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Originally Posted by winny
The simple answer is I don't know how the longitudal instability manifested it's self. As I understand it the BoB weight was specifically fitted because people were breaking spits when coming out of dives. As you say the bob weight didn't resolve the instability because it was an aerodynamic issue. So how could the pilot "make it happen"? Wasn't it happening all the time? I think it was Tim Viggors who recalled writing off a Mk1 spitfire simply by pulling out of a dive, the airframe was so badly bent it was un repairable. He was lucky, the usual result was you said goodbye to your wings.
Can you explain to me how fitting a bob weight would correct an aerodynamic problem? I've never claimed to be an aerodynamics expert and tbh it doesn't really interest me. Despite this, I'm learning quite a bit from this thread.
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As I understand as weight gained by the time of the Spitfire V's appearance, the airplane tended began to overreact itself in pitch. In short the amount of pitch to stick movement / physical effort on the stick was not linear, and the aiplane 'tightened up' the turn on its own. It wasn't the oscillations ripping apart the plane in the dive, but the fact that pilot could rapidly exceed the safe g-limit of the aircraft due to this. He pulled a bit on the elevator, he pulled 3 g; a bit more which felt natural to be 4 g and he pulled 6 g in fact, and the aircraft accelerated in the turn, increasing the force and he soon found himself either spinning or breaking up the airframe. That's just how a longitudally unstable aircraft reacts, especially as the loadings in the airframe - guns, radios, armor etc. increase - the CoG shift s backwards, making the plane even more unstable. The bob weights progressively increased stick forces, so he was less likely to do that.
At least that's my layman's understanding of it.
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The reason I ask is that in Morgan and Shacklady there are numerous mentions to the inertia weight, and none of them mention instability, they all however mention pulling out of high speed dives and that it was too easy to break the A/C because of the elevators being so light.
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Yes that's pretty much why I raised this thread. When I fly different aircraft, I want to feel they react different. I want a Spitfire, a Hurricane, a 109 whatever all handle different, good and bad, I want to learn how to fly them, that's what a sim is all about, right?
Right now they all seem to respond all the same, as if there was a generic handling code which kills the whole point.
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I thought the instability was more of a twitchy thing, as mentioned in the Rechlin trials? Specifically the "suffers from quick changes of trajectory along the vertical axis, coming from high longitudinal thrust momentum, and significantly disturb aiming" bit and the reference to "bad elevator and rudder stability on the target approach". So was the impact of the inertia weight a double edged sword? Ie it resolved the dive problem and softened the elevator problem?
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Instability/stability characteristics as I understand are about how much the plane moves more (or less) around its axis than its supposed to. Move the stick in one direction, and a positively stable plane stops movement after a while and sets in a stable new course (good for a bomber), a neutral one keeps turning the same, and an unstable one starts turning faster and faster. The latter is good for manouverability, since you can initiate a turn very fast (no delay), but not so great if you want to fly accurate (for aiming), or hold a steady turn and fly near the stall.
As a sidenote, its funny to read German and British test reports on the other guy's plane's control characteristics. In short the Brits write the 109 is too stable, the Jerries write the Spits are too unstable. Go figure, it simply means they had a very different understanding what control characteristics are good for a fighter.
Now stick forces are a different thing, the 109 in pitch required rather high stick forces (20 lbs/G), which is good from the POV it prevents you from whacking the aircraft in dive recovery by pulling to many Gs, at lower speeds the amount of physical effort naturally feels just about right for a given movement, but it is more tiresome for your arms and can even limit you in maximum G (which is kinda the point). In comparison the Spit had very light stick forces in pitch, around 4 lbs /G, which made manouvering a physically easy thing and which you could do without your muscles become tired, but at the same time it presented a danger that if you pulled the stick too far backwards in dive recovery (nothing like high physical resistence there to prevent you) you could easily break the aircraft in two or stall in turns for pulling too much G.
Now in Cod and also in Il2, one of the most annoying thing is that the Spits light elevators are not being modelled. No matter how I tried, I could not break the airframe, even with the stick in maximum deflection. At 4 lbs/G you should be able to do that easily in a dive, by pulling around 13 g. At lower speeds, at this point you are probably stalled and spinning out of control, since no aircraft can pull that much without stalling unless the speed being very very high (stall speed iirc goes up with the square?).