C No Ohmen

[Chris North 3]

Posted by Peter Miller on 06/05/2019 08:27:44:

You certainly produce parts to a far finer tolerance than I do!!!

Thanks Peter - its the combination of the Engineer in me and knowing that my Dad would have built it better. Its a curse, but if it says 6mm then 5.5mm just won't do - hence my previous comments regarding metric vs imperial !

Anyway I have found on previous builds that that that importance I place on accuracy is inversely proportional to the amount if time I have spent building it.

Chris

[Chris North 3]

Posted by Piers Bowlan on 06/05/2019 06:50:50:

I also make the blank from 1mm or even 1/32 (.4mm) ply, which I find adequate and easier than a thicker piece of ply to cut around.

Edited By Piers Bowlan on 06/05/2019 06:51:51

Piers,

Thanks for the feedback - I would have used a thinner piece of ply but the 3mm was to hand plus I am still tinkering with the idea of making separate wing panels and so the 3mm blank may yet be used as a root rib - but we will see.

[Chris North 3]

Posted by Percy Verance on 06/05/2019 07:09:31:

And forgive me for mentioning this, but that sheet balsa you cut the wing spars from doesn't look hard enough for the job. Hard to tell from the photo, but it does appear to look a bit on the light side colour-wise...... They need to be quite stiff for wing spars

Will cut 1/4 ply with ease, so thick balsa is no problem at all..... Sure, it's expensive, but it's one of those "why did I struggle so much before" tools, and it'll last for years too. 100% accurate cutting 100% of the time.

Edited By Percy Verance on 06/05/2019 07:36:38

Percy - a nice piece of cutting kit but I don't build often enough at this point to warrant such an item - maybe one day.

As for the wing spars I note your concern and so will double check whether i have any harder sheet stock - these can always be used for the false trailing edge and fuselage spars if need be.

Chris

[Former Member]

[This posting has been removed]

[Chris North 3]

Well after a bit of thinking i decided better safe than sorry so put the wing on hold for a few days until I had the chance to head to the LMS for some harder spars. Not a great selection but luckily they had had some 1/4" hard spars and i also managed to pick up a couple of sheets of hard 6.5mm balsa.

Before cracking on with the wing I decided that I would make a few modifications to allow a split wing if I wanted. The wing on the Dancing Wings hobby Space Walker has a neat aligning and joining set-up that holds the wing firmly and allows alignment of the joining wing spar. Unfortunately I had to leave this model in Thailand but luckily Uncle Google was able to find a copy of the build manual and so a similar set-up was devised.

The root and first two ribs were replaced with ply while a locating lug was incorporated into the front of the root ribs which will later align with F3 former. While I could have doubled up the dowels as Peter's design, the fun in building from scratch is that you can make changes.

[Chris North 3]

So not really a lot to show for a good few hours work at the weekend but there was a lot of cutting, sanding and re-working to make things fit.

So first up a few new ply ribs

Then it was on to wing layout..

[Chris North 3]

Quick confession to make here because I had actually started to layout the first wing section last week before deciding to replace the spars with harder wood.

Now I made life hard for myself by not only pinning down the lower LE sheet and TE sheet but also the lower center wing sheeting. I though this would make life easier later but it only really made harder at this stage. Anyway - more on that later.

So with all the ribs finished and modified I made a start with the rib installation. First up was a dry installation to check that all the ribs fitted where they were supposed to then, starting from the wing tip I lined up each rib with the plan and checked that it was vertical using a square. Note that I don't have 2 squares but I do have a bunch of old membership cards which are also ideal. Once straight and vertical the rib was tacked in place with a small spot of cyano on the spar and TE sheet. Once all in position, each rib was then fully glued using super phatic.

And once that was all none a metal ruler was placed over the TE and a sheet of balsa over the ribs and weight applied.

[Chris North 3]

oops - forgot the photo..

weight applied

[Chris North 3]

While that was drying i decided to make a start on the second wing panel. This time I though it would be easier to pin down only the LE & TE sheet and to then install the center sheeting later once the panel is removed from the board.

With the sheeting pinned down, the remaining ribs were dry fitted at which point a glass of while called thus curtailing building activities for the weekend.

I forgot to take some specific photos of the root mods but you can just about see in this photo the extended root rib and the alignment holes for the wing joiner / brace. You will also notice that the upper spar has also been added to the first panel and glued in place using superphatic.

Yes I know there are not many (any) pins holding the ribs up but they are all square and vertical, - honest, I measured them twice!

[Peter Miller]

Yes,the sequence does not need or want the centre section sheet pinned down.

If you are going ot make a two piece wing what are you doing to join them? I do not see any provision for tubes and rods.Only the tube for the servo leads.

[Chris North 3]

Peter, I have followed the spacewalker design which uses a ply wing brace which passes through the first ribs of each wing panned. It is glued one side and slides into the spars on the other. The wing is then held is place and together by lugs on the root ribs that fit into the fire wall and by a screw through each wing panel at the trailing edge. If this is not sufficient then I can simply glue the wing and the dihedral brace into one one piece. What would be your recommendation for how far a wing joiner has to go into the wing for a model of this type?

[Trevor Crook]

Chris, I've just remembered a minor mod I made to Peter's design. I wanted to retain the battery hatch with magnets at the back and a dowel at the front, so I angled the rear face of the hatch backwards slightly so it would drop down once the front dowel was engaged. This of course means re-profiling the rear former on the hatch and the corresponding top part of the fuselage. It works well, but was just my personal preference.

