You can calculate the turn rates
For example:
Ki-84
Loaded Weight: 3600kg
Wing Area: 21m2
Air density at sea level: 1.225kg/m3
Flap Area: 2.436m2
Wing Lift Coefficient: (according to its manual)
Flaps at 0 degrees: 1.46 CL_Max
Flaps at 15 degrees: 1.70 CL_Max
Flaps at 30 degrees 1.92 CL_Max
Step 1:
Find out the Lift Force:
Weight (kg) X Gravity
3600 X 9.81 = 35,316 Newtons
Step 2:
Look at the formula and fill in the numbers
V= Stall Speed
2L = 2x Liftforce (2x 35316)
CL = wing lift coefficient
p = Air density (kg/m3)
a = Wing Area (m2)
Note:
If you are looking for stall speed without using flaps (0 degrees) you do not add the flap area to the wing area in the calculation. It's only when you start calculating the stall speed with flaps deployed, that's when you add the 2.436m2 to the 21.0m2
So the wing area that will be used for calculating flaps 15 and 30 degrees is (23.436m2)
Step 3:
Do the working out, use scientific calculator which lets you write the entire format. Top is just 2x L, bottom is CL X p X a
The top is divided by the bottom and everything is square rooted.
The answer you will get is the stall speed in m/s, you need to multiply it by 3.6 to convert it to Km/h.
If you're struggling with the math, here's the easiest way.
Airplane Aircraft Wing Lift Design Equations Formulas Calculator - Velocity
Ki-84
At 3600kg weight , Sea level
Stall speed is:
Flaps at 0 degrees: 156km/h
Flaps at 15 degrees (Combat): 137km/h
Flaps at 30 degrees (Landing): 129km/h
Step 4:
Work out the Power to weight ratio
Weight (Kg) / Power (HP)
3600 / 1990 = 1.81kg/HP
Step 5:
Now you can compare the turn rate against other planes.
Yak-3
2692kg loaded weight
1300hp engine
That's 2.07kg/HP power to weight ratio
Yak-3 stall speed at 2692kg, sea level, No flaps (0 degrees)
163km/h
Which ever plane has lower stall speed, that plane has smaller turn radius and sharper turns. This is the initial turn.
Ki-84 not only has lower stall speed (better initial turn) than Yak-3, it has better power to weight ratio than Yak-3 (carries less weight per horsepower). This means the Ki-84 sustains it's speed better than Yak-3.
There are instances where planes have very good initial turn (they turn very well with energy) but their engine is underpowered and as soon as they get into prolonged turns, they turn into whales that do small turn radius but they take long time to complete one because the plane is fighting stall thus the plane isn't turning efficiently because it doesn't have enough energy to perform manuevers. One example would be the F6F-3.
Yak-3 sustained turn (no flaps, 1000m altitude)
18 seconds to complete 360 horizontal turn
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Ki-84 is rated at 17 seconds
La-7 is rated at 19 seconds