So, maybe I'll try a three-stager

[Joel Levinson]

How high was "not the altitude we wanted"?

 

[JimJarvis50]

How high was "not the altitude we wanted"?

142K. We might have made 275K. It will take some additional analysis to determine what happened.

Jim

 

[TonyL]

Hi Jim,
so do I recall correctly that you were using Kate2.0 with the pyro board for all your flight events? Any feedback on how that was to work with? Happy with staging, etc? Mine had more packet loss than I expected, but obviously there is no post flight analysis for mine...

br/

Tony

 

[JimJarvis50]

Hi Jim,
so do I recall correctly that you were using Kate2.0 with the pyro board for all your flight events? Any feedback on how that was to work with? Happy with staging, etc? Mine had more packet loss than I expected, but obviously there is no post flight analysis for mine...

br/

Tony

Yes, I was using it for all flight events, except for stage separation, which was done from below. I haven't lined up every event to confirm the timing, but so far as I can tell, Kate 2 did everything correctly. I found it very easy to work with. When it turns out that most flight events will be done via gps, you don't have to think as hard about "how" the altimeter will calculate the various quantities, and the programming is easy. With other altimeters, you have to worry about whether the accelerometer is accurate, how things are filtered, is the altitude spoofed, etc. This is what makes the programming hard. With Kate, it is easy by comparison. I'm not sure this is 100% good, but it is my experience.

Jim

 

[JimJarvis50]

I have posted the flight video from our Balls flight here:

Jim

 

[mpitfield]

Very cool flight. It looks like the rocket was tumbling for the last 20,000ish of flight. Am I interpreting that correctly?

 

[Nytrunner]

Great video!

So what's Tony's secret to getting there first?

 

[tfish]

started a few years ago. I was out looking for my rocket and came across a beautiful carbon fiber rocket. I assumed from the craftsmanship it belonged to some guy named Jarvis. I had seen his stuff on various forums. I went back to camp looking for him to let him know I found his rocket. This was how Jim and I first met. It's gone from that to me putting sticky notes "Tony was here!" on them as I found them..to almost dying getting one of his projects ...to this year. I knew how to drive close to where it was (because I had put about 40 miles on my motorcycle looking for my project out in that area). So, Jim and I hopped in my truck and drove to within about 1/4 mile of it...which is a nice change.






Tony

 

[JimJarvis50]

Very cool flight. It looks like the rocket was tumbling for the last 20,000ish of flight. Am I interpreting that correctly?

My opinion may change over time (with more time and expertise applied), but I believe we had a little lunar coning going on during the sustainer motor burn. Although there is IMU (tilt) data suggesting this coning, the picture at 10:18 into the video is the most compelling evidence. And, the video shows one revolution of the rocket for each coning revolution (thus, "lunar" coning). There are several potential reasons for this, but one consequence is that this motion apparently translated into tumbling rather early in the flight - around 110K I believe, but I haven't verified this precisely. In my 175K flight, tumbling from 140K cost about 10K in altitude. Therefore, I suspect we lost more altitude than that in this flight.

Jim

 

[JimJarvis50]

So, I can share some additional flight data from the on-board Kate file. The first graph shows altitude, velocity and acceleration. The altitude plot shows that the barometric altitude was pretty good up until about 125,000 feet. The gps data are missing in the altitude and velocity plot whenever the velocity was about 1,600 ft/s (which I believe is an ITAR limitation). Based on the inertial values during that period, the velocity reached about Mach 3.7.

The second plot is acceleration, and the plot includes the simulation results based on the burnsim simulations in RasAero II. There is at least some relationship between the predicted and actual acceleration results.

The third plot shows the gps trajectory and the inertial tilt measurements. The gps trajectory at the point when the motor lit was about 9.8 degrees. Since the motor took 5 seconds to come up to pressure, the trajectory was less when the ignition signal was generated. The inertial tilt compares well to the gps trajectory. Since the motor lit at 25,000 feet, the trajectory would have included the drift of the rocket as it entered the jet stream. The inertial data also show the effect of the coning during the sustainer motor burn.

Jim

 

[TonyL]

Hi Jim,
That thing really spun up during the second burn, any theories on it? Also how did your flight do on lost packets? Ours had a big drop out on the way up and reconnected near apogee.

