Throttle Quadrant

FLIGHT CONTROLS - THROTTLE QUADRANT

Flight Controls - General Information

Since the project began in 2011 there has been three throttle conversions, and each conversion has built upon knowledge learnt from earlier conversions. Initially, a 737-300 throttle was converted in 2012. This conversion was rudimentary and the throttle only operated in manual mode (the movement of the thrust levers were not controlled by the automation). In 2016 a 737-500 throttle was converted (full automation) and this was then upgraded in 2017.

The links below relate only to the conversion of Boeing 737-500 throttle quadrant (the second throttle):

The links below relate ONLY to the advanced rebuild of the Boeing 737-500 throttle quadrant:

Information concerning the center pedestal is located on a sister page.

OEM THROTTLE IN SIMULATOR. Despite the NG THROTTLES appearing more stylish than earlier series, they are still utilitarian

Second to the yoke, a throttle quadrant (TQ) is probably the next important item in the simulator.

The use of an OEM throttle unit is second to none; no matter what series throttle is used. The differences between the older series throttle units and the NG are mostly cosmetic.

There is more to a throttle quadrant than levers, buttons and backlighting. If the throttle is to function like the throttle in the real aircraft, it must be converted to be able to communicate with the avionics used in the flight simulator. The throttle is used on every simulated flight and is arguably one of the most important pieces of equipment; therefore, it’s wise to not scrimp with this piece of equipment.

Sine being involved in flight simulation I have used several different throttle units. In the Precambrian (dawn of time), I used a keyboard (FS1) prior to migrating to a throttle manufactured by CH Products, and then to a more higher-end unit manufactured by Precision Flight Controls (PFC).

A throttle quadrant has the following main functions:

Thrust levers
Reverse thrust
Fuel idle cut-off switches
Stab trim cut-off toggles
Speedbrake lever
Parking brake lever
Rotation of stab trim wheels
Stab trim tab indicators
Horn cut out
Flap levers

Important Point:

OEM is an acronym for Original Equipment Manufacturer.

For the purpose of this introductory article, a throttle quadrant refers to the actual quadrant and does not include the attached center pedestal.

Commercial Perspective

There are several throttle units commercially available for use in flight simulator, and selecting one is predominately based on the level of realism sought and budget.

At an early stage, I was moving towards a reproduction throttle quadrant produced by one of several companies such as ThrottleTec or Revolution-Sim. Without going into great detail, I was not convinced that the reproduction throttles would provide consistent and reliable service for the expenditure.

The more downmarket throttles, such as that produced by ThrottleTec did provide consistent operation, however, lacked realism and authenticity. It didn’t take much imagination to finally decide on a OEM 737 throttle from a real aircraft.

A 300 series throttle. Note the TOGA button square box assembly, lack of shrouds, and different colour in contrast to the NG throttle

Classic or Next Generation

The aircraft simulated in a Boeing 737-800 NG, so it stands to reason that an Next Generation style throttle quadrant should be used. Finding a Next Generation style throttle quadrant is no easy matter as most are still in service and those available as parts have been damaged. Therefore, I decided to use a throttle from one of the 737 classics (200-500 series).

The 200 and 300 series throttle units are rather antiquated, look slightly different to later classic series throttles, and usually have two-bay center pedestals. The 400 series units, with the exception of interval spacing and the stab trim cut-off switches, are very similar to the Next Generation. The 500 series throttle quadrants have the correct stab trim cut-off toggles as used by the Next Generation throttles and the thrust levers, apart from the lever shrouds are identical. They also have a larger internal working space and use a three-bay center pedestal.

There are inherent visual differences between the 500 series and Next Generation throttles, but for the most part the differences are marginal, and if engineered correctly, the differences can be rectified. The main disparity that cannot be altered is the flap gate détentes. In the Next Generation, the détentes are equally spaced where in the earlier throttles they are not.

Main differences in appearance between the 500 series and Next Generation throttles are:

Flap détentes in the flap arc
Speedbrake lever handle/knob (thinner in NG)
Throttle lever shrouds (enclosed in NG)
Stab trim indicator tabs (more defined points on the tabs in NG)
Square TOGA button assembly (part of shrouds in NG)
Stab trim cut-out paddles/toggles (T-Lockers in the NG and in some 500 series)
Colour differences (grey verses white)
Cosmetic differences in the mouldings (more streamlined on NG)
The 500 series throttle was converted to appear similar to a Next Generation throttle

To Avoid Confusion - Throttle Conversions

As you peruse this website you’ll discover numerous articles that appear to deal with different throttle quadrants. This is because since the inception of the B737 Project in 2011, two OEM throttle units have been used. Initially, a 737-300 was used, however, the conversion was rudimentary and there were inconsistent problems.

The first throttle purchased was from a 737-300 series with a two-bay center pedestal. This was converted by Northern Flight Simulations in Florida, USA. This throttle didn’t include any automation – it was a manual throttle only.

I wasn’t overly happy with the conversion, and in 2013 the throttle was sold. It’s replacement was a throttle from a 737-500 series. This throttle was converted with full automation, and as it came with a three-bay center pedestal, it was converted to appear similar to the Next Generation. This throttle was revamped further in 2014 to take advantage of improvements in technology. The rebuild was completed in May 2015.

