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C No Ohmen

Build blog for my attempt at the Ohmen

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Peter Miller05/08/2019 11:02:27
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10077 forum posts
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We all have our own favourite ways of doing things. No one can say "That is wrong!" or " That is right!" if it works.

When I make a comment I am not criticising anyone, just saying how I do it and why.

I have just got off the phone talking to a clubmate and we were discussing favourite ways of doing things. We both prefer different things, we are both right.

Funnily enough I was just saying to him that I really must get Peggy Sue out for an airing very soon. If next weekend is too breezy for test flying Peggy Sue will be a natural choice.

Chris North 308/08/2019 02:33:51
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279 forum posts
459 photos

As a bit of a change and to make sure I keep seeing progress I moved on to the tail feathers.

I had already cut out the horizontal stab and elevators from 5mm ply sheet and so first up I installed the hinges using the trusty hinge slotter to make sure the hinges were centered. Practice must make perfect as the slots were much easier to make this time and the hinges a nice tight fit.

Couldn't resist getting a feel for what it is going to look like..

20190806_214849.jpg

It looks a bit strange just now but once I have completed the fin and rudder I will take all of the paper off of the parts and sand back.

Next it was time to take the scalpel to the plan again so I could use it as cutting guides for the fin and rudder. The rudder was no problem however the fin dis not fit on the 5mm sheet I have and so the sheet was butt joined to create the correct width. There should be no issue with glue strength but either way the butt join has been placed so that it is at the front of the fin and will be supported by the thickest section of the fin cheek blocks.

20190807_220242.jpg

Putting that aside to dry I was trying to find something simple before finishing for the evening.

On the Batty build their was only a single elevator and so no need to join separate halves. Ohmen requires a standard wire joiner and so this seemed like the ideal item to look at.

Previously I have always struggled with pliers to bend undercarriage wires and so this time, given that the plan calls for 3mm wire I decided to get a small wire bender. 3mm wire looked a bit big for the elevator joiner and so rummaging through the spares bag I found an old set undercarriage legs I had made to suit some retracts in a flitetest spitfire which were slightly thinner at around 2- 2.5mm. One end was already bent to take the wheel and this turned out to be a perfect fit for the elevator.

So with a bit of thinking and some trial pulls to see which way it would bend (!) I set up the wire bender and bent the second 90 deg into the joiner. Wow so much easier than struggling with pliers.20190807_220053.jpg

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So feeling brave and since I had everything set-up i thought I'd try bending the undercarriage. Well the vice I have is a small desk mounted one and I have to say that it is not ideal for bending 3mm wire which is at the limit of this little bender I got. The main problem is that the vice is not stable enough and so any decent pull on the bender handle turns the vice on the bench. Holding it stead with my left hand did help but reduces the amount of pull that can be given. For sure the 3mm wire was a lot harder to bend but when I got the hang of it I die manage manage to make some progress.

All in all not bad for a first attempt. Anyway we are away for the long weekend so I will finish this off later next week. I can tell already that the trick is going to be bending the second leg so that it matches the first! Any tips and hints would be most welcome! 20190807_220147.jpg

Peter Miller08/08/2019 08:30:23
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10077 forum posts
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10 articles

The elevator joiner is 16 SWG, or a fraction over 1.5 mm.

At the moment I can't find my magazine plan but on my original it is 16 SWG

JUst checked on the PDFs, Yes!! 16 Swg Elevator joiner

Edited By Peter Miller on 08/08/2019 08:37:12

Chris North 308/08/2019 11:40:49
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279 forum posts
459 photos

Thanks for that Peter - I most likely didnt see it as I have cut part of the plan up. Still it is not installed yet so no problem. This was all the wire I had so I will have a look at the local shop after the long weekend.

Thanks again for keeping an interested and helpful eye out

Peter Miller08/08/2019 12:15:53
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10077 forum posts
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Hi Chris.

Glad to help. WE can all get things a little wrong (I know that I do!!)

Chris North 315/08/2019 05:54:03
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279 forum posts
459 photos

Very little progress this week as there has been no time to get to the building board plus I came across a problem with the wire bender which I put on the back burner

I think bending 3mm wire with the K&S mini wire bender is most likely fine if you have a decent vice but since I'm using a small hobby vice I think it is on the limit. The problem being that it is hard to clamp the hobby vice tight enough to the table to stop it spinning when trying to bend the wire. This means that one hand was required to support the vice and thus only one hand on the wire bender handle. For thin wire this would be fine but 3mm is at the limit and so I have slightly elongated the pin hole in the handle. This means that there is now slop and so the handle tends to ride up over the wire instead of bending it.

Here is the result of trying to bend 3mm wire one handed! Yes it is well and truly wedged!

20190814_204306.jpg

So, frustrated the thing was put aside for a day or two. In the mean time a trip to the LMS was made to pick up some 2mm wire (couldn't get 16SWG) for the elevator joiner.

Chris North 315/08/2019 06:10:42
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279 forum posts
459 photos

While at the LMs i did contemplate getting a new bender but I'm a bit of skin flint and can't abide buying things twice so decided to persist.

