Redundant blue ravens in a 29mm av-bay

[Adrian A]

For my recent testing, I rebuilt my 29mm test rocket to use 2 Blue Ravens in a redundant configuration:



To do it, I sanded down the edges of one of the 29mm active bulkheads so that it can go in the middle position within a coupler, rather than clamping around a coupler like the other 2 bulkheads do. I used pairs of small pattern nuts on each side so they connect the middle bulkhead electrically to the threaded rods.

The parallel "wiring" of the threaded rods is a little unusual and I had to give it some thought to convince myself it would work. The Apo+ rod is in common with the + of each battery, but the Gnd and battery(-) of each set is isolated. If either Blue Raven turns its Apo switch, current will flow from its own battery through the Arm+ rod, through the apo ematch, through the Apo rod, and then into the Blue Raven where the switch connects it to ground.

This is going to fly tomorrow on an H410 Vmax. The sims have it at 120 Gs, but when I flew this 2 weeks ago the burn time was longer than advertised and the peak Gs were around 85, except for one spike just over 100. I'm guessing the longer burn time might be caused by the very cold temperature of the launch (around 5-10F). Tomorrow I'll keep the motor warm until just before launch and we'll see if I can get a flight with over 100 Gs acceleration.

Here's the rocket it's going into, named Shot3:


It has BlueTube forward section and scratch carbon aft section. The av-bay sits in the bottom 4 inches of the forward section.

 

[Adrian A]

It had 80 Gs and lost a fin somewhere in the way to about 7500 feet apogee. The tower fell over after the rocket left. Both Blue Ravens recorded data which I’m downloading now.

 

[Adrian A]

Slow mo video of liftoff
View attachment IMG_0222.MOV

 

[alexzogh]

Was that really slow motion??

Who would have thought you would need tip-to-tip lamination on a 29mm rocket.

 

[A-ron]

That is by far the cleanest avbay setup I've ever seen, not a single wire in sight! Especially amazing is the dual-redundancy in a 29mm coupler tube. All it needs now is some 3D-printed retainers to replace the hand-crafted prototypes.

Thanks for sharing the launch video. Would be nice to see your Shot3 rehabilitated and flown on something a little less spicy next time. With the H410, blink and you'll miss it. And lose a fin, apparently.

 

[Adrian A]

Was that really slow motion??

Who would have thought you would need tip-to-tip lamination on a 29mm rocket.

It was on my phone, but not after I uploaded it.

Looking at the data there's no sign that the fin came off before apogee. I wonder if something weird happened to it during one of the deployments, like it collided with the upper section or something.

 

[A-ron]

Does your Shot3 have a drogue of some kind? Can't see one in the landing photo.

I imagine that an impact strong enough to break a carbon composite fin would have left a mark on the culprit.

 

[Adrian A]

Does your Shot3 have a drogue of some kind? Can't see one in the landing photo.

I imagine that an impact strong enough to break a carbon composite fin would have left a mark on the culprit.

I’ve always gone drogueless. I just looked at the upper tube and the nosecone, and there aren't any marks, so this is still mysterious.

 

[A-ron]

I’ve always gone drogueless. I just looked at the upper tube and the nosecone, and there aren't any marks, so this is still mysterious.

Good thing there aren't too many culprits to consider while solving this mystery. Very interested in learning what caused the missing fin for educational purposes. Might be worth checking the recovery harness too.

I once contemplated a drogueless design for my first few dual-deploy rockets because of the simplicity and space/weight savings, but after reading several posts on TRF, I ultimately decided against it for one simple reason: a lack of control. It seems that having a properly sized/positioned drogue will help prevent rocket sections from colliding after separation, which is just one plausible explanation for the missing fin.

 

[manixFan]

It was on my phone, but not after I uploaded it.

Looking at the data there's no sign that the fin came off before apogee. I wonder if something weird happened to it during one of the deployments, like it collided with the upper section or something.

I had some images of a fin being torn off by a main deployment - as the parts separated the shock cord looped around a fin, and when the chute inflated quickly it basically yanked the fin right off. It was a PML Lil Lunar Express, which has huge fins, but I was still very surprised when it happened. It was a windy day and it weathercocked quite a bit so it had a lot of horizontal speed. In your case since your rocket was drogueless, my guess is your descent rate when the main deployed may have been high enough to do something similar. If the shock cord doesn't have any additional flights on it, you might closely inspect it for damage from it grabbing the fin.

On the other hand, if you've already figured out the cause, maybe give us an update for future reference.


Tony

 

[Adrian A]

I had some images of a fin being torn off by a main deployment - as the parts separated the shock cord looped around a fin, and when the chute inflated quickly it basically yanked the fin right off. It was a PML Lil Lunar Express, which has huge fins, but I was still very surprised when it happened. It was a windy day and it weathercocked quite a bit so it had a lot of horizontal speed. In your case since your rocket was drogueless, my guess is your descent rate when the main deployed may have been high enough to do something similar. If the shock cord doesn't have any additional flights on it, you might closely inspect it for damage from it grabbing the fin.

On the other hand, if you've already figured out the cause, maybe give us an update for future reference.


Tony

That's a real possibility. I still don't know what the cause was. The shock cord has been used before and I didn't see anything obvious on it. I may take another look at the data. I think I remember seeing a relatively high-G, high-rate bit after the apogee deployment that might have been an impact.