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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
 
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

Thanks Bob !

nice insight to the issues.

I want to find out what brand of altimeters need to be calibrated to locals, IF ANY.

I think I might have found some old OOP ones that do not self calibrate.

also, if the altimeter does not record a flight profile, I might add I can't trust the record that was obtained by it, based on what you described much better then I could.

Some records seem like they are 4K feet higher then motors at the time could do.

But, as in the past, I simply could be mistaken :cool:
 
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 :p
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.

As unlikely as this event seems I still don't understand how increasing the pressure in an ebay is going to show a higher altitude. The higher the altitude the lower the barometric pressure so if the ebay is getting pressurized by the ejection charge then the altimeter would actually show a lower altitude due to a higher registered pressure.

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.
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.

Since guessing is so much fun then my "guess" is the apogee event occured in a pocket consisting of lower pressure/air density then the normal environment for the given altitude. This may explain the much higher altitude registered by the altimeter instead of the predicted altitude of the simulation.

These same "air pockets" or turbulence can cause airplanes to rapidly lose altitude and generates the bumpy movements felt by air crews and their passengers during flight. If you've ever experienced extreme turbulence in an airplane it isn't something you'll ever soon forget. :eek:

I would recommend to Nate to actually contact Missileworks and get their views on the subject. I'm very interested in what the manufacturers suggest so if you do contact them then please post their response.

This has been a good rocket science discussion. I like the ideas everyone has come up with, they've provided some interesting brain food.

Andrew
 
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.

The microcontrollers in flight computers do lots of things "at the same time", so the actual sampling rates aren't that great. Most altimeters don't take a huge amount of samples per second because they have to do other things, like decide if lift off has occured, if apogee has occurred, if a charge has to be fired, etc. Most altimeters take data a few hundred samples per second or less. For example, if an altimeter is recording 16 samples per second, it might just be sampling 16 times a second, or it could be oversampling to get extra precision. A x16 oversample with and 8-bit ADC at a recording rate of 16 12-bit samples per second is 256 only 256 samples per second. An oversampling altimeter would probably not be as disturbed by pyroshock as a single shot one. I don;t know for sure, but I'll guess the RRC2 does very little processing of the raw data.

Since guessing is so much fun then my "guess" is the apogee event occured in a pocket consisting of lower pressure/air density then the normal environment for the given altitude. This may explain the much higher altitude registered by the altimeter instead of the predicted altitude of the simulation.

Your guess is wrong. Pressure at any level is simply the weight of the air above it. While the density and temperature of the atmosphere can and does vary with altitude, the pressure always decreases with altitude. What's why barometeric altimeters work.

Weather 101. Cold air at altitude is denser so it sinks. Hot air near the ground is less dense than the air above it so it rises. It is the density/temperature gradient that creates convection currents we call turbulence, not vertical pressure gradients.

Bob
 
Bob,

Any thought the turbulence you've dismissed is responsible for creating a vacuum within the ebay as it crosses over the static ports hence the lower pressure and higher altitude readings of the altimeter at the moment of deployment? This is a known detrimental effect attributed to poorly placed, improperly sized or an inaccurate number of static ports. Often there is a failure of the altimeter to even recognize apogee so it never fires it's drogue charge. I guess the altimeter becomes the Energizer Bunny and it thinks it's just going and going and going. :)

I'm not convinced pyroshock is the cause of the anomaly since it's effects tend more to mechanical disruptions on a minor scale then electrical but I am still open minded.

Might the pyroshock spikes you've mentioned seeing on readouts actually be caused by the inflation of the drogue chute or the full extension of the shock cord after a strong deployment?

Great discussion!

Andrew

edit: By the way thanks for the pressure and weather lecture - I nevr knowed dat stuff befour I logged on dis morning.:)
 
these are all ideas I discussed with my RSO after my launch. admittedly we were perplexed by the enormous readout, and didn't really reach any conclusions.

However, I don't think deployment shock would necessarily cause a higher altitude readout as the RRC2 is barometric. had that altimeter in my rocket contained an accelerometer (which is what I originally planned, but had to scrap because the "control" sucked...) then deployment shock would be a possibility, but I fail to see how a physical shock to the airframe would affect a reading in air density
 
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
 
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

this is very good and interesting info Bob.

I think you have helped me explain some single frame anomolies I have seen in on board video at time of ejection.

I think the CCD/CMOS sensor gets warped and causes things to look very "bent" for only a single frame of video in a 29fps stream.

i.e. I have seen the booster section looked curved end to end for only one single frame while a payload section of a dual deploy ejected. The Camera was located on the ebay of the payload section that contained the violance of ejection.

This does not happen every time, but enough that I have seen it many times.

thanks !
 
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 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
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.

To me it's irrelevant since most modern cheap altimeters have some kind of recording capability. If you're really concerned about the actual altitude you reached, get a recording altimeter, download the data and fit it to a trajectory model. Easy and accurate.

