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-   -   A newbies impression of the 109 and spit (http://forum.fulqrumpublishing.com/showthread.php?t=31252)

bongodriver 05-13-2012 09:31 AM
Quote:
Originally Posted by Al Schlageter (Post 424642)
Some pilots had the slats were wired shut, but that was the exception not the rule.
Yes I just realised I meant disabled instead of 'removed', also it was an idea theorised by the americans on how the 109 might be improved after tests on captured aircraft.

MiG-3U 05-13-2012 09:34 AM
Quote:
Originally Posted by JtD (Post 424753)
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 05-13-2012 09:36 AM
Quote:
Originally Posted by JtD (Post 424753)
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?

robtek 05-13-2012 11:02 AM
Quote:
Originally Posted by NZtyphoon (Post 424569)
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 :rolleyes: Of course we have to believe these "experts' such as Crumpp or Barbi, and not Quill, who was the chief propagandist of the Spitfire: :grin:



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 05-13-2012 02:25 PM
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.

http://img832.imageshack.us/img832/2...htsresults.jpg

bongodriver 05-13-2012 02:38 PM
Quote:
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?

Crumpp 05-13-2012 07:38 PM
Quote:
Do you have a source showing thes unnacceptable and 'dangerous' in particular used to describe the Spitfire?
NACA......

Operating Notes....

RAE.....

Air Ministry....

Take your pick.

bongodriver 05-13-2012 07:57 PM
So you say the Spitfires own operating notes say it is an unnaceptable and dangerous aircraft?.......verbatim?.......post some scans.

IvanK 05-13-2012 10:48 PM
"Dangerous" I don't believe appears in the NACA Spitfire document that is imo an embellishment. The term unacceptable also needs to be qualified ... it was unacceptable to the criteria NACA was using.

Crumpp 05-14-2012 12:07 AM
Quote:
"Dangerous" I don't believe appears in the NACA Spitfire document that is imo an embellishment
No that is in the Operating Notes....

Quote:
The term unacceptable also needs to be qualified ... it was unacceptable to the criteria NACA was using.
Yes, the only defined standards in the world at the time besides the German's. Post-war, the RAE adopted the exact same standards as the NACA.

So, we can say in 1940, the RAE had no standards, they just knew they had a dangerous airplane so they warn the pilot often.

In 1946, the early mark Spitfires would have been labeled as "unacceptable" by the RAE but since they had to have bob-weights, there was no need.

You won't find a Spitfire flying today without bob-weights.


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