Nose Cones (through mach 1-3)

Howdy, my name is Noah Carter and I am the Airframe Manager for the Brazoswood High School Goddard Rocketry Team based in Texas. We are designing a rocket that will pass through Mach 1, 2, and possibly hit 3. I was wondering about nose cone shapes because I hear that conical work well for rockets reaching those speeds but have also read that a Von Kamren or parabolic are better? I use the programs RocksimPro and RASAero II, in RocksimPro, and conical nose cone seems to work better, but in RASAero II, a parabolic or Von Karman nose cone works way better (the difference between the two programs is 20,000-30,000 ft). Which one is actually better? Thank you so much for y'all's time.

Hi Noah- are you looking to maximize speed or altitude? Can you tell us more about the airframe + what motor you are using?

Rocksim creates inaccurate predictions for conical nose cones.

Incongruent said:

inaccurate predictions for cynical nose cones.

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Would you say they were "pessimistic" predictions?

"Yeah, this guy is cool and all, but I bet he's just going to lawn dart me like the rest of them"

djs said:

Hi Noah- are you looking to maximize speed or altitude? Can you tell us more about the airframe + what motor you are using?

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I would like to maximize altitude (our goal is 100,000 ft). The airframe is made of fiberglass (G12) and aluminum, the nose cone is fiberglass with a 21” long fiberglass tube (7.74” outside diameter) bellow which then fits to a transition made of aluminum that goes to 10.75” diameter fitting to the oxidizer tank (monocoque design) which is roughly 7.8 ft long and then a section of body tube made of aluminum roughly 5.5 ft long is welded to the bottom of the ox tank which houses the rest of the motor (hybrid). The fins have a tip chord of 10.5”, root chord is 21”, sweep length is 9”, and span is 8.625”. The motor we are using is custom made (we will manufacture it), it is an R class hybrid motor, 10,000 Newtons thrust.

Is this you (or someone from your team)?

https://www.reddit.com/r/rocketry/comments/7838nx/100000_ft_hybrid_rocket_issue/

If so, I think you guys are in waaaaaay over your head. What have you built/flown in the past 3 months to move towards this goal?

djs said:

Would you say they were "pessimistic" predictions?

"Yeah, this guy is cool and all, but I bet he's just going to lawn dart me like the rest of them"

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Thanks for pointing it out...

djs said:

Is this you (or someone from your team)?

https://www.reddit.com/r/rocketry/comments/7838nx/100000_ft_hybrid_rocket_issue/

If so, I think you guys are in waaaaaay over your head. What have you built/flown in the past 3 months to move towards this goal?

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That is not us, there are other high schools in Texas doing the same Goddard challenge.

noah_carter13 said:

That is not us, there are other high schools in Texas doing the same Goddard challenge.

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We are possibly going to work on a smaller scale rocket to test see the characteristics and behaviors of the rocket but we may not have the budget. We have not flown anything yet this year.

noah_carter13 said:

Howdy, my name is Noah Carter and I am the Airframe Manager for the Brazoswood High School Goddard Rocketry Team based in Texas. We are designing a rocket that will pass through Mach 1, 2, and possibly hit 3. I was wondering about nose cone shapes because I hear that conical work well for rockets reaching those speeds but have also read that a Von Kamren or parabolic are better? I use the programs RocksimPro and RASAero II, in RocksimPro, and conical nose cone seems to work better, but in RASAero II, a parabolic or Von Karman nose cone works way better (the difference between the two programs is 20,000-30,000 ft). Which one is actually better? Thank you so much for y'all's time.

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Study rockets that have been designed and manufactured in the last 10 years that operate in the velocities and altitudes that are desired. You will have your answer.

Greg

Incongruent said:

Rocksim creates inaccurate predictions for conical nose cones.

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OP mentions RocksimPro which I have no experience with, but I certainly hope is better than the hobby version.


@noah, Your project is quite interesting and ambitious. If you want to share updates and progress here, I'm certain others will find it interesting as well. *caveat* Thick skin required: criticism and strong opinions will be forthcoming.

Noah I think this is what your looking for....good luck with your project!

See pg. 9 pick your shape & go from there.


View attachment NoseCone_EQN2.pdf

noah_carter13 said:

We are possibly going to work on a smaller scale rocket to test see the characteristics and behaviors of the rocket but we may not have the budget. We have not flown anything yet this year.

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i may not know much but I do know you are picking a very lofty goal for a first rocket flown and with out practical testing are going to run into some some serious issues that could be worked out at the small scale for relatively few dollars (still a number in the hundreds) that are going to cost mucho dinero in a full scale trial.

solid_fuel said:

i may not know much but I do know you are picking a very lofty goal for a first rocket flown and with out practical testing are going to run into some some serious issues that could be worked out at the small scale for relatively few dollars (still a number in the hundreds) that are going to cost mucho dinero in a full scale trial.

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This is not the first rocket I have flown but no models have been made of this particular rocket. I will look into making a smaller model.


Sent from my iPhone using Rocketry Forum

Small world - I went to Bwood too. That is a seriously high set of goals. Good luck with it!