I see the big difference between your predicted motor burns and the actuals. It looks like the classic r=a*P^n model is not sufficient. I'm glad it didn't come apart.

br/

Tony

 

[JimJarvis50]

Hi Jim,
That thing really spun up during the second burn, any theories on it? Also how did your flight do on lost packets? Ours had a big drop out on the way up and reconnected near apogee.

I see the big difference between your predicted motor burns and the actuals. It looks like the classic r=a*P^n model is not sufficient. I'm glad it didn't come apart.

br/

Tony

I don't think the spin up is a bad as it appears in the figure. Around 2 Hz on the average (the initial rate was higher) but definately "lunar" coning from the video. Lots of possible factors, including being quite overstable, uneven ablative, passing through Mach 1 at the start of the sustainer burn, not particularly dynamic balanced - the usual suspects. I think our experience on the packets is similar. I know Vern is looking at it.

Jim

 

[UhClem]

I see the big difference between your predicted motor burns and the actuals. It looks like the classic r=a*P^n model is not sufficient. I'm glad it didn't come apart.

Spin rate is well known to enhance motor burn rate.

 

[Chad]

on the tilt plot, right at launch there's a sharp rise, then drop, then a slowly rising line until sustainer ignition. Is this the rocket coming off the rail and then the fins doing their job and straightening out the rocket?

edit: what figure would indicate spin rate?

 

[TonyL]

Sure looks like plain old erosive burning to me

Jim, I will be doing antenna testing to try to characterize how much 'shadowing' we get from the vehicle body. I have a source for some potentially very nice turnstile antennas for 900MHz, but they don't fit anything smaller than 6 in.

 

[manixFan]

Spin rate is well known to enhance motor burn rate.

From the link: "For composite motors, a spin induced acceleration of at least 10g's is required before appreciable burn rate augmentation results. Is this a concern for spin-stabilized amateur rockets, then? A simple calculation shows that for a motor with a diameter of 4 inches (10 cm), a spin of 420 RPM is required to develop a 10g acceleration normal to the motor axis. Such a high spin rate is well beyond that required for stabilizing, so for amateur rockets, acceleration augmented burn rate is not a concern."

The video does not show such a spin rate.


Tony

 

[jsdemar]

420 RPM is 7Hz which is a fairly typical spin rate for a sounding rocket.

Axial acceleration also increase burn rate and erosivity.

 

[mpitfield]

"lunar" coning

Jim what the heck is "Luna coning"? Google was not my friend on this one.

I have seen, as well as read about, coning, roll pitch coupling, inertia coupling, inertia roll coupling, but "Luna" is a new one!

 

[mikec]

Jim what the heck is "Luna coning"?

https://apps.dtic.mil/dtic/tr/fulltext/u2/1020435.pdf

"Lunar coning is the motion whereby the projectile flies at a constant angle, αα, with
respect to the freestream velocity vector while undergoing a constant angular
rotation, Ω, about a line coincident to the freestream velocity vector passing through
the center of gravity of the projectile."

 

[JimJarvis50]

on the tilt plot, right at launch there's a sharp rise, then drop, then a slowly rising line until sustainer ignition. Is this the rocket coming off the rail and then the fins doing their job and straightening out the rocket?

edit: what figure would indicate spin rate?

I think the sharp rise in the gps data is just bad data. The rise in the inertial tilt might just be a slight weathercocking. I see a little bend in the trajectory in the video.

It appears to me that rate of the coning and the roll of the rocket were at the same frequency. I can tell this from the video (the same "view" out the window repeats each half second). So, the oscillation rate in the tilt graph is also the roll rate. If it just rolled and didn't also cone, then the tilt value would remain constant, in theory. The graph would suggest a constant angle of attack of 3 degrees, but we are not convinced that this is actually what happened.

Jim

 

[mpitfield]

https://apps.dtic.mil/dtic/tr/fulltext/u2/1020435.pdf

"Lunar coning is the motion whereby the projectile flies at a constant angle, αα, with
respect to the freestream velocity vector while undergoing a constant angular
rotation, Ω, about a line coincident to the freestream velocity vector passing through
the center of gravity of the projectile."

thx

 

[manixFan]

Jim what the heck is "Luna coning"? Google was not my friend on this one.

