98mm Min Dia L3 Build

[CarVac]

I must admit that I have been toying around with the idea of using metal brackets in addition to the large carbon reinforced fillets and possible t2t. However I am not totally convinced to there usefulness. From my quick thoughts, it seems that these brackets (under the large fillets) are not under any load during the flight and therefore are extra unneeded mass. Now if the fillets fail then the brackets are under load. I think at this point in the flight the forces will be so strong that the brackets will be useless. This thought has kept me from wanting to use them. Any thoughts here guys?

It seems brackets may increase the pull strength but not prevent flutter (since that is dependent on the natural resonance of the fin material or mixtures there of). I do not think flutter will be an issue and I am more concerned with the adhesion strength of the fillets.

What you have to take into account is the relative stiffness of the probably nearly neat resin that makes up the bulk of the fillet, and the stiffness of the aluminum bracket.

Most neat epoxy resins are fairly flexible, thus allowing significant load to be passed to the stiffer aluminum bracket before the fillet fails.

For example, neat Aeropoxy PR2032+PH3660 has a Young's modulus of 418 ksi, while 6061 aluminum's is on the order of 10,000 ksi, over 20x higher.

 

[A5tr0 An0n]

What you have to take into account is the relative stiffness of the probably nearly neat resin that makes up the bulk of the fillet, and the stiffness of the aluminum bracket.

Most neat epoxy resins are fairly flexible, thus allowing significant load to be passed to the stiffer aluminum bracket before the fillet fails.

For example, neat Aeropoxy PR2032+PH3660 has a Young's modulus of 418 ksi, while 6061 aluminum's is on the order of 10,000 ksi, over 20x higher.

Now that is something I had not considered. I wonder how that differs when the resin in no longer neat, granted it depends on whats going into it, but I wonder… say, how much carbon strands alter that.

However it might be safe to conclude that it will not get close to the stiffness of metal, and thus the brackets might be a good idea. I am in the middle of the road right now. I know what has failed and what has succeeded but I do not know what is necessary. I think I am leading towards the brackets to be honest; that way chances of success are higher.
I would really like to leave them out but… well you know!

 

[A5tr0 An0n]

So I had a little time and through together a quick possible failure analysis. If there are any other things you guys can think of let me know. I will add edits/updates to the list later on.

 

[CarVac]

Now that is something I had not considered. I wonder how that differs when the resin in no longer neat, granted it depends on whats going into it, but I wonder… say, how much carbon strands alter that.

However it might be safe to conclude that it will not get close to the stiffness of metal, and thus the brackets might be a good idea. I am in the middle of the road right now. I know what has failed and what has succeeded but I do not know what is necessary. I think I am leading towards the brackets to be honest; that way chances of success are higher.
I would really like to leave them out but… well you know!

Adding fibers to the fillet will increase stiffness, but it's very hard to orient them properly to get the maximum benefit in a fillet. Randomly oriented doesn't help that much in my experience. Furthermore, when you add enough to reach the stiffness level you want, you start to lose adhesion.

So I had a little time and through together a quick possible failure analysis. If there are any other things you guys can think of let me know. I will add edits/updates to the list later on.

1. You may be interested in canting your fins to induce spinning. I was simulating Bare Necessities in Openrocket, which predicts that it goes unstable, but even when the CP is ahead of the CG, if I gave it a 1/2 degree fin cant it still went perfectly straight. (at Mach 4, it spins really fast, exactly when it needs the spin to remain stable).

2. Sure, make them decently thick, and you'll be fine.

3. Experiments are good.

4. Make sure your attachment is good. Paint can help, but it may require high-temperature curing.

5. FWFG nosecones don't seem to be a problem; they hold together fine in Mach 3 shreds from what I've seen.

6. The increased thickness is a good thing. Good enough? Time will tell.

7. It obviously depends on the specific setup you have, but yes independent batteries are good. I'd personally have no switches; just plug the batteries into connectors to power things on.




