Large Model Association Forum

I am just looking at a feasibility study of scaling up an existing design to fit a specific engines. It is a twin engine civilian design.

At the moment there isn't even a prototype of this model flying or even complete which doesn't help. The engine size would be 166% of the size of the original design, though there is a possibility of going to 200% if the airframe size I choose is big, but that would be an expensive mistake.

So as a rough guide, how would I calculate the increase in airframe size? Do I go by calculated volume of the actual airframe?, use the volume of the cube of the largest exterior dimensions, or is there some sort of neat rule of thumb guide I could go on? I know lots of you here have built scaled up models from plans.

I don't want to end up scaling it up say 25% and then it being to big for the engines when 20% would have been ideal. There is space in the cowl even if I scale it up just 10% so that is not a factor.

Thanks in advance and merry Xmas to all.

Tricky to make comment........a little more detail could be useful.

What aircraft is it, how big is the original plan & what size engine does it suggest for that?

What engines are you proposing using in the larger version?

Also.....look about for some 'similar' subjects of a similar size.......what engines do they use & do they perform as required?

Phil

Hi
Over the years I have scaled model plans up and down ,so this bit of info may help you.
I decided first on the wing span I require this is governed by building space, and will it fit in the car.
Then get the calculator out and find out by what % you need to enlarge your plan by to get your chosen wing span. The next step is easy just take your plan to a printers and get a copy knocked out. The type and size of materials used will different but looking at plans similar to your chosen size should help.
If you have engines and are looking to make a model for them, look at the models shown on this site to give some idea of what size engine powers what eg a 1/4 scale Spitfire starts at about 62cc and up.
What you propose doing is of cause a vey technical project, scaling up a small model a bit should not be a problem, but if you get into the big stuff, remember the 20kg rule.
With due respect, if you are planning to design a model from scratch you really do need to know what you are doing, other wise your efforts and money will be wasted and some one may get heart in the process. Good luck

Arthur, thanks for the response.

Please do not look at my gender and make assumptions of my abilities based on stereotypes.

Been flying RC since I was 10, building free flight models since I was 6 and and have built probably a good 50 RC models over the years from plans alone, from rubber band indoor models to 40% scale. i have no idea how many kits i have built, set up or repaired for other people or myself. my preferred way of building is to start with a plan and make changes which is what I will do with this project. I have even run a model shop, sold our own range of home designed kits, ( admittedly, small ones)and been specially invited to fly in front of the Queen. I keep to myself in RC now as I am a little fed up with the amount of mosogyny in UK modeling circles.

Present project on the build table is a 1/4 scale model of the Precious Metal P51 air racer.

I was asking advice as this potential project was a lot bigger than that, and I am short of the experience. Most of the time I know enough to know what I don't know, it is when I think I know something I don't that I faceplant.

Hence the feasibility study first.

Kate,

The questions Phil asked earlier are the the right ones if you're after some useful input...

What aircraft is it, how big is the original plan & what size engine does it suggest for that?

What engines are you proposing using in the larger version?

If what you're thinking of building will be over 20kg (and if it's a lot bigger than a 1/4 scale P51 it most likely will be), register your proposed project & get the help of the 'over 20Kg' machine.

Kate
Just a thought.
You might wish to consider scaling up to suit the propeller size of your engine, the largest diameter it will comfortably drive.
Scale models look real with scale size props but look like model aeroplanes with noisy, high revving, small props!
Don

Kate Thurman wrote:
Present project on the build table is a 1/4 scale model of the Precious Metal P51 air racer.

VERY cool........more details & some photos please?

(Hope that discussion via PM's helped out......best of luck)

Phil

Phil, yes, help by PM was useful, as was a few others. Thanks to all of you, size looks decided now, I have to look at 500 other things before starting. A very long term project for me.

As for the P51, it is a Don Smith kit, Sierra retracts, fuse is sheeted and built up to the point of engine install, but I had gotten stuck on that as I am loath to have unscale cooling holes in the cowl. I have only just recently decided to finish it as the Precious Metal air racer, originally I was going to do a tribute to the crashed and alas totalled Big Beautiful Doll until I found out there are still half a dozen full scale P51s in that exact same scheme and none the original.

It is like when i found out Milli Vanilli were just miming.

Engine looks now to be the new MVVS 116 inline water cooled, Build will restart when I have a delivery date.

I am kinda looking forward to doing a cooling system for it, using telemetary, a TX controlled ADI fogger onto the radiator and belly exhaust flap scoop thingy should be a fun and interesting thing to program and experiment with.

Maybe a build thread if others are interested, not seen too many water cooled RC warbirds. Also gives a place where better people than me can give input.

Don Billingham wrote:Kate
Just a thought.
You might wish to consider scaling up to suit the propeller size of your engine, the largest diameter it will comfortably drive.
Scale models look real with scale size props but look like model aeroplanes with noisy, high revving, small props!
Don

I agree , Scale prop size is one of the areas that is so often ignored, beautiful well detailed models that have an off the shelf small 2 blade prop on the front rarely look right.

Alas the only real option is gearing them down which isn't always a feasible choice that often or for me.

Check out this video, real size prop for the plane and it looks fantatstic, alas the gearbox alone cost as much as the a moki 250 engine.

http://www.youtube.com/watch?v=UNURB_Zg ... ata_player