8" rocket nose cone question

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Donnager

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I'm building an 8" Composite Warehouse Prometheus.

The question I have is how do you guys that build these large ones square the tubing coupler in the back/bottom of the nose cone?

I can get it close (probably more than close enough) by eye/hand, but I'd really like to know if there's a good way to align an ogive cone with a cylinder....errr inserted into its backside.
 
Not sure I fully understand the struggle. Unless I'm missing something wouldn't you just slide the coupler in until it stops? Are you saying your tolerances are loose enough that the tip is not square with the centerline of the coupler? That's how I did my 8" Formula 200. As tight as the tolerance is not sure how you would square it up if it was out of center.
 
I go Top Gun style and do it inverted.

I stand the nose cone vertical, add epoxy, insert the NC coupler, then place the airframe over the coupler and use a door frame or some angled aluminium to align the whole stack and get the NC and the airframe lined up.
 
Never had a problem with it, myself. Sand thoroughly with rough sandpaper on the outside of the coupler and the inside of the NC. I usually put the bulkhead in the top of the coupler, add a U-bolt for the chute/harness, epoxy over the nuts. When I am absolutely sure the bulkhead is epoxied on solid and cured, then put a ring of epoxy on the coupler and shove/tap it in. I don't see anyway it could go in unstraight.
 
I guess my question is more about how to properly align the coupler with the nose. I just want to be sure the coupler is square. This only seems to be an issue with the larger diameter fiberglass stuff.

I can put it in a little bit, and it wants to jam. That will be mitigated with a few hours with some sandpaper. Sanding a cylinder uniformly is a little bit of a trick. When this is finished, there may be some slop.

I am fairly sure I can handle this by eye and repetitive measurements, but wondered if there was a quick trick to verify the coupler (straight) was parallel with the nose (curved). My inclination was to remove the aluminum nose, and push the coupler in level, and check by putting into the payload section. The problem is doing all this with an epoxy time clock going. I may just mechanically (screws) attach the nose to the coupler, as that may give me some flexibility in the future, anyway.

Not really a big deal. I'm probably just picking fly poop out of pepper.
 
I guess my question is more about how to properly align the coupler with the nose. I just want to be sure the coupler is square. This only seems to be an issue with the larger diameter fiberglass stuff.

I can put it in a little bit, and it wants to jam. That will be mitigated with a few hours with some sandpaper. Sanding a cylinder uniformly is a little bit of a trick. When this is finished, there may be some slop.

I am fairly sure I can handle this by eye and repetitive measurements, but wondered if there was a quick trick to verify the coupler (straight) was parallel with the nose (curved). My inclination was to remove the aluminum nose, and push the coupler in level, and check by putting into the payload section. The problem is doing all this with an epoxy time clock going. I may just mechanically (screws) attach the nose to the coupler, as that may give me some flexibility in the future, anyway.

Not really a big deal. I'm probably just picking fly poop out of pepper.
Every kit is different and every builder is different, but I have built two 8" kits and a 7.5" kit, and never gave this much of a thought. I just shove it in till it won't go any more.
 
Every kit is different and every builder is different, but I have built two 8" kits and a 7.5" kit, and never gave this much of a thought. I just shove it in till it won't go any more.

Good enough. This coupler was very, very tight, but I have plenty of sandpaper and time, if not plenty of elbow grease.
 
Never done a FG nosecone this big, the smaller ones just get pushed in until they stop and end up square.
If the aft end of the coupler is cut square, and if the aft end of the nosecone is cut square, then you could insert it, and measure the shoulder length all around. If the shoulder is the same length all around, then the coupler is inserted squarely.
 
If I wanted it aligned, I'd put centering rings on both ends-inside coupler. Drill hole in center of each ring to insert a dowel--say, 1/2". Then insert long dowel (4-5 ft long) let dowel go down to tip of nose. Then you always have a center line from nose through your coupler. You can add your aft centering ring to nosecone with confidence that your coupler is centered in the nosecone.
 
YEAH!
I got the nose coupler installed. There was apparently a (very small) ridge of resin/epoxy on the interior of the nose that was preventing coupling. about 1/2" from the end. It's gone now. Time to paint and fly.

Thanks.

Pictures to come.
 
I put the coupler in the cone as far as it will go, wrap masking tape around the coupler at the base of the nose cone.
Then pull the coupler out, cut a 1/4 inch strip of heavy card stock or a file folder and trim the trip to fit the circumference of the coupler. Then glue the strip to the coupler slightly above the masking tape. For a 3 inch cone this is just enough for a tight fit at the base of the cone where you have a little bit of play so it centers perfect. you may have to dry fit a couple of different thicknesses to get the 8 inch right.
 
YEAH!
I got the nose coupler installed. There was apparently a (very small) ridge of resin/epoxy on the interior of the nose that was preventing coupling. about 1/2" from the end. It's gone now. Time to paint and fly.

Thanks.

Pictures to come.
Ah, so you had a one-off kind of problem that appeared to be systemic at first glance. Go figure. Glad you got it together.
 
Ah, so you had a one-off kind of problem that appeared to be systemic at first glance. Go figure. Glad you got it together.

Yes, apparently. As tube sizes go up, I have had more issues with fitment, and am fairly particular about how they slip together, when I want them to move smoothly. I am usually fairly patient, but was getting close to medieval hammer usage.

Thanks.
 
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