blackbrandt
That Darn College Student
- Joined
- Mar 18, 2012
- Messages
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Interesting. I was using the 1S based off of testing I've done in the past, using a 1S.
Interesting, as I'm planning on running the same combo as you and Matt. Perhaps it would be a good idea to run the RRC2+ as primary for the drogue, and program the -3 for a longer delay after apogee than the 2+'s one-second option.
This was my instinct as well (that horizontal velocity caused a stressful drogue deployment), but see my post earlier - his nose cone was only 4lbs, so assuming the shear pins weren't damaged and were all engaged (vs some having a looser hole), the rocket would have had to be moving at 300fps or more horizontally to shear the nose cone pins with a drogue that lowers the rocket at 50fps, and Matt was flying drogueless so it doesn't seem to be explainable by horizontal velocity.Matt,
Nice to meet you and cool boost, man! Sorry the big bird is missing; I'm confident it will turn up over time. I'll begin wading through photos today to see if I got a shot of the liftoff. If it's the flight I'm thinking it was, I remember watching for an apogee event, seeing a puff of powder smoke, noting it was apart, then the main blossoming a few seconds later....it appeared that the main "shook loose" following the apogee event. IE: the main charge did not deploy the main at apogee.
Based upon weather conditions, etc., I'd bet a nickel that the three #4-40 let go at apogee. Most rockets were headed upwind at a pretty good clip due to the winds...I too suspect that upper winds were 50+mph. For reference, my 7.5" Patriot that flew earlier in the day (calmer) with a very reefed drogue drifted 1.13 miles downwind after arcing heavily upwind and deploying as intended from 8175' up. It was definitely notably windy up there! Forces involved with a speedy horizontal deployment are significantly greater than those of a calm day where the bird really slows down before arcing over.
Note, I have #6-32 and even some mega #8-32 pins for certain big honkin' cones. (But I did use *only* four #4-40 nylon screws on the 7.5" Pat on Saturday and it worked well).
-Eric-
I definitely did have the shear pins in the nose cone. See below.
Agree 100% about pictures of the landing. Saved me twice this weekend. However, Matt's rocket was probably 2 - 3 miles away when it landed, and a smart phone camera isn't going to cut it. Without a really long lens, it won't be much good.
I wish I had been there to snap pics. I was out recovering when Matt launched. We saw it drift over, but did not see where it went.
And that's something that will only be determined if I can recover the rocket.Good deal! Now that still leaves whether or not they were adequate or if the drogue cord snagged. Unfortunately, I don't think you'll get answers to those questions.
Dave has a nice camera and camera skills (said in Napoleon Dynamite's voice). You don't need a long range lens, just a series of pictures where you can make out the rocket. A decent SLR with short lens at full zoom will probably capture a rocket even that far out.
The shear pin holes were slightly on the loose side. However, we did have a piece of tape over the heads to ensure that they stayed in, as well as twisting the nose cone slightly to lock everything in place.Shear pin holes were snug right? No abiilty of the nose cone to move before engaging them and all pins would have engaged at the same time right?
This thread is making me think I should confirm with a real-life test my calculation that on my L3 build my pins won't shear until ~85lbs.
PS...you can also (per one of Dave's other posts here or in one of the other threads about this rocket) do some math and count pixels to figure out how far out it was.
I would guess a decent amount? I have a knife that can cut an orange in two with no downward force from me other than the weight of the knife. A plastic knife, even if weighted to the same weight, not so much I believe (but someone else I'm sure can speak more authoratively on this!) that the shear pin strength calculations assume a true shear vs a cut with a blade.Each 4-40 should hold 50-76 lbs. My plan calls for 3. I do have cutting plates in place as well. I wonder how much they reduce the strength of the pins?
Here is my guess.
Wind data suggests wind direction was 320 - 330. I drew the line at 325 degrees from the away cell. Length is 4 miles. If you have better data on actual upper level wind direction let me know and I will redraw the line.
View attachment 317023
I am beginning to question this premise.
I have two rockets configured this way, and I keep having issues with the main (RRC3) and the back up (RRC2) firing at about the same time (with the RRC2 set with the delay). I have confirmed that it's NOT because the charges are interacting with each other and ripple firing. This is in 2 different rockets with 2 different sets of computers. I've had it happen twice on each rocket.
The first time it happened at about 3500 feet on each. After re-checking my math and again doing ground tests, I flew them again on motors to go about 1800 feet to make it easier to see. Sure enough, same darn thing, both ripple fired.
Don't rule it out just because it didn't happen on the ground (you did ground test your main charges with the back ups in place to rule out a ripple fire potential?) that it won't happen in flight. Mine NEVER failed on the ground in every ground test that I did, but BOTH rockets failed in flight BOTH times.
Since moving to only one altimeter in each rocket, they've flown 100%.
I'm thoroughly convinced that the sense of the RRC2 and RRC3 are so close that the delay set up for back up just hasn't worked for me. If I were to NEED to guarantee the back up, I would use 2 of the very same computer.
Matt, best I can do to help, which isn't much. Here is about what I saw. Anybody's guess. The large circle is a GUESS, not based on anything other than the direction of travel.
View attachment 317021
I was with John when we saw it. I wish I would have stayed with it. We were a little further north in the field that the me circle in the pic. Based on what I saw the arrow in the picture should be shifted up to the 313 marker right about it. That was consistent with the area I pointed out to you Friday afternoon. At that point we turned away and it was still between 2,000 and 3,000 ft AGL. Seeing the grid and going off what I saw I would have pegged the search radius right around mission branch road along that line. You didn't go back that far did you?
Mason Branch is one of those creeks, just FYI.
I suspect that the main deployed at apogee due to insufficient shear pin retention on the nose. On our big rocket (payload 36"x12.625") we used six 4-40 pins that were all tightly threaded in. We also used about half (4 grams of FFFF) the ejection charge. Even a little slop (it sounds like there was some) makes it very much easier to break the pins as well.
If there is slop in the shear pin hole the pin has a good chance of entering an elastic deformation state. If it deforms it can take 30-40% more energy to finally shear
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