8. Human error. Ah, yes, human error.

If you read the BN thread, you may find that we scrubbed our first launch in no small part due to it being a difficult design to assemble in the field. Our second design was such that it had almost no assembly to be done in the field: the deployment bag and ARRD were packed and ready to go days in advance, the av-bay was assembled (we just had to plug in the batteries), and the shear pins were pre-installed.

All we had to do at launch time was:
1. Plug in the avionics one at a time, verify that they worked.
2. Insert the avionics sled into the nosecone.
3. screw the tip on the nosecone (which held the avionics in).
4. Inserted the parachutes.
5. Tied the shock cord onto the booster's y-harness.
6. Verifying that there was no short-circuiting using lightbulbs, we installed the big black powder charge.
7. Applied thread sealing goop to the threads.
8. Screwed the whole front end onto the booster.

That's it. Everything else was essentially done before we got to Black Rock. Keep the list as short as possible, and human error goes away. It does help to have a partner who knows the entire rocket as well as you do go over it with you, though. That would probably be your L3 advisor. If they don't know it backwards and forwards, make sure that they do.

 

[A5tr0 An0n]

You are right CarVac… that is definitely something to consider. Spin stabilization could help out a lot; especially with unforeseen circumstances.

With the carbon layers on the .125' G10 plate, the thickness should be around ~0.265 (estimated). That seems a little to thick to me. I will have to play around with that to find the ideal thickness.

I am not worried about curing. A lot of things with this rocket have to be cured. I build a 8' oven just for that.

I am not worried about the switches. I will be using the flag-pin type. They fail open so there should not be any issues with G force or power loss due to damaging, etc. I have seen them used on 40G launches before with no problem.

I plan to assemble most of it the night before but all in all should be a relatively normal assembly. So nothing to crazy. I will make sure my TAP is checking everything out with me… I am sure he will

 

[bobkrech]

........On a side note, the vehicle experiences max Q ~3.25 seconds into the flight at an altitude of ~7kft and traveling faster than the speed of sound 3.5 fold. This is interesting since most rockets go through max Q at transonic speeds. At max Q the rocket experiences ~1,300N of force. Note, this is note a as-built sim.......

Not surprising.

Max-Q is the maximum dynamic pressure developed by the rocket during its flight. It occurs at or just after the maximum thrust during the burn of a hobby rocket motor as it is proportional to the product of the atmospheric density multiplied by the velocity squared. If your simulator calculates the drag force of your rocket, it calculates Max-Q, as it occurs when the rocket experiences its maximum drag force.

Bob

 

[A5tr0 An0n]

Not surprising.

Max-Q is the maximum dynamic pressure developed by the rocket during its flight. It occurs at or just after the maximum thrust during the burn of a hobby rocket motor as it is proportional to the product of the atmospheric density multiplied by the velocity squared. If your simulator calculates the drag force of your rocket, it calculates Max-Q, as it occurs when the rocket experiences its maximum drag force.

Bob

That is correct sir. During the launch of any rocket, the speed increases since the rocket accelerates, but air density decreases the higher the rocket goes. There is a point where the combination of increasing speed and decreasing density is a maximum. That point is know as Max Q; every rocket must be able to survive that point structurally.

 

[CarVac]

That is correct sir. During the launch of any rocket, the speed increases since the rocket accelerates, but air density decreases the higher the rocket goes. There is a point where the combination of increasing speed and decreasing density is a maximum. That point is know as Max Q; every rocket must be able to survive that point structurally.

I think what Bob's point was is that you were perhaps comparing hobby rockets against space launch rockets; hobby rockets accelerate so much faster that the decrease in air density is nearly meaningless during the burn compared to the magnitude of the velocity, until you get to staged moonburners for 100k+ shots.

 

[A5tr0 An0n]

I think what Bob's point was is that you were perhaps comparing hobby rockets against space launch rockets; hobby rockets accelerate so much faster that the decrease in air density is nearly meaningless during the burn compared to the magnitude of the velocity, until you get to staged moonburners for 100k+ shots.

Oh yes with the transonic speed… yes I was. I see the misunderstanding. I was just saying the difference between the 2 is interesting, but see how it appears.

