1990 tests; P-51/F6F/P-47/FG-1; all corner speeds close to max. level speed?

[Gaston]

   
    The Spitfire's advantage in "mushing" was described in company of the 3/4 inch stick top maximum pull range limit above 300 MPH, which, if exceeded, caused a very stable, full 3-axis control, high-speed "stall" that allowed to shoot easily inside the turning circle. Better than most other aircrafts in this respect... This is from an actual mid-late Spitfire flight test, not theories... (Probably a Mk V, but these characteristics were described as typical of all Spitfires.)

    In addition, with its slats deployed, the Me-109G has been quoted here as being capable of maintaining level flight in a continuous 40° nose-up attitude... Constant "mushing" in other words...
 

    The "lag roll" would indeed explain why Johnson rolled the opposite way to the target's turn, although I don't think he had much excess speed, since the 190 was higher, and the subsequent dogfight was quite prolonged. The term lag roll was never mentionned, nor climbing above the enemy, but it might make sense, if he assumed his faster P-47 would catch-up eventually, to buy extra turning room by rolling away from the enemy's turn.

    In any case, this instance would be the only time in thousands of reports that I hear of an attacker rolling opposite to a target's turn, and this happens to involve the very pilot who mentions, ambiguously to me; "mush-out a bit when you reverse your turn" and "Now pull hard. No mushing."...

    As for the 190D, that too seemed strange to me, but you read commonly from U.S. pilots, in early '44, about "modified" 190s, Me-209s, FW-290s "fighters" etc... Misidentification of non-existent types...

    Although I can't claim to know what Johnson was thinking, and thus I may very well be wrong, there are some factors that would tend to at least lean things towards "mush" being related to turn, not roll.

      1- "Mushing" is a common WW II-era term that is almost always related to turns, NEVER to roll. For roll, the more common terms would be; "lag", "soft", "delay" or "not crisp".

      2- At usual P-47 combat speed, which typically you would want above 200 MPH IAS, roll reverse lag is a negligible issue, especially in the P-47!

          Quote, Hitech;"2nd even though he does not state it, this roll reversal sounds like it is well below corner speed. I.E. he is at the Top of the lag roll. Because at corner speed I would have a very hard time believing the Ailerons felt soft."

          -For once we fully agree on this, because, as I explained earlier, the leverage of the engine's weight against the 30 foot distant elevators is obviously an infinitely bigger issue than the leverage of the weight of a 15 foot wing against the ailerons...

          At any reasonable combat speed that could be considered "typical", especially at the start of the fight, the "mushing" of the ailerons is simply not that big of an issue...

          The P-47's roll rate increased all the way to 230 MPH IAS+, and stayed high much further. Futhermore, the Razorback P-47 was NOT known for its slow roll reversal, and in fact I have read often that it was a particular strenght of the type...

          It just doesn't seem as being as big an issue as would be required for Johnson's quote, because unless the 190 reverses EXACTLY at the precise moment he reaches a 90° bank, it makes no difference whether his remaining 180° roll is right or left to reverse... Again, Hitech correctly pointed this out...

      3- Finally, I remember now yet another thing that made me lean towards a "mushing" turn interpretation of Johnson's words, rather than the simpler and more obvious "mushing" roll. This is said to be in his biography;

                                                   "When banking for a turn, the P-47 tends to auto-rotate."  This could have been;

                                                   "When banking RIGHT for a turn, the P-47 tends to auto-rotate."


              Now "auto-rotate" can mean one of two things; the nose drifts towards the bank side, which would be natural and would not require corrective rudder action. Hardly a problem worth mentionning...

              OR it could mean; the nose drifts OPPOSITE to the bank side, which would then open a whole new can of worms, because it would establish a link between the rolling action and the turn behaviour, which is what is not accepted here.

              So it could pay to have long "opposite" rolls, to drift the nose the (opposite) way you want, and this might affect how the turn will respond after a long 270° roll; with more "bite" (and reduced angle-off), perhaps because of a less disturbed prop airflow spiral? Hence; "pull hard. No mushing."

             At high altitudes, you don't expect many roll reverses from the opponent, because rolls are not as fast, so you start your roll OPPOSITE to the enemy's turn to drift the nose the right way, and so take out the angle-off and "mushing" with a full 270° opposite roll.

