Logo 500 Tail Issue

[nb8686]

Hi,

This is my second Logo 500 (with carbon tail). I have a few incidents with the push rod tore and lost control of the tail completely. I managed to bring the heli down safely with auto in two of the incidents but not the last one. After many days of effort, I found the cause was due to tail rotor shaft heated up to high temperature, and this was related to the carbon belt tensioner length. The carbon belt tensioner consists of one bearing (4mm thick) an two pvc sleeves (9mm each). This will give a total length of 22mm, same as the length of the tail hex bolt. However, what I found was the actual length of the pvc sleeves is only 8.7mm. This means the total length of the tensioner is only 21.4mm instead of 22mm. Because of the 0.6mm short, additional pressure is put on the bearings (on the tail rotor shaft). And this extra pressure caused the bearings to heat up itself and the tail rotor shaft. To solve this problem, I add a 0.5mm washer between the vertical CF fin and the pvc sleeve (see picture below).

[feudallordcult]

interesting find

thanks for sharing. just a query though: can the temp of the bearings be elevated to such levels that may cause tail failure? Wow, I thought nitro vibes was bad enough.

[nb8686]

Yes, the tail shaft temp is so high that I can't even touch it for a second. And the temp can be so high just after running the rotor for one minute. So, you can imagine after running it for 5 minutes. During the first two incidents, the push rod was damaged. I believe the pitch control sleeve actually jammed (it could not slide). But, during the 3rd incident I could hear loud sound "piak piak piak..." before I cut the throttle. I believe this time the tail rotor shaft jammed and the belt slipped.

[feudallordcult]

Erm, torque tube to the rescue?

[nb8686]

Logo 500 does not have a torque tube version. Anyway, the problem is not caused by the belt drive, it was an issue with part tolerance. Mikado really does not do a good job in part tolerance control.

[nb8686]

Just to share how you can strengthen the push rod for Logo 500. All you need is to put a heat shrink tube at the joint between carbon rod and the metal rod. See the picture below. I find this really improve the strength of push rod a lot.

[feudallordcult]

mind sharing how a piece of heatshrink can actually enhance the strength? I m v curious to learn more abt this...to enhance the 700n experience lah. Thanks in advance for sharing though.

[nb8686]

mind sharing how a piece of heatshrink can actually enhance the strength? I m v curious to learn more abt this...to enhance the 700n experience lah. Thanks in advance for sharing though.

In the first two incidents, the push rod was damaged when the tail control sleeve was jammed because of the heating of tail rotor shaft. The metal rod was pulled out of the carbon rod, with the carbon rod split open near the end.



What happen is the pull force (from the tail servo), through the metal rod with glue, generates outward forces against the inner surface of the carbon rod. When the outward forces reach a certain amount, it will split open the hollow carbon rob and the metal rod will just come out. So, by adding heat shrink tube, it will add extra strength to handle the outward forces so that the carbon tube will not split open easily. To add even more strength, you can use double layer heat shrink tube.