Originally posted by bobkrech
I did a couple of quick sims based on Nate's description, and I have to say the sim altitude is probably correct and the RRC2 altitude isn't.
The only plausible explanation is that Nate's RRC2 was digitizing at the moment when the pyroshock spike passed through the e-bay and the MEMS pressure sensor and the RRC2 mistaken logged it as the peak altitude.
The RRC2 is a basic barometric altimeter with dual deployment. It's not very smart and it doesn't record a flight profile like the Perfectflite MAWD which is functionally similar in all other aspects. Pyroshock spikes are almost always observed in high resolution altimeters. There's no way to verify this error was due to the pyroshock without a flight profile, but any other aerodynamic or deployment phenomon would result in a lower altitude reading, not a higher one. (The one exception to the above statement would be if an inadequate mach delay was used and a shock wave or a transonic negative pressure fluctuation crossed the static port and triggered the altimeter prematurely. At or near Mach, this results in a shread, which is an obviously different senerio than Nate's flight.)
As a side note, it is common that the altitude reported from the altimeter is different than the altitude derived from an analysis of the recorded flight profile in a PC. The reason for this is that most flight computers use a lookup table to report the altitude which is only an approximation due to the limited math capability of the flight computer. If you have a recording altimeter, a post flight computer analysis of the flight profile will usually give a different, and more accurate altitude.
Bob
OK, I think I understand what your saying. The apogee ejection charge ignites on a rocket moving in a normal forward flight pattern and the pressure of the charge got into the ebay through the static vent holes. I'll assume the static vent holes are properly located forward of the drogue compartment and ahead of the discharged pressure that's moving away from the ebay at anywhere from 10 to 30 mph.Originally posted by Nate
Well, the altimeter bay is sealed off, but you DO have vent holes drilled yes? I don't really know anything more about it, as my flight was the first time I had heard about it too. I know it has something to do with the pressure created by the deployment charges, but I can't give much more detail than that, hopefully somebody else can chime in. DenverDoc was the first one to tell me about this anomally after my flight, it seemed pretty likely as I was pretty sure my 10lb rocket didn't,
a) get 14K on a K motor, or b) overshoot the simulations by nearly a mile.it must happen, it makes sense to happen, I just don't know why
Good guess but it seems with the huge number of samples taken by the flight computer during each second of the flight this anomaly would occur so often it would be routine and everyone would experience it or at least know of someone that it happened to.Originally posted by bobkretch
The only plausible explanation is that Nate's RRC2 was digitizing at the moment when the pyroshock spike passed through the e-bay and the MEMS pressure sensor and the RRC2 mistaken logged it as the peak altitude.
Originally posted by bobkrech
A sensing element in MEMS pressure sensor is simply a thin silicon diaphragm over a sealed cavity with micro strain gauges whose resistance change when they bend. As the pressure changes, the curvature of the diaphragm changes and so does the resistance of the strain gauges. When a deployment charges go off, a weak shock wave or strong acoustic wave is generated in the rocket and it propagates through the structure and anything attached to it. This wave travels away from the charge and tries to accelerate mass in that direction. The diaphragm is light and will deflect slightly. If the altimeter happens to take a reading during this very short deflection period, the reading will be in error. How large an error depends on orientation, mounting method and a lot of other factors. If the altimeter is an oversampleing unit, the one bad datapoint is averaged out, but in an altimeter that doesn't average you will observe the error unaltered.
An acoustic wave in air travels travels about 0.001" per microsecond. It usually a bit higher in a solid, but when consider that the actual pressure sensing element is 0.01"-0.02"wide, the deflection occurs in a few tens of microseconds, and is quickly damped out. The sampling time for the ADC in the computer is in the 1-10 us range, so the probability of catching the pyroshock on any give flight on a simple altimeter is low. If your altimeter was sampling at 10 Hz and had a 10 us aperture time, is actually only taking data 0.01% of the time so 99.99% of the time you wouldn't see the pyroshock. Sampling at a higher rate, or increasing the aperture time, or lengthening the shock time would increase the probability, but even if these factors by 100x to 1000X the probablility would only increase to 1%-10%.
Again, the actual probability of interference depends on the electronics used, but just because the probability is low, it doesn't mean that you'll never see it. It just may be your lucky, or unlucky day.
Bob
Maybe, but it's not assured. I've mounted AED R-DAS altimeters to survive 20KG gun launches and 4 KG impacts with the ground. You get big spikes under those situations, but who cares, you have the data traces.Originally posted by agrippo
Bob,
Would cushioning the attachment point of the altimeter to the sled dampen or prevent the oscillations of pyroshock? One preventive measure may be to slip rubber washers between the attachment nuts holding the retaining screws of the altimeter at the sled interface.
