airhead

I am looking to take plans for a .40 sized plane and scale them down to a .25 sized plane.

Can I simply do this via a copier? How would I figure out the percentage to shrink the plans by? Would it be based off of the wing?

Thanks!

barto

Hi,

Measure the wingspan of the .40 size model.

Choose the new wingspan (depending on what model,I wouldn't go over 45 inches, but again, this depends).

Divide the new wingspan by the old one. Than go to a copy store and ask the to use this a the zoom. Everything will be scaled down by that proportion.


Anyway, that's how I think of it. Hope this helps.



Bart

SoCal GliderGuider

Material size will shrink. Just watch out for any spar or stringer notches and make them the right size.

CoosBayLumber

My Feedback: (1)

Most often when having plans in hand and wanting to re-size them in order to accomodate an engine in hand, you need to consider the wing loading or wing area first.

My old primer indicates that a .40 likes a wing area of 500 to 700 S.I. and a .25 likes a wing area of 400 to 500 S.I.

Not knowing what A/C you have plans at hand for, first thing would be to be to determine the wing area, and then secondly work out a proportion which will bring the resized A/C into that noted for the .25 size engine. That may mean you have to reduce the plans 77% or something similar.

Lastly you can then use one of the above noted systems to obtain a new set of plans to work off of. Do not apply the proportioning just to the wingspan, as that is only 1/2 the formulae.


Wm.

barto

You're absolutly right, never thought of that.



Bart

BMatthews

Yep, wing AREA rules all first and foremost.

From there you need to adust the structure. Some familiarity with the smaller sized designs helps. Download a few other plans of the size you want and study the wood sizes for guidance. And chose ligher wood for the smaller size. Weight counts for a lot more with the small ones.

Good luck with the new project.

SoCal GliderGuider

Guess if you are really careful you could shrink or enlarge a plan so that it matches the next size up/down material.

antonio104

So airhead, how is the project going?
If you have not found a similar plan to make your % reduction selection, it would help if you disclosed your model.
WW1,2 fighter, golden age, Cub?

Looking at a commercial model, a SIG Senorita has a 63" span with 746 sq in wing area with a .15 to .25 engine.
A SIG Kobra 45" span with 390 sq in wing area calls for a .19-35.

I have some plans lists and I am sure others have several as well.
For example RCM lists a Ryan ST .25 engine 50" ws.

So maybe someone will know of a .19-.30 plan for your model or similar model.

If you said P-51D then CoosBayLumber might list the
"N.A. P-51D, Redraw plans and parts for a House of Balsa 45" span glow powered model"
listed at:
http://www.mybloo.com/coosbay/laser/projects.htm