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C No Ohmen

Build blog for my attempt at the Ohmen

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Peter Miller24/06/2019 11:27:46
10077 forum posts
1192 photos
10 articles

I did say that they were flush with the tiop of the ribs and that the capstrips brought the level of the surface up tpo match the hatches

Chris North 326/06/2019 01:42:55
279 forum posts
459 photos

Well progress continues bit by bit....This evening I managed to trim and sand back the top and bottom leading edge sheeting on one wing panel. A length of leading edge was then stripped from 3mm sheet using the strip cutter. To make sure I had the right width and to reduce sanding later, I set the blade against the sanded leading edge which ensured the cut strip was just the right width. Once trimmed to approximate length (remembering to cover the wing tip this time!) this was glued and taped into position.

Next up I used some left over 6mm hard wood rib spar to cut a set of servo cover support rails for both wings which were then glued in place level with the bottom of the ribs. While not shown in the photos, 4 lengths were used in each servo bay to provide a solid support for the servo cover later on.

With this done, wing tip gussets were cut and attached. These are a smidge over size and will be sanded down later once the wing is complete.

So not a lot but then I only had a hour. - Photos below

Chris North 326/06/2019 01:46:13
279 forum posts
459 photos

servo rails glued and clamped


Multi-tasking! servo cover rails being installed while LE is glued and drying


Wing tip gussets



Chris North 327/06/2019 01:27:39
279 forum posts
459 photos

Only half an hour this evening but managed to get the hatches finished and most of the balsa sheeting applied to the bottom of the rib bay. (I need to raid the scrap box for the final piece!)

I will cut the servo arm slots and attached the servos later once the rest of the air frame is finished. No point doing it now as the hatches are a good tight push fit which means they will need to be sanded down a little to allow them to be fitted once covered. I will do all this finishing work at the same time. I know the sheeting looks a little rough but this will be fine once sanded ready for covering.

Hatch braces and servo bay bottom sheeting


and with cover in place - same wing but the photos upside down!


Hatch bay on second wing


And again with cover in place


Peter Miller27/06/2019 08:22:51
10077 forum posts
1192 photos
10 articles

That is very neat work

Chris North 301/07/2019 01:59:09
279 forum posts
459 photos

Thanks peter - I appreciate the feedback.

So this weekend I hoped to get the structural parts of the wings pretty much finished with only a bit of sanding and finishing bits left - almost made it!.

So starting with the left wing panel I trimmed the trailing edge sheet flush with the TE and then gave it a sand to ensure everything was flush. Again the sanding block was used flat on the table to make sure the TE was 90 deg to the bottom of the wing. Next up the aileron stock which has been laminated from 6.5mm and 2mm sheet was trimmed slightly over size and the edge sanded vertical and as straight as possible. Despite using a straight edge to help guide the sanding block it was tricky to get a completely flush finish between the TE and ailerons but it was near enough - or at least as near as I could get it!

Before shaping the ailerons I decided to cut the hinge slots so that i was sure they were in the middle of the sheet. So using the hinge slotter I marked up the hinge locations, applied the guide, cut the hinge slot and cleared out the slot using the scraper. This was very easy to do in the win Te but proved a little harder in the very hard stock I had used for the ailerons. Never the less hinges were completed.

Guide applied...


Slot cut with cutter...


Hinges complete....



Chris North 301/07/2019 02:18:21
279 forum posts
459 photos

With the hinge slots cut in both the TE and the aileron I then marked up the aileron for shaping. Note then when I say aileron I actually mean the aileron and center section trailing edge as this was all being shaped as one piece before being cut and attached as necessary.

With the aileron flat on the bench I used a piece of 3mm sheet to mark the required trailing edge (opposite side to the hinge slots!!) Rather than try to use the hand plane at an angle I decided to prop one side of the aileron on a sheet of 5mm balsa. This meant that I could then hold the plane flat relative to the building board while cutting a wedge into the aileron. I think I need to sharpen the blade in the plane as the cutting was not very smooth but this could also be due to the hard balsa sheet. Anyway after 5 minutes of shaving and sanding I was left with a nicely shaped aileron and a lot of mess.


With this done The aileron was reattached to the wing using the hinges and then marked up for trimming. Once happy, the centre section trailing edge was cut off and attached to the wing, the wing tip end cut and attached (similar to Trevor's I think). Now because the ailerons have a slight gap against the wing due to the hinges they no longer line up with the parts glued to the wing - so i shaved 1mm from the aileron to make eveything line up.

