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Ivan,
I agree that stall speed is a very important in turning time, but unless
you are flying a later model P-38, stall and cut is not your best option.
Yes same IAS, but the TAS is different. My bad.Hello Laurelix,
I believe I found your error.
See the Bold Underline above.
Stall speed in INDICATED Air Speed does not change with altitude.
Stall speed in TRUE Air Speed increases.
Do you remember I asked earlier about entry and exit speeds from the turns?
At higher altitude, a turn can be entered at higher true airspeed and I believe that although the radius is larger, the turn may end up quicker. I have seen photographs of this with F-16 versus F-4, in which the F-16 made a larger radius turn but turned at a faster rate in degrees per second, but to be sure in this case requires a few calculations.
Intuitively it seems like it should work.
Hello Corsning,
Stall speed actually does need to be considered for minimum turn times.
The reason is that you want to have enough speed to be able to sustain a turn without encountering an accelerated stall (perhaps at 6G) but don't want to be going so fast that the turn has too great a circumference and increases time.
Centripetal force increases as speed increases according to M*V^2/R, so going a little faster also makes numbers worse if the load limit on the pilot is limited.
....And then the turn needs to finish with enough speed to still be abl to pull some reasonable G which is probably a lot less than the peak acceleration.
It is a pretty fine balancing act as I see it and probably why different pilots sometimes get different results if they started at different speeds.
- Ivan.
Yes same IAS, but the TAS is different. My bad.
Because you need to retain higher SPD, your turn radius increases and with less power at 4000m, the power to weight ratio also gets worse. This is why planes turn better at 1000m than they do at 4000m.
Hello Corsning,
I am not really sure what you mean by "stall and cut". Does that have something to do with using engine torque to improve your turn rate?
Hi Ivan, perhaps stall and cut are not the appropriate words to use. The following
is the only quote I could find from the mock combat between a P-38H and Spitfire
XIV. I do not remember the P-38 dominating. I remember it as the two were turning
at a stalemate. All the rest of the story seem accurate though. It went like this:
" During the late winter of 1944 occurred the famous dual between a Griffon-engine
Spitfire XIV and a P-38H of the 364th FG. Col. Lowell flew the P-38, engaging the
Spitfire at 5,000 ft. in a head-on pass. Lowell was able to get on the Spitfire's tail
and stayed there no matter what the Spitfire pilot did. Although the Spitfire could
execute a tighter turning circle than the P-38, Lowell was able to use the P-38's
excellent stall Characteristics to repeatedly pull inside the Spit's turn radius and
rid the stall, then back off outside the Spit's turn, pick up speed and cut back in
again in what he called a 'cloverleaf' maneuver. After 20 minutes of this at 1,000 ft.
altitude, the Spit tried a Split-S (at a 30-degree angle, not vertically down), Lowell
stayed with the Spit through the maneuver, although his P-38 almost hit the
ground. After the Spitfire pilot brock off the engagement and flew home. this
contest was witnessed by 75 pilots on the ground."
TAIC 154a TONY I
Using 92 octane fuel.
1,160 hp./T.O.
1,100 hp./12,600 ft. (3,840 m.)
Rene J. Francillon:
1,175-1,180 hp./T.O.
1,100 hp./3,900 m. (12,795 ft.)
Keep in mind that these figures are if using 92 octane fuel. Late in the
war many of the Japanese fighter groups were using tree-sap fuel of the
the 85-87 octane range.
Jeff
.....
Please note on the chart (calculated) that the Spitfire could manage a 13 second turn (in theory) at either 6 gs at at an 800 ft radius or around 5.25 to 5.4 Gs (?) at a 680ft radius at a slower speed.
The real fly in the ointment however is that the plane has to be descending at at over a 20 degree angle in order to maintain speed. ( a few degrees higher angle of descent for the higher G/faster turn).
Hello Corsning,
Your numbers are correct, however you are comparing different ratings.
You are comparing a Take-Off / WEP Rating at Sea Level and a Military Rating at Altitude.
Here are the rest of the numbers to put it into context:
Sea Level:
1160 HP @ 2500 RPM @ +330 mm Boost for Take-Off and presumably War Emergency Power.
(This is also listed as 1175 PS)
1040 HP @ 2400 RPM @ +240 mm Boost for Military Rating.
Critical Altitude: 4200 Meters (13,780 feet)
1100 HP @ 2400 RPM @ +240 mm Boost for Military Rating
I pulled out my TAIC Manual No. 1. 154A-2 gives a war emergency rating off 1,100 hp.
at 12,600 ft. The engine rpm is not listed. It is the December 1944 report. Many aircraft
were updated in May of 1945.
Also, not that it makes much difference, but it should be listed as 91 octane fuel. 92 octane was the Navy standard.
TAIC says 92 octane. I am just saying...? I know that the IJNAF did have 100 octane fuel that
they used for experimental (testing?)work.
Gentlemen,
FWIW (If my maths aren't too screwed up):
6 G Turn - 800 feet Radius - 13 Seconds - 264 MPH
5.25 G Turn - 680 feet Radius - 12.61 Seconds - 231 MPH
5.4 G Turn - 680 feet Radius - 12.43 Seconds - 234 MPH
- Ivan.
..... the military power for Sakae 21 is quite a bit closer, but please remember that for the Oscar, TAIC notes that the aircraft is capable of pretty high "Flash Performance" because the pilots apparently disregard the limits in the manual and get away with it.