The patient spent the night and morning convalescing as the PC-7,  high compression, epoxy paste set up around her walnut stock and iron saddle.  (That, I’ll warrant, is a sentence never before uttered on the planet.)

The stock and its integral flight deck and bolt groove,  have been shifted in relation to their previous position by one degree in the XZ axis.  This effectively raises the nose of the flight deck by about 3/8″, so that now the string rests on the deck with a gentle pressure,  (i.e. the at rest string deflection suggests that the center line of the limbs is set at about  1/4″ below the deck).

Here is a photo showing the altered saddle.

I welded up the top edge of the saddle and milled it into the one degree angle seen here.   Now the edge margin on the forward slot is greater than the rear slot.

By afternoon,  she was ready for camera and action.   This is the exact same bolt used in the previous test when that pesky 3/8″ string gap caused the tail to lift up.  Click for 4X slow motion video:   20111107135003(1)(1)

And broken down into stills:

Our personal state of the art in video and such like,  makes these ghostly images the best that we can manage right now.  I’m not so sure that they aren’t telling me exactly what I had hoped to see.  To my eye the bolt seems a little less down pitched than the one in the stills from the previous posting.

Also, the flight of the bolt looked very clean to the naked eye.  No porpoising or waggle evident.   At 50 meters  it struck a foot to the left of its previous sight setting.   This shot vector is way off from what the center line of the bolt groove would indicate as ideal.  The divergence of the shot to the left suggests that another 7 1/2 degrees of washer rotation on the top half of the port bundle is in order.  It should be easy to correct tomorrow.

The important thing here is that the bolt showed no signs of porpoising.  Porpoising is when the bolt can be seen to be traveling nose up or nose down for a fraction of a second before the fins straighten it out.  Porpoising is a lot of wasted energy.

After the shot,  the line traced by the bolt going through the air should appear clean and minimal in your memory.  There shouldn’t be any fuss going on.

2 Responses to “The straight arrow.”


  1. Randi Richert says:

    Looks and sounds to me like you’re on the right track. Now you should be able to focus on using the twist to balance the arms and cut down on yaw without inducing loft. One variable at a time is so much easier to work with. It’s nice when a theory or tinkerer’s hunch is backed up by tangible results. If I had any doubts about underslinging on my current scorpion project, your experiment has alleviated them. This is just one more little example of why I think a total re-evaluation of the “convetional wisdom” is long overdue. Much of the so-called wisdom is just a series of assumptions and opinions made by esteemed men of letters with dubious skills in the mechanical arts.


  2. Nick says:

    I am finding that catapult development keeps knocking a hole in the bucket where I store my preconceptions. The more I learn, the less I take for granted.

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