Thanks,
Andrew
Originally posted by bobkrech
... I've mounted AED R-DAS altimeters to survive 20KG gun launches and 4 KG impacts with the ground. You get big spikes under those situations, but who cares, you have the data traces.
....
Originally posted by RickVB
Great discussion. I've often wondered since I got involved in HPR why rocketry electronics always seem to be hard mounted. I've been flying R/C planes for many years, and R/C electronics are never hard mounted. Even servos are mounted with rubber grommets on the screws. Radios, battery packs, engine controls, etc. are usually wrapped in foam and rubber banded/velcro taped/loose zip tied to a solid airframe component. Even with all this, regular inspection and testing is required because motor vibration eventually causes all manner of damage.
I realize that constant motor vibration is a more severe strain on electronic components than smoother high-G takeoffs and single shocks like deployments and landings, but the standard practices in HPR still don't make sense to me. They might go a long way towards explaining all those unexplained altimeter failures I hear about.
I hard mounted my L2 cert flight altimeters so as not to cause controversy in those circumstances, but from now on I plan to cut a foam insert that fits tightly into the ebay, with pressure vent holes cut in it to hold the altimeter and battery.
Originally posted by RickVB
I realize that constant motor vibration is a more severe strain on electronic components than smoother high-G takeoffs and single shocks like deployments and landings, but the standard practices in HPR still don't make sense to me. They might go a long way towards explaining all those unexplained altimeter failures I hear about.
Get an adult involved with your group.My friends and I have assembled a group in our high school with planning to build a high power sugar rocket. We have some expereince in medium power rocketry and trying to now reach, a great mile stone in rocketry, the 10,000 feet mark. Any and all advise to be given it will be greatly appreciated.
Work up an Apogee Aspire sim w/ the various non hazmat G's. Consider how you'll track and retrieve it.My friends and I have assembled a group in our high school with planning to build a high power sugar rocket. We have some expereince in medium power rocketry and trying to now reach, a great mile stone in rocketry, the 10,000 feet mark. Any and all advise to be given it will be greatly appreciated.
Thank you for the advise.Work up an Apogee Aspire sim w/ the various non hazmat G's. Consider how you'll track and retrieve it.
https://www.apogeerockets.com/Rocket-Kits/Skill-Level-2-Model-Rocket-Kits/Aspire#rocksim
https://www.thrustcurve.org/motors/...&csfmApproved=approved&availability=available
Just for future reference you can go ahead and create a new thread rather than reviving one older than you areMy friends and I have assembled a group in our high school with planning to build a high power sugar rocket. We have some expereince in medium power rocketry and trying to now reach, a great mile stone in rocketry, the 10,000 feet mark. Any and all advise to be given it will be greatly appreciated.
Just for future reference you can go ahead and create a new thread rather than reviving one older than you are
that it probably a better ideaJust for future reference you can go ahead and create a new thread rather than reviving one older than you are
Look for a Tripoly Prefecture near you and ask them about a mentor, https://www.tripoli.org/content.aspx?page_id=225&club_id=79
I'm hoping that with the responses you've gotten on your threads, you have come to understand that hitting +10,000 ft. isn't as easy as it may seem.that it probably a better idea
My group and I thank you very much for the advise.I'm hoping that with the responses you've gotten on your threads, you have come to understand that hitting +10,000 ft. isn't as easy as it may seem.
I started with MPR in 2003, L1 in 2007, L2 in 2009, L3 in 2015. My first flight over 10,000 feet was in 2022. Now I fly on the east coast so getting to a launch site that has a COA to allow you to fly that high is an issue and getting it back in the farm fields, woods, swamps, neighborhoods, etc. around most launch sites can a problem too.
You should have a much easier time finding an acceptable launch site being in the Las Vegas area, but your travel time will probably be much longer.
What won't change is the challenge of getting a rocket over 10,000 ft.
A minimum diameter 29mm rocket with a Pro29 - 6G motor sims to about 9500 ft. With a very light, strong, high tech build, you might get there with that.
A minimum diameter 38mm rocket can get you past 10K pretty easily, but probably requires a L2 APCP motor. I'm not sure about a sugar motor in that size.
I think it's time you decide what your goal is, just hitting 10,000 ft, or doing it on a motor you made? Then you need to decide if you want to make your motor from APCP or sugar.
In either case, get a TRA mentor. You can reach your goal, you will just need some help along he way.
Good Luck.
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