Recurring Theme in WW2 Aviation

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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?
 

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.
 
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.
 

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.
 
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!)
 
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
 
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
 
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.
 
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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.
 
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.
 
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
 
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.
 
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.
 

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