Anyone use a Kevlar loop in bulkhead for recovery harness attachment?

[Conway Stevens]

How many fliers have used a piece of tubular Kevlar instead of a U bolt or Eye bolt/nut.

Doing some minimum diameter projects and feel this could save some weight. But looking for info on what size you used? Size of the project? How did you attach it? Pictures of any used would be great. How about sealing the holes off in an ebay they go through? I have some ideas. But looking to see what others have done. Currently doing 2 different 3 inch diameter, and a 54mm diameter.

Appreciate the input.

Conway

 

[Steve Shannon]

I prefer metal or nylon connection points. Since graduating from elastic straps in model rockets I have built with Kevlar and nylon straps. I’ve never broken a nylon strap, but I have seen some melt through that we’re not protected from heat of ejection charges.
I have experienced Kevlar straps breaking that were connected directly to the motor mount and it’s a real pain. Kevlar has no give to absorb shock and unless rated for much more strength than anticipated it can just suddenly fail. It’s much better than nylon for heat though.

 

[David Schwantz]

I have done both tubular and woven kevlar. I have not had one break yet, but I do prefer using a method so they can be replaced. I have used a ring bulkhead, bulkhead with hole in the middle for BP charge and a grove on the outside to run the kevlar through. Then just tied off. Can be replaced easy. 29mm stuff I like 500lb kevlar, small easy to store away. 38mm same depending on NC weight. 54mm 1000lb kevlar. On the 75mm I would go with 1/4" tubular kevlar. I really like Top Flights. On the bigger stuff I have some of their 1/2", I towed the semi with it the other day

 

[Conway Stevens]

I prefer metal or nylon connection points. Since graduating from elastic straps in model rockets I have built with Kevlar and nylon straps. I’ve never broken a nylon strap, but I have seen some melt through that we’re not protected from heat of ejection charges.
I have experienced Kevlar straps breaking that were connected directly to the motor mount and it’s a real pain. Kevlar has no give to absorb shock and unless rated for much more strength than anticipated it can just suddenly fail. It’s much better than nylon for heat though.

Hey Steve. Hope your doing well.

Similar experiences. I quit attaching harnesses to motor mounts by gluing/epoxying them to motor mounts. I have for years now used metal attachment points ubolt/eyebolt on either forward closures or zippereless coupler. Same goes with all other points at av bay and nose cone. But for this instances looking to get some weight break, if i could utilize a loop of lighter material, either Kevlar or nylon that's attached at these points it could help equal for better altitude. Every ounce saved adds up to less pounds flown. ive seen.it done successfully. Just never used it myself and looking to try on these projects.

 

[Conway Stevens]

I have done both tubular and woven kevlar. I have not had one break yet, but I do prefer using a method so they can be replaced. I have used a ring bulkhead, bulkhead with hole in the middle for BP charge and a grove on the outside to run the kevlar through. Then just tied off. Can be replaced easy. 29mm stuff I like 500lb kevlar, small easy to store away. 38mm same depending on NC weight. 54mm 1000lb kevlar. On the 75mm I would go with 1/4" tubular kevlar. I really like Top Flights. On the bigger stuff I have some of their 1/2", I towed the semi with it the other day

Any pics? Thanks for the reply

 

[tfish]

I do, but then add a quick link to that to aid in my reefed chute line cutter setup.
Shock cord attachment....I usually attach one end to the threaded forward closure or to something attached to the forward closure. I've been putting my electronics in the nose cone for awhile now...once I got over my old school...don't put electronics in the nose cone because......

The quick link acts as a 'stopper' in the below setup. which is a 54mm rocket.


Tony

 

[rocketace]

https://www.rocketryforum.com/threads/build-thread-zoom-and-poof.162044/post-2049580
I had the same thought when I did my last minimum diameter build. I used no links and no knots, just all loops and spliced ends. Just FYI, It does add a significate amount of time and difficulty in setting it up for each flight.

 

[JohnCoker]

I have on occasion, although having an eye/U bolt is more common. I'm sure epoxying the strap is strong enough, but the question is wear over multiple flights.

 

[manixFan]

I've done it a variety of ways, although on my latest few I used a loop of Kevlar held in place by a small piece of stainless steel rod, then 'glued' in using sticky-tack. It's fairly easy to replace but does require a bulkhead in the fin can. Mine are usually a stack of a CF and wood ring for depth and better epoxy hold.

