Does paint smoothness matter - Aesthetic vs Aerodynamic

[Angel_of_the_Skies]

How important is a smooth finish to a rocket in order to achieve high altitude/ speed?

I am curious whether a smooth aesthetic finish is mainly for looks rather than practicality.

Insight: I’ve been looking for a smooth finish on my MPR, mainly for looks. My rockets look well about 3-5 ft away, but due to contamination of top coat I’ve been looking to sand.

Frankly, I find it difficult to sand the color coats, and would rather keep my rockets looking well 5 feet away.

I am curious now as to the previos questions. Also, which rocket parts are most important to keep smooth ?

 

[David_Stack]

Do you have a copy of Open Rocket? That program allows you to model surface finish, and then you can run simulations to see the impact on apogee, etc.

 

[Angel_of_the_Skies]

Do you have a copy of Open Rocket? That program allows you to model surface finish, and then you can run simulations to see the impact on apogee, etc.

I do not. Where could I get open rocket ?

 

[David Schwantz]

It is VERY important. The smoother a surface is the less drag it will have. Just think about things that are suppose to go fast, airplanes, race cars, bullets. They do not have orange peel.

 

[manixFan]

As @David_Stack describes, sim programs will help you understand the effect of surface finish. It’s much more important the faster the rocket flies. Once you go past Mach, tools like RasAero are much better at helping to model the effect of surface smoothness.

In OpenRocket, an easy way to see the effects is to select the nose cone, click Edit, and then select a Component finish, and choose 'Set for all'. Create a variety of motor configurations from mild to spicy (ok, low to high average impulse). Then run a sim and note the results. Repeat with a different surface finish and rerun the sims. That will help you see how the finish affects the speed and altitude.


Tony

to learn more about OpenRocket:
https://www.rocketryforum.com/threa...2-final-is-now-available-for-download.177835/

 

[Hobie1dog]

small difference, is a few feet extra at 4K feet really important?

 

[cwbullet]

small difference, is a few feet extra at 4K feet really important?

Not to me. I am trying keep it below 10k.

 

[Pinetree]

Smooth paint isn't that hard to accomplish... Wet sand with 1000 grit, polishing compound, and ceramic spray wax.. makes it feel like glass.

 

[David Schwantz]

The trick is to learn how to apply it without having to polish

 

[tsmith1315]

The trick is to learn how to apply it without having to polish

For clarity, isn't that rocket black, @David Schwantz? It looks silver.

 

[David Schwantz]

It is black.

 

[Angel_of_the_Skies]

Smooth paint isn't that hard to accomplish... Wet sand with 1000 grit, polishing compound, and ceramic spray wax.. makes it feel like glass.

Do you sand smooth or

The trick is to learn how to apply it without having to polish

how are you applying and what’s key ?

 

[David Schwantz]

First, it is not a spray can paint. I am lucky to have a spray booth in my basement. I use quality 2 part auto paint, PPG Omni for this one. I mix till paint is about like milk, and I will use lacquer thinner. It allows the paint to flow and smooth out very nicely. But the key to any paint job is surface prep. If you can see or feel an imperfection, paint will NOT hide it. I sand primer with 600 grit, then maroon scotchbrite pad. Clean with degreaser, tack rag and then spray. I like MH 167 fast hardener. Lighting is also very important. I have no shadows in the booth. This way you can see the paint flow as you apply from any angle. Then I guess it is just how you apply, smooth even strokes the same distance from the surface, don't use an arc type motion. Spray past the piece and start spraying before the piece. Never pull the trigger on the gun on the work. Always start off work and move to it. Use overlapping pattern so that you can see it going on wet with no dry areas in between. Then get out and let it dry. Don't want to stir up any dust that may float into paint. I use to paint in the garage. And I hated coming out in the morning and picking the bugs out of dried paint.
If by chance I do need to wet sand, I'll start with 800 and go to 3000. I use windex to wet out the paper. Keeps the paper cleaner. then I will polish with a fast cut fine grit polish. I also use an air polisher with foam pads.

 

[Angel_of_the_Skies]

First, it is not a spray can paint. I am lucky to have a spray booth in my basement. I use quality 2 part auto paint, PPG Omni for this one. I mix till paint is about like milk, and I will use lacquer thinner. It allows the paint to flow and smooth out very nicely. But the key to any paint job is surface prep. If you can see or feel an imperfection, paint will NOT hide it. I sand primer with 600 grit, then maroon scotchbrite pad. Clean with degreaser, tack rag and then spray. I like MH 167 fast hardener. Lighting is also very important. I have no shadows in the booth. This way you can see the paint flow as you apply from any angle. Then I guess it is just how you apply, smooth even strokes the same distance from the surface, don't use an arc type motion. Spray past the piece and start spraying before the piece. Never pull the trigger on the gun on the work. Always start off work and move to it. Use overlapping pattern so that you can see it going on wet with no dry areas in between. Then get out and let it dry. Don't want to stir up any dust that may float into paint. I use to paint in the garage. And I hated coming out in the morning and picking the bugs out of dried paint.
If by chance I do need to wet sand, I'll start with 800 and go to 3000. I use windex to wet out the paper. Keeps the paper cleaner. then I will polish with a fast cut fine grit polish. I also use an air polisher with foam pads.