Here is a link to a record-setting rocket flown back in 2015. 66k' and Mach 3.5 IIRC. Might give you some ideas.

https://forum.ausrocketry.com/viewtopic.php?f=10&t=4666

https://youtu.be/CFg2Z5YK4YM

OverTheTop said:

Here is a link to a record-setting rocket flown back in 2015. 66k' and Mach 3.5 IIRC. Might give you some ideas.

https://forum.ausrocketry.com/viewtopic.php?f=10&t=4666

https://youtu.be/CFg2Z5YK4YM

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Thank you very much!

I've designed two SEDS multistage solid fuel HPR L-1 supersonic airframes as part of a university senior design project for University Tennessee Chattanooga as a mechanical engineer student. We placed third nationally at SEDS 2017. I have designed two nosecones Von Karman profile with patentable features I will not go into detail on. The design process required flight testing and iterative design due to geometric issues with material failure stress vibration related not ground testable without extensive wind tunnel runs beyond our capabilities. The operating range was from Mach 1.5 to Mach 2.2. My recommendation material thickness of Nylon SLS printed is 1.5 millimeters from flight test experience. You want SLS print for part tolerance unless you have a CNC lathe for the Mach 3 application which may require thermally more stable materials. You may chose thinner printing thickness wisely if you have super money to spend on flight tests. We spent $3.5k and found out in two flights with custom prototypes that certain regions can be thinner than 1.5 mm while other regions can't. My advice is minimize places going thinner than 0.5 milimeter unless its mission critical. You may need an iterative flight test with component failure as approaching thinner than 0.5 milimeter. A power series 0.5, 0.61, or Von Karman with a high length to drag in excess of 5.8 are optimal. Longer L/D will move CP and reduce effects of oblique shocks if you can take a skin friction drag hit.

The drag coefficient on sustainer stage determined by SimCenter research professor, a hypersonic flow expert Dr.Sreenvias yielded a drag force of forty newtons at M1.7 by drag force equation. Linux hardcode handles supersonic particle plumes on exhausts and also oblique shocks up to Mach 25 on all 3D meshed solidworks models. Leave it to the twenty year experts. Or DOD. These guys were ex-DOD and ex-mil/NASA types. Normally you want to contact an engineering department at a university if you need that drag coefficient on the cheap. Some of the dorks in mechanical department can do a part design structural FEA given enough time.

The other option is UTSI has a Mach 4+ wind tunnel that does 8" diameter objects. This was not an option due to compressor and operating costs. This route would allow you to determine not only drag coefficient to the drag force equation but to see the effects of vibrations and possible material failure modes by destructive testing of just the nosecone. I also have a NAS tulhoma director phone number on file if you need beyond that capability but due to costs reasons the director recommended UTSI for a Mach 4 could you test our nosecone hypothetical question and practically I would recommend you ask a university aero or mechanical engineering department with 3D nosecone part ready to mesh rather than use a live supersonic/hypersonic wind tunnel. University of Tennessee Chattanooga wind tunnel is only Mach 1 as 1" by 1" cube de-rated to Mach 0.8. This is why I recommend a professional CFD to determine a drag coefficient for the drag force equation from fluid mechanics. The other issue from advanced fluids with compressible gas dynamics is actual wind tunnels have errors with oblique shockwaves of supersonic nosecones past Mach 1 reflecting through the wind tunnel itself which may introduce new measuring errors. My university had donated the researchers time, rather than pay possibly hundreds to thousands for a few wind tunnel runs. The DOD tunnels like Tulahoma have a combined force test matrix agreement I asked the director about, but those may cost well millions of dollars and are intended for AirForce projects with AEDC or possible an formal agreement with corporations in aerospace or automotive industry. And Airforce staff were running the tests to customer specifications.

I think a local engineering based university would love to assist your project in their free time for your high school. They would likely do any computational fluid dynamics work for free on agreement with the high school for recognition. The actual revolve a shape manufacture a nosecone anyone can do, but when you say hey I need a drag coefficient this value isn't in a college level book on fluid mechanics design because your nosecone is a new object not a tennis ball, it takes special people with talents few people have to actually understand it in the detail needed. I've done two CFD in an automotive class with the solidworks flow sim tool, and it wasn't near as detailed as the professional Linux hardcode the research center had. So the $55,000 solidworks flow simulation CFD didn't do angles of attack with drag coefficients. ANSYS also had F600.134, 601.135, and etc as labels for boundary layers which the researchers basically said hey undergrad kid don't worry we hate ANSYS too so we use our Linux codes. ANSYS had 60 boundary layers on a fin for example and not one letter number combo told where the force was on the fin in the program it was a nightmare. So there is a advantage to ask a university professional research professor who will gladly assist for educational reasons. Many of them prefer to write AIAA articles for personal satisfaction copyright related and could use your design in a research paper or simply do the project with you to take a break from their normal routines. Some do research for the fame not money and they just grin about having names on professional articles.

