scott finnie Posted January 28, 2015 Share Posted January 28, 2015 I Maidened my 70cc cub two days ago and became very proud of her scale like flying qualities. Today whilst taking off there was a strange noise just as I lifted off. I thought it was something getting thrown out the way on the gravel strip . anyway I overhead at 200 feet and bang one blade of my wood 24" propeller split and I cut the engine instantly . I managed to glide downwind and with adequate height perform a normal landing. Now I bought this engine with the prop attached. There's a main but then two security screws. I can't get the main nut to unscrew! Not sure if it's locktite or what but it won't budge. Anything that I can try. I'm beyond devastated since its taking a long time to get her airborne Quote Link to comment Share on other sites More sharing options...
Chuck Plains Posted January 28, 2015 Share Posted January 28, 2015 Heat up the nut? Is there a possibility it has a left hand thread? I know nowt about engines as I've always been into electric. Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted January 28, 2015 Share Posted January 28, 2015 Scott-as chuck says-put your soldering iron on it for a few min's - probably the prop was on its last legs anyway...check its not something like a left hand thread...... ? ken Anderson....ne...1 heat dept. Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 28, 2015 Share Posted January 28, 2015 Do you know what engine is on there? It is very unusual for a prop to split like this unless already damaged. A picture would be interesting to see what has happened Quote Link to comment Share on other sites More sharing options...
Shaunie Posted January 28, 2015 Share Posted January 28, 2015 Scott, If it's been loctited then warm it up with a heatgun or small pencil flame type of gas torch. That should free it up, doesn't need to be desperately hot. At least with the security bolts and the prop you have some means of the crank still, or is the prop completely off it now? Shaunie. Quote Link to comment Share on other sites More sharing options...
scott finnie Posted January 28, 2015 Author Share Posted January 28, 2015 Its an Avio Mac 70cc twin I'll post a photo later of it once I have the engine off Quote Link to comment Share on other sites More sharing options...
reg shaw Posted January 28, 2015 Share Posted January 28, 2015 Scott, was the prop fitted when you got it, and had you had it off since? Sometimes with wooden props, if its been on there for a while, the wood compresses and the bolts become loose. Then, on multibolt hubs the securing bolts either shear off or the blade itself fails. Could this be the issue here? Ian. Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 28, 2015 Share Posted January 28, 2015 You did mention flying off a gravel strip. A stone may have hit the prop and cracked it. Still doesn't explain its reluctance to come off though! Quote Link to comment Share on other sites More sharing options...
scott finnie Posted January 28, 2015 Author Share Posted January 28, 2015 Hi all the prop had never been off. Its a strange break. There's still two blades though one is split right from the hub to the tip. I recovered the absconding part aswel and its a clean break Quote Link to comment Share on other sites More sharing options...
reg shaw Posted January 28, 2015 Share Posted January 28, 2015 That sounds like the issue then Scott, the prop was loose and rotates around the centre, the fixing bolts then shear or in this case lever the blade apart. Ian. Quote Link to comment Share on other sites More sharing options...
scott finnie Posted January 28, 2015 Author Share Posted January 28, 2015 Clean split from near hub though there certainly was gravel flying around on the usually more solid ground Quote Link to comment Share on other sites More sharing options...
scott finnie Posted January 28, 2015 Author Share Posted January 28, 2015 Looks like previous owner had tried to make hub security screws elsewhere too. Could this have resulted in a weaker prop? Oh. I've the prop off now thankfully. A little hammer drill and heat thanks for all the advice Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted January 28, 2015 Share Posted January 28, 2015 Perhaps he started a hair line crack when he was drilling the hub, probably all but invisible to the eye, but the weakness would be found when it fired up Quote Link to comment Share on other sites More sharing options...
avtur Posted January 28, 2015 Share Posted January 28, 2015 Prop failure pretty catastrophic, just glad you had the height to recover and land. The drilling of security screws looks odd, must be at least some cause for concern. Maybe replace with one of those carbon fibre props recommended on the other thread! Quote Link to comment Share on other sites More sharing options...
scott finnie Posted January 28, 2015 Author Share Posted January 28, 2015 Yes Avtur I agree. I'm looking at a suitable carbon prop now. Just glad it happened at height. I'd also add that I should have checked the propeller properly though as it was attached I believed that the hidden part under the hub would have been in the same perfect condition as the res . Lesson learned , I'm hoping a 24x12 will be ok Thanks Quote Link to comment Share on other sites More sharing options...
Levanter Posted January 29, 2015 Share Posted January 29, 2015 I can see the four mounting holes in the hub but can I see a fifth hole top left of blade photo and bottom right of hub photo? Quote Link to comment Share on other sites More sharing options...
Jon H Posted January 29, 2015 Share Posted January 29, 2015 Posted by scott finnie on 28/01/2015 21:25:12: Clean split from near hub though there certainly was gravel flying around on the usually more solid ground There seems to be impact damage to the leading edge just at the pointy end of the broken off section. Looks like a large impact from the semi circular pattern I do however see that errant 5th hole, and looking at the hub of this ^ photo the hole seems to reappear. Most odd. In any event, a wooden prop is not any weaker than carbon from the point of view of damage resistance. Personally I would stick with wood Edited By Jon Harper on 29/01/2015 08:50:51 Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted January 29, 2015 Share Posted January 29, 2015 hello scot-may have been on its way when you bought the model? ....double check with the lads who know-if you are going to a 3 blader...you may need to lower the dia etc......save all your dosh been wasted........ ken Anderson...ne....1 wasted dosh dept. Quote Link to comment Share on other sites More sharing options...
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