Bunting

[pmccarthy]

I have been reading about RAAF fighting tactics. In a Spitfire or a Kittyhawk, a bunt was the best and possibly only way to get a Zero off your tail. In a Spit it was full left rudder, full left aileron, and full nose down. Described as everything in the corner. In a Kittyhawk it could be either left or right corner. Either way, it was a minus 5 g manoeuvre. 
I am trying to visualise what the plane would actually do in a bunt. You would certainly need some altitude to recover.

[facthunter]

Good way to get into an inverted spin, I would think. There's aspects of it that would help evade someone but you must retain control to be most effective and consider airframe loads and effects on yourself of high negative "G"  Nev

[old man emu]

51 minutes ago, pmccarthy said:

am trying to visualise what the plane would actually do in a bunt

Looking into this, I think there is a problem of semantics. What exactly does "bunt" describe? The “bunt” is really the first part of an outside loop. The pilot pushes the nose down from level flight to the vertical and then to the inverted position.

Easiest to do if you have model in your hands. Simply move the model to the response each control surface would cause, taking into account the "further effect" . This is the Aresti symbol in aerobatics for a bunt. 

 

English bunt

Half an outside loop starting from upright, straight and erect level flight. (The pilot pushes the stick forward and draws a half circle in the sky from the top down).

 

  

[BrendAn]

I can't imagine what minu 5 g would feel like.  

Bunting over in a gyro usually means certain death. 

[pmccarthy]

I think it is more than an outside loop. Given the roll rate of these aircraft, it turns into something else in a fraction of a second with full rudder and aileron.

[old man emu]

First consider the word "bunt". Its etymology harkens back to meanings implying a push by the head or horns as many animals do in a fight, and it may be related in concept to "butt"  from Anglo-French buter, Old French boter "push, shove, knock; thrust against". That would account for the first action of the manoeuvre - pushing forward on the control column to push the nose down.

 

Next we have to account for the aileron movement. Early in its development, the Merlin engine's lack of fuel injection meant that Spitfires and Hurricanes, unlike the Bf 109E, were unable to simply nose down into a steep dive. This meant a Luftwaffe fighter could simply "bunt" into a high-power dive to escape an attack, leaving the Spitfire behind, as its fuel was forced out of the carburettor by negative "g". RAF fighter pilots soon learned to "half-roll" their aircraft before diving to pursue their opponents. There's the reason for the aileron movement by Spitfire pilots, and once the technique has been developed, it becomes the standard.

 

Finally we have the rudder movement. The best explanation I can find is one that is an extension of the effects seen in an aircraft with a conventional landing gear (tail dragger) when the tail is being raised during the takeoff roll. This change in pitch attitude has the same effect as applying a force to the top of the propeller’s plane of rotation. The resultant force acting 90° ahead causes a yawing moment to the left around the vertical axis. Seen from the pilot's point of view, the Merlin engine spins in a clockwise direction, so during a normal takeoff right rudder would be applied to counter the left hand yaw. In an escape situation, moving the rudder to the left would enhance the rate of yaw so that the escaping aircraft would reverse direction causing the pursuer to overshoot. 

 

Once the bunt was completed it might have been possible for the pilot to complete a 360 turn and end up chasing the original pursuer.

[Yenn]

The bunt has been used in aviation terminology for many years. The combination of aileron and rudder described does not result in a bunt. It achieves a similar aim but reduces the negative G of a real bunt.

[old man emu]

28 minutes ago, Yenn said:

The combination of aileron and rudder described does not result in a bunt.

Which one are you referring to - PMC's or mine?

 

I'd say that the "bunt" part was the full forward stick which would rotate the aircraft around its lateral axis.  Any other movement of controls would be methods to affect the direction of the aircraft after it had rotated 90 degrees around the lateral axis.

 

But don't as me about doing aerobatics. I get airsick everytime I go up in an elevator.

[djpacro]

On 07/01/2023 at 11:44 AM, pmccarthy said:

... it was full left rudder, full left aileron, and full nose down. Described as everything in the corner. .... Either way, it was a minus 5 g manoeuvre. 

I'm certainly not knowledgeable on WW2 fighters however I know that -5G would be beyond their limit load factor.

 

I also know how an aircraft responds to control inputs and I've been to -5G many times. Response depends on the rate of control application with airspeed also a big factor. Flying along upright and suddenly hit full forward stick, full left rudder with full left aileron lagging a tad results in an outside snap roll. Easy to calculate the G based on entry speed and the stall speed at -1G.

