Bambina 31" sport electric building log

[robk]

As there doesn't seem to be much on this RCME free plan project I thought I might cover it here. I was looking for a smallish aerobatic model that would fit in the boot of my MX5, using the motor/esc etc from my very old and very well flown HK Kinetic which I retired as it was starting to become more glue than foam. This seemed a pretty little plane that would fit the big, and with the slightly more powerful motor from the Kinetic be quite interesting to fly. I will be making a few modifications to the design to suit my own needs but also because I think they might work a bit better. I will note these as I go along.

 

 

Edited March 7, 2021 by robk

[robk]

I did notice a few mistakes in the plan - e.g. there is no allowance in the wing rib layout for the 1.6mm balsa covering on the leading edge. The built model differs quite a bit from the plan as well - maybe because builder and designer were on different continents! I also extended the plan for the wing, which actually could have been fitted onto the sheet if they had arranged it better. I don't know why there isn't a fuselage plan but I think I can do without. These issues are only minor though. My motor has a front mounting rather than a rear one so I omitted F2 and changed the design of F1. First job in the actual build was making my own 'kit' tracing off the components from the plan and cutting them to shape. This took only a few hours.

 

 

Edited March 7, 2021 by robk

[robk]

Next afternoon it was building the fuselage. I used cyan for the first two formers and then alphatic for the rest putting in some aplhatic webs alongside the cyano joints. Whilst that was setting I pinned the cut ribs together and sanded them so they were all a pretty close match.  Thats as far as I have got so from now on post will be as the build progresses. 

 

Edited March 7, 2021 by robk

[robk]

My motor will fit behind the firewall rather than be mounted from the rear like the plan. There is no down or side thrust shown on the plan so I have kept it the same. My construction method is different for the front end, which on the plan just shows a circular ring of ply which you somehow have to carve/sand balsa to get a circular front end. I have made a square piece of ply and will glue my top and bottom balsa sheeting to that and shape it after the glue has set. I also put some triangular fillets inside to strengthen the nose.

 

Edited March 10, 2021 by robk

[robk]

View from underneath. I fitted a piece of ply to fix the wing retaining bolt to and also two bearers for the elevator and rudder servos.

[robk]

Here is the wing under construction. A bit of a fiddle to build because of the symmetrical wing ribs. I pinned the bottom wing spar down then glued the ribs in place, then glued the top wing spar in place and pinned the trailing and leading edge to the board with a 6mm spacer underneath. Then I went along the wing starting at the trailing edge gluing each rib in place with cyan and then did the same at the front. I have put fillets at the trailing edge because otherwise these seemed weak to me. I have also put a vertical shear web in for the centre section. Regarding the dihedral - I think it needs it as the wing does not taper and there is no sweepback. I chose to build the entire wing in one piece flat on the board. I will break it in the centre when I lift it and rejoin it with the dihedral. I am also inserting a ply brace across the centre break (nothing like this is mentioned on the plan).

 

Edited March 10, 2021 by robk

[dan h]

Nice one Rob 

I've been wanting to build one of these for a while. It is an ideal chuck in the boot and have some fun model. Following with interest great start by the way.

 

Dan

 

[patrick diviney]

Hi, I am starting this build with the sarik kit. I've also noticed many differences between the plan and the build article.

Will you make a bigger cut in the wing seat to allow for the leading edge sheeting. Are you going to sheet top and bottom?

Thanks

[robk]

HI Patrick - yes the plan has quite a few differences. I am going to sheet top and bottom because I am not having any u/c. The grass on our field will be too long. The rib section as drawn on the plan does not allow for any sheeting at all! I dont know about the sarik kit,  but you might need to narrow the rib section in front of the spar to allow for the sheeting.

 

Also, I made the ply rib for the centre of the wing, tried it in place and found that the projection that fits into the fuselage former was too short. I had to make a new rib with a longer projection. Regarding the wing seating, I have assembled the basic fuselage structure but I am waiting until I build the wing to try it in place in order to get a perfect fit. 