Regarding Kevlar, it really is not a very good material for our use, even though we use it extensively. It has the very bad property of not liking shock loads. If it experiences a shock load of a significant portion of its rated capacity, it suffers damage that is basically undetectable and can cause it to fail at a load far lower than its rating the next time it experiences a similar shock. I've started looking at the G load caused by the ejection charges and am trying to mitigate them though a variety of techniques, and I replace my Kevlar cords a lot more often than I used to.

The other big issue is abrasion resistance, or lack thereof. I now use a length of heat-shrink tubing to protect Kevlar anywhere there is contact between the cord and a body tube edge or other interface.

Below is an example (minus the CF centering ring and heat shrink) of the method I've used. I create loops using the 'finger-trap' method. As always, your mileage my vary.


Tony

after the rod is in place, I use a rod (from the motor end) to pack 'sticky tack' around it to hold it in place. (Sticky-tack is the stuff used to hold up posters - it's like like gum but not as sticky.) I also slide a piece of shrink wrap over cord right up against the loop and heat it to help protect against fraying.

 

[David Schwantz]

Hi Conway, sure. What would you like to see?

 

[Conway Stevens]

Hi Conway, sure. What would you like to see?

Thank you for the reply David.

Im curious how you fasten it to tge inside of the coupler/Av bay/ bulk plate. What size do you use? How much weight/size if rocket are you doing it with? How do you seal it off from letting ejection gasses into the av bay?

Appreciate your time.

 

[Conway Stevens]

I do, but then add a quick link to that to aid in my reefed chute line cutter setup.
Shock cord attachment....I usually attach one end to the threaded forward closure or to something attached to the forward closure. I've been putting my electronics in the nose cone for awhile now...once I got over my old school...don't put electronics in the nose cone because......

The quick link acts as a 'stopper' in the below setup. which is a 54mm rocket.
View attachment 453000

Tony

Hey Tony, hope your doing well.
Thank you for the post and picture.

So your doing mostly head end deployment? I have several i do that way.. i also utilize some of Mr Jarvis methods. if your doing head end what end are you bringing out the drogue? Or is your deployment different than a standard dual deployment?

Ss far as the harness attachment how does your Kevlar loop attach to the inside of the bulk plate?. What size for weight do you like to use?.

As always Tony your help is always appreciated.

Btw you ever get ahold of Mr Wilke? I need to messsge him and give him some grief lol.

 

[Conway Stevens]

I've done it a variety of ways, although on my latest few I used a loop of Kevlar held in place by a small piece of stainless steel rod, then 'glued' in using sticky-tack. It's fairly easy to replace but does require a bulkhead in the fin can. Mine are usually a stack of a CF and wood ring for depth and better epoxy hold.

Regarding Kevlar, it really is not a very good material for our use, even though we use it extensively. It has the very bad property of not liking shock loads. If it experiences a shock load of a significant portion of its rated capacity, it suffers damage that is basically undetectable and can cause it to fail at a load far lower than its rating the next time it experiences a similar shock. I've started looking at the G load caused by the ejection charges and am trying to mitigate them though a variety of techniques, and I replace my Kevlar cords a lot more often than I used to.

The other big issue is abrasion resistance, or lack thereof. I now use a length of heat-shrink tubing to protect Kevlar anywhere there is contact between the cord and a body tube edge or other interface.

Below is an example (minus the CF centering ring and heat shrink) of the method I've used. I create loops using the 'finger-trap' method. As always, your mileage my vary.


Tony

after the rod is in place, I use a rod (from the motor end) to pack 'sticky tack' around it to hold it in place. (Sticky-tack is the stuff used to hold up posters - it's like like gum but not as sticky.) I also slide a piece of shrink wrap over cord right up against the loop and heat it to help protect against fraying.
View attachment 453008View attachment 453009

Thank you Tony

 

[tfish]

Hey Tony, hope your doing well.
Thank you for the post and picture.

So your doing mostly head end deployment? I have several i do that way.. i also utilize some of Mr Jarvis methods. if your doing head end what end are you bringing out the drogue? Or is your deployment different than a standard dual deployment?

