An "R"-powered rocket build

Discussion in 'High Power Rocketry (HPR)' started by Rail Dawg, Nov 30, 2018.

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  1. Dec 19, 2018 #301

    Ez2cDave

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    Andrew,

    Excellent input !

    I found a couple of things that may be helpful . . .

    http://www.aerorocket.com/FinSim_Supersonic_Flutter.html

    http://www.aerorocket.com/finsim.html

    http://s605282183.onlinehome.us/wp-content/uploads/2016/01/Nose-Cone-Fin-Optimization.pdf


    Dave F.
     
  2. Dec 19, 2018 #302

    Andrew_ASC

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    Dave, I've seen those links before they have good knowledge. Here was the wing design book I've found for aircraft, the applicable section was P.224 in lower right for choosing sweep angle via a mach number. There's also a general overview of the handling characteristics of the wings by design traits. Ignore the stall behavior sections.

    http://www.aero.us.es/adesign/Slides/Extra/Aerodynamics/Design_Wing/Chapter 5. Wing Design.pdf

    I've experimented with L-1 projects with supersonic airfoils but do not recommend the added complexity to a project of this scale because of the additional difficulty in manufacturing and also an unknown flutter behavior beyond flat plate analysis.
     
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  3. Dec 19, 2018 #303

    OverTheTop

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    Are you worried about the whistle being inaudible to humans but setting all the dogs around off barking? :)

    There could be some interesting shock wave interactions generated. If the leading edge angle is always inside the Mach cone then it should be a reasonably tractable issue I would think. But don't take just my word for it. I'm an electronic engineer o_O.
     
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  4. Dec 19, 2018 #304

    ArchitectOfSeven

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    Okay I'll admit I haven't read all the thread yet and I apologize if this is redundant but you should really consider a rear-deploy drogue or even multiples. The idea is you pop out a series of small chutes that slow the rocket down without making it turn. This makes it easier to get to main deploy speed without breaking the whole thing into tiny pieces. Also, try looking into some sort of trap door on the side of the nose cone for the main to come out of. It would avoid the dodginess of separating huge tubes and allow it to launch out like a cannon ball with minimal tube volume and resistance.
     
  5. Dec 19, 2018 #305

    Andrew_ASC

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    I don’t like the idea of seams or holes from a door on a nosecone side with oblique shocks. There’s a rapid pressure and temperature change across a shock, shocks have unstarted supersonic wind tunnels. I’d hate for a side door to get blown in by a sudden pressure change across the shock. Your other rear deploy idea I respect.
     
    Last edited: Dec 19, 2018
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  6. Dec 19, 2018 #306

    Paulb06

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    I agree, " split fins" are a cosmetic feature likely to cause increased turbulence, possibly flutter.....if you go with a 9" airframe....plug in these numbers in OR... trapezoidal fin.... 24" root, 9" height, 4.5" tip chord and a 62.5 degree sweep angle...you'll come up with something similar to Derrick DeVilles rocket ...
     
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  7. Dec 19, 2018 #307

    Paulb06

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    If it's built " minimum diameter it will likely deploy in much thinner air.....the chute will automatically be far less effective until the rocket descends, then the drag will gradually increase as the rocket descends...
     
    Last edited: Dec 19, 2018
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  8. Dec 19, 2018 #308

    Theory

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    interesting split fin conceptual point that I though of on the way into work.

    I was thinking about where we have seen this sort of lay our accomplished in the past, specifically in vehicles that achieve high mach numbers. and while this is different as the leading "fin" is extremely long, the Phoenix missile uses a split lay out and it has a declassified speed of mach 5.

    no you are not building an air to air missile, but give the specs on the motor, and the use of aluminum, you are not far off...

    food for thought
     
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  9. Dec 20, 2018 #309

    Ez2cDave

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    If anything, it would be a "surface to air" missile . . . Hopefully, NOT a "surface to surface", however . . . LOL !

    Dave F.
     
    Last edited: Dec 20, 2018
  10. Dec 20, 2018 #310

    Nytrunner

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    I certainly hope its Surface to Surface. We cant just leave it up there.....
     
