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Ramjet BBMG

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Ramjet BBMG

Unread postAuthor: Demon » Sun Dec 11, 2011 12:34 pm

I want to install a BBMG on my FPV (Tracers 6mm airsoft for maximal cool effect).

But carrying an airtank might be too much for the already heavily wing loaded aircraft. What about an onbard air intake that would compress air and feed it directly into the BBMG's vortex ?

The particular design of the aircraft I own allows for a very big pop out under carriage. With a flick of a switch, the gun would deploy under the belly of the airplane and immediatly start compressing air.

The stall speed of the said aircraft is approx. 20kmh, it's cruise speed around 40kmh and the top one near 70.

Good idea, bad idea ? I guess it could be made lighweight.

http://upload.wikimedia.org/wikipedia/commons/thumb/6/6c/Ramjet_operation.svg/300px-Ramjet_operation.svg.png
Same air intake compression concept (Combustion aside).
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Unread postAuthor: evanmcorleytv » Sun Dec 11, 2011 12:37 pm

I like the idea!
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Unread postAuthor: Demon » Sun Dec 11, 2011 12:44 pm

There must be a reason why it has never been made before. I'm probably ignoring a basic physic law.

All thoughts are invited.
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 11, 2011 1:00 pm

Demon wrote:There must be a reason why it has never been made before. I'm probably ignoring a basic physic law.


... like the hypersonic speed needed before a ram compressor would be effective ;)

Have a look at this thread: http://www.spudfiles.com/forums/who-has ... 19506.html
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Unread postAuthor: Demon » Sun Dec 11, 2011 1:47 pm

Some ramjets can ignite at 40mph.
I think you're talking about a scramjet.

Is it possible to create a higher air pressure in the BBMG's air chamber than the one at the air intake by constricting the air flow ?
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Unread postAuthor: POLAND_SPUD » Sun Dec 11, 2011 2:11 pm

No offence but it isn't your best idea :wink:

Have a look at this thread: http://www.spudfiles.com/forums/who-has ... -bb-gun-it s-going-inside-a-uav-t19506.html
JSR doesn't always post links to relevant things but when he does it is worth checking

Either use a drozd or an airsoft gun... seriously it will be cheaper, lighter and more efficient than building your own BBMG
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Last edited by POLAND_SPUD on Sun Dec 11, 2011 2:17 pm, edited 1 time in total.
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Unread postAuthor: EpicMadness » Sun Dec 11, 2011 2:13 pm

sorry for linking to other sites btw, but i think this'll help the OP.

http://gofurther.utsi.edu/Projects/PulseDE.htm
http://www.pulse-jets.com/phpbb3/viewtopic.php?f=2&t=5605
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Unread postAuthor: Demon » Sun Dec 11, 2011 2:17 pm

...

C'mon guys. I checked that link many times before JSR linked it. A drozd or AEG airsoft gun is too heavy.

I just need one answer. Is it possible to increase the pressure from the air intake's tip to the BBMG's chamber by constricting the air flow ?

And how on earth would it be cheaper ? Seriously ?
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Unread postAuthor: wyz2285 » Sun Dec 11, 2011 2:19 pm

12V compressor that you have in your car, inside it´s only a small motor, gear and a little pump, very compact. I bought one in a second-hand store for 3 euro. But it may cause quite a lot vibration :roll:
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Unread postAuthor: Demon » Sun Dec 11, 2011 2:24 pm

The main point's to avoid the need of an onboard air tank. The constricted side of the air intake would be directly connected to the BBMG's vortex.

Yes, no ?!?
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 11, 2011 2:32 pm

Demon wrote:I just need one answer. Is it possible to increase the pressure from the air intake's tip to the BBMG's chamber by constricting the air flow ?


Do you think a RC plane will move fast enough generate the 100 psi or so needed for reasonable BBMG performance?

I seriously doubt it.

A drozd or AEG airsoft gun is too heavy.


I believe by making pressure vessels an integral part of the structure (eg PET bottles for a fuselage as suggested in the other thread) will keep weight within reasonable limits.

A small servo operated ball valve (perhaps plastic to keep weight down) will do as a firing valve. A lightweight aluminum tube for a barrerl, sorted.
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Unread postAuthor: POLAND_SPUD » Sun Dec 11, 2011 2:33 pm

And how on earth would it be cheaper ? Seriously ?
You want to collect incoming air and you think it will reach high enough pressure to propel bbs out of the barrel...

so you've got a tube that collects incoming air and another tube next to it that acts as the barrel...
don't you think that if you can generate X pressure at air intake the barrel will experience a similar effect ?


you need pressure difference to shot stuff out of the barrel


so something that is dirt cheap but doesn't work is worse than a cheapo airsoft gun you can get for 15$ or so
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Unread postAuthor: Demon » Sun Dec 11, 2011 2:44 pm

Do you think a RC plane will move fast enough generate the 100 psi or so needed for reasonable BBMG performance?


Of course not. That's where the Venturi effect would play it's part. By reducing the air intakes's diameter by two , the air would accelerate from 60km/h to 300fps, while loosing .0275 bars of pressure.

you need pressure difference to shot stuff out of the barrel


So that's impossible from reducing the air intake's diameter from 100mm to 6mm ? The air can still be accelerated by approx 4x it's initial velocity.

So that means the only way to churn out the BB's would be by having the air intake in line with the barrel making the BB'S ricochet in the opposite direction :D
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Last edited by Demon on Sun Dec 11, 2011 2:47 pm, edited 1 time in total.
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Unread postAuthor: wyz2285 » Sun Dec 11, 2011 2:44 pm

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Unread postAuthor: jackssmirkingrevenge » Sun Dec 11, 2011 2:48 pm

Demon wrote:Of course not. That's where the Venturi effect would play it's part. By reducing the air intakes's diameter by two , the air would accelerate from 60km/h to 300fps, while loosing .0275 bars of pressure.


Simple then - build it, get someone to drive you at 60km/h while you hang out of a car window ;)

Have you thought about the drag effect on performance, especially considering the thrust will be directed forward?
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