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Old 08-29-2006, 01:01 PM
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opjose opjose is offline
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Howto: Resize a plane

How To: Resize a plane
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There are a few things you need to do to resize a plane.

G3 does most of the work for you.

You must decrease or increase the visual model and the physics model scaling percentage in the editor appropriately. Try to keep both of these values the same.

One affects what you see and the latter, how it flies. G3 will normally scale the weight on the fuselage, wings, etc... but see below...

As you adjust these parameters check the actual physical size to see if you are getting close to the intended target size.


Decrease or increase the engine size/type used.

G3 bases the weight of the plane on both the scaled fuselage/airframe AND it adds the engine weight to it W/O scaling the engine. So you MUST choose a new engine.

G3 also does NOT choose a new prop for you. You'll have to also adjust the prop size and pitch accordingly.

When working with electrics, also note the gear ratio changes, etc. may need to be modified.


Change the Mass Scaling if required

If you are taking say a Balsa plane and trying to convert it to a smaller foam airplane, you'll also need to adjust the "mass scaling" percentage. When going to a LIGHT foamy, a ratio of .60 (60%) is appropriate.... if you are dealing with say a lightened version of a plane (e.g. the Skybolt Kit versus the ARF) use something less e.g .80. This adjusts how G3 deals with the mass/inertia calculations.

On small planes I also make the gear not so stiff, to account for increased deadening of bouncing tendencies produced by the lighter springier gear.

If you are going from Glow to Electric or vice versa. you'll need to pay attention to the battery/fuel tank locations.

When going from one to the other, G3 doesn't know what to do, and will frequently place the battery or tank in unusual places.

When I turned the Groove into a glow powered plane, G3 put the fuel tank at the very tip of the tail....


Adjust the C.G.

For this your best bet is to take some educated guesses on the weights of the various components. DO NOT rely upon the editor's ability to move the C.G. for you.

Rather use the latter to fine to the C.G. locations.

Instead adjust the weights of each component, trying to approximate real world weights for each model.

If you have more than one plane, or have built a few, even ARF's, this is very easy to do as you already have a good idea on how much everything weights.


Check out the Nextstar. Select "electric powered" in the editor and then choose the electric motor.

The 3D model includes a visual 3D electric engine, so you can easily turn the Nexstar into a small EP trainer plane.


Notes:

Doubled Weights: The weight for the Horizontal Stabilizer is doubled! e.g. one weight for each wing... The same is true of the main wings so keep this in mind.

Fuselage Airfoils:

Fuselage "airfoils" may have to be adjusted.

G3 treats the fuselage like another wing, with horizontal and vertical lifting surfaces. This is why there are two airfoil parameters for the fuselage.

Try to select an airfoil shape that approximates the shape of the fuselage. Remember to allow for the longer length.

If the fuselage shape does something unusual, such as in the case of an Ultimate Biplane that has a large frontal cross section that deflects the airflow down, pushing the nose up; you may have to move the center of lift backward or forward... Forward in the case of the Ultimate.


Wing loading:

Look up the specs for the wing loading for your new model plane.

G3 reports the model's wing loading as the "wet" weight (with fuel, etc.).

Adjust things so that your G3 plane approximates the real plane's wing loading.