Aerobee Stagging System

[JumpJet]

I just wanted to share a different way I came up with to ignite the upper stage engine on a scale type model like the Aerobee series of sounding rockets use. I created this about 9 years ago. I did one static test where the upper stage motor ignited. A while back I asked Steve and Emma Kristal if they could perform a firing test on a second unit I built using their high speed camera, so I thought I would share some images and video. It’s a little hard to see but you can see flame coming out the top of the staging system. The unique aspect of this stager is that the flame, heat and particulates that are generated from the burn through of the 18mm booster motor gets split into three separate streams that travel up 3/16” dia. K&S aluminum tubing; they then recombine at the top into a single mass to ignite the upper stage motor. All the parts show in the cad images were created on a rapid prototype machine, except of course for the three aluminum tubes. The different color pasts are the parts grown in the machine. Shown are two separate Red parts that were in fact a single unit but I separated the part so it is easier to see what it looks like.


John Boren











View attachment Aerobee SloMo .zip

 

[Woody's Workshop]

What is the purpose of dividing it into 3 tubes?

 

[rharshberger]

What is the purpose of dividing it into 3 tubes?

Looks like its to make use of the interstage connector as a means of guiding the gases between the booster and the sustainer motors for ignition of BP motors, without changing the scale appearance of the interstage connector like is usually done by cutting off the tip of the cone and gap staging.
Thats a neat looking setup John, what material would the interstage connector be made of?

 

[JumpJet]

I just used ABS Plastic.

 

[rharshberger]

I just used ABS Plastic.

I like the idea, a staged Aerobee has been on my list of scale buils for a long time. By doing it the way you did, the ablative cone on the booster is able to be left unmodified and scale correct.

 

[Peter Olivola]

I didn't see it in the CAD pix, but is there any venting? That's usually necessary with any approach that uses the booster motor burn through to ignite the upper stage.

 

[Tonimus]

I love it! E/F15 boosted would be pretty sweet indeed.

 

[JumpJet]

but is there any venting?

I didn't use any venting on the two prototypes I made, but one can certainly be added. I believe there is so little volume in this system that there isn't enough room for pressure to be build up before the flame hits the upper motor, but this is just a guess on my part.

John Boren

 

[Gus]

Photos below show a bit more detail on John's test article, and the test setup.

Test motor was a B6-0.

Video was shot at 1000 frames per second.

Because the area in the video is white it is a little hard to see but it is definitely a ball of flame erupting from the opening. Clearly enough to ignite a motor nested near the opening.

The video confirms what Emma found in her R&D project. In gap staging, it is not flaming little particles moving in a straight line that ignite the sustainer. Rather, a ball of flame erupts up the tube, similar to fireworks quick match. That ball of flame will follow the path of least resistance, bending around angles if necessary. Emma used this in her Little Joe and John very effectively uses it here.

In the case of John's Aerobee piece, the booster motor flame first moves laterally to pass through the aluminum tubes, then redirects medially on the other side of the tubes and then bends again to escape through the opening.

I know I've posted it a number of times but for anyone who hasn't seen it, here is the link to Emma's R&D report:

[video=youtube;1Nhe5Y78PRQ]https://www.youtube.com/watch?v=1Nhe5Y78PRQ[/video]
My thanks to John for such a great idea and for letting us test it.

Steve