rivets and shear pins for 7.67" dia. LOC Bruiser EXP3

eggtimer rocketry
madcow rocketry
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
J

James

Member
Joined
Mar 9, 2018
Messages
13
Reaction score
0
I'm building a LOC Bruiser EXP3.
1. Rivets: I'm planning to use rivets to attach the (plastic ogive) nosecone to the 7.67" airframe. How many rivets would you recommend? 4-5 rivets?
2. Shear pins: I'd like to use shear pins to secure the section of airframe that will be separated during ejection. How many shear pins would be enough?
Thanks.
 
James said:
I'm building a LOC Bruiser EXP3.
1. Rivets: I'm planning to use rivets to attach the (plastic ogive) nosecone to the 7.67" airframe. How many rivets would you recommend? 4-5 rivets?
2. Shear pins: I'd like to use shear pins to secure the section of airframe that will be separated during ejection. How many shear pins would be enough?
Thanks.
Click to expand...

Need more info. It sounds like you are not doing dual deployment. Is that correct?
 
Yes, I'm just planning a simple 3FNC and recovery using Jolly Logic CR.
 
Then you don't need rivets or shear pins. Just a good friction fit is all you need. I suppose you could rivet on the NC, but that seems like overkill. Shear pins are designed to do two things: 1) keep the parts together so that they don't separate prematurely, and 2) allow the parts to separate when desired. In a dual deploy situation, you need to retain your NC when the apogee charge goes off -- not applicable for you. And in some situations, you may need to prevent drag separation of the booster when the motor burns out. I doubt that is applicable to you, either. I'd just put some masking tape inside the parts and make sure they don't shake loose when you grab the rocket by the NC.
 
Question? Is that rocket 1 long airframe or does it have a booster section & a payload section. LOC website does not state parts list. Depending on your answer, I might use 3 rivets on NC and friction fit booster.
 
The airframe consists of 3 separate sections of tubing of equal length (including booster section). The rocket is 9' 4" tall including NC.
 
So is the payload section separated from booster with a coupling & some bulk plates? Can you take some pics? That’s a pretty big airframe if not.
 
Here's a (dry fit) photo of the LOC Bruiser EXP3 next to a Madcow SuperDX3 for comparison. I realize that dual deployment would be more common for this thing, but I can't afford more time on this hobby right now. The LOC/Precision guys told me that it should work with single deploy and simple JLCR recovery, although I'm worried about whether the regular 2g ejection charge in a CTI K675 will be strong enough to pop it apart at ejection.

Bruiser_EXP3_dry_fit.png
 
Got it. If it were mine and you plan on using DD in the future, I would put 3 rivets on payload side of coupler and friction fit the booster side of coupler. The NC should be secured as well. Rivets or shear pins, don’t think it really matters but you don’t want it popping off at apogee from motor ejection force.
As far as your BP charge, I fly a Warlock (same frame size) and bump my ejection charge up to 2.5 grams.
 
timbucktoo said:
Got it. If it were mine and you plan on using DD in the future, I would put 3 rivets on payload side of coupler and friction fit the booster side of coupler. The NC should be secured as well. Rivets or shear pins, don’t think it really matters but you don’t want it popping off at apogee from motor ejection force.
As far as your BP charge, I fly a Warlock (same frame size) and bump my ejection charge up to 2.5 grams.
Click to expand...

Great, thanks a lot for the advice!
 
James said:
Here's a (dry fit) photo of the LOC Bruiser EXP3 next to a Madcow SuperDX3 for comparison. I realize that dual deployment would be more common for this thing, but I can't afford more time on this hobby right now. The LOC/Precision guys told me that it should work with single deploy and simple JLCR recovery, although I'm worried about whether the regular 2g ejection charge in a CTI K675 will be strong enough to pop it apart at ejection.
Click to expand...

For the cost of the rocket , the motor hardware , the JLCR , and all the recovery gear , why would you not at least have a single altimeter ? 50 - 100 dollars is very cheap in the long run.

Eric
 
Thanks, yes I already have a JL Alt3. I forgot to mention that. It works great.
 
Ground test, 2.5g of BP sounds a bit light on a airframe that length and diameter. My 5.38 Loc airframe based Cherokee-D upscale used 3.0 and 4.0 for main deployment and the airframe was only about 30-36" long for that section. Have you used any of the BP calculators?

Stress again...ground test...ground test...ground test...failure is an option and a dangerous one!
 
I'm not familiar with many of the new motors. Or, motors made in the last 10 years. However, if it has an aggressive thrust curve I personally do use shear pins even for motor ejection. Large diameters, motor burn out, and drag separation can happen even with a good friction fit. As stressed, ground test. I'm flying a very similar set-up today with DD, and I have 6g mains with 9g backups. M4 x4 shear pins, on both sections.

Good luck!!!
 
LOC said:
I'm not familiar with many of the new motors. Or, motors made in the last 10 years. However, if it has an aggressive thrust curve I personally do use shear pins even for motor ejection. Large diameters, motor burn out, and drag separation can happen even with a good friction fit. As stressed, ground test. I'm flying a very similar set-up today with DD, and I have 6g mains with 9g backups. M4 x4 shear pins, on both sections.

Good luck!!!
Click to expand...

Okay, thanks a lot!
 
I agree that you should retain the nocecone and not rely on friction fit. It's a big NC and the mass could easily cause it to separate due to the ejection charge. 3 rivets should do it but I suspect most folks would use 4. Remember to offset one of the holes an inch higher or lower than the others to make it easy to index the NC when you install it.

I've had good luck with a BP calculator to help figure charge sizes. Measure the length of the open body tube you need to pressurize - don't subtract the space occupied by the coupler. Then use that length with the diameter and calculate enough bp to shear a couple of 2-56 plastic screws (since you are using friction fit that will be more than enough) and you should be right on the money.


Tony
 
manixFan said:
I agree that you should retain the nocecone and not rely on friction fit. It's a big NC and the mass could easily cause it to separate due to the ejection charge. 3 rivets should do it but I suspect most folks would use 4. Remember to offset one of the holes an inch higher or lower than the others to make it easy to index the NC when you install it.

I've had good luck with a BP calculator to help figure charge sizes. Measure the length of the open body tube you need to pressurize - don't subtract the space occupied by the coupler. Then use that length with the diameter and calculate enough bp to shear a couple of 2-56 plastic screws (since you are using friction fit that will be more than enough) and you should be right on the money.


Tony
Click to expand...

Thanks, could you please recommend a link for a good bp calculator?
 

Similar threads

lovingia
Shear Pins With Cardboard
2
Replies
33
Views
2K
b.wieting
b.wieting
PayLoad
Dual Deploy / Shear pin questions
2 3
Replies
63
Views
6K
Grog6
Grog6
strider07928
3 Two Stage Questions: Shear pins, Flyaway rail guide, and Sustainer igniter installation
2
Replies
32
Views
3K
bad_idea
bad_idea
J
Aerotech K185 - Have you had this problem?
Replies
10
Views
993
jdeveau
J
AllDigital
Nylon shear pin testing
Replies
26
Views
2K
AllDigital
AllDigital

Latest posts

Back
Top