Stability and Control characteristics of the Early Mark Spitfires

[Crumpp]

The Bf-109 is another thread.

This one is about the measured flying qualities of the early mark Spitfire. That means the ones in the game.

[Crumpp]

The British did not have Stability and Control Standards during World War II. Only the United States and Germany had them in place.

To determine flying qualities, the RAE relied upon the individual talent of the design firm and the opinion of its test pilots.

[Crumpp]

Thank you again Lane for posting those documents.

Problem is on a few in the discussion even understand the topic. For many it is a emotional affair riddled with fear their favorite gameshape will be somehow ruined.

I did not read the report but did look over the graphs from Lane's post. Here is what those graphs are telling us about the Spitfires Longitudinal stability in various conditions of flight.

Negative stability is divergent. Co-efficient of moment and Co-efficient of lift have an inverse relationship in a stable airplane. You can look at the Co-efficient of moment against Co-efficient of Lift plots in the other report Lane posted and see the slope is positive.

What does that mean in plain english. As the wing approaches CLmax, the Coefficient of Moment is well into the negative values and wants to push the nose down. Therefore, the pilot must pull the stick back to keep the nose up.

In a positive slope, as the wing approaches CLmax, the Coefficient of Moment is high in the positive values and wants to push the nose up. Therefore, the pilot has to push forward on the stick to keep the nose down.

This is confirmed behavior in our test flight document below.

[CaptainDoggles]

Originally Posted by Crumpp

Negative stability is divergent. Co-efficient of moment and Co-efficient of lift have an inverse relationship in a stable airplane. You can look at the Co-efficient of moment against Co-efficient of Lift plots in the other report Lane posted and see the slope is positive.

This is what I got from the report as well, but what I wasn't sure about was the difference between columns 1 and 2. Did they just run 2 trials at each flight condition and those are the results?

Additionally, it seems odd to me that in the "Engine Off" case, it appears stable in trials 5, 6, and 7 but #8 is not stable. All the other variable appear to be the same (flaps+gear are up, altitude is the same, trim set to -7.5).

Anybody know why that would be the case?

[NZtyphoon]

Originally Posted by Crumpp

The British did not have Stability and Control Standards during World War II. Only the United States and Germany had them in place.

To determine flying qualities, the RAE relied upon the individual talent of the design firm and the opinion of its test pilots.

Wrong, once again: the RAE did indeed have standards and supplied these to the aviation industry:




During WW2, however, the demands of production testing thousands of aircraft meant that each factory adopted its own techniques, designed to test aircraft to an acceptable standard, as quickly as possible, before delivery: this did not mean that there wasn't a standard set by the RAE, simply a divergence of ways in which it was done at a production level. The same thing happened in the 'States, each factory adopted a testing regime broadly following the NACA guidelines.

[lane]

Originally Posted by NZtyphoon

Nice find NZtyphoon!