The Spektrum Wireless Trainer (WLT) system is a very effective means of dual instruction, much preferable to a wired trainer connection.

Once people adjust to the system it’s liberating, but there are a number of possible misunderstandings that can stand in the way. Consequently, I wrote a set of instructions for instructors and students of our club Flight School. I hope they help others too.

The Horizon Hobby trainers such as Apprentice STS, AeroScout, Carbon Cub S2, and Sport Cub S all use what’s sometimes called “Three-mode SAFE”. The three modes are Beginner, Intermediate and Experienced.

Setup of such models is quite different from that for SAFE Select. Channel 5 is used for Flight Mode (3-position switch) and channel 6 for Panic Recovery mode (momentary switch). It’s pretty simple to set up on a TX16S.

The instructions below, combined with the instructions that come with the model, should get you going. Comments and suggestions are welcome.

File updated to correct a typo and make minor revisions.

It’s been a long time since I added to my blog.

Some months ago I was curious about the increasingly popular color transmitters using Multi Protocol Modules to control a variety of receivers. OpenTX was the principal operating system, but EdgeTX was making rapid inroads. So I bought myself RadioMaster TX16s and have experimented with it ever since, mostly on the bench, but also in the air.

Since I have alternated among DSMX and various open firmwares, I have long had an interest in translating from one to the other. So here’s my go at providing detailed instructions on how to set up a TX16S or similar transmitter to work with almost any Horizon Hobby BNF SAFE Select model using either the older AR636 receiver or one of the new Smart generation SAFE receivers.

I have done similar instructions for the Horizon Hobby trainers such as Apprentice and AeroScout, which use a different version of SAFE.

NOTE: The instructions may look like a fair bit of work to implement, but they are well worth it. Not only will you learn a lot about programming in EdgeTX (I did!), but once you have created a model you can copy it for similar aircraft.

UPDATE
Revised file with minor correction and addition.

UPDATE
BNF SAFE Select EdgeTX 01e
Clarification of a few points, especially selecting SAFE switch.

Polaris flies great as is. So why add a stabilizer?

The main benefits of a simple "rate" stabilizer such as the Lemon 7-Channel Stabilized Receiver are two-fold: first, it greatly reduces disturbances in turbulent air due to wind, and second, it smooths out flying generally and reduces and tail-wagging tendency. It also reduces wing rock during low speed/high alpha flying. The effect is particularly noticeable with the smaller members of the Polaris family, such as Polaris Mini (75%).

The Lemon Stabilizer Receiver works particularly well and at about $20 is a real bargain. Lemon receivers are noted for excellent range and reliable RF link. I've been flying several for over two years without a glitch. There is now a dual antenna "diversity" version, which adds to the sense of security, but all of mine have been the original single antenna version. You can also add a satellite but I haven't found it necessary.

Detailed instructions for the receiver can be found on the Lemon website at:
http://www.lemon-rx.com/shop/documen...0manual_A4.pdf

Please read at least the first half of the instructions to learn how to use the Lemon stabilized receiver.
(Full disclosure: I was one of the two authors of the instructions.)

People often ask for advice on the setting of the gain pots to suit Polaris or another model. I can’t be really specific because there are several variables involved. The gain settings required depend not only on the design of the...Continue Reading

How to set up Polaris
There's nothing more important to success on the first flight and smooth flying thereafter than setting the controls and balance correctly. Many of the models we hear about being difficult to fly simply have too much control throw, especially on aileron. You can see the result in some of the videos posted on the forum -- jerky control instead of the smooth flying a properly set up Polaris can offer. And sometimes the results are much more serious.

So here's a quick how-to re setup.

First set the linkages to get the correct throws. Here's the process:

Set the transmitter to 100% end points (travel) and 100% rate on aileron, elevator and rudder.

Install the servo arms with sticks, trims and sub-trims centered as close as possible to right angles to push rods. Use subtrim to fine tune. Not that it helps to have the elevator servo arm about 10-15 degrees back from straight across, as this will give more down than up desirable for inverted flight.

Hook up the linkages. Try using holes about 10-12mm out on the servo arms for aileron and elevator and 12-15mm for rudder.

Measure maximum throw on each control surface at the widest point. You want about the following:

Aileron: 15-18mm (about 3/4")
Elev: 15-18mm (about 3/4")
Rudder: 25-30mm (about 1 1/4")

For more throw, use a hole further out. Adjust till you get it right.

Leave high rate at 100% and set low rates to 70%.

Add 35-40% expo on high rate and 30-35% on low rate.

Fly on low rate initially.

Adjust battery position to locate center of gravity at the step +/- 1/4". Don't try to balance with model sitting on a table! Put marks on the fuselage above the wing directly over the step. Grab there with finger and thumb. Adjust battery position till it balances level at that point.

Double check that you have controls moving in the right directions (especially aileron, which fools many people). Check again!

This model has lots of power. Go easy on throttle initially. It should fly at half throttle.

