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Ogive versus parabolic which one is better for supersonic flights

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Which is most effective for supersonic flight the ogive or parabolic

  • Parabolic

  • Ogive

  • Other, please explain on thread


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ScrapDaddy

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I am chalanging my self I'm trying to take a 18mm minimum diameter rocket to supersonic flights but should I use a parabolic nose cone or an ogive?
 

TWRackers

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I've got a copy of a NACA (NASA's predecessor) report which tested a variety of shapes including those two up to around Mach 5. In the low supersonic range (say up to Mach 1.5) a parabolic shape or one close to it had a lower drag coefficient than anything pointy (ogive or cone). I'll try to dig up the reference for you.

UPDATE: Here it is:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930087274_1993087274.pdf
 
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ScrapDaddy

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The nc also has to be efficent in transonic flights for obvious reasons
 

The EGE

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For 18mm Machbusters, the nose shape does not matter a whole lot. What matters is the weight. For a D21, you want to keep the whole thing under 18 to 20g sans motor in order to break Mach, and as long as your Cd (drag coefficent) is under 0.8, you'll be able to break mach.

I'm running out the door now, but I'll have more on this later.
 

ScrapDaddy

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Wait An 18mm machbuster is possible? Well ege do you have any ideas or tips like add a boattail?
 

Microspeed

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This article and diagram might be of some use:

http://en.wikipedia.org/wiki/Nose_cone_design
http://en.wikipedia.org/wiki/File:Nose_cone_drag_comparison.png

You won't be able to break mach single-staged on a C6 (you'd probably want a C6-7), but it is certainly possible with a lightweight, well-finished model model on a D21.

I've attached a file and screenshot of an example design. It uses a LD-Haack nosecone (shape control = 0), which according to RockSim is a tad bit better than a parabolic, but they ought to be very similar. It uses 4 grams of nose weight in order to allow for a shorter tube and smaller fins, but even then it is only marginally stable so it would have to be carefully built. The fins are 1/32" carbon fiber. RockSim (which is probably a bit optimistic) says 900 mph with a D21 and 500 with a C6.

Maximizing speed is all about minimizing weight and drag.

Minimizing drag:
Frontal - 3 fins, thin fins (carbon fiber for fiberglass), no launch lug, minimum diameter
Skin friction - As short as possible, small fins, very well finished (gloss finished and/or polished)
Fins should be designed so as to not flutter, which can become a big issue around transonic speeds.

Always launch out of a tower to eliminate the launch lug, flying off a piston can also provide a nice speed boost off the pad.

minimachbuster.png


View attachment Machbuster.rkt
 
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ScrapDaddy

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Ok but I have to base my design around the apogee blue streak I have to make do with the parts but I can supply a boattail tell me the ways I can make it go supersonic safly
 

The EGE

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The Blue Streak is a perfect rocket to base this on. It's long, stable, and very light - just 15g stock. The nose cone is parabolic, and it's got a nice kevlar shock cord.

The problem is the fins. They're nice die-cut balsa fins. However, they're wept back and will certainly flutter at Mach 1. I would recommend making new fins (see picture for shape) out of 3/32" hard balsa and soaking them with epoxy or CA (superglue).

Don't bother with a boattail. The Blue Streak is minimum-diameter as is, so a boattail wouldn't really reduce drag at all.

I'd suggest using a piston - there's plenty of simple plans available online - for the speed and drag advantage, but if you have to launch it off a rod it'll be no big deal.

As for safety:
The first thing to do would be to download OpenRocket and do all your designing in it, so that you know before you build it that it'll be stable. That'll also let you adjust the fin size so they'll be large enough to be stable, but not too big and prone to breaking during trans-sonic flight. Once you build it and have the motor, do a good old-fashioned swing test for one last check.

Make sure the RSO knows that it's going to be a supersonic flight and that you have a waiver good to at least 3000 feet. (Don't launch it in a local park; defintiely find a local rocketry club). Having all the sets of eyes in the club will make it possible that someone might spot the ejection puff 2500 feet up.

Don't use a copperhead with it; use a Quest Q2G2 or find somebody willing to let you use a well-dipped quickburst igniter. You have to have instant ignition. If it chuffs on a piston, then it won't be stable when it comes up to full pressure, and a tiny rocket going unstable very fast is very, very bad.

Make sure you glue the fins on very well, preferrably with epoxy, and make sure to fillet them. The fillets add strength and reduce drag.

Paint just one coat of a bright color like red or orange. That way it's visible, but the paint shouldn't add too much weight.

Write your name, address, and phone number multiple places on the rocket with a permanent pen. If someone finds it, they'll be able to contact you.

Blue Streak.jpg
 

ScrapDaddy

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Where can I get coustum cut fins? And can you give me the dimentions of the fin?
 

Micromeister

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Mach+ flights have been done with model rockets for a very long time. Doug Pratt of Pratt Hobbies used to offer a kit for such attempts.

Funny things is; If your flying a mach busting model your never going to know it anyway unless you have others recording the flight well away for the launch site outside the mach cone. You'd thing one could come up with many other much more worthwhile expenditures of time and effort then something that's been done so many times before no real reward.
 
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ScrapDaddy

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Well I guess it's just for bragging rights, wing able to say you made a rocket go supersonic
 

The EGE

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Well I guess it's just for bragging rights, wing able to say you made a rocket go supersonic
Well... unless you manage to carry a recording altimeter on board your rocket, or have a nice, high-resolution tripod-mounted video camera, there's not much you can do to prove that your rocket went to mach.

There are currently no lightweight recording altimeters light and small enough for your 18mm machbuster; until the AT 24/120 and CTI Pro24 cases get released there's no motor smaller than 29mm that can bring one to Mach. It's too small to hear the sonic boom from; even a 29mm model will produce just a faint 'pop' as it's small and rapidly moving away.
 

ScrapDaddy

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but building and designing one already has bragability rights:roll: Yea thanks to THE EGE and MARKII especially without you guys i would be scared to death with the product I wouldve come up with........:y:
 

ScrapDaddy

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Out of curiousity, where does one get a Von karman nose cone?
 

ScrapDaddy

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Ok I'll take it there are no commerical Von karmons availible
 

dragon_rider10

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Forgive my ignorance,but aren't ogive and parabolic the same thing?
 

Bazookadale

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Forgive my ignorance,but aren't ogive and parabolic the same thing?
Nope - the non technical difference is an ogive comes to a point where a parabola is rounded - I'm sure someone will have the technical explanation for you
 

dedleytedley

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I've read the links and done some searching but I can't seem to find a nose cone profile template generator for producing custom shapes. For examples the Standard Arm nosecone, Harpoon nosecone or other complex shapes. Can anyone help? Ted
 

ScrapDaddy

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I think this is OTD and you should start a new thread
 

ScrapDaddy

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PLEASE NOTE! in subsonic rockets (99 percent of them) nose cone shape has no dramatic impact which is why you see many ogives they are aesthetically Pleasing
 

cjl

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PLEASE NOTE! in subsonic rockets (99 percent of them) nose cone shape has no dramatic impact which is why you see many ogives they are aesthetically Pleasing
It does have a significant effect on drag, even for subsonic rockets. Ellipticals are the ideal.
 
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