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Hi,

 

I have the plans for the Ohmen, a 47" sports plane.

 

I would like to build it, I'm not worried about the actual building but what is phasing me is working out how much wood I need to build.

 

I don't want to buy too much, but at the same time as I don't have a model shop that close by I don't want to end up short either.

 

I'm finding it quite overwhelming - do you have any tips.

 

Cheers,

 

Nigel

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If I assume correctly this is your first plan build, then you won't have any stocks of wood.

EB's advice to get the parts pack and additional wood from Sarik would be your easiest way of making sure you have the correct amount.

 

If you are intending building more models from plans, then obviously it would be better to buy more wood than you need so that you are building up your stock (and saving on carriage charges later). The other way is to measure and calculate. This model has a 47ins span so you would be better ordering wing parts in 48ins lengths rather than 36ins. The fuselage sides can be made from 36ins lengths.

Most magazine plans (like this one) are designed to utilise "standard" sized wood.

 

One useful tip for calculating is to scan the various parts (wing ribs, Formers, etc) from the plan and copy them onto paper. You can then cut them out and arrange them to fit on sheets of balsa in the most efficient way before cutting the wood. Just be aware of the grain direction.

 

The Ohmen is not a bad model to try for your first plan build and should go together fairly easy (as most of Peter's models do). If you get stuck there are plenty of builders on here to help with advice.

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Estimating balsa is fairly easy - basically get a full sheet of balsa and lay it over each part of the design and note down how many sheets are needed and what thickness.  Decide on whether 3 inch or 4 inch width sheets would be needed.  Also 36 or 48inch  as Kevin mentioned.  Allow for two sides plus top and bottom.  For smaller items move your thumb along  the sheet to see how many can be fitted in.    Same with stripwood.   Always buy a couple of extra sheets of each size for safety and to allow for errors in cutting..

  Note that there will be doublers made of ply alongside the balsa and you need to order ply of various thickness.   Buy wire for u/c at same time as balsa and also all fittings  to save postage.    Balsa Cabin  and also SLEC will sell all the wood, wire and fittings needed.    Buying balsa from a balsa supplier is usually cheaper than buying a wood pack even if you over estimate!  

 

There is a thread on Ohmen here and note the comment ( on page 3 I think ) about the engine bulkhead triangular bracing which was omitted from the plan.  Very important!

 

Edited by kc
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6 hours ago, EarlyBird said:

Hi Nigel,

 

I bought the plan, cut parts and additional wood pack from Sarik.

 

Steve


 

I looked there before I posted but it seems pretty expensive.

 

The laser cut pack is £59 and the additional wood pack is £66, that’s £125 in wood alone.

 

Is that realistic, is wood that expensive these days?  I do get the convenience of the laser pack but all the same seems quite pricey.

 

Cheers,

 

Nigel

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I bought a Kwik fly full kit a couple of moths ago for £200, looking at the wood list that was necessary to finish it I think I actually got a bargain, I did build my Bristol Beaufighter from a laser pack, that was an expensive and annoying build ordering the odd bits here and there it worked out costing me a fortune.

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16 minutes ago, Nigel Heather said:


 

I looked there before I posted but it seems pretty expensive.

 

The laser cut pack is £59 and the additional wood pack is £66, that’s £125 in wood alone.

 

Is that realistic, is wood that expensive these days?  I do get the convenience of the laser pack but all the same seems quite pricey.

 

Cheers,

 

Nigel

It is from Sarik because we are paying for a service that needs people and machinery. Obviously it costs less when cutting the parts oneself but I chose to pay for the service.

I have a second one in the queue of builds the idea being to make a better job on the second one. Price up the wood needed, from SLEC say, then you will be able to decide if the cost difference is worth it. 

 

Steve

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Read the plan, get to know it and understand what the designer intended and how to get there. Visualise how things fit together. If you can't make sense of it, ask before you get started. 

 

Cut out all of the bits as much as you can and put those bits in a box and make a kit. That way, you won't be scrabbling around to try to make/cut pieces on the hoof because you need part x to make part y fit to part z. It is a lot less hassle than trying to cut parts as you need them. 

 

Make a list of all the other bits that you will need and get them ready. You might find that some of them (snakes, servo mounts etc) need to be fitted during construction. Nothing more annoying than eg not being able to fit a top decking because you need to fit snakes inside first. 

 

Keep all the offcuts, however small. Scrap is really useful for fillets, gussets, filling gaps, making supports etc. 

 

Plan ahead and don't build yourself into a hole. For instance, finishing a fuselage before fitting the wing could mean accessing formers for wing dowel holes becomes difficult. 

