I am trying to figure out how much better performance I will achieve when I am sanding my rockets, making sure the fins airfoil, and keeping that paint job extra extra silky smooth. My wife asked me if all the extra effort really translates into meaningful better performance and I didn’t have an answer. I assume it’s significant because everyone takes it very seriously, but how much higher, how faster will the rocket actually go? 5% better? 30%? Difficult to answer I’m sure, but I’d appreciate the effort as my googling isn’t amounting to any solid answers.
How much higher will a rocket go if you try to reduce drag?
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GrouchoDuke
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You can use OpenRocket (or another sim) to get a good feel for this for your specific rocket. For a rough wag, airfoiled fins will help more than a polished rocket (at least when you compare those to square fins to a normal painted finish). A highly polished surface definitely helps though.
That said, it depends. If your rocket is a fairly slow flier, you won't see much difference at all. If you have a supersonic record attempt rocket, fin shaping, polish and perfect gaps between parts will really help. Another gotcha though is the faster you go, the harder is is to keep a perfect surface finish throughout a flight. For example, a Mach 2 rocket could lift off the pad as "polished," but it'll probably be more like "smooth paint" overall by the time it reaches apogee. YMMV, of course.
For a recent Mach 2 rocket of mine, the difference between smooth paint and polished in OpenRocket is about 9% in apogee.
That said, it depends. If your rocket is a fairly slow flier, you won't see much difference at all. If you have a supersonic record attempt rocket, fin shaping, polish and perfect gaps between parts will really help. Another gotcha though is the faster you go, the harder is is to keep a perfect surface finish throughout a flight. For example, a Mach 2 rocket could lift off the pad as "polished," but it'll probably be more like "smooth paint" overall by the time it reaches apogee. YMMV, of course.
For a recent Mach 2 rocket of mine, the difference between smooth paint and polished in OpenRocket is about 9% in apogee.
Here's a link to an OpenRocket discussion, with a link to the download site in the first post. The download is free, and you'll soon find yourself experimenting with a lot more than Cd.
https://www.rocketryforum.com/threa...2-final-is-now-available-for-download.177835/
https://www.rocketryforum.com/threa...2-final-is-now-available-for-download.177835/
GrouchoDuke
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Yep!
GrouchoDuke
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FWIW, if I'm flying a sport rocket (e.g. one for fun, not for a competition) then I don't spend time to get them past a smooth paint finish. That roughly equates to a quick wet sand of the color followed by a clear coat. After a flight or two, they'll have some dings & scuffs anyway. That 9% difference wouldn't apply to a subsonic rocket. The difference should be much less.
I also just round the fin leading & trailing edges with some quick hand sandpaper work. I prefer the extra toughness of rounded fins over sharp edges unless I really need the extra performance.
I also just round the fin leading & trailing edges with some quick hand sandpaper work. I prefer the extra toughness of rounded fins over sharp edges unless I really need the extra performance.
For some reason I can really improve performance by launching up at Hartsel Colorado on a hot July day. Darn chutes don't work so good and the 8800 foot elevation high Prairie is really hard to land on.
Like the old guys did with the Spitfires trying to catch the buzz bombs, a good canuba wax job can add up to 5 mph!
Don't want to see any rail buttons!
Perfect nose cone aerodynamics a must.
Back in the 70's an old guy (like 35) was trying to get his dirt bike to go faster with expensive light weight parts. He really needed to take some weight off the belly. Like the ski jumpers say, fat don't fly!
Like the old guys did with the Spitfires trying to catch the buzz bombs, a good canuba wax job can add up to 5 mph!
Don't want to see any rail buttons!
Perfect nose cone aerodynamics a must.
Back in the 70's an old guy (like 35) was trying to get his dirt bike to go faster with expensive light weight parts. He really needed to take some weight off the belly. Like the ski jumpers say, fat don't fly!
Remember, that 9% that @GrouchoDuke stated in post #2 comes with 2 caveats. First, as he stated: the faster you go, the more difference it makes. And Mach 2 is Really Damn Fast (RDF)! Drag is proportional (all else being equal) to the square of speed, so if you're only going M 0.5, the drag forces will be approximately 1/16 as great. It's actually a lot more complicated than that, especially in the transonic region. But the point remains that at greatly lower speed there will be a hugely reduced effect. If we go with 1/16, that would by 9/16 of a percent improvement, 0.5625%. If you're going Mach 0.75, it would be about 1.26%. And remember, these are very rough estimates.
The second, which he also stated, is that 9% is for perfect airfoils and finish compared to square edged fins and a "normal painted finish". Merely rounding the edges, as he touched on post #6 will get you a large portion of the potential improvement, as will doing a "really nice" paint job, if you're staying subsonic. I'll take a wag and say that, if perfect airfoils and finish give you a 1.26% improvement over square edges and a "normal" paint job, rounded edges and that "really nice" finish might give you about 0.5% to 0.75% improvement.
