Rookie HPR, question about recovery

[lr64]

Errr... With the altimeter inside the tube, that's why you vent.

Hans.

Right. And if the vents are in the wrong place, such as most places in the nose cone, you get larger and larger errors as the rocket goes faster and faster. Actually, I'm sure you get larger and larger errors anywhere, since nothing is perfect, but they'll start much smaller if you're using the right place. You will also get delays which will depend in part on the ratio of the vent size to the vented volume. Near worst case, as mentioned, if you put the vent at the very tip of the nose cone, your altimeter will insist the rocket is below sea level until it slows down or goes quite high. It's possible to get an even larger error if you put the vent hole at the wrong place on a curved surface. For instance, partway back on the back of a wing-shaped feature which is at a significant angle of attack. That would give you an error in the opposite direction. You'd have to try pretty hard to do that on a typical rocket, of course.

If you didn't, I suggest reading the Kitplanes article I mentioned above, or some other article on the art of static port location.

 

[OzHybrid]

Right. And if the vents are in the wrong place, such as most places in the nose cone, you get larger and larger errors as the rocket goes faster and faster. Actually, I'm sure you get larger and larger errors anywhere, since nothing is perfect, but they'll start much smaller if you're using the right place. You will also get delays which will depend in part on the ratio of the vent size to the vented volume. Near worst case, as mentioned, if you put the vent at the very tip of the nose cone, your altimeter will insist the rocket is below sea level until it slows down or goes quite high. It's possible to get an even larger error if you put the vent hole at the wrong place on a curved surface. For instance, partway back on the back of a wing-shaped feature which is at a significant angle of attack. That would give you an error in the opposite direction. You'd have to try pretty hard to do that on a typical rocket, of course.

If you didn't, I suggest reading the Kitplanes article I mentioned above, or some other article on the art of static port location.

You're right, but.....
For this particular use case, you are way overthinking it.
This is an altimeter, not a flight computer. There are no energetics connected, It's not a Mach flight. It's not a competition or record flight.
Other than a slightly wrong result, there are no consequences for getting a slightly wrong result. Wrap it in a small amount of cloth, put it in a plastic bag, cut the corner off the bag and tape it to the outside. Or do something else with it. It doesn't really matter.......in this instance.
Once you've got your L1 and have a bit more time, completely overthink it then.....

 

[loopy]

Okay since we're on the subject of recovery, my other question would be regarding running an altimeter. I'd like to use one here, but I know that I have to drill a couple small holes near the top of the body for the altimeter to get an accurate reading, and I'm wondering if that will throw off the ejection since it'll change the internal pressure of the body. Again, I'm sorry if this seems like a ridiculous question.

The simplest answer is that no - small vent holes in the body tube will not have a negative effect on ejection charges. What altimeter are you using? Is it a Jolly Logic type?

 

[Sooner Boomer]

Okay since we're on the subject of recovery, my other question would be regarding running an altimeter. I'd like to use one here, but I know that I have to drill a couple small holes near the top of the body for the altimeter to get an accurate reading, and I'm wondering if that will throw off the ejection since it'll change the internal pressure of the body. Again, I'm sorry if this seems like a ridiculous question.

I've been following for a bit and thought I'd jump in. For the past few years, I've been flying rockets based on a 54mm body tube (29mm and 38mm motor mounts). Most of the time I used a payload altimeter/tracker. The leads and ejection charge are the first things down the top of the body tube. Next goes extra recovery harness, followed by parachute and JLCR wrapped in a nomex protector. The payload section goes on top, being careful to keep ejection charge leads and parachute away from each other. The "long" body tube has four 1/8" holes down the length, the "short" tube has three. This helps equalize pressure inside/outside the body. I've never had any trouble with loss of ejection gasses through these small holes. I have, however, noticed a slight buildup of soot on the outside of the holes.

I just wanted to point out that the altimeter *shouldn't* fire when the pressure is changing (assuming it's a baro alti.). If the pressure is changing, the altitude is, too. It *should* fire if the pressure drops then holds steady (the rocket has reached apogee).

I once had the idea of bundling the altimeter/battery into a nomex protector and jamming it into the body with a parachute. I wrote to Cris Erving about this, concerned about how the baro sensor would handle the pressure. He didn't seem to think it would be a problem. Might try this as soon as I can clear some other projects out.

Good luck with your L1. Hope to see your build log for your L2 project soon.

 

[b0g_nerd]

You should be all straight now.

I got enough reassurance that drilling the vent holes won't throw off the ejection pressurization. It's all good! Today is flight day and I'm keeping all my fingers and toes crossed that everything goes according to plan. I'll update when it's over!

 

[MarsLander]

I got enough reassurance that drilling the vent holes won't throw off the ejection pressurization. It's all good! Today is flight day and I'm keeping all my fingers and toes crossed that everything goes according to plan. I'll update when it's over!

Good luck!!!

Let us know everything that you did and did not....(altimeter, etc.).

 

[Art Upton]

What launch are you going to today?

 

[b0g_nerd]

Good luck!!!

Let us know everything that you did and did not....(altimeter, etc.).

Everything went great! I just attached the altimeter to the bottom of the nose cone and added a gps just in case it went far. But it went as good as it possibly could have, and the wind was cooperative so it landed nearby. I ended up drilling 2 static holes for the altimeter and threw in a handful of dog barf. Success!

 

[OzHybrid]

Congratulations.

 

[tsmith1315]

Great job in the certification, extra points for appropriate attire!

 

[Sooner Boomer]

Woo Hoo! Congrats!

That's a good looking rocket!

Now on to L2!

