Damn it Latrobe! You are being lazy!
Get your arse on this. We want to see one of your dogfight reviews on this! 
Yes, yes I am lazy. Thank you for noticing.

Been playing a ton of Planetside 2 and Secret World lately so haven't been on AH2 very much or checking the BBS very often. There seems to be quite a few of these review requests popping up in here! I love when people want to learn!

You're merge was not very good. You started your attack from his front quarter and this let him easily nose up into you (using very little of his speed doing so) and almost get a HO shot on you. What you should have done is leveled off to gain some speed. You were only cruising at 170mph and the Yak3 is pretty good at gaining speed quickly, so level off to gain some speed and check the status on the P-51. What's his alt? A little bit below us. What's his objective? This is difficult for me to determine since I wasn't there and have no idea what has been going on, but my guess from this film is he might be heavy with ords for the CV, or the field. Don't assume that though as he could very well be here looking for fighters to kill. If he's here for fighters, he will target our Yak. If he's here to bomb stuff then he might ignore us but more importantly he might be slow, and that's the other thing we want to figure out. How fast is he? As we gain our speed we want to figure out what speed the 51 is at. We can almost immediately determine that he is quite fast, so he's probably not carrying ords in which case he will most certainly be targeting fighters now. Now as we gain our speed we'll want to roll a little left to keep an eye on him and also start a very shallow turn into him to get behind him. We want to watch him carefully to see what he does. Will he ignore us and continue to the base? Or, will he turn up and into us? If he keeps going to the base then we can easily drop down onto his 6. If he comes up for us then we want to fly some lag pursuits and lag turns to fly towards his rear quarter. This will help save some of our speed while we force the 51 to use up his speed turning and climbing for us. Your merge with the 51, diving straight in on him from the front, gets you into a Head On pass and also throws away the vertical and horizontal separations you had that you would needed to start working the angles.
First turn back into him is very tight and this bleeds off a lot of what little speed you had. The 51 we saw had a ton of speed so this should have been a big hint to you that he had the ability to climb up to and you and then some. With the small amount of speed you had flying more passive with lag turns and lag pursuits would have been a good choice to save your speed. Wait for the 51 to make his move after he's climbed up. Let HIM waste speed while you gain speed. A Yak 3 can easily out maneuver a P51 so you can avoid his shots pretty easily. Luckily the 51 does not judge your speed correctly and doesn't capitalize on your stalling out.
First defensive turn starts out very good. Turning into him and up to create horizontal and vertical problems for him. The only problem is you reverse your turn a little early and this almost puts you right back into the 51s gun.
Now you seem to have recognized that you didn't climb with him the first time so you're not going to be able to do it a this time either. You do the right thing and break off him but then you make some mistakes. What you should have done is a shallow climb away from him. Get some speed up if you're low on speed and start working away at his altitude advantage. Wait until he makes the first move and comes in to attack you and then start your defensive turn. If he breaks off his attack run early, then break off your defensive turn and keep climbing away from him. What you did by split-s'ing back into him is not a good move. For one it loses you some of your altitude that you want to keep. You don't want to be intentionally losing altitude, you're opponent is suppose to be trying to force you to do that, don't do his work for him

. The other thing this is doing is wasting E (both kinetic and potential). As I pointed out you lose altitude (potential E) but maneuver of any kind, especially tight turns like you did through the split-s, use kinetic E (speed).
The 51 sees the mistake you made and he goes vertical to try and rope you. You almost bite but you realize you're not going to make that climb and do the right thing breaking off to regain speed. Again, a shallow climb away from him would be a great choice right here.
Second defensive turn and again it starts out perfect, turning up and into the 51 to create problems for him but again you reverse it just slightly too early. Had the 51 had slightly better gunnery he would have read your reversal the instant you did it and corrected for a brief shot opportunity. Still though, I think I should point out that the reversal on this defensive turn was much better than the previous one. You were only very slightly early on the reversal so it still would get a passing grade in my book.

Now some interesting things go on in this next turn. You see the 51 rolling over the top to come down for another attack run and you start your turn nicely and in fairly ok position. Your mistake is pulling hard into the 51 trying to get your nose on him. This gets you nose to nose with him and he could very easily shoot you (though you could shoot him too, but it's always best to avoid the enemies guns at all times). The 51 however does not shoot. This tells us he is possibly one of those pilots who does not shoot on head on passes. We can use this against him to win the fight! If we can't get into position to avoid a shot then we can just put our nose on him and he will likely hold fire (don't count on it 100% of the time though as he may change his mind about holding fire at some point). What I personally would have done in this situation is kept a loose turn going up and into the 51 and keep my lift vector behind his 3-9 line. This will help me get inside his turn as he comes down and force him to pull an ever tightening turn bleeding some speed while my looser turn has helped save some speed. This saved speed will help in neutralizing the altitude advantage he holds.
Now you are able to just get up to the 51s altitude and you fly perfectly for the next couple turns. When you get into the rolling scissors fight around the 5:07 mark one thing I did notice is your lift vector was either placed on or ahead of the 51. This works in this instance because the Yak 3 can turn tighter than the P51 so this tighter turning ability helps keep you inside his turn while you cut the corner to close distance by putting your lift vector on or ahead of him. Remember though that in a plane that has an equal or worse turning rate/radius (I still don't know which correct term it is

) that you want to keep that lift vector behind him to fly to his 6. Putting your lift vector on or ahead of them in those situations can have you overshooting them in seconds and putting you in a very bad situation.
51 makes a nice and clever decision to climb into the sun to give you very difficult shot but this only works if he can stay in the sun. Now that you have neutralized the altitude advantage he had you can now climb with him and you land some hits as he is forced to dive out of the sun.
Back into the rolling scissors again and you do a great job staying behind him and setting up shots. When the 51 reverses him turn and you overshoot him you make the right decision by going vertical. At these speed the Yak 3 has a climbing advantage on the 51. Climb up, roll over, and attack again just like you did.