 

Don't assume that the position of various holes in formers on plans will be right for your motor/servo/snake/pushrod etc. Lay your rc installation out on the plan and work out where those holes etc need to be for YOUR equipment. 

 

Take breaks. Stand back. Take your time. You can easily get caught up in something and get too far before you realise you made a mistake earlier and find it difficult to undo. 

 

Making templates from card or paper is sometimes more accurate than following a plan for windshield patterns, decking sheeting patterns and so on. 

 

Some things, like stringer slots in formers, are better done from the model than from the plan. Use the plan as a guide, but ultimately, there can be mistakes, errors or variation which means that the right position to get a good fair stringer line (for example) is slightly different to the plan. 

 

If you find it hard to make a particular piece (for example cutting thick ply) then cut two from thinner ply and laminate them together with epoxy, rather than struggle to accurately cut the thicker material. 

 

Making sure that your model is straight and true is more important than sticking slavishly to a plan. If something looks off, check, especially if printing plans yourself or using very old (possibly distorted) plans. 

 

Plan your covering before you build. If you have projected seams over an unsupported area, a bit of thin scrap as a covering support can save a lot of headaches later on. 

 

Hope some of that helps somewhat! 

 

Cheers 

 

Matt

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On 26/07/2022 at 11:16, Nigel Heather said:

Hi,

 

I have the plans for the Ohmen, a 47" sports plane.

 

I would like to build it, I'm not worried about the actual building but what is phasing me is working out how much wood I need to build.

 

I don't want to buy too much, but at the same time as I don't have a model shop that close by I don't want to end up short either.

 

I'm finding it quite overwhelming - do you have any tips.

 

Cheers,

 

Nigel

Have you made any progress?

 

Would it help if I opened up my Sarik parcel and made a wood list?

 

Steve

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  • 2 weeks later...

Not really an easy solution. It really depends whether you want to use the minimum amount of wood or are happy to have some reasonably sized bits for another day. 4” wide or 48” probably costs more pro-rata  For a model the size of the ohmen it may not be justified, however it might be an argument that you could use one of the larger sheets rather than two smaller ones. Then you have to weigh up the value of the off cuts in this or another model. With the price of balsa less will be used to mix epoxy on. Good luck with the ohmen I will be building one myself. So far all I have done is to cut out a ply wing rib template

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My rough estimate is .....

Balsa

48 inch   1/16 by 4         2 pcs

48 inch    1/4 sq              4pcs

 

36 inch  3/16 by 4            2pcs

36  inch 3/32 by 4            5pcs

36  inch 1/8 by 4              2pcs

36  inch   1/16 by 4            2pcs

36 inch    1/4 by 4              1pcs  (  laminate 2 thickness to make the 1/2 for cowl and with some 1/8 to make 3/8  )  or buy a sheet of 1/2 and one of 3/8  if you prefer not to save money!

 

Spruce 1/8 by 1/4    36 inch length    1 pc

birch ply 1/16    4inch sq        

lite ply 1/8        11inch by 6

birch ply 1/8   9 inch by 4  

piano wire  10SWG    36 inch

 

Buy an extra sheet of most sizes to allow for anything I missed  and buy any fittings, wheels etc  at same time to save postage.

 

You may need to buy a sq ft of each size ply  but it will be enough for a model or two.

Don't blame me if I made any errors!    -  check for yourself if there is any size not specified by me.    There should be enough if you carefully plan how to use the balsa  - trial fit the ribs etc to get as many as possible from the sheet.    Cut larger parts first so smaller bit come from offcuts e.g.wing TE come from offcuts of wing sheeting.   LE is cut from sheet before other parts of 1/8.

48 inch sheets seem most economical for the wing sheeting.

 

 

 

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notes....

dont forget motor bulkhead triangular bracing ( not shown on plan but essential )   you could order a length of tri balsa but I suggest a 12mm sq bit of hardwood or firm softwood you may find at home

some items like wing ribs are on the Coquette plan side of the free pull out plan.

I think it was suggested that the tailplane and fin could be solid balsa - there should be enough in my estimate.

order wing bolts and captive nuts also motor captive nuts.  

 

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My calculations are that the balsa would come to about 49 pounds and the spruce & ply 8 pounds ( buying a sq ft of each ply size which should do a couple of models or maybe 3 ) and the piano wire 1.78 pounds if bought from SLEC or balsa Cabin.   So about half the Sarik price if you cut the ribs and ply yourself ( not difficut with all ribs much the same and mostly straight sided formers - real aeromodelling!)