With this complete I repeated the process with the second wing panel. All was going fine until after shaping when fitting the aileron back to the wing I realised I had trimmed it in the wrong place and it was now too short! I still have no idea how I did this but suffice to say I was not happy. Still only one thing to do and so another set of 6.5mm and 2mm sheet was laminated and left to dry ready for a second attempt this week sad

Chris North 301/07/2019 02:19:36
279 forum posts
459 photos

So while that was drying it gave me time to get ready for the next stage...


Peter Miller01/07/2019 08:24:08
10077 forum posts
1192 photos
10 articles

WE all do these things! A little lack of concentration and something gets trimmed wrongly.

I have to admit that I usually bodge it if it is not structurally important.

Chris North 322/07/2019 01:37:14
279 forum posts
459 photos

Well work has certainly got in the way of hobby time over the past few weeks - This weekend was the first opportunity to get some building time in for over 3 weeks so it was almost a case of trying to remember where I was up to....

Putting the wings to one side for now it was time to look at the fuselage.

First up was to cut the sides from balsa sheet and then the doublers from 1/8" ply. Given the size of the sides, rather than cut and stick the plan to the sheet I used the baking paper and pin method as shown earlier. This was very straight forward as most of the outline is straight lines and so for these I only needed to put the pin through intersections and then join the dots with a straight edge. For the wing cut out I simply made pin marks every 1mm or so which gave a good outline.

The same method was used for the thin ply although the pin marks were a little harder to make as the ply was harder. To overcome this, instead of the thin T pin I used a thicker map pin which worked fine.

I noted on the plan that there are some cross rails to support the rudder and elevator servos. To help provide an installation and location guide I decided to cut some slots in the ply so that the rails could sit on these (very small!) ledges later on. To get these in the right place I place I marked the snake hole positions on one of the fuselage sides, positioned the servo to suit and then marked where the supports would sit. This was then transferred to the ply doubler and cut out. whether this is in the right position, only time will tell!.

With cut outs done the doublers were glued into position and the sides left to dry



Chris North 322/07/2019 01:58:09
279 forum posts
459 photos

Chuffed with myself that I had managed to create two opposite sides smile d I stripped a 3mm section from 3mm sheet and attached this to the bottom of the rear fuselage. The plan shows that this fits over the ply doubler so this is how i installed it. There is a slight gap at the step but it was so small that I didn't bother sanding it out. The step is between formers anyway and so won't have any impact.

20190720_091819.jpg With these in place I then attached the hardwood doublers along the top edge for the hatch location. I couldn't find the same size as the plan at the LMS and so just got something close. Luckily I had thought that finding the exact sizes may be an issue and so had not pre-cut the former slots. So, with the all the formers and doublers in place I went through and cut all necessary slots and recesses in the formers to suit.

One former that needed a little thought was Former F3 since I had modified the wing locating method such that the dowel was replaced by extensions built int to the wing root ribs. The slot for the ribs needed to be correctly located and a nice push fit - tight enough to hold the wings together but lose enough to allow the wings to be easily installed and removed.

Sitting the fuselage sides on the wing ready in order to take some measurements it was clear that the wing seat needed a bit of fettling to let the wings sit nicely on both sides. A few minutes with the sand paper had this sorted and so measurements could be taken to ensure the slot was suitable located. Not trusting myself, I though it better to be safe than sorry and so made up a dummy former from some scrap balsa into which I cut a trial slot. Everything was fine and so this was then transferred to the ply former cut and filed to shape until the wings fitted neatly when held together.

Some photos of this below




Chris North 322/07/2019 05:05:51
279 forum posts
459 photos

So with all the cut outs in the formers complete it was on with the fuselage assembly..

one of the fuselage sides had a slight bow in after the ply doubler had been applied and so this was used as the first side. Placing the side on the board, a weight was added to flatten the bow and then former F2 was glued down and left to dry completely in order to hold the side flat.


Once dry, formers 3,4,5,6 and 7 were attached. It was at this point that I realised that i should only have glued up to former 5!

I did contemplate cutting formers 6 and 7 out but this was going top be a task and a half given the rails at the bottom. Instead I decided to keep going and fix it later. So with that decided, former F1 was glued in place.


Chris North 322/07/2019 05:27:39
279 forum posts
459 photos

Once dry, the second fuselage side was lined up and glued while everything was confirmed as square. To ensure that the side was fully in contact with the formers a weight was added to the top to keep everything flat and square.


I'm sure these weights could have other uses but I haven't found one yet......