A quick sharp jab of the palm had the wire bender free and so I decided to try again, this time with the thinner wire.

I found that if the hobby vice is clamped as hard as possible to the desk it will eventually stop rotating when a load is applied. The distortion to the wire bender meant that even with the thinner wire it would tend to run up over the wire but I eventually worked out that instead of trying to do all the bending with the handle, if the wire is pulled around with one hand in the direction of the bend, the handle then only has to do half the work and forms the bend quite easily.

Wish I had found this out before damaging the bender!

Anyway, a new elevator joiner was made up, trimmed to size and then the elevators notched so that the joiner sat flush with the hinge surface. Very straight forward and boring for most i am sure but since I took the photos, here they are..:

Joiner bent to shape and locations for drill holes marked...20190814_213346.jpg

Hole drilled slightly under size, grove cut to accept wire and little bit extra taken at hole location to account for wire radius...

20190814_213258.jpg

Wire inserted and groove adjusted until wire sits flush...

20190814_213322.jpg

Re-attach elevators and double check location of second location hole. Remove and repeat grove preparation for second elevator...

20190814_213221.jpg

Jobs a Good 'un

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20190814_213109.jpg

Chris North 315/08/2019 06:51:58
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279 forum posts
459 photos

And since I was now more comfortable with bending smaller wire I used the same approach for the main under carriage legs. To get the lever arm to help with the bending I used a single length if wire and bent a leg at each end!

All I need to do now is to cut them to length and they will be ready for trial fitting

20190814_213552.jpg

Peter Miller15/08/2019 08:09:38
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10077 forum posts
1192 photos
10 articles

I always bend the elevator joiners with a big pair of pliers.

I only use my wire bender on 12 SWG and larger sizes. I have even bent 6 SWG wire on my bender but that was really taking the micky out it.

piano wire 001.jpg

Chris North 319/08/2019 07:23:13
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279 forum posts
459 photos

Small bit of progress before heading to the airport....

I decided that I would make a start on covering the cockpit hatch cover as a bit of a test for the rest of the fuselage top. In an attempt to cut down on waste balsa I used a piece of scrap paper to assist with cutting a template for the sheet balsa. So taping one edge of the paper flush with the bottom of the hatch base, it was wrapped around the formers and then the center line of the spine marked. The paper was removed and its size marked onto a sheet of 2.5mm sheet

Since I had used 6mm square balsa strips as the hatch alignment rails, I also added 6mm to the width of the paper template so that the sheet when cut would reach the bottom of the guide rails.

A bead of cyano was run along one edge of the hatch cover and the balsa sheet was placed up against it. With the extra 6mm width the sheet was able to sit on the work bench and be held vertical against the side of the hatch using a couple of squares.

Once dry the outside of the sheet was throughly wetted with water and left to soak in. After a couple of minutes the sheet was gently and gradually pushed over the formers towards the center spine. Pushing a little at a time allowed the sheet to form without breaking.

The sheet was then released and a bead of cyano run along the top of each of the formers and along the edge of the sheet where it touched the spine.

The hatch was turned over and rolled against the bench, so that the sheet was tightly wrapped against the formers without any gaps, and was then held until the glue was dry.

Luckily the first sheet ended up just next to the latch lever and so no trimming was required to clear the latch mechanism.

The process was repeated for the second side however this time the sheet was started from the center spine to make sure the join was nice and tight. A notch was cut in the sheet for the latch handle and then the sheet wetted and rolled around to the hatch bottom edge.

Chris North 319/08/2019 07:27:27
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279 forum posts
459 photos

With the sheeting in place both sides were then trimmed flush with the base of the hatch cover. To do this a spare piece of 6mm strip was placed next to the hatch and was used as a guide for the box cutter. This way the sheeting was neatly trimmed and only required a quick sand to bring it flush with the base of the hatch.

I forgot to take pictures of the sheeting process but here are a couple of the final sheeting before trimming and the trimming process

20190817_064507.jpg

20190817_064517.jpg

20190817_064733.jpg

Peter Miller19/08/2019 08:16:47
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10077 forum posts
1192 photos
10 articles

Very neat indeed. I use the same technique roughly, just variations on where I start the sheet from

The main difference is that, like you, I stick the sheet down along one edge\ and when he glue has dried I wet the sheet and then apply heat with a heat gun which makes rolling the sheet over much easier.

On my current build I do not have any really bendable sheet so am going the have to use that more agressively

Edited By Peter Miller on 19/08/2019 08:17:02

Chris North 327/08/2019 02:55:45
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279 forum posts
459 photos

Back at home and back at the bench. Only had an hour this evening so spent the time adding the next piece of fuselage top sheeting.

First I taped piece of thick paper to the fuselage

20190826_212739.jpg

...then rolled it over and marked the center spine...

20190826_213219.jpg

..removed the paper, cut to size, taped to the edge of a piece of 2.5mm sheet and cut to the template..