 

It will be cheaper to use some of the 1/8 birch ply doubled to make the 1/4 u/c mounts or you could buy a sheet of 1/4 birch ply instead if you don't have any odd bits around.   You could economise and use any handy offcuts of DIY ply  instead of birch or even the lite ply but birch is nicer to work and dosn't splinter as much.

 

If you cannot get 48 inch lengths then you need double the quantity of 36 inch and end up with lots of offcuts.

In any case order a couple of extra sheets of the main sizes just in case of errors.  Postage is expensive if you have to reorder some bits and it's better to have the balsa in stock for repairs or the next model.

Edited by kc
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Correction.

 

I had not noticed the 1/32 birch ply doubler - 16 inches by 7 is needed.   If buying by post I would buy a 48 inch sheet which would help protect the 48 inch balsa from snapping in the post.    The extra will always come in handy for another model.

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Revised my estimate slightly after going over the plan again

( needs 5/16 for ailerons -not 3/16  and only needs 3 pcs of 1/4 sq 48inch )

 

new estimate quantity

 

Balsa

48 inch   1/16 by 4         2 pcs

48 inch    1/4 sq              3pcs

 

36 inch  3/16 by 4            1 pc

36 inch   5/16 by 3           1 pc

36  inch 3/32 by 4            5pcs

36  inch 1/8 by 4              2pcs

36  inch   1/16 by 4            2pcs

36 inch    1/4 by 4              1pcs  (  laminate 2 thickness to make the 1/2 for cowl and with some 1/8 to make 3/8  )  or buy a sheet of 1/2 and one of 3/8  if you prefer not to save money!

 

Spruce 1/8 by 1/4    36 inch length    1 pc

birch ply  1/32   16 inch by 8

birch ply 1/16    4inch sq        

lite ply 1/8        11inch by 6

birch ply 1/8   9 inch by 4  

piano wire  10SWG    36 inch

 

plus I would order an extra sheet of 1/16 , 3/32 and 1/8  just in case.

 

Edited by kc
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The other aspect to buying balsa is the grade -  SLEC offer soft, mediun or hard.    I suppose medium for this model in most places,  but if you can select the wood in person at a show or their works then I suggest -

 

for the wing sheeting  (48 by 4 ) get two sheets that will bend easily across the grain.

similarly one of the 3/32 sheets will be used for top decking so that also needs to bend easily.   But the other 3/32 will be used for fuselage sides - needs 2 identical sheets - and  2 for ribs, so medium weight but stiff sheets.

The 3/16 sheet will be used for tailplane, elevator, fin and rudder so a nice light sheet is needed but not one that is so soft it dents under slight finger pressure.   Worth sifting through a few sheets to get the right piece, if you can select yourself.

The 48 inch 1/4 sq needs to be really hard balsa for the 2 spars.    Personally I would choose spruce for this part or I would buy 6mm sq  'pine' from B&Q etc mouldings section.   Look for the 'finger jointing'  so it's not in the wrong place and  also check it's not warped or has missing corners.

Just a couple of inches of 1/4 dowel are needed too.

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On 26/07/2022 at 18:13, Nigel Heather said:

Is that realistic, is wood that expensive these days?

 

I just spent £130 on sheet wood for my current project, a 66" span sport aerobat. Hours of work just cutting parts, of course.

 

£125 for what is effectively a full wood kit is pretty good value. Even if the airframe is a bit smaller.

 

Myself. Building Ohmen, I would make use of cheap foamboard for ribs, fuselage formers (excepting firewall and front of wing saddle). I would probably make all tail surfaces from foamboard, with some balsa around the edge. It's great for sport airframes around this size. I would probably do flat foamboard ailerons, with balsa edges, just like the tail surfaces, too. Makes life very easy and they are quick and work just fine.

 

You might find that even the fuselage sides and underside could be foamboard. Especially with a 1/32 ply doubler inside holding things together. Edge it all with 3/16 sq balsa and that might work nicely.

 

Another thing that might be cheap and effective is to cut the fuselage sides from 2.5mm liteply, and forget the 1/32 ply doubler. Cut two or three big lightening holes at the back end and you're good to go. 

 

I used these sort of approaches for Bigga Bit a couple of years ago

 

 

Edited by Nigel R
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2 hours ago, kc said:

Revised my estimate slightly after going over the plan again

( needs 5/16 for ailerons -not 3/16  and only needs 3 pcs of 1/4 sq 48inch )

 

new estimate quantity

 

Balsa

48 inch   1/16 by 4         2 pcs

48 inch    1/4 sq              3pcs

 

36 inch  3/16 by 4            1 pc

36 inch   5/16 by 3           1 pc

36  inch 3/32 by 4            5pcs

36  inch 1/8 by 4              2pcs

36  inch   1/16 by 4            2pcs

36 inch    1/4 by 4              1pcs  (  laminate 2 thickness to make the 1/2 for cowl and with some 1/8 to make 3/8  )  or buy a sheet of 1/2 and one of 3/8  if you prefer not to save money!

