Modelling Nose Cone Weight in OpenRocket

[bad_idea]

I'm surprised the camera shrouds make that much difference in CP location and also in drag. If I move then to the bottom of the extension section which is aft of the CP and remove the nose weight, I can get to about the same 2.9 stability. One thing on this is that is that I have overridden the Cd of the shrouds to 0.25 because there lots of "holes" in them. I think this must have been close since my actual altitudes and sims were typically within 5-10%. The shrouds look like the attached picture. I no longer use an up camera, just redundant down cameras so I can redesign them with less "holes" and to be more aerodynamic. Note I am using cameras which are about a 1" cube.

I would model the camera shrouds as pods, not fins. Give the pod a body tube that has the same frontal area as your camera shroud, give it a nose cone that's the length of any fairing you have at the front of the pod. Based on tests I've run before, I expect you will find the CP shift is much less dramatic, though drag may be comparable.

 

[bad_idea]

Here's a couple of examples I whipped up from the "simple model rocket" example in OpenRocket. 30g camera pod that's 50mm long including a 25mm fairing and frontal area of a 20mm circle, around 314mm^2. One example uses a square-profile fin, the other a pod.

 

[atestani]

Here's a couple of examples I whipped up from the "simple model rocket" example in OpenRocket. 30g camera pod that's 50mm long including a 25mm fairing and frontal area of a 20mm circle, around 314mm^2. One example uses a square-profile fin, the other a pod.

Thanks for these....

I am going to redesign the camera shroud to be like the pod version. I actually have one like the square fin I used once. What I have now was to support an up, down, and side viewing camera.

 

[atestani]

Thanks for these....

I am going to redesign the camera shroud to be like the pod version. I actually have one like the square fin I used once. What I have now was to support an up, down, and side viewing camera.

Here's a couple of examples I whipped up from the "simple model rocket" example in OpenRocket. 30g camera pod that's 50mm long including a 25mm fairing and frontal area of a 20mm circle, around 314mm^2. One example uses a square-profile fin, the other a pod.

I changed my mind since I already have camera holders ready to 3D print in the "fin" configuration. They are even conformal to the body tube. When I will fly these I will put a piece of Gorilla tape over the holes other than the camera lens hole.

The problem is when I model them in OpenRocket, it complains with: "Warning Thick fins may not simulate accurately". What does "may" mean and can the simulation be trusted? ORK file is attached. Note that I have moved the cameras to the extension tube end. That picks up almost an entire caliber and has another benefit of the camera always facing the ground.

If I could bring myself to ditch the cameras altogether, the sim is over 10K feet, but... do I believe dropping the cameras picks up 1200 ft.!?

 

[bad_idea]

I changed my mind since I already have camera holders ready to 3D print in the "fin" configuration. They are even conformal to the body tube. When I will fly these I will put a piece of Gorilla tape over the holes other than the camera lens hole.

I did not mean to change the shape of your camera holders, I meant to sim their frontal area though they were a pod instead of a fin, as that will affect the CP calculation. Though admittedly I am not an aerodynamicist, it seems unlikely to me that your camera pod will act like a fin, so I wouldn't sim it as such.

 

[atestani]

I did not mean to change the shape of your camera holders, I meant to sim their frontal area though they were a pod instead of a fin, as that will affect the CP calculation. Though admittedly I am not an aerodynamicist, it seems unlikely to me that your camera pod will act like a fin, so I wouldn't sim it as such.

I've looked at several shapes since you pointed out the large effect the thick "fins" were having way forward of the CP. Thanks for that. I am finding the location is most important and I am clearly moving the cameras aft. By doing so, nose weight is reduced to almost nothing and I can still meet my self-imposed goal of 3+ caliber/13% with ~1000 ft. more altitude.