I have never tried this. It does sound like a simple approach compared to sanding

Here you are prepping the surface and applying the paint evenly, overlapping, never leaving dry spots, and done

Do you sand till smooth or are you sanding off the gloss from the paint

In my case, when I’ve tried sanding orange peel, I’ll get a smooth surface but with visible small low gloss spots. When attempted to sand down, I seem to get too close to the primer. I start with 1000 and end with 1500

 

[Angel_of_the_Skies]

Smooth paint isn't that hard to accomplish... Wet sand with 1000 grit, polishing compound, and ceramic spray wax.. makes it feel like glass.

When would compound be handy?

I’ve heard some folks use compound then polish

Also, do you sand all the way down to low spots or only till a smooth finish as achieved?

 

[Angel_of_the_Skies]

As @David_Stack describes, sim programs will help you understand the effect of surface finish. It’s much more important the faster the rocket flies. Once you go past Mach, tools like RasAero are much better at helping to model the effect of surface smoothness.

In OpenRocket, an easy way to see the effects is to select the nose cone, click Edit, and then select a Component finish, and choose 'Set for all'. Create a variety of motor configurations from mild to spicy (ok, low to high average impulse). Then run a sim and note the results. Repeat with a different surface finish and rerun the sims. That will help you see how the finish affects the speed and altitude.


Tony

to learn more about OpenRocket:
https://www.rocketryforum.com/threa...2-final-is-now-available-for-download.177835/

Thank you Tony, kind of you to provide a source of info

 

[David Schwantz]

When you sand you must use a sanding block. Mine is a hard foam I just wrap paper around it. Don't try to do it with just your hand.
I use a maroon scotchbrite pad after color and before clear to scuff it to prep for the clear coat. Just enough to remove the gloss, this gives something for the cleat to stick to.
Guns are, Finex, Iwata, DeVilbiss. Water trap, water in your paint sucks. A couple more after clear.

 

[Angel_of_the_Skies]

When you sand you must use a sanding block. Mine is a hard foam I just wrap paper around it. Don't try to do it with just your hand.
I use a maroon scotchbrite pad after color and before clear to scuff it to prep for the clear coat. Just enough to remove the gloss, this gives something for the cleat to stick to.
Guns are, Finex, Iwata, DeVilbiss. Water trap, water in your paint sucks. A couple more after clear.

Funny you mention that, I was indeed not using a sanding block of any form haha

I will try that from now on. Any advice on not sanding off paint near the edges ? Also, sanding in straight lines, circles ?

By the way your setup and you results are very awesome looking, I hope to be there one day too!

Thank you for the information

 

[Jim Cook]

When you sand you must use a sanding block. Mine is a hard foam I just wrap paper around it. Don't try to do it with just your hand.

I take it that the block you use is contoured roughly to the rocket diameter, not flat, except when doing fins. How to do other areas - fin fillets, moulded nosecones (think canopy), etc. - is another question.

 

[samb]

@David Schwantz Is it fair to say that you didn’t learn your craft from reading forum posts or watching YouTube videos ? At some point you had a mentor/apprenticeship situation, correct ?

 

[David Schwantz]

Sanding block is flat, but being a hard foam it will conform to the tube and into fillets.
samb, in another life I used to paint full size aircraft, before that I painted equipment that was used for packaging. Guess I just watched and listened to the guys I was replacing. this was long before the word "mentor" was ever thought of

 

[David Schwantz]

I guess I just sand up to the edge and try to be more careful there. Try not to push down off the edge. I always use straight lines in sanding. Sanding marks are much easier to remove if they are not cross hatched.

I'm off to the woods with my dogs now. When I get back tonight I'll post some pics of sanding block and stuff, if people want to see. Thanks.

 

[Pinetree]

@Angel_of_the_Skies I just use the 1000 grit to remove any minor imperfections in the final paint, such as dust, dead bugs, cat hair... it's very minor.

 

[samb]

…
samb, in another life I used to paint full size aircraft, before that I painted equipment that was used for packaging. Guess I just watched and listened to the guys I was replacing. this was long before the word "mentor" was ever thought of

Ok. My point is you saw how it’s done up close and personal. You could smell the fumes. That is the way.

 

[manixFan]

Sanding block is flat, but being a hard foam it will conform to the tube and into fillets.
samb, in another life I used to paint full size aircraft, before that I painted equipment that was used for packaging. Guess I just watched and listened to the guys I was replacing. this was long before the word "mentor" was ever thought of

Mentor: mid 18th century: via French and Latin from Greek Mentōr, the name of the adviser of the young Telemachus in Homer's Odyssey.

So, maybe not so much! Not to be too pedantic, but the concept of being an apprentice to learn a trade goes back to the middle ages, and being an apprentice requires a mentor. It's a time-honored way of passing on a skill or trade that requires a lot of practical, hands-on learning.


Tony

 

[SolarYellow]

You could smell the fumes. That is the way.

No. Smelling the fumes is not the way.

Using PPE so you don't smell the fumes is the way.

 

[cbwho]

No. Smelling the fumes is not the way.

Using PPE so you don't smell the fumes is the way.

Perhaps realizing that sanding is a ton of work and being fine with a 5 footer is a better way?

 

[samb]

No. Smelling the fumes is not the way.

Using PPE so you don't smell the fumes is the way.

Agreed with the stuff David is spraying. I was trying to make the point to the op that first hand observation of some technique you want to master is the best way IMO. Don’t huff the fumes kids!

 

[David Schwantz]

Are you kiddin me. I spray Imron here at the house, that stuff will kill ya. Love them fumes

 

[Hobie1dog]

Are you kiddin me. I spray Imron here at the house, that stuff will kill ya. Love them fumes

Sorry to derail the thread, but what is the current replacement for Imron ?