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C No Ohmen

Build blog for my attempt at the Ohmen

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Peter Miller22/07/2019 10:00:07
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SLEC **LINK** Will ship overseas and they are fast, and you can order on line.

You won't need the clamps until model is covered anyway.

Chris North 329/07/2019 01:58:08
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315 forum posts
512 photos

Not much progress last week as I have been traveling for work. Saturday I did manage to get an hour or so in but I spent the time soldering on some XT60 connectors to the 4max batteries and speed controller I bought for the Ohmen while in the UK.

So, Sunday's free time before lunch was spent making a start on all the fuselage innards prior to boxing it in with the top and bottom sheeting.

First activity was to make the hatch cover. The F3A formers had all ready been cut using the plan and so a base was simply cut from balsa sheet making sure that it matched the outside of the fuselage ply doubler. When the F3A formers were dry positioned on top I noted that they were not as wide as the base. Since the top sheeting is meant to go on the outside of the base plate to match the fuselage sides the formers should be full width.

Checking the fuselage showed that F3 and F5 formers were also too narrow. This is not a problem with the plan but is the result of me not sanding the side of the formers enough to take the hatch double. I had sanded it so the hatch doubler was flush but had not allowed for the 1/32" ply doubler. - See F3 below

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So I decided it was best to make some new F3 doublers. Placing the base in position, I held a piece of scrap balsa against F5 and drew around it. Obviously F5 is too narrow and so I simply extended the arc by eye to meet the required width of the base. This was then cut out and used as a template to make the 4 new F3A doublers which, once cut out, were pinned together and sanded to shape.

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With this done the formers were glued into position and left to dry, after which the top spar was added.

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Chris North 329/07/2019 02:04:58
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315 forum posts
512 photos

It is clear from the plan that the top spar needs to be cut away where the seat locations are and so this make sense to do once covering is complete. What is not so clear is whether the hatch and the fuselage are covered separately or whether the base is installed, everything is covered together and the hatch cut away.

Covering everything together would make sense and this is how I have done it in the past as this would allow the incline at the front the of hatch to align properly but I am not 100% sure this is the right way to go in this case. Any suggestions would be appreciated.

Chris North 329/07/2019 02:20:39
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315 forum posts
512 photos

next up was the installation of the control snakes for the rudder and elevator.

The holes for the guides had been pre-drilled based on the plan locations and so it was simply a case of feeding the snakes through. The holes had been drilled as a push fit to make sure everything was tight but in hindsight I could have had them a little looser to ease the pushing of the guides. No real issue to report here other than the fact that the position of the guide in F6 appeared to be incorrectly placed and caused quite a kink in the guide. To fix it I simply removed the guide tube and widened the hole in F6 until a nice curve was achieved.

Note below that the F6 guide hole has been widened to allow better snake profile.

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With both guide tubes installed and push as far aft as possible I was able to Identify where to make exit holes in the fuselage sides (something that is not shown on the plan). This was simply done by measuring the location of each tube in relation to the back of F9 former and from the bottom of the fuselage and transferring these measurements to the outside of the fuselage to create a starting cut point. From here slots were then sut to allow the tubes to exit to the outside of the fuselage.

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Peter Miller29/07/2019 08:12:37
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10278 forum posts
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With regard to covering, the answer is what ever you feel is better/easier.

I do them separately so I can run the covering round the edges.

The snake exits are lined up by eye. I cut them with a sharpened brass tube which gives a close fit .

I apply canopy glue to hold the snakes in the formers.This glue is made specially for gluing canopies down so works well on wood to plastic joints.

Edited By Peter Miller on 29/07/2019 08:13:06

Chris North 329/07/2019 10:15:27
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315 forum posts
512 photos

Hi Peter - thanks for the quick feedback as usual - I'm afraid I may have been less than clear (again) as when I said covering I actually meant applying the sheeting to the fuselage front and hatch. Is this done as separate items or as one and then the hatch cut free?

Thanks

Chris

Peter Miller29/07/2019 10:24:28
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10278 forum posts
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10 articles

It can be dome either way. I did it with separate panels but if your formers are a perfect match you could do it either way

Chris North 330/07/2019 01:48:16
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315 forum posts
512 photos

An hours work this evening saw the undercarriage mounts made and installed.

Over the weekend I had cut, fitted and glued the 3mm ply plate at the base of F3, level with the bottom of the fuselage. The front of the fuselage had been weighted down to ensure it was kept flush and left to dry.

