Scaling down plans??
01-09-2008, 06:17 AM
#1
Senior Member
Thread Starter
Join Date: Nov 2006
Location: AS, AUSTRALIA
Posts: 295
Likes: 0
Received 0 Likes
on
0 Posts
Scaling down plans??
Hey all.
My question is, how do you go about scaling down plans?
I have the plans to build a Bf 109E, but it will wind up having a 5 foot wingspan that I simply have no room to store for a LONG time, but I will build her in the future.
I thought about shrinking the plans down maybe 30% so I can build it, but I'm not sure how it would fly.
When scaling down what needs to be taken into account?
Does it affect the wing loading or aerodynamics making an exact copy in 'shrunk' form?
Any ideas.
Thanks in advance.
Cheers
Sean
My question is, how do you go about scaling down plans?
I have the plans to build a Bf 109E, but it will wind up having a 5 foot wingspan that I simply have no room to store for a LONG time, but I will build her in the future.
I thought about shrinking the plans down maybe 30% so I can build it, but I'm not sure how it would fly.
When scaling down what needs to be taken into account?
Does it affect the wing loading or aerodynamics making an exact copy in 'shrunk' form?
Any ideas.
Thanks in advance.
Cheers
Sean
01-09-2008, 11:45 AM
#2
RE: Scaling down plans??
ORIGINAL: Krener
Hey all.
My question is, how do you go about scaling down plans?
I have the plans to build a Bf 109E, but it will wind up having a 5 foot wingspan that I simply have no room to store for a LONG time, but I will build her in the future.
I thought about shrinking the plans down maybe 30% so I can build it, but I'm not sure how it would fly.
>It SHOULD fly the same as the larger model, sometimes better.
When scaling down what needs to be taken into account?
>You need to use COMMON SENSE !!! Do the ribs need to be spaced that close ?
>Is plywood really needed in this location ? Do I really need balsa that thick ?
>I have scaled down several plans and they have all flown well. The biggest thing is
>the dimensions of the wood. In a 40 size plane (up to ABOUT 60" span ) you typically
>only need 1/16" balsa for the ribs and 1/8" light ply or "balsa ply" for the fuselage
>formers. Try to lighten the plane as much as possible without compromising
>structural integrity.
>
>You may also find that the way something is done on the larger plan can not
>reasonably be done on a smaller version, so you will need to find a different
>way to do it.
>
>One MAJOR thing you need to be careful of is having the plane come out tail
>heavy. This is typically caused by not selecting lighter/thinner wood and/or
>not modifying the tail feathers to a lighter weight design.
Does it affect the wing loading or aerodynamics making an exact copy in 'shrunk' form?
>With the plans I have reduced in size, the wing loading was less than the larger
>model. I reduced a 96" span (1/4 scale ) Bellanca Airbus (circa 1930 type ) to 60" span
>and a 100" span (1/4 scale ) Miles M-38 Messenger to a 62" span. In both cases the
>wing loading was several ounces less than the larger model. With other planes the
>wing loading was also reduced, but not as drastically as with those 2.
Any ideas.
Thanks in advance.
Cheers
Sean
Hey all.
My question is, how do you go about scaling down plans?
I have the plans to build a Bf 109E, but it will wind up having a 5 foot wingspan that I simply have no room to store for a LONG time, but I will build her in the future.
I thought about shrinking the plans down maybe 30% so I can build it, but I'm not sure how it would fly.
>It SHOULD fly the same as the larger model, sometimes better.
When scaling down what needs to be taken into account?
>You need to use COMMON SENSE !!! Do the ribs need to be spaced that close ?
>Is plywood really needed in this location ? Do I really need balsa that thick ?
>I have scaled down several plans and they have all flown well. The biggest thing is
>the dimensions of the wood. In a 40 size plane (up to ABOUT 60" span ) you typically
>only need 1/16" balsa for the ribs and 1/8" light ply or "balsa ply" for the fuselage
>formers. Try to lighten the plane as much as possible without compromising
>structural integrity.
>
>You may also find that the way something is done on the larger plan can not
>reasonably be done on a smaller version, so you will need to find a different
>way to do it.
>
>One MAJOR thing you need to be careful of is having the plane come out tail
>heavy. This is typically caused by not selecting lighter/thinner wood and/or
>not modifying the tail feathers to a lighter weight design.
Does it affect the wing loading or aerodynamics making an exact copy in 'shrunk' form?
>With the plans I have reduced in size, the wing loading was less than the larger
>model. I reduced a 96" span (1/4 scale ) Bellanca Airbus (circa 1930 type ) to 60" span
>and a 100" span (1/4 scale ) Miles M-38 Messenger to a 62" span. In both cases the
>wing loading was several ounces less than the larger model. With other planes the
>wing loading was also reduced, but not as drastically as with those 2.
Any ideas.
Thanks in advance.
Cheers
Sean
01-09-2008, 11:48 PM
#4
Senior Member
Join Date: Aug 2005
Location: Austin,
TX
Posts: 1,333
Likes: 0
Received 0 Likes
on
0 Posts
RE: Scaling down plans??
I did it once. I took the plans for a .40 sized pattern plane and had a blueprint company make a 66% copy of the plans. I chose 66% because I felt this would fit a .15 size engine that I had on hand. The plane flew quite well.
When scaling up or down, the engine size needs to increase or decrease with the cube of the scale factor. For example, a full scale Cessna might have a 200 cubic inch engine, a quarter scale version should have a 200 X .25^3 or about 3 cubic inch (50cc) engine.
Another example, building a half scale version of a .40 size model airplane, and the engine size should be .40 X .5^3 or .05 cubic inches. (cox .049 is close enough)
When scaling up or down, the engine size needs to increase or decrease with the cube of the scale factor. For example, a full scale Cessna might have a 200 cubic inch engine, a quarter scale version should have a 200 X .25^3 or about 3 cubic inch (50cc) engine.
Another example, building a half scale version of a .40 size model airplane, and the engine size should be .40 X .5^3 or .05 cubic inches. (cox .049 is close enough)
