A newbies impression of the 109 and spit

Putting weights to the tail for what purpose?

[NZtyphoon]

Originally Posted by 41Sqn_Stormcrow

Putting weights to the tail for what purpose?

Better to say inertia weights (or bob weights) were added to the control circuits of the elevators - I'm not sure if later Spitfires with the bigger elevator mass balances continued to use them.

[winny]

Originally Posted by 41Sqn_Stormcrow

Putting weights to the tail for what purpose?

The weight was built into the elevator circuit, in simple terms it was used to counteract the effect of light elevators and high g forces. The weight was effected by the g forces so if there was a high load the elevators needed more force to move them.

It was fitted to spitfires to solve the problem of spitfires breaking up when pulling out of a high speed dive, which was a known, and big problem at the time.

Because the elevators were so light pilots were pulling out of the dives and over stressing the airframe. There were loads of examples of this happening.

So basically the more g that was pulled the harder the elevators became to move. As far as I know it had nothing to do with any instability.

Thanks, winny. That is now pretty clear to me. Wouldn't have made sense to put weights to the tail in order to improve stability. It would just worsen it.

[winny]

Originally Posted by 41Sqn_Stormcrow

Thanks, winny. That is now pretty clear to me. Wouldn't have made sense to put weights to the tail in order to improve stability. It would just worsen it.

Yeah, it was only a small weight, 3.5 or 6.5 lb, depending on which wing was fitted, the lighter was for browning wing heavier for cannon wing, added to the actual control cables. It was about 3 quarters of the way down the fuselage.

[IvanK]

"The stall warning possessed by the Spitfire was especially beneficial in allowing the Pilot to reach maximum lift coefficients in accelerated maneuvers. Because of the neutral static stability of this airplane, the pilot obtained no indication of the lift coefficient from the motion of the control stick, nevertheless, he was able to pull rapidly to maximum lift coefficient in a turn without danger of inadvertent stalling...."

A nice feature in a fighter !

[Al Schlageter]

If the Spitfire was such a terrible a/c, at least according to Eugene, why did the USAAF accept them for service?

[Crumpp]

You might find the following RAE comments of the NACA test to be of interest, in case you havn't already seen them.

You might find the following information useful....

Gilruth's developed the concept of stick force per G, control movement measurement, and pretty much wrote the standards of measurement for stability and control as used by the NACA.

Only two nations in the world had stability and control standards during World War II, the United States and Germany.

The NACA's measurement and classification system developed by Gilruth was not published until 1941 and was classified. It was not released to Allied Nations until 1943.

Even Gates, a very prominent RAE researcher who pioneered stability and control standards for the RAE was not privy to them during his 1942 "dash around America" tour of the United States research facilities. Gates was the one who defined Aerodynamic Center, stability margin, and maneuver points during his lifetime. He had a passion for stability and control and published some 130 papers before his death. Before him, the neutral point was termed the metacentric ratio.

Unfortunately, nobody at the RAE paid much attention to Gates and it was not until post war that the United Kingdom adopted any defined standards of what is acceptable and what is not in terms of stability and control. When they did, it was a mirror of Gilruths work at the NACA.

So, by what standard is the RAE refuting the NACA? The answer is really none. The RAE had no defined standards of stability and control except subjective opinion.

[NZtyphoon]

Originally Posted by Crumpp

You might find the following information useful....

Gilruth's developed the concept of stick force per G, control movement measurement, and pretty much wrote the standards of measurement for stability and control as used by the NACA.

Only two nations in the world had stability and control standards during World War II, the United States and Germany.

The NACA's measurement and classification system developed by Gilruth was not published until 1941 and was classified. It was not released to Allied Nations until 1943.

Even Gates, a very prominent RAE researcher who pioneered stability and control standards for the RAE was not privy to them during his 1942 "dash around America" tour of the United States research facilities. Gates was the one who defined Aerodynamic Center, stability margin, and maneuver points during his lifetime. He had a passion for stability and control and published some 130 papers before his death. Before him, the neutral point was termed the metacentric ratio.

Unfortunately, nobody at the RAE paid much attention to Gates and it was not until post war that the United Kingdom adopted any defined standards of what is acceptable and what is not in terms of stability and control. When they did, it was a mirror of Gilruths work at the NACA.

So, by what standard is the RAE refuting the NACA? The answer is really none. The RAE had no defined standards of stability and control except subjective opinion.

Still doesn't prove the Spitfire was a dangerous aircraft to fly; apart from that I'd like to see Crumpp provide some documentary evidence that Spitfires regularly broke up in flight during spin recovery.

[Kurfürst]

Originally Posted by winny

The weight was built into the elevator circuit, in simple terms it was used to counteract the effect of light elevators and high g forces. The weight was effected by the g forces so if there was a high load the elevators needed more force to move them.

It was fitted to spitfires to solve the problem of spitfires breaking up when pulling out of a high speed dive, which was a known, and big problem at the time.

Because the elevators were so light pilots were pulling out of the dives and over stressing the airframe. There were loads of examples of this happening.

So basically the more g that was pulled the harder the elevators became to move. As far as I know it had nothing to do with any instability.

As I understand and from RAE papers the installations of bob weights to the elevator and longitudal instability were related. To my best understanding - and do correct me if I am wrong - instability means that if you pull the controls (in whatever direction), the aircraft will not only change its roll/pitch/yaw to the extent of control movement, but also keep increasing it on its own, as if there were some kind of inertia/acceleration going on. This was noted on Spitfire Vs by the British.

By adding the bob weights and making the controls progressively harder to move for greater deflections, it made this increased acceleration problem more difficult to encounter.. It did not cure the instability itself, which was an inherent aerodynamic feature of the design, but made it harder for the pilot to make it happen.