My quest for an O motor launch.

Discussion in 'High Power Rocketry (HPR)' started by Bat-mite, Apr 17, 2019.

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  1. Sep 29, 2019 #181

    manixFan

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    Hmmm, that is a crazy L/D ratio. If you look at other 98mm motor cases, you'll find that most top out at about 43" or so, or a L/D of about 10, which is considered to be a reasonable maximum. Scott from Loki does have smaller diameter motors that approach your L/D but his 98mm motor case stops at 46". The 6XL case from CTI is just shy of 50". How are you going to mitigate erosive burning in such a long case? The steps in the core will have to be carefully designed and the propellant itself will require careful selection and characterization to make sure it has the right physical properties. Nearly all of the very high ISP propellants from commercial makers use small AP (30 micron) that carries considerably more risk than the larger sizes we typically use.

    Scott's K627 and M1378 are good motors to look at to help inform your motor design. Also do some research on Frank Kosdon's long motors - they are in the same L/D as yours. You'll find some references to them in the research section as well as elsewhere on the web.


    Tony

    here's a good example for Kosdon motors: https://www.rocketryforum.com/threads/o10000-tpl.153963/
    (requires access to the restricted research sub-forum)
     
    Last edited: Sep 29, 2019
  2. Sep 29, 2019 #182

    Bat-mite

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    Thanks, thanks, and thanks!
     
  3. Sep 29, 2019 #183

    Bat-mite

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    Thanks. I am no motor designer. MDRA VP and TRA MD prefect Scott S. is designing the motor. He has made many O, P and Q motors, and he really knows what he's doing. I'll be there to mix and pack propellant, but I'll leave the physics to Scott. Scott made the 8-foot long Q motor that launched Tom C.'s Yellow Submarine back in April.
     
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  4. Sep 29, 2019 #184

    eggplant

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    I'm sure Scott knows what he is doing, but an 8"x8' (12:1) motor is very different in aspect ratio than a 3.875"x6' (18.6:1) motor. From what I have seen, many successful amateur motors with such high aspect ratios used very large cores, low pressure, and slow propellant to keep things in check, at which point they might as well have built a shorter motor without those compromises to get a comparable total impulse with a lower motor mass overall. As I typed that out, I realized further discussion would be more appropriate on the research forum, and that what I describes sounds just about perfect for the east coast flying we do.
     
  5. Sep 29, 2019 #185

    manixFan

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    Good to hear you are working with such an experienced motor maker. I've been making motors a long time but I stop at an L/D of about 10:1. I would love to be able to go longer but it's not a trivial exercise to scale up to something like what you've got. I will be watching with interest and maybe we can get Scott to share some motor design details on the research sub-forum.


    Tony
     
  6. Sep 30, 2019 #186

    mbeels

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    Based on the trend of your profile pictures, it appears that you're getting smaller. If you keep this trend of monster rockets up, you'll end up as a tiny dot.
     
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  7. Sep 30, 2019 #187

    Bat-mite

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    Hmmm ... maybe I should get myself an Atom or Ant Man Halloween costume. :D
     
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  8. Sep 30, 2019 #188

    Tobor

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    lol....
    Or just wear to pair of stilts for your next Profile pic.
     
  9. Sep 30, 2019 #189

    Buckeye

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    Scarlet and Gray with black accents. I approve!
     
  10. Oct 1, 2019 #190

    Bat-mite

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    Hmmmmmm....

    [​IMG]
     
  11. Oct 2, 2019 #191

    Buddy Michaelson

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    Hello John, just finished up your parachute and deployment bag, they’re on the way too you! Btw absolutely beautiful job on this rocket, I cannot wait to see the flight at Red Glare! 29D9712B-209E-47FB-A30B-935457C6D854.jpeg
     
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  12. Oct 3, 2019 #192

    Bat-mite

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    Looks great! USPS says it will arrive tomorrow. Thanks.
     
  13. Oct 5, 2019 #193

    Bat-mite

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    And here it is spread out a bit (although my family room's not big enough!):

    [​IMG]

    Thanks, Buddy!
     
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  14. Oct 5, 2019 #194

    manixFan

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    I was next to Buddy at BALLS and got to know him a bit. It was really cool to hear him talk about his chutes and get some insight on how to rig them. I had an older Rocketman drogue chute and he inspected it and noted how the new ones are different (better) and then untangled the lines for me. He also noticed that I had some Technora (a variation on Kevlar) and I was really surprised that he could tell the difference at just at a glance, but it just showed how well he knows his stuff. He is another example of one of the many great vendors we have supporting his hobby. There are several excellent chute vendors so no matter what kind of chute you need someone will likely already have it or make it for you. We are very fortunate for such a small hobby.

    I just hope that's not an Eggtimer kit in the background!


    Tony
     
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  15. Oct 5, 2019 #195

    jmwoody

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    I'll second Tony's endorsement on Buddy's fine chutes and your great choice John.

    Good luck on your first flight and safe recovery
     
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  16. Oct 7, 2019 #196

    Buddy Michaelson

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    Wow that was quick! Btw I would not recommend taking the parachute outside in the wind, I might see you over the Atlantic :)
     
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  17. Oct 7, 2019 #197

    Bat-mite

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    I already had to tell my kids hands off! :D
     
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  18. Oct 7, 2019 #198

    Bat-mite

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    Ha ha ha! :D That's what it would look like if I tried to build one!
     
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  19. Oct 12, 2019 #199

    Scott S

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    Here's a few more pieces for the motor. All the machining is done expect for the nozzle throat.

    O Motor carrier-1.jpg O Motor carrier-2.jpg O Motor carrier-3.jpg O Motor tube.jpg

    I'll bring it to the launch this weekend.

    Now to think about the motor design.
     