[Peter Miller]

Hi Chris.

I should take the joiner out as far as the end of the centre section sheet.

[Peter Miller]

Trevor's idiea is right.

I used a dowel at teh rear and a latch at the front. I angled the front former by adding some sheet to the rear face of ghe front former and shaping that to the angle.

[Chris North 3]

Peter / Trevor - Thanks for the info. I shall have a look at that when I get to the fuselage. As for the wing joiner I will look again but if its too hard then I'll just join the wing so no big deal.

Unfortunately I have to travel for work for the next couple of weeks and so there will not be much progress until I get back - somebody mentioned time should be spent this week helping with the packing...!!

[Chris North 3]

Well 3 weeks away working in the UK and Norway has meant that there has been very little progress on the Ohmen. The upside was that since I was passing through the UK I managed to get the recommended 4Max motor and speed controller so the model should have plenty of power once finished.

With a number of household items to catch up after being away I only managed a couple of hours this weekend but I did manage to get the false LE shaped on the right wing panel ready for the top sheeting, false TE edges on both wing panels, scrap balsa installed at all hinge locations, the false TE shaped to match the ribs and the TE top sheeting installed on the left panel. A paper tube was made up and installed in the right panel but I have left it out of the left panel; for now as it is missing the root rib which is installed later.

I see that on the plans both panels have the paper tubes running to the root rib and top sheeting over the center section so I am assuming that this needs to be modified a little to let the servo leads exit the top of the wing. Once I am a little further along with both panels I will see about stopping the paper tube at the 1st rib and making a hole in the top sheeting.

A few photos to follow

[Chris North 3]

false LE attached to right panel

False LE, scrap for hinges and paper tube in right hand panel

False trailing and leading edges attached to left panel

Trailing edge top sheeting on left hand panel

[Chris North 3]

Unfortunately, despite noticing it on the plans at the start, it was not until I had installed the false TE that I realised I did not not leave sufficient overhang to cover the wing tips - I will have to fix this later but hopefully it will not be too much of a problem as there is sufficient LE strip to help secure the wing tip.

I'll put this down to jet-lag!

Well most of this week I'll be working in Bangkok so it will be another slow week on the build.

[Peter Miller]

Looking very nice.

[Chris North 3]

Managed to grab a couple of hours this weekend so managed to get a progress on the wing panels - although looking at the photos it doesn't really look like it!

Anyway they are coming along and getting closer to top sheeting which will help them look as if progress is being made.

The root rib in the left panel was attached and glied vertical as i could see this as a bit of headache later on given my wing joiner solution.

The lower LE sheeting was lifted and glued to ribs on left hand panel using a combination tap, pins and cyano to tack it in place before all the joins were run with superphatic. While drying shear sheeting was cut for both wing panels and then glued to the spars and bottom sheeting. The sheeting was left just over length and then sanded down level with the top of the upper spar once dry.

The paper tube for the servo leads was installed in the left wing and then both tubes were cut flush with the servo bay and root ribs.

As noted earlier I have changed the dihedral brace design into a combined dihedral brace / wing joiner and so cut this from ply using the same dihedral angle as suggested on the plan / build article. This was then test fitted in both wings resulting in a really nice a snug fit.

Deviating from the suggested build sequence a little, I removed both panels from the board at this point and trimmed the sheeting and spars flush with the root rib. Then, having propped up the wing tip by 20mm I put the sanding block on its side on the table and sanded the root rib until it was vertical. This was repeated with the second panel.

A test fit was then made with the wing brace joiner and the two wing panels together resulting in a nice neat and solid fit. Happy with this, the panels were separated, the joiner glued to the left wing panel and the separate panels pinned back down on the board ready for top sheeting.

[Chris North 3]

Wing joiner / brace trial fit

[Peter Miller]

Coming along nicely

[Chris North 3]

Thanks for the feedback Peter - I know the building is slow but it supposed to be a hobby not a race...

Managed to get half an hour in tonight so cut the 1.5mm top sheeting for the first wing panel. This was cut slightly over length and little over width. Using super-phatic the back edge of the sheet was aligned with the back of the top spar and then the sheet curved along the ribs and secured to the lower sheeting using masking tape to hold everything down. The back of the sheet was weighted using a steel rule and some car tire balance weights and left overnight.

Hopefully I will be able to put the sheeting on the second wing panel this evening before looking at how and where to run the aileron servo cables up through the wing sheeting. I suspect I may cut the paper tube back to the second rib and leave an access hole in the top center sheeting.

If this blog is showing too many steps then let me know

[Peter Miller]

Hi Chris.

Your work is excellent. and no need to worry about "too many steps". The more information and ideas the better as others always can learn from them and say "Oh, I like that way better"

I agree that cutting the tubes aback a little and a hole in the top centre section sheet is the obvious way to go, in fact the only way to do it.

When I am gluing down the top leading edge sheet I clamp it to the spar with a paper clip in each rib bay. THen I pin it down to the leading edge with map pins every couple of inches. THis just my way of doing it and what ever system works is fine.

[Piers Bowlan]

For the sake of clarity (probably unnecessary) the 'paper clips' Peter is referring to are sometimes referred to as 'fold back clips' (or even Bulldog Clips, which are very similar). Whatever one calls them it is a good tip .