Overly aggressive destabilization in 109s during turning... and, the lack of any destabilization at all with the P-47 and the P-51.
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Pyro or HT, how does stall limiter work?
The reason I'm asking this is that I've met a strange phenomenon while testing out sustained turn rates.
I've tested out a P-47D-11 against a Bf109G-6. The conditions are as follows:
* Full ammo load for both planes. The P-47 uses the "extra ammo" load of 3400 rounds. The 109 uses MK108 30mms.
* Fuel burn set to minimal
* No wind
* Climb to 10k, level out facing 360
* Decrease speed to 230mph TAS(all speeds hearby measured through E6B)
* Increase throttle to full military power(not using WEP). Upon reaching 250mph IAS, give 45~50 degrees bank(indicated by artificial horizon) and start a turn with full stick deflection.
The Stall limiter values are from 0.05 to 5. IIRC, this indicates the amount of "margin" the stick pull will be limited to, before the plane reaches an AoA which will induce a stall.
ie) Stall limiter value 1 = max joystick deflection will put the plane into an AoA 1 degrees short of stalling out.
The reason why the stall limiter was used for a turn test, was to minimize pilot errors or skill issues when comparing pure turn rates for planes.
The tester will go to full military power and enter a coordinated turn at a certain set bank angle with max stick deflection.
Since the Stall Limiter will mechanically prohibit an accelerated stall(only stalls induced from flying under stall speed is possible), one can continue this turn and wait until the speed stabilizes.
When the speed stabilizes, timing a full 360 turn will give you a value of a plane's turning ability when it enters a sustained turn with the tightest radius possible.
Although this figure is not the optimum turn rate, nor an absolute value - it does provide a useful info on how tight a plane can maintain its turn, and what speed a plane can fly at that kind of angles.
I've timed the P-47 with no problems at all. I've made only recordings so far, and didn't use a real stop-watch to time the full 360, but rough data set it out - the P-47 can sustain about 2Gs at 155~160mph TAS with a 45~50 degrees bank. With full flaps the P-47D-11 sustains about 1.7~1.8Gs at 130~135mph TAS at 45~50 degrees bank.
The problem is, this test is impossible with the Bf109. The Stall Limiter is the same - set 0.05 AoA before reaching stall. Starting at the same speed, full fuel load, same bank angle.
Pull a max deflection - the plane stalls out. It refuses to turn.
Either the stall limiter is broken and doesn't work only on the 109, or there is something wrong here(I think.. ).
So I tried other planes out, which I personally had some suspicions about, such as the C.205. Same thing. Can't turn. The system regulates reaching full stall AoA - yet it still stalls out.
The rough data I got, was that the 109G-6 can pull a 2.3G turn at 190mph - for 1 second. And then, it stalls out.
Well, it doesn't actually stall out - what happens is the plane wobbles uncontrollably at the roll and yaw axis. It starts a snaproll - and then the snaproll stops.
By this, I am guessing that the Bf109 starts a snaproll BEFORE the stall is reached. Continued stick deflection would make the plane tumble over, but the stall limiter halts the plane to its final limit - and the plane recovers. And then, as it recovers it snaprolls again.
Without the stall limiter, at that state the 109 would have flipped over as it met the stall AoA.
And this wobbling, you cannot 'ride this'.
Some planes will gently falter while stalling, which an ease of stick or change of aileron deflection would correct, so the plane would smoothly continue the turn. The 109 doesn't do that. It's more like 'turn-stop-turn-stop-turn-stop'.
This process repeats. Hence, the plane wobbles left and right before reaching actual accelerated stall status.
The 109 becomes controllable, at a 2G pull at about 190~200mph. That was the best I can do with my ability.
So basically, I think I was right. It's impossible to outturn a P-47 in a 109. At least, when it becomes a sustained, tight-turn contest, the 109G is about barely par with the P-47D-11. The 109 starts a destabilization serious enough to halt normal flight, before it reaches its critical AoA.
I was curious of why this such thing was happening. So I've tested a P-51 out. The P-51 may not have a torque as bad as a Bf109, but IIRC some people do quote that a sudden full throttle would flip the plane over(which I do think is an exaggeration).
Basically, I don't think there's any reason a P-47 or a P-51 would be considered a plane with weak torque, although their heavy weight may mean it is effected less.
So I tried various planes out.
*Bf109F-4
- stalls before reaching stall AoA, due to extreme destabilization
- sustained turn with tightest radius around 160mph TAS, 2.5G
*Bf109G-10
- stalls before reaching stall AoA, due to extreme destabilization
- sustained turn with tightest radius around 162mph TAS, 2.1G
*C.205
- stalls before reaching stall AoA, due to extreme destabilization
- sustained turn with tightest radius around 169mph TAS, 2.3G
*F4U-1
- can maintain max stick deflection
- slight wobbling but controllable
- sustained turn with tightest radius around 160mph TAS, 2.2G
- sustained turn with tightest radius and full flaps around 125mph TAS, 2.0G
*Fw190A-8
- stalls before reaching stall AoA, due to moderate destabilization
- sustained turn with tightest radius around 189mph TAS, 2.0G
*Fw190D-9
- stalls before reaching stall AoA, due to moderate destabilization
- sustained turn with tightest radius around 200mph TAS, 1.9G
*Ki-84-Ia
- can maintain max stick deflection
- slight wobbling but controllable
- sustained turn with tightest radius around 154mph TAS, 2.8G
- sustained turn with tightest radius and full flaps around 117mph TAS, 2.2G
*La-7
- stalls before reaching stall AoA, due to moderate destabilization
- sustained turn with tightest radius around 168mph TAS, 2.3G
*N1K2-J
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 158mph TAS, 2.5G
- sustained turn with tightest radius and full flaps around 134mph TAS, 2.5G
*P-38L
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 178mph TAS, 2.4G
- sustained turn with tightest radius and full flaps around 122mph TAS, 2G
*P-47D-11
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 157mph TAS, 2G
- sustained turn with tightest radius and full flaps around 133mph TAS, 1.7G
* P-51D
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 175mph TAS, 2.3G
- sustained turn with tightest radius and full flaps around 125mph TAS, 1.9G
* Spit14
- turned to its right due to different prop rotation
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 158mph TAS, 2.4G
- sustained turn with tightest radius and full flaps around 129mph TAS, 2G
The list is puzzling at best.
If high torque is causing such destabilization, then how does one explain the stability of the P-47 or the P-51 when it is 0.05 degrees before reaching stall AoA?
One clue may be that the planes with slats - all 109s and all Las - cannot reach its maximum AoA during a forced turn with no alt-loss.
If the slat is supposed to stabilize a plane at low speeds, now I'd really hate to think how bad the 109 would be without slats. If it can't reach its data-fed maximum AoA even with the slats.. then how worse is it gonna be without them!
