P-51 Tailwheel Question

[Kyleb]

Something that has always struck me as odd about the P-51 is how far forward the tailwheel is. On most taildraggers, it is way back towards the rudder post, but on the Mustang it is probably 3' farther forward than that. Looking at the fuselage geometry, there doesn't appear to be anything that precluded locating it farther aft, but there had to be a reason to give up that much wheelbase length and tracking stability.

Is there something in the aft fuselage that prevented locating the tailwheel farther aft? Was it a CG thing - moving the retractable tailwheel 3' (or whatever) forward was necessary to place the CG in an appropriate location?

[Cvairwerks]

Been along time since I was in the tailcone of a Mustang, but from what I remember, the cone tapers down fairly quickly and runs out of space for the gear if you go back much more.

[Archer]

The space further back in the tailcone is also used to hide a bit of metalwork to enable movement of elevator and rudder. Also, you don't need room just for the wheel, there's a bit more attached to it that enables it to be retracted, as Cvairwerks mentioned it may not fit within the width of the cone if you move it aft.

[k5083]

Might also have allowed them to install a beefier unit than, say, the retract t/w on late Spitfires, which was far aft, but was a dainty little thing that failed sometimes.

August

[BigGrey]

The size of the assembly was pretty big, This photo will show it.

Attachments

[r1830]

The P 51 tail wheel is most likely located further forward than other aircraft because of how much weight is on the tail. The radiator is well aft of the cockpit and CG making the weight imposed on the tail wheel fairly significant. Therefore a significant amount of structural framing is required to prevent the fuselage from being damaged if the tail comes down hard. It’s also why it has the shock absorber to absorb that load and disperse its energy over distance. The empty weight of the mustang is well over 7000 lbs.

The spitfire radiator was located in the wing and therefore much closer to the CG. If you look at the tail cone design of both airplanes, you will see the mustang has a lot more weight aft of the CG.

[bdk]

If you look at the tail cone design of both airplanes, you will see the Mustang has a lot more weight aft of the CG.

Weight aft of the CG changes the CG. No matter what, longitudinal balance (CG) has to be maintained near the wing's center of pressure.

I suspect the position was just one of the myriad of design decisions that were made. The Mustang was steerable and retractable from the initial design, whereas the Spitfire was not.

[r1830]

If you look at the tail cone design of both airplanes, you will see the Mustang has a lot more weight aft of the CG.

Weight aft of the CG changes the CG. No matter what, longitudinal balance (CG) has to be maintained near the wing's center of pressure.

I suspect the position was just one of the myriad of design decisions that were made. The Mustang was steerable and retractable from the initial design, whereas the Spitfire was not.

I agree with your statement that the CG has to be maintained to the wings center of pressure. However I was trying to point out that in regards to the spitfire and other aircraft most of the accessories are located closer to the CG, whereas on the mustang a significant amount of weight is located further aft of the CG (which is offset by the weight forward of the CG) and the wings location on the fuselage structure.

The design of the Mustang makes it in inherently heavier aircraft. The empty weight of a Spitfire is approximately 5100 pounds with a Takeoff gross weight of 6700 pounds, while the mustang empty weight is approximately 7600 pounds with a max takeoff weight of approximately 12,000 pounds. This required a heavier structure and tail wheel assembly. Looking at the difference in tire design and pressure it is clear the mustang had a much greater load on the tail wheel tire. If they put the tail wheel further aft it would have to be offset by weight upfront which would increase the overall weight of the aircraft and decrease the performance. I believe the design or location of the tail wheel in the mustang was two fold. It was designed to be much stronger than the Spitfire to support the load it was subject to and as a result it was located further forward to decrease its overall effect on the CG of the aircraft.

The mustang is a tail heavy aircraft. That is why they had to burn the fuel in the fuselage tank first otherwise the aircraft was nearly unrecoverable in a spin. Also power on spins are not recommended and as it required at least 5-6 turns to recover and minimum of 10,000 feet to recover. The rotational force from the radiator and fluid aft of the cg was hard to overcome even with idle power and full rudder.