I have always used the standard wire pushrod setup as shown in the kit manual. It works well and is easy to do if you approach it correctly. The keys are using the correct wire, stiff enough but with flexibility, and getting the plastic tube guides correctly positioned and angled through the fuselage sides so the pushrod has a straight run and doesn't bind.

To get a sense of how the whole setup works, go to my earlier blog on control setups for the XL. I first install the servo the with suitable output arm and use Dubro Mini EZ Connectors to provide for adjustment and make it easy to remove the pushrod if necessary later.

I install the usual plywood control horns in the ailerons and make sure the hinges work freely. I generally use Blenderm Surgical Tape for the hinges.

I run a straightedge from the connector on the servo arm to the control horn and use it to draw a line across the bottom edge of the fuselage side to get the position and angle right. It takes a bit of eye-balling to do this but it isn't terribly hard. Then I establish the correct vertical position on the fuselage side to give a straight line from the connector to the hole in the horn. I do this by measuring from the wing underside to the wire attachment at the servo and at the control horn and then using an appropriate intermediate value (about half).

Now I make the two right angle bends on the end of the wire to go into the horn (it isn't a z-bend -- see photo in earlier blog). I cut the wire to...Continue Reading

The following pictures of two Polari, including my ancient and battered Polaris #1 (fourth season of flying) may help to answer some questions about where the servos go, how the hatches are done, what sort of cooling can be used, etc.

I strongly advise not doing anything that adds major weight to the Polaris, as its light wing loading is a big part of its excellent flight characteristics. But there are some things you can do without adding much weight at all.

Here are the additions I have made to improve the durability of the Polaris on the ones I have built recently:

• Add an extra bulkhead under the battery tray about mid-way between the existing ones. This helps to support the battery in a hard landing.
• Add thin carbon rod, Kevlar thread or 1/8" square spruce inside the rear fuselage sides at the very bottom, running from the base of the fin forward to about 1" ahead of the step. This greatly strengthens the rear fuselage by preventing failure in tension in a sudden stop, when the tail wants to swing forward.
• Add Scotch Transparent Tape or Scotch Multitask Tape over all the wing spar joints, top and bottom. I slot the 1x6mm CF spars (no plywood) into the wing without glue and put tape full length of each spar, ensuring that the joints are tight. Then I flip over, remove each spar in turn and reinstall it with 30-minute epoxy, pulling the joints tightly together with lots of strips of masking tape crosswise. No epoxy squeezes out on the topside because the clear tape prevents it and I wipe off any excess on the bottom. I make sure the spars are flush on the top side, then weight it top down on a flat surface for several hours. Finally, next day, I strip off the masking tape and

...Continue Reading

Just crashed my nice Polaris! Should I scrap it or can it be repaired?

That's an easy choice in all but the most drastic cases of damage. Repair it! Much less effort than building from scratch.

My original Polaris is now in its fourth season and has been repaired at least five times from serious damage (including three straight-in dives due to radio problems and one collision with a 40-powered model that took the entire tail off). The prototype XL suffered a high speed dive at 45 degrees onto asphalt and lived to fly again (that was a really serious accident, but I calculated that it took about half as long to rebuild as it would have taken to build a new one).

Foam that is cleanly broken can simply be butt-glued back together, using either epoxy or foam-safe CA (accelerator is mandatory for the latter).

First you need to cut away any foam that's crushed or bent. Then, assuming the nose is seriously broken, make a cardboard template for the fuselage sides that includes the wing slot, thus ensuring proper alignment.

If the nose is still intact, you can reuse it and just splice in new sections of fuselage sides. Don't remove more material than you need to -- for example, there's no reason the cuts on the two sides need to be in the same place. I always make the splices at an angle to maximize the gluing area.

I use the battery tray as the main means of aligning the fuselage sides, and I don't add top or bottom replacement sections till the interior is...Continue Reading

XL Servo Setup
While building the latest XL, I took photos and notes on the servo installation, so I could do it more efficiently next time. They might help others who are building the XL (or the Polaris, allowing for the different horn length).

One particularly useful bit of information I gathered is the required length of servo arms (measured from the center to the attachment point). This is based on using the standard plywood control horns, which when installed normally in the slots, place the hole about 14mm from the control surface. Since it's made of 6mm Depron and hinged at the top, this means that the total control horn arm length on the XL is approximately 20mm. We want less angular throw on the elevator and aileron than the servo provides, so we need to "gear down" the response by using a servo arm of 10-12mm. For rudder we want a bit more throw, so 14-16mm works well. These dimensions should give all the throw you'll ever need. You should then use travel adjust (endpoint) on your transmitter to give the throws shown in the manual for the starting points. For me this meant setting throw at about 80%, but your results could vary.

Note that for the Polaris the horn place the hole about 10mm from the surface, giving a total effective horn length of about 16mm. So you need a servo arm of 8-10mm.

Please use these dimensions only as a guide in doing your own setup as not only may the mechanical arrangements differ,...Continue Reading