Official Armadillo Q&A thread

Good points all of them. I wonder how hard it would be to split the faring into thirds hinged at the bottom to raise the center of pressure during decent. It would require a fairly forceful deployment but it could include a toggle over of some kind to keep it locked once open.

Well, I am amazed that didn't end up as scrap metal!! Recovering from that off axis event was pretty impressive. As others have said, the oscillation under chute was pretty bad. Would a bigger chute help? Keep the descent speed lower to reduce aero effect causing the oscillation?

I like the idea of a splitting aeroshell though.

I think if the strings connecting the chute to the rocket were longer, then the swings would have been wider, thereby giving greater stability maybe. Also, if they'd gone higher, and let the rocket fall for longer than just a few seconds, then perhaps it might have sorted itself out. Anyway, I'm sure it's a fairly trivial problem compared to the many other issues they've surely encountered during the building of this thing =)

I don't think the length of the rope matters. it is a characteristic frequency of the rocket. Changing the location of the mounting point could fix it. I need to think about it more, but even offsetting it to one side could help.

Direct links to the 3 videos:
video 1
video 2
4 view video

3rd one includes a view of mission control.

@armadillo: It seems Russ needs a third hand (struggling with the radio and the mouse). Wouldn't a a PMR headset and an easy to press 'send' button be a nice addition for Mission control? Or bidirectional radio communication with all team members.

Perhaps it would be more stable if the drogue parachute was smaller and produced less drag, i.e. just enough drag to straighten the rocket out rather than slow it's velocity so abruptly. I suppose when it's used for real though there'll be plenty of time for it to stabilise.

Looking up from nearly underneath, it sure seemed to be coming down fast. They've done it often enough now that they know when to hit the brakes I guess, but it was still a bit unnerving to me.

It seems to me that when the chute first opened, the mod was pretty stable, but that the oscillations got worse after that. Was that the chute dragging the rocket around, or the rocket dragging the chute around? Do they really shut down the engine, or is there some small residual gas flow? Or if it was the chute dragging the rocket around, why would it do so in such a circular fashion? Russ had quite a lot of trouble dragging the mod around in the rocket tug of war, why does it seem less stable now?

Well heck, if John says it's perfect, then it's perfect.

It looked to me like they unfolded the chute while the mod was still traveling(slowly) upwards. That doesn't seem like a good idea.

I was thinking the same thing.

I'm thinking the opposite - the chute is too small, and this means the rocket is traveling too fast, and it decidedly un-aerodynamic underside is causing the oscillation. Slow the speed down and the effect of the drag will reduce (drag is a square of the speed I think?), and hence reduce the oscillation.

Imagine a flag. At slow speeds it doesn't oscillate much, at high speeds it really starts to flag around at high frequencies.

Maybe....

The engine shuts down completely as far as I know (Masten has demonstrated that as well a few days ago (on a VTVL), although of course Armadillo has done in flight relights for quite some time now with the Rocket Racers ).
And that's (part of) the reason for the instability: at low speeds a VTVL gets it's stability ONLY from flight computer precisely pointing the engine(s). Once the engine is off, there is nothing the vehicle can do to keep it's position.



While I'm not sure if the Mod was really still climbing (you could hear them say "apogee" before the chute opened), it can be seen quite clearly, that the engine was still on, when the drogue was deployed.

I agree, that this probably isn't the best idea.


Off Topic: I find it quite amusing, that people all over the world argue on the internet about what Armadillo is doing right or wrong. Most of them (myself included) have no experience with aerodynamics and/or rocket propulsion whatsoever.

"While I'm not sure if the Mod was really still climbing (you could hear them say "apogee" before the chute opened), it can be seen quite clearly, that the engine was still on, when the drogue was deployed."

If I was going to perform this test, I would have done exactly what they did, ensure that the chute was deployed before stopping the engine, and then start the engine immediately before chute release. Just throwing a guess out there, but I bet if the engine didn't start they would have at least had the chute still attached to slow the rocket down to reduce the size of the crash, even though I'm sure it would have still totaled the vehicle.

I have a bit of aero from car racing, but I bet there are a lot of people out there commenting who have more experience than AA on aerodynamics! After all, there are a lot of aerodynamisists around, whilst there are very few rocket scientists.

Whoa, something wrong with the quoting there. That was Marcus writing that, not me. Personally, I find it comforting more than amusing. For sure if all those inexperienced people were to actually start building rockets, rather than talking about them on the Internet, people would get killed...

@JamesHughes: That sounds right. I can also imagine the rough underside of the vehicle having more drag than the smooth upper sections, which would make a slightly tilted rocket be inclined to rotate farther until it was upside down (if I were a proper rocket scientist, I think I'd be saying that the centre of pressure is rather low). Also, that cone may well be heavier than the engines, so that the centre of gravity is high, and then the whole thing will tend to flip upside down. Unless you move the centre of pressure farther upward using a parachute, but the parachute has to be big enough, otherwise it doesn't work. So, they need a bigger parachute and a slower descent.

Of course, from a regulatory and insurance point of view a slower descent may not be desirable, because it increases the potential range the vehicle can travel if it goes out of control. I wonder if they had to get special permission for using a parachute on the rocket...

Would using a streamer instead of a drogue chute help (It works on Estes model rockets)?