"Finless" Rocket Design - Ram Air Intake Stabilization?

Discussion in 'Oddrocs' started by KenECoyote, Jan 18, 2016.

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  1. Jan 20, 2016 #61

    KenECoyote

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    Wow! Great links! I'll have to take time to peruse all that info...should be good food for mindsim. :)

    Regarding the compression of airflow, it may not be a factor in my first tests; however it will come into play with later upscale and larger motor/higher speed tests (if it gets to that point). Also I think nose cone shape may have some effect (especially at higher speeds) since cones like the Nike Smoke behave differently than the usual conical (ogive?) ones we see - I've read that sampling holes on the smoke should be farther away from the nose cone since that one creates odd readings close to the cone...I'd guess the shape creates a lower pressure area at the base since the air is pushed in a straight line away at an angle whereas a curved side profile of the normal conical cones likely allows the air to follow the curve due to the tendency of fluids to follow the surface of an object (Coanda effect?).

    On the topic of outlet & inlet size I think for the initial tests I'll try larger than inlet, same area as inlet and smaller than inlet. I think larger than inlet may be best since it would be least likely to create too much pressure inside the shroud (which means drag) and also would possibly allow the air to be drawn out of the slots on the back end more easily (we'll see).

    Thanks for all the homework prof! ;)
     
  2. Jan 20, 2016 #62

    bill_s

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    I built and flew a rocket somewhat similar. It was actually based on a Big Daddy kit (3") which was purchased to use the nose cone on another rocket. I left out the centering rings. I used the laser-cut fins (TTW) and pre-slotted body tube but cut the fins to minimal stumps outside the tube. The airframe was from a cheap BT50 kit extending the BD motor mount tube and providing a BT50 nose cone. The total length was a little over twice the legth of the stabilizing tube. There were some additional balsa sticks between the airframe and the front of the outer tube for more structure and a little bit of jet engine intake look. It was fairly neat looking and flew great.
     
  3. Jan 20, 2016 #63

    CrazyOB

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    I would perform these tests in reverse order smaller, same, larger. That way you only need one tube, and can bring some of your cutting tools to the field. Once you get to a point where the slotting is 'oversize' from the most effective setting, you can adjust with a judicious use of masking tape. It ain't pretty but this is 'proof of concept' testing.

    Yes, the nose cone shape does effect things obviously. Lift/drag/laminar flow. This is why a VonKarman NC is supposed to be the most efficient, and the true conical is one of the least efficient AKA Nike Smoke, Black Brant, etc... The true conical is cheap and quick to make versus the others.

    I have some ideas for faster/larger rockets but kind of germane for the moment. Need to sit down with the calculator, along with my 100,000 other little projects.

    Just remember I am no expert! Following my advice can lead to lawn darts, etc... But what the heck it certainly can be exciting.
     
  4. Jan 20, 2016 #64

    rstaff3

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    CrazyOB, quit inducing lawn darts, I thought that was my job. :)

    Too bad Dean Black quit following TRF. He's an actual rocket scientists and since he came up with GDS, I suspect he could lend useful insight.
     
  5. Jan 20, 2016 #65

    rstaff3

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    Now that the rocket is getting longer vs the outer tube, I wonder if said tube will just start acting like a ring fin? Did you put it in Rocksim? I'm again sorry if this was mentioned earlier but I guess it would be ideal to make the rocket neutrally stable.
     
    Last edited: Jan 20, 2016
  6. Jan 20, 2016 #66

    CrazyOB

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    Sorry can't do that. Ken was there when I darted my 3" Wildman Punisher from 4,800 feet. We still haven't found it, although I spent a full day on my mountain bike looking for it. So ' King of Darts' am I.
     
