Audemars Piguet Launches The Royal Oak Jumbo RD5 Chronograph Flying Tourbillon

The Audemars Piguet “RD” (Research and Development) series of watches was launched in 2015 and since then, the project, which is designed to offer a limited production testbed for novel and innovative watchmaking, has introduced a perpetual calendar with all indications set-able from the crown; the ultra-complicated “Universelle” Code 11.59; an extra-thin RO Jumbo flying tourbillon; a selfwinding ultra thin perpetual calendar with a novel movement architecture; and the Royal Oak Supersonnerie, a minute repeater constructed to produce as loud, clear, and harmonious a chime as possible. The entire series represents some of the most ingenious micromechanical precision engineering in horology, and with the newest and, according to AP, last watch in the series, Audemars Piguet rounds out its exploration of advances in the repeater, perpetual calendar, and tourbillon with perhaps the single most challenging complication for exploring new solutions: the chronograph. The Jumbo RD5 uses a number of new features, in a very slim watch measuring 39mm x 8.1mm. This is exactly the size of a standard, time-and-date Jumbo, despite the considerable additional complexity.

The idea behind revisiting the chronograph complication began, according to AP’s Director of Watchmaking Design Giulio Papi, with frustration over the amount of force necessary to actuate a modern, industrially produced chronograph, relative to the soft, smooth pusher feel of hand-adjusted classic chronographs. The goal was to reduce both the travel of the pushers and the force necessary to use them. Papi says:

“Their travel – that is the distance they must be pressed – is often 1 mm or more and requires a force of around 1.5 kilograms … Our aim was to reduce these values to enhance the client experience, drawing inspiration from smartphone buttons which typically have a travel of 0.3 mm and require 300 grams of force.”

Start, stop, and reset in a conventional chronograph is coordinated by a column wheel or cam; the lateral clutch design is the most traditional, although most modern automatic chronographs use a vertical clutch design for smoother engagement of the going train with the chronograph mechanism. Reset mechanisms typically use heart shaped cams on the axes of the chronograph wheels, and when the chronograph is reset to zero, flat hammers drop onto the cams, which rotate until the hammer faces come to rest on the lowest part of the cam, which corresponds to the zero position for the chronograph hands. There are very few alternatives to these basic systems, whose characteristics are well known; one of the very few is the Agengraphe chronograph, which exists in both a hand-wound and peripheral rotor configuration, and which has been used by several makers seeking interesting and technically sophisticated alternatives to conventionally designed chronograph movements; MING is one of them.

One glance through the caseback is enough to tell you that this is no ordinary chronograph. The AP caliber 8100 is a flying tourbillon flyback chronograph, with instantaneous jumping minutes, and with a peripheral rotor winding system (which helps keep the thickness down. In the image below, the chronograph seconds wheel is at the center, with the instant jumping minutes wheel to the right, and the hour wheel to the left. All three wheels are held under a single seven-sided, skeletonized bridge, with the clutch wheel visible under a tension spring at the 4:00 position.

The Reset To Zero System

The chronograph reset to zero mechanism seems very complicated at first, but the basic idea’s pretty straightforward.

Instead of using the hammer and heart piece system, AP’s caliber 8100 uses a system of racks on pivoting levers; the racks are geared to pinions on the respective chronograph wheels.

The curved rack for the chronograph seconds wheel is visible just above the seconds wheel pivot and pivots on the bronze bushing above it; the rack for the minutes wheel is below it, and it pivots on the bronze bushing directly below the minutes wheel itself.

The rack for the hour wheel is visible above the hour wheel pivot. The long blade-shaped spring that rotates the rack, and hence the hour wheel, back into the zero position is visible as well.

How the system works is clarified by diagrams from AP’s patents.

Here the three racks can easily be seen: 26 is the minute rack; 14 is the seconds rack; and 34 is the hour rack (the positions of the racks in the patent filing are slightly different from their final positions in the actual watch but the basic principle is the same). Once the chronograph starts, the wheels begin to turn and the racks begin to pivot on their levers. Once each wheel had made one full rotation, the racks snap back to its starting position under the influence of their springs (36, 28, and 20) and begin pivoting again.

Naturally this raises the question of how the racks can snap back to zero and start again if the chronograph wheels continue to rotate in one direction, and the answer to that question’s a pretty neat bit of engineering.

In the picture above, the rack 14 has just snapped back to zero on the pinion 12 of the chronograph wheel 8. If you look closely, you’ll see that the pinion 12 is missing a couple of teeth. The absence of those teeth provide the clearance necessary for the rack to return to its starting position, and an extension 18 on the rack stops the rack from moving too far to the right. In the image, the chronograph wheel is turning counterclockwise (this is the view from the back) and the pinion can continue to turn uninterrupted; the rack will start to move immediately to the left again as the first tooth on the pinion picks up the inside of the indentation for the first tooth on the rack. If you look closely, you’ll see that the pinion 12’s first tooth is slightly shorter than the others; again, this is to allow clearance for the return to zero of the rack.

