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Adding Bootstrap to the Century NSD

With the increasing popularity of today's storm detecting instruments (excluding radar), and pictorial map displays, many aircraft owners are upgrading their panels and need these devices to stay aligned with the heading of the aircraft. This can be accomplished with the Century slaved NSD system by adding the Bootstrap option. Century has been making slaved HSI's for over 20 years. The Bootstrap option came about with the popularity of the RMI in the late 70's.

The Bootstrap capability in our system is developed by the 1D755 Bootstrap Slaving Amplifier. In this unit the Bootstrap capability is an actual five wire synchro output that is excited externally (normally by 400Hz 26 VAC). The 3 stator wire will be applied to the unit requiring the bootstrap.

For those slaved NSD systems that do not have the Bootstrap option, it is a simple process to change the Dual Channel Slaving Amplier (1C714) out and with minimal wiring, install the 1D755 Bootstrap Slaving Amplifier. The main connector from the 1C714 slaving amplifier (CD115) and the 1D755 are directly compatible. The minimum wiring comes into play with the slaving switch. The Slave 1/OFF/Slave 2 switch on the 1C714 is a 3PDT switch that allows the pilot to select either slave channel or a free gyro mode. Since the 1D755 is a single channel amplifier, the #2 channel wires from the 1C714 that went to the slaving switch can be removed. The #1 channel wires are removed from the slaving switch and attached directly to the NSD connector (CD111). A SPDT switch (Century P/N 40S35) is installed between pins E and K of CD111 to provide the Slave/Free Gyro switch. The additional connector on the 1D755 (CD129; Century P/N 28S66) will then be wired to the external inverter and the unit requiring the bootstrap signal.

Navs, Lorans & GPSs

Let's try to simplify all these new navigational wonders that are available to aircraft owners today, and how to interface them to the autopilot. First, let's understand how an autopilot will use the information provided by the nav receiver. The receiver will output a voltage of +/- 150mvdc to indicate left or right deviation. This voltage is applied to the radio inputs of the autopilot. At this point all the autopilot knows is if it's supposed to bank left or right, or if the signal is 0 Vdc it will level the wings. This type of autopilot is known as a "tracker". Our Century I autopilot is this type (if it has the tracker board installed). Tracking is good, but that has it's limitations. Why? If the autopilot only knows it's supposed to bank left or right, it's possible for the autopilot to put the aircraft into a circular pattern, orbiting somewhere to the left or right of the radial you wanted it to track. Because the autopilot doesn't know at what heading it should level out at in order to start tracking that signal it must keep banking the aircraft in a certain direction until that radio signal becomes 0 Vdc. Therefore it has no intercept or crosswind capabilities.

So how does a system have intercept capabilities? What is required is for the autopilot to know what direction it needs to fly in order to get to that radial you wanted to track. You tell it by giving it a heading that corresponds to the radio you wanted to track. Most autopilots have an intercept angle of 45°. The polarity of the radio signal and heading signal inside the autopilot is such that they cancel out each other. Therefore you have the intercept capability.

Crosswind is the ability of the autopilot to keep the left-right needle centered and ignoring the airplane's true heading. Using an HSI is even simpler than a DG due to the fact you only have to turn the course knob in order to select the radial and course direction. So far so good using the VOR, but what about LORAN and GPS? They output left-right information just like the VOR does, except they also give you a bearing to fly. This means you must turn your heading bug on your DG, or course knob on your HSI to that bearing in order for the autopilot to track to that waypoint. One other point to keep in mind is that some LORANs and GPSs have programmable course widths. This is measured in nautical miles of full scale deviation. The range can be anywhere between 5 miles down to 1/4 a mile or lower full scale. Having a course width too wide would result in the autopilot being sluggish tracking the radio. The opposite would result if the course width was too narrow.

Interfacing these systems into the autopilot is not very difficult if you use a little common sense as to what will be required. Some autopilots only require left-right signal while others also need a nav flag signal. If the autopilot has a DG, it's just a matter of using a good quality switch or an electronic switch box and annunciator. If the system is using an HSI it's a good idea to present all navigational information on the HSI for the particular nav unit you want to use. As an example, if you are trying to switch NAV1 and NAV2 you will have 8 resolver stator wires, 4 resolver rotor wires, 4 nav flag wires and 4 to-from wires to properly display the information. Anything else could be confusing to the pilot.

Radio Couplers - When & Why

Radio couplers perform two functions in the autopilot system. First, they are an interface for an HSI system. Second they receive the radio information, where it is processed and mixed with the heading/course information. This composite signal is then passed to the amplifier for autopilot command.

The following couplers are used with our standard DG (52D54M): the 1C388, 1C388M and 1C388P. The 1C388 is the older version coupler made before the use of HSIs in general aviation. Although this unit is compatible with newer CIIB and CIII autopilots, it is not recommended. Improvements in circuit design of the 1C388M have made the older couplers unreliable. The 1C388M and 1C388P are identical units inside and out except for the face plate. The 1C388P was made especially for Piper Aircraft for use in the Autocontrol and Altimatic autopilot series and is no longer in production.

The next model of couplers are the ones used in ARINC (synchro) based systems. These models are the 1C388C, 1C388MC and the 1C388PC couplers. These couplers only accept heading signal (not course) from the HSI. As with the couplers mentioned earlier in regards to age and production status, the same applies to these models: the 1C388C and 1C388PC are no longer in production.

The next model is the 1C388-2 used with our NSD series of HSIs. It will also work with certain models of HSIs manufactured by Sigma Tek. For specific models, contact the HSI manufacturer. The 1C388-2 has separate input lines for heading and course datum information. Operation of this coupler differs from the standard coupler, in that when intercepting a VOR or LORAN signal, the course needle will be set to the radial or bearing for the autopilot to properly track. In the reverse mode the 1C388-2 will automatically reverse radio and course sensing to the autopilot for proper LOC/BC function.

