BP Charge concerns

[brentius]

Here's the ORK of the rocket i'm planning to fly in a few weeks for my L1 cert. It is 4'' in diameter and 150cm long. However, I am slightly worried about the BP charge not being enough to push the nosecone out, and before you tell me to ground test, I live in the UK, where BP is illegal. The calculator shows that I need 1.7 grams of BP to push the nosecone out, but CTI Pro38 reloads only have 1.4g. What should I do?

 

[SolarYellow]

Add a stuffer tube.

 

[MarsLander]

Contact these good folks, I'm sure they can help you...

http://www.ukra.org.uk/

 

[brentius]

Add a stuffer tube.

Problem is, I've already made the MMT. Should I just add a stuffer tube maybe 5 cm in front of the mount?

 

[Titan II]

I believe magicians flash cotton is legal and available in the UK. Some have commented they have used it with success.
Start with post 9.
https://www.rocketryforum.com/threads/help-with-ejection-charge.184709/#post-2547769

I have also flown a stock Mad Cow DX3 with 38mm CTI motors. It is 4" x 66". The NC had a bottom so as not to add volume.

Another option...If you have a bulkhead on the coupler, split it in the middle.

 

[brentius]

I believe magicians flash cotton is legal and available in the UK. Some have commented they have used it with success.
Start with post 9.
https://www.rocketryforum.com/threads/help-with-ejection-charge.184709/#post-2547769

I have also flown a stock Mad Cow DX3 with CTI motors. It is 4" x 66". The NC had a bottom so as not to add volume.

Another option...If you have a bulkhead on the coupler, split it in the middle.

Does the DX3 have a payload bay?

 

[Titan II]

Does the DX3 have a payload bay?

Yes.
https://www.madcowrocketry.com/4-super-dx3/

If I were you, I would split in the middle. There is plenty BP for that method

 

[brentius]

Problem is, I've already epoxied the coupler in place... But in all fairness, this is a L1. Do I need more than 8 psi on my NC?

 

[Titan II]

Problem is, I've already epoxied the coupler in place... But in all fairness, this is a L1. Do I need more than 8 psi on my NC?

Glued to both halves?

Have any Klima motors? Steal some BP out of one or two.

 

[brentius]

Glued to both halves?

Have any Klima motors? Steal some BP out of one or two.

To both halves, yes. But again, I can sacrifice some stability for the rocket coming back in one piece... Again, is 8 PSI enough to push a nosecone out?

 

[Handeman]

Problem is, I've already epoxied the coupler in place... But in all fairness, this is a L1. Do I need more than 8 psi on my NC?

That depends on the size of the nose cone. The bigger the diameter, the larger the surface and the less pressure you need for the same amount of force.

A big part of any cert is the rocket has to be flyable afterwards. If you have the piston in there with no way to exhaust the ejection pressure between the motor and the piston, I expect you will blow the case out past the retainer or split the body tube. Either case is a fail on the cert. It doesn't matter what cert level.

 

[brentius]

That depends on the size of the nose cone. The bigger the diameter, the larger the surface and the less pressure you need for the same amount of force.

A big part of any cert is the rocket has to be flyable afterwards. If you have the piston in there with no way to exhaust the ejection pressure between the motor and the piston, I expect you will blow the case out past the retainer or split the body tube. Either case is a fail on the cert. It doesn't matter what cert level.

Well, it probably will work, the calculator gives exactly 1.4g for 25.5 inches of BT at 8 psi, and for 8 psi, there's abt 90 ish lbs of force against the NC.

 

[SolarYellow]

Problem is, I've already made the MMT. Should I just add a stuffer tube maybe 5 cm in front of the mount?

Is the MMT glued into the airframe already? Even if it is, you should be able to make an external coupler by wrapping several layers of cardstock or a few more layers of paper around the end of the stuffer tube and gluing it onto the end of the MMT. Just make sure you don't get squeeze-out of glue into the ID where it could block the motor from being inserted.

 

[2-0turbo]

Personally, I think you’d be fine with the standard charge. I’ve flown a bunch of rockets on “various” motors from E to H (in the same rocket) and have never adjusted the BP quantity.