             At lower, more typical altitudes, you EXPECT the 190 to reverse at some point, so you match his roll side, knowing that, if he reverses, it will give you again the full 270° or 180° roll that drifts the nose the opposite way and takes out both "mushing" and angles.

             This matches my perception that "mushing" in turns was a P-47 problem (diminishing with speed) while the P-47 "mushing" in rolls is not a characteristic of the P-47 I have ever heard, on the contrary...

             
             I don't intend to defend this interpretation all the way to the Supreme Court, as I think the "roll" meaning is 80% more likely to be correct, but I would appreciate if someone could quote in detail Johnson's book, and tell me what is the meaning he intended for the P-47 "auto-rotating" in a roll...

            Gaston.
           

             
   

     

       

         
     

   

   

[Charge]

"The Spitfire's advantage in "mushing" was described in company of the 3/4 inch stick top maximum pull range limit above 300 MPH, which, if exceeded, caused a very stable, full 3-axis control, high-speed "stall" that allowed to shoot easily inside the turning circle. Better than most other aircrafts in this respect... This is from an actual mid-late Spitfire flight test, not theories... (Probably a Mk V, but these characteristics were described as typical of all Spitfires.)"

Let me explain why this is not accurate. First of all Spitfire has a 13% thickness ratio (NACA 2213/NACA 2209.4) wing profile i.e. thinner than other planes of that era. The relative thickess to other wings is nearly the same but aerodynamically its own thickness ratio is what determines how it behaves at extreme AoAs. In general the thickness ratio enhances the max AoA behaviour, to a certain limit, of course. If the wing had the same thickness (15-16%) as other aircraft of that era it would have been very thick (for that wing area) and the drag would have been excessive. Also the rather low relative thickness allowed the Spit to make a very fast dive even to the extent that the airframe was not able to withstand such speeds.

Secondly the elliptical planform is very good, if not ideal, in terms of dealing with drag but the negative side of such planform that has even span loading is that it loses all the lift at once in a stall. This, mildly said, disturbing feature was countered with 2 degrees wash-out (quite standard, as in P51 and FW190) which gave ample warning of stall. However due to overly sensitive elevator control it was still easy to pull too quickly too much AoA which caused a full span stall, although veteran Spit pilots were not likely to make such mistake. The bob weights in controls in later variants further helped in preventing this.

109's maximum level flying angle is claimed to be as high as 60 degrees (supposedly for G2 or G6). While it certainly had advange of its wing tip slats I find it somewhat hard to believe this and have never heard or read of this being used to advantage in actual combat.

-C+

[Stoney]

First of all Spitfire has a 13% thickness ratio (NACA 2213/NACA 2209.4) wing profile i.e. thinner than other planes of that era. The relative thickess to other wings is nearly the same but aerodynamically its own thickness ratio is what determines how it behaves at extreme AoAs. In general the thickness ratio enhances the max AoA behaviour, to a certain limit, of course.

Generally, thinner airfoil sections stall faster than thicker airfoil sections.  Certainly most 15% sections stall later than 13% sections.

If the wing had the same thickness (15-16%) as other aircraft of that era it would have been very thick (for that wing area) and the drag would have been excessive.

Compared to what?  The P-51 profile was thicker and even at maximum thickness at the root chord, the P-51 had less profile drag at the design lift coefficient.  The P-47, Corsair, Hellcat...even the 190 had a thicker root chord and the common 23015 section they shared had lower profile drag.  The Spitfire turbulent airfoil is a section that possesses an extremely high profile drag coefficient compared to most other NACA airfoils.

Secondly the elliptical planform is very good, if not ideal, in terms of dealing with drag but the negative side of such planform that has even span loading is that it loses all the lift at once in a stall. This, mildly said, disturbing feature was countered with 2 degrees wash-out (quite standard, as in P51 and FW190) which gave ample warning of stall.

 

And, in doing so, Supermarine eliminated the only advantage the planform offered.  With the washout built into the wing, the elliptical lift distribution was lost, and the Spitfire laid claim to a wing that ranked as one of the highest drag wing designs in the war.

[hitech]

Gaston: I have a few question.

1 Do you wish to learn basic physics

2 Do you believe physics will never change and can not be ignored in any evaluation of flights?

3 Do you wish to understand basic terms as they relate to flying?

HiTech