A newbies impression of the 109 and spit

[NZtyphoon]

Originally Posted by robtek

All this writing, or better copy 'n pasting, doesn't change the fact that the stick forces and stick travel for the elevator control in the early marks of the spitfire were too low and that has been changed in the later marks with the "BoB-weights".

If the low forces in connection with the small travel weren't regarded as dangerous, no change would have been necessary!

The reason bob-weights were adopted was because several Spitfire Vs had been destroyed through poor loading at squadron level; this has been explained by Supermarine's Chief Test pilot Jeffrey Quill, although some Spitfirephobes consider him to be so totally biased he's incapable of telling the truth Of course we have to believe these "experts' such as Crumpp or Barbi, and not Quill, who was the chief propagandist of the Spitfire:

In general configuration the Mk I and Mk II production aeroplanes were almost identical to the prototype and so there was no problem with their stability. (231-232)

The Mk III Spitfire did not go into production, but the success of the bobweight experiment in curing its instability...opened up the possibility of its use for later marks of Spitfire....which was just as well as we had to...respond to a nasty situation which developed in 1942.

The Mk V aircraft was...in full service with Fighter Command and,...a fair amount of additional operational equipment had gradually crept into the aircraft, most of it stowed within the fuselage. The aftmost acceptable position for the aircraft's centre of gravity had been fixed in the normal course of flight testing by the firm and by the A & AEE....Any rearward movement of the centre of gravity in service, for whatever reason, would begin to destabilise the aircraft. Therefore, for each sub-variant of the Mk V detailed instructions for the correct loading of the aircraft were issued to squadrons....However the importance of these loading instructions was not generally appreciated in squadrons and in the daily round of operational activity they tended to be disregarded....

There was thus a real chance that, as of that moment, in almost every squadron in the Command Spitfires were flying in a dangerous state of instability....Up to that time there had been a distressing and increasing incidence of total structural failure of Spitfires in the air, which was causing great concern in the MAP and especially at Supermarine. (pages234-235)

Once the bobweights had been introduced and, in later marks, the modified mass balances on the elevators...it was statistically established that, as soon as the longitudinal stability of the Spitfire was thus brought under control, the problem of the unexplained breakings-up of aircraft in mid-air,...'softly and suddenly vanished away'. (page 238 )

To say that they were adopted because of inherent design problems with the Spitfire Is and II is wrong; they were used on the Spitfire III because it had developed cg problems and adopted in Spitfire Vs because of poor loading and increased equipment.

[robtek]

Originally Posted by NZtyphoon

The reason bob-weights were adopted was because several Spitfire Vs had been destroyed through poor loading at squadron level; this has been explained by Supermarine's Chief Test pilot Jeffrey Quill, although some Spitfirephobes consider him to be so totally biased he's incapable of telling the truth Of course we have to believe these "experts' such as Crumpp or Barbi, and not Quill, who was the chief propagandist of the Spitfire:



To say that they were adopted because of inherent design problems with the Spitfire Is and II is wrong; they were used on the Spitfire III because it had developed cg problems and adopted in Spitfire Vs because of poor loading and increased equipment.

Sorry NZTyphoon, but to say that the bobweights were introduced because of the "poor loading ad squadron level" sounds absolutely unconvincing to me.

The bobweights were used to reduce the ease of motion when actuating the elevators, reducing this way the possibility to inadvertently overstress the airframe, regardless of the flightsituation (spin, overspeed or else).

[NZtyphoon]

Originally Posted by robtek

Sorry NZTyphoon, but to say that the bobweights were introduced because of the "poor loading ad squadron level" sounds absolutely unconvincing to me.

The bobweights were used to reduce the ease of motion when actuating the elevators, reducing this way the possibility to inadvertently overstress the airframe, regardless of the flightsituation (spin, overspeed or else).

It might sound unconvincing to you but its the truth - unless, like some others on this forum, you believe that you are more of an expert on the matter than Jeffrey Quill.

[JtD]

It is always possible to exceed safe margins through improper loading, but in case of the Spitfire, this margin was small by design; and if it is impossible to maintain safe limits in everyday service, it is a design problem. Saying it was just improper loading, or saying it was just faulty design for that matter, imho only is half the truth.