  11. Dec 20, 2018 #311

    Ez2cDave

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    My main concerns would be :

    ( 1 ) Flutter / Structural Failure.
    ( 2 ) Turbulence, possibly rendering the lower fin set less effective.
    ( 3 ) Heat issues, from turbulence / air fraction.

    Dave F.
     
    Last edited: Dec 20, 2018
  12. Dec 20, 2018 #312

    Ez2cDave

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    I meant during powered flight or a shallow, ballistic trajectory . . . LOL !

    Theoretically, if it could reach 100,000 feet, vertically, and the flight path deviated to 45 degrees, the potential impact site would be 200,000 feet downrange ( almost 38 miles ).

    Dave F.
     
  13. Dec 20, 2018 #313

    Andrew_ASC

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    Aeroheating is a known theoretical hand math computable value to a certain degree of verifiable accuracy. While scary and not negligible it is at least a easier known item.

    Shocks take a CFD from a cad model by a flow expert or wind tunnel with schrelin (I’ve misspelled that) from an actual model at a actual real Mach number. A professor told me the FEA for structures can take experimental turbulence data. Guess what happens when you design a new rocket? You don’t simply have experimental turbulence data to compute structures accurately. These techniques are beyond most undergrad college engineering courses. You’re talking a masters student or a PhD dork knows. Until the technical limit they hit when they say they can’t solve it either.

    There’s going to be tip vortices off those leading fins smacking the aft fin. That could lead to fin bending and deflection then failure.

    The reality is it’s mostly unknown until flight tested in hobby rocketry. Flutter is slightly more predictable but the predictions have a larger error. Note I did not volunteer for structures on this project. Somebody really experienced engineer or hobby wise needs that role. I do not trust my level of expertise with that critiCal task.

    For these technical reasons I dislike split fins on the R project. The smart thing was split fin solved a tooling constraint in manufacture. The bad downside is well theoretically it’s a scary math game getting harder to do until flight tested. I’m not an aero so take that advice with a grain of salt. I did do homework on a supersonic kit jet called BD-10 and it killed two test pilots because the engineers both mech and aero screwed up structures from an unknown turbulent cross flow in finite element analysis. They weren’t dumb. They assumed wrongfully when they couldn’t solve it. It broke up before the sound barrier: below the flutter prediction speed. Oh the horror of reality. It had twin tails like a superhornet. The tails sheared off.

    At least unlike the plane nobody is physically riding in it, lol.

    And unlike the Mach 5 missile this isn’t created in Arnold Engineering Developement Complex with national resources and millions in money, lol. This is a group of nerds doing it for fun on a very limited budget. Many theoretical issues are left unsolved by engineering standards. It’s a very large undertaking anyways even by hobby standards with very real technical challenges the same that aerospace companies face. The same physics and engineering techniques apply.

    If somebodies done an O or something with split fins maybe I’ll shut up. The idea scares me for what we can’t solve with math by hand without a flight test. It’s one thing when it’s a H motor split fin. And you try it again after you break something. But this is an R. I just lump an R into a spacecraft category, lol. Don’t make an R project harder than it needs to be unless you truly have full confidence in your ability to design it or do it safely. An R project is very costly and more dangerous. It demands the utmost flight experience and respect by hobbyists. It demands teamwork.

    To be honest it blows my mind what hobbyists have achieved. What other hobby lets you build a spacecraft motor? Test it? And fly it. Really wish an Aero would chime in on the split fins. They would have a better grasp of what the hell is happening in a concept level. Sorry if I got rambling way off.
     
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  14. Dec 20, 2018 #314

    OverTheTop

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    That's what I would be worrying about.

    The leading edge of the front fin should set up a strong shock wave and, assuming it doesn't dissipate, the rear fin should be in the lew of that, which might give it a lower experience regarding total pressure and temperature. Not too sure on my theory in that area.
     
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  15. Dec 20, 2018 #315

    Rail Dawg

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    Ok I’m not responding but am definitely enjoying this discussion!

    Call me the biggest geek ever but I eat this stuff up.

    Actually being able to build such a rocket is such a privilege.

    Thanks guys!

    Chuck C.
     
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  16. Dec 20, 2018 #316

    Theory

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    could very well be the best statement in the thread thus far
     
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  17. Dec 20, 2018 #317

    Rail Dawg

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    Agreed.

