kevlar chord/baffle kit

[leen_iz_meen]

first things first hello all!!!
im new to model rocket but not to this type of hobby ive raced rc cars on road/off road drag cars boats electric and nitro but havnt been in yrs so i came across model rockets and here i am.i have a few questions reguarding kevlar chords and baffle kits so here goes...by the way this is for an estes hornet i just picked up.

1)kevlar chord....replacing it with the elastic type from kit.installing it from the motor mount as i seen in a thread here cant remember where.
what strength and type?
how long should it be?
should i use 1/2 kevlar chord 1/2 elastic?
is this overkill?

2)baffle kits....
is it worth using?

i want to build a very solid rocket from the start.since where im from it gets a bit windy this rocket and others in the near future will be using streamers as well.

3)how long and what type of streamers is recommended?


thankx in advanced.....leen_iz_meen

[UrbanKnight]

I'm also interested in the baffle topic. I'm about to buy a dual 18mm motor mount fro Sunward, and was considering adding a BT60 and BT50 baffle kit to the order to try out. It would be nice to not have to stuff wadding down the tube every time, but I want to make sure that (a) the baffle won't increase the risk of the nose cone not popping off, and (b) it will in fact keep the recovery system from getting scorched.

[Wayco]

I build my own baffles using a coupler and two bulkheads with holes drilled in them, or adding BT-5 tubing for a cold air baffle. For lighter models like my Aspire, I use 300 lb. kevlar from Apogee, and larger mid-power models, I buy 400 lb. kevlar from Balsa Machining. For high power 1/4" (1500 lb.) is available from both vendors.

[jflis]

There are advantages and disadvantages to baffles, so there is no right or wrong answer with regard to using them...

good points:

• Faster model prep (no need for recovery wadding)
• Save on recovery wadding (duh... )
• Longer lasting shock cord/line
• Added weight to nose (and keeping laundry up top) adding stability margin

Not so good points...

• Baffles are NOT perfect (none are.) No more than wadding is. Baffles simply decrease the CHANCE of a burn spot on a parachute. No more.
• Baffles wear out. When they do, they can be a bear to replace. For very popular rockets I recommend that you put the baffle in low enough in the tube so that you can add a replacement on TOP of the original one...
• With the low cost of celulose (sp?) insulation, the cost savings of baffles is iffy...

To answer your question about Kevlar, I recommend #90 for smaller rockets (up to BT-55) and #150 for larger. You're not looking so much at the pull strength of the Kevlar as you are its resistance to heat (NOTE: Kevlar is NOT flame proof, just flame retardant). Also, I recommend your "shock cord system" be made up of a length of Kevlar cord from the body tube to an equal length of elastic cord from the end of the Kevlar to the nose cone.

hope this helps!
jim

[bjphoenix]

I want to make sure that (a) the baffle won't increase the risk of the nose cone not popping off

It will help because without wadding there is less stuff to have to blow out, and wadding can get packed too tightly into the tube.

You should also make sure that your parachute or streamer is not packed too tightly in the tube, and they your nose cone is not too tight. (But your nose cone has to be a little tight so it doesn't come off prematurely.)

3)how long and what type of streamers is recommended?

Some people use yellow tape like surveryors tape or "crime scene" tape. Some people use long strips of shiny mylar because it will be easier to spot at high altitude. I use crepe paper, which has the added advantages of being cheap and resistant to ejection charge heat. In a small rocket like the Hornet you will want as much streamer as you can get in there, but not so much that it fits too tightly. I have a similar sized rocket with 2 streamers. I roll up one of them and slide it in the tube, then roll up the other one and slide it in the tube on top of the first one.

[UrbanKnight]

Baffles wear out. When they do, they can be a bear to replace. For very popular rockets I recommend that you put the baffle in low enough in the tube so that you can add a replacement on TOP of the original one...

Any indicators or estimates as to how many flights most baffles will withstand? Since I'm enjoying the building more than the flying, I have no problem with each of my rockets having a finite number of flights before they are retired to a display or dismantled for parts.

[Wayco]

Any indicators or estimates as to how many flights most baffles will withstand? Since I'm enjoying the building more than the flying, I have no problem with each of my rockets having a finite number of flights before they are retired to a display or dismantled for parts.

That's gonna depend on what you make them from, and a few other factors that relate to your rocket. I think I still have a simple baffle in an Aspire that is several years old and has over a dozen flights. Made from cardstock and a coupler. My first "cold air" baffle has already been destroyed from a too fast deployment on a Vagabond. Lesson learned there was heavier rockets need stronger bulkheads for anchor points. OK, I never claimed to be a rocket scientist. Now it has two anchors in 3/32" plywood. But I had to do major surgery to repair it. I made a couple of baffles using thin aluminum sheet, and found it doesn't stick to well with epoxy, so now I just cover any hot spots with JB weld.
If you do a search here on "baffles", I'm sure you could find all sorts of designs to work from.