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The Ohmen


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Posted by Peter Miller on 31/08/2018 21:00:38:

It is a smaller version of Miss Alliance.

It could easily be made to look like a Magister or a Moth

You've set me off, Peter. I'd forgotten about the DH94 Moth Minor and it was a plane I thought would make a nice model. It was kitted a few years ago IIRC) The wings are different though with a bit of taper. I may build the Jerry Bates 1/8 th scale (54" ws ) . I'll see.

Geoff

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Piers Alley Cat wing looks a bit non standard - seems to have shorter ailerons than the plan shows. Plans for both Alley Cat and Ohmen have similar aileron lengths. The wing seat does not need to be adjusted because the airfoil seems exactly the same on all 3 plans. Wing fixing might need slight change.

My Swamp Rat wing and the spare are slightly shorter span than the Ohmen due to tip being slightly different shape. Interesting to know what difference the tip shapes make- probably very little except in appearance and the ability to be able to stand a wing on end for storage!

There is some conjecture in another thread on whether the Ohmen would be a good design for the Mass Build. Ohmen builders might like to comment there.

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You are right kc Alley Cat and Ohmen have the same length ailerons. Naughty me decided to fit flaps to my Alley Cat, then I changed my mind so the ailerons are a bit shorter, (can't see it making a vast difference). If I decide to do it as per the plan I only have to fit new trailing edge stock. The section is very similar as is the planform (Alley cat chord is 3mm shorter but that may be down to the TE stock I used. Rib spacing is slightly different.

Ideal for a mass build I would think, at least this may be one I actually finish!

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Hi Piers, Thanks for the good wishes. Maybe it will stop my model dissapearing every so often which is worrying!!

All the wings were designed separately for each model believe it or not. Now you know why I suddenly feel and urge to produce something really different.

Most of the effect of the ailerons is out at the ip. so the reduced aileron length will not make much difference.

I have never really noticed that tip shape has much effect but that could be down to me not being a precision flyer.

I have jjust spent a perfect afternoon throwing "The OHmen" round the sky with only the odd moment when it vanished.

Well as a subject for the mass build.IT is easy to build, cheap and electric.

One modification I would make is to take the 1/32 ply wood doubler another inch further back. Also use hard strip for the tailplane if not using sheet.

A little while ago I got completley dissoriented. The model was coing down verytically at speed. I hauled in full "UP" and the model hit the ground dead flat. Bounced into the air with only one prop blade and ended up in the wheat.

The only damage was a clean break from the rear of the hatch to the rear of the wing cutoit and a crack or two in the cowl

Half an hour with glue and it wass back as good as new and has flow a lot since.

The doubler was short because I was using my last scraps of 1/32" ply.

Edited By Peter Miller on 02/09/2018 18:22:52

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I have noticed that the plan as printed in the magazine does not show any bracing for the 1/8th ply motor bulkhead to the sides or battery tray. The photos of Peters model clearly show triangular bracing to the fuselage sides. Experienced modellers will automatically brace with triangular but this type of plan will appeal to new builders who may not realise this is needed, especially with only a thin 1/8th bulkhead. Only a very thin line of glue holds the motor on as per the plan!

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Well spotted kc. Yes, I would have used triangular section stock as reinforcement myself. A point that could be mentioned if it was voted the 2019 mass build. Also, if it was selected, better the MB voting starts sooner rather than later as it would give Sarik/SLEC (or whoever) time to produce a CNC set of parts for those who might want that (in time for Jan 2019 start). I think the availability of a CNC kit encourages more participation whatever the model selected.

I wonder if there are others on the Forum who is, or planning to, build an Ohmen?

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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.

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  • 2 weeks later...

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.

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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!

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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

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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.

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  • 2 weeks later...

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

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