Width based on engine crutch required?

I'm no engineer but why push more through the air than you have to? Also, wider will mean heavier.

Craig

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Why as wingspans got bigger the Fuse width stayed the same? Seems like a larger wing should also have a wider fuse.

Some "designers" of our stunt models over the years have been obsessed/concerned about frontal area.  Some have gone to extremes to design a fuselage with minimal frontal area.  It is interesting to consider what the total frontal area is for our stunt designs. 

Let's start with a "typical" stunt wing that has a 56" span and the average airfoil thickness is 2.25 inches (or maybe more).  Not allowing for a slight reduction for rounded tips, that gives a wing frontal area of at least 126 sq in. 

Then there will be a tail say of 24" span and at least 1/2" thick for another 12 sq in of frontal area, not allowing for rounded tips.  Total frontal flying surface area of about 138 sq in.  (There is also the frontal area of the vertical tail, but is not included in this discussion.)

Now let's look at a semi scale design (like the Bearcat or Sea Fury) where the fuselage may be 6" deep (or slightly more) at the canopy and up to 4" wide.  Assuming it is about an oval shape, that gives a frontal area of almost 20 sq in of which 9 sq in is covered by the wing, so that fuselage adds about 11 sq in to the total frontal area or about 8% (11/138) to the total model frontal area.

OK, let's look at the skinny fuselage for this wing that is maybe 2.5" wide and 5" high.   This thing will have a rounded top and bottom with  approximate straight sides for a cross section of something just less than 11 sq in.  The wing already covers more than 6 sq in of that so the fuselage adds about 5 sq in more to the total frontal area or about  4% (5/138) to the total frontal area.

Then, we need to add some increment of total flying system frontal area because of the lines which by some estimates is as much as 50% of total flying system drag or more.  So the added cross section of a large "semi-scale" stunt ship compared to a conventional design is even less pronounced when considering the line frontal area and drag.

Modern power plants can easily make up that 4% increase in frontal area (8% - 4%), or less when considering the line drag,  from the large semiscale type fuselage to the "yardstick" type fuselage.  Furthermore, there are some structural advantages with the larger cross section fuselages with little or no weight penalty with appropriate design, construction, and materials used.

So, what does all of this mean.  It becomes a matter of taste and aesthetics held by the designer/builder whether to use a wide bodied fuselage or not.

(A more exact analysis could be performed, but the relative differences between the wide bodied and skinny fuselages on a stunt ship will be similar to the above numbers and will be quite small.  The real culprits in total frontal area of a stunt ship are the wing/tail and the lines.)

Points to ponder

Keith