Edited March 13, 2021 by robk

[robk]

Started sheeting the centre and front of the wing. I have also put in a solid balsa section towards the rear of the wing ribs where the wing bolt goes otherwise this area will be crushed. This is not shown on the plan as the bolt is shown going through the very narrow trailing edge - not strong enough in my opinion so I moved it a bit further forward.

[robk]

Cut and assembled the tail. Very simple sheet but adequate for the job. Something else not on the plan is how you join the two parts of the elevator together. I have used a piece of wire bent to shape then inserted into pre-drilled holes and a groove in the rear of the tailplane and fixed with epoxy.

[robk]

I am placing the servo arms on the top surface of the wing because I am not having wheels - saves the control rods etc. being ripped off. You see the plane mostly from the underneath anyway when its in the air! I was going to wrap shrink wrap around them and epoxy them to a beefed-up wing rib but I didn't have the right size shrink wrap, so instead I put in two 4mm spruce bearers. The balsa around the servo is to provide somewhere to fix my covering film to. It will be tidied up a bit once I sand the wing.

 

[robk]

So I've been carrying on with sheeting the wing, top and bottom on the centre section and along the leading edge. The green string is there to pull my servo wires through. A couple of 10mm wide scrap balsa blocks form the wing tips. Mine are slightly different to the plan in that instead of reducing them in width towards the trailing edge I have left them square so they can form a bit of protection for the aileron.

 

 

Edited March 16, 2021 by robk

[robk]

I have begun work on the fuselage again too by planking in the front end, 6mm thick balsa on top and at the front on bottom and then 3mm elsewhere. The original design had no hatch at all, assuming you put the battery in by removing the wing. That is awkward in my view, so I have included a hatch - and its a big one so I can place the battery wherever I like from the CG to quite a way forward. Because I have a heavier motor and battery in mine I am not sure where the battery is going to need to be placed. The hactch also gives me access to the ESC and means I can install the motor after sanding and covering (I did a dry run before gluing in the planking). I need to put in some ventilation holes in the fuselage, probably the sides so they don't fill up with dirt when it lands.

Edited March 16, 2021 by robk

[patrick diviney]

1 hour ago, robk said:

I have begun work on the fuselage again too by planking in the front end, 6mm thick balsa on top and at the front on bottom and then 3mm elsewhere. The original design had no hatch at all, assuming you put the battery in by removing the wing. That is awkward in my view, so I have included a hatch - and its a big one so I can place the battery wherever I like from the CG to quite a way forward. Because I have a heavier motor and battery in mine I am not sure where the battery is going to need to be placed. The hactch also gives me access to the ESC and means I can install the motor after sanding and covering (I did a dry run before gluing in the planking). I need to put in some ventilation holes in the fuselage, probably the sides so they don't fill up with dirt when it lands.

On 13/03/2021 at 17:33, robk said:

HI Patrick - yes the plan has quite a few differences. I am going to sheet top and bottom because I am not having any u/c. The grass on our field will be too long. The rib section as drawn on the plan does not allow for any sheeting at all! I dont know about the sarik kit,  but you might need to narrow the rib section in front of the spar to allow for the sheeting.

 

Also, I made the ply rib for the centre of the wing, tried it in place and found that the projection that fits into the fuselage former was too short. I had to make a new rib with a longer projection. Regarding the wing seating, I have assembled the basic fuselage structure but I am waiting until I build the wing to try it in place in order to get a perfect fit. 

Thanks for the heads up, they are amazing quality pics and give me alot to work with. This is my third build and I have never built a ribbed wing so I'm grateful for the guidance. I have just finished the Tony nijhuis hunter and hawk and they were very easy builds compared to the Bambino. 

[robk]

Thanks Patrick - I want to make the Nijhuis Mig 15 at some stage - glad you thought they were a quick build.