    With the materials available and the vast resources available for study I’ve got high confidence this will be a successful flight.

    Chuck C.
     
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  18. Dec 20, 2018 #318

    ThirstyBarbarian

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    Personally, I was more drawn to the Big Dumb Rocket than I am to the supersonic moon-shot rocket. But I’d definitely be happy to watch either one.
     
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  19. Dec 20, 2018 #319

    Rail Dawg

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    Definitely going with an aluminum fin can from Mike at Binder Design.

    Mike’s recommending the Nike Smoke fin design as there can be less root and more span.

    The big decision before ordering parts is whether to go with an aluminum airframe or carbon-wrapped G-12 fiberglass.

    Each has it’s positives and negative.

    Aluminum tubing is readily available but would require custom machining of certain parts along with various welds.

    The G-12 route is one I’m very familiar with and can be done with off-the-shelf parts. I really like working with G-12 and the rocket is built with mostly my own hands and not a machinist.

    My only concern with G-12 is the strength of the airframe under such high loads.

    However my idea to “fill” a G-12 airframe with G-12 couplers along with some wraps of carbon I think is a good one.

    That’s where I’m at right now. Working with Binder Design to determine the size of the fins.

    Once the tougher decisions are made the build itself will be enjoyable.

    Ideas and suggestions from you all is always appreciated.

    Chuck C.
     
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  20. Dec 20, 2018 #320

    Rail Dawg

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    I’m hearing you but the BDR has a lot of design issues using sonotube. Recovery a big issue along with not using couplers.

    The 12” design can be built heavy so it can be easily recovered to fly again.

    Still in the planning stage which in many ways is just as much fun as the build.

    Chuck C.
     
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  21. Dec 20, 2018 #321

    Theory

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    honest question: has anyone ever successfully flown a rocket of this caliber (Q or R) that was built out of G12? I ask because most at this level are aluminum. yes there have been some composite "P" powered birds, but a P is not an R.
     
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  22. Dec 20, 2018 #322

    Andrew_ASC

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    Do you have a openrocket sim with a rough mach number yet from a custom motor file?

    Not trying to bash Mike at all he’s correct about Nike fins, the problem I foresee is fin flutter or shocks, I would hold off on ordering fins until a sim is developed. You can change fin design last minute when fins are the last item completed. I nearly got burned in a first group project once and recommended do fins last to other groups.

    But in the past I’ve tried to optimize fins around the rockets for stability. But on a much much smaller scale.
     
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  23. Dec 20, 2018 #323

    ThirstyBarbarian

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    Absolutely! It’s going to be a cool project either way.
     
  24. Dec 20, 2018 #324

    eggplant

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    CF instead of FG, but yes. Everything on this rocket is composite including the motor case:

    http://www.uscrpl.com/updates/2018/11/24/traveler-iii

    They had some... issues... with recovery but it had nothing to do with the materials chosen. For reference, the linked flight was a minimum diameter R motor and it was probably a 350kft flight or very close. I have seen some confusion in this thread when the rocket is called 'minimum diameter 12 inch'. If it is actually minimum diameter (the rocket is the same diameter as the motor) you are probably looking at M4+ flight and over 150kft. If the rocket isn't 9" in diameter, it isn't minimum diameter but will obviously still be very high performance. I bet a 12" rocket on a 175kns motor will still be good for over 75kft. Is that the rocket you want to build?
     
    Last edited: Dec 20, 2018
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  25. Dec 20, 2018 #325

    Ez2cDave

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    To All,

    A thought just occurred to me, after treading Andrew's post . . .

