So, based on USA flying of NAR-certified motors, how is this technology best employed for 13mm, 18mm, 24mm, & 29mn NAR Altitude models ( 1/4 A - G impulse ) ?
How would those design principles be applied to egglofters ?
Dave F.
B Engine Altitude Competition
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How would those design principles be applied to egglofters ?
Dave F.
Thanks for sharing your FAI A altitude simulation results. I would like to contribute to the laminar flow design discussion, but you should really start a new thread first. This thread is about B altitude at NARAM, and you have not yet supported your claim that a fatish laminar flow design is better than a minimum diameter design at this event.
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I think we're talking past each other. I don't think NAR altitude requires the broad cross-section FAI does. The events have different constraints.
Alan- it's all about constant curvature. NAR rules for altitude do not have diameter/length constraints as you know. So, my hunch and for an optimum NAR alt laminar flow design is that it will start with a pointy nose that gradually increases in diameter all the way to the front of the motor and perhaps a bit past (which could increase the diameter > than the motor diameter). And then there are crazy flow interactions at the fins located at the motor which will trip the flow. Also, on the nose, one should look at a curved shape. So, I'd recommend a very long curvy nose extending to the front of the motor in the model. The length should be minimized of course and within limits to accommodate the recovery device/altimeter. All of this, I have zero interest in optimizing an NAR altitude event nor starting a new thread on!
Also, if an altimeter is used, the size and where its located (typically front of the model to keep the Cg forward) will impact the overall shape. So, this may be a "fatty" after all and the model having a greater than minimum diameter.
Kooch,
In all seriousness, I just got a "mental image" of the "Cosmostrator" airframe . . . Is that similar to what you are describing ?
Dave F.
That's OK, I will not ask you again to start new thread for the discussion of FAI and NLF design, but I will continue that discussion in this thread and hope readers do not get confused.
What are the current rules for FAI altitude? I stopped following that stuff decades ago. Last I heard. good FAI altitude models were all two stage models with the large fattness built into the booster stage, and an 18mm upper stage with a prescribed total impulse split between the two motors, and of course you need special European made motors to do that effectivley. To complicate matters , I think the next WSMC is being held in the US using mostly Estes motors provided by the host. To further complicate maters, the photo you posted above appears to be a simple single stage model, that might be more representative an FAI SD design.
This is awsome. Who was the first to successfully use NLF designs in FAI competition? Who is most responsible for the NLF rocket design? I think this is a significant milestone, and I want to make sure they are acknowledged in any similar efforts.
Here is some information about altitude competition from the NAR website. Some of these ideas have already been mentioned on the first page of the this thread.
https://www.nar.org/contest-flying/competition-guide/altitude-events/altitude/
https://www.nar.org/contest-flying/competition-guide/altitude-events/altitude/
Kevin, these are some of the practical issues of FAI NLF design that I hope you can address. The design has to not only perform every aspect of it's mission, but be producible as well. One could imagine rear ejection through a 10mm motor hole, but that is not practical for most events, and a more traditional separation line and ejection is needed. This separation line could cause the flow to transition from laminar to turbulent, so it's location and mitigation is important. Furthermore, low airframe mass is also important. The structural efficiency of cones and cylinders is higher that that of constant curvature structures, so one might have to accept higher mass in a NLF design, or adopt more extreme construction methods. I know that you have adopted a somewhat traditional composite hand layup in a female mold using a bladder. You have validated an overall performance increase of 30%, so you are obviously doing something right. I had been considering winding fiber over a male mandrel, which may have to be sacrificial, and would also require a bit of surface finishing. Placing the separation line at the maximum body diameter would certainly make removal from the mandrel easier. The logical place to put the separation line is at the the laminar to turbulent flow transition ramp, although this places the separation line pretty far aft, but with a large aperture. I noticed that placed your separation line forward, where a more traditional nosecone cylinder separation line would be. Did you find transition at that line to be a non-issue, or did you have to induce a favorable pressure gradient at that point to avoid transition?
I found your "crazy flow interactions at the fins" most distressing. I had hoped that that would just be a non-issue. The boundary layer flow should already be turbulent, so transition is not the issue, but flow separation is. A related concern is if the motor jet could have an adverse effect on the flow, or even if acoustic and vibration noise could cause the boundary layer to transition. More generally, how did you address robustness in your NLF design? How mush angle of attack can you tolerate before the flow transitions?
I abandoned my research in 1990 before reaching the flying stage. It is great to see that this technology finally got off the ground, and also sad that I could have advanced the state of the art by 30? years. I still find NLF sport rocketry a fascinating subject and I hope that you will continue to discus it.
Alan
MadRocketer
Determined to do it differently
Interesting discussion. I have been thinking about how the shape of the airframe affects the flight. I’ve built this shape
And I am working on the opposite shape currently
And I am working on the opposite shape currently
Very reminiscient of the airframe of the Cosmostrator, from "First Spaceship On Venus".
Dave F.
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Of course, a simpler design than those shown in post#41 would be to go with a straight minimum diameter tube based on the motor diameter as shown in the NAR reference from post #39 for a typical NAR A-altitude competition rocket shown below. I am thinking that the model shown in post#19 looks like a F.A.I. parachute duration competition model. Apogee sells a similar model (see below) for NAR parachute duration. Such a design has a diameter larger than the motor diameter, but could be optimized to carry a large enough parachute to win a duration competition. Obviously, a larger tube diameter will have more drag because the drag formula includes CD, air density, velocity squared, and cross sectional area. The graphs in post#28 are interesting. I don't know what ECB stands for, but I assume that the comparison between the laminar model and the ECB model are for models with the same or near the same diameter and same motors. I assume that the graphs are the results for CFD calculations and that actual flight performance is similar. Keep in mind 3D CFD computer programs are beyond most model rocketeers (RocSim and OR are not CFD codes). I assume that the turbulence model in the CFD code is pretty good and reliably calculates the transition from laminar flow to turbulent flow.
