When you start to assemble an EDF jet, one of the required tasks is to work out and install your retractable landing gear. Modifying and installing E-flite gear in a jet is relatively simple and MAN contributor Ken Park recently accomplished the task for his new Viper Jet. Check it out, it’s easier than you may think.
Before you can get in the air, you have to get your jet up on its landing gear.
For many years I had shied away from models that required retracts because I thought they were too complicated, heavy and unreliable. Based on my observations of fellow club members spending half the day working on their gear, I took a pass. Recently however, I have fallen in love with EDF jets and as my jets got bigger and bigger, my need for retractable gear has grown. Actually the hobby has forced me into finally biting the bullet and using them. My first experience using traditional air-powered retracts with the necessary hardware and an air tank that needed to be pumped up, worked well but the onboard equipment took up a lot of room inside the model and the air lines and possible leaks was always a concern. So, for my newest project, the new Teng-Jet 90mm EDF Viper Jet (jet-teng.com), I decided to skip the air systems entirely and I went with the .25-.46-sized electric retracts from E-flite.
From everyone I spoke with, the E-flite electric retracts came highly recommended, but also they recommended replacing the main gear’s trunions with more beefed up ones available from Tam Jets. The new trunions stand up nicely to the strain of rough flying fields conditions with models of higher wing loadings and electric ducted fan jets in general, always seem to fall into this category.
Replacing the main trunions is as simple as putting each main gear into a vice on its side and removing the screws that hold both sides together. You can then slip the Eflite trunion out and replace it with the Tam Jet one. Then you screw the case back together and you’re good to go. The standard E-flite wire struts and axles work very well but for a true “big Jet” look I switched them out with TamJet struts and axles. This is also a simple upgrade easily done by loosening the set screws and pulling off the strut’s retaining clip.
The E-flite electric retracts come with a 3-way servo harness that allows you to attach together the two main gear and the nose wheel servo connectors so you the entire retract system operates from a single channel. A nice safety feature is that each time the receiver is powered up, you must flip the retract switch on/off on your radio to arm them. This eliminates the chances of the gear cycling unexpectedly should the switch be in the wrong position when you turn on your receiver. Another nice feature of the nose wheel gear is the option to use either a tiller-arm or pull-pull method for steering. The tiller-arm can be mounted on either side if need be.
In most EDF jets you don’t have much room and the pull-pull method is your only option for steering. The tiller-arm setup works nicely with my jet, and it provides a direct, slop-less link to the steering servo. Each of the three retract units simply screw down into place on the model using four mounting holes. Quick and simple. To go the next step you can also add working gear-doors sequenced with the movement of retractable gear— way-cool and very easy!
Functional gear doors
The electronic brains for doing this job come simply by plugging in the “ASSAN Gear & Door Sequencer” (hobbyking.com). This little unit can handle two separate doors so, in my case with the Viper, the two main gear doors on the fuselage count as one door. To do this I installed one servo to open both doors at the same time. The other door sequence is used for the nose gear door.
The Door Sequencer has three basic modes—F1, F2 and F3. Once you decide on which mode is best for you, you’ll be able to fine tune each step by setting the servo travels and/or delay times required to make your mode work. The instructions so the breakdown for each mode, so it is pretty easy to get the sequences and time delays dialed in. First setup up your door throws using a regular servo tester (or your radio,) to get the linkage throws where you want them. Mark or measure the position of the linkage in the open and in the closed position. This doesn’t need to be super accurate, just approximate (for later use with the sequencer programming.) Then retract your gear and disconnect your door linkages. This is important; otherwise you could break something when you plug in the sequencer.
Now connect power to the sequencer (without the servos, or gear). It should start in the F1 mode. For my model with electric retracts F3 mode works best. To switch modes, press and hold FUNC+ and FUNC- for two seconds to advance to F2 mode, then press and hold again to advance to F3 mode. Next press and hold VOL+ and VOL- for to move into the programming mode. The number on the left corresponds to the function in the look up table, (see the manual under F3 mode.) Here you can change each setting of each function with FUNC+ and FUNC- used to move you through the functions. VOL+ and VOL- changes the value of the current function.
Experiment with the programming until you are comfortable with the features. Then to exit programming mode and save your settings, press and hold VOL+ and VOL- again which them returns the sequencer to the F3 mode. Then power the unit down completely to save the chances, otherwise you’ll have to start all over.
Now reconnect power and check to make sure the sequencer starts in F3 mode, then connect your door servos one at a time, (no linkages yet).
In the F3 mode, DOOR 1 is for the nose gear and DOOR 2 is the main gear. Adjust the settings for each door first (using the measurements you took for the throws), then with the linkages connected, try them one at a time to fine tune. Once you are happy with the operation of the doors, disconnect the linkages again and open the doors fully. Now plug in the gear and the door servos (still no linkages) and adjust the gear and the door delays by noting when the gear/door servos move.
Once you’re happy, save your settings by pressing and holding VOL+ and VOL- again for two seconds and exit the programming mode. Now, try the whole thing again with the door linkages connected together. Note: Door hinges are available from BVM Jets and Sonic-Tronics.
CAUTION—I strongly advise not going back into the program mode with both the doors and the gear plugged in, and the linkages connected. As you step through the functions you will end up with a door or gear out of sequence and this will damage something. Always unplug or disconnect either the door servos or the gear themselves if you want to fine tune a particular function again.
Regardless of the sequencer’s settings, all the gear doors have to be hinged properly and work smoothly for everything to work in unison.
E-flite has really taken the trouble and effort out of using retractable landing gear and now anyone can look like a pro with the simple flip of a switch!
E-flite Electric Retracts (e-fliterc.com)
Type: 25-46 Electric Tricycle
Current draw—Idle: 5mA.
Operating: 900mA (max).
Pulse width trigger points—Down: 1.331ms; Up: 1.690ms.
Operation—FM: 22ms frame rate, 5V signal; DSM: 20ms frame rate, 3.3V signal.
Operating voltage range: 4.8—7.4V
Aircraft weight: 5.00–9.50 lb (2.25–4.30 kg)
Unit weight—Nose gear: 3.5 oz (99.5 g); Main gear: 2.8 oz (79.5 g) each
Tamjets trunion upgrade kit for E-Flite 25-46 tricycle gear: $59.95
Struts and Axles: TK
ASSAN Gear & Door Sequencer: $13.39