Piston, Baffle, or Wadding?

I voted for piston as I have used them very successfully in a few large LPR and some MPR birds. Anything larger, I guess I would lean towards a nomex shield pending some testing of my piston designs.

On the subject of the dog barf, I'd like to get a description of the packing techniques used by the people here who "swear" by it. I've started to use it in some LPR stuff, but I apparently do not pack it correctly as I have had several scorched chutes, and not only plastic ones.

Can someone give me a tutorial?

Preferred MPR/HPR, for me, is a nomex.

For LPR, baffle. Unless there's little room (<BT20), then wadding/dogbarf combo.

OK, my vote went for NOMEX but let me expound on that.

In my case NOMEX chute protectors happen to be the most expedient measure for MPR and HPR. This is due to the fact I design a lot of rockets that look like me, short and fat. *Reality is harsh but one must accept it*
Stubby fat airframes have precious little room in them for anything but the chute, protector and SC.
In a more perfect world I would use baffles, as they are easy to make, don't get lost in your range box, and you just load and launch. Now that we are branching off into LPR I may try including baffles in new kits in the future.

I plan on trying out a kevlar chute protector from Giant Leap in my big Mosquito this weekend. Like Layne mentioned, it's the epitome of of a stubby rocket and there's precious little room in the airframe once the 29/40-120 is locked and loaded. There will probably be a little dog barf in there too.

Hospital_Rocket said:

Actually I lifted the idea from a Nike Apache by Cosmodrome. The net effect is to move the anchor point of the shock cord to a point essentially flush with the end of the BT. Of course 20' of tubular nylon at the end of that does not hurt either

Of course, it's all about seeing if what comes down resembles what you sent up.....

A

Click to expand...

The main point of this set-up was to get the quick link to come in contact with the end of the body tube, not the thin cable. The more surface area, the less likely it is to zipper.

mike
cosmodrome rocketry

I voted piston. I have used 'disposable' pistons in all my rockets and have not had any issues with deployment. I did build a rocket with a piston that could be slid back in to position after the flight, but under estimated the forces and wrecked the body tube.

I even used a piston in my latest rocket 'Rock-It Fuel' which only had a body tube 1 1/2"dia. x 2 1/2" long, and again it worked well.

I like the way the piston pushes the chute etc. out and use a lot less pressure.

As others have mentioned, it depends on the type of rocket. For low-power, I mostly use dog barf. Some of my mid-power rockets have baffles, but for others I use a 'chute protector and/or dog barf. For high-power, I usually use a 'chute protector, but sometimes I use a lot of dog barf.

-- Roger

I have a fantastic baffle which works extremely well and is very simple to build.

1) Harden end of motor mount with CA

2) line inside with a single layer of Aluminum duct tape

3) Using a hole punch or drill, add holes to the tube for ejection gases to escape (the end of the motor mount will be capped in the next step)

4) Cut a V8, Red Bull, or Coke can in half. (Needs to be large than the motor mount diameter but smaller than the body tube diameter). Glue this to the end of the motor mount with epoxy so you cannot see the holes you made in step 3.

That's it! Ejection gases and burning particles have to make a 90 degree turn and go through the holes from step 3, then they have to make another 90 degree turn to go to the engine mount bulkhead, then turn 180 degrees to go back up towards the nose cone.

I've built at least 8 rockets this way starting about 10 years ago and they all perform perfectly. I also epoxy an eyebolt to the center of the can for a bungee mount.

taaadaaaa!

Heh, none of the above. I'm workng on a non-pyro ejection system design right now.

Hospital_Rocket said:

So lets take a brief survey.


What is the best MPR/HPR recovery system?

Click to expand...

Now I see your real question. The one that was asked when I opened this was, "What's your favorite recovery system?" Different question.

Anyway, I put down the dog barf, because it's what I use the most. I have a rocket with a baffle, a piston, and nomex shield. I haven't used the nomex yet but hopefully tomorrow. Not sure about the best but the dog barf is so cheap, I got an "opened" bale of it for $3.49 and should last years.

I've used 4", 6", 9.5" and 12" diameter pistons for several years without a failure. For smaller diameter rockets I use Nomex cloth to protect the parachute.

Just because a device is called a piston does not mean it is exactly the same as another device called a piston.

Here's a summary of my experience with pistons.

A piston should be solid. This eliminates the possibility of it deforming during use and sticking.

A piston should fit loosely in the tube because the airframe tube can flex. If a piston is too tight then it can get stuck. When the airframe is upright, drop the piston in. It should slide to the bottom. If not then it is too tight.

