high speed and couplers

From people, video's and shreds I have seen at the launches, when it is a fast rocket it seems it is either the fins or the coupler that fails. My fins are very sleek and bolted into the ring so no worries there. What worries me is the couplers. The rocket is 3" diameter, about 80"s long, K650 or K570 first flight. See my building thread. Should go 900MPH if the wind is nice. So I have on coupler that connects the lower fin section to a tube that holds the drogue bay, this will be connected with 6-8 small plastic rivets, I want it removable so if it were to zipper or dent it could be replaced, it is a 3" coupler, I also have 3"s of FWFG coupler that holds the drogue in, this parts worries me the most because it is an actual deployment section and cant be held down with 8 rivets, it will been stug fitted and have 3 2-56 nylon shear pins. Then the upper 3"s of the FWFG alt bay is attached to the main chutes body tube, with 6-8 small plastic rivets. The nose cone will have three 2-56 nylon shear pins but I am not as worried about it. So what do you think? Is 8 plastic rivets enough to hold it in? What about for the drogue deployment section, is 3 2-56 shear pins enough? BTW, the lower coupler and all body tubes are phenolic, the coupler is as I stated FWFG (filament wound fibergalss). I have never flown into this speed regien with larger rockets so please, any helpful hints would be great... from what it seems, you want all sliding parts to have a tight fit and some sort of other device, either a shear pin or rivet, to hold it in there. Will I have any problems shearing the 2-56 nylon screws with a tight coupler as well? Normally when I use shear pins I have a loose fit with the body tube... guess some ground testing will answer that question.

Hi guy.....you only need the last inch....closest to the upper airframe to be "tight"...the remaining part...going into the fincan should be snug...that last inch will prevent any flex in the airframe during mach transition....you have plenty shearpins....they just keep the airframes from drifting apart during the coast phase of flight....when I say tight I mean just tight enough....you can hold the rocket by the nosecone and shake it .....having nothing come loose....anything more is overkill, and could jeoperdize deployment.....I have similar rocket only 4 rivets holding sections together .....rather than evenly spaced around rocket....they are 2 stacked an inch apart on one side and 2 stacked an inch apart 180degrees on opposite side of rocket.....I think you have more than enough....this rocket has flown successfully on a k550.... ,it's a Wildmanrocket.....check into one they are lifetime gauranteed against shredding! www.wildmanrocketry.com don't know how he does it...... witnessed a drag race where they used k-700's...but I chickened out....2 0f the 3 were nver found and the one that was had a tracker in it....found about 3.5 miles from launch.....even though it was dual deploy....so based on this if you put yours together right you'll be ok on the flight.... it's just finding it!

It is simmed, with heavy winds no more then 1.3 miles of drift. But of only the first inch is tight then the other two inches could wobble, wouldnt I want the top and bottom of all couplers tight, so that they dont wobble at all?

You misunderstand.....you want that last inch tight...this prevents any shifting under thrust.....the rest of the coupler should be snug enough that there is no wobble....but not snug as to make it difficult for seperation....remember you have shearpins....so your only concern is gettig the fit just so...if you do it this way...there will be no problems....tight means no play...not hard to seperate....I don't know if you have much room in your drogue bay....but here is a nifty little trick old timer's use....back before the days of trackers.....get some chalk line powder.....the stuff carpenters use in their little box the string comes out of to snap lines when marking wall's etc....comes in different sizes, up to gallon jugs at the usuall places....[home depot etc.].....red is the easiest to see....put as much as you can fit in the bay....make a pouch out of paper towel fill it up put on top of every thing else in bay......the amount equivlant to filling a coffee cup, will give you a cloud somewhere between 8-10 in diam and be quite visable on a clear day......at least you will know where it was at apogee..there is also a company called magic chalk...they make a flourescent orange which is really visable just for this purpose.... www.thortools.com/rockets.html ...chck it out, cheap way to see you apogee

Meant 8-10 feet not inches.......don't know for sure if they are the ones who sell the flour. orange....but as you can see from their site it works