Yes, the data shows that for this flight, the accel-based apogee was just about right on.
So, this past weekend I had a very interesting occurrence with my Featherweight Parrot V2. I'd post the file, but it's 1.7MB and too big for the forum.
I don't need to see the data file because I have seen this before using other altimeters. The problem is a combination of three things:
1) Altimeter inertial (accelerometer based) deployment algorithm is late or something else is early.
2) Something else causes the apogee event. In your case motor deployment.
3) The altimeter is mounted so that after the apogee event, it has the same orientation as at the pad. Mounting between the fins does this.
What happens in this situation is that after deployment the accelerometer is reading almost exactly 1G but the firmware is subtracting almost exactly 1G from that before the integration step. The result is that the integrated velocity changes very little and can delay the altimeter apogee event a very long time.
Look at the velocity data and you will see a slope change at deployment. If there is an error in the 1G offset then it will be something other than a horizontal line. When the rocket lands there will be another slope change. Now velocity is decreasing and it is only a matter of time till the altimeter fires the charge.
Including a timer as a backup will make sure that the charge fires in the air. Depending on charge location having it go off on the ground could be really bad if the rocket lands in dry grass.
Many altimeter firmware implementations inhibit or don't check for main event unless the apogee event occured.
This could be remedied by an apogee detect override for baro + accel altimeters. If the barometric system detects that an apogee has likely occured then the main altitude event is enabled even if an accel apogee detect was programmed. In this case of an acceleration integration anomoly that prevents an apogee event the main will still fire as the rocket descends through the main programmed altitude.
There is at least one altimeter on the market that incorporates this implementation.
Patelldp was kind enough to email me his FIPa file.
I don't know the Parrot, all I have are 2 Ravens. It looks like all 3 of the e-match outputs are added together in the data into a single channel called 'continuity'. (Do I have that right?)
Also I guess Parrots don't log the battery voltage. So the only way to get a sense of battery voltage is indirectly, by looking at the voltage reported under 'continuity'.
Anyway the 'continuity' shows the highest voltage as only 0.4 (4 tenths of a volt)! Could this be indicative of a severely drained battery?
And the [Altitude (Accel - Ft)] data is really weird. It shows the flight ending at -375,000 feet. Which I somehow suspect isn't actually the case View attachment 122811LOL.
Based on the extremely low voltage reported on 'continuity' I wonder if your battery was nearly dead?
I flew my Raven3 as a passenger on Saturday at a NAR NARHAMS launch at the Mt Airy Maryland Rec Fields. I will post the FIP and see if you can guess what happened.
Dick Moran
NAR 6306L1
Tri 14074L1
A magntic field is not generated by a solid rocket motor when it burns, so the conbustion of the motor will not effect the magnetic switch.
There can be a percent of 2 of ions present in the combustion, but there is no net charge since the number of positive ions equals the number of electron so the net effect is charge neutral. You are confusing what could happen to the ions if a strong magnetic field were present along the axis of the motor. In that case the positive ions would travel in one direction and the electrons would travel in the opposite direction, but that is not the case.
Bob
A magntic field is not generated by a solid rocket motor when it burns, so the conbustion of the motor will not effect the magnetic switch.
There can be a percent of 2 of ions present in the combustion, but there is no net charge since the number of positive ions equals the number of electron so the net effect is charge neutral. You are confusing what could happen to the ions if a strong magnetic field were present along the axis of the motor. In that case the positive ions would travel in one direction and the electrons would travel in the opposite direction, but that is not the case.
Bob
I didn't want to say anything because I didn't know for sure, but there's no reason a solid motor should ever exhibit any non-negligible amount of charge separation and motion of said separated charges.