I create a solid piston by taking a length of coupler, glueing an internal bulkhead to one end, filling with two-part foam, and glueing an internal bulkhead to the other side after the foam hardens. Then I cut a slot through the center and coat it with epoxy. After the epoxy cures I thread the shock cord through. The piston slides on the cord.

The 12" piston was part of a sabot. The bulkhead was at the bottom. The side was cut into two pieces, which were not attached to the bulkhead but sat on the bulkhead. After leaving the rocket the sides fell away to release the parachute. The 24 foot chute, in a deployment bag, sat in the sabot pressing the sides outward against airframe.

A little dog barf and wrap the parachute and harness in Nomex.

I've used pistons successfully in all my birds but now am leaning toward building a Z-pard into my next one. Anyone used one?

Edward

edwardw said:

I've used pistons successfully in all my birds but now am leaning toward building a Z-pard into my next one. Anyone used one?

Edward

Click to expand...

What is a Z-pard?

I have used wadding and piston and baffle.

I have never had a problem with my PML piston systems on my PML rockets. They only complaint is being in Minnesota and temperature changes you find yourself adjusting/fine tuning your piston in cold weather.

I haven't had a problem with Aerotech's baffle system on my their rockets.

I have used dog barf on my mid power Loc and had no problems. I have melted a few plastic chutes on my LPR rockets in my younger years.

I simplicity! I am a firm believer in K.I.S.S. (Keep It Simple Stupid)

The easier the better!

BAsically a Z-pard is a small device that uses a metal piston to deploy the nosecone. You are using basically a 1/4" tube and piston and use a tiny amount of BP. I saw it in ER and have been constructing one for my next rocket.

Edward

pyrovette20 said:

A little dog barf and wrap the parachute and harness in Nomex.

Click to expand...

What is the point of the dog barf if you are using nomex?

Andrew

agrippo said:

What is the point of the dog barf if you are using nomex?

Andrew

Click to expand...

Belt and suspenders? I've seen dog barf "blow through" and scorch the 'chute, but I've also seen 'chutes get scorched with nomex, if the packing job wasn't quite right. Personally I'd drop the nomex first, then dog barf on top (rather than barf, then nomex), sort of along the lines of using a single sheet of estes wadding underneath a dog barf "piston".

-Rick

I use nomex in a couple of my rockets. The first time I used it, the nomex was too close to the ejection charge and now has a dime size hole in the center. A little dog barf would probably have prevented that.

I had such good results with my side eject drogue that I'm really thinking of using it for the main on a large rocket. It adds some complexity but when you think of all the problems that it eliminated I think it is a winner.

I used a cup sized for Newton's 3rd charge holders, a cap with an o-ring fits over it and the door is secured with press in panel fasteners. I had a deployment bag tied into the cavity with the door acting like a drogue. Deployed perfectly, no black powder touching the chute and the rocket looked very cool coming down like a weather vane pointing into the wind.

I've used all forms or recovery "protection" mentioned with good results - it depends on the rocket.

bfraley said:

I've had good luck with pistons. But they need to be installed correctly or they can jam easily. See...

https://www.deltavrocketry.com/piston.htm

Click to expand...

That's what bugs me. I contact PML about my Miranda because I read that document but yet PML instructions show the plate installed on the end away from the motor and according to that document creates an unstable situation. They commented about thousands of flights and years of support for their way. I'll just leave it at that.

Michael

Generally use dog barf and a nomex shield, but have started experimenting (a little) with Baffles.

I love pistons, on my small stuff just use wadding

Baffle, but with some LPR baffles, a nomex protector would still be good.

HPR baffles (especially the Semroc style double-pipe baffle) should obviate the need for an extra protector.

Of course, if you're using dual ejection. then nomex protector is definitely the way to go.

hehe

I use baffles whenever possible and available; I don't have to worry about my parachute protection getting stuck and blocking the tube and preventing the chute from deploying. I also use the other alternatives, too, but my preference is for baffles, especially those that I modify so that I can remove them to clean or replace them.

please inform me on what dog barf wadding is. im not sure if it is actual dog barf or what

nootnam said:

please inform me on what dog barf wadding is. im not sure if it is actual dog barf or what

Click to expand...

Cellulose insulation.

nootnam said:

please inform me on what dog barf wadding is. im not sure if it is actual dog barf or what

Click to expand...

What 'kaos2' said, and it looks like this: