People in this thread will appreciate this document. Completely unrelated by the way.
ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19630011448.pdf
Good onya Evipanda, isn't rocket science great stuff, we can get onto that when we wrap this up. Amused to be blah, blah blahed by a fellow with the name of Reflex Films. Via youtube! that's pretty technical, why not carrier pigeon?
Anyway, given up on experiments for the moment my preloaded CK95 aparatus is now in 44 deg + sunshine.
Did find out that that when the CK95 is loaded up with 20 kgs, given a small disturbance, it keeps going for quite a while. Each amplitude is only a few percent less than the previous. But it goes at a much lower frequency, about 0.8 cps compared to the unloaded 4 cps. Close to what we'd expect with the frequency proportional to the inverse of the sqrt of mass.
Back to the unweighted masts.
The unloaded masts, although they both oscillate for a long time both lose a lot of amplitude on the first couple of cycles. I've done the calculations for the amount of energy lost due to wind drag. Doesn't quite add up. I calculated 0.15 joules would be lost in the first half cycle out of the 8.3 joules required to bend the mast to the initial position. A loss of 0.3 joules in 8.3 joules is equivalent to losing 3mm out of 170mm of amplitude due to air resistance in that first oscillation. Actual observations indicate it loses about 15 mm of amplitude in each of the first couple of oscillations. Lost damping!!! Where is it?
So damping, if there is some going on inside the mast material, I figure comes in 3 basic forms.
plain old friction - a constant mainly independant of speed.
viscous friction - as in lubricated bearings - linear with speed
and turbulent drag of a fluid - goes up with the square of speed
Any more?
So my problem is there's a rapid loss of amplitude in the first couple of cycles when the mast is oscillating quickly unloaded. Air resistance calculations can't explain the rapid loss. The heavily weighted mast does small scale oscillations without any dramatic losses of energy.
One explanation is that my wind resistance calculations are out. Maybe drag coefficient is much higher when passing through the turbulence of the previous oscillation? The wake will be moving to collide with the returning spring, drag is the square of this collision velocity, that will up things.
If, on the other hand, the friction intrinsic to the mast goes up linearly with velocity, and it was oscillating 5 times as fast when unloaded, the rate of energy dissipation would be up by a factor of 25, that could also explain it ?
So how do you pre load it without the extra mass that slows down the oscillations? Downhaul it with a piece of string with low air resistance. Bow and arrow style. Then lightly oscillate it in a direction perpendicular to the plane of the "bow". Will this differentiate between the 30% and 95% carbon masts? I'm worried it won't like the out of balance, you might have to bend two and link them together in a heart shape or it will wriggle out of the mounting.
Here's the CK95 loaded with 20kg, give it a little vertical oscillation and it just keeps bouncing at about 0.8 Hz for quite a while.
^^^ Looks like you need to spend less time calculating bending moments & more time in the garden.
Like I said before: Bull**** marketing spin!
I must do that experiment comparing masts of the same MCS by loading them with another 10KG bag of lead shot..... ah Bug**r, I think I have shot it all off!! Looks like another trip to the Shot Tower...........
Anyhow, my backyard theory is that the larger diameter of the SDM lower tube section come under more stretching and compression resistance than the RDM section. I'll find a way to test it soon. It does not look like much wind next week anyhow.........
Looks like another trip to the Shot Tower...........
