As BigRat said, the problem isn't the flaps, it's combat trim adjusting to your slower speed without taking the flaps into consideration. Without the flaps, combat trim would set the elevator for level flight at your current speed with the stick centered. Because you have flaps down combat trim causes you to pitch up and you have to push the stick forward for level flight.
A quick fix is to map combat trim to a button and turn it off before you use flaps. This is easy to do and easy to forget to do.
You can also turn off combat trim and briefly use auto level to set your trim to cruise speed before the merge. This will give you some nose heavy trim for the fight which is generally a good idea. In addition to fixing your problem it also lets you avoid any deadband at stick center when you're making fine adjustments to your aim. You just pull more or less instead of push/pull across the dead spot.
Yep, what FLS and BigRat have posted above.....
I have flown he F4U-1 since it first showed up in Aces High, and prefer it over all other F4U models......with that said, I approach the combat trim vs flaps fighting each other in the following way:
upon launching my F4U-1 and taking of / grabbing altitude, I will normally use auto climb as well as use combat trim turned on, as I am inbound to my target or patrol area. Now as I get closer to where I am going to be patrolling or dogfighting, etc... I will level out and build my level flight cruise speed up to between 310 mph IAS upwards to 330 mph IAS ( IAS = Indicated Air Speed = the WHITE MPH needle ), now once I have reached this desired 310 to 330 IAS speed while having CT ( combat Trim ) enabled and in level flight with no stick inputs ( be sure to have no aileron input, no elevator input, no rudder input), disengage CT (Combat Trim )!!! Also, be sure to not be using WEP either, while setting your desired speed / trim.... WEP being on will just throw your trim off a little and make it less beneficial once you start to dogfight
The reason I set my controls / trim up in this manner is for several reasons, FLS mentioned it slightly in his above post when he said:
You can also turn off combat trim and briefly use auto level to set your trim to cruise speed before the merge. This will give you some nose heavy trim for the fight which is generally a good idea. In addition to fixing your problem it also lets you avoid any deadband at stick center when you're making fine adjustments to your aim.
Another tip: if you are flying towards some enemy planes and you do not have quiet enough speed built up to get your controls trimmed out and set properly, you can engage combat trim , make sure all flaps are up/in and hit WEP and put your F4U into a slight shallow nose dive ( nose just slightly below the horizon so you do not give up a lot of altitude ), carefully watching the speed increase to 310 IAS and keeping your stick inputs to a minimal, just maintain wings level..... Once you hit around 310 IAS disengage WEP first, then disengage CT.................continue in your shallow dive for a couple more seconds before leveling out and climbing back up to your desired altitude......
As FLS posted, it is easier to shoot at your bogey, when you have a gentle pull on your joystick which makes it much easier to steady your piper/bore-sight and hold it on your target, verses trying to fight the Combat Trim / Flaps struggle of pushing and pulling your joystick trying to hold a good bead on your target!
Another benefit of using manual trim, when flying the F4U series is that when I am climbing up or chasing someone up in the vertical and they proceed to drop flaps.... I can drop notches of flaps with out any impunity of having to worry about CT ( combat trim ) fighting against my stick inputs or extended flaps, which could possibly cause me to stall or spin even....
Also, while dogfighting and when one might get slow as they near the top of their loop or reversal and they may need to drop a notch or 2 of flaps to help them get over the top, if they have CT turned on, it will take them a few extra seconds to regain that speed once they are heading back down, to where as I, myself, am able to regain / pick up speed a good bit faster being already trimmed out at around 310/330 IAS.... once my nose is pointed back below the horizon I am immediately raising as many notches of flaps as I deem necessary according to the situation...
Hope this helps....
TC