I have a theoretical question I am curious about and need to know. I have no desire right now to attempt this but may be interesting in the future, like I said a theorectical question.

Here it is: For scratch-building an airplane is it possible to photocopy a set of plans at a reduced setting and build the airplane at the reduced size? Or would it take a professional designer to determine the precise sizes of the motor, fuel-tank, wheels, etc.

Has anyone ever done this? Just curious to know, thanx.

Tigerdude,
Yes, it's possible to resize plans both larger and smaller. Builders do it all the time. I personally have taken a few 40 size planes and enlarged the plans to make the 60 size planes (or even larger). The same process works in the other direction too, you can shrink the plans to make a smaller plane. But there are things that need to be taken into consideration. Many times structures are designed with specific sizes of wood for strength, and when you shrink the size of the wood the structure no longer is as strong as it's supposed to be. I'm not saying that you can't do what you want to do. But rather I'm saying that when you do shrink a plan down you need to have the experience to look at the plan and be able to tell if the structures of the plane will still have the strength that they need.

Something to think about.

Ken

This includes things like sheeting that tends to get so thin it breaks too easily.

Once you shrink it down, now you need to find new standard size wood to make it with which means MORE changes to the drawings or making your own custom wood. Neither is easy.

Easier to go to the 1/2A forum and see if anyone knows of any plans/kits first.

'nother question: Would the CG measure point be different as well? More-than-likely "yes" as the wood sizes and densities would change? Am I correct?

It would really be nice to see some photos of some airplanes scratch-built from RCU members in this fashion. Please post some pics of planes you have built from either reduced or enlarged plans.

Wrong. It would still be at the same relative point. It may require more weight to balance it but the DESIRED point would be the same.

As Bruce said, the desired position for the CG should be the same no matter how big the plane is. If the smaller version of the plane does not have the CG in the proper place then you'll have to make adjustments to get it in the proper position.

Posting pictures of scratch-built planes is WAY above the level of the Beginner's forum. If you would like to have member post pictures of their scratch built planes I suggest that you post a thread in the [link=http://www.rcuniverse.com/forum/forumid_174/tt.htm]Scratch Build forum[/link] and ask them to post pictures.

Ken

I have done it. I took plans for a .40 size pattern type plane and had a local blueprint company make a 66% full size copy of it and built a 2/3 size plane out of it. Powered it with an OS .15 FP. It flew quite well. It came out a little heavier than I had hoped though.
Really, you should change designs when you scale down, a scaled down D-tube wing with the same rib count as the larger prototype is needless overbuild for a 1/2A airplane. How often have you seen an 16-20 ounce 30-36 inch wingspan 1/2A plane fold its wings in flight from overload?

Speaking of scaling down planes... I have a World Models Sky Raider Mach-2 ARF that I won in or club raffle. I thought the covering was kind of ugly so I removed it and planned on redoing it with my own scheme. Then I got to thinking. Most of the glue joints seemed to just pop apart with very little effort or damage. Why not take measurements and trace parts then reduce them to build a smaller, electric version of the Sky Raider? I have a ton of other projects to do first but I am really interested in this one. It won't be a miniature identical, piece by piece of course. I will reduce the number of wing ribs, balsa thickness, etc. The overall design will be the same though.

The other project I want to take on (after the US 40+, US .60, and OMP Edge 540) is an enlargement of my Profile Hots. It has a 40" wingspan and flys great with a .46-LA. If I enlarge it 20%, it will have a 48" span. It would still be excellent with a good .46 like an OS AX but a .60 would really make it fun.

I won't run out of stuff to do any time soon.

I love small planes and big planes. 40-60 size is just ARF stuff. As mentioned go to the 1/2a forums. Rainedave, CombatPig, BobHH, and a whole slew of others will jump all over this question and tell you all the in's and outs of modifying plans and scratch building. Kinko's is your freind with scaling down plans.

Good point. If I was a complete beginner, some of this stuff my intimidate me a little.

Depending on the size you are scaling down to, you basically will have to take the scaled down outline of the plane and design a completely new internal structure with appropriately sized wood. It does require some effort and thought, but in the end it's not all that difficult. I'm in the process of doing this to a couple of plane - keep the outline with a new internal structure.

Hogflyer

http://www.hobbyhangar.com/test/kits.htm#hgr170

Here are some kits that are already scaled down if you're interested. My personal favorite is the little Edge 540 kit.

I'll try to post a pick of a scratch built plane that my Dad built years ago. I'll take a pic & post it for ya tomorrow if I can.

As promised, here are some pics of one of Dad's scratch-built racers. No plans, no magnetic building system, just some wood & a plan in his head.