Muzz wrote:
Bit of a thread hijack, or maybe it's already too late...
Dawger,
Curious on relative turning capabilities of the p-51d as compared to the Spit 9b at equal weights. Anecdotally the Spit should turn better in most flight conditions, especially given relative wing loading. Has the new combat flap setting given the pony better turning capability (instantaneous and sustained) as compared to the Spit?
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Edited for auto spell correct errors
A complex question answer in all respects.
First they can never be at equal weights. The P51D with no fuel weighs 1200 lbs more than a Spit 9 full of fuel.
Stall speed drives ALL turning capability with excess power available determining the sustained turning capability.
I build each model to stall POWER OFF in a CLEAN configuration at the SPEED and WEIGHT published on the datasheet I am presented.
So the Spit 9 B is built to stall at 85 mph IAS at 7300 lbs. The P51D is built to stall at 103 mph IAS at 9611 lbs. (The current P51D was about 900 lbs light and this has been corrected in the new FM)
The first 10 degrees of ANY wing flap system is mostly lift. A Fowler flap system that increases wing area AND changes camber produces more lift than a wing flap system that only changes camber but they all produce lots of lift with little drag in that first notch.
Maneuver flaps are just the ability to use that first notch of flaps at a high speed in Warbirds. Most airplanes of the era had flap controls that allowed selection of any flap deflection so Warbirds has always had multiple stages of flaps available at varying speeds. I have always had a bit of heartburn with this because the reality is that these flap controls that allow any selection are rather finicky and nailing a particular deflection angle in a combat situation would be fairly difficult. This is why "Maneuver Flap" settings were built into later versions of these aircraft, to give the pilot a positive detent or stop to easily position the flaps in combat. Modern aircraft have very positive flap detents with no option for intermediate positions so pilots dont rip them off.
So the P51 has a maneuver flap setting allowing it to select the first "notch" up to 400 mph. This increases available lift and decreases stall speed? How much?
My research indicates a 15 to 25% reduction in stall speed depending on type and total area of flaps. I have to approximate this stall speed reduction by adjusting the lift value for the first stage of flaps.
So at first glance the P51 with maneuver flap would seem to possibly equal the Spitfire 9b in turn but two things make a big difference.
The Spitfire 9b is much lighter so it has plenty excess power. It can sustain a 4 G turn from a 300 mph entry for 360 with no problem at full fuel (7327 lbs). The P51D cannot do that at 67% fuel (9611 lbs)
And the P51 laminar flow wing creates a LOT of induced drag so sustained turn performance suffers.
The maneuver flap gives the P51 tremendous instantaneous nose rate at high speed (it does this for everything that has it) but it isn't going to be a better turn fighter than the Spit 9.