The 737-500 series throttle wrapped in bubble wrap after opening the freight container

Evolutionary Process - Advanced Rebuild

The rebuild of the 737-500 series throttle has been an evolving process with the rebuild duplicating many of the systems found in the real aircraft.

The throttle before the rebuild worked well, but there were several matters which needed attention, in particular the automation and movement of the thrust levers.

There were also 'niggling' issues concerning the operation of the clutch assembly. The clutch assembly would become loose from the vibration of the rotating trim wheels, and the loose clutch would cause several flow-on problems.

Although the outside of the throttle quadrant may appear identical, the rebuild has replaced nearly everything inside the quadrant. The infrastructure that was previously located on the outside forward section of the throttle bulkhead is now located inside the throttle unit.

The rebuild centered around the following components;

Replacement of thrust lever motors and clutch system;
Removal and replacement of linear potentiometers with rotary string potentiometers;
Replacement of the parking brake system;
Replacement of speedbrake motor, and installation of a slipper clutch;
Implementation of dual Polulu JRK cards (automation logic);
implementation of 2 interface modules;
Replacement of TOGA buttons with OEM counterpart; and,
Cosmetic enhancement of thrust levers.

737-500 throttle with NG cosmetic upgrade

Improvements

The automotive fan-belt system/clutch system that was a chapter from the 'dark ages' has been replaced with two mechanical clutch assemblies. The clutches, that are installed inside the throttle unit, have been professionally designed and made from machined aluminium.

The use of new clutches will remove, once and for all, the 'niggles' that the previous system exhibited when the fan belt slipped. Each thrust lever has a dedicated slipper-clutch that is powered by an independent motor.

737 throttle 5 v incandescent backlighting

The use of high-end adjustable 12 Volt motors, and the replacement of linear potentiometers with rotary string potentiometers has improved the synchronised movement of the thrust levers; this is now consistent and reliable. It has also improved the accuracy that the thrust levers can be calibrated to in ProSim737. The parking brake now replicates the system used in the real aircraft whereby the toe brakes must be depressed before the parking lever can set or disengaged. Additionally, an actuator located inside the throttle quadrant, is used to lock and unlock the brake mechanism.

The potentiometers controlling the movement of the flaps and speedbrake were also replaced with rotary string potentiometers. This has improved the accuracy that can be attained during Direct Calibration in ProSim737, removing the need for calibration in FSUIPC.

Prior to the rebuild, there was an issue whereby the speedbrake didn't deploy consistently on landing. The problem was caused by the motor not being powerful enough to push the speedbrake lever to the UP position. The motor was replaced with the same type as used to power the thrust levers and a slipper clutch installed. The slipper clutch enables the torque to be adjusted so that the speedbrake lever moves at a specific speed.

The speedbrake is mechanical and replicates how the lever moves in the real aircraft; therefore, a software interface is not required for it to operate, although the movement of the lever must be calibrated in ProSim737.

The Phidgets advanced servo card and motor that was used to control the movement of the stab trim tabs (trim indicators) has remained, but the motor that provides the power to rotate the trim wheels has been replaced with a more reliable motor with greater power and torque. The replacement motor, in conjunction with three, speed controller interface cards, has enabled the trim wheels to be rotated at four independent speeds. This replicates the four speeds that the trim wheels rotate in the real aircraft.

Although unnecessary, the TOGA buttons were replaced with OEM buttons. The OEM buttons are much firmer than the buttons supplied by Mouser Products.

Dedicated Interface Modules (throttle communication)

The way that the throttle communicated with the avionics (ProSim737) also received a major overhaul. The Interface Master Module (IMM), which was a trial and testing module was replaced with two dedicated modules.

The throttle now directly interfaces with two dedicated modules called the:

The new modules accommodate the interface cards, busbars, power supplies, USB hubs, relays, and wiring, that controls the automation and function of the throttle. There’s no interface cards mounted to the forward section of the throttle or MIP; everything is mounted inside the modules. The use of interface modules has, amongst other things, kept the amount of wiring to a minimum. It also enables troubleshooting to be done easily.

Additionally, the system incorporates a revised Interface Alert System (IAS) which evolved from the original concept used in the IMM.

The conversion of the throttle quadrant and subsequent rebuild has been a learning process, and the result has been an improvement in accuracy, consistency, and reliability.

Avionics

The avionics that controls the throttle is ProSim737 (ProSim-TS).

The clean white coloured lines of a Next Generation throttle are unmistakable

Opinion Regarding NG Conversion

Generally speaking, converting an older classic series throttle to appear similar to a Next Generation throttle is purely cosmetic.

If I was converting another classic throttle, I wouldn't do the Next Generation conversion, but rather maintain the appearance of the 500 series. By doing the conversion you are destroying a piece of aviation memorabilia.

Although the conversion has been successful, there is a lot of scope for error, especially in relation to the fabrication of the throttle lever shrouds and the TOGA button assembly. And after cosmetic changes, the handle of the speedbrake lever won't be identical to the Next Generation, nor will the flap détentes that will remain unequal (unless you replace the flaps détentes arc).

For additional information see Major Differences Between Classic and Next Generation Throttle s.