  7. Jan 20, 2016 #67

    KenECoyote

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    Nice! Do you have any pics? :)

    I wanted to start with a larger outlet first since: 1) it would allow more air through the tube and reduce back pressure; 2) It's easier for me to start with a larger cut hole and use masking tape to close off as I go (rather than removing the shroud and cutting it in the field) and 3) I forgot the third reason. :)

    The rocket is currently longer vs. the outer tube so that it can allow incremented tests. Even in the current "almost looks like a regular rocket" there are calls for safety. I can't imagine what would happen if I first try the one with the full length shroud/outer tube. I want to be able to have a good first flight and gradually try increasing the shroud length to see the progressive effect. I'm not familiar enough with Rocksim to put this in. Also I'm not sure if it could even calculate it correctly because it's not a ring fin since the end is blocked off and it's not a transition since it allows air through and to the side. :confused:

    Lawn darts? Nah...more like unguided SCRAM missiles! :) Yes, I saw your GDS thread hijack last night (although I think I read it earlier last year). However with complex designs, there are often many factors which are hard to predict as well as account for. Even rocket scientists make mistakes. :wink: Still, I think educated scientific feedback is invaluable in this case since I'm currently theorizing a lot of stuff based on logic and my limited knowledge of aerodynamics. This is also why I really appreciate the feedback from GlenP and CrazyOB.

    Just an update on a few things. Given the current weather forecast, there may not be a club launch this weekend. I think I can still do a personal launch; however I may first make a even smaller prototype using hi-teck rockit partz (tp tubes and similar) and launch it using an A motor.

    Just for kicks (assuming this works and crossing my fingers), future possibilities include making it 2 stage where the first stage is basically the entire shroud and then the 2nd stage separates out most of the main bt as well as some of the internal vanes (which would be the upper stage rocket fins). Also a possible Apollo Command Module-like rocket with air inlets in the nose cone but covered with a thin fabric that allows air in and through. I like to think outside the box (or is it fantasize?). :)
     
    Last edited: Jan 22, 2016
  8. Jan 20, 2016 #68

    rstaff3

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    Give me the dimensions and I can put it in rsim for you, just to get an idea of the cp/cg with the ring fin effect. BT diameters, tube lengths, nc length and CG with the laundry installed. I would assume that the full ring fin will give a good first order estimate.
     
  9. Jan 20, 2016 #69

    KenECoyote

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    That would be terrific! :)

    Here you go...
    Estes Converter (Long): Length = 978mm; Width = 34.3mm;
    Estes Converter (Short): Length = 620mm; Width = 34.3mm;

    Shroud (Short): length = 280mm; Width = 56mm
    Shroud (Long): length = 455mm; Width = 56mm​

    Nosecone is 65mm extending out of bt. First test includes the bolded items. I'll have to update later with the CG since I can't get to it right now.

    Thanks Dick!
     
  10. Jan 20, 2016 #70

    rstaff3

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    Here's first cut. Rather than put in all the internals, just give me the weight and CG and we'll see what it looks like! 2016-01-20.jpg 2016-01-20.jpg
     
  11. Jan 20, 2016 #71

    KenECoyote

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    Okay, I had to mock things up since the internal vanes aren't in place and the rocket isn't completely built yet. I do plan on using a simple altimeter and likely will be adding clay weight into the nose later, but here is what I have:

    Weight rtf: 176g
    CG down from tip: 590mm
     
  12. Jan 20, 2016 #72

    KenECoyote

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    Would you believe I measured and listed the CG before looking at your attached pics? The RS shot you have lists CG at 587mm!
     
  13. Jan 20, 2016 #73

    CrazyOB

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    What is less than 1/8" among friends? Nice job guys.
     
  14. Jan 20, 2016 #74

    rstaff3

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    That's what I call a coinkydink! Here it is with your latest numbers and a C6. Unless I mucked up the data entry, it should be stable without air slots. Or so sez the mighty RockSim!

    2016-01-20 (1).jpg
     
  15. Jan 20, 2016 #75

    rstaff3

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    BTW, a C6 won't lift this rocket safely.
     
  16. Jan 20, 2016 #76

    KenECoyote

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    Yes, I figured that much with all the extra baggage being thrown on (saw this happening as I was putting it together and then adding in the altimeter as well as expecting to add in nose weight). I have a D11-3 reload I plan to use. :)

    Thanks!
     
  17. Jan 20, 2016 #77

    KenECoyote

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    I'm also giving thought to a smaller diameter shroud...it should mean less drag and weight as well plus I think it would be better for a higher speed boost. I'll try some different things out, but a really cool eventual goal would be a fast HP version with a shroud close to the bt. We'll see.
     
  18. Jan 21, 2016 #78

    rstaff3

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    I don't have a D11 motor file but a D13 gives a much nicer profile...470 ft, optimal delay between 3 and 4, and you could use a standard rod instead of a 30 footer :D Magin drops to .7. That might be good for a first flight.
     
