Rcandy Aerospike

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re: Candy rocket rules of thumb

Post by Mike Everman » Fri Dec 23, 2005 10:04 pm

Steve, is that a spike nozzle I see on your casing in the video intro picture? Does it work?
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re: Candy rocket rules of thumb

Post by pezman » Fri Dec 23, 2005 10:50 pm

What, no schlieren image? Would have made an ideal subject!

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Re: re: Candy rocket rules of thumb

Post by steve » Fri Dec 23, 2005 11:51 pm

Mike Everman wrote:Steve, is that a spike nozzle I see on your casing in the video intro picture? Does it work?
So far the aerospike has only been tested with compressed air @ 150 psi and that was very impressive! I couldn't believe how much thrust was generated even at such a low pressure. The throat area is equivilant to that of a conventional bell nozzle with a 3/16" throat dia. (pi x 3/32 squared) so that it will be interchangable on the same motor casing. I would eventually like to static fire or even launch the aerospike, but I want to get a bit more experience with making the fuel etc. first. Also, I have to figure out a way to reliably ignite the fuel with the aerospike installed.

The test I did today was basicly to see if I made the fuel correctly and to ensure that my scratch built motor case wouldn't explode. All my seals held up well and the fuel burned quickly and completely. The nozzle used for this test was the small stainless bell nozzle in the center of the big pic.
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Aerospikenozzle.JPG (33.24 KiB) Viewed 7544 times
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re: Candy rocket rules of thumb

Post by Mark » Sat Dec 24, 2005 4:20 pm

As all things have advantages and disadvantages, I wonder what are some of the downsides to the aerospike nozzle?
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Re: re: Candy rocket rules of thumb

Post by steve » Sat Dec 24, 2005 8:42 pm

Mark wrote:As all things have advantages and disadvantages, I wonder what are some of the downsides to the aerospike nozzle?
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added complexity? other then that I can't think of anything.
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re: Candy rocket rules of thumb

Post by Mark » Sat Dec 24, 2005 9:36 pm

Well off the bat I thought of high heat and then I took it upon myself to look up an article on aerospike nozzles, some fun facts along with the chaff.
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http://flab.eng.isas.ac.jp/member/ito/w ... 1-1051.pdf
http://pdf.aiaa.org/preview/1998/PV1998_3522.pdf
http://www.hq.nasa.gov/office/pao/Histo ... ro_faq.htm
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re: Candy rocket rules of thumb

Post by Mark » Sat Dec 24, 2005 10:41 pm

It might be fun to try an aerospike nozzle of some sort on a pulsejet, just for the heck of it. And maybe Mike or Larry would like to work with me on an aerospike jam jar, following and improving on the footsteps of Reynst and all. Maybe store the fuel in the spike. ha ha
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Re: re: Candy rocket rules of thumb

Post by Viv » Mon Dec 26, 2005 4:03 am

steve wrote:
Mike Everman wrote:Steve, is that a spike nozzle I see on your casing in the video intro picture? Does it work?
So far the aerospike has only been tested with compressed air @ 150 psi and that was very impressive! I couldn't believe how much thrust was generated even at such a low pressure. The throat area is equivilant to that of a conventional bell nozzle with a 3/16" throat dia. (pi x 3/32 squared) so that it will be interchangable on the same motor casing. I would eventually like to static fire or even launch the aerospike, but I want to get a bit more experience with making the fuel etc. first. Also, I have to figure out a way to reliably ignite the fuel with the aerospike installed.

The test I did today was basicly to see if I made the fuel correctly and to ensure that my scratch built motor case wouldn't explode. All my seals held up well and the fuel burned quickly and completely. The nozzle used for this test was the small stainless bell nozzle in the center of the big pic.
Well I have to admit Steve as some one who has had to learn how to be a machinist for part of my living (from an electronics engineer) I am pretty damn impressed by your work on that nozzle.

