B737 Throttle Quadrant - Flaps UP to 40; Conversion and Use — Flaps 2 Approach

This post examines the flaps lever on the refurbished B737 throttle and how it was converted to flight simulator use..

Flaps are used to slow the aircraft by creating drag, and to apply positive lift during takeoff. The flaps lever is located on the First Officer’s side of the throttle quadrant.

Subsequent movement of the flaps lever is indicated by illumination of the Le Flaps Transit and Le Flaps EXT lights located on the Main Instrument Panel (MIP), movement of a needle in the flaps gauge, a change of indication in the Primary Flight Display (PFD) and illumination of the Leading Edge Device (LED) panel located on the aft overhead panel.

There are other less obvious indicators, but this is not the direction of his post.

The flaps lever is an integral part of the throttle unit. Ensuring it operates correctly and with accuracy is important.

oem 737 throttle showing flaps arc and takeoff cg%mac

Safety Features

Newcomers to an OEM throttle quadrant are often surprised at how difficult it is to manipulate the flaps lever; it isn't a simple pull or push of a lever - there is a reason for this.

When flaps are extended, especially at slow air speeds the flight dynamics of the aircraft are altered. To protect against accidental flap extension, Boeing has designed the flaps lever so that a flight crew has to physically lift the lever before moving the lever to the required flap setting.

Further safety has been designed into the system by having flaps 1 and flaps 15 guarded by a flaps gate. The gate prevents straight-through movement of the flaps lever beyond flaps 1 and 15. The pilot must actually lift, push and drag the lever through the gate to the next setting.

It takes a short time to become accustomed to how to move the lever for smooth operation.

Traditional Approach used in Flaps Conversion

In most throttle conversions, a single potentiometer is used and the flaps are calibrated directly through FSUPIC. A linear rod is attached to the potentiometer and then to the lower end of the flaps lever. When the flaps lever is moved, the rod is moved forward or aft causing the potentiometer to turn to a defined and pre-calibrated position. The analogue movement of the rod is converted to a digital signal that can be read by Flight Simulator.

In such a conversion, it’s important to ensure that the physical position of the flaps lever matches the flaps position used in Flight Simulator and in the flaps gauge. It’s also vital that flaps are calibrated to ensure accurate operation.

The benefits of using this traditional method are that it’s “tried and true”, inexpensive and relatively easy to implement. Calibration is the major key; however, using FSUIPC can be troublesome and time consuming, although once calibrated everything should operate reasonably well.

Potentiometers - Accuracy and Longevity

Potentiometers came in a variety of sizes with differing throw values. A throw is the length of movement that a potentiometer will allow a linear rod to move. The larger the potentiometer the more throw allowed. The potentiometer for the flaps must fit within the throttle unit beneath the flaps mechanism in a relatively small space. Unfortunately, with Boeing 737 late model throttle’s there is minimal room to allow a larger than 60mm potentiometer to be installed. Using a 60 mm potentiometer means that the device has a minimal throw.

This throw, if lucky, can be stretched to cater from flaps 0 to flaps 40, but only after facetiously calibrating with FSUPIC. More often than not, the throw will only reach flaps 1 or flaps 30. Often this lack of throw goes unnoticed and many virtual pilots select flaps 40 believing they actually have flaps 40, but in reality it is flaps 30.

Longevity is another more minor issue when using potentiometers. Most potentiometers have a +- tolerance during manufacture, are made cheaply and depending upon the type selected are open to contamination from dust and debris. Dust on a potentimeter can affect the accurancy of the unit. At the very least, maintenance is required if the potentiometer is located in a dusty area.

Several Ways to Skin a Cat.....

To solve these potential problems two methods were assessed. The first was using two micro- buttons at each end of the linear rod that connects the flaps lever with the potentiometer. These buttons can be assigned directly with FSUPIC to flaps UP and flaps 40. This theoretically would solve the shortness of throw experienced with traditional conversion and calibration. Flaps UP and 40 are controlled by micro-buttons and everything in-between is calibrated within FSUPIC.

Working through an issue with the Flaps 5 micro button, custom VGA cable and PoKey card. it's not all fun. Chasing problems can be frustrating and very time consuming

Micro-buttons

The second method is to replace the potentiometer with micro-buttons; thereby, rectifying the issue of minimal throw. Replacement will also alleviate the chance of a potentiometer being inaccurate, remove any chance of contamination, and also remove the tedious task of calibrating flaps in FSUIPC.

The use of micro-buttons to control flaps movement is relatively novel, but the potential benefits of implementing this into the throttle unit could not be overlooked; therefore, it was decided to use this method.

Problems with Micro-buttons - Design of Lower Flaps Arc Plate (LFAP)

The first initial problem encountered is that micro-buttons are small, delicate and can be easily damaged if mounted directly onto the metal flaps arc. Manipulating the flaps lever requires considerable pressure to pull, drag and drop the lever into the correct flaps detent position. Clearly, mounting the buttons on top of the metal flaps arc for direct contact with the flaps lever was not feasible.

After much thought, it was decided to fabricate from aluminum, a plate that replicated the arc that the flaps lever moves over. This plate has been called the Lower Flaps Arc Plate (LFAP). The micro-buttons were then strategically mounted to the plate, each buttons’ position corresponding to a flap position. The LFAP with the mounted buttons was then mounted directly beneath the existing flap arc plate.

Design Considerations

Before implementing a new design, considerable thought must be taken to potential problems that may arise from the design. In the case of using micro-buttons the issue was connectivity and the possibility of a damaged or faulty button. The LFAP can be accessed relatively easily by removing the First Officer's side panel which allows access to the plate from behind the trim wheel.

