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Budro0

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So I'm getting to the point of drilling shear pins. I think I'm more nervous about that and shims than anything else here. Anyway, I will hopefully get that done this week.

On another note, I getting much closer to final weight. It's currently right at 3kg (with generic weights for the parachutes and nose ballast). I'm spec'ing chutes and wanted to get an idea of what drogues others are using. As I said previously, I'm looking hard at spherachutes, but not sure about using their chutes as drogues. Which do you all like and use (or which would never touch again)? And any thoughts on sizing for drogues?
 

boatgeek

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So I'm getting to the point of drilling shear pins. I think I'm more nervous about that and shims than anything else here. Anyway, I will hopefully get that done this week.

On another note, I getting much closer to final weight. It's currently right at 3kg (with generic weights for the parachutes and nose ballast). I'm spec'ing chutes and wanted to get an idea of what drogues others are using. As I said previously, I'm looking hard at spherachutes, but not sure about using their chutes as drogues. Which do you all like and use (or which would never touch again)? And any thoughts on sizing for drogues?
I can't really comment on chute brands (I scratch build), but I'd look for something in the 12"-18" range with a spill hole. Ideal world descent rate under drogue is in the 80 fps range, but don't worry about 60-100 fps predictions if it gets you to a standard size. I tend to go a little high on speed under drogue because the body tubes will likely add some drag as well.

Also, if you choose a vendor, they should be able to give you a chute recommendation for drogue and main given weight at burnout and desired drogue/landing speeds.
 

Budro0

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As previously promised, a little peek inside the av-bay. I went all-in with Missileworks on this - RRC2Ls and their printed sled. The sled is pretty good but I felt that it could have been a little more thoughtfully laid out for wire management. It'll work for now, but I'm keeping my eyes open for better options.

Less apparent, I got Rocket Junkies charge wells. Saved me a bit of time building my own, and they look great, so I can justify the expense.

In other news, I've got just about everything drilled and prepped, so I'm about ready to get brass shims into the airframe. For those that have done it, do you do epoxy over the hole, then shim, then more epoxy? I'm thinking about laying some wax paper or mylar over the shim as it cures to try to keep it as smooth as possible. I'd like to hear what's worked for you (or not worth the time/effort).

IMG_20210216_201443.jpg
 

Budro0

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I can't really comment on chute brands (I scratch build), but I'd look for something in the 12"-18" range with a spill hole. Ideal world descent rate under drogue is in the 80 fps range, but don't worry about 60-100 fps predictions if it gets you to a standard size. I tend to go a little high on speed under drogue because the body tubes will likely add some drag as well.

Also, if you choose a vendor, they should be able to give you a chute recommendation for drogue and main given weight at burnout and desired drogue/landing speeds.
My math with drag on the fin can gets me about ~75fps with a 12" flat sheet. I'm perfectly alright with that descent rate, but there is plenty of variation in drogue sizing and construction making it a less than straight forward research project. I appreciate the confirmation that I'm headed in the right direction though.
 
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jqavins

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As previously promised, a little peek inside the av-bay...
That mounting bridge for the switches reminds me of:
1613568106446.png
In other news, I've got just about everything drilled and prepped, so I'm about ready to get brass shims into the airframe. For those that have done it, do you do epoxy over the hole, then shim, then more epoxy?
I have not done it before, and what I have is a question, not advice. Don't the shims go in between the airframe and coupler? Keeping the sheer force from damaging those, and also cutting the pins like scissors? Doesn't that mean that they are flat against one another? If so, wouldn't that mean that you mustn't put anything like more epoxy on top of them?
 

David Schwantz

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Hi BudroO, all kind of depends on location of brass plate. If inside avbay, scuff brass and glue over already drill holed. Let dry and redrill. If plate is going in between NC shoulder and body tube, as in single deploy, then I will use a piece of baggie and clamp it down till dry. and again, redrill hole. Can send pics if you need. Dave.
 

Budro0

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have not done it before, and what I have is a question, not advice. Don't the shims go in between the airframe and coupler? Keeping the sheer force from damaging those, and also cutting the pins like scissors? Doesn't that mean that they are flat against one another? If so, wouldn't that mean that you mustn't put anything like more epoxy on top of them?
That is what I'm tracking/planning. But you bring up a good point. I was not planning to go brass to brass... But to do brass on the inside of each - coupler and body tube. Now i'm questioning if I even have the right concept in mind.

What do you say, @David Schwantz? For a coupler/av-bay and airframe connection, where do you put shims?
 

David Schwantz

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1st 2 pics are the inside of a 1/5th V 2. They are on the inside of the sonotube, sonotube is glassed on outside. Located at the bottom of the NC shoulder. The screws will go through the shim plates and into a tapped aluminum bracket that is bolted to the base of the NC shoulder. Can take a pic of that tomorrow if you like as it is in the paint booth now with primer drying. The last 3 pics are LOCs 4" V 2. Again the brass plates are on the inside of the cardboard tube. With the last pic being the inside of the NC shoulder. I like to glue a plate with a blind nut in place. Just like the big V 2, by screwing into a threaded housing, it will hold the screw securely and does not allow it to roll over. They shear very cleanly. This also allows for very easy removal of the sheared off threaded portion.
 

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Budro0

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1st 2 pics are the inside of a 1/5th V 2. They are on the inside of the sonotube, sonotube is glassed on outside. Located at the bottom of the NC shoulder. The screws will go through the shim plates and into a tapped aluminum bracket that is bolted to the base of the NC shoulder. Can take a pic of that tomorrow if you like as it is in the paint booth now with primer drying. The last 3 pics are LOCs 4" V 2. Again the brass plates are on the inside of the cardboard tube. With the last pic being the inside of the NC shoulder. I like to glue a plate with a blind nut in place. Just like the big V 2, by screwing into a threaded housing, it will hold the screw securely and does not allow it to roll over. They shear very cleanly. This also allows for very easy removal of the sheared off threaded portion.
Awesome notes, thank you. I think I'll steal that blind nut idea too.
 

Budro0

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Quick update: First shim is in and curing with a large roll of butcher paper and a bit of mylar to keep everything smooth. I finally found some 2-56 blind nuts (Eugene Hobby for the win) which should be here on Saturday. If everything goes well, I could be testing charges on Sunday. Except I don't have any chutes yet. I'm still waiting to hear back from Spherachutes as they have a couple drogue chutes which could work and I asked their advice on which they'd recommend.

We are really dangerously close to painting - I need to start getting all the stencils cut out...
 

David Schwantz

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I have , in the past, substituted "old" bathroom towels for chutes. Only cause I like playing with BP :)
 

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