Operation of Differential Braking

The Venom had pneumatics as shown, apparently just one rod to the rudder pedals.

Not into the tech bits, but just set me thinking (I know that’s dangerous), the EE Lightning must have been good fun to handle on the ground, with no steering on the front, reliant on brakes alone until the rudder became effective.

Thankyer kindly

Cornovii, wonderful, thank you, does it for me very well. Here’s a set of well worn Mosquito rudder pedals with a bracket coming off the shaft that would readily connect with the arm on the ‘square one’. There just seems to be no detail within the usual Vol I Mosquito APs for this sort of thing, I figure that this was a ‘standard setup’ for pneumatic brake control across a number of types, self evident and not worthy of detailed description.

[ATTACH=CONFIG]241746[/ATTACH]

[ATTACH=CONFIG]241683[/ATTACH]
This any help with the “square” one?

Fantastic ! Thank you comrades for the detail and information. By reference to the photos and plans of the pneumatic unit, and in the absence of taking the unit apart or seeing an AP cross section :

The rudder linkage is connected to an articulated, joint set of levers, bearing against a return spring.
The geometry of the linkages means Port rudder ‘pulls down’ port valve, opening an internal valve directing air flow to Port brake, while reducing airflow to Starboard.
The volume of air is controlled by the handgrip, running to a valve in the centre of the unit. No handgrip input, no air to brakes, irrespective of rudder position.
The default position of ‘centred rudder’ would allow equal airflow to both Port and Starboard, if the handgrip was actuated.

What sort of aircraft were fitted with the vee design of valve?
What sort of aircraft, with pneumatic brakes, were fitted with the later ‘block’ design of valve?
Does anybody have any images of the linkage setup on the Mosquito, which had pendulum type rudders?

I wonder if a statistical link can be drawn between left handed pilots and nose overs with pneumatic brakes, in that the ‘natural’ left hand was typically on the throttle, while the less coordinated right hand was ‘on the brake’.

[ATTACH=CONFIG]241661[/ATTACH]

Does this do it?

In the movies, the Top Gun, say someone from Tenessee in a Wildcat, coming into the revetment does, what my 18 year old self released into my first abused car would call a ‘hand brake stop’, slashing the aircraft into a neat sideways stop. Everybody needs to know how to do this, in case the girlfriend is watching and you have the chance to slash a Mosquito sideways…

Try that and you would skid to a rapid halt , very red faced, with the aircraft on its belly

Thank you for all your replies.
What I would really like to find out is the ‘typical’ physical connection between the rudder pedals and the brake unit, of which the earlier (Anson, Hurricane 1 etc) is shown on left and later (Mosquito – Canberra) units are shown below :

Don’t have a pic but this illustrates the push rod from the Horsa rudder pedals to the valve. You’re is missing the plastic cover unfortunately.

[ATTACH=CONFIG]241642[/ATTACH]

Here’s a photo where you can just see the end connection of the push rod the right hand side of the valve apex.

[ATTACH=CONFIG]241643[/ATTACH]

Ironically, one of the reasons we decided to make a March 1943 spec. Horsa was that we couldn’t find a valve to put Mod 51 in 😀

On the square valve the rotation is done using a swing arm attached to the square boss on the top.

The connection, quite simply is a pushrod from the rudder pedal to the unit in question.

The later type you show is a hydraulic version, so for Canberra to Hunter etc. The pneumatic one is similar, but quite different.

How did pneumatic systems compare with hydraulic? I can see the no-freeze advantage, but was the response to input adequate?
And what was the pump used at what pressure? Thanks

FP, My understanding of original 1930’s hydraulic fluid was that it was castor oil, which did not freeze. In fact the later Mosquito, designed for high altitude recon, had a castor oil (Lockheed Red) based hydraulic system from the outset for this purpose, with natural rubber seals. More aircraft of WW2 used mineral based hydraulic fluids (Lockheed Blue) with synthetic seals. So freezing was not the problem that determined selection of hydraulic over pneumatic.

In a recent conversation with a pilot in respect of Shuttleworth Hawker Hind with pneumatic brakes and Hawker Demon G-BTVE with hydraulic brakes the reflection re brakes was that the hydraulic system was sluggish, with much foot pressure and raised eyebrows as expensive machinery hurtled towards the hedge, while pneumatics fitted in the Hind were much more effective.

The next reflection is how many prewar Hawker biplane photos you see with the aeroplane on its back and a sheepish trainee pilot posing near it. By the late thirties, I would suspect that the preference from experienced pilots for pneumatics and the development of engine mounted compressors would have moved constructors to pneumatics. This then met the influx of novices as the Air Force grew from 1938, less capable of dealing with the bite of pneumatics. So sluggish hydraulics were good for preventing training aircraft from nosing over, while pneumatics were better at the serious end of things.

