XF631

Model Airplane News, May 2001 by Aberle, Bob

The engineers at JR have come up with yet another new, easy-to-operate computer radio system: the XF631. This intermediate-level radio offers the same basic features as JR's entry-level XF421 (reviewed in the June 2000 issue) yet also has an extra channel function (six in total), three model-memory positions, digital trims, throttle cutoff and dual rates on elevator and ailerons.

ABOUT THE SYSTEM

The JR XF631 system includes a 6-channel transmitter and receiver, four ball-bearing NES-537 servos, a dual-output battery charger, an airborne Sanyo Ni-Cd battery pack, a switch harness, aileron extension cable, extra servo output arms and mounting hardware, frequency flag set and the usual excellent, easy-to-follow instruction manual. The system is offered on 72, 50 and 53MHz RC channels. Operation is FM (PPM) with deviation on the high side, so it's compatible with Airtronics equipment. The transmitter doesn't have a removable radio-frequency module, but the crystal is accessible from the rear of the case. As is common with many of the JR computer transmitters, a lithium battery maintains the computer memory when the battery power is turned off. This battery has an expected life of five years, after which you must return the transmitter to the factory for battery replacement. The JR service department will check overall operation and tuning at the same time.

ABOUT THE TRANSMITTER

Control-stick lengths on the transmitter can be adjusted, as can the spring tension, if you remove the rear case cover. Because they're more precise and easier to store in the computer memory, digital trims are becoming more popular in modern computer radios such as the XF631. Because you input the trim using a push-button instead of a lever, it can be difficult to determine the amount of trim employed. To help with this, apply trim in one direction, observe the momentary digital readout on the LCD screen, then restore the trim back to its original position.

JR was also kind enough to include throttle-cutoff on the XF631. After landing your model, you can cut off the engine (completely close the carburetor) by pressing this button. Without this feature, you would have to pulse the throttle digital-trim button many times to kill your engine, and then you'd have to remember to return it to its original position.

The usual JR transmitter features are also included in the XF631, including an audible and visible low-battery warning when the transmitter power drops below 9 volts; an optional DSC cable to allow you to operate your model controls without creating an on-air signal; and provision for an optional trainer cable that will work with most other JR transmitters.

A fifth channel (retract) switch is at the top left corner of the case. This non-proportional channel has endpoint adjustment but no trim feature. The elevator dual-rate switch is just below this switch and can easily be reversed, i.e., dual rate can be "on" in the upper and lower positions. The trainer-- enable button is just to the right of this switch.

On the top corner of the right side, a sixth channel function switch is identified for flaps but could be used for any auxiliary function. It is also a non-proportional channel with endpoint adjustment but no trim available. The aileron dual-rate switch is just below this switch, and to its left is the throttle-cutoff button.

A 1 1/2 x 1-inch LCD screen in the center of the transmitter case displays all of the stored computer data. When the transmitter is first turned on, the model memory position or three-character model name of your choice will appear. In addition, the transmitter operating voltage is shown digitally.

Computer inputs, or commands, are easily made using two momentary contact slide switches below the main power switch. The left switch is identified as "Scroll/Channel" while the right switch says "Increase/ Decrease." Push both of these switches up for an "Enter" command.

The XF631 uses two menus: "Systems Setup" and "Function Mode." To access the systems-setup menu, press both computer slide switches upward while turning the main power switch "on"; to access the function mode, push both switches up with the power already "on." The proximity of these two switches on the XF631 makes this task easier than it was on the XF421 system.

Systems setup includes model-memory selection, naming the model, reset (to return to factory settings) and a choice of mixing circuits (flaperons, delta and V-tail). The function menu includes servo-reversing, endpoint adjustment (on all six channels), dual rates and subtrim. Subtrim allows you to store the actual digital trim position in memory and then place the trim button back at zero. This is a really worthwhile feature when you use one transmitter to operate three different airborne packs in different planes. All computer settings are saved automatically when you go to the next menu item or turn the power off.

AIRBORNE EQUIPMENT

The XF631 comes with the new JR R700 7-channel receiver, which is even smaller and lighter than the excellent-performing JR R600. This new receiver measures 2 x 1 x 9/16 inches, weighs 0.65 ounce and has a 39-inch-long antenna. The connector block is on the end of the receiver case, so it's even easier to install in narrow fuselages. JR proprietary connectors have the positive pin in the center and are compatible with most other brands of connectors. This receiver conforms to all FCC and AMA guidelines, and independent testing has proved it to be even better than the R600!