 

[A5tr0 An0n]

I had some time today so I went ahead and did some recovery testing… well sort of. More like E-match testing to be exact. I was curious and was sure others were also. Enjoy.[video=youtube;9e4-UgDE0Z4]https://www.youtube.com/watch?v=9e4-UgDE0Z4&feature=youtu.be[/video]

 

[REK]

Magnificent test Mat. You can clearly see how the e-match doesn't burn at higher altitudes.


Alexander Solis

Level 1 - Mariah 54 - CTI-I100 Red Lightning Longburn - 6,345 Feet

 

[butalane]

Magnificent test Mat. You can clearly see how the e-match doesn't burn at higher altitudes.


Alexander Solis

Level 1 - Mariah 54 - CTI-I100 Red Lightning Longburn - 6,345 Feet

Were we watching the same video?

 

[CarVac]

Were we watching the same video?

Burns less strongly, certainly.

 

[edwinshap1]

As long as your charges are well sealed and tight, you'll have plenty of energy to still light even in a vacuum. There just can't be free space, or it'll just sputter out.

Maybe make some small charges and give them a test in your rig?

 

[A5tr0 An0n]

As long as your charges are well sealed and tight, you'll have plenty of energy to still light even in a vacuum. There just can't be free space, or it'll just sputter out.

Maybe make some small charges and give them a test in your rig?

It is not necessary to hold pressure for the charge but is so for the e-match. I am not sure what you mean by sputtering out. The point of this was to actually see the difference with pressure differential on the e-match.

I have a different chamber that I use for charges; I just had scraps left over so I built a smaller one for the e-matches. That being said I will at a later date record charges (probably in a couple months, when I have time) but I was more interested in the e-match itself.

 

[CarVac]

It is not necessary to hold pressure for the charge but is so for the e-match. I am not sure what you mean by sputtering out. The point of this was to actually see the difference with pressure differential on the e-match.

I have a different chamber that I use for charges; I just had scraps left over so I built a smaller one for the e-matches. That being said I will at a later date record charges (probably in a couple months) but I was more interested in the e-match itself.

It actually is necessary to hold pressure for the charge: if they have the chance to scatter in a low-pressure area then they will fizzle out.

That's why for Bare Necessities, instead of using long tubes like Don't Debate This or Jim Jarvis's t-shaped structure, neither of which we had room for, we instead sealed atmospheric pressure into the entire parachute bay.

 

[A5tr0 An0n]

It actually is necessary to hold pressure for the charge: if they have the chance to scatter in a low-pressure area then they will fizzle out.

That's why for Bare Necessities, instead of using long tubes like Don't Debate This or Jim Jarvis's t-shaped structure, neither of which we had room for, we instead sealed atmospheric pressure into the entire parachute bay.

What I meant is BP has its own oxidizer and is not dependent on O2 levels in the atmosphere to burn. It is however necessary to keep the BP together long enough for the chemical reaction to occur and thus burn all surrounding BP instead of blowing the BP away. This is caused by poor heat transfer; heat transfer obviously raises the temperature and initiates a chemical reaction that releases the BP's oxidizer. However the charge does not need to be sealed to allow enough heat transfer to burn a very high percentage of BP. Actually most of the time (in my case anyways) when a charge was sealed it did not actually help much at all. This is due IMO to the charge breaking the seal due to the rapid increase in pressure before the remaining BP can burn thus resulting in a smaller portion of the charge burning and the remaining being blow away.

 

[CarVac]

What I meant is BP has its own oxidizer and is not dependent on O2 levels in the atmosphere to burn. It is however necessary to keep the BP together long enough for the chemical reaction to occur and thus burn all surrounding BP instead of blowing the BP away. This is caused by poor heat transfer. However it does not need to be sealed to allow enough heat transfer to burn a very high percentage of BP. Actually most of the time (in my case anyways) when a charge was sealed it did not acutally help much at all. This is due IMO the change breaks the seal due to the rapid increase in pressure before the remaining BP can burn thus resulting in a smaller portion of the charge burning and the remaining being blow away.

Experiments Jim Jarvis has run say otherwise. Even though black powder has oxidizer in it, you need pressure for the reaction to proceed. Same with APCP: it can burn without oxygen, but only at elevated pressures as found in a motor case.

