QUOTE="InlineRanger, Here's my understanding of the topic:
Maximum speed = thrust - drag. Thrust is engine power x propeller efficiency. At maximum speed, drag is almost entirely parasitic. The larger the difference between thrust and drag, the higher the maximum speed.
Your equation is for Force, not velocity.
When Thrust=Drag, acceleration =0. At that 'point' (for that altitude, MP, RPM), Vmax is attained. That said, deriving actual Thrust Hp is very complicated, particularly when Ram air and exhaust Thrust for the engine is required to solve. Total Drag is reasonably straightforward for level flight in incompressible flow range <0.3M. As flight speeds approach Mcr the drag rise factor is a Major delta. Incremental Drag factors over Zero Lift drag for say, climb or turn, must take into account RN, Form Drag due to AoA, pressure Drag due to airframe components immersed in prop vortex, Cooling drag, etc.
The determinant for achieving max velocity (and increase climb and Turn) is Power achieved - Power Required = T*V-D*V and is quite a bit more complicated analysis with Conventional aircraft.
You maximize engine power by increasing the oxygen mass flow rate, increasing compression ratio and reducing parasitic losses. You increase propeller efficiency by reducing span loading (low disk loading, high aspect ratio blades), maximize lift distribution (elliptical loading), and keeping wave drag to a minimum (tip speed below critical mach, thin airfoil/sweep to increase critical mach).
Parasitic drag is defined by the well known equation drag = zero lift cd * .5 * air density * velocity^2 * wing area. In reality, this is just an approximation that assumes all aircraft share similar fuselage to wing proportions. A more relevant metric would be the wetted area drag coefficient and wetted area. So drag can be reduced by flying higher and/or in hotter temperatures (reduce air density), reducing the wetted area, and streamlining.
CD= (CDp1+DeltaCDp1+DeltaCDp2)*CD/CDinc + Cdi where CDp1 is a f(RN) and will decrease with Velocity and density
CDp1 is minimum Parasite Drag Coefficient of the aircraft in zero lift at a particular RN and is comprised of wind tunnel measured component characteristics of the airframe (wing, fuselage, empennage, cockpit enclosure, carb duct, radiator duct and exhaust stacks for P-51)
'Delta' CDp1 are CD of individual components such as external antenna, machine gun ports or fairings, leaks and surface roughness)
Delta CDP2 are increments due to Angle of Attack and expressed as CL. Included are Cooling Drag/Net internal Flow losses during climb, external load items such as fuel tank/bombs, and Immersed items in slipstream (fuselage/empennage/cockpit, etc plus 1/3 of the wing) --------> for the latter, wind tunnel data are power off. Calculations of Power Required mandate accounting for the free stream dynamic head in the increased velocity slipstream behind the prop. The usual method is to apply increased drag for increased velocity over those components assuming velocity is constant throughout the slipstream. This calculation is extrapolated for RN in same fashion as CDp1
CDi is the Induced Drag component due to lifting surfaces, including Wing, H.Stab/Elevator and slats if ya got em'. There is also a small delta component due to washout of leading edge which changes the chordwise Lift distribution.
For Power Required calcs, the momentum loss in Carb air is also considered a loss in Power Available.
CD/CDinc is the compressibility factor over CD for incompressible flow.
For your THp data, you need to correct Static Hp with following:
Adiabatic temp rise
Friction Hp of Engine
Manifold Temp
Aircraft True air speed.
The Jet Thrust is a factor of;
Outside air pressure
Total Stack exhaust area
Engine charge consumption, slugs/sec
Ratio outside static air pressure to manifold pressure
With these data in hand the next step is to calculate prop efficiency - normally taken from Manufacturer's data
Then, make corrections to Power Available by deriving Power losses due to Slipstream, engine air momentum loss and corrections to Thrust Hp prop efficiencies
During the analysis phase, particularly for a two stage/two speed supercharged engine - the Power Available and Power Required for each desired Weight and stores condition and altitude are calculated to point to achievable Velocity and climb and range performance as function of MP and RPM.
Flying higher reduces thrust (reduced oxygen mass flow rate, lower propeller efficiency due to decreased critical mach) and also reduces critical mach (drag divergence occurs at a lower TAS). Supercharging (mechanical, turbine) and oxygen injection (compressed/liquid O2, nitrous oxide) help restore mass flow rate. Larger, slower turning propellers and/or increased blade count mitigate propeller efficiency losses at altitude.
The wetted area can be reduced by increasing thrust/weight ratio, increasing wing loading, using a low moment coefficient airfoil (reduce tailplane size), decrease cg range (reduce tailplane size), reduce area forward of wing quarter chord (reduce tailplane size), and reducing protuberances (canopy, antennas, lights).
Wetted area is what the term implies ---------> the total surface area top to bottom, side to side, of the airframe. The Wetted Area Drag coefficient is simply based on Total Drag divided by wetted area while the conventional CD is derived by dividing Total Drag by Wing Area.
The wetted drag coefficient can be reduced by using a long chord wing (higher reynolds number), reducing pressure gradients (laminar flow wings, long shallow canopy, generous radii at stagnation points), reducing interference drag (area ruling fuselage/wing/tailplane intersections), removing protuberances (antennas, lights), reducing surface roughness, decreasing cooling drag.
To the extent that Total Drag of the studied airframe can be reduced by any/all of your proposed changes will alter Wetted Surface Area, the Wetted Drag Coefficient will also change but;
1.) increasing chord without changing wing area will move the needle on RN but not change Wetted Area or Wetted Drag Coefficient unless the Wing change to alter chord also changes the CDp1 of the wing. This is true for P-51H wing in contrast to P-51/A/B/C/D/K
2.) All of your cited factors are functions of Parasite Drag (Form drag, interference drag, friction drag, etc) - independent of Wetted area. If you maintain Wetted Area but say, change the Parasite Drag CDp1 by making an airfoil change that achieves lower Drag as function of CL, then Wetted Area is same but Total Drag is reduced so both Total Drag and Wetted Drag reduce. If you change aspect Ratio while maintaining Oswald Efficiency but make no change to Wing Area - you may or may not change parasite drag but will reduce Induced drag - so possible change Wetted Area Drag to same extent Total Drag is altered.
All this is memory driven and of all the things I miss, I miss my mind the most.