Half-moon Provides Accuracy, Reliability and Repeatability

To enable the micro-buttons to be triggered by the flaps lever, a half-moon piece of aluminum was fabricated using the same dimensions of the lower portion of the flaps lever. One end of the "half-moon" was curve-shaped pointing downwards. The "half-moon" was then screwed to the lower section of the flaps lever handle

LEFT: Rough initial sketch of half-moon showing relationship to flaps arc and micro-buttons.

When the flaps lever is dropped into a flaps detent position, the curved side touches and depresses the micro-button mounted on the lower flaps arc plate. When the flaps lever is moved to another flaps setting, the lever is first lifted breaking contact with the button, moved to the next setting and dropped into the detent position triggering the next button and so forth.

Interface Card

A standard PoKeys 55 interface card was used to connect the outputs from the buttons to the avionics suite software. ProSim737 software allows easy interfacing by allowing direct connection of a button to a specific flap position. If ProSim737 is not used and the chosen avionics suite does not support direct connection, FSUIPC can be used to assign individual buttons to flap positions. The PoKeys card is installed in the Interface Master Module (IMM).

Advantages of Micro-buttons - It's Worth The Effort...

The benefits of using micro-buttons cannot be underestimated.

100 % accuracy of flap movement from flaps UP to flaps 40 at all times.
No calibration required using FSUIPC.
Non-reliance on FSUIPC software as the installation is mechanical.
Very easy configuration of flaps UP through flaps 40 using ProSim737 software configuration.
Removal of the potentiometer and possible inaccuracy caused by +- variation.
No concern regarding possible contamination of the potentiometers.
Enhanced reliability of operation with no maintenance required.
Easy removal of the Lower Flaps Arc Plate to facilitate button replacement.

Back-up Potentiometer System

Although the use of micro-buttons is successful, I still have a potentiometer installed that can be used to operate the flaps. The reason for installing the potentiometer was in case the micro-buttons did not work correctly; it would save time installing a replacement system. To change from buttons to the potentiometer is as easy as disconnecting one quick release connector and reconnecting it to another.

qamp. the quick access mounting plate enablse 4 linear potentiometers to be mounted in one location. the qamp is located in throttle unit

Quick Access Mounting Plate (QAMP)

The potentiometer is mounted directly onto a custom-made aluminum plate that is attached to the inside of the throttle unit by solid thumb screws.

The reason for the plate and screws was easy access should the potentiometer need to be cleaned or be replaced.

To access the potentiometer requires the side inspection plate of the throttle be removed (a few screws) and then removal of the thumb screws on the access plate that allows the potentiometer to be dropped from its bracket.

Unfortunately, I failed to photograph the flaps QRMP before installation; however, its design is similar to all quick release plates used within the throttle unit. The plates are made from aluminium and are attached to the throttle unit by thumb screws rather than nuts and bolts. This allows for easier and faster change out if necessary. The above image shows the QRMP for the throttle levers - the flaps QRMP is far smaller and thinner.

Troubleshooting

During testing a problem was observed with the micro-button for flaps 5. For an unknown reason flaps 5 would not register correctly on the PoKeys 55 card. After several hours troubleshooting the buttons and wiring, it was determined that the PoKeys card must have a damaged circuit or connection where they flaps 5 wire was installed to the card.

The problem turned out not to be the PoKeys card, but the Belkin USB hub installed to the Interface Master Module (IMM). I had replaced the first hub (which I damaged) with another hub that had a lower voltage. For some reason this lower voltage was not enough to allow operation of all the functions running from the hub.

After replacing the hub with a higher voltage device, the issue with the flaps was immediately rectified. Of course, this was after I spent literally hours troubleshooting flaps 5! As stated earlier, teething issues on a new design can be frustratingly time consuming...

Video

I decided to make a short video that explains the button set-up a little better. In the video you can clearly see the flaps arc, half-moon pencil and the micro-buttons. The video is not the best quality as it was hand held in dim light after I removed the F/O side inspection plate of the throttle quadrant. It's difficult if not impossible to setup a tripod in the flight deck once the throttle unit is bolted to the platform.

737 throttle flap arc buttons

Acronyms and Glossary

Flaps Arc – A curved piece of aluminum positioned directly beneath the flaps lever and corresponds to the curvature of the light plate.
Lower Flaps Arc Plate (LFAP) - A curved piece of aluminium that is the same size as the flaps arc and is mounted directly beneath the flaps arc.
Half-Moon Pencil – a custom fabricated piece of aluminum with a curved edge at one end. Used to depress micro-buttons on flaps arc as flaps lever is moved..
OEM - Original Equipment Manufacturer.
Quick Access Mounting Plate QAMP – Quick Access Mounting Plate for the potentiometer that is a redundancy system for flaps movement.
Avionics Suite - Software that interacts with Flight Simulator to control avionics, gauges, etc - ProSim737, Sim Avionics, Project Magenta, etc.

Update

on 2014-02-12 02:13 by FLAPS 2 APPROACH

Several individuals have contacted me asking for a picture of the half moon, that is roughly sketched in the main post. During a recent upgrade, the side panel and trim wheel were removed so I took the opportunity to take a photograph of the half-moon.

The half moon is secured to the lower section of the flaps lever by a screw, with the lower curved side facing downwards towards where the micro-buttons are positioned. The half-moon moves in unison with the flaps lever (when moved) and the curved section triggers micro-buttons as it passes over the button. The micro-buttons are positioned at the correct position that relate to a specific flap detente.

Update

on 2019-09-09 07:29 by FLAPS 2 APPROACH

FLAPS OVERHAUL (LATE 2018/2019)

The mechanism used to convert the flaps on the throttle quadrant has been overhauled and replaced. The method described in the above article worked well, however, a number of problems developed that were only noticeable after continual use.