Ss far as the harness attachment how does your Kevlar loop attach to the inside of the bulk plate?. What size for weight do you like to use?.

As always Tony your help is always appreciated.

Btw you ever get ahold of Mr Wilke? I need to messsge him and give him some grief lol.

Conway,

I'm not sure if it's called Head end deployment of not. My electronics are in the nose cone. Everything comes out at apogee. The main is in a make shift deployment bag...in the above photo, the deployment bag is the canvas 'packaging that the Aerocon 60" chutes come packed in.. some times it's the 'leg" cut from nomex pants"
It's all drougeless. The line cutters cut the zip tie holding everything inside the bag. Everything in the bag is a loose fit and can fall out once the zip tie is cut.

The Kevlar loop (2500 to 3500 #) is held in place via a stopper knot and epoxied into a "well" I guess a photo would be helpful at this point.. Thee epoxy "well" is the clear area near the zip tie. The electronics board is epoxied to the "bulkhead plug" In this case a 54mm with dual altimeters and GPS tracker. The holes in the shoulder on the nose cone are, shear pin, vent/tool port and flat head screw hole... to hold the nose cone (shell) to all the other stuff.




The bulkhead plug is made from some artificial exterior trim from Lowes. PVC

https://www.lowes.com/pd/Royal-Buil...5-in-x-8-ft-Common-Board-PVC-Board/1000443053
Mr. Wilke...yes in May I was able to locate him via FB. I had some KestreL questions for him. He's doing well in NZ.

Tony

 

[Conway Stevens]

Conway,

I'm not sure if it's called Head end deployment of not. My electronics are in the nose cone. Everything comes out at apogee. The main is in a make shift deployment bag...in the above photo, the deployment bag is the canvas 'packaging that the Aerocon 60" chutes come packed in.. some times it's the 'leg" cut from nomex pants"
It's all drougeless. The line cutters cut the zip tie holding everything inside the bag. Everything in the bag is a loose fit and can fall out once the zip tie is cut.

The Kevlar loop (2500 to 3500 #) is held in place via a stopper knot and epoxied into a "well" I guess a photo would be helpful at this point.. Thee epoxy "well" is the clear area near the zip tie. The electronics board is epoxied to the "bulkhead plug" In this case a 54mm with dual altimeters and GPS tracker. The holes in the shoulder on the nose cone are, shear pin, vent/tool port and flat head screw hole... to hold the nose cone (shell) to all the other stuff.

View attachment 453087
View attachment 453088

The bulkhead plug is made from some artificial exterior trim from Lowes. PVC

https://www.lowes.com/pd/Royal-Buil...5-in-x-8-ft-Common-Board-PVC-Board/1000443053
Mr. Wilke...yes in May I was able to locate him via FB. I had some KestreL questions for him. He's doing well in NZ.

Tony

Thank you a ton Tony.

 

[David Schwantz]

Removable bulkhead in NC with eye bolt. Kevlar loops around eye bolt.
Ring bulkhead in tube. Make a bulkhead that fits inside of tube that is hollow so BP charge will flow through. Then cut a groove on the outside of bulkhead so the kevlar will thread though the slot. Can cut and replace easy.
Recovery layout.
Bulkhead glued into NC with kevlar looping through.

 

[Bruce]

Regarding Kevlar, it really is not a very good material for our use, even though we use it extensively. It has the very bad property of not liking shock loads. If it experiences a shock load of a significant portion of its rated capacity, it suffers damage that is basically undetectable and can cause it to fail at a load far lower than its rating the next time it experiences a similar shock.

I'm interested in learning more about that undetectable damage that Kevlar can suffer.

Might you be able to post some links?

 

[David Schwantz]

This is true. That is why it is so important that you ground test and get your BP charges correct. Don't want it snapping the NC and cord.

 

[tfish]

"Break points" in the shock cord..using electrical tape....can help ease the shock loading to Kevlar cords.



it may take a few flights to dial things in...It's cool to see one break point left after a flight.



Tony

 

[Conway Stevens]

"Break points" in the shock cord..using electrical tape....can help ease the shock loading to Kevlar cords.

View attachment 453453

it may take a few flights to dial things in...It's cool to see one break point left after a flight.

