I Know this can easily be a silly question, but here goes.
I have a parkzone champ and absolutely love it. Im thinking about getting the um p51 as my first 4 channel plane.
Is throttle always proportionate to altitude when you move into 4 channel planes?
let me explain.
I Fly indoors and always fly around 6 to 15 feet, but if i fly at 6 feet and like to climb AND MAINTAIN altitude at 15ft, i have to add more throttle -and keep it there- and thus have the plane fly faster. If i want to fly at the same speed im doing at 15ft, but at a lower altitude, i cant...well, i can but id have to constantly stay on the elevator input. Is this common behaviour of all rc planes?
I can understand that i need to add throttle to climb, but once its at the altitude i want, why cant i let off the throttle a bit without the plane decending? and if i want to make a fast fly-by at a lower altitude, why cant i do that without constant elevator input?
Im just wondering if theres some mixing happening on the champ as its classified a 'beginner' plane, that wouldnt happen on a more 'advance' rc plane such as a 4 channel plane.
Hope im making sense.
Any help is much appreciated.

The P-51 has much less lift than a Champ, so you won't get that much more altitude with increased speed

In general, a trainer is designed to fly at around 1/3 to 1/2 throttle. It is sometimes necessary to add down elevator trim to a trainer when flying at high speeds. If the P-51 is set up correctly, no elevator trim changes should be needed between 1/2 and full throttle.

awesome. Thats the answer i was hoping for. It just didnt seem right that a rc plane would always climb with more throttle, so i assumed it had something to do with the champ.

one more question regarding the p51... ive been watching alot of videos on it but none of them show a straight flight with the wings perpendicular to the ground. The only time i see it is when its turning.... so im wondering if its at all possible?
can you fly a straight line with the plane rotated 90degrees?? or even 45 degrees?

Its doubtful it will fly a good knife edge.

In knife edge flight the fuselage provides the lift because the wings are now 90 degrees to the ground. That maneuver requires a fair amount of power and coordination of the control surfaces. The rudder now serves the function of the elevator, the elevator serves as the rudder once the aircraft is rolled to 90 degrees. At 45 degrees the wings are still producing some lift, it still requires good coordination of controls to maintain a straight line of flight.