This evening then I cut a strip of 6mm ply which I then cut to length / shape. Using the plan as a guide I measured out the first slot location, marked it up and then cut the slot slightly undersize using a hack saw. Using the 10 SWG wire (3mm) as a guide I then eased the slot open with the sanding bar until the wire was a push fit.

Once this was done I used the first slot as a guide for the second slot to ensure that when installed the undercarriage legs will sit side by side and not on top of each other - well that's the plan anyway..........

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Next up I used the slots in the supports as a guide for marking out where the holes needed to be drilled in the base plate for the undercarriage to pass through. since everything was backwards and upside down I started with a 1mm drill to ensure I was in the right place before expanding to 3mm. This was a good plan as you can see from the plan that the first hole was measured the wrong way around. Oh well, at least this shows I know myself!

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I found that a 3mm drill hole for 3mm wire was way to tight a fit and so the hole was drilled out to 3.2mm which gave a nice push fit. Once happy, the supports were fitted and glued - making sure the correct support matched the correct hole! This was then left to dry.

And just for good measure I installed the top spar at the front of the fuselage so that i can think about starting to sheet this section.

Lastly I had a look at the latch I had purchased from 4max for the canopy. I am not sure how i an going to get this to fit given the top spar that is installed on the canopy so I will have to have a think about this - no rush just yet.

Trevor Crook30/07/2019 07:07:27
869 forum posts
65 photos

Probably too late now, but I used magnets at the back and a dowel at the front, and angled the rear former instead of the front. Very secure, 20 plus flights with no issues.

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Chris North 330/07/2019 07:12:57
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315 forum posts
512 photos
Posted by Trevor Crook on 30/07/2019 07:07:27:

Probably too late now, but I used magnets at the back and a dowel at the front, and angled the rear former instead of the front. Very secure, 20 plus flights with no issues.

Thanks Trevor - its never too late! I did think about magnets so perhaps i'll have another think.

I have to finish the wings now so that I can install and drill the wing retaining bracket and blind nuts. With that done I can start to look at adding the top and bottom sheeting.

Peter Miller30/07/2019 08:48:42
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10278 forum posts
1229 photos
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Just a very tiny comment, you refer to the 1/4" sq. as a spar. I always call it the spine to avoid confusion with spars.

I trimmed the spine away at the front and fitted a small oblong of 1/16" ply behind the front hatch former and screwed the latch to that.

Personally I prefer mechanical methods of retention. I have traipsed too far looking for other poeples hatches and canopies to trust magnets.

Chris North 331/07/2019 01:02:10
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315 forum posts
512 photos

Thanks for all the feedback and advice guys - it all helps.

Since I had already bought the latch I though I may as well give it a go and so for this evening's entertainment set about adjusting the hatch. As suggested by Peter, I cut a section of 1.5mm slightly wider than the latch and then cut a slot for the handle to slide in. The latch was glued to the ply making sure that no glue got on the latch or its spring.

With this done, a section of spine was cut away just behind the front former slightly shorter than the ply base. Both the the front and rear sections of spline were then notched to receive the ply base and to provide a good gluing area. A hole was made in the front balsa former for the latch pin to pass through and then the ply base was glued in place between the front former and spine.

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To make sure that the receiving hole in F3 was in the right place, a pencil was rubbed on the end of the latch pin, the hatch put in position and the pin marked against the former. The pin mark was then drilled with a 2mm drill and eased out with a file.

I have just updated to windows 10 and now I can't seem to rotate photos properly so apologies for the following..

pencil on the pin...

20190730_214947.jpg pin mark on F3

20190730_215026.jpg

hatch and latch in place..

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All I need to do now is fit a keeper peg to the rear and then add the bottom location rails and the hatch will be ready for sheeting.

Date night tonight so further updates in a few days time...

Peter Miller31/07/2019 08:16:17
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10278 forum posts
1229 photos
10 articles

Ah! Another person who hates Windoes 10. I still use my Vista and even XP. for working with even though I have a laptop with Windows 10 (a freebie from the |Amazone Vine program)

That is a nice jod with the latch and I particulalry like the dodge of rubbing pencil on the end of the latch to mark the location of the hole.

Chris North 305/08/2019 01:03:04
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315 forum posts
512 photos

I posted this update in the wrong thread so re-posting here just to catch-up!

Today I attached the bottom keeper rails to the hatch cover. Simply taped the hatch in position...

