Its kinda hard getting your hear around it but it happens on cars and motorcycles too at the limit with some types. When you are on the as coming out of a corner in a rear wheel drive rally car you are steering right on a left hand corner but the steering input is just to keep the angle of the car correct for powering out.
P-51 fuselage fuel tank (3 Viewers)
- Thread starter Barrett
- Start date
Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Thank You for posting those pages Bill,
Yes, plate II-1 is Static Stability and shows push or pull forces on the control stick for maintaining level flight with speed deviations away from level flight trimmed at 100mph, at different
CG, %MAC, as shown.
Plate II-1 cont'd shows a simple illustration of linear stick force per G at varying CG, %MAC.
Neither of these plates appear to represent the P-51 data.
Going back to the 4-43-23-1 Eglin test report of the P-51B aircraft with rear 85gal tank, we can see that the results were much more complicated. Although the results are not presented in a detailed or graphic way, we can read in section 6.c that, with a full rear tank, stick force reversal occurred above accelerations of between 3 to 5g. Presumably, below 3 to 5g the
stick force response was normal and, in fact, the criticism of handling only really seems to be aimed at tight turns and pull-outs. Going back to plate II-1 cont'd, we can see that stick force per G is shown there as a straight relationship, but here the relationship seems to have changed at about 3g. We know that the full rear tank is taking the CG, %MAC some 1.8" to 2.7" beyond it's normal rear limit. My guess is that the limitations and characteristics of the pitch control system pretty much bounded the normal 102" CG, %MAC limit, and so this extra weight so far aft was just causing the undesirable handling that is described. Fortunately, careful operation of the aircraft and crew training allowed the use of this great increase in capability.
Thanks for the extra info.
Eng
Yes, plate II-1 is Static Stability and shows push or pull forces on the control stick for maintaining level flight with speed deviations away from level flight trimmed at 100mph, at different
CG, %MAC, as shown.
Plate II-1 cont'd shows a simple illustration of linear stick force per G at varying CG, %MAC.
Neither of these plates appear to represent the P-51 data.
Going back to the 4-43-23-1 Eglin test report of the P-51B aircraft with rear 85gal tank, we can see that the results were much more complicated. Although the results are not presented in a detailed or graphic way, we can read in section 6.c that, with a full rear tank, stick force reversal occurred above accelerations of between 3 to 5g. Presumably, below 3 to 5g the
stick force response was normal and, in fact, the criticism of handling only really seems to be aimed at tight turns and pull-outs. Going back to plate II-1 cont'd, we can see that stick force per G is shown there as a straight relationship, but here the relationship seems to have changed at about 3g. We know that the full rear tank is taking the CG, %MAC some 1.8" to 2.7" beyond it's normal rear limit. My guess is that the limitations and characteristics of the pitch control system pretty much bounded the normal 102" CG, %MAC limit, and so this extra weight so far aft was just causing the undesirable handling that is described. Fortunately, careful operation of the aircraft and crew training allowed the use of this great increase in capability.
Thanks for the extra info.
Eng
While this will probably be wrong, and overly simplified: Is this almost like that the tail wants to keep going forward in a turn on momentum, and you end up doing a donut?
*scratches head* Is this something to do with neutral stability (no AoA change with speed when AoA is increased), deceleration (which drives up AoA), and potential effects of the tractor-prop on stability?
Last edited:
drgondog
Major
Explain your logic for 'much more complicated', please.
Facts to support 'presumably' and 'only seem' would be nice.
explain 'seems to have changed' from straight line relationship. Conclusions regarding acceleration force of 3G?
I believe the phrase was 'control reversal' - well illustrated in Horkey's graphics between Push and Pull forces plotted for CG and airspeed.
I am not a pilot so I havnt a clue about how it works in the air. On the ground in motorsport the car or bike is "balanced" between all the forces acting on its centre of mass, even though the back wheels arent following the front and the whole thing isnt pointed in the direction it is actually going, its a controlled slide. The input into the steering is just to maintain that balance. If ever you go to a kart track, even with the beginners type powered by 5 HP lawn mower engines, the steering is really heavy until you really start to corner on the limit and then it feels like the steering wheel is disconnected.
Hi. This is quite complicated really, because it is a case where the aircraft is being modified to operate beyond the normal limits where it handles in a stable and easily handled way.
The base line here is that for stability and normal handling in upright normal flight, the horizontal tail produces a downforce to balance the aircraft weight and the wing lift, the lift being behind the C of G weight and the tail pushing down a bit to balance. A simple stable aircraft has a generous amount of stability if the horizontal tail has plenty of effect available compared to the Lift/Weight couple. Now, high performance aircraft generally reduce the margins of control to minimise structural weight and drag, but must still handle well. However, if you take any normal aircraft and put more weight towards the tail, it becomes less stable because the horizontal tail has to generate smaller control forces to balance the aircraft. The normal C of G limit defines the normally acceptable handling range so, if you break that limit, you get into handling problems. In reality, this is a very complex subject.
Eng