 

Slower control movements - obviously forward stick into a dive results in a speed increase. WW2 fighters have similar flight load limitations as current GA airplanes. Rolling G limitations and Va, maneuvering speed. Something will break doing that.

[old man emu]

1 hour ago, djpacro said:

Something will break doing that.

Somehow I don't think that obtaining a long service life in a military vehicle would be uppermost in a pilot's mind when someone was hurling lead and fire at you with the intention of causing you more than a little more paperwork on your return to Base.

[facthunter]

If you overstress the airframe you don't get back to base. Bombers are as weak as Airliners structurally.  Negative "G" will  cause brain and eye haemorrhaging . Negative G is extremely unpleasant to  experience.  A pressure suit can help positive G . Lying prone helps both.  Nev

[pmccarthy]

I understand this was a manouver to avoid death, when bullets were hitting your aircraft from behind. There is a good illustration of how real the fear was. At Moresby, bulbs kept blowing in the sights so the fitters installed ring sights at the side of the windscreen. The pilots were reluctant to use them, as it took their head out from the protection of the seat armour plate.

[Yenn]

I was refering to PMs comment. i reckon full left ruder would be the start of a left rolling turn and full left aileron would bring the wings into the turning bank, then full forward stick would negate some of the high G loads. This would negate the negative G from a straight full forward stick.

[facthunter]

The control to change AoA is the elevators, No other control does it. How this works out depends on the order of sequencing the control applications and when they are centralised... The prop on the Merlin goes in the opposite direction to the motor, so it's likely much of the gyroscopic precession is cancelled out. The Griffon engine has an extra idler gear in  the drive, so even apart from the different prop direction being the same as the engine. the gyroscopics are worse . Quite a few people have expressed not being a fan of the Griffon powered version, though a lot of that may be due to the EXTRA power.  When each  aeroplane is at a  positive angle of attack is when the "P" factor causes the roll that can't be controlled.  Nev

[facthunter]

Armour plate is mostly in the American radial engined planes like New Zealand pilot's had. I've read some very interesting comments from some of them about unloading the wings.  The ACTUAL pilots and that answered  a few questions about what I had been doing in the way of confirmation.   Most of them had to learn the hard way, on the job  They all got thrown in with the minimum of training and losses were high.  Some of the Yanks used to skoll a bottle of whiskey when taxiing out, in PNG. Nev.

[pmccarthy]

The Kittyhawks had armour plate and I’m pretty sure the Spitfires did too. Edit…just checked.. had head and back armour and armour on the glycol tank.

Edited January 9, 2023 by pmccarthy

[old man emu]

3 hours ago, facthunter said:

The prop on the Merlin goes in the opposite direction to the motor,

Damn! I have to question that point, but I can't pull up good references to back my comments. The Merlin and Griffon did cause the prop to rotate in opposite directions, one from the other. 

 

OK a bit of research and I come up with this. If the crankshaft, viewed from the right hand end of this diagram rotates in a clockwise direction, would that cause the reduction gear to turn anti-clockwise? 

  

 

[facthunter]

Two gears cause a reversal and they are straight cut not helical. THAT causes no end thrust.Nev

[old man emu]

9 hours ago, facthunter said:

they are straight cut not helical.

The diagram I posted of the motion of the gears was simply to show the direction of movement. I didn't take into regard the cut of the teeth, which can be seen in the illustration of the Merlin showing the gears to be straight-cut.

[Old Koreelah]

14 hours ago, facthunter said:

…The prop on the Merlin goes in the opposite direction to the motor, so it's likely much of the gyroscopic precession is cancelled out. The Griffon engine has an extra idler gear in  the drive, so even apart from the different prop direction being the same as the engine. the gyroscopics are worse…

European motorcycles like Guzzis and BMWs have always produced a noticeable torque reaction due to the engine.

Honda cancelled much of this by spinning the Leadwing’s clutch (or was it alternator?) the opposite direction to the crankshaft.

[BrendAn]

On 09/01/2023 at 1:48 PM, facthunter said:

If you overstress the airframe you don't get back to base. Bombers are as weak as Airliners structurally.  Negative "G" will  cause brain and eye haemorrhaging . Negative G is extremely unpleasant to  experience.  A pressure suit can help positive G . Lying prone helps both.  Nev

i knew i did not like neg g for a reason

[facthunter]

Worst sensation ever IMHO.  Nev

[old man emu]

Is the -ve G feeling of an outside loop, or bunt, the same as you get from a ride on a drop tower? 

[facthunter]

In a drop tower you won't get negative G. The best you will get is near zero G (weightless)..  Nev

[old man emu]

If high +ve drains the blood from your head, do high -ve Gs flood it?