Center-Line

[Rogger]

Can someone please tell me how to find-locate-define the center-line of a model airplane...

I have spent 2 days searching for an example and all I can get is a reference to it, but no visible image or description of where it is.

I assume that it's derived from the Cord Line of the airfoil, since that seems to be the most commonly used reference point.

I know that when you are aligning an elevator to the wing, when using a Robart Level, you want the elevator to be at 0 degrees. Since the Robart Level uses the leading edge and trailing edge, which is normally where the cord line runs, that's where I'm taking my assumption from.

 

[Wurger]

If I have grasped it properly the centerline of a model is a line that divides the model into two symmetrical halves while looking down on the model. The line should be traced in drawings. Unless you mean the side fuselage datum line that should be also traced in drawings.

But if you need to make your model balanced you may need to find the MAC ( Mean Aerodynamic Chord ). Its location depends on the kind of a wing.

I would suggest visiting the site.... Stability Concepts

 

[Rogger]

Thank you very much for your reply and illustration. That was my 2nd guess, as I have made molds of a few composites that I have. I've been doing a lot of reading and the way that the center-line was being referred to was starting to get confusing, because I'm designing my 1st model at the moment.

 

[Rogger]

Um, cvan you give me the same reference for the side fuselage datum line? It would be greatly appreciated as well. As I said before, I'm working on my 1st design....

 

[Wurger]

My pleasure. Glad I have helped a little bit.

As far as the side fuselage datum line is concerned... its location depends on a kind of a shape of a fuselage a model is going to be of. Also it depends on the model type. Generally it can be said that the line is the horizontal line , usually going through the center of the spinner and the engine main axis and running to the tail ( the fuselage ending ). Here a couple of examples... hope it will help.

BTW ... May I ask about what kind of model you design?

 

[Wurger]

Additionally, please note that also the fuselage ( model ) centerline has been traced as the black, dotted line ( just I didn't mark it with the red ) in the second and third drawings above.

Also please pay your attention to the fact that actually the fuselage centerline and the fuselage side datum line is the same line. The name depends of the the kind of projection of a fuselage on the flat surface. I mean the horizontal projection and the vertical projection. What is more the fuselage side data line is a reference line for attaching of the fuselage halves seen from above. And the fuselage centerline is the reference line for attaching the top and bottom parts of the fuselage seen from the side. The attaching is done with at a right angle (90 degrees). A such structure with attached fuselage bulkheads ( cross-sections ) makes the 3D structure of the fuslege block.

 

[Wurger]

Here is a graphic explanation to my post above. I have attached a couple of pics of a 3D structure of a paper hull of a ship. It is a good way for understanding, methinks. Also I uploaded a picture of all projections for Bf 109E fighter plane. The source of all images: the net.