Backing up the apogee “drogue” event at lower alt. to mitigate separation fail in high alt. flights

Discussion in 'Recovery' started by jahall4, Nov 22, 2019.

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  1. Nov 22, 2019 #1

    jahall4

    jahall4

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    It is my understanding high altitude separation of the airframe with BP I plagued by at least 2 conditions: 1) the reduced pressure at altitude results in a failure that would otherwise be successful in ground testing. 2) More BP goes unburned, in part because the lesser pressure at altitude (#1) results less containment of the BP. Consistently mitigating for #1 should be relatively easy, but #2 not so much.

    Seems to me both these conditions could be mitigated for safety by having at backup “drogue” event occur at a lower altitude where the pressure is not that different from ground level testing.

    Has anyone tried this? Maybe using the “Main” ignition circuit on an altimeter to trigger the backup “Drogue” event or a programmable event on a more advanced flight computer.
     
  2. Nov 23, 2019 #2

    blackjack2564

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    Please define high altitude.
     
  3. Nov 23, 2019 #3

    jahall4

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    Leave that up to you Jim. If you have tried this type of configuration to mitigate separation failures because of altitude I'm interested in your experience.
     
  4. Nov 23, 2019 #4

    manixFan

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  5. Nov 23, 2019 #5

    watheyak

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    I must be misunderstanding.

    So the apogee charge fails to separate, it's coming in ballistic at Mach 2 and a backup drogue event occurs?
     
  6. Nov 23, 2019 #6

    jahall4

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    Thanks Tony, I'm aware of some of the techniques, already use at least one them regardless of altitude, but as I stated in the OP I'm interested in whether what I described has been tried.
     
  7. Nov 23, 2019 #7

    jahall4

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    Nope you're not, Mach 2 sounds a little fast :), but I'd rather get it separated than not. Keep in mind this is a last ditch effort type of thing where for whatever reason the primary and secondary apogee events failed. Seen or heard of a few of these were special techniques where used, but still failed. :(
     
    Last edited: Nov 23, 2019
  8. Nov 23, 2019 #8

    tfish

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    if you watch some videos of some high altitude flights 70K and above. You'll see that the it takes a while for the drogue to start working. Not much 'air' up there to inflate the chute. Some of those flights attain some pretty high air speed (on their way down) before there is enough 'air' to inflate the drogue. So you can be pretty far off on your apogee event and still deploy 'safely'.

    It's also interesting in you loose most sound above 50K.



    The other Tony
     
  9. Nov 23, 2019 #9

    jahall4

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    Yes, That's why the thinking that high speed deployment of a drogue for that purpose may be manageable. We have all seen mains shred and maybe the rocket be torn apart, but it can't be thought of that way. The drouge is simply not creating that much drag even if it deployed near the ground.
     
  10. Nov 23, 2019 #10

    tfish

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    it would all depend of weight, speed, air density and how strong your recovery **** is.

    Tony
     
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  11. Nov 23, 2019 #11

    TimothyG

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    I had my rockets drogue deploy at just over Mach one at 8000 ft and it destroyed the airframe and left a debris field. There is absolutely that much drag and force on your drogue at high speeds don’t forget it is to the square of velocity.
     
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  12. Nov 23, 2019 #12

    jahall4

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    Sounds like worst case, but better than a ballistic impact. At least you could find the rocket and determine its speed and altitude from the electronics. :) I'd rather the rocket shatter than go through someone's house.
     
  13. Nov 23, 2019 #13

    manixFan

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    If you really are coming down from a very high altitude it might be possible to do a simple airframe separation without any kind of drogue. With the right design you could avoid a zipper. Then using a cable cutter or something similar open a small drogue once the velocity has decreased due to the broken airframe. And use a slider or something similar on the main. I watched a test of the SpaceX capsule and it seemed like there were 3 drogues before the main released.

    I would not consider 8000' to be high altitude in this particular case, it would have to be more like 30K - 50K'. For a frame of reference, at 50K' air density is less than 20% of sea level, so a chute deploying at that altitude is obviously much less effective. We saw that at BALLS this year when a flight to 50K' put out the main at apogee. The descent rate was more than 4X faster at at apogee than just before landing.

    And not to nitpick, but terminal velocity isn't going to be anywhere near Mach 2. You can pretty easily do the math to find the terminal velocity of a rocket. For the reasons stated above it's going to be higher at altitude than near the ground but a chute will be similarly less effective.

