Kyle,
You want one at the end of the rocket.
Reason is if you move it forward from the aft end you essentially shorten the
rail by that distance.
Maybe not an issue with your design, or the length of rail you use.
I like to mount the forward button at the forward centering ring.
That gives me structure to mount it to.
But also once that forward button leaves the rail you have no guidance as one
button does nothing.
So there for shortening the rail by the distance between the buttons.
That is the reason if it’s windy people leave the bottom button in the rail as
it gets ripped off and causes rail whip.
The rail doesn’t move but the rocket does ripping the button off causing the
rocket to not fly in the direction you pointed the rail.
If you have a longer rocket, a heavier rocket, or just concerns of getting it
vertical without ripping the buttons off then add a third button.
Robert DeHate
AMW/ProX
From: tccrockets-bounce@xxxxxxxxxxxxx <tccrockets-bounce@xxxxxxxxxxxxx> On
Behalf Of Kyle Brookes
Sent: Tuesday, June 2, 2020 9:27 PM
To: tccrockets@xxxxxxxxxxxxx
Subject: [tccrockets] rail button placement advice
Hi all, I have yet to be able to make it to a TCC launch, hopefully someday
soon. but it you can't fly em, might as well keep building them.
So i wanted to see if anyone in the group had a rule of thumb for rail button
placement. I see that Apogee recommends placing them so that they capture the
CG. this make some sense as binding on the rail has less of a lever arm.
However Apogee doesn't appear to adhere to this rule in their own designs. Both
the Zephyer and Katana have the forward button ~70% of the way between the CG
and the rear button with large motors installed. both systems also have the CG
at 30% of length from the aft, however keep the button spacing at 12 inches.
As far as math goes, i figure one way to look at it is allowable angle
deviation from the rail. so essentially the slop between the button and the
rail over the span button to button. this would lead to a constant spacing
independent of length (with some reasonable amount). My scratch build is a near
min diameter fiberglass so i have flexibility and constraints on the placement
that would differ from thru fin motor mounts as well.
Would love to hear thoughts form the list?
Thanks
Kyle