  19. Jan 21, 2016 #79

    KenECoyote

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    You are ahead of me sir...I had incorrectly recalled that reload andit is actually a D13-4W (I only remembered it was 1 off from a D12). :)
     
  20. Jan 21, 2016 #80

    KenECoyote

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    Just another update that I've started building smaller rockets to test this (one mini and one A size)...should make building and testing much simpler while I wait for a club launch. :)
     
  21. Jan 21, 2016 #81

    rstaff3

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    Will be watching for what you come up with.
     
  22. Jan 22, 2016 #82

    KenECoyote

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    Okay, watch this! :wink:

    Well, I dug up what parts I had. I had plenty of BT-20 parts, so I grabbed the weighted nose cone from a Hi-Flier and stuck it on. Looked good, but I thought it might still be too big, so I wanted to go even smaller.

    I knew I had purchased a mini customizer set since I was using the launch pad last year (probably used it for larger rockets than it was intended for, but it was fine).

    I found a few parts while I was still looking for the kit. I had a 4" BT-5 tube and I stole a nose cone from an Estes Blenders set.

    I figured I'd use Estes D and E motor tubes as shrouds for the mini.

    [​IMG]
     
  23. Jan 22, 2016 #83

    KenECoyote

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    Found the Mini Customizer set!

    [​IMG]

    Boy, the stuff is really piling up on my work table...

    I next figured I can build two minis...one short and one long. I can also use my modular building system to swap shrouds around. When's the last time you've seen a modular rocket build? :)
     
  24. Jan 22, 2016 #84

    KenECoyote

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    Here are the two planned minis...long and short. I have most of the parts I need shown here...two small fiber disks to use as shroud stops (center marked off for cutting), two other disks for shroud bottoms and balsa pieces sized for shroud vanes/supports.
    [​IMG]
     
  25. Jan 22, 2016 #85

    KenECoyote

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    Here I figured I'd start with the shorter shroud (D size motor tube).

    Marking for the 3 vanes and precut strips ready:

    [​IMG]


    I have the precut balsa strip glued to one side and will trim off the excess.
    [​IMG]

    Later on I realized I should taper the leading edges since at this size, the balsa strips are relatively wide. For the next two strips I trimmed down one end before gluing.
     
    Last edited: Jan 22, 2016
  26. Jan 22, 2016 #86

    KenECoyote

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    Here is the finished short shroud. Notice the fronts of the vanes are air foiled.

    [​IMG]

    You'll also see that I have the shroud bottoms cut (what a pain cutting all those little circles out by hand!). I've also glued on the black bottom stop ring to the motor tube.

    ARRGH! I used a blade with the tip already broken off since I would usually have them break when cutting circular patterns in cardboard anyway.

    [​IMG]
     
    Last edited: Jan 22, 2016
  27. Jan 22, 2016 #87

    KenECoyote

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    Test fit! Looking pretty good to me!

    [​IMG]
     
  28. Jan 22, 2016 #88

    KenECoyote

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    Okay, time to do some math...I can't believe I actually remembered the formula for the area of a circle! Unfortunately I chose too small of a piece of paper. :facepalm:

    I figured out the area of the inside diameter of the shroud minus the outside diameter of the bt minus the cross-section area of the three vanes. This is to figure out the inlet area since CrazyOB and GlenP were saying I should follow area rule and have a 1:1 inlet-to-outlet ratio. I took the liberty of adding 10% since I felt there would be other factors going on such as drag inside the tube and the air hitting the bottom,etc. Once I had that figure, I divided by three outlets and came up with what I felt was a good size to first start with.

    So out came the Estes tube marking tools (I used all three Estes marking tools on this!). :)

    [​IMG]

    [​IMG]
     
    Last edited: Jan 22, 2016
  29. Jan 22, 2016 #89

    KenECoyote

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    I next glued on the shroud bottom, then when that was dried, I cut the outlets out. I then slipped the shroud onto the bt. Looks good to me!

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    I weighed this one and even with some clay nose weight already added, it came out to only 12 grams with motor! Given that, I should really use the 1/4A3-3T motors and unfortunately I don't have any. It may be a while before I can get them. :facepalm: given that, I may have to finish the longer mini and launch that first (we'll see).
     
    Last edited: Jan 22, 2016
  30. Jan 22, 2016 #90

    neil_w

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    Cute!
     

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