[RGN]

I'm considering enlarging a 1990's 1/4 plan to 1/3 scale. Does anyone have any tips or advice, please?

The subject is the DH.71 Tiger Moth so not an overly large or overly stressed airframe.

Thanks.

Richard

[stukno]

There is a large printers in Doncaster that will scan and scale up or down to any size desired. Spot on accuracy and keeps thin line.. but expensive at around £15 per sheet.  If its a large plan, there is a limit on the paper size but they can print the top half and then the bottom half to get the new enlarged size but thats £30 and if the original is a two sheet plan... you see where it goes!

Advisable to hand copy all the  essential bit into one half of the plan and just get half of it enlarged.  - the half with all the formers on.

I enlarged a plan recently, In retrospect I should have taken one sheet of paper with the formers and ribs on it, get  that scaled up only.
It would have been easy to outline the wing and fus centreline without a full size plans

is a 71 the monoplane racer??  Nice!

stu k

[RGN]

Thanks, Stu K - yes the 71 is the monoplane!

I should have been clearer in my post. I'll probably re-draw most of the components and perhaps even enlarge them at that time. What I meant to ask was more along the lines of how do I size the stringers, spars etc. I can't imagine it is simply a matter of enlarging them by 1.33x? Or is it?

Richard

[Jamie Duff]

That's what most people do, and it usually works. If you want to be a little more scientific about primary structure then the first thing you'll need is an estimate of weight.

Is the 71 a braced or a cantilever wing? (Sorry, I'm not very familiar with it) If it's a cantilever, then I'd strongly advise upgrading the materials used for spars etc to either proper Sitka spruce or Cyparis if the 1/4 scale plan calls for balsa.

There's a reprographics place here who enlarges stuff for me, usually free! He says it's more interesting than his day job copying documents for businesses (including ours, admittedly). If you ask around, you'll probably find one who has experience of model plans whether they be aeroplanes, boats or whatever. The guy I'm using was already aware that modellers didn't like their drawings stretched and mangled 

[RGN]

Thanks, Jamie. The 71 has a braced wing but I'd probably upgrade the spar material anyway as I'll need to incorporate a wing joiner.

Richard

[Erez]

I think you should first look at the smaller model's structure and decide if it is what you want or do you want to change it. If it is built as a sport model with cantilever wings then probably the "times 1.33" would work but there are other considerations like - do you want to change the structure to more closely follow the real one's structure? do you want cantilever or braced wings? is it built using the well established structural principles e.g. is there vertical grain webbing between the spars or has the designer omitted this? sometimes the material dimensions can remain the same as in the smaller model if you correct some structural details like this one, or you add functional rigging etc. so it is a little difficult to give a definite answer based only on "model size". BTW, comparing to a very similar and successful model may also give some direction as to whether or not things need to be changed.

[leckyBB]

The full size DH 71 has a rather thin wing section. Does the plan you are enlarging have that profile or is it a little thicker for model structure purposes? The bracing wires might well need to be active.
The original DH wings of that era had two spars with metal compression struts between them and the whole thing was internally wire braced. A very light but remarkably rigid structure which was then braced by dual flying and landing wires.
I have worked on a few of those wings in my time.

[RGN]

Thanks, guys  I'm still waiting for the plan so I can't comment on it until it arrives. The original had an RAF 15 section built very much as Lecky describes (at least from the diagrams I have seen). I plan to make the rigging functional but haven't decided on section - I'll have to do some research on that and may well post another question on this fine forum!

An interesting exercise this and I'm looking forward to it as a winter project. My only previous enlargement from a plan worked well but was a smaller percentage increase of only 17% to make a 1/4 scale Midget Mustang from a free magazine plan. At that time I just used the very unscientific 'x1.17 then use the nearest standard size' approach! I just feel that this increase in size warrants a more considered approach!

 

Richard

[RGN]

The plan arrived today but it isn't 1/4 - it is only approx. 18.5% so I have to enlarge it by 1.8 to get to 1/3 scale.

It appears to be a remarkably simple plan, though, and I'm not foreseeing any show stoppers (well at the moment at least!) The challenging bit is probably going to be recreating the sprung undercarriage with the bungee cord in the hubs 

I'll also have ato add a fair amount of scale detail (functional bracing wires, rudder fairings etc.)

Richard

[leckyBB]

Good luck Richard. Do keep us posted on your progress and maybe a build thread once you have the design finalised.

I must admit whenever I saw the wings and fus of the replica in the Aero Antiques hanger I wondered about building one myself. Now I live out here with a desert flying strip all my models are EPP for longevity. I don't think a wooden model would last long in this heat and very low humidity.