20190826_212318.jpg

..using cyano, I attached the sheet to the top of the fuselage sheeting and let it set..20190826_214118.jpg20190826_214130.jpg

....the sheet was then wetted on the outside and the water allowed to soak in. After a couple of minutes the sheet was slowly rolled over the formers until it aligned with the spine. The sheet was released, cyano added to the formers and the edge of the spine and the sheet rolled back into position. The fuselage was turned upside down and pressure applied until the glue was dry and the sheet was attached...20190826_215045.jpg

...leaving me with a nicely rolled top sheet... 20190826_215107.jpg20190826_215130.jpg

Now I just need to repeat for the second side and then trip up so it is flush with the fwd and rear formers. Since I have to try to align two edges on the next piece of sheeting I expect there may be a rough join along the spine however this can be filled and sanded before covering so no need to worry to much about aesthetics at this point.

I'll see how I get on this evening.

Peter Miller27/08/2019 08:18:32
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10077 forum posts
1192 photos
10 articles

Very neatly done

Chris North 329/08/2019 01:12:46
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279 forum posts
459 photos

Measure, cut, glue, wet, bend, glue hold, repeat.....

20190828_211257.jpg20190828_211306.jpg20190828_211323.jpg20190828_211355.jpg

I have to say that I am quite pleased with the way the sheeting has turned out. There are a couple of spots that i could have done better on but all in all in it is looking neat and tidy. The only thing I am a little worried about is that the fit is nice a tight and so I am not sure if this is going to be a problem once I apply the covering - i.e. should there be a 1 mm gap to account for the film covering at the joins?. I have the change to loosen everything off a bit when sanding prior to covering so we will see.

Chris North 329/08/2019 01:20:31
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279 forum posts
459 photos

So a quick check list of items left to do:

  • attach bottom fuselage sheeting
  • add packing block below wing bolt retainer
  • attach tail feathers
  • add & shape support blocks to side of fin
  • build cowl;
  • cut top and bottom openings in hatch cover
  • attach battery tray & velcro
  • add all electrics;
  • finish shaping wing tips;
  • sand, assemble, stand back, smile and enjoy;
  • cover and set-up for maiden;

Well that doesn't sound too bad...

Chris North 329/08/2019 01:37:48
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279 forum posts
459 photos

Now that the fuselage sheeting is essentially finished (it needs a bit of sanding and filling along the joins) I thought it would be a good time to move onto the fin support blocks.

I don't want to glue the stabilizer and fin before covering as I can see that this will make covering more difficult but I do need to position the tail so that I can sand the support blocks to shape.

Since I still have the paper template on the tail I used the center line to ensure the tail was pushed up against F9 and centered over the rear fuselage. A T-pin was inserted through the stabilizer and the support plate to hold it in position while still allowing it to pivot slightly. A tape measure was used to verify the check the distance from one tip to the centre point at the rear of the hatch. A minor rotation was all that was required to get both sides equal and then a second pin was installed at the front of the stabilizer to fix it. The plan being that these pin holes can now be used to reposition the stabilizer once the template is removed.

The templates had been attached using pritt stick and so a quick wetting of the paper and the whole template was able to be scrapped back easily. While the paper comes off no problem the glue gets sticky again when wet and so this rubbed off and then given a quick sand with a fine sponge sanding block.

20190828_215403.jpg

While I was at it I went ahead and removed the templates from the stabilizer, fin, and elevators.

Chris North 329/08/2019 01:44:30
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279 forum posts
459 photos

So the plan now is to use a scrap piece of balsa sheet to represent the fin and to attach and shape the support blocks.

So a question to anyone who may be following : do you normally glue the finished support blocks to the stabilizer or the fin (or both) before covering or do you cover all items separately and then glue them together afterwards (ensuring balsa to balsa bond of course)?

Also a question for Peter - should the leading edges of the stabilizer and fin be rounded off or left square? I am sure it will look better rounded off but does it make a lot a difference as far as performance is concerned?

Thanks in advance

Peter Miller29/08/2019 08:19:25
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10077 forum posts
1192 photos
10 articles

Oh Yes, you round off the edges of the fin and stabiliser.

Also this is how I make my fin fairing blocks.

moon dancer const 015.jpg

moon dancer const 016.jpg

These afre from my new Moon Dancer 2

Yes, I know that the fit could have been better. However my rolled sheet is not too bad.

In answwer to your second question. I cover all of them separately but I leave some covering on the front of the blocks to iron down onto the fuselage

Edited By Peter Miller on 29/08/2019 08:20:53

Edited By Peter Miller on 29/08/2019 08:23:35

Edited By Peter Miller on 29/08/2019 08:49:11

Denis Watkins29/08/2019 08:35:59
3814 forum posts
54 photos

Your idea to cover those bits, then glue Chris, is probably the best way.

I must admit that I bowed out on my last two builds from covering these parts, and I painted them after glue had set.

Reason being, I cannot get my iron in and around snake exits and into fin and stabilizer corners well enough, with my fat fingers too while trying to steady small areas of covering.

I will cover small parts in future, then glue them in thanks

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