spitfire set up, because no subsequent aircraft was a spitfire.

The F4F landing gear was, in my opinion, an elegant solution it was also not continued because it would not work on the F6F which also had an elegant solution that would not work on an F15. Put an inverted V12 water cooled engine on an F4F and see how it performs. The landing gear is where the engine is.

These are the facts. The Bf109 was the most produced fighter in history, it had the most aces of any aircraft produced, it was a front line fighter from before WW2 started until the LW collapsed. I have never read any report by any Bf109 fighter that said he was completely outclassed one on one with any allied fighter. Show me a LW pilot saying he wished the LW had Hurricanes instead of 109s because they were easier for novices to land. You never will, because the argument is preposterous. All RAF pilots said the Spitfire was more difficult in take off landing and ground handling than the Hurricane, none of them would trade the Spitfire for the Hurricane except for the few seconds they fired the guns and would like the concentration of the Hurricanes 8MGs.

Steve, if you want you talk about subsequent aircraft tell me how they perform on 85 octane fuel and 1000BHP maximum. I have quoted the accident rates in USA TRAINERS, if you wish to continue the discussion tell me how many German pilots were killed or injured in BF109s and how this compares to the Fw190, Spitfire Hurricane and US fighters.

Having seen your complete BS on the other thread, dont bother.

 

[stona]

The advantage of attached the landing gear to the fuselage is that the landing forces are transmitted from the landing gear directly to the fuselage and therefore the wing structure doesn't have to be reinforce as much. The further outboard on the wing that landing gear are mounted equals a longer lever arm between the landing gear and fuselage and the wing must be designed to withstand.

True. But what is the penalty compared to the advantage? No subsequent Messerschmitt design did the same, nor did any contemporary British designs or subsequent British or German designs. This suggests that the disadvantage in handling of such an ungainly design outweighed the advantages.
The F-4F was designed that way to absorb the very much heavier loads of carrier landings, particularly given the designed sink rate of all WW2 US carrier aircraft, and might in that way be a justifiable compromise, but not the Bf 109.
Cheers
Steve

 

[Elmas]

At the time when Mitchell and Messerschmitt started to design Spit & Bf 109 the theory of bending and stretching of plates was in its infancy, so structural designers were very conservative about the loads that wing could support, also because calculation, with just a slide rule as an aid, was very difficult. Very soon, hovever, they did realize that thin wing with stressed skin were much stronger that expected, and they act consequently.

 

[wuzak]

Is it not the case that the wings have to resist similar bending loads in flight as they do in the landing gear?

 

[Shortround6]

In part it may be due to the suddenness of the load being applied and strength of the whole wing vs local portions of the wing.
The Spar or Spars may be the main source of strength for bending loads but the skin contributes a certain amount as the entire wing is trying to bend in flight. In a hard landing the landing gear is trying to rip it's attachment points loose (attachment points on spar/s) and punch through the top surface of the wing. Or bend the spar in a specific location, not across it's entire length. It may even be a bit of a double wammy. fuselage and outer wings are trying to go down (inertia of decent) while the resistance (upward force) is being applied at only two points. It may depend on the design load factor used for the landing calculations. some planes were designed for a 4.5 G impact. others used a different limit.

 

[drgondog]

The primary design limits for the wings were Angle of Attack loads imposed by high G pullout from a dive, but could be approached by a very hard/high G turn maneuver.

The Naval aircraft also considered landing loads to test Limit G/Ultimate G applied loads - but most design landing loads were less than high AoA loads.

Elmas explanation was correct. Conservative approach to bending loads was to consider a beam with a 'wider' flange - top and bottom due to skin riveted over the spar as neither the theory nor the computational methods were adequate to calculate bending stresses of complex boxes created by spar/rib/longeron connected to shear panels.

In addition to the complex analytical requirements imposed by looking at such structure with assumed rigitdity, airframe structures are elastic under applied loads - which adds another layer of complexity to the analysis as both deformation of the structure as well as frequency response must be taken into account.

 

[stona]

At the time when Mitchell and Messerschmitt started to design Spit & Bf 109 the theory of bending and stretching of plates was in its infancy, so structural designers were very conservative about the loads that wing could support,

Just to be clear, a Spitfire undercarriage leg rotates on a pintle which is attached to the wing (effectively the back of the main spar) and not the fuselage, though close to it. It is the angle of this pintle that allows the undercarriage to fold up and back so that the wheel clears the spar/D-box.
Though the track of the undercarriage is very similar to the Bf 109, the geometry is therefore quite different.

Cheers

Steve

 

[Old Wizard]

 

[Reluctant Poster]

The FW 190 was a later design with a more powerful engine, the 109 first flew with a Kestrel engine. I have already said I consider the "inexperienced pilot" argument to be misleading, I guarantee that I would crash all of them. The 109s centre of gravity was further behind the front wheels than that of a spitfire, it was tail heavy and much less likely to "nose over".

Ray Hanna flew one and said it was easier than many aircraft to make a three point landing, maybe that was because it was designed to do just that. He also said that on the ground it was much different to other planes, you should not roll off the runway after landing but come to a halt and slowly taxi.

Pilots were killed taking off and landing in all sorts of aircraft, statistics would probably "prove" that basic trainers were more dangerous than some combat aircraft, I would think the most difficult flight a pilot ever makes is his first solo and every pilots remembers it My opinion is that given correct training the 109 was safe to fly, its record shows that, with incorrect training it was dangerous but they all are. The B26 gained a terrible reputation for landing crashes purely because of its high landing speed, pilots ignored the manual tried to land too slow and crashed, is that the fault of the plane or its designer? It went on to have one of the best safety records of any bomber.

The b26 still had a higher accident rate (and fatality rate) than the b17,b24 and b25 right up to the end. Only the b29 was worse.

 

[MiTasol]

Procedures, man! The "Sabre dance" resulted from pilots using take-off techniques learned in straight wing aircraft that were inappropriate in the Sabre.

And that was the cause when the Sabre crashed into the Sacramento ice cream parlour in 72. The pilot over-rotated and stayed nose very high and on the runway right up until he hit the berm. From the Bee Archives: Old jet plane kills 22 in crash into Crossroads ice cream shop

Bob Hoover and the NTSB watched the news video at Leroy Penhalls Fighter Imports. Leroy's team put the aircraft on the register and sold it to a middleman who passed it on to the guy that crashed it. Leroy had refused to sell him the aircraft because he failed the T-33 training program.

Hoover said during flight trials at Edwards?? he travelled over-rotated the full length of that very long runway and there was no way the Sabre was ever going to fly.