The Bixler build and maiden flight - RC Groups
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This thread is privately moderated by klaw81, who may elect to delete unwanted replies.
Oct 16, 2012, 01:51 AM
Registered User

The Bixler build and maiden flight

There are heaps of threads about how to put a Bixler together, and frankly it's so easy that there's not much more to say. But I've finished building mine, and I'm pretty happy with the result.

I've made a number of modifications to the stock plane, in an effort to make it more suitable for FPV. Most of these modifications have been prompted by other threads on this forum about the Bixler - thanks for the assistance and the valuable information about what works.

My whole fuselage was joined together with hot-melt glue. I am hoping this will allow me to open it up again, should the need arise. The whole process only took 10 minutes or so. I also removed some of the more garish decals, and did a paint job to make the plane a little more distinctive. The tail and undersides of the wings have been repainted, and I will probably add some aluminium foil to the tops of the wings as well. This simple trick reflects the sunlight, even on the greyest of days, and is very helpful with long-distance orientation (and lost planes in long grass).

Here's a list of my mods to the airframe:

1. Remove weights from the nose. This is a simple operation, but they're very well stuck with big globs of hot glue. They took quite a lot of force to remove.

2. Additional reinforcing in various locations:
- a 3mm hollow carbon rod about 550mm long in the base of the tail boom fits perfectly into the groove provided and stiffens the whole structure nicely.
- a 2mm solid carbon rod about 150mm long embedded in the underside of the horizontal stabiliser, just forward of the elevator and glued flush.
- 2 x 2mm bamboo skewers embedded in the vertical stabiliser. The base of the skewers are embedded in the tail boom.
- a 6mm x 0.5mm carbon strip x 500 long, embedded in the underside of each wing. This overlaps with the main wing spar by 200mm or so, and makes the ends of the wings less floppy.

3. I swapped the elevator and rudder servos for new HXT900 servos. I considered moving them to the rear of the plane, but found that I had plenty of room in the fuselage without this extra task. If I end up needing the extra space, I can always do this later.

4. Additional ventilation for the battery, ESC and motor:
- I used a hot metal rod to melt vents into both sides of the nose, and create a similar vent at the top of the tail boom, below the motor. These allow air to blow over the ESC and battery.
- I trimmed around the motor and motor vent to allow more air to flow past the motor and help it to run cool.

5. Velcro wing joiners. I am still experimenting with these, trying to avoid external joiners or hooks - so far it's working while the airframe is fresh and new, but I may have to resort to more drastic measures after a few heavy landings.

6. Additional magnets on the canopy - the stock arrangement has magnets in the fuse and only metal strips (not magnets) in the canopy itself. I have replaced all the magnets with new rare-earth items, and the canopy now clips down very firmly.

7. I replaced the standard prop with a 6x4E prop. The stock prop in my kit was a very low-quality affair, with casting dags around the centre boss and trailing edge of the blades. It was also rather poorly balanced, and way too flexy for my I threw it away. The 6x4E prop was much stiffer and better-constructed, and I just had to carefully ream out the centre to suit the standard Bixler prop adaptor.

8. I have installed flaps to assist with slower landings, and in areas where I don't have much runway. I cut away the rear of the wing, inboard of the ailerons, bevelled the foam, inserted plastic hinges and cut in servo recesses into the underside of the wing.

9. I installed a 'lost-plane beeper' in the Bixler, and glued it to the outside of the fuselage under the wing. It's actuated from the Gear switch on my radio, or if the Rx loses signal. Hopefully, it will help with finding the plane if it goes down in long grass or scrub.

The maiden flight went beautifully. It was perhaps a little too windy for prudent pilots, but I was sick of waiting for the right conditions. Thankfully, the Bixler is so easy to fly that I didn't really have to try; half-throttle, a light toss into the wind and it fly away with very little input. It just has a tendency to dip the nose during launch (due to the motor angle?) but is otherwise very simple.

I had forgotten how relaxing a plane like this is to fly - it's really quite capable of looking after itself. It has plenty of power for steep climbs to a safe altitude, it handles steep banks with only a small touch of rudder required, and it glides very nicely. In fact, it glides so well that I had trouble landing it - I needed 3 passes to get the speed correct and set it down.