 

Anyway, Ive been putting in the control runs over the last couple of days. I wanted something light but also something I just had in the bits drawer. In the fuselage I have used a couple of short plastic snakes, leftovers from cutting down longer ones on another job. I fixed the wire ends using cyano and heat shrink. Another problem with the plan appeared whilst doing this. The rudder does not protrude below the elevator far enough to allow both to operate without fouling each other. I therefore cut the horizontal section out of the rudder and replaced it with with a slightly deeper piece (twice as wide as the one on the plan). The rudder now operates freely. I will put a tail skid in so it doesn't foul the ground on landing.

 

 

 

 

 

 

 

 

 

Edited March 18, 2021 by robk

[robk]

Here is the wing servo mounting and control run.

 

 

 

Edited March 18, 2021 by robk

[robk]

I put it together and it is a pretty plane - if it looks right....

 

[patrick diviney]

Will you need quite a large spinner carry on the graceful lines of the fuselage. Great idea on the rudder, should save a load of hassle later on. Thanks

[robk]

Hi Pat - I have ordered a replacement 35mm diameter spinner and folding prop from HK but might just use the Kinetic one which is also 35m. I have sized the fuselage for this.

 

Made a bit more progress on the fuselage. I planked the top of the rear fuselage with 3mm square balsa strips using cyano so they would hold in place without a load of pins, then filled with polyfilla advanced lightweight filler. This sets quickly but is fairly fragile. After sanding I fitted the fin strake. 

 

[robk]

The rear fuselage floor is just a 3mm balsa plank with an added 'tail-skid' balsa block. I will toughen that up with a coat of varnish.

[robk]

This is another modification from the plan. I didn't fancy the pop bottle canopy so have built a balsa 'racing canopy'. I quite like the look of this - others might not. It also allows me to have my long top hatch. If you look back at my first photo of the plan I had already drawn this in before I started construction. Next is to let the filler dry completely, followed by a very light sand and then a coat of sanding sealer. I still haven't decided on a colour scheme.

 

Edited March 21, 2021 by robk

[patrick diviney]

Robk, Very Reno. I started the wing as I realized my motor was too big for this bird and I have to wait for the replacement to arrive before I finish the fuselage. I reckon there should be two of the W1 ribs on the plan and in the kit. Otherwise how do you join the two separate wing panels together to achieve the 20mm dihedral. Also the receiver in the fuselage for the wing pin is twice as wide as W1. It's such a poorly drawn plan, no plan view of the fuselage either. Are all plans generally like this?. I've only built from Tony nijhuis plans and I've never found any decrepencies on his plans.

[robk]

On 21/03/2021 at 22:25, patrick diviney said:

Robk, Very Reno. I started the wing as I realized my motor was too big for this bird and I have to wait for the replacement to arrive before I finish the fuselage. I reckon there should be two of the W1 ribs on the plan and in the kit. Otherwise how do you join the two separate wing panels together to achieve the 20mm dihedral. Also the receiver in the fuselage for the wing pin is twice as wide as W1. It's such a poorly drawn plan, no plan view of the fuselage either. Are all plans generally like this?. I've only built from Tony nijhuis plans and I've never found any decrepencies on his plans.

Hi Pat

Yes this is a poor plan and no not all plans are like this. This is my first RCME free plan build but I think it depends on who has drawn it. Others I have used have been very good with no errors (except my own when building!). The Tony Nijhuis one you built was also a free plan and I am assuming that was good as he is a well-respected designer.

 A plan view would definitely have been useful. 

 

Regarding W1 - I did just have one of these in my build as I made the wing in one piece flat on the board (its so small) and then cut trailing and leading edge and spars on one side of W1. I then rejoined the two wings with the appropriate dihedral and a 3mm ply central brace cut into the top of W! in front of the spar up to the second W2 on each side. You are right about the fuselage former having too big a gap to receive W1 correctly. I built the wing and finished it and then offered it up to the semi-built fuselage and glued in a new piece of ply (not light ply) behind F6. I have previously said that the projection on W1 is too short and made a second one with a longer projection.

[robk]

Here is how I made my hatch. I glued a pin in the hatch cover and then put some graphite on the end of it and offered it up to the fuselage former to make a mark which I then drilled. A SLEC hatch catch is glued with epoxy into the front of the cover and I repeated the same process.