Paper two-stage build

[banjonate]

Another paperboard-and-balsa rocket, this time two stages. Haven't flown yet: waiting for when the grandkids can come over and be part of the fun.

Dimensions are 19.25" sustainer, 2.75" booster for 22" of tube, 4.75" of nose. Tubes ended up 29mm outside diameter (yes, I really like that 29-30mm size).

I came up with the design but I really feel like it reminds me of an old Estes design, so I may have subconsciously ripped it off.

Here it is:

 

[BABAR]

Looks great.

Since it is a paper rocket, save yourself some time and trouble and paper the fins. If you do it with white glue, it also makes the stronger. This may be more important on your Rocket for two reasons.

The tumble recovery on the booster tends to be tough on fins.

Given it is two stage you may consider a streamer rather than a chute on the sustainer. But with those aft swept sustainer fins, it’s gonna hit at least one fin hard on landing. Hope you have soft grass!

 

[banjonate]

Looks great.

Since it is a paper rocket, save yourself some time and trouble and paper the fins. If you do it with white glue, it also makes the stronger. This may be more important on your Rocket for two reasons.

The tumble recovery on the booster tends to be tough on fins.

Given it is two stage you may consider a streamer rather than a chute on the sustainer. But with those aft swept sustainer fins, it’s gonna hit at least one fin hard on landing. Hope you have soft grass!

Depends. With the kids there, I am tempted to fly on an A-A or B-A combination to keep it low with a parachute... kids like the parachutes. Now, after we do that once, or if we have a wide-open area, the full-bore C-C with a streamer will be used.
I never thought about papering the fins unless we are talking close-to-Mach 1 flights, which... I... have never...done.

 

[GlenP]

That looks great. There were a few multi stage kits from Estes that had the sustainer fins fit together with the booster fins like that, always good to use a known proven kit design as inspiration for a scratch build design.

kind of hard to tell in that photo, but what direction is the balsa grain on those sustainer fins?

 

[cbwho]

I like the design!

I am new to 2 stagers, on both I've built recently but yet to launch, the lower booster fits rather tightly* to the upper. With the motors taped together, should the booster be a looser fit?

* It is very difficult to pull apart by hand

 

[banjonate]

I like the design!

I am new to 2 stagers, on both I've built recently but yet to launch, the lower booster fits rather tightly* to the upper. With the motors taped together, should the booster be a looser fit?

* It is very difficult to pull apart by hand

When I have done 2-stagers, I have never taped the motors together; always just made sure that the booster motor butted up against the sustainer motor when loaded, then taped the booster motor to the motor mount at the bottom so that when the sustainer ignites it pushes the booster away.
The booster should be loose enough that it ALMOST falls away under its own loaded weight.

 

[banjonate]

That looks great. There were a few multi stage kits from Estes that had the sustainer fins fit together with the booster fins like that, always good to use a known proven kit design as inspiration for a scratch build design.

kind of hard to tell in that photo, but what direction is the balsa grain on those sustainer fins?

Grain runs approximately perpendicular to the body.

 

[GlenP]

Grain runs approximately perpendicular to the body.

then maybe seriously consider papering them, the lower triangular section where the grain runs out to the trailing edge and is not supported by the body will definitely snap off along a grain line on landing. Typical practice is to cut fins with grain along the leading edge so all grains are supported by the body glue joint.

 

[banjonate]

then maybe seriously consider papering them, the lower triangular section where the grain runs out to the trailing edge and is not supported by the body will definitely snap off along a grain line on landing. Typical practice is to cut fins with grain along the leading edge so all grains are supported by the body glue joint.

Thanks... I always considered the grain being “along the leading edge” as “approximately parallel to”. Seeing that the triangular shape really kind of messes that up, I never really though about that.
I really kind of have this idea that booster stages can be expendable, though. A pretty high percentage of them end up damaged upon landing, even in the best of circumstances.

 

[BABAR]

A very light friction fit for the booster should be fine. The sustainer needs a firm fit. Do you have a motor block at the REAR of the booster? Not a must have, but helpful

 

[GlenP]

I like the design!

I am new to 2 stagers, on both I've built recently but yet to launch, the lower booster fits rather tightly* to the upper. With the motors taped together, should the booster be a looser fit?

* It is very difficult to pull apart by hand

to be clear, when you use cellophane tape between the two motors, they should both still be very loose in the sustainer and the booster. Then you use masking tape to add friction as needed in the sustainer and to the booster. The cellophane tape should not really add any more friction between the booster and the sustainer, it should melt immediately during staging and allow them to separate. The booster motor should be tight in the booster, the sustainer motor should be tight in the sustainer, and with no cellophane tape at all, the fit should be about loose enough to fall under the weight of the booster, but snug enough to keep them aligned and straight, almost kind of like a nose cone. I hope that makes sense. There are some basic instructions on this from any Estes kit that utilizes the direct staging. You don't want the sustainer to light and push the booster motor out the back while the booster body tube itself is still friction fit too tightly to the sustainer motor, then you have a Krushnic situation where the sustainer just burns through the booster and has no thrust.

I think the idea is that the cellophane is just sticky enough to prevent a drag separation for the short instant when the booster no longer produces thrust and the sustainer is about to ignite. The heat melts it and the sustainer blows it away pretty quickly.

 

[cbwho]

I think I now got it from the advice:

The booster should slide into the sustainer like nose cone friction.

As for the motors, they should be cellophaned together and not masking taped together. Masking tape is for a snug fit of the motors into the booster and sustainer.

 

[BABAR]

I think I now got it from the advice:

The booster should slide into the sustainer like nose cone friction.

As for the motors, they should be cellophaned together and not masking taped together. Masking tape is for a snug fit of the motors into the booster and sustainer.

You got it.

You can make a very short motor block for the rear end of the booster that adds almost zero mass (relative to the booster itself) and takes up very little space so it won’t cause Krushnic effect.

Assuming a minimum diameter tube (or whatever your motor mount size is) cut a piece 1/8” long. Glue it just inside the tail end of the booster.

This may not work for your prebuilt rocket, however, you may not have enough length in the booster section. So you may need to friction fit both the booster and sustainer motors securely.

Also, you only need one wrap of cello tape for the motors.

Hope you get two straight trails and two short walks!

 

[BBB]

Yes, nice design! I have a more generic question about staging low-power rockets. I have done two-stage 18 mm engines by taping them together. Has anyone tried two stage with an 18 mm booster and a 13 mm sustainer? If so how did you connect the different sized engines?