The trick for getting rockets out of the ground is not to let them grow so big before harvesting them.
When they get their roots that deep you’re going to have problems every time.
Now personally I’d be too embarrassed to post pictures such as these and to be asking this question.
Having been asked I’d use a posthole digger
and work around the rocket a bit at a time.
I enjoyed your joke about not letting them get too big before harvest, but I gotta admit, the part about how you'd be too embarrassed to post pictures or ask questions like this (implying to me that perhaps I should be as well) got me a bit torqued. My first response was, "Well, I'm glad my desire to learn from others is stronger than my ego, unlike your own", but realized that would be childish (sorry, I still said it, because...well, reasons), and yet in reality your answer is (perhaps unintentionally) the most helpful. Even if I were to try to NOT ascribe intent (maybe you really ARE too embarrassed to admit failure, and hate learning from others), I still wish to highlight the learning potential my situation provides for people in similar scenarios.
I'm not a physicist, but I welcome the insight of any (amateur or otherwise) that care to weigh in, but first, some facts: My EggTimer seems to have survived (it's behaving like it should when fed battery power after recovering from the crash site), and provided an altitude of 2230 feet, with a maximum return velocity of 131 m/s (sorry for the mixed units, it's how my brain works). Kinetic energy is calculated by KE=1/2mV^2, so my 10lb (4.53 kg) rocket dissipated nearly 39kJ upon impact. This impact was stretched over almost 2m, so it's about 34Gs. This is mentioned as a note of how durable a properly mounted EggTimer can be (the fact that it's still working). I would love to have similar data for the EggFinder, but as I said earlier, it's not yet retrieved.
Moving on: The reason the rocket cannot be simply plucked from the ground is that no earth was removed to make room for the rocket- the soil was compressed laterally by the rocket as it entered at high speed. This means that that 39kJ of energy is potential again, and is stored in compression against the circumferential length of my embedded parts. I've already released about 42% of it by digging out 30" of tube and removing the booster and av bay, leaving 16.4KJ of energy remaining compressed on the payload tube and nose cone. Removing the rest the way I have is not as easy!
When digging earth like this, a conical area must be removed, with roughly a 45 degree wall angle (it's crumbly, and readily collapses in on itself, plus the shovel angle increases with each stroke). Given the volume of a right cone is equal to pi*r^2*h/3, I had to remove nearly 6 cubic feet of dirt (36" circle, 30" depth) to free the booster. To continue on in this fashion (to the depth of the nose cone), I would have to remove almost 44 cubic feet of dirt. For the Anglophiles, that's more than 1.6 cubic yards of dirt. With caliche at an estimated 90 lbs per cubic foot, I would have to excavate almost 4000lbs of dirt, requiring a hole with a diameter of 5.5'.
Here are some reality checks though- I was able to dig the first 30" in about an hour- so the dirt I'm dealing with is not as dense or problematic as true caliche. Even so, Digging a 6'x6' hole in the desert is not my idea of a fun time...and this is where you, kind sir (AKA boomtube_mk2), come in: I need not dig out the entire volume, I just need to relieve the remaining 16.4kJ of potential energy. By way of analogy, I'll explain how this will work:
You, Boomtube_mk2 must never have broken a limb by dint of your perfect approach to all things physical, or, if your ego is as fragile as you claim, you hid it from those that could help. Regardless, I'm sure you saw a picture of a limb in a cast at some point. If not, I'll assume you have, and move on. The cast is a rigid body surrounding another, and is intended to provide extracorporeal support to a healing bone. My rocket is the bone, supported by the "cast" that is the earth surrounding (and exerting that 16.4kJ of energy to the surface). When you (or your friend, or the person on TV who was your friend and HAD a cast) had the cast removed, the doctor didn't try to grind the cast away completely, little by little; that would've worked, but would've been a waste of energy and time. Instead, the wise person used a narrow reciprocating blade (so as not to injure the underlying flesh) and sliced the cast lengthwise with a narrow kerf. The majority of the cast remained in place, but the stored energy of the unit has been compromised to the point that simple finger pressure can split the otherwise impenetrable restraint of the form.
Your mention of using a post hold digger triggered the analogy for me, and should solve both problems- with such a device, I will not have to dig a right cone in the earth to reach the needed depth, nor will I have to dig a complete circumference around the restrained tube- I can use the post hold digger's "kerf" to relieve the accumulated pressure, assuming I can dig a parallel and contacting hole adjacent to the payload. Even if it's incomplete, working on a roughly 6x6 hole is far favorable than digging a 70" diameter hole. At a certain depth, that 16.4kJ force will be mitigated enough that a pull sideways will release the force on the rest of the body.
So, Boomtube-mk2- I'm curious what mk1 was- maybe it wasn't so bad, and there were others here that could help you the way you've helped me?
