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need of fan?

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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need of fan?

Unread postAuthor: SpudFarm » Sat Mar 01, 2008 9:27 am

look at the picture

do i need a fan? i thought i don't bechause the compressed air coming in mixed it for you.

i did the first handheld shot today with a marble at 5x in the sky to look if i heard the sound barrier. (it was a shorter and more intese bang than lower mixes) is that a sign that i am on the sound barrier?

my goal is the SOS
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marble at 5x and the only change is the fan
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Unread postAuthor: rcman50166 » Sat Mar 01, 2008 9:37 am

well the answers that the program give you are ideal results. (without real world losses) The easiest way to find if you broke the sound barrier is to place a camera down range and fire a marble past it. If you hear a small snap in the video, followed by the bang of your cannon, the projectile has broken the sound barrier. You want to do this multiple times to ensure the snap was the sound barrier and not an anomally like the marble exploding due to friction. Also see ant's homemade chrono
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Last edited by rcman50166 on Sat Mar 01, 2008 9:42 am, edited 2 times in total.
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Unread postAuthor: bigbob12345 » Sat Mar 01, 2008 9:38 am

you shouldnt need a chamber fan but if you do then just use 6x it will get to the speed of sound guarrenteed.
And what calculator is that Ive never seen it before.

Edit:beaten by rcman
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Unread postAuthor: SpudFarm » Sat Mar 01, 2008 9:44 am

i have a real chrony in the mail now but i don't know when i get it.
(just want to know if i need a fan)

thanks to all
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Unread postAuthor: jimmy101 » Sat Mar 01, 2008 12:45 pm

A chronometer is the only reliable way to tell if you've reached the SOS. Listening, or recording, down range has the problem of how much the round slows down over the particular distance.

BTW, it is also a good idea to record the temperature and barometric pressure at the time of the shots. If your chrony readings are close to ~1100FPS then whether or not you actually reached the SOS comes down to the conditions. Of course, if the chrony reading says 2000FPS then there is little doubt you reached the SOS.
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