    Obviously the correct solution is avoiding all this in the first place by using a system that will deploy the drogue at apogee. A lot easier than trying to build a system to survive a high speed deployment. The flight that went to 50K' feet was supposed to hit 100K' and used a redundant CO2 system rather than BP to avoid the whole issue of what happens to BP at high altitudes.


    Tony
     
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  14. Nov 23, 2019 #14

    SpaceManMat

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    So your question is sort of “how far does my rocket need to come back down to try a backup charge such that it’s not going to affected by thin atmosphere at high altitude”. I’m thinking this is not a worthwhile solution to try and aim for, you’ve got to come a very long way back for low pressure not to be an issue and since your rocket is still in one piece it’s likely to be going extremely fast. Your not going to get a safe landing using this strategy. I think you are better off concentrating on solving the actual problem of BP containment at high altitude, which is totally doable.

    Also the BP containment issue and the not burning issue are not separate issues. The BP does not burn properly because the atmosphere is not pressing in on the BP holding it together (containing it) as it would closer to sea level. As a result of the lack of air pressure the BP is spread apart before it has time to burn, so yes if you contain BP properly it will burn properly.
     
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  15. Nov 23, 2019 #15

    blackjack2564

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    Are you currently building something that requires this high altitude data ....or is this just a topic for discussion?

    Why I was asking you to define high altitude for your needs.....not mine. I have already studied,and figured out what to use for my needs. However what I do is based on where I am going.
    Not one solution answers all.
    For simplicity and under 25,000 nitrile finger tips, over 25k long charge holders, or tubing plugged ala Tfish. All these are used depending on what diameter, how much room and attempted altitude
    now onto BKNO3 for deployment as some sounding rockets do, it produces same amount of gas/pressure regardless of altitude or temp.

    My take is making deployment function correctly when/where I need it to.
    I do not believe in adding complexity, that being said, you may/maynot be on to something...best of luck.
     
    Last edited: Nov 23, 2019
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  16. Nov 23, 2019 #16

    jahall4

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    Or a very small drogue, but keep in mind what folks are not getting here that this is a last ditch effort to get the airframe apart for SAFETY's sake. Anything else is gravy.

    I don't either, but he point is whatever the altitude was that contributed to the failure.

    Well sure, but again not an replacement for a configuration the should work. Don't know why folks are not understanding the phrase "mitigated for safety by having a backup".

    Tony[/QUOTE]
     
  17. Nov 23, 2019 #17

    jahall4

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    No, my question is exactly what I stated.

    QUOTE="SpaceManMat, post: 1938203, member: 15412"]Also the BP containment issue and the not burning issue are not separate issues. The BP does not burn properly because the atmosphere is not pressing in on the BP holding it together (containing it) as it would closer to sea level. As a result of the lack of air pressure the BP is spread apart before it has time to burn, so yes if you contain BP properly it will burn properly.[/QUOTE]

    I thought that was what I said.
     
  18. Nov 23, 2019 #18

    jahall4

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    Thanks, Given the nutty things I've seen tried I am a little surprised no one is saying they have tried this. Could be flyers are thinking all or nothing as opposed to just getting the rocket apart for safety. Success in the configuration I'm describing would not necessarily result in a rocket that is flyable.

    Given the countless drougeless recoveries using a big main NOT designed for higher speeds, this seems to me to be in the realm of
    possibilities.
     
  19. Nov 23, 2019 #19

    manixFan

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    My solution does take into account what you are trying to do. That's why I suggested just breaking the rocket apart. The terminal velocity will be far slower and safer for all involved, regardless of what happens next. But you might as well and take that into account when designing your overall recovery plan and your main deployment and do more that just ensure safety, but ensure complete recovery.

    Another thing to consider is that a rocket coming in ballistic had a lot of additional force on the nosecone and would require a larger charge to separate it. I've got video of rockets that were coming in ballistic and fired their main deployment charge but it failed to separate the parts, but under normal flight conditions it would have been successful. So you'd need to calculate how much additional BP you'd need to separate things due to air pressure on the nosecone.

    I think you are right to try and plan for safety. I've been at BALLS when big rockets have come in ballistic from 100K' and they make a very scary noise when they enter the playa.


    Tony
     
  20. Nov 23, 2019 #20

    jahall4

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    I understand where you are going and yes larger BP charge, much larger than normally required. Definitely a blow it apart or blow it up approach, but if you are talking about simply shedding a fin can I don't reason it is as much as you might think given the momentum (and relatively low drag) of the forward section vs. the aft fin can. Simply shearing the pins may be enough for drag to pull the fin can from the rest of the rocket. After all that's why pins are used on the aft section. Certainly something some flow analysis could predict.