    There is one "Aero", that came to mind, that could be contacted . . . A former, long-time "Rocketeer" and a REAL "Rocket Scientist" ( MIT ) . . . John Langford at Aurora Flight Sciences !

    http://www.aurora.aero/who_we_are/

    9950 Wakeman Dr
    Manassas, VA 20110

    703.369.3633

    jsl@aurora.aero
    jlangford@aurora.aero



    JOHN LANGFORD.jpg
     
    Last edited: Dec 20, 2018
  26. Dec 20, 2018 #326

    Andrew_ASC

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    Cutting_Planes.png
    If he needs a hypersonic flow expert, Dr. Sreenivas, from University Tennessee of Chattanooga may be worth a shot to email. Last year at university he found a drag coefficient on a M1.7-2.4 scratch build sustainer so we could begin drag force calculations for a rocketry club engineering competition. He uses Linux hardcode over Ansys and is a twenty year experienced at that stuff calling supersonic flight trivial. The CFD analysis method takes time, but is doable compared to a full scale supersonic or hypersonic windtunnel with a physical rocket. Capabilities include full particle effect modeling and even down to exhaust plumes if you provide enough motor/fuel data. Limitations high angles of attack so keep it within 10+/- degrees or limit turning. Anybody can do a CFD, few understand the theory, and even fewer you want to trust. I personally recommend this guy from my experiences. You just need a CAD/Solidworks/Creo or other 3D files of the actual rocket. These 3D files are then meshed into a format the Linux code likes at very high resolution. Note for reference the oblique shocks forming at the nose and the leading edges of the fins are weak shocks. If you want to be exact about it, well there's things in life you can't hand solve. Sometimes a computer will chew through a sh*tload of differential equations for yah. I don't know how well the uni will work with outsiders, but I do know guys at the Sim Center get bored simming the same trivial models over and over. A Dr.Newman is good with fin stabilization through hardcode, vibrations, and structures however he was too busy to help last year. Theses references do lack hobby rocketry experience so keep that in mind, they have industry experience instead, but I consider them as Sheldons...

    Sreenivas@utc.edu

    Again not trying to de-rail the thread but show how complicated it can get to model a shockwave.
     
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  27. Dec 20, 2018 #327

    Ez2cDave

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    Chuck,

    In addition to high structural loads, in all axes, don't forget aerodynamic heating, particularly if G-12 is used.

    Dave F.
     
    Last edited: Dec 20, 2018
  28. Dec 20, 2018 #328

    jqavins

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    Coming late to the party with perhaps a dumb idea.

    Early in the thread, before I skipped to the end, there was much talk of what material to use for the fins, and there's one possibility I didn't see mentioned. Honeycomb panel. If you don't know, it's a honeycomb of very thin material, sometimes aluminum and sometimes some sort of composite, with either aluminum or composite face sheets. At a half inch thick it can be very strong and VERY stiff and weigh very, very little. The edges need to be filled, typically with epoxy. Material can be added beyond the leading, tip, and trailing edges to shape airfoils, up to a point. (That is, most of the fin surface has to be the flat face sheet and only a little "extension" beyond that can practically be shaped.) Nuts or studs could be embedded in the epoxy on the root edge, then bolts or nuts used inside the airframe to attach the fins thereto.

    You'd get the stiffness to fight flutter while having very light fins, at the expense of finely shaped fins and probably lots of dollars.
     
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  29. Dec 20, 2018 #329

    Andrew_ASC

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    It’s not dumb. It saves aft mass. It’s just riskier on a project this size. The problem is with flutter analysis in a range of Mach 3-4 is rather important and the programs that do that assume it’s a solid material. Not honeycomb. Not airfoil. Not multi material.

    By simply swapping to honeycomb core you screwed yourself on an accurate flutter prediction. Do you want it lighter or do you want to know if the fins stay on? Pick one.

    Bolts would likely be a bracket and double shear scenario. You’d need to know the aero and thrust loads to size the bolts right. You also have to space them right or bad things happen.
     
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  30. Dec 21, 2018 #330

    Paulb06

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    In the real world, split fins exist to provide steering of the rear fin set...in hobby rockets they exist for style....and when it comes to extremely high impulse levels, they don't exist at all....
    The first thing you have to decide....is whether to build a BDR, ....a high altitude " throughbred" ...or something in between.....the thrust curve on the motor Pat designed looks more like a thoroughbred than a BDR to me....either way you go the most valuable resource you have are the guys that have " been there ...done that"...and the " techies" who can help you learn from others mistakes....and avoid making some new ones....you're already starting to attract some of the people who can help make this a successful project...as It progresses you'll undoubtably find more people willing to offer advice or help...just my opinion...
     
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