20190801_210025.jpg..turned the fuselage upside down, placed the rails hard against the fuselage sides and tacked with a drop of cyano....20190801_210037.jpg...then removed the hatch and ran a bead of superphatic glue along the inside edges of the rails.

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Job done and a nice tight fit.

(Still haven't figured out how to rotate my photos in W10 as they are fine on the laptop but not once uploaded to the website)

While this was drying I decided I had better finish the wings so that I can install the wing keeper plate. First thing is to shape the replacement aileron and so this was started with the razor plane- no pictures as it is the same as before and the building board is a complete mess!.

Hopefully I can find some more time over the weekend.

Chris North 305/08/2019 01:13:19
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315 forum posts
512 photos

Ok so first job of the weekend was to finish the replacement aileron so with the laminated blank shaved and sanded to shape, the hinge slots were marked and cut. Once complete the fixed center section was cut - this time measuring three times and cutting once!! - and then glued to the center trailing edge. Then the small wing tip section was cut and stuck to the wing. This is a deviation from the plan but I saw it on Martin's and thought it looked neat so am trying to do similar.

The aileron hinges will be adjusted to close the gap but for now this will allow me to make up the wing holding bracket.

20190803_092721.jpg

Chris North 305/08/2019 01:37:41
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315 forum posts
512 photos

I changed the wing mounting bracket to 5mm instead of 3mm ply as I had a piece spare and thought that since I am using M5 attachment bolts the blind nuts would be sticking out the bottom. Probably not an issue really but I swapped it anyway.

The ply was measured up and sanded square to ensure a neat fit and was then glued in place. Great job but I had forgotten to drill the pilot holes! Anyway no major issue as there was plenty of space to drill the holes from above. The blind nuts were then pushed in. To knock them home without hammering the plate out (!) I placed my sanding block on the floor and then the fuselage over the top which proved a good fit. A hammer and a screw driver were then used to knock them home before applying epoxy around the top.

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With the ply plate in place I test fitted the wings and did a little sanding around the leading edges and the fuselage wing cutout to get as neat a fit as possible with the rear of the trailing edge nice and tight against the front of F5. There is still a bit of a gap around the wing / fuselage join caused by the trailing edge not quite matching the wing cut-out profile but I will try to tidy this up once everything is finished and before covering. I know it doesn't have to be perfect but.........

Holding the wings in place with a couple of strips of masking tape, I cut and tapered a nylon bolt and then threaded this through the captive nuts and down onto the top of the wing. Using these marks pilot holes were then drilled through the wing trailing edges. With a bolt in each wing the wing is nice and secure but can still be removed and separated into tow sections for transport if needed.

Lastly a 1.5mm ply keeper plate was made up to fit on the bottom of the wing.

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Chris North 305/08/2019 01:41:05
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315 forum posts
512 photos

It doesn't sound like much when you write it down but it took the couple of hours available this weekend.

Still I think we are starting to get somewhere and I am happy that the wing and fuselage fit as well as well as they do. There is still a bit of adjustment required until I will be happy but at least I can see where we are headed.

20190803_174728.jpg

Chris North 305/08/2019 01:47:32
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315 forum posts
512 photos

Not many chances to do much on the Ohmen this week due to some work commitments and a long weekend coming up this weekend in Singapore. Still I will see what gets done.

Next Stage of activities....20190804_114921.jpg

Peter Miller05/08/2019 08:20:31
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10278 forum posts
1229 photos
10 articles

Looks great.

Just a couple of comments.. The 3 mm ply plate for the wing hold down nuts is actually above the shaped balsa.

I do it this way because A) the plate then lies flat .not angled to match the top surface of the wing.and B) the balsa gives a lot more gluing area to the fuselage sides and makes sure that the plate never pulls out.

I have short pieces of nylon bolts sharpened but without heads so I can screw them in from the under side when there is no access from the top.

I always chamfer the ends of all my wing bolts the easy way, just a couple of turns in a pencil sharpener.

Chris North 305/08/2019 10:11:56
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315 forum posts
512 photos

Thanks for the tips Peter - I did notice on the plan that the ply plate was above scrap balsa. At this stage I have only installed the ply plate and plan to add scrap balsa next to provide packing / spacer between the top of the wing and the ply plate. I don't always seem to build in a logical manner which I am sure makes life difficult for myself. Still, every build is a learning exercise and so I am hopeful that all these mistakes and work-arounds will lead to a more streamlined build experience down the track!

When getting this plan copied I also made a couple of copies of Peggy Sue 2 just in case so you never know..mind you there is still plenty to do on this one first.

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