XP-51F/G vs P-51H length.

[BarnOwlLover]

I know that the P-51H was at least a foot longer than the XP-51F/G it was developed from. The added length from what I read was added to try and offset the directional stability problem that the Merlin Mustangs had that became more pronounced in the F/G during testing.

My question is where was the length added. The distance between the tail and the trailing section of the radiator scoop/duct seems about the same (and the ductwork seems to be about the same length). However, for sure, the nose on the P-51H was longer (engine was moved forward several inches for CG reasons). Thus, were was the added length added, and about how much fore vs aft?

 

[drgondog]

I know that the P-51H was at least a foot longer than the XP-51F/G it was developed from. The added length from what I read was added to try and offset the directional stability problem that the Merlin Mustangs had that became more pronounced in the F/G during testing.

My question is where was the length added. The distance between the tail and the trailing section of the radiator scoop/duct seems about the same (and the ductwork seems to be about the same length). However, for sure, the nose on the P-51H was longer (engine was moved forward several inches for CG reasons). Thus, were was the added length added, and about how much fore vs aft?

Front and back. The distance from tip of spinner to 1/4 chord line in wing
P-51B/D = 133 7/16"
P-51H = 139"

Distance from 1/4 chord line in wing to reference rudder datum
P-51B/D =253.87
P-51H = 261"

 

[BarnOwlLover]

One other thing I noticed is that the engine on the F/G seems to sit further back than on the B/D (based on engine cowling TE relationship to the wing), though the length was similar (a couple of inches longer) than the D model. Is this true, or are my eyes playing with me?

 

[Bedders]

What follows is the product of my own research as I try to create models of the Lightweights in 1/72.

The D length was 32' 2.5", and the F length was 32' 3". So basically the same overall (for 1/72 purposes). But the F was shorter in front of the wing than the D (the firewall having been moved backwards compared to the D), and longer behind the wing than the D, as the rear fuselage/radiator/tailwheel area was a new design. Apart from the propellers, the Gs (NA-105A) started out externally identical to the Fs (NA-105), but then got fin fillets and latterly got the big new tail unit, like the one on the H and J, which gave the Gs another couple of inches between the tailwheel well and the rudder post. I have cutaway fuselage drawings of the early G and the J, which show the additional frame at that point. But other than that the F, G, H and J were all the same length behind the wing, with the big changes for the H being at the top of the fuselage to create the smaller bubbletop. The H also had the firewall moved forward once again, to give it similar length to the D in front of the wing. (As far as I can see the angle of the firewall on the lightweights was more vertical than on the D.) The J (NA-105B) used the airframe of the late G, with that long Allison engine which made it 33' long overall. The H (NA-126), with the Merlin and the firewall moved forward, was 33' 4".

It's worth remembering that the J only flew well after the H, and was essentially an Allison engine mule using the G airframe. I suppose they could have used an H as the basis for the J but perhaps the firewall positioned further forward would have made the aircraft unstable with the very long Allison engine. Remember that the P/F-82 had the fuselages further lengthened behind the wing, presumably to compensate.

I have a question of my own. The fin on the F and early G is a different shape to that on the D, being slightly more vertical to give a bit more area. But height is similar to the D and the rudder is similar in shape to the D, albeit metal-covered rather than fabric. What I don't know is whether the original horizontal stabilisers on the F were the same as those on the D, or different. Can anyone help with that? I imagine that the stabilisers on the late G and the J were the same as on the H.

Justin

 

[drgondog]

What follows is the product of my own research as I try to create models of the Lightweights in 1/72.

The D length was 32' 2.5", and the F length was 32' 3". So basically the same overall (for 1/72 purposes). But the F was shorter in front of the wing than the D (the firewall having been moved backwards compared to the D), and longer behind the wing than the D, as the rear fuselage/radiator/tailwheel area was a new design. Apart from the propellers, the Gs (NA-105A) started out externally identical to the Fs (NA-105), but then got fin fillets and latterly got the big new tail unit, like the one on the H and J, which gave the Gs another couple of inches between the tailwheel well and the rudder post. I have cutaway fuselage drawings of the early G and the J, which show the additional frame at that point. But other than that the F, G, H and J were all the same length behind the wing, with the big changes for the H being at the top of the fuselage to create the smaller bubbletop. The H also had the firewall moved forward once again, to give it similar length to the D in front of the wing. (As far as I can see the angle of the firewall on the lightweights was more vertical than on the D.) The J (NA-105B) used the airframe of the late G, with that long Allison engine which made it 33' long overall. The H (NA-126), with the Merlin and the firewall moved forward, was 33' 4".

Before diving into details, what is your source pool of data - NAA or 'other'.For example 105-00001 Three View General Assy or something else? Is the regerence 1/4 chord location at FS 99? or?

It's worth remembering that the J only flew well after the H, and was essentially an Allison engine mule using the G airframe. I suppose they could have used an H as the basis for the J but perhaps the firewall positioned further forward would have made the aircraft unstable with the very long Allison engine. Remember that the P/F-82 had the fuselages further lengthened behind the wing, presumably to compensate.

The H was lengthened both in front of firewall and aft of wing. 6" more in front of A.C. and 7 inches lnger aft of A.C. than the B/D. The J had modified empennage from F/G and H (larger H.S)

I have a question of my own. The fin on the F and early G is a different shape to that on the D, being slightly more vertical to give a bit more area. But height is similar to the D and the rudder is similar in shape to the D, albeit metal-covered rather than fabric. What I don't know is whether the original horizontal stabilisers on the F were the same as those on the D, or different. Can anyone help with that? I imagine that the stabilisers on the late G and the J were the same as on the H.

Justin

The H.S. on G was different from H and H/F different from J.

 

[Bedders]

Before diving into details, what is your source pool of data - NAA or 'other'.For example 105-00001 Three View General Assy or something else? Is the regerence 1/4 chord location at FS 99? or?

The H was lengthened both in front of firewall and aft of wing. 6" more in front of A.C. and 7 inches lnger aft of A.C. than the B/D. The J had modified empennage from F/G and H (larger H.S)

The H.S. on G was different from H and H/F different from J.

Thanks for these clarifications. My sources are secondary rather than primary ones, and as I'm looking down the telescope from the UK I'm quite distant from the original sources. Also I'm a modeller rather than an engineer hence my probably rather woolly descriptions. So if there are good 3-views of F, G, H and J out there, I'd be very keen to see them.

Justin

 

[BarnOwlLover]

I wouldn't mind seeing them, too, as well as maybe engineering cutaway similar to the XP-51J that got posted here for the F/G, H, and the Merlin F-82s.