The last coupler we offer is the 1C388-3 used with ARINC HSIs that have heading and course datum outputs. This coupler is also recommended when a King KI525A along with the KA52 adapter is used. We do not recommend the use of the 1C388M and the KA57 adapter when the KI525Ais installed.

Century 2000 Autopilot

Century understands the real world of the cockpit and knows how to transpose these conditions to reliable hardware. Now it's done in a way to allow each pilot the equipment needed to do the job.

Century 2000 Autopilot

As new requirements arise, functions can be added as desired to the expandable Century 2000.

To begin with, the main frame is the best designed single axis autopilot built today fully worthy of the legacy of Century autopilots. The capture, track, soft-ride, and gust alleviation of this system are unparalleled!

The pitch axis comes complete with altitude hold, glideslope grabber circuit, capability for altitude preselect, automatic and manual electric trim, all certified to the safest standards so that test lockouts are not required.

Flight director or yaw damper expansions may be easily added to the Century 2000.

Options: The NSD slaved or non-slaved HSI system or other compatible HSIs may be substituted for the directional gyro. Altitude preselect is also available.

Century 2000 General Information

  Roll Pitch Flt. Dir. Total
Weight: 5.8 lbs.9.3 lbs..4 lbs.18.3 lbs.
Power: 4.5 amps @ 14 or 28 VDC
Panel Size: DG and AG - 3-ATI
6.24" X 2.25"


Century 2000 Specifications

Single Axis System

Panel Space 6.24 x 2.25 inches
Weight 5.8 lbs.
Power 1.2 amps @ 14 or 28 VDC

This complete roll axis autopilot features continuous roll/nav/voltage monitors, heading hold, heading select, NAV (VOR/RNAV) /LOC/BC anticipative intercept and track, automatic soft track, auto 45-degree intercept, and all angle intercept with HSI.


Second Axis Expansion

Panel Space No additional required.
Weight 9.3 lbs.
Power 1.1 amps @ 14 or 28 VDC

Pitch expansion adds altitude hold, attitude command, electronic altitude hold, G/S capture and track, proportional pitch trim, control wheel steering, continuous pitch/GS monitors, and automatic pitch synchronization to the existing roll section.


Flight Director Expansion

Panel Space No additional required.
Weight 0.4 lbs.
Power 0.3 amps @ 14 or 28 VDC

Flight Director
The flight director expansion computes the necessary roll and pitch attitudes needed to intercept and maintain headings, courses, attitudes, and altitudes. These computations are then displayed through the flight director horizon as steering commands, greatly simplifying instrument flight.


Yaw Damper Expansion

Panel Space No additional required.
Weight 2.8 lbs.
Power 1.9 amps @ 14 or 28 VDC

Yaw Damper
The Yaw Damper is a subsystem which enhances directional stability by reducing short-term oscillations in the yaw axis, therefore enhancing passenger comfort. In addition, it maintains coordinated flight during turns. The yaw damper is activated with autopilot engagement but may be operated independently. This expansion may be added to any package.


Century 2000 - The Total Solution

Panel Space 6.24 x 2.25 inches
Weight 18.3 lbs.
Power 4.5 amps @ 14 or 28 VDC
TSO's C4c, C6c, C9c, C52a

Complete Century 2000
The complete Century 2000 is a true 3 axis, flight director/autopilot. Its advanced design provides the smoothest, most precise ride possible. The flexible design provides the economy of expandability.


Century 2000 Packages

AK ( ) Kit is priced complete with all necessary installation hardware, brackets, and manufactured electrical cable harness.

KitsDescriptionSuggested List Price
Century 2000C2000 Single Axis Autopilot system, (no gyro)    CALL
C2000 Trim PrompterC2000 2 Axis Autopilot system  (no gyros)    CALL
C2000 AutotrimC2000 2 Axis Autopilot system with autotrim  (no gyros)    CALL
Artificial Horizon
52D267MSquare 3-ATI Lighted Artificial A/H (SIGMA TEK) 1yr warranty    CALL
94A578552C77-4, Single Que Flight Director Steering Horizon, 3-ATI Lighted    CALL
Directional Gyro
52D254MSquare 3-ATI Lighted Directional Gyro    CALL
Heading Situation Indicators
NSD360A-15Square, 3-ATI Lighted, non-slaved, vacuum  CALL
NSD360A-26Square, 3-ATI Lighted, slaved, vacuum  CALL
NSD360A-35Square, 3-ATI Lighted, slaved with RMI bootstrap, vacuum  CALL
NSD1000-26Square, 3-ATI Lighted, slaved, electric 14 or 28 V  CALL
NSD1000-35Square, 3-ATI Lighted, slaved with RMI bootstrap, electric 14 or 28 V  CALL
YK ( )Yaw Damper. See STC List.    CALL
Digital Altitude Preselect1D960 (DAP Kit)    CALL
AK1081GPS  (roll steering) convertor    CALL
Expansion Kits
Trim Expansion2030 (14)V, 2130 (28V)    CALL
F/D Expansion2031 (14V), 2131 (28V)    CALL
92S8VOR/LOC Converter Kit for use with NSD when radio receivers do not have built-in OMNI converter or nav flag output. Uses converter P/N 1C707-1.    CALL
92S791C930, Adapter required for use with KCS55A Compass System.    CALL
 92S969  1D969, 400Hz ADI/HSI adapter box for 200 mv/deg error.    CALL
 92S969-1 1D969-1, 400Hz ADI/HSI adapter box for 60 mv/deg error.    CALL
 92S929-2  1B929-2, Century ARINC heading interface box for KPI 552/553.    CALL
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