Translate

    Translate to:

Categories

Recovery Wadding for Rockets – Protecting the Parachute

Model Rocket Cut-Away (courtesy NASA)

For those new to model rocketry you may not be aware of the need for recovery wadding in your flight.

Recovery wadding is used to protect the streamer or parachute from the hot ejection gases from the motor. In this article I will discuss the importance of recovery wadding for rockets and show you two different types of wadding you may use in your flights.

Parts of a Model Rocket

The picture on the right shows what a model rocket would look like if it was cut in half. The parts, from the left to the right, are as follows: nose cone, launch lug, shock cord, parachute, recovery wadding, engine mount, rocket motor, and fins.

As you may be aware the rocket motor not only provides the thrust for the rocket it also creates an ejection charge to push the parachute out of the top of the rocket.

The recovery wadding is put in the rocket tube between the parachute (or streamer) and the rocket motor. The wadding is designed to take the brunt of the hot gases in order to protect the parachute. Without wadding the parachute (or streamer) would most likely melt and the rocket will fall quickly to the ground after the ejection charge.

Estes Recovery Wadding for Rockets

Estes type recovery wadding


The “Toilet Paper” Type Wadding

For those familiar with the Estes brand of products you no doubt have used their wadding. What many people observe about the Estes brand wadding is that is looks like toilet paper.

But don’t let its appearance make you think that you can use toilet paper in its place as Estes wadding is treated with chemicals to keep it from catching on fire. Using toilet paper in place of proper wadding is not only careless but very dangerous.

Estes wadding is widely available and relatively inexpensive for the job it does.

Below is a table showing the recommended number of Estes wadding sheets for the given body tube diameters.

Table 1 – Estes Wadding Amount
Body Tube Diameter Number of Sheets
19 mm (0.74 in) 2-3
25 mm (0.98 in) 3-4
34 mm (1.33 in) 5-6
41 mm (1.63 in) 7-8
66 mm (2.60 in) 10-11

The ”Dog Barf” Type Wadding

I must admit I do not know where this type of wadding got its nick name from. My best guess is that it’s due to its appearance. Although not an expert in the field of animal regurgitation, I’m pretty sure real dog barf looks nothing like this stuff.

Cellulose Fibre Insulation (Dog Barf)

Cellulose Fibre Insulation (Dog Barf) Wadding

The proper name for this type of wadding is cellulose fibre insulation and it is used for insulating houses. You can generally find large bags of it at your local hardware store. A large bag used for wadding can last years.

Cellulose fibre insulation is usually made from 100% recycled newspaper fibres which has been treated to make it fire retardant. It is non-toxic and non-irritant and makes for an eco-friendly choice.

Although it is a little messy when loading it into your rocket, it dissipates in the air better than the sheet type wadding. Thus there is less to clean up afterwards.

Other Ways to Protect the Parachute

Besides wadding there are other methods that may be used to protect your parachute or streamer from the hot ejection gases. Parachute blankets made of Nomex material may be used to wrap up the parachute and shroud lines. As well, ejection baffles may be built into the rocket to cool the ejection gases. Both these methods are well suited for larger rockets and we will cover each of these methods in future articles.

Toilet Paper or Dog Barf?

If you have never launched a rocket before than I would suggest sticking with the Estes type wadding for your first flights as knowing how much wadding to use comes with experience. Too much or too little wadding can result in a rocket returning more quickly to Earth than it should thus creating a safety hazard. Using the table above and on the packaging will give you a guideline to follow in knowing how much wadding to put into your rocket.

After a few flights under your belt you will start to be able to gauge how much wadding is needed. After such experience cellulose fibre insulation is a good and very economical choice.

©2011 Sigma Rockets Inc.