OpenRocket Needs Surface Roughness of Painted Surfaces

H. Craig Miller

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We're looking into adding additional Component finish settings; the current selections are rough, unfinished, regular paint, smooth, and polished. The thought is that the selection names would be changed to better describe what the surface roughness is like. For example, regular paint could be changed, and additional selections added, so that the new selections would be flat paint, gloss paint, and high gloss paint. The problem is determining what the surface roughness is for different types of paint so that OpenRocket can use that data to calculate the correct Cd.

Does anyone have or know of where to get a chart (or any data source) showing the surface roughness of different types of paint?
 

Handeman

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I don't know where to find that, but is there really a need for that many different surface types? Is there really that much difference between them and does that amount of granularity really matter considering the wide range of other variables like motor thrust? Seems like you're looking at the trees and not the forest.
Just my opinion...
It just seems like there might be other areas to look at that could provide a greater improvement to accuracy then finish smoothness, like base drag. Seems like we shouldn't have to use the base drag hack to get accurate sims.
 

Handeman

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an existing article referencing OR and this subject:
That is interesting and seems very theoretical, but I've left blue painter tape loosely stuck to the fins when I've launched my HPR and after 3000 ft and +250 mph, the tape is still stuck to the rocket after the flight. That indicates to me that if the Latimer flow can't blow a piece of low tack blue painters tape off when going +250 mph, the paint surface finish shouldn't have much impact on the actual altitude the rocket reaches either. Just my observations...
 

rharshberger

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I don't know where to find that, but is there really a need for that many different surface types? Is there really that much difference between them and does that amount of granularity really matter considering the wide range of other variables like motor thrust? Seems like you're looking at the trees and not the forest.
Just my opinion...
It just seems like there might be other areas to look at that could provide a greater improvement to accuracy then finish smoothness, like base drag. Seems like we shouldn't have to use the base drag hack to get accurate sims.
Maybe just a slider in the "roughness" section, it centers on whatever the mid level Cd currently is, but by moving the slider the altitude can be "dialed" in to the actual flight numbers (not that Cd is the only thing affecting altitude). Finish smoothness iirc are measured in microns....maybe....
 
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