Multiplex Fun Cub

[Stephen Grigg]

What do you think causes the problem then Steve,I imagined the strengthening being above and below because the fuselage itself had weakened

[Steve W-O]

Posted by Stephen Grigg on 31/10/2011 09:35:11:
What do you think causes the problem then Steve,I imagined the strengthening being above and below because the fuselage itself had weakened

 

 

When I saw the descriptions of yours ans others problem, an lookking at mine, I thought that we could not all have missed an unbalanced prop or loose mounting.

 

Then I thought about how mush meat I had removed from the prop to get a static balance, and thought that my problem was caused by unequal thrust on each blade.

 

Thje only movement I could find that could be caused by this was a side-to-side flexing of the motor mounts, most likely where the section is suddenly reduced behind the screw holes. That was the thinking behind the strengthening.

 

And yes, you would be right, when the fuselage is new, that would have been damped by the firmer foam, but after time and natural vibration, the foam "gets a bit softer" or deforms slightly, allowing the vibration.

 

If it works on yours to, the theory is probably correct, if not, I was just lucky

[Terry Walters]

A new Fun Cub has taken to the skies over SW France today!

 

Finally got to maiden my FC today. Weather has been a problem since I got back from UK and wind especially frustrating. Today - we had a really nice almost Spring-like morning so took the plunge and decided to fly early pm. Got to the club and guess what - yes the Lot Department decided to have fun with the wind! Gusting 15/20K at times and swinging about 90 degrees when it fancied doing so! As it was french wind I decided that as a Brit I could handle it. As I hadn't flown at all for about 5/6 weeks I flew the Cessna 185 foamie first and managed to get that down without incident.

 

So - decision taken - flew the Fun Cub. As it lifted off the tarmac and went vertical after about 2 metres SWMBO (who bought it for my birthday in Sept and came along to support me) screamed! Wow - the E-max 2815/09 on a 2300 3s took it vertical no problem! After a safe height I throttled right back and sat into wind on the hover. A quick stall check - no probs and then a few turns - checked flaps were working fine and then did a few mock approaches. Very interesting trying to get it down on the strip in the gusty conditions but we made it thanks to a stall at about 4 feet when the wind dropped suddenly! No damage.

 

Off again for another 3 short flights and landings - all on the one Lipo. Had about 9mins in all with plenty to spare but a lot of the time the throttle was almost off in flight. Might try a 2700 or 3000 next. Discretion the decreed that I should quit whilst I was ahead.

 

Verdict - Brilliant - real lot of 'fun' - great turn of speed and really slow flying too. Looking forward to lots of flights. Now I have tested it I will be happy to fly it over the field at the back of my house without wondering if it will end up with it's tail sticking out of my neighbour's tobacco poly- tunnel (yes it has happened before but the entente cordial has been restored after I repaired it!)

 

Terry

[Stephen Grigg]

Congratulations Tony now you can have fun.Ive kept my with a 2200 battery and get up to 20 minutes pewer flight depending on how Im flying .I have 5 of them so i get plenty of flying in.

[Stephen Grigg]

Steve W-O has kindly sent me the square rod he used on his Fun Cub to strengthen the motor mounts which may be flexing.Ill shortly do the mod he has shown on a post a little furthr back and report in when ive glued and tested.Suffering with a real man cold at the moment so not much energy.

[Stephen Grigg]

At the field today a new Fun Cub arrived.The gent is a new member and had fitted the motor on the outside making a new mount for the motor from plywood instead of the supplied mount.He had the battery under the wing. centre.The reason he fitted the engine as he did was he was convinced you couldnt move the motor shaft.He seemed convinced of all of his facts and wasnt to be swayed.The model flew very well so what do i or Multiplex know!!

He flew without the hatch because he had misplaced it!!

[Steve W-O]

I would call that as a funny cub, not a Funcub.

 

Very odd placement of the internal organs

 

edit:  Looks like quite a small motor too, though I'm sure it will fly fine

Edited By Steve W-O on 17/11/2011 18:23:26

[Stephen Grigg]

The motor looked a lot smaller than mine,didnt see him take off he paid £12 for it from Hobby King

[Stephen Grigg]

Im ready to do the mod recommend by Stevie W-O .he kindly sent me the parts,I filed them in a safe place,sp safe Im tearing the house apart looking.Its a picture as clear as day but seemingly as dark as night,the search continues

[Stephen Grigg]

Ive searc hed and found what I was looking for ,thanks Stevie W O,so I can now try the mod he recommends

[Steve W-O]

I hope it turns out as successful as mine, no problems now

[Stephen Grigg]

Ive carried out tghe mod to your recomendations using epoxy,Ill let it cure overnight and let you know the result tomorrow

[Stephen Grigg]

Refitted the motor today and ran it up and Stevie W-O "S mod appears to have worked.Havent flown the Fun Cub for ages so put some batteries on charge and as soon as there is a "window " in the weather I can have a go.

[Stephen Grigg]

Spent time charging batteries and fitting the right ends on sm=ome fresh batteries ready for today.With a fresh battery decided to give the Fun Cub a final test.Slowly brought the revs up to over half and all sounding fine.Gave it a bit more and saw the front end suddenly vibrate and the carbon rods flew every where and the vibratition almost took the front end off.Back to the drawing board.Im going to mount the motor in a vice and test it before I do anything else.

