10 replies to this topic

[aquarius]

I have sucessfully made a "few" Solid Rocket Motors (SRM's) and launched them in homemade rockets, complete with fins, nose cone and all.
They fly high, straight and extremly well, but my parachute/streamer does not seem to work.
I know of Nakkas design, but I am trying to make this small, and this seems to be the problem.
My bodytube ID range from 20 mm and up...

I can make the SRM's with or without a ejectioncharge, move the ejectioncharge further up in the tube and use a spoulette or fuse for timing etc. But I have problems making this practical and working.
Any hints or tips will be appreciated.

[fishy1]

Use a larger parachute? Use more/less ejection charge?

[aquarius]

Haven't gotten any further on the recovery, but I tried a dummy load on my 15 mm ID rocket just to see how much it could lift and how much my rocket can weigh.

195 grams was lifted with a bit slow takeoff and to approx 50 m, I find this quite good...

[aquarius]

My motors are working out well and I used some Alder BP (scary stuff!) for the ejection charge, but it charred the parachute.
The project is a "all-amateur"-build, truing to utilize comon and easy to find compononts.

My main problem now is the 'chute, I used a Nylon showercurtain, but it does not hold up to the temp of the ejection gasses. Any suggestions?

[ProfHawking]

How is the rocket constructed? I think the parachute shells use a shell packed with sawdust to help protect the parachute from the (weak) burst charge.
If you have the 'chute in a rocket with a tube, try using some wadding, and try to "pop" the parachute out quite gently using a very small amount of fast burning charge instead of a large amount of slow burning charge.
Also, a plastic based parachute sounds quite vulnerable. Paper is probably better, even more so if it is treated to be flame-resistant. Plastic will melt at lower temperature than paper will burn.. I think! Im sure it depends heavily on the materials involved though.

[burningbush]

You need wadding, IMO
You can try making a good seal w/ cardboard to protect chute , like a circle below the cord and wadding to act as a gasket.
Ive had great success w/ low eject charges this way.

ENJOY
P.

[aquarius]

Thanks for the advice, I just used curled newsprintpage for the dummy test, and it charred my 'chute. I can make a spare without cost, but I'd like to konw WHY this happens. The idea of a thighter gasket has struck my mind...

I'll post some pictures of the rocket if any intterest. and I'll might video the launch to see how the timing is.

[portfire]

Yeah pics are always nice,and helpful.I'v read somewhere you can use some sort of piston that uses the ejection gases to deploy the chute.I sure iv still got the info somewhere if your interested ?


dean

[aquarius]

I know the ejection by piston, I think i read it at eigther nakka-rocketry.net or inveseengineering.com. I might have to give it a go.
Rigth now I'm trying the "cardboard-gasket" idea.

My main problem now is the weight, as I have assembled the whole thing, balanced it out and with live motor, chute and all, is a hair under 250 grams.... Without the motor, weight is 197 grams. Yupp, it's a heavy motor for a 15 mm, but it works with most kinds of fuel.
Knowing that is around the upper limit for my 15 mm driver, I look forward to testfiring it.
Dive!

Anyways, it's a "developing rocket", the weight will be reduced to a minium, by using lighter material, smaller ID/OD, less wood etc. Hopefully, the weight will be from 70 to 100 grams when the testing is done.

As for now, I'll have to take som pic's with my mobile phone camera, as I totally forgot my digicam...

[aquarius]

So, I did a test of the new parachute, ejection system, ignition and motor, all at once today.

The Rocket is made of a spiralwound tube, a container wich originally was made for protecting photos and posters.
Heavy, strong and cheap.

Wings are made of some surplus acryllic I had lying around, nosecone and divider I turned on my lathe out of some surplus three roundstock.
Chute from a shower curtain, and the rest is homemade.
The igniter is a X-mas-tree light bulb with a bit of BP. Works every time, cheap in the off-season, and easy to make.

I knew it was too heavy, but I wanted to try it out, just to see if it worked.
And it did!

Trying to upload the pictures came out bad, can anybody give me a quick tutorial?

[YT2095]

if you make a strong soln of Boric acid (use hot water, it doesn`t dissolve well in cold), or Borax (any water temp), and soak kitchen paper in there and carefully hang it out to dry, this makes Great wadding and it`s quite fire proof too, there are Flame retardant sprays also (Flame Guard is one) and these work also.
I use this myself for all recovery rockets and it works a treat

if you get the Spray stuff, give the inside of the rocket tube a blast also (don`t get it soggy though).