    Playa is the least of my concern, around here it could be someones back yard. :eek:
     
  21. Nov 23, 2019 #21

    Exactimator

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    If your rocket might return ballistic from an altitude with thin air into a house, you're not flying the field correctly.

    Which is worse, having a 4" diameter rocket ballistic return hitting the ground in a 4" cross section (plus fins), or a debris field of disintigrated rocket bits (including steel eyebolts, allthread, 9v batteries, etc.) raining down over who knows how many square feet?

    I would focus on separating the rocket correctly at apogee rather than trying to use another back-up system.

    One of the Eggtimers does include a safety feature where if it senses a rapid descent it will fire a backup charge, but I can't recall which one it is. And I don't believe it's programmed to fire a charge at a specific altitude where the air may be thicker.
     
    Last edited: Nov 23, 2019
  22. Nov 23, 2019 #22

    SpaceManMat

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    QUOTE="SpaceManMat, post: 1938203, member: 15412"]Also the BP containment issue and the not burning issue are not separate issues. The BP does not burn properly because the atmosphere is not pressing in on the BP holding it together (containing it) as it would closer to sea level. As a result of the lack of air pressure the BP is spread apart before it has time to burn, so yes if you contain BP properly it will burn properly.[/QUOTE]

    I thought that was what I said.[/QUOTE]

    You said they were two different things and the burning could not be solved. They are one thing and the burning can be solved.
     
  23. Nov 23, 2019 #23

    jahall4

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    I thought that was what I said.[/QUOTE]

    They are connected, BUT the lack of pressure alone is enough to fail. IOW it is possible to burn all (or at least nearly all of the BP) and still not separate the airframe.
     
  24. Nov 23, 2019 #24

    jahall4

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    I thought that was what I said.[/QUOTE]

    You said they were two different things and the burning could not be solved. They are one thing and the burning can be solved.[/QUOTE]

    They are connected, BUT the lack of pressure alone is enough to fail. IOW it is possible to burn all (or at least nearly all of the BP) and still not separate the airframe.
     
  25. Nov 23, 2019 #25

    jahall4

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    Generally I would agree, maybe it should not be flown at all, but a house is just one example, how about a barn or vehicle if that is a more realistic example of a object on the ground, but in the recovery area or cylinder. A rocket hitting the ground is not of a concern I'll take the non-aerodynamic pieces any day. Yes most definitely better the rocket shatter than come in ballistic in most all circumstances.
     
  26. Nov 24, 2019 #26

    blackjack2564

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    ??????
     
  27. Nov 24, 2019 #27

    jahall4

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    Maybe, best I can tell you.
     
  28. Nov 24, 2019 #28

    Handeman

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    I agree you need to contain the BP correctly,but I'm not sure its because the lower air pressure prevents if from burning correctly.

    The way I see it, and I could be completely wrong, but we use the BP as a gas generator. It generates gasses to pressurize the BT and create a desired amount psi to push the rocket apart. At near sea level, you are starting with near one atmosphere of pressure inside the BT and the gas generated by BP only has to add to that existing pressure inside the BT to reach the desired psi. At high altitude the is little air in the BT. The BP must generate the gas to replace what would normally be in the BT at low altitude plus what it needs to build to the required psi to separate the rocket. Needing that extra gas volume and the time it takes to generate that extra it is why you need more BP, not containment or burning rates.
     
  29. Nov 24, 2019 #29

    richP

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    Wouldn't the deployment of the main handle that risk? Of course you'd have a shredded chute and damaged rocket, but it would still be separated, not-aerodynamic and possibly similar to drogueless profile.
     
  30. Nov 24, 2019 #30

    Reinhard

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    The amount of gas that needs to be generated is the same at sea level and at high altitude. The important part is the pressure differential to ambient, not the absolute pressure. That's why parachute compartments on high altitude birds should be vented, so the rocket wont separate prematurely just from the near sea level pressure inside.

    The problem with black powder on high altitude is that the ambient gas plays a role in the heat transfer between the grains. Black powder will not burn well at low pressures. Therefore at least partial containment is necessary for high altitude charges until the charge has burnt completely. If the containment fails before that, combustion will likely not continue completely. Tony Alcocer and Jim Jarvis have documented ways to achieve this.
    A while ago, I had a chat with a professional in the area, who mentioned that ambient oxygen also plays a role in the combustion of BP. Apparently it has a negative oxygen balance. Don't quote me on that though, I might miss-remember that part, and the context was a different one, namely industrial safety and not high altitude deployment.

    Reinhard
     
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