Stopping the chronograph brakes the wheels and stops the pinions from turning. When the chrono is reset to zero, the brakes are lifted off, and the racks, under the influence of springs 36, 28, and 20, will rotate their respective wheels to the zero position. It’s pretty nifty and in terms of parts count, not all that much more complicated than a heart cam and hammer system, but you do need some very high precision micro-machining to make it work.

The Chronograph Clutch Mechanism

The clutch mechanism is a vertical clutch that looks for all the world like a lateral clutch.

The chronograph seconds wheel is driven by the clutch wheel, which sits under the flat tensioning spring and which is located at about 4:00 in the image. The clutch wheel is driven in turn by the driving wheel on the rear of the tourbillon carriage, with which the clutch wheel is constantly engaged regardless of whether the chronograph is switched on or off.

The clutch wheel looks like a lateral clutch wheel, but it cannot pivot as its under a fixed jewel on a fixed bridge. However, it can move up and down. In its upper position, it’s disengaged from the chronograph seconds wheel, but when the chronograph is switched on, it drops down into engagement with the chronograph seconds wheel, which begins to turn. To enable smoother and surer engagement of the clutch wheel teeth with the chronograph seconds wheel teeth, the undersides of the clutch wheel teeth are actually beveled, as if they were tiny guillotine blades, which is something I’m pretty sure I’ve never seen before; you can see the bevels in the patent drawing (in which you also get a clear view of the missing and oddball teeth on the chronograph seconds wheel pinion 12).

One interesting feature of the design is how the possibility of additional friction from engaging the chronograph is handled. Since the clutch wheel is constantly driven, it’s always slighly under drag from the tension spring. When the chronograph is switched on, the chronograph pinions are being pushed on by the racks as the pinions turn, but since the clutch wheel’s in its lower position, the friction from the tension spring’s decreased so the overall load on the going train stays about the same.

The dial side of the movement is relatively simple by comparison:

The going train, and this is one of the reasons the movement’s so flat, is on the dial side, along with the mainspring barrel cover; usually, there’s a ratchet wheel on the mainspring barrel but here we have a flying barrel with no upper bridge and with the click on the upper right side of the barrel. The going train is largely confined to the area under the hourglass-shaped bridge to the left of the tourbillon, and it’s flanked on the left by the automatic winding bridge and gear train. You’ll notice that there’s a stacked double star wheel on the keyless works lever; that’s there because you switch between hand setting and winding by pushing the crown in and out.

The entire movement has been engineered so that layering of different levels is done away with as much as possible. Ordinarily in a chronograph the chronograph works are an extra layer on top of the movement mainplate and going train; here the going train has been confined to a small region of the mainplate and of course, the automatic winding system (and rotor) are on the same level as well. Most components sit in milled recesses in the mainplate. Even the sapphire crystal construction plays a part; the crystals are flat on top but domed internally, to increase available clearance for things like the hands on the dial side, and the chronograph bridge on the movement side.

This is a watch that wears its complexity and innovations lightly; the combination of titanium and palladium alloy BMG (bulk metallic glass, an amorphous metal alloy) makes for a very discreet, elegant design and the work that went into engineering the caliber 8100 more than pays off in keeping the watch urbanely slim. There is probably room for discussion about the actual technical advantages of the caliber 8100 – like the Agengraphe, you could argue that all of that wizardry is (a) more about engineering and prototyping in CAD than watchmaking per se and that (b) a well adjusted, column wheel and lateral clutch chronograph can work so smoothly, when adjusted properly, and work so well, that the elaborate rack and pinion and vertical-ish clutch systems are a bit solutions in search of problems.

However, as an example of what you can do with modern design and precision machining tools, this is incredibly impressive. Whether the high tech movement and high tech manufacturing behind it is attractive or not really comes down to personal taste (and how you feel philosophically about repair; none of those ingenious little precision components are exactly off the shelf and servicing and repair is going to be AP only. But this is what you get into with any modern high performance machine. A trained watchmaker at the bench won’t be able to service this thing, but then, your cousin Joe who’s handy with rebuilding transmissions is not the guy you want working on your million dollar hypercar. This is what it is: a showpiece for the possible, not the pragmatic, and with that as its goal it succeeds admirably well.

The Audemars Piguet Royal Oak Jumbo Extra Thin Flying Tourbillon Flyback Chronograph RD5, ref. 26545XT.OO.1240XT.01: Case, titanium case middle, palladium alloy BMG bezel, pushers and crown; water resistance 20 meters. Sapphire crystals front and back, domed internally for component clearance. Movement, automatic caliber 8100, 31.4mm x 4mm, 379 components, running at 21,600 vph in 44 jewels. 72 hour power reserve. Instantaneous chronograph minutes counter; rack and pinion reset system; vertical/lateral hybrid clutch. Limited edition of 150 pieces worldwide; price, CHF 260,000.