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  20. Oct 12, 2019 #200

    Tobor

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  21. Oct 13, 2019 #201

    Bat-mite

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  22. Oct 13, 2019 #202

    ksaves2

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    Getting into this late but I presume the motor is based on a prior successful design? If an O motor maven is mentoring you stand a better chance. How many firings do you expect it to last?
    I’ve only witnessed and was involved with one O motor and it failed on the 4th firing. It was of conventional design with a standard casing and full diameter graphite nozzle with beautiful knurled threaded closures.
    The maker had the proper equipment and looked very nice. Unfortunately the rockets failed but the motor survived until the last firing. The 4th firing failure occurred in this fashion. The aft casing simply ruptured circumferentially well above the external threads of the aft closure. The grains slid out the aft end as the rocket was half way up the tower. They did not stop burning and consumed the rocket and the tower trailer.

    The heat flux at the distal (nozzle) end of the casing can start to become a problem as the Aluminum case starts to lose strength with each firing. Using a straight graphite nozzle as was described above, allowed a pretty significant transfer of heat to the case each time the motor was fired. A nozzle carrier may help but I’ve seen pictures of the results of test firings of such arrangements where the aluminum carrier starts eroding between the proximal carrier/graphite nozzle interface making it a single use arrangement. Now I understand some folks consider these types of projects as one off “achievement” project and don’t intend to fire these things very often but should take consideration of the above thoughts if they expect to use the system more than once.
    Is there another way around this issue? One remedy I’ve read is using a phenolic nozzle but then one runs into the erosive properties of said nozzle as opposed to the generally non-erosive nature of graphite. The phenolic plastic I’ve been told has lower heat transfer. The non-erosive characteristic of graphite allows for a more precise computer simulation than an erosive nozzle. I’ve seen some experiment with a phenolic carrier for a graphite nozzle but don’t recall the outcome. I discovered this variability with a straight phenolic nozzle experimenting with smaller research motors and the motor sims. The starting nozzle throats had to be smaller in order to achieve a satisfactory burn and was only discovered by trail and error.
    Scaling up to an O motor is another ball of wax and what is seen on a small scale generally doesn’t apply as well to a larger scale motor. Best of luck. Kurt Savegnago
     
    Last edited: Oct 13, 2019
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  23. Oct 14, 2019 #203

    Bat-mite

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    Thanks. That's a lot to think about. I have no plans (at present) to fire it more than once, but I haven't ruled that out. And Scott and I are sharing the casing and closures, so he may have some plans for it.

    We'll have to discuss.
     
  24. Oct 14, 2019 #204

    eggplant

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    A pretty typical arrangement for 6"+ diameter or very high aspect ratio motors is to use a relatively small diameter graphite throat that sits in an LE/CE phenolic carrier that is mounted into an aluminum aft closure. It worked for me on a 6"x79" 74,000 Ns P and I have seen it on this forum in projects like Qu8k and Honeybadger II. It is the same idea that Scott at Loki uses for his 54/4000 nozzles. I made a thread with more details about how the P nozzle was constructed in the research section a while back.
     
  25. Oct 14, 2019 #205

    ksaves2

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    Ditto and Bingo to Andrew. I looked back in the thread and see the motor is with a high L/D ratio. Things like that can go erosive early on and get squirrely. This isn’t the research thread so can’t go too far. I would think that a proper motor mix would have to be used to minimize risk and maybe something called stepped grains. Using a motor mix that is temperamental could lead to a less than nominal flight leading to a re-kitting of the component parts early on in the flight profile.
    Especially if a test fire of the motor can’t be carried out.

    One thing going for you is you consider it single use but that single use will have to be near perfect. I wished I had the link of the video of a test firing of a high L/D motor of which the makers were warned about heat flux. They had the cojones to fire it at night and post it. Rear end got red hot and the whole nozzle end separated circumferentially from the casing as it failed and blew up into the night sky. Again, be careful and consider advice from folks like Andrew who’ve actually done it. I admit, I’m only parroting what I’ve read and from that limited experience I’ve outlined above. Good luck. Kurt
     
  26. Oct 14, 2019 #206

    Scott S

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    Something similar to this?

    20191014_064814.jpg

    Or these?

    20191014_064836.jpg

    We're not going with an Al based formula but if John wants the added thermal insulation we can go that direction.
     
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  27. Oct 14, 2019 #207

    eggplant

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    Yup, something exactly like that ;). Is that the redstone nozzle in the second picture? To be clear, I was responding to Kurt who was asking about the track record of phenolic carriers in large motors. You've definitely been building motors for far longer than I have, so I had no doubts that if I have tried something, you must have too. That said, I was curious about the use of full-diameter graphite here but hearing about the formula I guess it makes sense.
     
  28. Oct 14, 2019 #208

    Scott S

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    No worries. I appreciate Johns kind words about my experience but I'm no expert and I continue to learn something every time I make a motor. You're right that the phenolic carrier will provide better insulation and they hold up well on larger motors where you can have a large amount of phenolic around the graphite. I've got 6 flights on the one carrier, I just swap out graphite to suite the motors. On 4" and smaller motors I've found them to be single use on hot propellants but they do their job!

    The 7.5" nozzle is from a test we did with a group trying to use a home rolled G-10 motor case and closures based on PML 7.5" tubes and couplers for casters and liners. It wasn't successful but the nozzle held up great. The Redstone nozzle was very similar.
     
  29. Oct 14, 2019 #209

    Bat-mite

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    Good stuff here! Thanks, Scott! And thanks, everyone contributing ideas and experiences.
     
  30. Oct 22, 2019 #210

    Scott S

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    Couple more hours in the shop and the hardware is finished once again.

    20191020_175743.jpg

    20191020_175645.jpg
     
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