Spitfire Mk.XIX - Airfix 1/72

[Polux]

Every day is looking much better!!

You have nearly finished

 

[Ziper_it]

Every day is looking much better!! You have nearly finished

Not yet Polux, not yet ...

But now yes, it's done.

The target (clean build) has not been fully achieved but at least it took less than 8 work sessions to complete it and I'm overall satisfied.

Since last time you've seen it I just glued the slipper tank, wheels and antenna, plus one layer of matt clear.

Here are the pictures.

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[AVB99]

Great stuff. Love the cockpit especially, in the original set of pics!

 

[Stevekir]

Looks great Francesco.Increasing the number of blades on a propeller is one way of improving power absorption through propeller solidity (the solidity of the spinning disc). When you consider that the Griffon 65 as seen in the Spitfire Mk.XIX could put out almost 2,000HP, that is nearly twice what the early war Merlins could produce. That is why you see an increase in blades as the type developed with more powerful engines. Later, contra-rotating propellers did the same thing, but also reduced torque effects as they turned in opposite directions. An interesting fact is that many pilots struggled to control the later aircraft on take off due to the massive torque produced from these enormous engines. More than one experienced Spitfire pilot came to grief because the Griffon actually turned the propeller the opposite direction to the Merlin (anti-clockwise as viewed by the pilot). Wrong pedal and full power = significant loss of ground control.

 

[Stevekir]

Looks great Francesco.Increasing the number of blades on a propeller is one way of improving power absorption through propeller solidity (the solidity of the spinning disc). When you consider that the Griffon 65 as seen in the Spitfire Mk.XIX could put out almost 2,000HP, that is nearly twice what the early war Merlins could produce. That is why you see an increase in blades as the type developed with more powerful engines. Later, contra-rotating propellers did the same thing, but also reduced torque effects as they turned in opposite directions. An interesting fact is that many pilots struggled to control the later aircraft on take off due to the massive torque produced from these enormous engines. More than one experienced Spitfire pilot came to grief because the Griffon actually turned the propeller the opposite direction to the Merlin (anti-clockwise as viewed by the pilot). Wrong pedal and full power = significant loss of ground control.

I came across the principle of reverse torque (could that be the correct technical name?) last year in single-engined planes. On a rapid opening of the throttle while taking off, the whole plane (fuselage) could roll violently. This presumably is due to the sudden high torque applied by the engine to the spinner. Because of Newton's third law "When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body", the spinner exerts a huge torque on the fuselage in the opposite direction. The pilot must counter this quickly.

But during normal especially high constant speed flight at full throttle, why doesn't the fuselage permanently spin (roll) in the opposite direction to the spinner? Could the answer be that the pilot has to keep the ailerons always adjusted in a position to counteract that roll? If so, the added air drag must slow the plane down considerably.

Added:

Also, I would think that despite counter-rotating props, the torque applied by the engine to the spinner (and the reverse reaction torque by the spinner) would still be there unchanged.

 

[Polux]

This Spitfire looks excellent

Great stuff!

 

[flyjoe180]

I came across the principle of reverse torque (could that be the correct technical name?) last year in single-engined planes. On a rapid opening of the throttle while taking off, the whole plane (fuselage) could roll violently. This presumably is due to the sudden high torque applied by the engine to the spinner. Because of Newton's third law "When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body", the spinner exerts a huge torque on the fuselage in the opposite direction. The pilot must counter this quickly.But during normal especially high constant speed flight at full throttle, why doesn't the fuselage permanently spin (roll) in the opposite direction to the spinner? Could the answer be that the pilot has to keep the ailerons always adjusted in a position to counteract that roll? If so, the added air drag must slow the plane down considerably.

Added:

Also, I would think that despite counter-rotating props, the torque applied by the engine to the spinner (and the reverse reaction torque by the spinner) would still be there unchanged.

Hi Steve.

1. Swing on Takeoff.

Yes, the engine torque actually twists the airframe around the engine axis. This puts more weight onto the wheel on the 'down side' of the roll effect. This in turn creates more drag/friction and therefore that particular tyre grips harder. The more power you have and the more suddenly you apply it, the more adverse this effect is. But it is not the only effect that causes swing.

With tail wheel aeroplanes there is an amplified asymmetric blade effect (P-factor). That is caused when the aeroplane is sitting tail down; one blade will actually travel further in it's conical spiral for any given turn of the propeller, creating more thrust. The thrust is then placed 90 degrees to the plane of rotation (gyroscopic precession), which will also contribute to the swing.

Slipstream from the propeller is also spiralled, and as it hits the leading edge of one side of the tail fin, it creates a force out to one side. This contributes to the swing when using high power at low speed.

2. As you accelerate the forces causing the swing are reduced. Torque is better controlled by an increase of airflow over the rudder, making it more effective and giving you more control over that particular nasty. Asymmetric blade effect is negated once the tail is up or the aeroplane is level. Slipstream is countered primarily using the rudder. Again, as airflow increases with speed the effectiveness of the rudder helps to combat the slipstream effect. At a high enough speed the slipstream will not affect the tail fin at all. If it does, designers can introduce offset fins, trim tabs etc.

So airborne and happily flying at speed, the aeroplane will not turn about it's engine axis due to torque.At low speed and particularly on the ground with the tail down, these forces are at their worst.

3. Contra-rotating propellers help to reduce asymmetric blade effect, slipstream effect, and the gyroscopic precession. Torque is still present yes.

Hope this helps to answer your questions.

 

[flyjoe180]

Awesome work too Francesco, it looks well painted and weathered, a nice job mate.