Conclusion: in LP rocketry, perfect airfoils and polished finishes are more about aesthetics than performance. Which does not mean they are not worth perusing if you want to, as long as you understand what you will and won't get: a beautiful model and great performance improvement respectively. It's only in high power, supersonic stuff that the performance improvement is great.
The second, which he also stated, is that 9% is for perfect airfoils and finish compared to square edged fins and a "normal painted finish". Merely rounding the edges, as he touched on post #6 will get you a large portion of the potential improvement, as will doing a "really nice" paint job, if you're staying subsonic. I'll take a wag and say that, if perfect airfoils and finish give you a 1.26% improvement over square edges and a "normal" paint job, rounded edges and that "really nice" finish might give you about 0.5% to 0.75% improvement.
Conclusion: in LP rocketry, perfect airfoils and polished finishes are more about aesthetics than performance. Which does not mean they are not worth perusing if you want to, as long as you understand what you will and won't get: a beautiful model and great performance improvement respectively. It's only in high power, supersonic stuff that the performance improvement is great.
GrouchoDuke
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Excellent pile on points. However, the 9% difference I quoted above was just the difference between smooth paint and a polished finish. That's from sim data for a rocket that's otherwise very optimized (my current I-motor record rocket), including airfoil shaped fins. On that same rocket, while holding the finish constant (at my flight-data-measured finish), going from airfoil shaped fins to square fins loses 8% of apogee. Again, that's a Mach 2 rocket. Most rockets will see much less difference.
For my sport high power rockets, I really like to have a good looking finish. That said, I almost never shoot for a perfect paint job. If they look great in a launch photo, that's honestly good enough for me. In reality, I usually have about "3 foot" paint jobs when a rocket is new - they look great from a 3 foot distance, but closer inspection reveals flaws. For launch photos, a 10-foot paint job is probably more than plenty. There are several people here that do absolutely gorgeous paint jobs where you can't see flaws at any distance.
One of the biggest easy things to do to improve your rocket's appearance is to have nice fillets. There are some chunky fillets out there - they appear to work for people, but they're easy to spot as ugly in photos.
On the other hand, for fully optimized rockets, I don't care how the rocket looks to eyeballs or cameras. I only care about how it looks to the air. Colors don't need to match, etc. So, super polished finish, but it might be ugly.
FWIW, this rocket of mine is pretty ugly with landing/lakebed/hangar rash when you get up close. But, I think it looks pretty darned good in launch photos. (It has rounded fins and nice looking filets
)
A mirror finish like what "Nathan" on here produces comes at a big labor cost.
Angel_of_the_Skies
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Nathans work is one I admire. I can never seem to get past the spray paint application.A mirror finish like what "Nathan" on here produces comes at a big labor cost.
I’ll fill spiral, airfoil fins, filler primer the rocket, sand, prime, sand the primer, mask, and paint, but that’s as far as my patience allows me.
I find sanding the color coats require skill, maybe I’m just lousy lol.
Back on topic, has anyone experimented with actual launches on the effect paint smoothness has on their apogee altitude ?
Would be cool to see before and after pics as well !
I think that would be practically impossible as there are too many variables involved in a rocket launch with the variations in motors and launch conditions.
I am not certain how much of a difference, but we had a guy would spray his rockets with lubricant before flights and his rockets would go 10-30 feet hight with the sam motor.
I suppose you have seen the advertisements for these ceramic coatings / wax alternative that is advertised all over the internet where the guy sets the bottle on the hood and it immediately slides down the slope and falls on the ground in front of the car because the surface is so slick. So maybe that's what you should try.
That is exactly what that guy used.
Tom Flint
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I have found that trying to make my model sized rockets smooth and pretty decreases their altitude performance because all the fillers, sealers, and extra coats of paint add a significant amount of weight. I used to just round the leading and trailing edges of the fins, not seal the balsa grain at all, and give it one coat of rattle can spray paint. My older rockets are lighter and go a bit higher than newer pretty ones I've built, when two rockets of the same design are compared.
Here's a bit of exploration in OpenRocket. We'll stay in the subsonic region for this exercise.
Starting with the Dual-deploy example rocket, which shows 3787', 543 mph on an I1299:
Here's what the drag looks like:
Friction drag is more than half of the total drag. Let's see the effect of getting rid of friction drag entirely, by overriding the Cd of the whole rocket to 0.174 + 0.132 = 0.306:
And our new results:
So by removing all friction drag, we went from 3787' -> 6055', an increase of about 60%. That's huge. Of course, in reality you can't achieve a frictionless surface finish, but it gives you an idea how much the friction drag is contributing to your flight profile.
Let's undo the drag override and set the component finishes to "Finished/polished". Looking at the component analysis again:
Friction CD has decreased from 0.509 to 0.349. Let's see the effect on flight:
So changing from "regular paint" to "polished" took us from 3787' -> 4301', an increase of about 14%. That is pretty significant if you're really going all-out for altitude. I'm not sure how close to a perfect "polished" surface most builders can get, but I would venture to guess that @Nathan for example is pretty darn close, if not all the way there.
