Shock cord anchoring suggestion

[gpoehlein]

Got a question for you mid-power gurus out here. I'm building a 130% upscaled Estes Trident (using BT-50 for the outboard tubes and BT-60 for the center tubes). The forward section is a length of BT-60 with a Der Red Max nose cone on the tail and a Stormchaster nose cone on the front. I'm trying to decide what the best method would be for attaching the shock cord into this recovery section.

Obviously, using the Estes trifold shock cord mount is not going to be strong enough to fly this baby on E reloads. What I am thinking of is somehow attaching a braided Kevlar cord to the rear cone somehow and then attaching elastic to that to finish out the shock cord. I'm afraid just tying the cord to the attachment loop on the plastic DRM nose cone might not be strong enough either. Any other ideas?

 

[BobCox]

Don't trust the plastic ring molded onto the nose cone. Instead, drill two holes in the base of the nose cone and pass your shock cord through both of them.

The gasses should be pretty well cooled by the time they reach the front section. You can probably skip the Kevlar and tie the elastic directly to the DRM nose cone.

 

[Handeman]

I'm not sure about how your rocket is configured, but I have a Stormcaster that I fly on composite E & F motors. The shock cored anchor is a loop of Kevlar epoxied to the BT. I then buy the 3/16" wide cloth trim spools in the sewing section at Wal-mart for $.39 for 6 yards and use that as the shock cord. They come in a variety of colors so you can match your rocket. I use about 10 ft of trim between the Kevlar loop and the plastic loop on the nose cone. Works great, just don't use the full load of BP that comes in the reloads.

 

[MarkII]

The design of the Trident is supposed to eliminate the need for wadding, so just elastic or thin tubular nylon or polyester should work. With the greater mass of the upscaled tubes plus the stronger ejection charges, I would worry more about how well bonded the tubes are to each other and how well the vent holes between them are sealed from leaks. They would probably be the more likely failure points. If the built model undergoes any flex under boost (which it could potentially do) it could crack the fillets (or the tubes themselves) that are sealing the ductwork.

MarkII

 

[gpoehlein]

As far as the vents are concerned, I plan to line each one with a piece of cardstock surrounding each hole - kind of like a gasket in each. It'll only have a 24mm mount so I can't put too large a motor in it.

 

[Micromeister]

As far as the vents are concerned, I plan to line each one with a piece of cardstock surrounding each hole - kind of like a gasket in each. It'll only have a 24mm mount so I can't put too large a motor in it.

First I don't know where Mark-II got the idea the ducted ejection gas tubing of the Trident-III or Trident-II for that matter are supposed to eliminate wadding or act like baffles? Neither do! Both models instruct the owner to install squares of FP wadding in the forward passanger pod before the chute during preflight prep.

You'll find it makes alignment much easier if you line each vent hole on both duct and pods with cardstock pieces creating flat matching plates for the vents to attach. once jointed,aligned and allowed to dry the gaps between tube and cardstock plates can be filled in with additional glue or epoxy forming completely smooth and sealed fillets.

Not sure how your determining the area needed for your ejection ports, but all thats needed is to ensure the total of each set of three ports (aft and forward) equal to or slightly larger then the internal diameter of the largest motor you plan on flying.

As for anchoring I used a similar method to an Engine mount system in that I file a small ring in the base of the aft Passenger pod NC shoulder just enough to bury the kevlar or Stainless leader with a single side channel leading up or forward from the ring holding the knot or eye splice of the shock cord anchor flush with the ID of the tube and od of the shoulder. These lines are embedded in the attachment glue or epoxy holding the aft NC in place. To this anchor point tie your extending Kevlar and/or Elastic Shockline. That's how I did it in my original Tridant-III back in the day replacing that nasty Teabag, and current Trident-II and Micro Trident-III. Works like a champ!

 

[gpoehlein]

First I don't know where Mark-II got the idea the ducted ejection gas tubing of the Trident-III or Trident-II for that matter are supposed to eliminate wadding or act like baffles? Neither do! Both models instruct the owner to install squares of FP wadding in the forward passanger pod before the chute during preflight prep.

You'll find it makes alignment much easier if you line each vent hole on both duct and pods with cardstock pieces creating flat matching plates for the vents to attach. once jointed,aligned and allowed to dry the gaps between tube and cardstock plates can be filled in with additional glue or epoxy forming completely smooth and sealed fillets.

That's what I was trying to describe - just didn't do a very good job in the description.

Not sure how your determining the area needed for your ejection ports, but all thats needed is to ensure the total of each set of three ports (aft and forward) equal the internal diameter of the largest motor you plan on flying.

I scaled up the length of the ports from the original Estes design while only increasing the width by an extra 16th or so - I figured scaling the ports up would help compensate for the "Shotgun" ejection charges Estes has been putting in their motors, as well as the black powder charge from Aerotech reloads. The liner should compensate for the larger size as well.

As for anchoring I used a similar method to an Engine mount system in that I file a small ring in the base of the aft Passenger pod NC shoulder just enough to bury the kevlar or Stainless leader with a single channel leading up or forward holding the knot or eye splice of the shock cord anchor which is embedded in the attachment glue or epoxy holding the aft NC in place. To this anchor point tie your extending Kevlar and/or Elastic Shockline. That's how I did it in my original Tridant-III back in the day, and current Trident-II and Micro Trident-III. Works like a champ!

Actually, since I'm using the plastic nose cone from a Screaming Mimi for the tail cone, I'll probably use Bob's suggestion of drilling two holes just above the shoulder and threading the kevlar braid through that. I should note that I built an original Trident back in high school ('74), and I've still got it - I'm refurbing it as well so the two should make a great set! (Might also build a smaller one for 13mm motors using BT-20 and a smaller tube like T-3 or T-4 (haven't run the numbers but I'll make it work! )

 

[Spurkey]

First I don't know where Mark-II got the idea the ducted ejection gas tubing of the Trident-III or Trident-II for that matter are supposed to eliminate wadding or act like baffles? Neither do! Both models instruct the owner to install squares of FP wadding in the forward passanger pod before the chute during preflight prep.

...why wouldn't they act like baffles? They'd reduce/trap the burning particles from the ejection since there's no longer a direct path from the motor to the chute. It's effectively the same design as FlisKits' BT50 baffle:

https://www.brshobbies.com/catalog.php/BRSHobbies/dt1138/Ejection_Baffle_Kits__Nomex_Cloth

I have Hawks Hobbies' Super Trident and have never needed wadding.

https://www.apogeerockets.com/Hawk-Hobby_Super_Trident.asp

(I realize I'm also over a month late replying to this thread :bangpan: )

 

[Micromeister]

...why wouldn't they act like baffles? They'd reduce/trap the burning particles from the ejection since there's no longer a direct path from the motor to the chute. It's effectively the same design as FlisKits' BT50 baffle:

https://www.brshobbies.com/catalog.php/BRSHobbies/dt1138/Ejection_Baffle_Kits__Nomex_Cloth

I have Hawks Hobbies' Super Trident and have never needed wadding.

https://www.apogeerockets.com/Hawk-Hobby_Super_Trident.asp

(I realize I'm also over a month late replying to this thread :bangpan: )

Spurkey:
The FACT is that the ducting may stop "some" of the burning particles and gas but it's not enough to protect the recovery system on the upper end. That you haven't burned holes in your chute so far is great, but if your not using any form of protective measure in the cuthe compartment at some point your not going to be very happy with the outcome. Of course on an upscale "Super Trident" the longer distance and larger ducting tubing should be working in your favor