 

[brentius]

So, here's the updated design. I'll use a spare Estes BT-60 as the stuffer tube, and it'll get attatched to the forward centering ring with a coupler. Will this work, or will it be slightly sketch?

 

[David Schwantz]

Stuffer tube will NOT work if there is a gap between it and the top of MMT. You will exhaust all of the pressure through the gap.

 

[brentius]

Stuffer tube will NOT work if there is a gap between it and the top of MMT. You will exhaust all of the pressure through the gap.

I was thinking that because the coupler (and the gap) has limited volume, that the pressure would go up the stuffer.

 

[David Schwantz]

It will take the path of least resistance. Just seal any gaps.

 

[bobbyg23]

Don't overthink this. Many people have used the stock ejection charge with success. It will be plenty for your application.

 

[JeffShort]

View attachment 634228
Here's the ORK of the rocket i'm planning to fly in a few weeks for my L1 cert. It is 4'' in diameter and 150cm long. However, I am slightly worried about the BP charge not being enough to push the nosecone out, and before you tell me to ground test, I live in the UK, where BP is illegal. The calculator shows that I need 1.7 grams of BP to push the nosecone out, but CTI Pro38 reloads only have 1.4g. What should I do?

Hi, I also live in the UK and BP is not illegal so long as you have the correct documentation

 

[brentius]

Hi, I also live in the UK and BP is not illegal so long as you have the correct documentation

Yes, but I'm doing this as part of a school project and H&S will kill me if i brought black powder to school...

 

[David Schwantz]

Kind of funny, at the High School where my son went we got a call about a bomb scare, we had to come to school and pick him up. The scare was because a student had Estes engines in his locker.

 

[brentius]

Don't overthink this. Many people have used the stock ejection charge with success. It will be plenty for your application.

I understand, I was just slightly concerned about whether or not the NC would come off. I spent quite a bit on this, and it's a big rocket, so I would not like for it to become a very expensive lawn dart.

 

[JeffShort]

Hi, I also live in the UK and BP is not illegal so long as you have the correct documentation

Ok, but you didn't mention that in your post and it doesn't mean that BP is illegal in the UK. I would suggest if you have any issues then check out the UKRA website.

 

[brentius]

Don't overthink this. Many people have used the stock ejection charge with success. It will be plenty for your application.

The calculator shows that I might be able to get away with the stock charge (barely) at 9 lbs, which has a force of 110 lbs on the NC. Is this enough?

 

[brentius]

Also, when using the calculator, should I start measuring the BT length from the end of the MMT?

 

[acalver]

Yes, but I'm doing this as part of a school project and H&S will kill me if i brought black powder to school...

Where are you intending to launch for your L1 certification attempt as it may be possible to obtain some additional ejection charge material? As has been mentioned BP is not illegal in the UK but requires an explosives licence.

 

[2-0turbo]

The calculator shows that I might be able to get away with the stock charge (barely) at 9 lbs, which has a force of 110 lbs on the NC. Is this enough?

To help you evaluate this in your head, turn your rocket upside down and secure it in a vertical config. Make sure it’s secure. Now grab the nose cone with your hands (I don’t know how big you are, but this COULD be your entire body weight) and pull down with 110 lbs of force.

Now answer your own question. I’m not being a smarta$$. It is def enough. Try to evaluate things based on known quantities. 110 lbs to pull a nose one off is a lot. Unless it is completely jammed on there, it is coming off.

 

[Ronz Rocketz]

Yes, but I'm doing this as part of a school project and H&S will kill me if i brought black powder to school...

I still like the idea of splitting it in half and adding a bulkhead to the coupler. If you already glued the two halves, use a saw and a new coupler with a bulkhead. Actually, my 4in LOC Patriot worked great with two sections. For my next flight, I added too much love to the ejection charge and blew off the chute, probably because the extra powder wasn't needed in the limited area. Later, I used a I280DM with the 14in motor case. This put limited distance between the ejection charge and bulkhead. With the Nomex blanket, wasn't a problem.

 

[Back_at_it]

If this were my rocket I'd do one of two things. Add a stuffer tube and be sure that the tube sits flush against the top of the upper motor mount ring. Or, split the rocket at about the halfway point as long as you have enough room for the recovery gear.