Cub MJ3410Z Scratch build

[john66]

I understand that the following questions are probably answered throughout other posts. I simply like others would like to document my build in one thread and therefore have answers for my specific questions contained within.

When it comes to reinforcing the wings is there a structural preference to reinforcing from the top of the wing or underside?

I am inclined to think it would be preferable to do it from the top as I will be definitely adding at least ailerons and therefore have more electrics/rods/linkages on the underside.

I would appreciate any viewpoints on this.

Next I was wondering Is there any structural strength significance between using carbon rods or strips inserted vertically.

I prefer the idea of using strips vertically as I imaging they will be easier to conceal, I have seen some 3mm x 0.6mm which I think would be ideal.

This leads me on to question whether I should leave any dihedral when fitting ailerons? This would take away alot of the stability & self righting properties I understand, but again it would be easier to insert & conceal carbon rods/strips in a flat wing.

Lastly for this post what is the overall consensus on flaps or not? I guess I need to make this decision in advance before covering for a better finish.

Thanks, John

[Legot]

I'm not sure what most do, but mine is slotted into the top in the thickest part of the wing. you can't even see it now that it's covered.

I say vertical strips, it isn't necessary to stop forward backward flexing, it doesn't happen. also, vertical strips offer the most support (easily) on vertical flexing when slotted vertically, as is to be expected.

It is up to the builder weather or not he takes out the dihedral, you are correct about the effects of removing dihedral. From experience, I prefer removing dihedral with ailerons. Dihedral + ailerons + cub = sluggish in in my opinion. When I tried ailerons+dihedral, it reminded me of the rudder only controls. It also doesn't allow for very Axial rolls.

On flaps, (the fun part ) I like them it allows for slower landings with a higher alpha. I see no reason to not put on flaps, if you use the method that Helikiwi thought up, it adds a more scale appearance. You don't have to use them If you don't like them!
It also creates more lift , allowing for heavier payloads and for the cub to really float.
supercubclub.proboards.com/index.cgi?action=display&board=aelrns&thread=3091&page=1#21107

In conclusion, CF can slot, Dihedral can stay or go, and flaps can make it float
~Legot

[john66]

Thanks for the input Legot, appreciated.

John

[Dillzio]

Well as you probably know I'm building my new cub at the moment, so I can't offer any feedback on how it flies, but I can share with you the experience I've had with mine so far.

I put three thin carbon strips in the top of mine, I would highly recommend them as they are very easy to install and conceal - I used the 3mm by .6mm in mine too. You can install them just by making a single cut with a hobby knife then pushing them down into the cut, no need to cut out a channel. You have to stretch open the cut with a flat head screwdriver to open it up a bit, but after that the carbon goes straight in, and it's tight enough a fit it allows you to bend the wing to adjust the angle of the dihedral and it will stay where you bend it. I have decided to go with a small dihedral, the wing tips are about 9mm higher than the level of the base (vs 37mm stock), so hopefully it will be flat enough to still roll well, and have enough dihedral to still have some of the cub's self-righting attributes.

I recommend putting the carbon in the top, because that is where it will give you the most structural support to prevent the wing from folding upwards. After I installed two spars in the top of my wing, I found they prevented the wing from bending upwards much more than bending downwards, so a carbon spar on the bottom of the wing didn't really seem necessary, and I put the third spar in the top too. I think this works out much better, because it leaves the underside of the wing free and clear for any ailerons servos or wiring you may want to install.

I did make a bit of a video build log if your interested, but it wasn't rocket science really. The only trick was to use slow setting epoxy so you can take your time and get it right.

With regard of whether to use flaps or not? Well the super cub it a pretty slow flying plane anyway, it's not a jet. It would be hard to argue that our foam RC cubs NEED flaps. I think we just add them cos we think they're cool, they make the plane more true-to-life, and it's an extra toy to play with :-)

When it comes down to it, if you're putting ailerons on your plane, it's not much extra work to put flaps on too. Just make sure you've got a spare channel on your radio.

[john66]

Thanks for the feedback dill. I have bought the 3mm x 0.6 carbon strips, and have decided to add the flaps as I intend to cover the plane and dont want to decide I would like them later, so thanks for the input.

I have also decided against trying to add the clear canopy for a couple of reasons.

1. It looks quite a difficult mod to get right!

2. I would really rather get rid of the rubber bands and put a wing bolt in instead. I therefore think you wouldnt see much worth seeing through a clear canopy.

I figured if im not going to attempt the clear canopy I would give this stuff a try instead of the black window stickers.....

cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120566066728 I contacted the seller to find out the sample size which is 10cmx10cm he was more than happy to supply any size. He normally sells it in rolls.

I was able to order 20cm x 40cm for £1.99 inc postage that should be enough for 2 attempts at getting it right. I figured that cos it normally sticks to the window from the inside I may need to put it on back to front and put some clear adhesive / tape across it to get the reflective side on the outside and probably stick it to a grey background window template. Not sure how it will look but figured worth a try.

John

[Dillzio]

HEY! nice idea on the window film! I've been thinking about something similar because my cub is black, so black window stickers are a bit useless. I'm looking forward to seeing how it works for you :-)

A wing bolt sounds to me like something that may make the cub much more breakable. If your wings run crash into something with rubber bands on, the rubber bands bend, the wing struts break and your cub lives to fly another day.

