2.75 in FFAR rocket

[Spaceinvader]

Hello, I posted this in restoration aswell, im going to clean it up a bit. Found it on local classifieds for 100$, I think its a pretty decent price for the motor. It has a few either corrosion holes, or burn through holes in the sides, and the nozzles are rusty. I will need to find a warhead, but that wont be to hard. I am wondering what the symbol on the side was with the box, and eagle holding arrows in its claws, aswell with the triangle with the letters HD in it. Anything welcome, Rhys

 

[weberoed]

The symbol is the government inspectors stamp indicating it has met all requirements. If you don;t find a warhead, this motor body makes for a great 6 pack of beer carrier

 

[Spaceinvader]

Haha, great idea, if I could get it open!

 

[HAZORD]

Your motor case is the Mk43, which is the older pre-Vietnam era motor. It looks like parts for it were made in the 55 to 58 timeframe. It is also the older design motor due to the screw in adaptor at the warhead end. It is most likely Navy or Marine Corps due to the gray color. Newer manufactured Mk43 motors have a unitized bulkhead at the warhead end (All aluminum one piece).

You can get the fins/nozzle section out by removing the square aluminum wire that is holding them in place. Look near the back end of the motor for a small slot cut through the side. You can see the wire through that hole. Hold onto the motor body and rotate the fin section. The wire will rotate with the fins. When you see a gap in the wire, stop rotating. Get something small and pointed, like an ice pick or awl, and push it into the gap and try to work it under the square end of the wire so you can pry it up towards you. As you pry it, rotate the fins and wire towards the tool, so that your rotation pushes the wire up out of the hole. once you get the end of the wire above the outer surface of the motor body, continue to rotate the fin section, and it will keep pushing the wire out until it pops out all the way. Now just grab the fin section and work it back and forth. It has a neoprene O-ring around it to seal the gas, so the o-ring will give some resistance, but just keep pulling on it and it will work out eventually. You can also pour some rubbing alcohol into the joint to lube up the o-ring against the aluminum motor body.

Once you get the fin section free, you can use some penetrating oil on the center pin. It should move freely forward and backwards through the hole. The firing wire actually goes through the middle of the pin and runs up to the front of the motor. The center pin is pushed to the rear upon firing, and pushes the fins out, once they are free of the launcher. The locknut will unscrew from the pin, and the star plate will come off and you can remove the pin by pushing it towards the inside of the motor. It might take a while to free the pin up so it moves.

The single powder grain for these motors was around 33 to 35% nitroglycerin. It would burn for about 2-1/2 seconds to get to full speed. It was also quite dangerous because it would detonate high order like a giant stick of dynamite if initiated properly.

 

[US-Subs]

- Just answered the other thread, that will teach me to read one at a time -

 

[HAZORD]

I didn't see the other one till after I answered this one. This one was on top and that's where I started.

 

[Spaceinvader]

Yeah sorry that my bad, should have only posted it in one place. Once the wire is out, how does the fins/nozzles stay in once you put it back together? Or does the wire somehow fit back in again somehow?

 

[US-Subs]

If you are careful in taking it out you may be able to re-use it, but most fit snugly and are not so loose that they need it for display.

 

[Spaceinvader]

Alright, sounds great, thanks for the help guys, when I get home I will be cleaning it up. Any ideas for getting the rust off the nozzles? I have some stuff that works great, but if it's left to long it gets gray and starts eating away the metal.

 

[HAZORD]

You could sandblast or bead blast the nozzles. There are also some very mild rust removers like "evaporust", which works great.

When you put it back in, the o-ring will provide enough friction to keep it in, but you can also use the original retaining wire if you are careful not to abuse it when you take it out.

There will probably be a lump of propellant residue with some steel wire embedded in it stuck to the inside of the motor. You might be able to break it loose and pull it out. It smells pretty bad.


Sent from my NSA/FBI tapped iPhone using Tapatalk

 

[Spaceinvader]

Yeah bits of it are falling out the nozzles, along with what looks like multicolored sand. It looks like glass or bits of obsidion. I will post pics when cleaned up and such. I think I'm just gonna get a blue practice warhead.

 

[SHAKY]

If you have difficulties finding a practice warhead either is available if interested.