The Ohmen

[Nigel R]

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 McIntosh]

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 Miller]

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 Crook]

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 R]

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.

[Peter Miller]

Posted by Nigel R on 09/10/2018 03:24:32:
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.

From what I have seen most ARTF manufacturers would benefit from using that set up....or at least theri customers would!!

[Martin McIntosh]

Here is my finished effort ready to go.

Weight 2 3/4lbs (1270g). Draws 250W on 11x7 which makes it lighter than air.

[Peter Miller]

THat looks really smart.

I will be very interested in hearing your verdict.

This week end is looking great, especially tomorrow

[Martin McIntosh]

Thanks Peter. No excuses now so tomorrow it will be.

[Martin McIntosh]

Three very successful test flights today, it is basically a pussy cat in the air.

Ist, 2200 pack, 11x7 wood prop. 2 clicks of up. Timer set for 6 mins, another 1 min to land which was a doddle. Only 14% left in pack after stooging round on 3rd to half power with quite a lot of full throttle for loops and rolls.

 

2nd, down elevator travel increased by 33% and aileron low rate by a bit. The wind suddenly got up and became very turbulent which is my excuse for breaking the prop.

 

3rd, 12x7 wood prop fitted since it was my only suitable spare. 3000 pack this time,as far back as it would go but even on high rate it refused to spin so some lead needed in the tail. I reduced the dihedral to 1" total on mine and the slow and point rolls will only need a little mixing to sort them out. Wind eased for landing which was slow and easy.

 

Next time out I shall see just how further rearward the cg can be. At the moment it is very slightly forward of the plan position. I still need to find a couple of brave chaps to occupy the empty seats and provide them with wind shields.

Edited By Martin McIntosh on 20/10/2018 14:46:42

[Peter Miller]

Hi Martin

So glad to hear that you are happy with The Ohmen. FInal trimming to suit ones own prefercences is always needed.

Have fun

Peter

[Martin McIntosh]

This is it with the cockpits now populated.

Tried moving the cg back by by about 10mm, don`t do it.

[Peter Miller]

Hi Martin.

Looks great. I see you have the same lady in the front cockpit!

Interesting about the CG. I always put it at 25% back and don't try anything else. Now I know that I am right!!

[Dean Sarelius]

Hi Peter,

I am just getting back into model plane building in part due to my 15 year old son.

I recently purchased a Chinese K40 Laser cutter as one of my pet hates is the time taken to cut out the wing ribs not to mention the plywood bulkheads.

What I normally do is take a PDF copy of the plan and trace it in Solidworks before laying out each part onto a DWG file and saving as a DXF ready for cutting.

I have already purchased the October 2018 RCM&E magazine and would like to build The Ohmen but would need to get the plan in PDF format.

Do you know how I can arrange to obtain a copy of the plans in PDF...?

Best regards

Dean

[Levanter]

Dean

Welcome to the forum. I am a Peter Miller fan!
Take your plan to a decent copy shop. They will be able to scan it to pdf. I do this a lot with drawings of full size ships and yacht to digitize and archive.

I am strange however. I find cutting out wing ribs and then putting holes in them exceedingly good therapy.



Sandwich method for the wing ribs of one of Peter's designs Yuppy Love. It is a bipe so lots of them!



And then the holes made with sections from an old transmitter aerial.

Yeh, I know!


Levanter

[Nigel R]

For really big (1/2" or 3/4" holes in balsa - sharpened copper solder Tees.

[Geoff S]

I recently acquired a set of these - brilliant for boring soft balsa.

Your Ohmen look splendid, Martin. It was on my short list for this winter but I decided on building the ancient Easy Built Models RYan instead. Peter's Ohmen would have been much easier - his drawing are well detailed and he's always here for advice and encouragement if needed.

Incidentally I noticed a book lying on the table in the club today - 'Four Stroke Engines' by Peter Miller. Not really much help to me as a dedicated (almost) electric flyer nut still interesting.

Geoff

[Peter Miller]

Posted by Dean Sarelius on 15/11/2018 09:35:16:

Hi Peter,

I am just getting back into model plane building in part due to my 15 year old son.

I recently purchased a Chinese K40 Laser cutter as one of my pet hates is the time taken to cut out the wing ribs not to mention the plywood bulkheads.

What I normally do is take a PDF copy of the plan and trace it in Solidworks before laying out each part onto a DWG file and saving as a DXF ready for cutting.

I have already purchased the October 2018 RCM&E magazine and would like to build The Ohmen but would need to get the plan in PDF format.

Do you know how I can arrange to obtain a copy of the plans in PDF...?

Best regards

Dean

Hi Dean.

The Ohmen ribs a re easy as they are basically all the same. I make one in 1/16" (1..5mm) ply. I stich a strip of balsa to the bak and drive a cpuple of map pins through this so they proturde through the ply. Now you justLay it over the wood, press down and cut it out witha scalpel. It doesn't take long and as Levanter says, very theraputic

PM me and I can organise PDF files for you. My own original plans

[Peter Miller]

Hi Geoff.

THat is an old book but I like to think that it is still useful

[Martin McIntosh]

Where did you get those tools from Geoff, they look useful.

[Geoff S]

Martin: I don't think Softbore tools are made any longer. They were amongst a load of 'stuff' left to the club to sell for funds by a recently deceased member. The 'Easy Built Models' (haha) Ryan ST kit I'm building at the moment came from the same source. The kit makes every builder a designer as well, so a never ending joy which allows me to pretend I know what I'm doing.

I recall they were mentioned in the old Electric Flight magazines as a means of weight saving in the days when successful electric flight was more of a problem and every gram saved helped. I'm almost sure they've never been used until I used one on the ribs for this model.

Peter: The book is still useful, I'm sure. It's just that I so rarely run glow engines these days. I also have a copy of your 'Designing Model Aircraft' which certainly gets referred to from time to time.

Geoff

[Trevor Crook]

Mine's approaching the covering stage. I use a variation of your rib cutting method Peter - a couple of short, pointy self-tappers screwed through the ply template rib. No problem cutting out the ribs, did them in 3 short sessions. I admit I did "sub out" cutting the ply formers to my father-in-law as he's got an electric fretsaw.

Really enjoying the build, it's the first complete plan build I've done in a few years. It's making me consider something a bit more ambitious next time.

[Dean Sarelius]

Hi Peter and Geoff,

Really appreciate your good advice.

While I appreciate the therapeutic benefits of cutting my own ribs and bulkheads I now have a new toy to which I need to put to good use so will look forward to share with you my build at some stage in the not too distant future I hope..!

Cheers,

Dean

[Martin McIntosh]

Oh well, back to the sharpened tubes then.

[Trevor Crook]

Let us know how you get on with it Dean. I've never looked into them, so I've no idea how big they are or how much they cost. Where did you get yours from?