Originally posted by Straiga
Also when you shoot the tail off an airplane the nose of the airplane will pitch down, not up. Because a resultant tail down force is produced by the horizontal stab to balanced airplane. The airplane first of all has a very heavy engine in front this makes for a nose down situation, second the center of pressure on the main wing moves aft at higher airspeeds this still makes a nose heavy situation you now need the horizontal stab to do its thing in the opposite direction to balance every thing out in flight, so when you shoot the tail off the nose pitches down not up. Just threw that in.
Hi Straiga,
I believe the behaviour of the aircraft in AcesHigh in that respect is correct. I think there may be some confusion in this discussion regarding the system of forces involved for the stability of an aircraft, particularly when you try to apply that to explain what happens when the tail has been shot away.
Allow me to explain what happens… Let's assume that you are flying along, minding your own business, in level flight at constant speed. Further assume that the forces on your aircraft are balanced. The prop’ thrust is balanced with drag, the lift with weight and so on. All the moments are balanced too, the pitching yawing and rolling moments are all in equilibrium. The nose down pitching moment caused by the weight and lift couple is balanced at the tail, and so on.
Now, since you raised the question about what direction the nose points when the tail goes away, let’s just think about those longitudinal pitching moments. Most folk, including you, think like this… During flight the weight and lift couple was trying to rotate the nose downwards, and the tail was preventing this from happening by providing a downward force. So, if we remove the tail, there will be nothing to prevent that rotation, and the nose will drop… Not so fast! That’s not what happens, you might not see this right away, so bear with me, I’m going to go slowly… But first, the flaw in that reasoning is that it overlooks the fact that the nose down pitching moment that existed during controlled flight, also goes away with the tail. You see, the tail wasn’t only responsible for the balancing moment, it was also indirectly responsible for the lift that produced the nose down pitching moment in the first place. Once the tail has gone, the forces normally associated with static/dynamic stability no longer apply… So what does happen?
Firstly, the wings are only producing lift when they are forced to do so by the control surfaces at the tail. Those surfaces (using a small force but long lever arm) rotate the wings against the airflow, forcing the wings to fly at an angle to the free air stream, thereby causing downwash, circulation, and thus lift. When the elevators go away with the tail, the lift goes away with it, and the wings weather vane, and no longer produce a nose down pitching moment. That all happens very quickly and only leaves an engine, with the wings and forward/mid fuselage acting as little more than dead weight that simply wants to fall downwards, with a propeller attached to it that is still producing thrust.
Now, all you really need to consider at this point is how a heavy lump of metal with a propeller attached to it would fall. I think most people can see intuitively, that the heavy lump would fall first, dragging the propeller behind it. An admittedly weak analogy would be the stable condition that arises with a man hanging beneath a parachute. The aircraft falls, dragging the prop behind it, and falls more slowly because the prop is producing thrust and slowing it down.
That's exactly what happens in AcesHigh... Kudos HT!
Hope that helps.
Badboy