The RRC2 and MAWD are functional equivalent and reliable, and cost about the same, but the MAWD has recording capabilities.

Bob
 
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.
....


Any openings where you work Bob :D
 
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
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.

I understand what you are saying. BUT be cautious on what you do. Covering a wrong componet with foam will cause a failure as well. Ive always belived in giving my electronics some breathing room. So that way Barrow sensors and such can do their jobs.

The reason for the hard mount is just that of the G forces at Take off and those harsh deployment yanks.

If a Part was soft mounted lets say on rubber bushings or the likes how will an Accelaratometer react. I would think it would creat some issues there as it checks for movement and if it is bouncing back and fourt as Acceleration hits then it decles quickly.. well. I think it may go into deployment mode. Just some thoughts anyhow.

I really I cant see where the statment of "All those Altimeter failures" come from as its pretty Rare that ive ever even seen many if any fail that werent completely user error issues over 10 years. Sure it can happen and does. But anything made by human hands can fail. Its not a perfect world that why we have the word warranty in our language. LOL.. Anyhow I would blame more failures on people in use thenon manufactures in the product itself. Just my experince anyhow.
 
the reason it seems like there's tons of altimeter failures is thusly:

when you have a great flight, and you get all your junk back, you tell some people, and you're happy.

when you have a flight that turns into a homemade bunker buster, you tell EVERYONE (!), you post on TRF, you post on ROL, you get a tatoo, and bumpersticker, and call your mom.

there really aren't all that many altimeter failures in hobby rocketry, you just don't hear as much about the successful ones
 
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.

I have been using the same AltAcc (which mounts directly to the airframe) since 1999. It has never failed in flight and the only problem I ever had with it was the ceramic resonator broke as the result of a hard landing when I didn't pack the main parachute correctly.
 
It's clear that 99% of all deployment failures (and that's obviously what we're talking about here) that are not mechanical are due to user error. If you search TRF you might find 10-15 failures that have not definitively been attributed to user error. That's the "all those failures" I was referring to. I didn't mean to imply that there were many failures at all. Just that if there actually are electronics failures, they very well could be attributable to lack of vibration isolation.

I understand what you are saying. BUT be cautious on what you do. Covering a wrong componet with foam will cause a failure as well. Ive always belived in giving my electronics some breathing room. So that way Barrow sensors and such can do their jobs.

Electronics of this sort have no large power handling requirements, so heat buildup should not be a problem. If you cut pressure vent holes in the foam the way I proposed, the barometric sensor should have the what it needs to function properly.

If a Part was soft mounted lets say on rubber bushings or the likes how will an Accelaratometer react. I would think it would creat some issues there as it checks for movement and if it is bouncing back and fourt as Acceleration hits then it decles quickly.. well. I think it may go into deployment mode. Just some thoughts anyhow.

The movements you are talking about must be sub-second, and non-occillatory or very small (one relatively large slow increase in acceleration if we're talking foam, many small bounces back and forth if rubber grommets). If an accelerometer-based altimeter goes from pre-launch to launch to deployment in less than a second, I'd say that module has severe design problems and I wouldn't want to use it anyway. Give me a scenario where you'd want a deployment less than a second after an altimeter has determined a launch.
 
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.
 
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.
Get an adult involved with your group.

Find a rocketry Mentor.

Do not use "regular table sugar" (sucrose) in your formula. It's melting temperature is very close the ignition temperature of 'sugar propellants'!

Tony
 
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.
https://www.apogeerockets.com/Rocket-Kits/Skill-Level-2-Model-Rocket-Kits/Aspire#rocksim
https://www.thrustcurve.org/motors/...&csfmApproved=approved&availability=available
 
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.
Just 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=795696
 
Just for future reference you can go ahead and create a new thread rather than reviving one older than you are :)

Actually he did. On his first day on the forum he started two new threads, and resurrected a 16 year old thread, with the same question.

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.

I am a high school student part of a group that is in the planning stages of building a high power sugar rocket. We are tyring to reach an important milestone, the 10,000 foot mark! Any and all advise would be much appreciated.

My friends and I have assembled a group in our high school to build a high power sugar rocket. We are trying to reach a great milestone, the 10,000 foot mark! Any and all advise will be greatly appreciated!
 
that it probably a better idea 😂
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.
 
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.
My group and I thank you very much for the advise.

We understand what hitting 10K isn't easy and that why we set that goal. We want to put in the hard work it takes to get there. We would absolutly love to hit 10,000 with a motor we made but we also understand that if it comes down to it, we woud much rather use a motor we build to reach a tremendous altiude that we can and later hit that 10,000 foot mark.

The Las Vegas Tripoli club does launches beasically every month and the drive, for me at least is only 30 min to an hour to the launch site. The FAA doesn't care all to much becasue the launches are so often and they basically cleared flight paths from thar area. And geographically speaking, its winds are the perfect direction going away from any solar panel farms and away from the Las Vegas valley.

I will take the luck you have given me and put it towards a hopefully successful build and launch.

Thank you
 
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