The containment used by Jim Jarvis is a metal fixture that doesn't get blown apart; aquarium tubing indeed isn't good enough containment. In Bare Necessities, by making the whole deployment bay be the vessel, we had the advantage of releasing all the pressure as soon as it is no longer needed. Once the nosecone is off you don't need the BP to burn any longer, but the pressure is gone once the nose is off.

 

[A5tr0 An0n]

I am not saying you do not need pressure per se; I am saying the charge does not need to be sealed. A sealed charge can lead to more problems than good, if you do not know how to prepare it correctly.

Even though black powder has oxidizer in it, you need pressure for the reaction to proceed.

BP can in fact burn in a vacuum. You do not need pressure for the reaction to proceed per se. If the BP is touching each other it will burn. You need gas (air is the media in this case) to provide heat exchange for the BP that is not touching the area of initial ignition to allow the reaction to occur and thus ignite via its own oxidizer.

The containment used by Jim Jarvis is a metal fixture that doesn't get blown apart; aquarium tubing indeed isn't good enough containment

It does not matter what the canister of the BP is made out of, it matters if it can withstand the pressure long enough for the remaining BP that is not in contact in the area around the e-match, to burn. Aquarium tubing, surgical tubing, lab containers, some plastics, etc. are generally not good for that.

In Bare Necessities, by making the whole deployment bay be the vessel, we had the advantage of releasing all the pressure as soon as it is no longer needed. Once the nosecone is off you don't need the BP to burn any longer, but the pressure is gone once the nose is off.

I don't know what exactly you mean by this. Could you explain this please. I mean, generally is that not almost always the case? If you are doing DD then once the separation has occurred you do not need internal pressure inside the bay.

EDIT: I reread your other post. I see you sealed ~sea level pressure internally, but I still do not see how that is an advantage (in the sense of releasing pressure). That should always happen once separation occurs, no matter whether it is in the bay or a canister. Maybe I am still missing something?

 

[dixontj93060]

I don't want to be discouraging, but you are spending time reenacting experiments (in much less controlled and accurate conditions) that were conducted over 60 years ago and were the basis of NASA's selection and operation of pyrotechnics in the Mercury through Apollo programs. BP degrades in performance as pressure decreases, not because it doesn't have an oxidizer, but because the particles are not in close proximity to each other once the reaction begins resulting in a less energetic and incomplete reaction.

https://buymyfirstgun.com/Pyrotechnic/Black_Powder/Black_Powder_Blackwood_and_Bowden.pdf

https://www.dtic.mil/dtic/tr/fulltext/u2/687124.pdf

 

[JimJarvis50]

Experiments Jim Jarvis has run say otherwise. .

My interpretation of the long tube effect is that as the BP starts to burn, the gases need to make their way out of the tube. If the tube is longer, some pressure will begin to build up. This causes the BP to burn faster, making more gas, and then whammo. In my tests, this whole process would work just fine starting from a complete vacuum. I do seal the tube, however, so that the ematch itself works better, and it appears from Mat's test that this is a good idea.

Jim

 

[A5tr0 An0n]

I don't want to be discouraging, but you are spending time reenacting experiments (in much less controlled and accurate conditions) that were conducted over 60 years ago and were the basis of NASA's selection and operation of pyrotechnics in the Mercury through Apollo programs.

Oh, so you're that guy. And your point is? Why is that a negative thing? I do not know how to go about answering this without sounding rude, so if I do sound rude then know that I do not mean to insult you. I am also thankful that you are considerate of me not "wasting my time." However this was by no means a waste of time seeing as it took me only 2 hours to complete and that is including making the video.

One of the points of science is to be able to replicate something and observe the same findings, unlike taking someones word for it, i.e. superstition. Show me where you can actually see an e-match burn in a vacuum chamber, because I am not aware it is available. When we commercialize space, do we expect everyone to be a physicist or engineer? No. This video show you whats happens without having to understand it; that is helpful to others without a doubt.