I made the mistake of using only engine deployment in this GPS radio test. I did not have enough time to install the new Raven3 and the ejection wiring. The 3.5 lb rocket flew sort of nice on a CCI G78-15 but the whole flight from start to finish was 15 seconds. The motor ejection blew .5 sec after "landing". The whole rocket went in just as you see. The Raven3 was still working and the GPS radio had a broken battery wire or it would have still been sending. The only loss was the battery, and the av bay case which had to be cut in half to remove the hardware. I really lucked out. Once the video is cut down I will post on YouTube. The camera survived also. The video shows the whole flight looking at the back of the rocket which was looking down at the beginning and up at the sky through the remainder of the flight. As the rocket hit earth you can see the ejection charge puff out the rear of the rocket .5 seconds later. If the front had not been buried it may have separated the rocket while stuck in the ground.
Dick
A magntic field is not generated by a solid rocket motor when it burns, so the conbustion of the motor will not effect the magnetic switch.
There can be a percent of 2 of ions present in the combustion, but there is no net charge since the number of positive ions equals the number of electron so the net effect is charge neutral. You are confusing what could happen to the ions if a strong magnetic field were present along the axis of the motor. In that case the positive ions would travel in one direction and the electrons would travel in the opposite direction, but that is not the case.
Bob
I know Adrian navigates this thread once in a while, so I would like to repost a question that was asked in the middle of another thread:
"Now, this issue is something a little more interesting. I am not fully up to snuff on this theory, actually not up to snuff at all, so I will mention it and hope that the educated individuals make themselves known!
From what I understand, a magnetic field is generated by a rocket motor as it burns. Strength is determined by the amount of mass flowing through the motor (I think) and it becomes more severe as motor size increases.
I think that I recall Adrian of Featherweight state that the Delta that they flew a few years ago actually experienced toggling of the magnetic switches as a result of this phenomenon.
Butalane, Daveyfire, MClark, and Adrian will have more knowledge on the subject."
In my particular situation, I am using 2 Ravens, each mounted on the Power Perch. They are located around the motor mount tube, hence pretty close to the motor. Is this a real issue? Should I consider using a different approach, and is there a way to use the Power Perch with an external switch instead of the magnetic switch?
The thread is located here
Do a search on MHD thrusters (magnetic hydrodynamic thrusters)Funny you should mention this. It's something I've always wanted to try - for no good reason. Like... would there be any net change in the direction of thrust...? Would one propellant vector one way and another anther way? Depends on the relative masses of the +/- species.
Do a search on MHD thrusters (magnetic hydrodynamic thrusters)
Also found 1 reference on enhancenent of burnrate of propellant in a strong magnetic field. Didn't read article (journal) but I'm skeptical it would be practical.
Bob
Yes a 38mm CSI. I am used to flying with an H or I motor at our MDRA field in Price MD on the Eastern Shore. There I use my Raven 3 to fire charges. This may be the 1st time I have ever used motor ejection on a G and it was because the field limit is a G. Anyway I do not normally use motor ejection so I did not invest in the "tool" used to shave down the delay that Animal Motor works sells. I had made some changes to my av bay to lighten it up and ran out of time to wire up the Apogee and Main charges. Hind sight is 20x20 and it was a learning lesson for me. I have flown about 12 or so HPR flights and this is the first real failure. I may do the sim next time that I need to before using motor ejection.
Dick Moran
NAR 6306L1
Tri 14074L1
USAF [4yr2m1d]
Here are a few interesting ones
Beautiful flight on the Space Cowboy; very clean. Looks like it temporarily got into a spin with the drogue on the way down at 7000 feet.
Do you know what caused the breakup of the Mega DarkStar at 16,000 feet? Since it had already slowed down and I don't see anything like fin flutter before that, my guess is that you had a premature separation due to differential pressure. The sudden decrease in pressure during the event would be consistent with that. Were all of your sections shear-pinned?
We didn't see any problem like that with the Mega. The main came out at apogee, but that was all. All sections were bolted together except the nose section, it was pinned.
This is why I like it when you read these files. You really have a better understanding of them. I wish you would "diagnose" all of theses and give a little incite.
Enter your email address to join: