Designing a rack rocket

For the next season I am planning to build a two stage rack rocket. It will be my first rack design. To test some ides I did a little experiment that may be of some interest to someone here.

The aim was to establish the motor (B or C) exhaust envelop and to come up with a rack design that would not be damaged by the exhaust heat.

Here is the video.

[YOUTUBE]Uarya-8GGBE[/YOUTUBE]

Detailed description of the test and its results can be found in notes at the bottom of the page here.

• In a two-stage design it is possible to avoid any exhaust heat damage to elements of the rack and fins by removing them from the heat-damage envelop (+- 8.5 degrees)
• Exhaust deposition envelop is +-30 degrees.
• It is not possible to avoid burn damage to racks longer than 60 mm. However damage from B6-4 motor is relatively minor thus the rack can be reused several times.

You can see my rack rocket build HERE



I've applied small strips of the silver heat resistant foil duct tape to the inside of my rails on my latest rack's. I've had very little damage due to exhaust.

I too vote for metal tape. I used metal EMI shielding tape and it worked OK. It did it's job but the adhesive was destroyed by the heat so it needed replacing. But that was easier than replacing the rack itself!

Sweet! I like the high speed shot.

but your youtube ID is malformed, when using the youtube tags all you need is the video ID code, on other words, everything after watch?=



-Braden

Here's a thread about a 4 stager I've built a few of. I consider them expendable.
https://www.rocketryforumarchive.com/showthread.php?t=14063

Based on the experiment results I designed a small rack payloader for B6-4/C6-0 or C6-5/C6-0 combinations to test the fin-rack configuration.

At least 20g payload will be required for the correct balance. The hole in the payload bay (actually there is another one on the opposite side) is for a ultra bright LED. A bettary and two LEDs will have gust about the correct minimum weight.

The rocket is very small and there is a good chance I will never see it again after the first flight, but with LEDs I may be able to spot it :eyepop:. It'll be a second objective of the test.

Unfortunately I won't have any launch opportunity this year.

Im new so what is a rack rocket

Dude.......see above.

basically a rocket the uses more than one motor without staging. As each motor fires it expels the one under it. Motors all all stacked or "racked" up.

i've seen the design, but a question remains...what happens to the spent casings? i can't imagine many clubs would like the like the idea of ejecting hot stuff into the field or over peoples heads.:bangpan:

edwinshap1 said:

i've seen the design, but a question remains...what happens to the spent casings? i can't imagine many clubs would like the like the idea of ejecting hot stuff into the field or over peoples heads.:bangpan:

Click to expand...

I just got a strange mental image of something like that canvas strip that attaches to a horse's butt to catch the manure rather than letting it fall into the street. Now imagine that same type of device mounted to the two lowest fin tips, to catch the spent casings!

CG aft of CP once again!!

G.D.

edwinshap1 said:

i've seen the design, but a question remains...what happens to the spent casings?

Click to expand...

The casings just fall. This is a BP motor method, so the cases are usually small. I have made one with BP G motors. It dropped 4 cases about the size of a 38/480.
[YOUTUBE]sIEKCBRKyZ4[/YOUTUBE]
APCP motors require an onboard ignition system. Protecting the structure from the exhaust is a much more difficult problem than with BP motors.

edwinshap1 said:

i've seen the design, but a question remains...what happens to the spent casings? i can't imagine many clubs would like the like the idea of ejecting hot stuff into the field or over peoples heads.:bangpan:

Click to expand...

There may be different solutions to this. In my case the first motor will have a short streamer wrapped around its casing. You can’t see it on the photos, but there is a gap as large as the BT20 tube wall thickness that allows a couple of wraps of streamer. In turn it’ll hold the casing at place.

After several months of waiting for better weather, larger field etc I tested the rocket last weekend. To be correct it was flown a couple of times before, but without the first stage. After these test flights the payload section with LED flashlight (see post#6) was replaced with a different design. It is a small RF tracker that fits into BT-20 (18mm) tube. It is 105mm in length and weights 16g. I will post details in the Electronics section.

For the two-stage test C6-0 + B6-4 motors were selected. Staging worked perfectly and the rocket disappeared in the sky. I could not see the chute deployment and due to strong wing I could not hear it either. However, the transmitter’s signal was strong and I managed to track its bearing for the whole time it was descending. As soon as the transmitter was on the ground the signal was lost. Unfortunately the shock cord got torn leaving only the payload section attached to the parachute. It was too light for rapid descent and it got carried down the range. It took me over an hour of waiving my Yagi around but eventually I managed to pick up some noise and then a strong signal coming from about the right direction. The payload was discovered just over 1400 meters from the launch site.
All and all, despite lost booster section, I consider it to be a very successful launch. Rack rocket staging worked perfectly; considerable altitude was achieved; visual contact with the rocket was lost; the descending rocket was tracked and recovered using instrumental observation. The only unfortunate aspect is that I forgot to take a god picture of the rocket before the launch.

While not exactly a “Rack Rocket” I built this two-stager before I had ever heard of a rack rocket. This is “Thump” and is the third iteration of this design the first two coming to bad ends.




The booster pod has a small streamer to aid in recovery and locating it once down, as the small fins do little to impart any tumble.





I haven’t had a chance to launch this version.

blackjack2564 said:

basically a rocket the uses more than one motor without staging. As each motor fires it expels the one under it. Motors all all stacked or "racked" up.

Click to expand...

Many years ago we had a design called the "Lil Augie". Instead of a rack framework to hold the fins, it had a larger tube at the bottom. It works just like the framework except that the tube is supposed to allow air coming into the tube to be heated by the exhaust and provide additional thrust like a ramjet.

https://www.spacemodeling.org/JimZ/eirp_10.htm

The "Lil Augie" used CHAD staging. Of course if your rocket is stable enough you can CHAD stage even a rocket intended to fly only as a single stage.