Aeroelastic loads cause vibrations in the airframe which couple with the aerodynamic pressure loads and inertial loads created by high thrust motors to create a buckling failure in a minimum diameter airframe at the top of the motor casing which acts as a stress concentrator. The failure occurs with the top of the rocket folding over and being ripped off by aerodynamic forces.
Airframe column buckling failure is due to high velocity dynamic pressure loading and/or high acceleration inertial loading of a vibrating airframe and is due to a lack of airframe stiffness, not a high angle of attack. It is prevented by stiffening the airframe by inserting a full length coupler inside the airframe to stiffen it, or by wrapping the airframe with FG or carbon.
Bob
That is true, but much more common with paper or LOC tubing. It is not as common with Blue Tube or Magna Frame.
I am no where near as eloquent as Bob nor due I have his knowledge or education, but I do have years of experience, seeing most of this stuff happening & understanding it....all for the wrong reasons...Lol but learning from them.
Us old timers call this...... "finding the speed of paper" meaning that speed at which it will go no further.
Several years ago a couple of my buddies tried an experiment to prove this: [yeah Mike this means you & JB!]
They had a contest to see who could break Mach, closest to the ground. [before Warp or V-max]
Built a rocket called "Shred Me" and began to stuff various motor in it starting with K-550's then reds & blues.
Hit the wall with the K-1100 blue thunder. Got to mach around 1000ft [If memory serves] but shred me imploded.
self destructed, other configurations were built, all paper or phenolic, double coupled, double walled, etc.
But after Shred Me 1 and finally Shred Me 2 [or 3?] no paper rocket could get them past the realm of a brute K-1100 [or might have been the red 1275?] They had G-whiz on board for data, any how after the last flight, which I was standing under, when it imploded at 700ft, and rained down all the debris from a spectacular shred, nothing but small pieces.
We all had a good laugh & they finally decided that after many attempts with different configurations........ we
"found the speed of paper".....
Many others have tried before & since....now there is Magna & bluetube....so the bar has been raised a bit....BUT without any re-enforcement......you too will find the speed of paper/fin flutter. Now you know "the rest of the story" & why I suggested a smaller K before the L due to seeing 2 of these find the "speed of paper" with L's un re-enforced.
Once again good luck with your experiment and "Shred Me 4"...Lol
I hope it survives....really I do.
PS Bob.... I was there and remember the Boris flight/posts AND learned a lesson or 2 from that also!