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The Ohmen

My first electric powered aerobatic model

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Peter Miller18/04/2019 18:13:47
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9929 forum posts
1160 photos
10 articles

Ah Well, ASfar as I am concerned my sports models are just designed to be thrown around in a long sequence of aerobatics. As I always say, the only time they fly straight and level is when they are inverted.

A Currare it is NOT and is not intended to be.

Dean Sarelius16/05/2019 14:28:22
13 forum posts
14 photos

Hi All,

Here are some pics of the Ohmen so far.

Parts have been cut with my Chinese 40W laser cutter and the bulkheads and wing halves glued with epoxy. Will make a start on the undercarriage next and will take Martins lead and mount it to the outside.

Cheers,

Dean

Laser cut bulkheads

Wing halves epoxied together

Fuselage

Wing

Wing and fuselage 1

Wing and Fuselage 2

Dean Sarelius16/05/2019 14:37:48
13 forum posts
14 photos

OK not sure what happened with the pictures so have provided the links here below.

Laser cut bulkheads

**LINK**

Wing halves epoxied together

https://www.dropbox.com/s/zd9m9qkwhu9m6bd/IMG_20190329_190435.jpg?dl=0

Fuselage

https://www.dropbox.com/s/qnmxc3zqs2jo1rl/IMG_20190516_072558.jpg?dl=0

Wing

https://www.dropbox.com/s/pwssr3r57n874e7/IMG_20190516_072625.jpg?dl=0

Wing and fuselage 1

https://www.dropbox.com/s/0i5qdsbchfe0v4l/IMG_20190516_072658.jpg?dl=0

Wing and fuselage 2

https://www.dropbox.com/s/xruyixoiichwr5s/IMG_20190516_072706.jpg?dl=0

Percy Verance16/05/2019 18:48:18
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8110 forum posts
155 photos

Have you uploaded your photos to an album here Dean? It's much easier and quicker to post pictures on here if you do........

Dean Sarelius17/05/2019 00:21:21
13 forum posts
14 photos

Thanks Percy,

Here are the pics from my album.

Cheers

Dean

img_20190313_221903.jpgimg_20190329_192425.jpgimg_20190516_072558.jpgimg_20190516_072625.jpg

img_20190516_072658.jpg

Peter Miller17/05/2019 08:19:09
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9929 forum posts
1160 photos
10 articles

That is looking very nice indeed.

Just one thought. You do sandpaper all the charred black off the edges befofre gluing don't you?

Dean Sarelius18/05/2019 00:36:43
13 forum posts
14 photos

Hi Peter

I sand off the burnt edges with 220 and on account of the laser I also square off the edges before gluing.

The balsa cuts much quicker so tends not to get as burnt as the ply.

Cheers

Dean

Peter Miller18/05/2019 08:32:59
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9929 forum posts
1160 photos
10 articles

I only mention it as we had someone whose engine came out because they had not sanded the char off

Dean Sarelius19/06/2019 12:19:32
13 forum posts
14 photos

img_20190619_205803.jpgimg_20190619_205725.jpgimg_20190619_205721_burst001_cover.jpgimg_20190619_205611.jpgHi All,

I am just setting up to build the cowl for the Ohmen.

After fitting I find there is very little space between the cowl ring and the motor. If I was to provide a 1mm gap between the spinner and the cowl ring the cowl ring will be rubbing up against the motor.

Just wondering if anyone else has run into the same problem and if there could be any easy fix..?

Cheers,

Deanimg_20190619_205530.jpg

Peter Miller19/06/2019 12:39:29
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9929 forum posts
1160 photos
10 articles

It looks as if you are using a different motor and prop driver to my original.

If using a different set up it is just a case of cutting and adjusting to suit.

It looks as if you could open up the hole in the ply ring to clear the motor. The cowl ring might end up about 1/8" wide but it isn't load bearing so that is no problem.

Your prop driver looks thinner thanthe one on my 4-Max motor. possibly you could pack the prop forward a little The other possible option would be to cut the ring from 1/16" ply.

I hope this helps.

Dean Sarelius19/06/2019 13:09:33
13 forum posts
14 photos

Hi Peter,

Thanks for the quick reply.

I am unable to pack the prop forward for fear of running out of thread.

I think I will take up your advice and open up the cowl ring.

I might just change the shape of the cowl to allow more air to flow around the motor what are your thoughts on this as I think there will be very little air flow around the motor if the cowl is to restrictive..?

Cheers,

Dean

Peter Miller19/06/2019 13:23:49
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9929 forum posts
1160 photos
10 articles

By all means change the cowl shape. Cooling air is pretty important. A small scoop on top of the cowl and of coure the chin intake help.

You should be able to fit a slightly bigger spinneras well.

Modifying and customising a design to suit ones own needs and/or ideas is part of the fun of modelling

kc19/06/2019 13:42:19
5901 forum posts
168 photos

Sometimes with ic engines the area around the engine was restricted to get more airflw where it was needed. So as long as you have sufficient exit space for the air it should be OK with electric. If in doubt you could always try the plane without the cowl. It's more essential to cool the ESC than the motor.

So you either buid a cowl to suit the motor or perhaps buy a different motor that fits more easily ( that might be one where the shaft projects out front and takes a prop adaptor which has a collet fiting )

I cannot quite see from your photos but did you use triangular stock to reinforce the bulkhead to fuselage sides - an item omitted from the published plans as noted previously.

Peter Miller19/06/2019 14:24:15
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9929 forum posts
1160 photos
10 articles

The ESC should be cooled OK as the chin intake makes sure that there is a flow straight onto it

Dean Sarelius19/06/2019 14:24:20
13 forum posts
14 photos

Hi KC,

Thanks for the heads up.

I use slow curing epoxy for all the bulkheads and since the engine bulkhead is mounted directly to the inside plywood laminate sheets there is plenty of strength provided by the epoxy joint so no need to add any stock. By the way the epoxy I use is called Bote-Cote and its the same as that which I have been using for building plywood boats.

You can see some of the boats I have built on my webpage, www.boatandhobbies.com.

One of the advantages with Bote Cote is the long curing times which can vary depending on the ambient temperature anything between 2 hours and 10 hours on a cold night. The longer curing times allow for longer setup and when mixed with a filler provides an extremely strong joint.

I think I will take Peters advice and laser cut a slightly larger cowl ring.

Regarding the air flow do you think it would be advised to add an exit behind the wing perhaps..?

Thanks again for all your good advice.

kc19/06/2019 15:26:39
5901 forum posts
168 photos

Dean, I think most experienced aeromodellers would consider that reinforcing the engine bulkhead to fuselage with triangular fillet is absolutely essential. It is a feature of most designs.including this one. The consequences of an engine pulling out and hitting someone is too awful to contemplate.

There is really no reason to leave the fillet off - it can be made from scrap balsa and does not need to be triangular or neat - and weight is usually added to the front of most models so no need to save weight.

Peter Miller19/06/2019 18:14:06
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9929 forum posts
1160 photos
10 articles

THere is a big hole in the front cockpit floor which allows the hot air out

Martin McIntosh19/06/2019 19:40:56
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2834 forum posts
1050 photos

I think that you are worrying about nothing. There are huge holes where the pilots sit. No need for anything else.

Dean Sarelius20/06/2019 01:28:23
13 forum posts
14 photos

Hi Martin,

I dont intend on having holes where the pilots will be seated so this is why I asked the question...?

Trevor Crook20/06/2019 07:34:50
810 forum posts
63 photos

p1010429.jpg

You can just see the cooling air exit in front of Dick Dastardly's chest. It's where Peter says, in the front cockpit floor.

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