TN and Nose Cones

I'm making my existing PML AMRAAM 3 into a DD version. A question I have is how does everyone attach their shockcord to the nose cone? I just do not trust the eyelets. This is a 3" PML nosecone (obviously).

I think you may be underestmating the strength of the eyelet. I have always, when there wasn't a payload bay in the way, attached my TN to the eyelet. I guess you would have the option of putting a screw in the base of the nosecone, but I would think that that would be even less safe since it could strip out.
Cheers,
Reed

You can drill or cut out a couple of larger holes in base of the shoulder of the nose cone, thread the TN through the holes, & then tie a knot in the TN. It won't go anywhere!

I have no input on whether the eyelet is strong enough, but for a really strong nose cone (used on 4"-7.5" rockets that I have flown)... cut off say, 1/2"- 1" of the nose cone shoulder (off the bottom). This leaves a hole in the bottom of the nose cone, then make or purchase a bulkplate that fits in the hole. Rough that nose cone up a LOT and then I usually tack it in with CA. Then make large epoxy fillets. The eye let is only holding the G-force of deployment (well below 20 G's, so we will use that number) so if you multiply the weight of the cone by 20, you get an approximate amound of weight the eye let needs to hold.

I cut the base out of one of my nosecones but I fitted the bulkhead in the BT, below the shoulder. There's a U-bolt through the bulkhead for attaching the recovery gear. This is probably stronger than fitting it in the nosecone and I can use the space created as a second avionics bay....

Originally posted by jraice
I have no input on whether the eyelet is strong enough, but for a really strong nose cone (used on 4"-7.5" rockets that I have flown)... cut off say, 1/2"- 1" of the nose cone shoulder (off the bottom). This leaves a hole in the bottom of the nose cone, then make or purchase a bulkplate that fits in the hole. Rough that nose cone up a LOT and then I usually tack it in with CA. Then make large epoxy fillets. The eye let is only holding the G-force of deployment (well below 20 G's, so we will use that number) so if you multiply the weight of the cone by 20, you get an approximate amound of weight the eye let needs to hold.

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Hi Jordon,

I have seen this method fail much more then once with the nose cone coming in fast and sticking in the ground next to a bystander.

Epoxy does not hold to the plastic of nose cones well at all.

The shear strength of the epoxy / poly joint fails when the TN gets tight. This happens usually about the third or forth flight flown this way.

One member I know after the failure had to put about 8 screws to hold the bulk plate in the nose from the outside of the nose cone.

Using nylon to make a secure holding loop like posted above, or putting in a screw eye with a nut on the other side works well.

Cut an access hole in the "side" of the nose cone shoulder say about 3" square to gain access to the inside.

I have seen u bolts used on 5.5 and 7.5 nose cones.

Jraice's method works really well in fiberglass and CF nosecones, although in my experience, it's a PITA to get it to stick to plastic (it can be done, but it's a pain). My method involves usually just putting a u-bolt in the nc (if it is big enough), or if it is smaller, I use the stock eyelets (I thread it through both of them). Never had a failure of either method.

Here's a method i've seen used on smaller or light weight mid/high power rockets, using LOC nosecones (I have heard of the eyelet breaking on those):

Get an eyebolt that fits through the hole in the nosecone (My 4" LOC nosecone came with a hole the same size as the eye bolt that came with a bulkhead).

Cut a hole in the shoulder, big enough to fit a washer and a finger or two through.

Put a washer through the hole in the shoulder, and screw the eyebolt into the nosecone, up through the washer. You may want to use another washer between the eye bolt and the nosecone, but its up to you.

This is the most pain-in-the-arse bit: Try to get a nut onto the eyebolt, and tighten it down. It took several attempts to get this right, but once its done it should give a stronger attachment point than just the eyelet.


You could probobly fill the space under the washer with epoxy, and put some over it and the nut once its installed for extra strength, but I'm not sure how much that would really add.

I'll post a photo once I find my USB cable....

EDIT: Here we go...and yes I do plan to replace that shockcord with TN.

https://nerull.sourceforge.net/ncbolt.jpg

I don't trust those eyelets, that is how I lost my Minni Magg trying to cert. L1 at NSL at Hearne two years ago.
I use a medium to large eyebolt with washers and nuts. Drill a hole( big enough to put the nut in) about half an inch above the base of the shoulder and get a Dremel with a cutting wheel and slice a cut cenetered on the hole that was drilled( just big enough to put the washer in). I like to make my hole and slice a little bit smaller than the nut and washer so the hole won't be too big. Screw in a nut on the eyebolt all the way until it stops and put a washer over it and install the eyebolt with nut/washer into the hole on the bottom of nose cone(the factory drilled hole, not the hole you made ;-)
You may have to force the 2nd nut in the nose cone with the 2nd washer after it through the hole and slice you made and have someone hold the nose cone upright while you fiddle with the eyebolt and use a screwdriver to align the washer and nut onto the threads. Tighten the eyebolt with the screwdriver and another screwdriver in the side hole holding the nut from turning. Mix some epoxy and pour into the hole and let it rest on the bottom of the cone covering the washer, nut and part of the threads. Let dry, you can pour another batch of epoxy into the hole again and put masking tape over the hole and turn the cone sideways until the tape/ hole is at 6 o clock position and let the epoxy cover the hole that was covered with tape and let dry. Remove tape and the hole is replaced with the dried epoxy. No need for that, I just leave the hole open, in case I need to add weight. My 2 cents.
Mark

OOps, someone gave you my idea. ;-)
Mark

Originally posted by Nerull


Get an eyebolt that fits through the hole in the nosecone (My 4" LOC nosecone came with a hole the same size as the eye bolt that came with a bulkhead).

Cut a hole in the shoulder, big enough to fit a washer and a finger or two through.

Put a washer through the hole in the shoulder, and screw the eyebolt into the nosecone, up through the washer. You may want to use another washer between the eye bolt and the nosecone, but its up to you.

This is the most pain-in-the-arse bit: Try to get a nut onto the eyebolt, and tighten it down. It took several attempts to get this right, but once its done it should give a stronger attachment point than just the eyelet.

https://nerull.sourceforge.net/ncbolt.jpg [/B]

Click to expand...