A lesson in thrift. Traditional modellers will know this but new builders might learn something.
|David Davis||11/07/2019 10:30:46|
3528 forum posts
Last year I built a Baron. This is a simple three-channel trainer and I entered it in a competition, "La Coupe Des Barons," or the Barons' Cup, in which you fly four rounds. Two of these are at high speed, the other two are flown close to the ground and all four rounds are flown in company with up to nine other models, so it's not unusual for sixty percent of the entry to become seriously damaged during the course of the day. More details here for those who are interested: scroll down to "Video Coupe 2018." **LINK**
I damagerd my first tailplane in practicing for the event last year so built a second tailplane using basswood to reinforce the leading and trailing edges of the tailplane instead of balsa. The picture below shows the original all-balsa tailplane under construction but you get the idea.
Since building my first Baron, I've built a second incorporating some modifications to save weight. As this year's rules allow for the use of a four-stroke motor up to a 52 I fitted an OS 52 in the nose and used carbon fibre pushrods for the first time.
I did not realise that you had to fit locking nuts to the clevises when using this system and the rudder pushrod unscrewed itself. I had no directional control and the model crashed. I had substituted basswood for balsa fuselage longerons so the fuselage was undamaged and the wing was only superficially damaged at the trailing edge of the centre section. The engine however, suffered a damaged cylinder head anybody got a spare one they would like to sell?
The tailplane didn't look too bad at first but further examination revealed that considerable surgery would be required. So I stripped off the covering, then my eyes fell upon the original tailplane. "Surely" I thought, " I could scarf in some of the old tailplane into the new one." The picture below shows one half of the old tailplane still covered in checkered film, the other half stripped of its covering and the model's tailpalne taken down to sound wood.
Having cut a couple of 45 degree lines on the leading and trailing edges of the old tailplane I matched them up to new tailplane and cut matching 45 degree lines on that. Then I drilled four holes into the leading and trailing edges of the structure to accept short lengths of carbon fibre rod to reinforce the joint. The picture below shows a dry fit before I used half hour epoxy to glue the wood together. The trailing edge carbon fibre rod is just visible.
A little sanding and the tailplane structure is repaired.
The elevator was also damaged in the crash and I resorted to scarfing in new wood over the plan.
A little more work with the sanding block, some hinges and covering film and the job's a good un or at least an acceptable one! The model will probably get wiped out in La Coupe anyway!
The cognoscenti will say that the diagonals of a scarfed joint should be four times the size of the wood. E.g. with 1/4" sq balsa the joint should be 1" long but using carbon fibre rod I think I'll get away with less and I won't forget to use locking nuts either!
721 forum posts
The mjetion of a locking device for use with carbon control rods prompts me to ask how to these ( the silver items) work? I’ve tried to fit them in various guises, but nothing I’ve tried is correct, or doesn’t appear to be!
Cheers to all.
|will -0||11/07/2019 13:42:22|
582 forum posts
Those are clips which go over the end of the pin on the clevis to stop it opening. They slide on sideways into the small grove in the pin.
Belt and braces.
Edited By will -0 on 11/07/2019 13:44:01
Edited By will -0 on 11/07/2019 13:44:59
721 forum posts
Oh it’s so simple now! Thanks will-0
|Nigel R||11/07/2019 15:12:12|
3405 forum posts
On Sullivan snakes, then you also definitely want a locknut up against the threaded part of the clevis. Bizarrely (I think) Sullivan do not supply any in the pack with the snakes (either 2-56 nuts or 2mm nuts, depending on imperial or metric flavour).
|Percy Verance||11/07/2019 15:36:32|
8108 forum posts
Also be aware that the normal commonly used Sullivan snakes - the yellow and blue variants - are not thermally stable, which means they expand and contract in hot and colder conditions. If you don't want this (and it can be a pain) then go for the carbon versions. But again, do these cause issues with 2.4ghz gear? I ask because I have yet to try them.
721 forum posts
Ok, I have noticed any expanding/ contraction issues, if they were there I probably unknowingly trimmed them out.
searching for nuts now, as stated none included, and no mention of them instruction wise.
Thanks for the info.
|Nigel R||11/07/2019 16:17:05|
3405 forum posts
they do, but they're not that bad, its a click or two at most in my experience
any effects of expansion can be minimised by using a nice big control horn and a long servo arm
|Steven Shaw||11/07/2019 17:11:17|
344 forum posts
Glyn - Sullivan also sell a very handy little TOOL that makes installing and removing the clips very easy.
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