[MiG-3U]

Originally Posted by JtD

It is always possible to exceed safe margins through improper loading, but in case of the Spitfire, this margin was small by design; and if it is impossible to maintain safe limits in everyday service, it is a design problem. Saying it was just improper loading, or saying it was just faulty design for that matter, imho only is half the truth.

In some degree I agree, the same revised loading table also has limits for the modified elevators:

1. With modified horn balance elevator (Spitfire modification No. 789): - 9.0 in. aft of datum point.
2. With Westland convex elevator (Spitfire modification No. 743) - 8.2 in. aft of datum point.
Note: - 1. & 2.apply to all propellers no elevator inertia device should be fitted.

So there indeed was design changes to solve the problem but I won't call that as a design problem because the loading needs grew over the original specification.

Over and out

[NZtyphoon]

Originally Posted by JtD

It is always possible to exceed safe margins through improper loading, but in case of the Spitfire, this margin was small by design; and if it is impossible to maintain safe limits in everyday service, it is a design problem. Saying it was just improper loading, or saying it was just faulty design for that matter, imho only is half the truth.

I think you're right about the narrow cg margin, not forgetting that when the Spitfire was designed in 1935-36 features like CS propellers, armour plate, armoured windscreen, IFF - even apparently small details such as extra ducting for gun heating equipment, shrouding for the gun bays etc - were three to four years into the future. Compare the equipment loaded into a pre-war Spitfire I with that loaded into a 1942 Mk V and the margin for error must have been relatively small.

Does anyone have any idea of how the Spitfire cg margins compare with (say) the P-51?

[MiG-3U]

Originally Posted by robtek

Sorry NZTyphoon, but to say that the bobweights were introduced because of the "poor loading ad squadron level" sounds absolutely unconvincing to me.

The bobweights were used to reduce the ease of motion when actuating the elevators, reducing this way the possibility to inadvertently overstress the airframe, regardless of the flightsituation (spin, overspeed or else).

http://target4today.co.uk/_posted_im...11/CoG_Iab.jpg

The inertia device (bob weighs in other words) was not needed if the CG was forward enough and the later marks, (VIII, IX...) did not have the device because the heavier engine moved the CG forward, 4-5 in. aft of datum point, except rare case of rear fuselage tank.

It can be said that the original CG limits were too aft with Rotol propeller and longitudal stability suffered, hence warnings in the early version of the Spitfire II manual. However, warnings were removed once the limits were revised.

Over and out

[robtek]

Originally Posted by NZtyphoon

The reason bob-weights were adopted was because several Spitfire Vs had been destroyed through poor loading at squadron level; this has been explained by Supermarine's Chief Test pilot Jeffrey Quill, although some Spitfirephobes consider him to be so totally biased he's incapable of telling the truth Of course we have to believe these "experts' such as Crumpp or Barbi, and not Quill, who was the chief propagandist of the Spitfire:



To say that they were adopted because of inherent design problems with the Spitfire Is and II is wrong; they were used on the Spitfire III because it had developed cg problems and adopted in Spitfire Vs because of poor loading and increased equipment.

The text you quoted, nztyphoon, says that the Spit1a b and the spit 2 had no stability problems and then continues with the cog problems of the spit 5.

There is nothing wrong with this text, but is it really applicable to this topic?

If the spit2 didn't had have stability problems, as you quoted, why were bobweights mounted?

[Crumpp]

Bob-weights have absolutely nothing to do with CG limits. The stabilty margin will shift with CG limits and the early mark Spitfire did have stable load conditions.

However all of that is completely irrelevant. CG shirts from consumption of consumables like oil and avgas. The NACA was well aware of all these characteristics and could do weight and balance.

The solution for the unacceptable and dangerous longitudinal instability of the Spitfire was bob-weights. These were added not because the NACA made a mistake in some half baked theory on weight and balance calculations. They were added by the RAE to correct a serious stability and control issue with the design.

[bongodriver]

The solution for the unacceptable and dangerous longitudinal instability of the Spitfire

Do you have a source showing thes unnacceptable and 'dangerous' in particular used to describe the Spitfire?