Re: Featherbed frame design went against all engineering pri
Rohan said:
texasSlick said:
regarding the elasticity of the curved tubes has failed to account for the fact that the engine side plates, engine, and head stay, make for a very strong triangular gusset sitting inside the loops, which taken in toto, makes the frame very rigid.
Thats not strictly true, when you study a featherbed closely ?
The engine/gearbox unit is really only attached to the front downtubes and above the rear swingarm,
and the top of the cylinder head is attached to the steering head with the head stay.
That actually gives the frame considerable scope to flex without influencing the power unit,
when you think about it ??
Now whether this was done deliberate or merely incidental is another matter entirely.
But the earlier Norton engines/gearboxes (pre featherbed) were attached to far more points on the frame.
And they had considerable troubles with those lugged frames breaking, at a number of possible places...
I have previously written on this Forum that my Atlas had some unique singularities (6 start oil pump with '62 build date and other performance differences), but if Rohan is correct, then
my Atlas has another singularity in that the frame is not uniquely Featherbed. The engine/gearbox/side plates comprises a unit which is attached at the following points each side:
1) on the front down tubes at bottom before tubes commence bend to lower horizontal run. (per Rohan?)
2) about 4 inches from point 1) on the lower horizontal run just about where the bend straightens out
The engine and small side plates effectively gussets the bend between points 1 and 2. There cannot be any flex in the bend unless the bolts shear or the lugs break off.
3) there is a cross-tube welded between the lower horizontal tubes where the tubes commence to make the bend upwards to pass behind the oil tank/battery box. There is a lug from this tube to each engine side plate.
4) about midway up the rear vertical tubes is another cross-tube with another lug to each engine side plate. (per Rohan?)
These attachment points 3) and 4) effectively gussets the lower rear bend in the frame tubes in the same way as points 1 and 2 did for the front bend. So far I count four mounting points that are arranged in a rough triangle about 11 inches vertical and 17 inches horizontal, that very effectively stiffens the lower part of the front downtubes, the lower horizontal tubes, and the lower half of the rear downtubes.
The head stay is a triangle with one point on the headstock, one point to a cross-tube between the top horizontal tubes, and one point on the head. The engine/gearbox/sideplates/head stay is a rigid unit of triangular or perhaps more trapezoidal form, and when rigidly mounted inside the frame makes the entire assembly very rigid.
Where the rear vertical tubes bend to make the upper horizontal, the bend is gusseted with an equal sided triangle of approximately 12 inches per side, formed from tubing. This is the tubing loop where the rear dampers mount. My practiced engineer's eye tells me that any shock originating from the rear wheel will be transmitted straightly into the upper horizontal tubes without any bending moment on the bend area of the frame tubing.
I think the FB frame was well engineered. By itself, it is light weight and flexible. But it was not meant to be used by itself, but rather with a rigidly mounted and stiff internal structure (engine/GB/side plates, etc) that when taken together made a strong rigid assembly. Any attempt to isoelastic an engine and GB into a FB frame will most likely negate the internal structure that the original designers assumed would be there, and would likely end in failure.
Slick