By the way, the chemicals that have made up BP have been fairly the same, the ratios of different chemicals however, have changed. Do I think this will alter what happens in a vacuum? Probably not. Why probably? Because things are never 100% true/fact. My point is, things and conditions change. Surface preparation for example, is different depending on the material. With regular hobby materials not all of them bond equally. Can you tell me if 4525 bonds better to FWFG or FWCF? Does it bond better to FG or CF when they are rolled? I have yet to read that and I have yet to see that. Maybe they bond is the same OR maybe it doesn't even matter on this scale. However I for one, read first and then like to see it for myself.

Now for record (cause apparently this needs to be said) I am not trying to reenact any previous experiment. I am trying to build on them, using "less controlled and less accurate methods" (methods that every one here is guilty of), because that is how all of our rockets are being built. I think there is always progress to be made or there is always things to change and this helps me build better and it helps other build better.

BP degrades in performance as pressure decreases, not because it doesn't have an oxidizer, but because the particles are not in close proximity to each other once the reaction begins resulting in a less energetic and incomplete reaction.

Thanks for repeating what I have already said.

EDIT: By the way, thank you for providing links. (Not sarcastic, in case it sounds that way)

 

[A5tr0 An0n]

I do seal the tube, however, so that the ematch itself works better, and it appears from Mat's test that this is a good idea.

Jim

Now if you wait till I get home I can get on my other computer and I will upload a video that shows about this.

 

[dixontj93060]

I am not saying you do not need pressure per se; I am saying the charge does not need to be sealed.

Actually, I didn't repeat what you said, I clarified your wish-washiness. You've been all over the place with your opinions on this thread. One of your last statements is quoted above which is dead wrong. And you only got that close after much coaching from others. Inaccuracies needed to be negated/clarified for others reading this thread.

 

[bobkrech]

I am not saying you do not need pressure per se; I am saying the charge does not need to be sealed. A sealed charge can lead to more problems than good, if you do not know how to prepare it correctly.

......Maybe I am still missing something?

What you are missing is the 60+ years of professional practice of using hematic sealed pyrotechnic charges because after much experimentation that's what works.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710020870.pdf describes the ignition process and provides design guidelines backed by data to permit the design of pyrotechnic igniters.

You can do it anyway you want to as a hobbyist, but this is how it's done in the professional world where failure is not an option.

Bob

 

[A5tr0 An0n]

Actually, I didn't repeat what you said, I clarified your wish-washiness. You've been all over the place with your opinions on this thread. One of your last statements is quoted above which is dead wrong. And you only got that close after much coaching from others. Inaccuracies needed to be negated/clarified for others reading this thread.

Yes you are right you did clarify what I said, but did not negate what I said. I also agree inaccuracies need to be clarified, but you have yet to do so. I am not the best at speaking I will give you that, so I could say something incorrectly.

I fail to see how that statement is wrong. The BP does not have to be sealed, it will burn in a vacuum.

Who has coached me???

You've been all over the place with your opinions on this thread.

Explain please.

 

[A5tr0 An0n]

What you are missing is the 60+ years of professional practice of using hematic sealed pyrotechnic charges because after much experimentation that's what works.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710020870.pdf describes the ignition process and provides design guidelines backed by data to permit the design of pyrotechnic igniters.

You can do it anyway you want to as a hobbyist, but this is how it's done in the professional world where failure is not an option.

Bob

Bob,
Link is not working for me. Is it working for you (or anybody else)?

EDIT: Opened in chrome.

I think you mean hermetic, and I am not saying I do not think that is a superior design (obviously my video showed that the e-match possibly benefits from being sealed). I am just saying that BP will burn in a vacuum, without it needing to be sealed. I never really specified that I am testing different BP methods, I did say I have another chamber for charges but that does say I am doing anything other than testing my DD at a simulated altitude.

Not saying that you have, but I also think it is ridiculous to hint that one is wasting time in checking their high altitude deployment, especially since there have been so many failures at a hobby level. I agree that one should possibly start looking at what professional aerospace agencies have done, but it is not always practically possible to replicate what they have done.

To everyone:
If you feel I have been rude to you then you should know that I have not meant to come off as rude.