Most people will settle for Open Rocket, RAS AEro, or Rocksim because they don't fully appreciate the level of detail an advanced method will provide. The advanced methods may take a few weeks. An impulsive person would lob nosecones skyward. Either method works. There is a lot of design that is iterative in real world even in engineering where everything theory wise isn't alway well picture perfect once tested in reality. You just accept the failure of a prototype and fix what breaks if it breaks. What the software and knowledge allow is further optimizing materials and thicknesses provided you can iterative fix any issues out of it the math didn't catch. You can create it from nothing but concepts and formulas.

And a lot of rocketeers have more experience than I do at Mach 3 designs practically.

noah_carter13 said:

We are possibly going to work on a smaller scale rocket to test see the characteristics and behaviors of the rocket but we may not have the budget. We have not flown anything yet this year.

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This would be a good way to gain experience. Tragically, the Mach number range determines which nosecone profile works best. And if your small rocket doesn't hit the Mach number that the full scale one does you are wasting your time and effort. You need a supersonic wind tunnel or a 3D Model of each cone with a CFD with help from a college for the kind of answer you want before you ever produced a part especially in the Mach 2-3 range as answer isn't always published. And I hate to sound worse but going real fast costs a lot of money to just play with the idea so ask someone experienced or use research help from other schools or even the Internet for data already tested.

Below Mach 2 generally power series 0.5, above Mach 1.8 Von Karman, below Mach 1.2 Von Karman, and wiki will have a design chart you can borrow for Mach numbers. Cone is inferior but it is easier and cheaper to manufacture. Nearing Mach 3 you may not even find the data and it will a university or equivalent engineering staff for technical know how to theoretically answer your problems on paper or by small scale tests. Offwegorocketry also had a few power points with some slides of drag coefficients, Cd of nosecone shapes. You want the parts with graphs showing lower Cd vs Mach number as NASA and others already did tests in the 60's. NACA also has technical documents.

In college level fluid mechanics a concept of similitude uses dimensionless numbers from Reynolds numbers and another complex method buckingham pi theory to develop a way to scale say a micro 2" long , 0.26" diameter nosecone printed part in power series, Von Karman, or cone shapes to full scale model by math theories using a wind tunnel on the small model nosecones at a higher Mach number 1,2,3 before you model and make the Full size nosecones to save money on mathematically finding which one performs best when data doesn't exist. This is what engineering does beyond high school. Supersonic wind tunnels are a pain to operate and are very expensive. You may run a higher viscosity fluid at subsonic conditions below Mach 1 to simulate the supersonic conditions. That allows you to test supersonic nosecones without even building the rocket or flying it. The computer models CFD methods do it with differential equations and do not even need actual parts built but just the nosecone as 3D model. Ask a university for help on that part in all seriousness. Or you could copy the nosecone some flyer shows you or has already done. But you picked nosecone design so I explained well this is how they do it. And it gets complicated. Basic idea is easy. It's the how, why, and math behind dictating why one shape is chosen over another.

My God, you picked an object with oblique shockwaves. Do you grasp what kind of mathy underworld you have opened? I know you can solve a nose cone equation. You may not understand why one is better or what will happen if you design it wrong it may fail in flight. It just gets complicated. Try to pick the nosecone off of the Mach number the rocket goes in flight if nothing else makes sense to you.

My God, you picked an object with oblique shockwaves. Do you grasp what kind of mathy underworld you have opened?

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holy wall of text Batman

solid_fuel said:

holy wall of text Batman

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Amen Reverend!

solid_fuel said:

holy wall of text Batman

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It requires an ancient technique, known as "reading for content" . . . So many people today, thanks to electronic technology, have the attention span of a fly and are simply unable to concentrate and focus long enough to read more than a few blurbs at a time . . . The younger you are, the worse it is !

Ez2cDave said:

It requires an ancient technique, known as "reading for content" . . . So many people today, thanks to electronic technology, have the attention span of a fly and are simply unable to concentrate and focus long enough to read more than a few blurbs at a time . . . The younger you are, the worse it is !

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Holy delayed post that brought nothing to the thread, Batman.

tl;dr -- use the chart, then scale up

I enjoy reading long, informative posts. There is much information to be absorbed and utilized, for those who are perceptive enough to make the effort to do so. AndrewASC is a very knowledgeable individual and I currently have the privilege of working with him, as part of a team, on a very large project, which should be completed in a few months.

Dave F.

It changes nothing about your post.

Ez2cDave said:

It requires an ancient technique, known as "reading for content" . . . So many people today, thanks to electronic technology, have the attention span of a fly and are simply unable to concentrate and focus long enough to read more than a few blurbs at a time . . . The younger you are, the worse it is !

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Yes, I read all of his posts at the time they were posted and learned a lot. I also took his advice. Of course some of it was way over my head because I was in high school, but I did the best I could, even learning along the way. It was a very far stretched goal for a high school team, however we were “successful” in launching a rocket of this caliber. The flight was beautiful!

For those interested, I did post about this launch under my thread “Brazoswood High School 2018 WSMR Launch”