View attachment 453454

Tony

Great info Tony, i reef my shock cords as well. Usually use masking tape or have even done rubber bands. But it helps with taking some of that energy out of the yank on the cord.

 

[tfish]

The following is not meant to be mean....

I consider the use of masking tape and rubber bands to be more of a organization and packing aides..and offer very little force reduction.

Electrical tape placed on, in very tightly wraps, in 1, 2 and 3 places on each bundle of shock cord takes a lot of energy to get the shock cord pull through.

It could be sold on TV as the next best greatest exercise devise to store under your bed.

Grab a piece of shock cord and some tape and see for yourself..its easy to taylor the number and tightness of wraps to fit the size and weight of HPR.

Tony

 

[Conway Stevens]

The following is not meant to be mean....

I consider the use of masking tape and rubber bands to be more of a organization and packing aides..and offer very little force reduction.

Electrical tape placed on, in very tightly wraps, in 1, 2 and 3 places on each bundle of shock cord takes a lot of energy to get the shock cord pull through.

It could be sold on TV as the next best greatest exercise devise to store under your bed.

Grab a piece of shock cord and some tape and see for yourself..its easy to taylor the number and tightness of wraps to fit the size and weight of HPR.

Tony

Definitely not taken mean. Lol. All good Tony. Will try it out that way. Appreciate your experience and information as always.

Conway
Ps on another question aluminum fasteners vs steel? Preference? Weight vs strength? And think im gonna hit you up on the whole drougeless and cable cutter thing. Not something ive done yet.

 

[Bruce]

Wouldn't putting tape on the Kevlar leave a sticky residue?

 

[tfish]

Wouldn't putting tape on the Kevlar leave a sticky residue?

It does..

I guess it that bothers you, you could put it on upside down. I'm not sure how effective it would be then.

Tony

 

[rocketace]

Which tape you use, just make sure to ground test and fly as you tested. For my small 38mm rockets I have used masking tape. I do three separate loops bundles with the kevlar. First loop gets one section of tape, second gets 2 section of tap, and third gets three sections of tape. Each section is 3 wraps.

Most of the time when I recover there the first two bundles have broken free but the third is pulled tight but not broken. If I am interpreting it correctly, you can see this in the accelerometer data. First spike here is the nose cone being accelerated by the ejection charge at almost 30Gs. Then #1 is the first taped bundle breaking and #2 is the second bundle breaking.

 

[Bruce]

Why wouldn't the 2 bundles break at the same time?

But, you're right, the graph does show otherwise....

 

[rocketace]

Why wouldn't the 2 bundles break at the same time?

Because with more tape on the second and third bundles, it takes more force to break them. The weak link fails first.

My set up is almost identical to tfish (I probably saw it years a go in one of his posts and copied it ). You can see in his recovery photo that the bundle with three did not break.

 

[JoePfeiffer]

I measured the force required to break a one foot long (so it expanded to three feet) bundle of 1500 pound kevlar completely wrapped with masking tape a couple of days ago, and got 36 pounds.

 

[Handeman]

Are you putting the tape wraps on the Main SC, or both Main and Drogue?

I think if you are pulling the Drogue SC to full length with three taped bundles with electrical tape, you need to reduce your apogee charge. Probably by half. You only need enough to open the rocket and get the drogue in the air flow. You don't even have to open an un-bundled SC to the full length. Reducing the drogue charge will also greatly reduce your need for shear pins or extra tight friction fit on the nose cone.

 

[Hyak]

"Break points" in the shock cord..using electrical tape....can help ease the shock loading to Kevlar cords.

View attachment 453453

it may take a few flights to dial things in...It's cool to see one break point left after a flight.

View attachment 453454

Tony

This is very similar to what manyy OSHA fall protection leaders use. A length of the leader is shrink-wrapped (with what looks like heat shrink, but I am sure its not) together in a folded bundle. When a load hits, the shock pulls the leader out of its fold to absorb some (much of?) of the shock.

I have been thinking about doing this exact thing as I recently had a kevlar cord break on an H flight, where it passed out of the MMT centering ring. I got the entire rocket back with only a cracked fillet on a fin and the payload section, still under chute landed another ~6k feet away, so I got lucky but everything now gets built with welded eyes and in a manner that the Leader is more easily replaceable.