I had disabled the flaps for the maiden flight, in case they were going to cause trouble. But since it went so well, they were quickly reconnected. I programmed them to be controlled from the 3-postion switch on my 9X, so I can engage them in two stages, and I've programmed a mix into the elevator so that the plane remains relatively level when the flaps are down. They're gratifyingly effective - even when carrying a fair bit of ballast, you can slow right down and the plane will just slowly descend while maintaining a nose-up attitude. I am extremely pleased with this mod, it was totally worthwhile - plus it's lots of fun to play around with.

I'm absolutely thrilled with the Bixler - it's exactly the training platform I hoped it would be. It's a well-built craft with excellent flight characteristics and it's a doddle to fly. Money well spent, I think.

My next project was to build an FPV platform on the front, so I could mount my camera. More on this next entry.....
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Oct 16, 2012, 09:48 AM
polyfractal's Avatar
Looks awesome! Would you mind posting some more pictures and description of the flaps mod? I've been thinking about adding flaps to my Sky Surfer.

Also curious about which "lost plane beeper" you added. How far away can you hear the beep?
Oct 16, 2012, 04:38 PM
Registered User
The flaps mod is actually quite simple - I just copied the arrangement for the ailerons.

You'll need a sharp knife, some glue, hinges, two spare servos, 2 control rods and 2 control horns, and either (a) one spare receiver channel, and a servo Y-lead, or (b) Two spare receiver channels and 2 servo extension leads.

The process went something like this:
1. Mark out flaps on the underside of the wings - follow the hinge line of the ailerons for a neat finish. Make sure the flaps will stop an inch or two short of the fuselage, to avoid weakening the joint.
2. Carefully cut the flap sections away from the main wing with a sharp knife or scalpel.
3. Bevel the front edge of the flap and the rear edge of the wing. Copy the bevels on the ailerons to make it look 'stock'.
4. Insert hinges along the bevelled edges and glue them in place. I used fabric hinge tape from an old project, but you can use pin hinges or pretty much any sort of flexible plastic strip if you like.
5. Mark out the servo recesses on the underside of the wings. Once again, copy the arrangement for the ailerons, but the recesses should be well clear of the main wing spar area to avoid weakening it. Make sure that you mount the servos in a manner that both flaps will move downwards when engaged. See Note 1 below.
6. Cut out the servo recesses to allow the servo to be mounted flush with the underside of the wing. Be careful not to cut too deep, or you will weaken the wing. Cut along a narrow trench along the edge of the wing spar cover to allow the servo leads to run to the wing joint.
7. Mount the servos in place with hot glue, double-sided tape or whatever takes your fancy. Make sure they're held firmly in position.
8. Attach control horns and control rods, and adjust the rod lengths to align the flaps with their original location. The flaps should now be held firmly in place.
9. Plug in the flaps servos, program your radio to suit and you're good to go.

I will try to post some decent photos of the flaps later on.

Note 1: Your flaps servos need to pull both flaps in the same direction at the same time, rather than moving in opposite directions like ailerons. How you achieve this will depend on which servos you're using, and how you connect them to the radio receiver.

I'm only using one channel to control the flaps - they're both connected to Channel 5 via a Y-splitter from an old plane's ailerons. This would normally make the servos move in opposite directions, but I've mounted one of the servos backwards, so they both "pull" in the same direction.

You could achieve the same result by pulling the servos apart and re-soldering the connections to reverse them, but that is too much bother. Alternatively, you could run the servos from 2 different channels. But mounting the servos so they move in the right direction seems like the easiest solution.

I'm using a HobbyKing beeper: It's not amazingly loud, but it's audible at 100m. If you have a rough idea of where your plane went down, you can follow the sound the rest of the way.
Oct 16, 2012, 07:48 PM
polyfractal's Avatar
Awesome, thanks for the detailed response. I had a vague idea how to do it...your instructions really clarified it. Think I may try to do this on my plane over the weekend.

Definitely going to get that beeper. I'm super paranoid I'll lose my plane somewhere and never find it again
Oct 17, 2012, 08:18 PM
Registered User
The beeper is very cheap insurance.

There's a different one on HobbyKing - depending on your preferences, you might want this one instead:

It can't be triggered by a channel like mine, but it doesn't use up a channel either - instead, it is triggered by a loss of radio signal. So you can turn it on, simply by turning your radio off.

I have tested the beeper in the air, on a still day you can hear it faintly from around 200m away. Note my beeper is mounted outside the plane on the fuselage, rather than inside the battery compartment.
Last edited by klaw81; Dec 30, 2012 at 06:55 PM.

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