You can do similar exercises experimenting with fin profile and other factors.
Starting with the Dual-deploy example rocket, which shows 3787', 543 mph on an I1299:
Here's what the drag looks like:
Friction drag is more than half of the total drag. Let's see the effect of getting rid of friction drag entirely, by overriding the Cd of the whole rocket to 0.174 + 0.132 = 0.306:
And our new results:
So by removing all friction drag, we went from 3787' -> 6055', an increase of about 60%. That's huge. Of course, in reality you can't achieve a frictionless surface finish, but it gives you an idea how much the friction drag is contributing to your flight profile.
Let's undo the drag override and set the component finishes to "Finished/polished". Looking at the component analysis again:
Friction CD has decreased from 0.509 to 0.349. Let's see the effect on flight:
So changing from "regular paint" to "polished" took us from 3787' -> 4301', an increase of about 14%. That is pretty significant if you're really going all-out for altitude. I'm not sure how close to a perfect "polished" surface most builders can get, but I would venture to guess that @Nathan for example is pretty darn close, if not all the way there.
You can do similar exercises experimenting with fin profile and other factors.
Use OpenRocket, you can find out.
Hi. I see everyone painting their rockets. Is it part of NAR necessity or well why not. https://www.rocketryforum.com/threads/is-painting-the-rockets-necessary.156163/
I built a scratch Bt60 rocket with a small tailcone to 24mm mmt. I intentionally built and left the rocket as un finished as possible. The fins were square rough cut, and nothing painted or sanded.
I did a test flight of my basic 3fnc rocket on a Estes E12 motor to 875'. I then did finish up work on the rocket: rounded fins, fillets, paint etc. I flew it again on another E12 to 1,182', about 35% improvment on a light sub sonic rocket.
I built a scratch Bt60 rocket with a small tailcone to 24mm mmt. I intentionally built and left the rocket as un finished as possible. The fins were square rough cut, and nothing painted or sanded.
I did a test flight of my basic 3fnc rocket on a Estes E12 motor to 875'. I then did finish up work on the rocket: rounded fins, fillets, paint etc. I flew it again on another E12 to 1,182', about 35% improvment on a light sub sonic rocket.
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IMHO, the (kit) model rocket with the lowest coefficient of drag that I'm aware of is the old Estes Astron Sprint. Apparently there is a new XL version!
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Consider the old CMR Humpty Dumpty.
You can still buy the nose cone and tail cone to make your own. I'm working on one which is now waiting to be painted.
Is this based on one flight of each configuration? These are interesting results but I wonder what the results would be if you averaged the results of 3 flights in each configuration, or 5 flights in each configuration. IOW how much variation is there in each motor? Maybe other people here can answer that question.
Good question, I had 17+ flights on that rocket. Only the 1 flight completely unfinished in late summer at a sports center, the finished flight was that winter on a frozen lake. Overall it was a finished look but not polished smooth and weighed 5.2oz.
I did not fly another E12 in this rocket but several D12 and D15t motors burned and after recording the first few they were within a couple % then just kept flying it as a test for watching winds for higher flights and predicting the LZ.
I had another rocket scratch built bt60 3fnc, it was longer and 1oz heavier. I had rounded fins and smooth paint that flew on some E12's to 1023'-1082'.
Overall with these rockets on BP motors a variance of 5% is what I am seeing.
I did not fly another E12 in this rocket but several D12 and D15t motors burned and after recording the first few they were within a couple % then just kept flying it as a test for watching winds for higher flights and predicting the LZ.
I had another rocket scratch built bt60 3fnc, it was longer and 1oz heavier. I had rounded fins and smooth paint that flew on some E12's to 1023'-1082'.
Overall with these rockets on BP motors a variance of 5% is what I am seeing.
That is very interesting! From whom may we purchase these delectable items?
Over the past two years my little team of two has been experimenting and collecting data with HSR (horizontal spin recovery) designs. To be very sure of a model's performance, especially repeatability and durability, as well as descent rate, we like 10 or more tests. In so doing, we learned that too many consecutive tests of a given model resulted in moisture build-up inside the tube. So, for us, 5 per session backed up by another session under slightly differing conditions to make firm conclusions on unique designs.
I bought an Estes 3-pack of BT-60 nose cones and it came with the parts for the Sprint XL. It also came with the nose cone and tail cone for the ESAM and another somewhat generic pointed nose cone that I don't know what kit it came in. Apogee has the pack, called "BT-60A Nose Cones 3-Pak" for $10.10, and acsupply has it for $9.99. I bought the pack and used one of the nose cones then later realized what the Sprint nose cones were for and I'm building one of those. Previously I built a BT-55 size Sprint borrowing the nose cone from my Goblin and using a tail cone that I rolled from card stock. You can barely tell in the photo of the BT-60 version that there is a small blister on the side of the tail cone to accommodate the engine hook. For my BT-55 version I built it to use friction fit for the motors.
This is the BT-60 version waiting for paint.
This is the BT-55 version. I couldn't find a photo of it after paint.
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