Basically, there are two types of drag in subsonic flow, skin drag and form drag. Skin drag is directly proportional to the velocity gradient at the model's surface. Form drag is caused by the creation of large flow structures like separated flow. In general form drag can be much greater than skin drag. In a laminar boundary layer the velocity gradient at the wall is not as steep as a turbulent boundary layer, hence, the skin drag is much lower. The following is off subject a little bit, but the paradox is interesting and fun. Probably, many people here know this answer. Why does a golf ball have dimples? It is to make the boundary layer go turbulent earlier. But wait a minute we know that the skin drag will be larger. Yes, but the high velocity edge of the free stream flow will be brought closer to the aft end of the golf ball, giving more energy for the flow to push the separated flow to the back of the ball. With the area of the separated flow reduced (pressure recovery is better) the overall CD is reduced and the drag on the ball is lowered. Hence, a dimpled golf ball will go farther than a smooth golf ball.
https://www.apogeerockets.com/Rocke...odel-Rocket-Kits/International-Thermal-Sailor
Basically, there are two types of drag in subsonic flow, skin drag and form drag. Skin drag is directly proportional to the velocity gradient at the model's surface. Form drag is caused by the creation of large flow structures like separated flow. In general form drag can be much greater than skin drag. In a laminar boundary layer the velocity gradient at the wall is not as steep as a turbulent boundary layer, hence, the skin drag is much lower. The following is off subject a little bit, but the paradox is interesting and fun. Probably, many people here know this answer. Why does a golf ball have dimples? It is to make the boundary layer go turbulent earlier. But wait a minute we know that the skin drag will be larger. Yes, but the high velocity edge of the free stream flow will be brought closer to the aft end of the golf ball, giving more energy for the flow to push the separated flow to the back of the ball. With the area of the separated flow reduced (pressure recovery is better) the overall CD is reduced and the drag on the ball is lowered. Hence, a dimpled golf ball will go farther than a smooth golf ball.
https://www.apogeerockets.com/Rocke...odel-Rocket-Kits/International-Thermal-Sailor
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Alan
The nose overlaps the body and is slip on. It is also very thin (0.004”) and less than the BL thickness, so tripping at that juncture in not a concern. There are other things though that are of concern and that were addressed in my 2nd iteration. My latest model/design is round two and something I started in 2012. Bob Parks was a huge mentor.
More comments later as I’m getting married on Sat!
Kooch
Thanks, and congratulations.
An aside. I'm a member of a number of forums, rocketry and model airplane and a professional engineer. I see a lot of people wanting analysis first, and lots of analysis and theory before anything gets built. This is the bane of engineering focused companies. At some point, a near point and where one has done a comparison, old and new, and one has proven principally that new is better than old, build it, test it and then re-group. If it never gets built, you will never be able to confirm whatever much or little of your analysis. The ultimate goal of making a winning model can only be had by executing and actually making it.
Kooch
Kooch
Welcome back.
An aside: I'm not a PE, or even an aerodynamicist, at least no more than anyone else with a masters degree in aerospace engineering. I have zero interest in building or competing FAI fatrocs. Historically, the skill level of FAI competitors was too low for them to figure out how to get altitude models tracked, or perhaps to optically track contest rockets. So they make it easier by adopting the fat rocket approach to drastically reduce performance and increase optical signature,. Then they abandoned optical tracking and went with barometric altimeters, but they needlessly retained the fatroc design rules. These fatrocs bear little resemblance to models commonly flown, and require competitive motors that are nearly impossible to obtain in the US. I refuse to play that game.
Nevertheless, I recognized that those simple fat tubers could be substantially improved by NLF design. I thought that it would be an interesting problem in constrained design optimization, and that I might be able to do it on my C64 computer, dispelling the myth that you need full blown CFD and super computers to address this problem. Had I been successful in designing this victory-maker wonder-thing, I would have just sent it to my old teammate Dave Cook for the win, or chose some other worthy rocketeer. Obviously, I did not create such a design in 1990. I did write a good higher-order surface-source program that worked very well on my C64 for calculating the flow-field about a body of revolution. So it did bear some fruit, but it was also apparent that the C64 was not fast enough to solve the inverse design problem in a reasonable amount of time. I had all my ducks in a row and I just need to crank faster. I think porting my code to a crusty used 386 PC would have made the project too easy and I lost interest.
I'm happy to share more info on the work I did in 1990, etc, but I really want to make this discussion about your efforts that have born real competitive fruit.
Alan
Well, NARAM-63 is this coming weekend (July 16) and B-Altitude is one of the competition events. It will be interesting to see the results. I wonder if any of the competitors have been posting here. BTW A-Altitude is listed as one of the NAR competition events for next year.
It might be a good idea to read completely through this thread . . .
https://www.rocketryforum.com/threads/naram-63.167611
Dave F.
Alan- there are programs out there and 3D cfd sims. You want a 3D vs 2D for rocket drag analysis.
I assume that the NARAM-63 B-Altitude record results are in.
https://www.nar.org/site/naram-63/contest-range/naram-63-results-b-altitude/
https://www.nar.org/site/naram-63/contest-range/naram-63-results-b-altitude/
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