Quote:
Originally Posted by 3-Wheeler
Hi Phil,
I'm trying to understand your geometric description above, and spent about an hour using the CAD to analyze your numerics. Here's what I came up with so far, but I am making some assumptions:
1) Not knowing the exact shape of ideal airfoils, one assumption I am making that that all extended radii used to duplicate the airfoil shape are referenced to the maximum camber of the wing, or the thickest point of the airfoil.
2) This means that all radii center point originate from a tangental line draw through the maximum cordal thickness.
3) Being that I am not designing my own wing shapes, the assumptions above may not be true.
The first graphic shows four large circles draw over the AeroHead Streamlining Template.
The second graphic shows that the transition from the 3.35-H radius to the 5.294-H radius is incredibly short, and shown in location by the short black line. Your pictorial that you are working from must be much more detailed than the one I have to work with, because I could not make out that much detail.
The 5.294-H radius curve fits the pictorial quite well, and for quite some distance.
This graphic shows that the transition to the third larger radius occurs close to the 60% position on the streamlining template.
Notice that the point of intersection between the two lines, there is a small
"dip". This transition should be smoother to match the pictorial.
And here is the intersect point for the third and fourth radii. Again there is a dip at the point of intersection.
One way I can think of to avoid these dips is to create a airfoil shape where the wing curving surface is created with a constantly enlarging radius, or at least broken into smaller sections so that these dips would not be an issue.
Based on the above, it still appears that my constant radius Master Template made for the Insight would provide a good match to the AeroHeads Streamlining Template out to about the 60% point.
Because the car is currently jacked up I can't measure the height of the roof line exactly, but estimating with a tape measure, I got about 50 inches.
The 60% point on the Streamlining template is therefore about 103 inches back from this point, and this ends up about 42 or so inches behind the hatchback spoiler trailing edge.
Assuming the Master Template has the proper curvature in it, the tail extension should work fine by creating the remainder of the extension distance utilizing the same curvature it has up to the two-foot point, and extending out another 1-1/2 or so.
Jim. |
Hey Jim,just caught your post.
The relationships I came up with are from Mair's boat tail research.His table appears in Hucho's 2nd Edition as Fig.4.41,after reference 4.40.It also appears in an SAE Paper from around 1969 when he first published his results.
I figured that his Doctorate trumped my B.S.,and we'd be able to bet on his work.
It turns out that if you remove the cylinder portion of his windtunnel model,substituting the 1.3 d nose section onto the tailcone,you end up with a body-of-revolution of L/D = 2.5,just like the 'Template.'
My numbers are realized at 'small' scale,so it's not surprising that there's some 'wiggle' in the coordinates.
And the axis of rotation is exactly like your doing,merely moving further and further away from the point of max camber ( max thickness for a wing section ).
I think that as far as DIY'ing,if one just follows the 'trend' line of the 'Template' curve,you'll end up with fully-attached high-quality flow to wherever one decides to do the truncation.
When I build,I literally bend a length of 1-inch Schedule-40 PVC pipe across some bulkhead stations to define the points in between,allowing the pipe to do the curve-smoothing.It's kind of a Clarence 'Kelly' Johnson thing.
Stainless steel would be better,as it has superior uniform elasticity during bending deformation.
If I were building an experimental aircraft,I'd sweat every detail.
I am learning to have the 'discipline' you demonstrate on your projects but oftentimes,time constraints and immoveable deadlines force me to wam,bam,thank-you-ma'm things together,which led to the 'Template',as it was meant to help expedite the build with a high degree of confidence of road success.
Hope this has helped,I'll await your response,happy modding!,Phil.