Cars still run hydraulic braking, but with vacuum assist. It is always frightening to try and stop a car rolling down a hill with no engine running, just relying on hydraulics. Then you see articulated trucks which just run pneumatic brakes. Generally drivers dial up the hydraulic pressure delivered to the trailer when it is loaded, but then the careless ones forget to dial it down once unloaded, and you see the back wheels lock up at traffic lights. Feck the boss’ tyres, eh!!

In conversations with a Mosquito pilot he said it was ‘tricky’ to master the pneumatic brakes, some pilots ‘got it’ and some never did. A gentle ‘pip’ of the brake on one wheel could correct a tendency to swing on takeoff and I suspect with not enough airflow over the rudder you could find a ‘sweet spot’ with the rudder pedals in the crucial seconds before the tail lifted that came with practice.

I think each aeroplane is different. There may be too much mass to stop and not enough brake friction area for some designs that would make them sluggish whatever the transmission means. I have had the pleasure of taking apart a wheel brake assembly for a Boeing 737 which is astonishing for its compactness of design in comparison to friction area, and which is hydraulic, but I guess servo assisted. If this hydraulic design was put into a Hawker Hind then the pilot and engine would no doubt end up in the cafeteria while the aeroplane stayed a long way back on the grass.

Knee bone connected to the thigh bone…

Thank you for all your replies.
What I would really like to find out is the ‘typical’ physical connection between the rudder pedals and the brake unit, of which the earlier (Anson, Hurricane 1 etc) is shown on left and later (Mosquito – Canberra) units are shown below :

[ATTACH=CONFIG]241617[/ATTACH]

[ATTACH=CONFIG]241618[/ATTACH]

Some rudder pedal assemblies are like the steering of a childhood ‘billy cart’ while others are pendulum type jobs, so the constructor would have to devise some means of transferring the movement of the pedal to the pictured brake unit. Does anybody have photos of these types of connections, or an AP dealing with the servicing of the actual brake unit ?

How did pneumatic systems compare with hydraulic?

I can see the no-freeze advantage, but was the response to input adequate?
And what was the pump used at what pressure?

Thanks

Though of course our beloved steed had a proper brake system full of glorious OM-15 and nitrogen, none of this weeny pneumatic tomfoolery! 🙂

Nitrogen ? – you must be dreaming young man LOL
When I were on Canberras we still used Air,we had an ‘L’ type compressor to inflate the tyres – although I assume it all changed to N2 at some stage !

To touch on what OneEighthBit mentioned……

I think the Canberra BCV was a type of Dual Relay Valve – similar nomenclature to pneumatic system BCV i believe

ISTR that on the B2 one could either touch the BCV or look at the BCV but not at the same time : ) – the T4 was easier in that you could swing the nose open and touch/see the valve easily.

In use the Yak system works pretty well. The brake lever is on the stick. It doesn’t do to run out of air pressure though.

Moggy

Still current in the GA world – Yak 52 for instance.

Moggy

Re built and fitted to our Proctor 3. Time will tell how efficient or otherwise they are!!

Yes even in to the 60’s – british aircraft were built with differential brakes,in the Canberra B2 .

Though of course our beloved steed had a proper brake system full of glorious OM-15 and nitrogen, none of this weeny pneumatic tomfoolery! 🙂

I’ve seen two types of Dunlop differential valves myself – one a square format and another “V” shaped – AH364 & AH1010.

In the case of the V valves, there is effectively a valve for the brake on each side of the aircraft – source pressure in and pressure out to the wheel brake itself. When the brake lever is pulled, it allows air in through the source ports of both valves. How much is allowed through and to the out port for their respective sides depends on the position of the rudder pedals.

As for the gauge, it has three ports – the source shows how much pressure is in the source line (200-300 psi for example) and the port/starboard ports show the pressure going to each wheel brake from the out ports of the differential valve (usually about 80 psi). Should also point out that before the high pressure source air reaches the differential valve it passed through a reduction valve and filter to get it down to the lower pressure the brake units need.

You can get a understanding of the whole system from the Hurricane pneumatic diagram.

Ironically I learnt all this from Horsa gliders. They originally just had a pneumatic handbrake which operated both wheel brakes together. As the original plan is that the wheels would be jettisoned after take-off and the glider would land on a skid so differential braking had no use. As they were towed when being marshalled again, no need for differential brakes.

However, once the decision was made to not jettison wheels, they discovered that on a mass landing, the low landing speeds made the rudder ineffective and there was no way for pilots to steer the aircraft on the landing roll to avoid other aircraft of obstacles. So there was a mad dash after D-Day to retroactively fitter differential brakes to all gliders (Mod. 51).

Still current in the GA world – Yak 52 for instance.

Moggy

Yes even in to the 60’s – british aircraft were built with differential brakes,in the Canberra B2 the BCV (Brake Control Valve) was under the floor and controlled by a rod off the rudder bar and also a lever on the control column.
Left pedal forward would (as you surmise) allow brake pressure to the LH mainwheel when the lever was operated by the driver – or rudder bar neutral would give equal pressure to both wheels and allow straight ahead braking.