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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.Well, I obviously know that. It was just an instinctive guess.
Regardless, what caused the control-reversal?
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?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.
Explain your logic for 'much more complicated', please.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.
Facts to support 'presumably' and 'only seem' would be nice.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.
explain 'seems to have changed' from straight line relationship. Conclusions regarding acceleration force of 3G?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.
I believe the phrase was 'control reversal' - well illustrated in Horkey's graphics between Push and Pull forces plotted for CG and airspeed.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
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.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?
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?
Hi Bill,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 believe the phrase was 'control reversal' - well illustrated in Horkey's graphics between Push and Pull forces plotted for CG and airspeed.
Explain your logic for 'much more complicated', please.
It said words to that effect in the report I posted, ''considerable forward pressure on the stick'' was required to stop the aircraft from tightening it's turn which I assume means it'll rapidly enter a flat spin if not corrected.Actually at stick force per G reaches zero, there is a control reversal where fwd pressure on stick is required to maintain the turn
explain 'seems to have changed' from straight line relationship. Conclusions regarding acceleration force of 3G?
It is quite clear in Horkey's discussion in which the stick force steadily decreases from positive to zero, then continues to a 'push; on the stick as turn accelerations increase with aft cg condition.Hi,
The Test report 4-43-23-1, Sect 3. b "violent (!) pullouts or tight turns must be carried out with caution as stick loads rapidly reverse; with the fuselage tank half empty these manoeuvres may be executed in practically the normal manner".
This would indicate that the "stick load" change from "practically normal" to "reversed" above half fuselage tank full.
See above.Sect 6.c
Sect 6.d . These parts describe the change of handling at Full and Half tank contents. The emphasis is on the CHANGE of handling with Full Tank that occurs at "three (3) to five (5) "G" with Full tank.
Therefore, with the above (sect 3.b and 6.c/d) it would seem that the variation of C of G made a big difference in the handling.
No, but enough information that NAA developed Bob Weight for control stick to alleviate some of the 'impending reversal' notification. Unfortunately the necessary flight safety provisions ranging from Dorsal Fin and Reverse Rudder Boost Tab and Bob Weight chipped away at the superb handling qualities of the Mustang.Unfortunately, no detailed figures or graphical information.
Eng
Yes, and No. Mathematically Horkey's plots as shown are of Mustang calculations. In a perfect fluid, they would be linear as shown. In the real world, constantly varying turbulence motion air is an everchanging influence on flight controls, particularly in a turn in which the aerodynamic loads are asymmetrical. The 'high' wing is at a relatively higher AoA, more CL and more drag than the lower wing - requiring rudder input to trim the turn as contrast with a skidding turn.Hi,
I feel that the handling described in the Eglin test report 4-43-23-1 is much more complicated than the illustrations and text in Horkey's information that you posted.
Eng
see post 213. That said, most of the B-15, C-10, mid block D-5 & Subs had the Bob weight delivered at factory before July 1944.So, that big pdf is the Technical order No. 01-60J-29 dated 18 September 1944 North American-Installation Of Elevator Inertia Weight-P-51B, P-51C And P-51D.
The modification introduces an approx 20lb lead "inertia weight" onto the elevator control run.
I believe this shows that the P-51 aircraft did not have such a weight in the elevator before this modification.
The addition of the weight is likely to have increased the stick loads to pull positive G, enough to prevent stick force reversal with a full rear fuselage tank on these aircraft.
Eng
Yes, and No. Mathematically Horkey's plots as shown are of Mustang calculations. In a perfect fluid, they would be linear as shown. In the real world, constantly varying turbulence motion air is an everchanging influence on flight controls,
WRT the flight test itself, the original fuel tank did not have an internal baffle to retard rapid changes internally of center of mass of the AvGas as it reduced from full. That could be particularly 'interesting at about 60-65gal where the real time center of mass fluctuates due to accelerations.
I thought the dorsal-fin root extension was a net positive across the board, fascinating.Unfortunately the necessary flight safety provisions ranging from Dorsal Fin and Reverse Rudder Boost Tab and Bob Weight chipped away at the superb handling qualities of the Mustang.
I thought the dorsal-fin root extension was a net positive across the board, fascinating.