 

[Art Upton]

Everything went great! I just attached the altimeter to the bottom of the nose cone and added a gps just in case it went far. But it went as good as it possibly could have, and the wind was cooperative so it landed nearby. I ended up drilling 2 static holes for the altimeter and threw in a handful of dog barf. Success!

Congrates on the Cert! And that you got the other items working to make it even more interesting.

Is that at Skybusters? I see a Semi in the background that might be the highway. It's been some years since I have been there.

 

[MarsLander]

Everything went great! I just attached the altimeter to the bottom of the nose cone and added a gps just in case it went far. But it went as good as it possibly could have, and the wind was cooperative so it landed nearby. I ended up drilling 2 static holes for the altimeter and threw in a handful of dog barf. Success!

Nice.

Altitude? How far away did it land?

 

[bad_idea]

Congrats!

 

[bjphoenix]

Congratulations. The finished rocket looks great.

 

[4regt4]

Everything went great! I just attached the altimeter to the bottom of the nose cone and added a gps just in case it went far. But it went as good as it possibly could have, and the wind was cooperative so it landed nearby. I ended up drilling 2 static holes for the altimeter and threw in a handful of dog barf. Success!

Congrats.

You obviously are an official rocket scientist, as you are holding a roll of masking tape.... Welcome.

Hans.

 

[loopy]

Congratulations!

 

[kjhambrick]

Nice.

Altitude? How far away did it land?

Congrats !

+1 and what motor did you end up flying ?

-- kjh

p.s. so someone else can say that a Zephyr + MotorXXX = YYY ft altitude

 

[bjphoenix]

p.s. so someone else can say that a Zephyr + MotorXXX = YYY ft altitude

There is a table of those on the Apogee website for this rocket, using G through J motors. For level 1 using H motors the altitudes range from 1400-2600 feet.

 

[lordofthecampsite]

I've found 2 different types (I'm sure there are probably more...) of "fire resistant" bulk cloth. One is "modacrylic". It's nice and soft, cuts easily. But it's best described as "self extinguishing". If you put a cigarette lighter under it, it most definitely burns, however the flame immediately goes out as soon as the lighter is removed. But you end up with a cloth with, at best, a toasty section, at worst, a hole in it.

I've found bulk "aramid" cloth. It looks in color like what we typically use for shock cords. It's a b*tch to cut. When subjected to the lighter test for 10-15 seconds, it shows no evidence of burning at all. I'm using it for homemade chute protectors, it's working well. It doesn't fray around the edges, which surprised me.

Hans.

Hans (or other) can you share the supplier you found for bulk “aramid” I would like to experiment with a few of my own designs and would like to start with a known good fabric source.

Thank you

 

[4regt4]

Hans (or other) can you share the supplier you found for bulk “aramid” I would like to experiment with a few of my own designs and would like to start with a known good fabric source.

Thank you

I get it from Ebay. The sellers seem to change over time, but a search for "Para-Aramid" should bring results.

Hans.

 

[lordofthecampsite]

I get it from Ebay. The sellers seem to change over time, but a search for "Para-Aramid" should bring results.

Hans.

Thanks, I'll check this out.

I happened to stumble across GiantLeapRocketry and they make full para-aramid "kevlar" chute protectors. I ordered one to try out.

https://giantleaprocketry.com/collections/fins-1/products/kevlar-chute-protector-up-to-2-6-airframe

 

[4regt4]

Thanks, I'll check this out.

I happened to stumble across GiantLeapRocketry and they make full para-aramid "kevlar" chute protectors. I ordered one to try out.

https://giantleaprocketry.com/collections/fins-1/products/kevlar-chute-protector-up-to-2-6-airframe

For less than half that, you can make perhaps 20 of your own chute protectors:

https://www.ebay.com/itm/3036701870...=2047675&ssuid=&widget_ver=artemis&media=COPY

Hans.

 

[lordofthecampsite]

I looked at that specific eBay link previously. When I was researching the different types of cloth, this specific one looks like cloth used for bonding with composites such as epoxy. The weave is very coarse and will come apart easily, it didn't look like the fabric that I expected.

If you have used this material before do you have any photos of how you finished the edges or if you attached it to another substrate and bonded it?

 

[4regt4]

I looked at that specific eBay link previously. When I was researching the different types of cloth, this specific one looks like cloth used for bonding with composites such as epoxy. The weave is very coarse and will come apart easily, it didn't look like the fabric that I expected.

If you have used this material before do you have any photos of how you finished the edges or if you attached it to another substrate and bonded it?

No need to finish the edges. It doesn't unravel. I doubt this particular cloth is used for layups. It's fairly thick and I think you would play hell getting epoxy to wet it well. I've seen other listings for it, supposedly it's intended for fire protection purposes.

Attached is a pic of a chute protector that's been used about a half dozen times. I have some older ones, but they aren't handy right now.



Hans.

 

[lordofthecampsite]

No need to finish the edges. It doesn't unravel. I doubt this particular cloth is used for layups. It's fairly thick and I think you would play hell getting epoxy to wet it well. I've seen other listings for it, supposedly it's intended for fire protection purposes.

Attached is a pic of a chute protector that's been used about a half dozen times. I have some older ones, but they aren't handy right now.

View attachment 688426

Hans.

Wow, that photo is a much tighter weave than what I perceive is in the eBay listing. It may just be a zoomed in photo. I’ll order some and try it out too.

 

[4regt4]

Wow, that photo is a much tighter weave than what I perceive is in the eBay listing. It may just be a zoomed in photo. I’ll order some and try it out too.

Good luck cutting it! I bought a special pair of scissors just for it.

Hans.