Stability and Control characteristics of the Early Mark Spitfires

[CaptainDoggles]

Originally Posted by bongodriver

You just don't have the evidence that that is actually what happened for a start, and even if it did happen it only would have happened when the CoG was at the point it created the 'slight' instability i.e. with a full fuel tank, so the effect you talk about would be dependent on fuel burn, the less fuel in the tank the lesser the effect.

It's unstable unless the CG is in the forward position.

We just spent 46 pages hashing this out so I'm not going to get into it with you; don't bother replying.

Go back and read the thread; it's all there. This thread has devolved into fanboys re-interpreting the presented evidence into "merely a slight" instability because their egos can't handle it, so I'm not going to perpetuate it.

Ta ta

[bongodriver]

It's unstable unless the CG is in the forward position.

Which is pretty much what I said

it only would have happened when the CoG was at the point it created the 'slight' instability i.e. with a full fuel tank

A full fuel tank is what makes the CoG move back, as the fuel empties the CoG shifts forward and the aircraft becomes more stable, it's got nothing to do with fanboyism, it's just plain and simple facts, I do CoG calculations as part of my day job remember.

This thread has devolved into fanboys re-interpreting the presented evidence into "merely a slight" instability because their egos can't handle it

No the pilot's notes also say it is 'slightly' unstable

[robtek]

The fuel tank is right above the line between the first and the second third of the wing, thats where the cog usually lies, so if it gets lighter the cog doesn't move at all, afaik.

[bongodriver]

Originally Posted by robtek

The fuel tank is right above the cog, so if it gets lighter the cog doesn't move at all, afaik.

CoG is not a stationary datum, the CoG is dynamic and will shift with change in weight, the datum you are talking about is the AC aerodynamic centre, the point at which all the forces act, if the CoG is behind the AC then the aircraft is unstable and vice versa, so....given the Mass of the engine sits ahead of the AC and the fuel is sligtly behind then any reduction in the combined weight will bring the CoG forward.

Sorry my mistake, AC is where lift acts and CoG where weight acts, but the point is the same.

I meant to add, the reason I believe this is the effect is because the only Weight and balance diagrams I have seen of the Spitfire place the fuel tank moment just behind the datum point, as fuel reduces then the moment weight is offset by the constant moment weight of the engine which I think we can all agree is ahead of the datum.

[TomcatViP]

Originally Posted by bongodriver

I meant to add, the reason I believe this is the effect is because the only Weight and balance diagrams I have seen of the Spitfire place the fuel tank moment just behind the datum point, as fuel reduces then the moment weight is offset by the constant moment weight of the engine which I think we can all agree is ahead of the datum.

You've probably seen a doc related to the AFT mounted tank of the spitfire, scarcely used on fighters but primal on the reco version.

[bongodriver]

Originally Posted by TomcatViP

You've probably seen a doc related to the AFT mounted tank of the spitfire, scarcely used on fighters but primal on the reco version.

No it was the diagram on this thread, and let's face it, if the fuel tank was forward of the datum then the Spitfire could not have possibly been unstable, so in this case I am argueing 'for' your cause.

[Al Schlageter]

If the early Spits were so tail heavy then why did the MkVIII have 22.5lb added (weight and mount) to the tail? moment arm 175.5"

[Al Schlageter]

Originally Posted by CaptainDoggles

Go back and read the thread; it's all there. This thread has devolved into fanboys re-interpreting the presented evidence into "merely a slight" instability because their egos can't handle it, so I'm not going to perpetuate it.

Ta ta

So a NACA engineer is a Spit fanboy?

"FIGURE 4.5. Supermarine Spitfire airplane. A high-performance fighter noted for its role in the Battle of Britain and throughout WW II, the Spitfire had desirably light elevator control forces in maneuvers and near neutral longitudinal stability. Its greatest deficiency from the combat standpoint was heavy aileron forces and sluggish roll response at high speeds. "

Some fanboys have a short memory.