Debugging Two-stage Flight at MHM – The Twins

[slipstick]

I made a vacuum chamber tonight, to test the rocket controllers, using a 2-1/2 gallon “Montana” Jar from Target $19.95. After modifying the top, which has a seal in it, I connected it to my little 1.5hp shop-vac and was able to suck the insides down to an altitude of about 3200 feet elevation, indicated by a common dashboard car altimeter. A 3.25hp vac brought it to 4000 ft, but it was akward to use.

I then tested the RRC2X and RRc2 Mini, still mounted in the avbay, with 12V LEDs from Radio Shack, and they both read within 150 feet of each other, 3280 and 3165. When I let off the vacuum before 12 seconds, which is what I programmed mach delay to be, the apogee charge on the RRC2X went off only after the altimeter was less than 800 feet. I believe that is by design. However, the RRC2-mini’s apogee went off as soon as apogee was detected, when I turned off the shop-vac. That wasn’t right – I think.

I took the avbay apart and rechecked my settings on the RRC2-mini and I think its possible that there was no mach delay set. I was getting a long series of 10 beeps with a double chirp continuosly on that set point menu. I reset it to 12 seconds and put it back in the jar for another test.

Now when the vacumm is applied for less than 12 seconds, both of the apogee charges will not fire until the altimeter reads less than 1000 feet. The main charges fire immediatley after. If I wait more than 12 seconds, then the apogee charges fire as soon as I flip the switch off on the shop-vac. Now they are acting the same.

Root Cause: Pilot Error The transition through Mach created a reversal in pressure and because the mach delay was not set, the RRC2-mini decided it was at apogee and fired the drogue charge. This is what caused the separation during the boost of the sustainer at high speed which created excessive forces on the shock cord system, causing the shear of the cord and the loss of fin can. 😳

Good news: The rest of the design was OK. There is something to be said for the simplicity of the RRC2X over the mini. And…I can now functionally test my altimeters before all future flights. Yay! 😀 (anyone is welcome to come over and use my set up – beer is in the fridge). 😉

Adrian [and Jim A. if you happen to read this]. Do you concurr with my findings?

[new2hprParticipant]

Give me DIP switches or jumper blocks any day!

Ken

[MikeSModerator]

I want Slipstick on My side. 😆

[AdrianParticipant]

Adrian [and Jim A. if you happen to read this]. Do you concur with my findings?

Yep, I think you nailed it. Good sleuthing, Mike. Any luck finding the fin can yet?

[muleParticipant]

Mike got sick on sat and I pulled a newbie stunt and didn’t cross the fence about 1.2 mi to the west. 😳 So no luck on my trek.

[slipstick]

Joe Hinton also gave it a good try on Friday. I’d like to thank Both Joe and Greg for taking the time and putting forth the effort in looking for the fin can. I think (according to Art) that its at least 2-3 miles away.

[muleParticipant]

Since I don’t have rocksim figured out yet, I have to ask this.

Can you sim the sustainer and see if it would have been stable? Is there a possibility that it went squirrelly after we lost sight of it?

I talked to Jeremiah and we both agreed that what we saw was the top half after the separation. So, all that tumbling talk I said earlier was false. The pictures you posted cleared up what we saw, they are worth their weight in Gold…..

Where did you post that landowner map? Someone told me about it, but can’t seem to find it.

[Jeremiah Johnson]

I believe that this is the map referenced.

This thread has some discussion about the map and a suggestion that we start tracking landings.

[slipstick]

Can you sim the sustainer and see if it would have been stable? Is there a possibility that it went squirrelly after we lost sight of it?

Rock sim says it would have been unstable (-8 margin), but it may have entered into a flat spin see the below photo and the next post – very revealing sequence of events from Ray’s Camera, that I zoomed in on and played around with the contrast.

[slipstick]

Here’s a flight sequence, shows separation and Fin can coasting (possiby – I hope – a flat spin in free fall) afterwards – scroll away!!

[Author]

Posts