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The Ohmen

My first electric powered aerobatic model

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Peter Miller10/09/2018 13:40:25
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Posted by Peter Miller on 10/09/2018 10:29:09:

OOPs I missed when proofing the plan. Sorry.

If anyone would like PGF files of my original plan. PM me with your email address.

Edited By Peter Miller on 10/09/2018 10:30:05

Of course that should read PDF files

Martin McIntosh12/09/2018 21:07:30
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Very surprised to see a thread on this started so early since it has only just been published in the mag.

I have an unusually empty building board at the moment so I was looking around for something to keep me occupied for a while.

I once built Peter`s Cap 21 which was excellent so I thought about scaling this back up for an OS52S, but not wanting a protruding silencer I found that the exhaust systems I have for the motor would not allow this.

I have a TGY 3548 and an AXI 2820/14 doing nothing and fit the power requirements so saw sense and have almost decided to have a go at it `as is`.

Will keep you posted on the results of my effort.

Jon Robb12/09/2018 22:09:23
5 forum posts

After a recommendation to build this model on a thread I posted recently, I to am looking to build this model in the near future. I’ll be looking forward to seeing your build progress in tandem. This will be my first plan build balsa kit, as opposed to a balsa WOT4.

Peter Miller13/09/2018 08:01:51
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Hi Martin

The thread was started when I first cut balsa for my prototype. Always glad txo see others adding to tthe thread.

NOTE that the triangular stock in the corner betwen F-1 ans the sides is missing. I checked and I am guilty, I forgot to add it to my own original plan.

Martin McIntosh23/09/2018 14:30:04
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Well, been hard at it since my last post and here is the result so far.

ohmen.jpg

I changed the wing assembly method a little just to suit me but the component parts and end results are similar. I added large holes in the rear formers since I shall be using pull- pull on the rudder, and substituted vertical 1/32 balsa for the ply doublers to save a little weight. Not clear to me how the u/c is held in place so may go a little more conventional here and maybe make up a steerable tailwheel.

Percy Verance23/09/2018 16:38:30
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Martin Re: Ohmen undercarriage.

I just had a look at my copy of the plan, and the u/c wires are a fairly straightforward job. They're held/screwed to the underside of the fuselage with those little grooved nylon things ( can't remember what they're called ) and the vertical ends of the u/c wires - which go up into the fuselage, against the fus side ply doublers - are trapped in the two grooved ply blocks glued to the fus sides. It's just here you could have done with that ply doubler!  You can of course retro fit some in the areas where the u/c wires will be.

P.S. The nylon things I referred to earlier are saddle clamps......

 

Edited By Percy Verance on 23/09/2018 16:52:33

kc23/09/2018 17:08:09
5589 forum posts
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The plan shows a 1/8 ply plate across the fuselage and appears to show it covered with 3/32 balsa like the underside . 6mm birch ply would seem a good idea instead - something to get the saddle clamp screws to bite into.

The point about using 1/32 ply doublers is that in a severe crash the ply usually remains intact while the balsa splinters. The ply keeps the model straight enough to rebuild! And as Percy said it's really needed in the u/c mount area. For my model i would choose to use just a 2 inch wide strip of ply instead of the 3.5 inch height shown. Maybe with a triangle to extend up to top of F1 and a couple of filler strips at F2 and F3 to keep the surface level where it meets those formers. Save a lot of weight and expensive ply!

Nigel R23/09/2018 17:48:41
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Crikey Martin that was quick. That's about four or five months building for me!

Would it be worth doing a wing mount uc at this stage?
Peter Miller23/09/2018 18:23:29
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Yesw, there should be triangualr stock in teh F-1/ fuselage side joint.

The 1/32 ply doublers are very important they hold the sides tin one piece.

The 1/8 ply plate under thefuselage for the U/C mount is fine, Due to the long legs going up into the 1/4 ply slotted members it won't pull out.

I got disoritened and the model came down vericlly. I pulled it our and it smashed into the ground dead flat. The U/C just splayed out flat and the model bounced and flew into the field. The fuselage had a clean break just at the rear of the trailing edge. The U/C just needed bending straight (10 SWG insread of my usual 8SWG

Martin McIntosh23/09/2018 19:41:39
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Thanks for the comments. If I build the u/c as per plan then I shall obviously use ply between F2 and F3. I just asked the question because the plan does not appear to show saddle clamps so I wondered if it simply plugged in. Anyway, I do not try to make my models crash proof as I have no intention of bending them if possible!

Update soon.

Percy Verance23/09/2018 20:40:46
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The undercarriage does sort of plug in Martin, and the saddle clamps ensure it stays in.

Martin McIntosh07/10/2018 18:19:04
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My version now about ready for covering. C of G with the motor/prop/spinner fitted is about right as it is so it will be interesting to see how this turns out later.

ohmen 001.jpg

ohmen 002.jpg

Peter Miller07/10/2018 19:16:51
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Looks very neat and tidy.

Allowing for the covering and the U/C and battery you might need a little lead in the tail. Mine did but there is plenty of room to move the battery back and forth

Martin McIntosh07/10/2018 19:27:15
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That`s what I was expecting Peter. I have lots of 2200`s and have just bought a 3s 3000 to try in it. I always try to build the tail end as light as possible! I may just cover the fus. in HK ally film which is quite heavy so that may help.

Here goes.

Peter Miller08/10/2018 08:04:23
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9360 forum posts
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The 3000 battery might be a good idea.

I spent a full flight at full power yesterday and the 2200 ran out of power before the normal 8 minutes.

Mind you It never flew straight and level in the whole time except when it was inverted. It is one of those models that I just spend the whole time throwing it round all over the sky. I have a few like that, Peggy Sue 2 is like that.

Edited By Peter Miller on 08/10/2018 08:04:43

Nigel R08/10/2018 13:27:28
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Martin, that looks really good.

I did exactly this kind of U/C on the RM Aerobat I'm logging - couple of pictures here

https://www.modelflying.co.uk/forums/postings.asp?th=135764&p=4

although I'm sure I'm not showing anything you don't already know.

 

Edited By Nigel R on 08/10/2018 13:27:46

Martin McIntosh08/10/2018 17:24:54
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Thanks Nigel. A new way of u/c fixing to me since most of mine are scale and/or have retracts, but I have stuck with the plan on this.

Peter, I am surprised that you got nearly eight minutes on a 2200 since at 30A the maths say only 4 min. at full power, assuming that your motor is similar to the one which I intend to use.

Peter Miller08/10/2018 18:18:13
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I checked the amperage drawn when I first flew the model, IT draws 25 amps at full throttle. The power died on my last flight at about 7 minutes and I landed about 30 sec0nds later.

Normally I fly about half the flight on full power and half at alower throttle setting and get 8 minutes and land with about 11.3 volts in the battery.

As a total novice with electri flight i rely on experienced club members who say that is OK

Trevor Crook08/10/2018 21:31:16
700 forum posts
53 photos

Just started fuselage construction on mine, it will be quite a few weeks before the airframe is complete at my rate of building! I'll prop mine to pull around 30A at full throttle as that's the continuous rating of the esc I have to hand. I would normally use a 40A for safety, but this esc had worked happily in a model that I discovered pulled 35A max!

Martin, the torsion bar u/c on the plan works well and is my favourite layout for sport models. I moved my Ballerina u/c from the wing to the fus so I could use this layout. Never had anything break, and it will only take a bend in a really heavy "arrival".

Nigel R09/10/2018 03:24:32
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Surprised you haven't come across it before martin. My favorite sport setup, like Trevor. Strong and light. The wire work is a piece of cake too, only three simple bends and no soldering needed.

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