[Stephen Grigg]

I carried out a test on the motor this afternoon.I placed it in a vice and havin the FC behind was able to use the power set up in the model to control the motor.It ran perfectly so the weakness appears to be the fuselage.Dont know why Steve w-o mod faile.I have agood sized motor that is now black .Although it spun free obviously was rubbing the carbon rods maybe that affected the epoxy and they failed.Im trying to think of an alternative to a new fuselage

[Stephen Grigg]

My test bed

[Steve W-O]

Sorry to hear it didn't work.

 

I wonder if the rods were stuck, I'm not sure epoxy would stick to the white engine bearers i each side of the fuselage.

 

I am using a smaller motor, which I imagine would make the problem less stressful to the fuselage.

 

Are all four of your adjusting bolts in far enough to manke firm contact with the bearers?

 

I wonder if Multiplex have any ideas, as there are at least three of us who have had the problem so far here, so I'm sure there must be more.

[Stephen Grigg]

Hi Steve I know that Galaxy told me that if anyone has reapaired the front end of the Fun Cub it vibrates afterwards.A clubmate bought a Fun Cub at Blacebushe and he was also sold a power set but not Multiplex.He couldnt get the motor to fit it was so big,.He shaved the fuselage down to get the motor to fit and that also has a massive vibration.I think his is a cnbination of to much power and having shaved off so much material he has weakened the fuselage as well.Im chewing over some ideas

[Steve W-O]

Posted by Stephen Grigg on 02/01/2012 16:18:26:
Hi Steve I know that Galaxy told me that if anyone has reapaired the front end of the Fun Cub it vibrates afterwards.A clubmate bought a Fun Cub at Blacebushe and he was also sold a power set but not Multiplex.He couldnt get the motor to fit it was so big,.He shaved the fuselage down to get the motor to fit and that also has a massive vibration.I think his is a cnbination of to much power and having shaved off so much material he has weakened the fuselage as well.Im chewing over some ideas

 

 

Interesting, I imagine the repair would take some of the rigidity out of the nose section.,

 

It would explain why the mod worked on mine, though I don't know why it didn't work on yours.

 

I think I will make some cuts into the outside of the fuselage and CA some thin carbon strips into the cuts, it should extend the lifespan by making the front rigid.

 

I have another one still in the box (actually an Easycub, but I have spare Funcub wing joiners) I think I will insert carbon strips inside before joining the fuselage.

 

I think it only the front section, so to take the strips back as far as the leading edge should do the job.

[Stephen Grigg]

I think thats a good idea,someone suggested I glass fibre inside the front.Did you use cyano on your strips,I could try that.I also have a smaller motor I could try also

[Stephen Grigg]

What glue would you recommend if I used fibreglass.I thought of sticking the carbon rods on before fibreglassing

[Steve W-O]

Yes, I used cyano, epoxy does not stick tp many plastics.

 

I don't think glassing would be a practical idea, because the epoxy will not stick well to the elapor.

 

A smaller motor may help, but the problem needs fixing, oterwise it will come back.

 

I have some carbon strips that are .5mm X 3mm, so easy to glue into a knife cut, and in the 3mm direction would be very rigid, about 4 strips on each side and a couple on the bottom should add a lot of stability.

 

May also be worth checking if your white motor bearers are not loose, and drop some ordinary cyano (not foam safe) between the bearers and fuselage.

 

I think the carbon rods need to be stuch back with cyano, sand the epoxy off first though (stick some wet or dry on a piece of wood to get in easily)

[Stephen Grigg]

I can do that Steve and see how it goes.I had benn thinking that.The Motor brarers are good and tight

[jeff2wings]

Steve , I’m afraid to say that all the suggestions made are just “sticking plaster” fixes and you need to be braver to make a proper repair (IMHO that is) in the form of some light ply doublers that you can attach a ply motor plate to , there seems to be a fundamental weakness with the motor mount that is being made worse with the bigger motor , the doublers will stabilise the structure and give you a sold mounting area , if that makes no sense I can do a sketch for you

[Steve W-O]

Posted by jeff2wings on 02/01/2012 21:44:55:

Steve , I’m afraid to say that all the suggestions made are just “sticking plaster” fixes and you need to be braver to make a proper repair (IMHO that is) in the form of some light ply doublers that you can attach a ply motor plate to , there seems to be a fundamental weakness with the motor mount that is being made worse with the bigger motor , the doublers will stabilise the structure and give you a sold mounting area , if that makes no sense I can do a sketch for you

 

I don't know which Steve you are answering!

 

I don't think the problem is the motor mount, the problem is flexing of the fuselage, which it seems happens with age, or after being bent.

I'm sorry you see embedding carbon rods as a sticking plaster fix, it is an accepted way of stiffening foam, which is the aim.

 

Fitting light ply doubles may be an option at the original build time, but would be quite hard after the fuselage sides have been joined, as in SG case, material would have to be removed to allow his big motor to fit. Of course the fuselage could be split with a knife, but that is one option.