How do you go about Friction Fit for 4" carboard dual deploy rocket?

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josong

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I'm about to fly a Madcow Super DX3 on a Aerotech J420 with a dual deploy recovery. I want to try flying with friction fit nosecone and aft end. I've read that this works fine with these kind of rockets. I don't expect this to fly crazy high (maybe below 3000ft). I also understand that the BP ejection charges should NOT be so energetic. It should be enough to seperate the aft end and let its momentum take the drogue chute out and not send the main bulleting out. So I guess my questions are:

1) What is your defintion of friction fit?

2) How does it hold the aft end as the motor is finished burning to prevent drag separation and how does it hold the nosecone before main deployment.

3) How do you guys do your friction fits? What kind of tape do you use?

4) How confident are you in friction fit based of your experiences
 
The first thing you have to understand is that this is a "feel" thing. "Feel" is developed over time by experience. Experience is gained by repetition. "Feel" is generally not teachable over the internet.

People that say it works fine likely have a lot of experience with it. There are a lot of variables. Nose cone weight, tube diameter, drogue charge size, tube volume, humidity/temperature, Etc.

I have used the blue tape with reasonable results, aiming for the fit to be tight enough not to move when picked up, but a slight movement when shaken strongly, if that helps, using a "healthy" ejection charge. I also do not have a lot of experience with it. 😇

The reason to use the pins is that it removes the semi random nature of the "feel" and substitutes a repeatable fit that can be ground tested, and also translates well to flight results.

I do think that the pins are a pain in the 🫏,
 
you should be able to hold and lift the loaded rocket from each section and not have it slide apart..I'd add some jiggling and up and down motion to the lifting to ....it to just confirm it's "good to go".

Tony
 
I use friction fit on a few of my DD rockets and it works well if you have it tight enough and don't overdo it on the ejection charge. I usually use blue tape to adjust the fit. As tfish described, I usually make sure I can pick up the loaded rocket by the NC without it separating even with a bit of shaking.

I'd strongly encourage ground testing of your charges. If the NC comes off when you ground test the drogue, then you probably need a tighter NC fit or a bit less drogue charge.
 
I don't use blue tape because the adhesive is not reliable enough. I've had it bunch up and jam. Also it gets gummy with motor case heat. Instead, 3M beige tape only.

Do not get duct tape or Gorilla tape anywhere near the range, they are awful! Speaking of gummy adhesive, yuck!

Spirals along the motor case. On couplers and nose cone shoulders: Vertical, longitudinal strips only. Not wraps around the shoulder, those can peel and jam.

Again, yeah, it's the feel thing.
 
I use friction fit on a few of my DD rockets and it works well if you have it tight enough and don't overdo it on the ejection charge. I usually use blue tape to adjust the fit. As tfish described, I usually make sure I can pick up the loaded rocket by the NC without it separating even with a bit of shaking.

I'd strongly encourage ground testing of your charges. If the NC comes off when you ground test the drogue, then you probably need a tighter NC fit or a bit less drogue charge.
Thanks! I think I'm more concerned of the nosecone friction fit. I'm just wondering how it does not fall out of the forward tub when the rocket is travelling down or when the drogue chute comes off.
 
Thanks! I think I'm more concerned of the nosecone friction fit. I'm just wondering how it does not fall out of the forward tub when the rocket is travelling down or when the drogue chute comes off.
Learned from @waltr, to test a coupler (ie nosecone shoulder or tube coupler) for DD he would give the assembly a good toss downward and a quick yank on the cord or body. The coupler shouldn't come out by itself. Whatever is the minimum amount of tape to do that is probably the ideal amount. Regardless, you should ground test the charges after the fit to be safe.
 
I use friction fit with LPR. You want it tight enough so the motor will positively not eject itself. But you need to be able to take the motor out when you get the rocket back without pulling the motor mount out with it which I've also seen happen. For a bigger motor in a 4" rocket another limitation is how well you can grab the motor. Whatever you choose you should ground test it if you can to be sure it doesn't eject the motor. Ejection charges in LPR are somewhat standard and fairly wimpy, ejection charges in larger motors can be pretty strong.
 
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