Full scale Patriot

Rising out of the ashes of Big Girtha is the Patriot.
Big Girtha was a 16in dia rocket I built. On it's first flight it sustained landing damage.
Because it was built so light(50#) the damage was more severe.
Instead of rebuilding her my buddy Joel wanted to follow his dream of a full scale Patriot.
The original Patriot is 16in dia so we could transform the beast into a bigger beast.
Not very easily as the Girtha had 3 fins where the Patriot had 4.
The airframe of Girtha along with one fin mount was damaged so this wasn't a major show stopper.
We would just need to remove the damage fin mount, remove a second and install 3 new fin mounts.
I call them fin mounts because the fins are removable as I don't think I could even get a 4foot fin span out of the basement.

The Girtha was a coaxial tube rocket.
It is composed of a strong 8in inside tube centered in the 16in tube. The 16in tube is really only for show to get the desired OD w/o adding too much wasted weight. The 8in structure takes all the thrust. The Patriot will take this one step further. It will be flown on a 6in motor so we need a 6in to 8in adaptor.
This 6in motor mount will extend 8feet from the aft end of the rocket to the forward end of the second airframe tube. It will act as a thrust transfer tube to directly push on the upper 10 feet of airframe/nosecone. It will also couple the two lower tubes which will be recovered as one 8foot section.
Of course we wont be making a 8foot long motor mount!! It will be broken into 3 pieces two of which are 3ft long.
The nose will be made of foam shaped with a belt sander then glassed.
We decided to 1 1/2 X upscale the Patriot fin span for stability. The Girtha used 1/2in foam vacuum bagged with carbon. These fins were not the same scale as the Patriot.
We decided to trim them a bit to have the same taper as the leading edge of the Patriot fins. Then use them as the core for the new fins. To this core we would glue 1/4in ply forward skins and use foam to build up the aft fin. This would allow us to closely match the Patriot fins.

Fincan

We decided to start with the fincan.
Using a jigsaw we cut the damaged 16in tube off the centering rings that made up the old airframe.
It is very interesting to disect a rocket and see how your internal fillet's worked out.
With the tube off we used a grinder to remove the existing fin tab fillet's and take them out.
A little cleanup with a chissle and sanding drum and we were ready to install the 3 new fins
Here is a shot after the fillet was installed and glassed over. See where the old fin was?

Fillet/glass

We test fit the fin cores in the fin tabs. We reused the old fin tabs were possible. This is why some are black(carbon) and some are brown(just glass) as can be seen in the following photo

Core test fit

And of course you have to take a shot of the aft end. We searched all over and found a beer bottle to show scale ;-).

Aft end showing 8in mount

Fins

We attached 1/4in ply to the fins from the central ridge forward.
This would give us a hard point to run the hotwire against when we trimmed the aft foam and also created the forward taper.
The notch cutout in the plywood allows it to clear the tabs. This will not be visible when the fins get glassed.

Forward section added

Next we added foam to the aft section and cut it with a hotwire. After this was applied we put one layer of 4oz glass over the foam because we kept denting it.

Foam created a nice aft taper

What you can't see in the photos is the expanding foam we put inside the hollow forward section of the fin. After we put a generous fillet on the inside.

Fincan body tube

We could not reuse the BT we cut off the fincan so we rolled a new one with the 16in sonotube mandrel that was used for the Girtha.
This is 1 wrap of 5.7oz carbon and 3 wraps 8oz fiberglass.

16in BT waiting to pull mandrel

And an end shot showing the large foam centering rings.

Foam CR and conduit shaft

Once we pulled it off the mandrel we strapped the fin tab section down and made marks to cut fin slots.
Finslots were cut with a jig saw.

Marking the fin slots

Once the finslots were done we had to check it out with the fins on.
We started to finally get a feeling for how big this thing is going to be.

Test fit

Shows the 1/2in leading edge

Next to a 4in V2

The two lower sections of BT had 8in tubes centered in the 16in tube.
We made an adapter out of fiberglass. This was not only designed to center the motor in the tube it was also designed to transfer the thrust to the upper rocket section.

Half the 6in to 8in adapter

Since the upper two sections of body tube would hold the parachutes we decided to use an internal 10in tube to give us more room. Here is one of those tubes being made

Using a 10in sonotube mandrel

Yet another 16in tube

The upper airframe sections were each 3 feet long so we used 3 centering rings on each section.
Here is one inner tube with it's rings glued on. You can see the extra tube sticking up past the top CR.
Once the outer tube is glued on I trimmed both flush with the CR using a hand saw.

CR's mounted on 10in tube

I made a thrust plate out of 1/4in aluminum plate. Here is an aft picture showing it and the motor installed.

Thrust plate with 6in motor

A side shot shows the thurst plate and you can also see the small hatch in the side of the airframe that allows us to install the internal nuts that hold the fins on.

Side view of fincan

Nose Cone

To make the 16in nosecone we decided to use 2in pink foam glued together with gorilla glue.
We cut rings using a hotwire cutter. We built it with a pin in the center that the foam turned on to give us a perfect circle. The pin was sized to match the hole my hole saw cut at 1 1/4in.

Cutting foam ring

We mounted the rings on a dowel with Gorilla glue so we could shape it.

Rings glued to shaft

We didn't want the basement to look like the inside of a snow globe!!
So we put up plastic walls around the saw horse jigs supporting the foam.

Walls half installed

With the walls up we used a belt sander to shape the cone.
While I ran the sander Joel ran a shop vac to help control the foam dust.
Worked like a charm.

Nice looking cone

'Empty' beer bottle for reference only

We had to go outside to test the fit on one of the body tubes.

Test fit is good

In glassing the cone we decided to mount a plate to the bottom of the foam and put 4 lag bolts sticking out.
This would give something to bolt onto. We also decided to run 4in wide Kevlar straps across this plate and up the side of the foam. When we layed the glass on it would bond with the kevlar making it impossible to rip the plate off the nosecone. We put 3 layers of 6oz glass on.

First layer of glass

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