Question on plane acceleration.

[Crispy]

I was wondering how you measure acceleration in comparrison to RL?  I fly the hog all most exclusivley and the one thing I think is off bad is the acceleration. For example I can be 1.0k behind a pony and gaining pretty good, he see's me and points nose down and in like 5 seconds he is 1.5k ahead of me...the hog feels like it has a parachute dragging behind.  I know the pony probably did out accel hog but by that much that fast?  What happened to my faster closure rate?  The hog is fast but man it takes forever to get there but once there holds it well & zooms well.

Just curious, Thanks  Cris

[TexMurphy]

That situation also has to do with dive characteristics.

You have both pure "engine forced" accelleration and "dive enhanced" accelleration.

The Pony is both a diver and has better accelleration that is why the difference is so much noticed when going into a dive.

Tex

[hitech]

It realy can't be off with out every thing else being incorrect. Also Acceleration and climb rate are realy the same thing, for any given speed.

To talk about acceleration, and messure it, you realy should talk about instantainous acceleration.

As an example at 320mph a plane might acclerate 1 FPS per sec.

And at 350mph it might be .01 FPS per sec. At top speed level acceleration would be 0 fps per sec.

So to be able to estimatie the acceleration start with the top speed of a plane and estimate  it's total drag. Since Thrust = drag at top speed we can calc drag from HorsePower.

Thrust = HorsePower * PropEff * 550.0 / SpeedFPS

Fair number for HPeff would be about 0.82

You can then aproximate drag at other speeds by making it change with the square of the speed.
CurrentDrag = (CurrentSpeed/MaxSpeed) ^2 * MaxSpeedDrag

Next we can calculate added thrust from the dive.

That is given by sin(DiveAngle) * PlaneWeight.

Now for accelation.

Aceration  = Force / Mass

Mass = PlaneWieght / 32.2
Force = EngineThrust + DiveThrust - CurrentDrag.

These can be used to aproimate performance , but do not account for the small change in induced drag with 0g push overs. But that is a realitvly minor number at higher speeds. And also it does not account for increase in drag as you get into thicker air from the dive.

HiTech

[Seeker]

Originally posted by hitech

Tech stuff.

Cool. I can understand why developers don't post much... I can sense a shark-cirlcle of guys waiting to make smartass "you missed this!" posts.

But you guys at HTC are posting more recently than you have for a couple of years.

That's cool.

[Crispy]

Thanks for the reply.  I will have to ...absorb all that for a bit.  So the hog has a much higher drag then?

[bustr]

Does this mean HiTech you model the air over large bodies of water near the deck denser from water evaporation than air over land masses in the game?

[JB73]

Originally posted by Seeker

Originally posted by hitech

Tech stuff.

ROFLMAO!!!!!!! that is SO how i read most of that stuff.

[TexMurphy]

P51-D
1490 HP
7,125 Lbs (Empty)
Max speed 437@25k

F4U-1
2,000 HP
8,982 LBS (Empty)
425@25k

The HP/LBS ratio of the F4U is higher then the HP/LBS ratio of the P-51D.

Since Thrust=Drag at max speed the pony has a lower MaxSpeedDrag. Since it also has a higher max speed the (CurrentSpeed/MaxSpeed) ^2 will always be lower for the pony then the hog. Meaning Pony has a significantly lower drag since both its max drag and its current speed drag is lower then the hogs.

Next factor is the PropEff. Even though the Hog has more HP from the engine its PropEff is lower then the PropEff  of the Pony. As climb rate and accelleration really are the same thing, as said by HT.

So in the force part EngineThrust + DiveThrust - CurrentDrag Pony has better in 2 out of 3. Considering equaly massed planes the pony will always out accellerate the hog. Considering that the hogs are usually heaiver the DiveThrust is higher of the Hog but since Accell = Thrust/Mass the positive effect of the increased DiveThrust is not outweighed by the negative effect mass has on accelleration.

So in short. Hog has higher drag, less efficient prop (meaning less engine thrust) and is heavier and hence accellerates ALOT slower then the Pony.

Tex

[MANDO]

Originally posted by Crispy
So the hog has a much higher drag then?

To accurately know the drag force you need the following data:

C = Drag coeficient of the object (constant for a given shape and material).
A = Frontal area (varies with AOA as speed increases or drecreases at level flight).
D = air density (constant for a given height if you keep temperature and humidity constant).
V = Current speed.

Drag Force  = 1/2 * C * A * D * V^2

[stantond]

My opinion, and it is only that, is that the F4U-1 prop efficiency is the main reason for the lack of acceleration.  The primary differences between the -1 and the -4 are the four bladed prop, which the P51D uses.    It could very well be that all four bladed props produced before 1944 went to europe due to the priority on defeating Germany.  After VE day, the four bladed prop was more readily available and put on the -4.  But, I really don't know the whole story.

The XF4U was extensively 'cleaned up'  before production for drag reduction in the NACA full scale wind tunnel now operated (at least for the time being) by Old Dominon University in Hampton, VA.   With an extra 500 HP over the pony, the F4U had it outclassed.  In fact the F4U-4 outclassed the P51-D in acceleration, climb, dive preformance, top speed, and maneuverability.


Regards,

Malta

[Traveler]

There is a reason they called it a HOG!