Again everything was left to dry while I had a bit of a tidy up...and, with everything dry - and some clear space to work-in - the fuselage was removed from the board.

I don't have a fuselage jig and so instead I simply taped a piece of paper (the back of the wing panel plan!) to the board and then drew a center line along it. Since the F1 former still has the paper pattern attached, I was able to align the fuselage onto the drawn center line using the center line markings on the F1 former. A pencil mark was then made either side of the fuselage . The fuselage was moved to the other end of the paper and the process repeated. Using a straight edge I could then easily create two parallel lines defining the sides of the fuselage.

The fuselage was then placed back over the center line and a couple of pins inserted either side to stop it moving. An engineers square was then placed on the center line at the tail, and the sides brought together such that they were even against the square and a peg was placed at the top to hold the sides in place.

With this done, a flat sanding bar was run between the fuselage sides at the tail along the center line to taper the sides ready for joining. A second peg was placed on the bottom, the top peg removed and the process repeated to taper the top half of the fuselage sides.

With a nice fit achieved the top peg was reattached and a bead of cyano run down to fix everything together.

Formers F6 &7 did not cause any binding problem because as the sides were drawn together they rotated forward slightly. So these were then simply eased back until they were horizontal across the fuselage and secured with cyano. Once complete, formers, F8 & 9 were dry fitted, tapered slightly and then glued into position.20190721_211251.jpg

Chris North 322/07/2019 05:32:03
279 forum posts
459 photos

The last task for the night was to mix up some 5 min epoxy and to install a couple of gussets either side of the F1 firewall.

Note that to secure the motor mount I had already installed and glued some M3 captive nuts into the back of F1

Hopefully tonight I will be able to find some time to insert the top longerons and to look at how to go about making the hatch.

I will be travelling again later this week but hopefully will find a few hours before then.

Its now starting to look as if there is progress being made.......20190721_213152.jpg

Chris North 322/07/2019 05:35:59
279 forum posts
459 photos

Peter, - I plan on using your undercarriage method but can you confirm whether the legs are glued into the ply blocks or is this just a support? I also assume that the legs are fixed to the bottom of the fuselage using u -type clamps but I see that the two legs run parallel so do you use a clamp over both legs?

If you have any photos showing the arrangement under construction (I could't see one in your blog) or as-finished then this would be much appreciated.

Thanks in advance!

Percy Verance22/07/2019 06:55:58
8109 forum posts
155 photos

Well Chris, I'm not Peter but here we go anyway. The ends of the undercarriage wires are not glued into the ply blocks Chris, they simply slot in and have a smooth friction fit. A further ply piece is glued on top of the slotted bit creating a box for the wire to slide into. The clamps on the crossmembers hold it all in place. And yes, you use clamps which have a groove wide enough for two wires. They are available, but do sometimes take a bit of tracking down. This arrangement was very popular on many models at one time Chris.


Edited By Percy Verance on 22/07/2019 06:58:23

Peter Miller22/07/2019 08:36:13
10077 forum posts
1192 photos
10 articles

Did you say 1/8"ply doublers on the fuselage sides????!!!! They should be 1/32". Oh well, you will have a totally indestructable fuselage.

Yes, as Percy says, the legs just slide in to the slots. I don't even put any extra ply to box them in and the set up is strong enough that if the legs get bent backwards I just place the spinner against my chest and heave the legs forwards again with no trouble.

Double 8 SWG saddles are available from SLEC which is what I use to hold the legs on. They do all sorts of saddles among a huge range of other bits.


Edited By Peter Miller on 22/07/2019 08:37:48

Piers Bowlan22/07/2019 08:50:35
1826 forum posts
44 photos

'1/8th ply doublers' - probably a typo Peter as they look like thin ply from his photos. Here is a nice pic of the landing gear slots from the Little Miss Honky Tonk blog, which is pretty clear (same system).

Double saddle clamps here.

Edited By Piers Bowlan on 22/07/2019 08:55:12

Peter Miller22/07/2019 09:06:23
10077 forum posts
1192 photos
10 articles

I hope it is a typo...I am very good at typos myself.sad

Yes, in that plan view photo they are thinner.

Chris North 322/07/2019 09:37:07
279 forum posts
459 photos

Hi Peter et al,

yes it was a typo as the doublers are 1/32" which is 0.8mm so I shall say that that is where the confusion came from blush !

Percy & Piers - thanks for the details, this all makes sense so i will see if I can get hold of some double saddle clamps.

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