So, the wind was blowing 11 mph (16 ft/sec) at the time of launch. The rocket
was going about 85 mph (125 ft/sec) when it exited the 6’ long rail. If the
buttons were about 3’ apart, the rocket was exposed to this wind when only the
bottom button was still on the rail for about 0.024 seconds. Keeping in mind
that the wind was acting on the whole airframe and the fins at the aft end were
still mostly guided by the bottom button because most (maybe everyone?) secured
the bottom button to the aft centering ring. Is this all true? If so, does it
seem like this could send the rockets off at an angle witnessed in the video?
There could be problems when there is a cross wind to the rocket being held on
the rail. Not because of the potential rotation around one of the buttons, but
because rail buttons resist moving when they are at an angle to the rail. This
we know from inserting the rocket onto the rail and feeling it grab if not
going on straight. You can really feel any rotational torque. So the rail
buttons are grabbing on the rail guides and could induce a ‘snap’ as the rocket
goes down the rail.
I’m curious when rails and buttons started being used. Rails are stiffer than
rods but perhaps the buttons we use are not so great.
From: Kurt Gugisberg
Sent: Friday, June 19, 2015 9:01 AM
To: roc-chat@xxxxxxxxxxxxx
You are right Chris that it rotates around that bottom button but it really
wants to rotate around the cg. So what would be the best way to space the
buttons to lessen the rotation? I would think the top button at the cg and two
at the bottom spaced about three or four inches apart.
If we do another mass launch, how about sparky motors!
Kurt
On Fri, Jun 19, 2015 at 7:52 AM, Chris J Kobel <Chris.J.Kobel@xxxxxxxx> wrote:
I recall measuring 11 mph from the WNW at 88 degF at our ~9:50am launch time.
I believe as soon as the top button clears, any rotation would have to take
place about the bottom button.
Chris
From: Kurt Gugisberg <kurtgug@xxxxxxxxx>
To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>,
Date: 06/17/2015 05:40 PM
Subject: [roc-chat] Re: Punisher Drag Race and Discussion of Thrust
Misalignment
Sent by: roc-chat-bounce@xxxxxxxxxxxxx
I still am voting for the rail button thing. As soon as the top button clears
it will want to rotate around the cg. Now what is causing the force that
makes it want to rotate? Did we discuss weathercocking on a barely stable
rocket? How hard was the wind blowing at the time?
Kurt
On Wed, Jun 17, 2015 at 4:44 PM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
So, what do you think? Malformed nozzles, chamber pressure too high, exhaust
gases thrust vector rocket...
Sent from my iPhone
On Jun 17, 2015, at 4:24 PM, "Kurt Gugisberg" <kurtgug@xxxxxxxxx> wrote:
From the video, I could see that my Punisher also veered off after it left the
pad. I had to leave my casing with David because it had a heat bulge in the
end near the forward seal. So it was probably close to catoing too.
Looks like we have a cast of characters that might lead to to behavior we saw:
misaligned thrust vectoring, rail button placement, low level of stability with
high thrust motor. The only thing it might not be is rail whip.
Kurt
On Wed, Jun 17, 2015 at 1:02 PM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
I’m sure we can come up with things to investigate and even reduce this
misalignment problem.
Who’s interested in a Punisher 2 mass launch? I think we should use the same
K1440 engine and leave it up to each flyer if they are going to modify the rail
buttons, pad, whatever else. We have lots of time to collect details on each
project.
Chris, would it be possible to post some details of the AC stand used to test
for misalignments?
Do you think that creating a way to hold the rocket on the pad until max thrust
is achieved would help?
I’m wondering why David Reese has not joined this discussion because wouldn’t
he be one of the best people to advise on something like this?
Again, I think building a large launch pad/test stand for ROC launches would be
cool and we probably wouldn’t need the contribution of many people to do it.
We could use the pad at Black Rock for XPRS or BALLS. Again, I’m offering to
buy the trailer for the project.
Richard Dierking
