Diverting ejection gas around a payload

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Mar 14, 2017
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Hello everyone, new guy here.

After a 30 year hiatus I'm going to try to get back into rocketry (low power for now) and wanted to bounce an idea off some more skilled folks.

I'm building an approximately 1:24 scale Mercury-Redstone.
Since I have an old Flip video camera lying around I'm going to build a camera bay into the body.
My intent is to keep the camera within the main body so that once the chute deploys it will remain (more or less) upright during descent.

Since the nose cone and chute will be forward of the camera, I figure I'll need to route the ejection gasses past the camera bay by drilling holes in the bulkheads fore and aft of the camera to permit the gasses to pass through.
I see some people use baffles to protect their chutes so I don't foresee any problems with my concept, but being out of practice I want to make sure I'm not missing something.

Does this sound like a viable plan to the more experienced fliers out there?

Depending on the size of the camera it might be possible to surface mount it. However, the Mercury Redstone is not that stable to begin with. How big and heavy is the camera?

If the camera is small enough you can consider surface mounting or putting it into a half cylinder shaped camera bay. If not, it might be better to put it into the marcury capsule or a payload bay directly u derneath for stability purposes. If you have a chute connected to the top of the capsule (two chutes overall, comes down in two pieces) and the camera will still face down for landing.

Are you going to put tubes connecting the holes in the front and rear bulkheads? If you do an have large enough holes, I don't think there's any problem with your design except maybe stability.

Which motor are you using? What tube size and length? Depending on the size of the motor the ejection charge might be on the small side and have trouble pushing out the recovery. That can be solved by extending the motor tube, though, but it's a design consideration.

Also, I'm not an experienced flier or a skilled folk.
Thanks for the feedback.

I'm still in the early stages of planning/construction so I don't have final weights and specs yet.
The Flip camera is 50mm x 11mm x 100mm and looks roughly like this. Due to the shape and orientation of the lens, mounting outside for the angle I want (approx. 30 degrees below horizontal) isn't really an option.
The body tube is 81.6mm diameter, and 78.74cm long.
I'm planning to run some tubing between the bulkheads to ensure the gases don't obscure the camera bay.
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Since your model is larger than the Estes Redstone, I don't think you'll have a problem adding necessary stability weight.

Inco's idea of a Half-circle bay is something to think about. 2 half-bulkheads: the bottom one fixed/sealed, a dividing wall piece that divides the tube in half, and a removable half bulkhead on top. Place it as far forward as you can without interfering with the shoulder of your nose, and the parachute/shockcord can tuck down the open side of the tube.
I would think it should be fine as long as you keep an eye on CG and provide enough space for the ejection gases. I agree the video is better when the camera points down during descent.
Watch some videos of rockets with cameras mounted on them; all the cameras point down. And the boost phase is the best part of the video in my opinion. So unless you have a specific reason for shooting the video up I recommend putting the camera on the outside pointing down. And instead of the flip phone camera you can just get one of those small key fob cameras for about $10 to 15. People just tape them on their rockets. You wouldn't think tape would be enough, but the cameras stay on even if the rocket goes 300 to 400 miles per hour.
You could use a coupling and plywood bulkheads to build a normal electronics bay but drill 2 extra 20mm holes in each bulkhead (like 2 motor centering rings). Install BT-20 / 18mm sized tubes to run between the holes drilled in the bulkheads. Fasten the bulkheads to each other with some threaded rod nuts and washers. The gasses will pass through the 18mm tubes & your camera will be safely inside the e-bay. Make sure to glue the 18mm tube to the bulkhead on the motor side, and have a slip fit on the other side (which would need to be sealed around before flight.) If you position the 18mm tube correctly, it could also serve to help hold the camera in place.

You didn't mention what size motor you will be using, but I would think that 2 18mm tubes should pass the ejection gas from even a 54mm motor without incident. If you think you need a bigger passage, obviously you can use bigger, (24mm), tubes as long as they leave enough room inside for your camera.

If you want the entire assembly to be removable, don't glue the coupling in place. Secure it with a couple small screws / rivets driven through the main body tube. Be mindful of your CG......

Your mileage may vary / I'm not a rocket scientist, only play one on the weekends / No warranty implied or given.....
Thanks again everybody.
I'll probably be using an E,F or G size motor, I don't have a ballpark weight estimate yet.
I was considering this shape for my bulkheads. The flat sides would be covered with something thin and heat resistant and one curved side will be the window for the camera.