I have seen, as well as read about, coning, roll pitch coupling, inertia coupling, inertia roll coupling, but "Luna" is a new one!

This is my dog Luna, with a cone, i.e., Luna coning:


She's learned a lot from this discussion. Very interesting that the rocket starts tumbling. I remember when I did some research about the Super Loki Dart and it had some of the same issues. Once the atmosphere thins out another means of stabilization becomes necessary. It had a spin rate of about 360-480 RPM.


Tony

 

[OverTheTop]

Hmmm. The collar of shame .

 

[jderimig]

So, the oscillation rate in the tilt graph is also the roll rate. If it just rolled and didn't also cone, then the tilt value would remain constant, in theory. The graph would suggest a constant angle of attack of 3 degrees, but we are not convinced that this is actually what happened.

Jim

The frequency probably is a good estimate of the roll and cone rate, however the amplitude(s) of the tilt are not consistent to your video. Especially in the 3rd regime of the data up to apogee.

The frequency is very very high at sustainer ignition. I can tell from the graph but is it possible that the roll rate exceeded the limit of the gyro there?

 

[JimJarvis50]

The frequency probably is a good estimate of the roll and cone rate, however the amplitude(s) of the tilt are not consistent to your video. Especially in the 3rd regime of the data up to apogee.

The frequency is very very high at sustainer ignition. I can tell from the graph but is it possible that the roll rate exceeded the limit of the gyro there?

Vern can see the roll rate in the data file, and he says it was around 800 degrees/sec (2.2 Hz) until the rocket started slowing down. The gyro range is to 2000 degrees/sec.

What do you mean about the amplitude of the tilt? Just looking at the video, the first time the rocket goes to 90 degrees is at 63 seconds into the flight. That agrees with the inertial tilt. By the way, the speed was still above Mach 2 at that point.

Jim

 

[jderimig]

What do you mean about the amplitude of the tilt? Just looking at the video, the first time the rocket goes to 90 degrees is at 63 seconds into the flight. That agrees with the inertial tilt. By the way, the speed was still above Mach 2 at that point.

Jim

Ok, you are right. Nevermind.

 

[JimJarvis50]

Ok, you are right. Nevermind.

Please keep asking questions. We might give this another try at some point, and it would be nice not to just repeat it.

Here are a couple of GPS plots. Nearly all of the tilt in the flight was in the direction shown (from 90 degrees to these pictures, the flight is nearly vertical). Vern pointed out how little of the flight is actually motor burn (in red).

Jim

 

[0011001100]

Maybe you need to either purposely impart a spin or need larger fins in order to stay stable at the high altitudes? I've not done any of this extreme stuff but am trying to learn and understand it.

 

[Charles_McG]

If I understand the analysis of one of the other high altitude flights (maybe even one of Jim’s) keeping the spin all the way up is an issue because angular momentum naturally transfers to the longest axis. So spin becomes tumble.

The other thing is that there’s no air for the fins to work on. If I understood the post about two up, the rocket went 90 degrees sideways at Mach 2. Not possible in substantial air.

If anything, I’m waiting to see them try a de-spin mechanism.

 

[JimJarvis50]

Maybe you need to either purposely impart a spin or need larger fins in order to stay stable at the high altitudes? I've not done any of this extreme stuff but am trying to learn and understand it.

We considered spinning this rocket. The sustainer fin can could have been made to do that. The reasons that we didn't go that way include the difficulty of spin balancing a rocket, no way to un-spin it, and Kate objected. On the spin balancing, I heard that this was difficult to do. Imagine trying to spin a rocket 400 rpm, measure that it's out of balance and then add weight appropriately to correct it. I don't know how to do that.

One problem with this sustainer is that it is already overstable. With the long motor and Kate in the nose cone, it is hard for it not to be that way. It is possible that being overstable contributed to the coning. So, I have considered trimming the fins to reduce this, but then at some point, the fins being too small could cause coning.

There are some professional ballistics programs that might be helpful to me. I think that is my next step.

Jim