 

Spruce 1/8 by 1/4    36 inch length    1 pc

birch ply  1/32   16 inch by 8

birch ply 1/16    4inch sq        

lite ply 1/8        11inch by 6

birch ply 1/8   9 inch by 4  

piano wire  10SWG    36 inch

 

plus I would order an extra sheet of 1/16 , 3/32 and 1/8  just in case.

 

Not sure why you have gone for 48” lengths of 1/4 square and 16th sheets. There is plenty of opportunity to use the 13 inches you would cut off 36 “ lengths 

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Cheaper because there is less waste with 48 inch spars because you only need 3 lengths while 36 inch would need 6 lengths and give waste that's not needed for this model.     £3.06 pounds compared to 5.16 pounds with 36 inch.

The 48 inch sheet also provide the TE material and seems more convenient, although the 1/16 waste could be utilised on this model.   And if you want to make the wing in one piece with no dihedral it's easier  ( this wing is very similar to the Swamp Rat wing which is flat and one piece, therefore quicker to build. )    It's the builders choice - use 36 inch or 48 inch for these parts

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4 minutes ago, kc said:

Cheaper because there is less waste with 48 inch spars because you only need 3 lengths while 36 inch would need 6 lengths and give waste that's not needed for this model.     £3.06 pounds compared to 5.16 pounds with 36 inch.

The 48 inch sheet also provide the TE material and seems more convenient, although the 1/16 waste could be utilised on this model.   And if you want to make the wing in one piece with no dihedral it's easier  ( this wing is very similar to the Swamp Rat wing which is flat and one piece, therefore quicker to build. )    It's the builders choice - use 36 inch or 48 inch for these parts

Clearly done the sums them. A necessary reality these days

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Very refreshing to see this thread. Well done KC you have obviously put a lot effort in to help the OP. If you put all this into a single piece you would have a very useful article for the magazine. This would not only be helpful to new builders but also show that perhaps kit prices are actually quite good! 

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Of course if the 48 inch means a higher carriage charge then it may not be worthwhile.  Damage to longer stuff in transit might also be a consideration.   If collecting in person this may not apply but the overriding factor is whether a nice piece of balsa ( bendable in the case of wing sheeting ) is available or it's better to look at the 36 inch stock.

 

Masher - lets hope the OP has actually seen this material list! 

 

 

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15 minutes ago, Nigel Heather said:

The OHMen, no, no progress, I need to clear space.  To be honest, I'm juggling too many different hobbies and house/garden jobs at the moment.  Realistically at best it will end up a winter project for flying next year - that is if I decide to do it at all - must admit it is looking to be much more expensive than I imagined.

I justified the cost to myself by the build being a large part of the fun. It was not until later that I realised I had made a very robust model that would stand lots of abuse and last a lot longer than an ARTF.

 

Steve

 

 

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On 09/08/2022 at 13:17, kc said:

Revised my estimate slightly after going over the plan again

( needs 5/16 for ailerons -not 3/16  and only needs 3 pcs of 1/4 sq 48inch )

 

new estimate quantity

 

Balsa

48 inch   1/16 by 4         2 pcs

48 inch    1/4 sq              3pcs

 

36 inch  3/16 by 4            1 pc

36 inch   5/16 by 3           1 pc

36  inch 3/32 by 4            5pcs

36  inch 1/8 by 4              2pcs

36  inch   1/16 by 4            2pcs

36 inch    1/4 by 4              1pcs  (  laminate 2 thickness to make the 1/2 for cowl and with some 1/8 to make 3/8  )  or buy a sheet of 1/2 and one of 3/8  if you prefer not to save money!

 

Spruce 1/8 by 1/4    36 inch length    1 pc

birch ply  1/32   16 inch by 8

birch ply 1/16    4inch sq        

lite ply 1/8        11inch by 6

birch ply 1/8   9 inch by 4  

piano wire  10SWG    36 inch

 

plus I would order an extra sheet of 1/16 , 3/32 and 1/8  just in case.

 

 

 

Thanks for all this work, very helpful, much appreciated.

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Thanks Nigel.   It's alway fun to study a plan so it's not really work - just armchair aeromodelling.

 

I have now put this list on the Ohmen thread as well with very slight amendments to the ply sizes to allow for a couple of unnoticed parts ( wing bolt seat and also wing bolt protection on wing itself)  

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