 

[JimJarvis50]

One of your last statements is quoted above which is dead wrong.

Tim, regarding the dead wrong statement:

"I am not saying you do not need pressure per se; I am saying the charge does not need to be sealed."

I'm not so sure I would agree. I use a 3-inch-long brass tube for my BP containment. I use about 1.5 grams of BP, which means that the bottom one-third of the tube is filled with BP. This tube can remain unsealed (such that you can look down the tube and see the powder), and then placed in a nearly complete vacuum, and I assure you that 100% of the BP will burn. The trick is that the extra length of tubing causes some backpressure to build, which makes the BP burn faster, and this progresses to the point where the BP burns very quickly. So, maybe the statement in question should be that you don't initially need pressure (because you don't, if your method allows pressure to build) and the charge indeed does not need to be sealed.

In spite of the fact that this happened every time I've tried it, I still take Bob's advice to seal the charge. I do this because while I know the BP will burn under with the physical configuration I use, I'm much less sure about how an ematch will perform. I put a thin (1/32"?) layer of epoxy over the end of the tube just to seal in the air so that the ematch can fire at atmospheric pressure. Once the ematch fires, the deal is done. The picture shows the sealed tubes as I have used them in my high altitude flights.

Jim

 

[dixontj93060]

Jim, so if I'm reading it right, in the end, you do seal the long charge tubes, right? I'm sure this increases their effectiveness. If you read the literature, which you likely have, the conclusion is that with decreasing pressure the performance of black powder degrades as the burn becomes less energetic and incomplete resulting in reduced pressure wave from the charge. Adding BP to the under-pressurized charge does not really help, only good, tight containment helps. I believe your long charge tubes are certainly beneficial in providing that containment, but at high altitudes you will always benefit by keeping the BP contained (contained in my mind equals sealed, at least that is the surest form of containment, but I suppose that could be interpreted more broadly). I also assume you pack your charges before sealing, (i.e., with dog barf) to hold the BP at the e-match head, right?

 

[JimJarvis50]

Jim, so if I'm reading it right, in the end, you do seal the long charge tubes, right? I'm sure this increases their effectiveness. If you read the literature, which you likely have, the conclusion is that with decreasing pressure the performance of black powder degrades as the burn becomes less energetic and incomplete resulting in reduced pressure wave from the charge. Adding BP to the under-pressurized charge does not really help, only good, tight containment helps. I believe your long charge tubes are certainly beneficial in providing that containment, but at high altitudes you will always benefit by keeping the BP contained (contained in my mind equals sealed, at least that is the surest form of containment, but I suppose that could be interpreted more broadly). I also assume you pack your charges before sealing, (i.e., with dog barf) to hold the BP at the e-match head, right?

In the testing that I did, which included the double-sided "T" approach and the single-ended tube approach, I did not seal the charges at all, other than to use a little Estes wadding to hold the BP in place. In all cases, a couple of dozen times anyway, the charge fired very energetically with 100% of the powder burned. This only happens with the longer tube. I do seal the charges now, but other than possibly improving the effectiveness of the ematch, there is no improvement in the performance because the charges are already burning 100% of the powder.

In the longer tube, the "sealing" function if provided by the longer tube itself. As the charge begins to fire, I suspect that the BP tries to scatter by moving up the tube. However, this scattering is contained within the tube instead of being released into the drogue cavity. There is enough pressure produced by this initial burning to build up some pressure - like sealing might otherwise do - so that the charge completely fires. It is very energetic, very simple, and very reproducible. I typically use a little less BP than I might use with a conventional charge at lower altitude, because 100% of it is going to burn.

If the tube is limited in length to that of the charge itself, and even if it's taped shut, the BP does not entirely burn (in my tests, about 50% burns in this configuration). Here, as soon as the seal ruptures, the BP scatters and stops burning. In the longer tube, the BP can't escape fast enough, and it burns before it can get out of the tube.

As I always say when discussing this method, deployment is very energetic. Anyone doing it should do ground testing first, and conduct that testing carefully (because another name for a one-sided charge is "bullet").

Jim