Viv

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Re: re: Candy rocket rules of thumb

Post by HattoriHanzo » Tue Dec 27, 2005 1:09 pm

steve wrote:
Mike Everman wrote:Steve, is that a spike nozzle I see on your casing in the video intro picture? Does it work?
So far the aerospike has only been tested with compressed air @ 150 psi and that was very impressive! I couldn't believe how much thrust was generated even at such a low pressure. The throat area is equivilant to that of a conventional bell nozzle with a 3/16" throat dia. (pi x 3/32 squared) so that it will be interchangable on the same motor casing. I would eventually like to static fire or even launch the aerospike, but I want to get a bit more experience with making the fuel etc. first. Also, I have to figure out a way to reliably ignite the fuel with the aerospike installed.

The test I did today was basicly to see if I made the fuel correctly and to ensure that my scratch built motor case wouldn't explode. All my seals held up well and the fuel burned quickly and completely. The nozzle used for this test was the small stainless bell nozzle in the center of the big pic.
Wow, thats a piece of art:)
Do you have any calculation on the nozzle to share with you?
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re: Candy rocket rules of thumb

Post by steve » Wed Dec 28, 2005 3:29 am

calculations? no not really, more like guidelines-

the nozzle throat, or rather, the area of greatest gas flow restriction is just inside of the lip, followed by a small area for expansion between the lip and the throat. Because of the nature of this nozzle design, the dimensions of the spike aren't critical and as long as they are reasonably similar to existing designs it should work fine. (obviously it will not be optimized, but not everyone has the time and money to test out 500 diferent variations- It will be good enough! its not like were launching into space or anything like that. OK rant over) There are several things to take into considderation with the spike design (all of which are sort of related)- surface area exposed to hot exaust gasses, weather your material will be able to withstand the heat, weight of spike (effect rocket CG), length, and angle (or curve) of cone.
Increased surface area means increase in weight and a decreased spike angle. this translates into a more streamlined , but heavier engine. also there is a good chance of the tip melting off. Alternatively a shorter spike will weigh less, be more tolerant of the heat, but might not work quite as efficiently.

two more things to considder- weather or not to cut the tip off and weather to use a curved or conical spike. According to a CFD study I have seen, cutting the tip off doesn't hurt performance of the engine nearly as much as you might think it would. Aparently the exaust gass behaves very much like it would hat the tip still been there. the loss in efficiency is only a few percent while the weight savings is quite signifigant when you cut off as much as they did for the X-33's engine. also there is less surface area to keep cool. A normal cone can be substituted for a curved one with only about a 1% efficiency loss, but it will weigh a bit more. This would make it alot easier to machine though.

OK thats everything I can think of right now.

BTW Viv, thanks for the compliments on the machining!
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re: Candy rocket rules of thumb

Post by HattoriHanzo » Wed Dec 28, 2005 2:35 pm

Please, notify me(us) when you do a "hot" test with the spikenozzle.
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re: Candy rocket rules of thumb

Post by steve » Thu Dec 29, 2005 7:19 am

I just finished making some more fuel and loading it into the motor. I will be lighting it off with the aerospike nozzle sometime late tomarrow morning. this batch of fuel came out much better then the previous one so this test should be a lot more intense then the last one- I'll be behind a tree in case it explodes!

If everything works correctly it should be pretty spectacular. video tomarrow!
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re: Candy rocket rules of thumb

Post by steve » Thu Dec 29, 2005 10:54 pm

Everything worked better then I expected! (which is to say that nothing exploded)

here are the promised videos

notice the spike glowing after the run. If I ever make a larger nozzle I will have to use graphite.
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re: Candy rocket rules of thumb

Post by steve » Thu Dec 29, 2005 11:13 pm

BTW, the big block of aluminium was a blast shield in case anyone was wondering.

here are some stills taken from the videos
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aerospikestatic.JPG (27.81 KiB) Viewed 7399 times
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re: Candy rocket rules of thumb

Post by HattoriHanzo » Fri Dec 30, 2005 11:21 am

Very nice!
Do you know the exit pressure of the nozzle?


I love the ignition with a match on the C-motor. It is the same type of ignition Nasa used on the Saturn V rocket :lol:
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