Oh right, thanks for clearing that up. I understand now
X axis is aoa and y axis is coefficient of lift.
Hope that helps. By the way since the data points are all on the same x axis it means that the tip and the root has the same Aoi
And by the way. This graph represents modern day P-51s with fuselage tank removed. So we can't use it for our aoa discussion since a2a p-51 has the fuselage tank.
Lol one more note. I found CLcruise in other documents to say 0.3 - 0.5 and we have no idea what load config the CLcruise of 0.2 calculated at.
Oh wait, hold on a minute. Okay, maybe I don't fully understand, since I'm not quite getting that ~ +0.5 AoA you arrived at (though I did follow you up to the hump, which indicates buffet and stall). Looking at "CL vs Alpha" graph, if Cl Cruise is 0.2, then reading 0.2 in the Y axis puts AoA at pretty much close to 0. Then, referencing the third graph, the points there are in the 0 to -0.1 range (implying possible negative AoA)? Also, while the graph is based on a modern P-51 with the fuselage tank removed and is therefore irrelevant, I was still just thinking: A rear fuselage tank would put the P-51 tail heavy, no? (hence the nose down trim for take-off). Wouldn't this require a more pitch down attitude (an even lesser angle of attack) then to keep the thing level? Sorry if I'm all over the place with this. It's just that for some reason, those graphs make me feel that a negative AoA seems somewhat plausible, even if it's based on a modern P-51.
Don't read this while your driving by the way, lol.
LOL, ok at the comp and not driving...
Looked at the graph again and it does infact look like cruise at 0.2 CL is at zero aoa. Still better than the -1.67 degrees. I wish there was more info with the graph to establish what factors helped to calculate CLcruise. After many hours searching the web that one graph is the only place I was able to find any mention of the Coefficient of lift durring cruise (CLcruise) for the P-51. I was infact able to find numerous pages from flight tests that have CLmax, which makes sense, since they designed this plane to be a dogfighter, but any mention of CLCruise is limited to that one paper. I still find it hard to believe that the P-51 can maintain level flight, under a typical weight at a cruise power setting with 0 AoA. But it is still alot more believable than -1.67.
In regards to the third graph... This is the amount of pitching moment (torque) or pitching moment coefficient (CM) the airfoil (wing) exhibits at certain AoA. This would help define dynamic longitudinal stability and this force would need to be countered by the horizontal stabalizer and elevator. This would have a very small effect on cruise AoA, so you can ignore that graph.
In regards to with or without the fuselage tank....
If aircraft weight and airspeed remains a constant, then by moving CG foreward (within the CG limits), will make cruise AoA increase and by moving it rearward (within the CG limits), will make cruise AoA decrease. But also, by increasing aircraft weight without moving CG, will make the cruise AoA higher. So, depending on where the fuselage tank sits along the Longitudinal axis in relation to the aircrafts empty CG and the wings Aerodynamic Center Of Lift will determine how much difference the fuselage tank will make to the planes AoA at cruise.
Ouch that hurt...
I still didn't answer your question about the fuselage tank... If we had the weight and ballance worksheets for the P-51 with the length that the fuselage tank sits along the longitudinal axis from the CG, then we would have the arm, with that we could determine the weight of the tank filled and empty and then we could come up with the moment of inertia for a full tank, an empty one and no tank and calculate the effect it would have on the AoA.