Landing is Inevitable

Thursday, March 01, 2007

Extra build log (continued)

I was thinking about writing a whole build log but I'm not really that good at it. Anyways, there are tonnes of better builds of this plane on RCGroups and this other German forum (the website eludes my memory at the moment). I figured I'll just show some pictures and have some short description of it at the bottom.

At long last my motor arrives, the AXI 2814/20 (thanks Mack). It was a very good deal. Initially I planned to adhere strictly to the recommended prop size by the manufacturer. But after reading through the forums, most of the motor users said that it can take up to a 12inch size prop and still handle the load eventhough it was considered grossly over-propping the motor. I did some bench testing of the motor with different props and this was what I got:

APC 12x3.8SF prop at WOT: 22amps (no spinner)
APC 12x3.8SF prop at half throttle: 3-4amps (no spinner)

APC 12x6SF prop at WOT: 25.5amps (no spinner)
APC 12x6SF prop at half throttle: 5-6amps (no spinner)

APC 12x6SF prop at WOT: 29.5amps (with spinner)
APC 12x6SF prop at half throttle: 7amps (with spinner)

Not bad numbers for bench testing. The motor was barely warm in all the tests and at half throttle the plane was already quite a handful to hold back. I expect the amp draw to unload a bit in flight and that would give me a piece of mind. Even though the spinner cap does add to the amps drawn, I'm leaving it on for both aesthetic reasons and I believe that it will help in the aerodynamics department however miniscule.

During this build, the component which has caused me the severest of grief was the prop adapter. I went through two "no brand" ones from two different local hobby shops and was frustrated with both of them. In the end, I went for original AXI prop adapters which was just a few dollars more expensive and was immediately gratified. It stuck to the shaft with no budging and with a simple tilt of the sleeve it was out. Amazing! Word of advice, go for the good shit. It will not let you down.

The other component which was a pain in the posterior was the spinner cap. As expected the stock spinner cap was causing major vibrations. I could easily see the tip of the spinner making a circle with a 1cm diameter at half throttle and dare not go any faster. I shudder at the thought of the major vibrations it will cause at higher rpms. I got another one with a thicker base from another local hobby shop. It looked good, but alas, I had increased the size of the mounting hole for one of the dud prop adapter and it was way to loose for the AXI one. Safe to say, I was not going to use it, not on this plane anyways. Finally I got one spinner with an aluminium base plate. It tracked well and the tip did not move from what I could see. Now the plane looks good.

The motor mount was a bit tricky. The given holes were not lining up to the AXI motor I had. If I were to drill new one on the existing motor mount it will severely compromise the integrity of the whole mount. My simple solution was to CA a balsa sheet to cover the mounting area and drill new holes. It works and looks rather solid. After finding out what the funny sticker with the mounting holes markings, that came with the motor, was for some time back, I successfully used it to line up my new mounting holes on the new balsa plate. Personally, I'd rather front mount the motor, it's so much easier and it provides for better cooling of the motor. planes has this kind of mounting and I love it. And there are no pre-drilled holes so customisation is a breeze and there is no structural compromise of the motor mount plate.

I thought that the cowl was rather flimsy and guess what, before anything there was a crack at the front. I CAed it at the crack and in an attempt to strengthen the front part of the canopy, I coated it with a blend of Epoxy and micro baloons. That should do the job, I hope.

The other thing almost worth mentioning in my build is the extension of the servo wires. For the wire extensions to fit into the servo wells, I had to remove the extension wire connector cover. This also helps in reducing some weight. Yeah that's it.

Also had loads of fun checking the throws with my new throw meter. Makes this process a breeze. What used to be a chore is now kinda fun. And it also gives me that piece of mind that its all accurate.

I do plan to remove more weight after initial test flights though. The back part of the battery plate is slated to be removed and I will be making two 1cm wide holes on the firewall. That should knock off a few more grams.

I will also add ball bearings to the wheels so that id doesn't get eaten up by the threaded axles. This will also help the wheel track better and improve the general lifespan of it.

"The elevator and the horizintal stab."

Woah, that was a wordy post. So much for just slapping in pictures and writing descriptions. I'm just your typical talkative uncle. What to do? As I identify anymore significant mods to be done to the Extreme Flight Extra, I'll progressively update it on the blog.

Signing off,


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