I'm just using rubber bands to hold my wing on, I don't think there will be much need for struts with three 1m carbon strips in the top of the wing. I am however considering supplementing the rubber bands with a few little neodymium magnets - I got 50 of them for like $4 off ebay so I may as well put them to good use.

[john66]

Jun 4, 2010 6:36:29 GMT 1 Dillzio said:

HEY! nice idea on the window film! I've been thinking about something similar because my cub is black, so black window stickers are a bit useless. I'm looking forward to seeing how it works for you :-)

A wing bolt sounds to me like something that may make the cub much more breakable. If your wings run crash into something with rubber bands on, the rubber bands bend, the wing struts break and your cub lives to fly another day.

I'm just using rubber bands to hold my wing on, I don't think there will be much need for struts with three 1m carbon strips in the top of the wing. I am however considering supplementing the rubber bands with a few little neodymium magnets - I got 50 of them for like $4 off ebay so I may as well put them to good use.

Its gonna be a while before I get to the stage of trying the film out, so I will post a pic of it against a black background for you to see when it arrives. Matt or gloss black dill?

Yes I agree I have been considering the structural integrity of bolt on wings and the forces that will be exerted on the inside of the fuse walls.

ginginho your multiplex twinstar is bolt on wings I recall, any chance of some close up pics of the fixings inside the fuse?

helikiwi, have you had any probs with the bolt on wings from bad landings?

It just seems such a shame to put time and money into making a pretty lookin bird only to sling some rubber bands over the top! Like you say about the flaps dill, more for looks than use.

John

[ginginho]

Jun 4, 2010 12:09:14 GMT 1 @john66 said:

ginginho your multiplex twinstar is bolt on wings I recall, any chance of some close up pics of the fixings inside the fuse?

John

John, the twinny does have bolt on wings. The mounts in the fuse are slotted into the two fuse halves during construction. Additionally, the wing is a two piece and is held in place by plates that have n!pples that sit into dimples in the wings themselves, allowing the wings to come away in an impact.
The Gem has similar mounts but the bolts are through sleeved holes adding a bit of strength around those areas, both in the top and bottom wing. I know if I stack that, it will be damaging.
I'll take some pictures and post them.
Have you been getting plenty of crash free air time? I don't want to sound like the voice of doom, but you really want to be sure that you can fly confidently and without any incidences before you pretty up your baby, or it could end in disappointment.

[john66]

Cheers for the info ginginho, the cub im referring to is not gonna go in the air until Im fully confident with my first one.

I have had some more flight time recently due to the fantastic weather in the last 3 weeks but unfortunately due to long grass in the local field and my own skill, my landings need alot more work. albeit the last few times I have taken my cub out I have managed to bring her down without sustaining any damage, so somethings improving!

Look forward to seeing the pics.

John

[ginginho]

OK, pictures taken. First shows the MPX manual on how the mounts (parts 33 and 34 which are threaded in the middle) are fitted in the fuse of the twinny (pretty much the same on the Gem):

This is how the wings are bolted on, notice the plates with n!pples and dimples in the wing:

This is the real rear mount on my Twinny:

Part 34 in this one is the top sleeve that strengthens the mounting area of when the bolt goes through on the Gem. The bolt head is recessed in parts 7 and 34. The top wing is glued to the two near vertical uprights (part 6):

Hope that helps.

[ginginho]

Jun 4, 2010 12:51:45 GMT 1 @john66 said:

Cheers for the info ginginho, the cub im referring to is not gonna go in the air until Im fully confident with my first one.

I have had some more flight time recently due to the fantastic weather in the last 3 weeks but unfortunately due to long grass in the local field and my own skill, my landings need alot more work. albeit the last few times I have taken my cub out I have managed to bring her down without sustaining any damage, so somethings improving!

Look forward to seeing the pics.

John

Good stuff. Weather is looking good for tomorrow and possibly Sunday, fancy coming over our way again?

[john66]

Jun 4, 2010 13:04:56 GMT 1 ginginho said:

Jun 4, 2010 12:51:45 GMT 1 @john66 said:

Cheers for the info ginginho, the cub im referring to is not gonna go in the air until Im fully confident with my first one.

I have had some more flight time recently due to the fantastic weather in the last 3 weeks but unfortunately due to long grass in the local field and my own skill, my landings need alot more work. albeit the last few times I have taken my cub out I have managed to bring her down without sustaining any damage, so somethings improving!

Look forward to seeing the pics.

John

Good stuff. Weather is looking good for tomorrow and possibly Sunday, fancy coming over our way again?

Definitely....will talk to the gf when she gets home, re car usage.....fingers crossed for me. I really could do with some help with my landings.

John

[john66]

Thanks ginginho for taking the time to take & upload the pics of the wing mount diagrams, appreciated.

John

[john66]

Jun 2, 2010 23:14:09 GMT 1 Legot said:

I prefer removing dihedral with ailerons. Dihedral + ailerons + cub = sluggish in in my opinion. When I tried ailerons+dihedral, it reminded me of the rudder only controls. It also doesn't allow for very Axial rolls.

Out of interest what method did you use for removing dihedral...Did you cut a v out of the foam either side of where the wings meet the fuse & glue or did you just use weight to flatten it?

Thanks, John

[Legot]

I just cut half way through the wing along the two angled areas where the dihedral begins, then I clamped the wing to the table flat, and filled the channels that were formed with gorilla glue.

after the glue was in, I covered each channel with a peice of tape to prevent glue over expansion.