Altimeter dilemma

I'm nearly done with my latest scratch build, a two-stage rocket meant to carry a camera in a balsa transition. The payload bay is made of a PNC 80, a 3-inch length of 2.6 inch BT80, and the 80/60 balsa transition.

Here's a picture:



The hole in the transition is for the camera view.

The nose is attached to the body tube section itself, after having a bit of the shoulder end cut off so everything would fit. Having seen that, I thought, "Heck, there's room in there for an altimeter!"

Just about to drill a 1/16 inch vent hole, and I thought I should do a bit of reading.

Now, I'm not sure I can bother. Since the tube is only 3 inches long and 2.6 in diameter, and the altimeter would sit on top of the transition, the furthest back it could be from the nose-to-tube joint is about an inch and a half. I've read you need to have a vent hole at least 3-4 diameters from that joint - not possible with this payload bay.

I wanted to ask, how much would it throw off the readings if I did install one? I like the idea of having a payload bay with more than one function (this is my first time putting any payload in a rocket that isn't an egg), but if the readings are going to be wildly inaccurate, I don't think I'll bother.

Thanks!

Put the vent hole in the NC just above the shoulder.

Go for it. Many guys put vent holes in nosecones and near transitions with no issues. For basic DD or peak altitude recording, you should be fine.

If "air" can go around your camera lens, in/out the transition opening up through the transition to the Altimeter, wouldn't that be enough?

I'm thinking the same thing, and you're not going anywhere near sonic I would presume, so the camera hole should be just fine.

The problem with vent holes near transitions and other irregular surfaces is that you can have vortices and other strange air flow from the surface. The strange air flow could cause the altimeter to read the air pressure incorrectly. In this case I think you should try it. If you are just using the altimeter to get an altitude sample it won't hurt to try.

accpool said:

If "air" can go around your camera lens, in/out the transition opening up through the transition to the Altimeter, wouldn't that be enough?

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In this case, no. There's only a small hollow for the camera, which sits snugly inside a balsa cocoon.

Too bad, I love the outside the box thinking. Nice design.

lcorinth said:

In this case, no. There's only a small hollow for the camera, which sits snugly inside a balsa cocoon.

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I bet you have a Dremel?

Woody's Workshop said:

I bet you have a Dremel?

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I borrowed one from a guy who came to one of my launches. I need to figure out some more uses for it before I have to give it back (didn't come with instructions - I had to figure it out through trial and error).