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Noise cannon for RC planes

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Re: Noise cannon for RC planes

Unread postAuthor: jackssmirkingrevenge » Wed Jan 10, 2018 7:37 am

Futterama wrote:Now the question is, do I get too much air into the air intake or not enough? The easiest to do would be to restrict the air flow and start there, see if less air will make a difference. If not, I will have to make a bigger air intake or start fiddling with forced air from a blower but I hope the natural air intake will do.


If it works when static but not in the air, the logical conclusion would be that it's getting too much air when in flight. With you level of expertise it shouldn't be too hard to cook up a carburetor type valve that can be adjusted in flight with a servo to limit the amount of air fed into the system, or alternatively make a blower that can simulate in-flight airflow on the ground so you can pre-set the restriction for a typical airspeed before takeoff.
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Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Wed Jan 10, 2018 7:54 am

jackssmirkingrevenge wrote:With you level of expertise...

Thanks! :D

Great idea with the servo controlled carburetor type valve!
I'll start by testing on the ground and use a blower to blow air into the intake and barrel and see what that gets me.

Remember, when the plane is in the air, the barrel on the wing is pointing forward and also functions as a kind of air intake.

My theory is that if the airspeed is equal around both the barrel and the air intake, I will need the same exposed area on the intake as on the barrel to even out the pressure created from the air hitting the barrel. Barrel area is around 133mm². Intake area is at the moment much larger. And the propeller probably also adds to the airspeed at the intake, along with some turbulence, so my guess is I'm getting too much air. A simple test can verify, which I'm going to perform as soon as weather is good for it. It will only include blowing air with a blower as I need to fix my engine exhaust before I can run the engine again and that requires a bit of work.
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Re: Noise cannon for RC planes

Unread postAuthor: jackssmirkingrevenge » Wed Jan 10, 2018 8:03 am

Futterama wrote:My theory is that if the airspeed is equal around both the barrel and the air intake, I will need the same exposed area on the intake as on the barrel to even out the pressure created from the air hitting the barrel.


That would be my feeling too.

Good news is I did not crash, the frozen ground did undo all my foam tires from the wheel hubs, but no damage to the plane.


Retraction would be difficult but you could consider tracks :D

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Re: Noise cannon for RC planes

Unread postAuthor: hectmarr » Wed Jan 10, 2018 9:26 am

What we use for the pulsorreactores, not to impoverish the mixture of combustible air, when it is in flight, especially in chopped, is a "static air bell". It is a simple element that deflects the air inside the diffuser of the carburetor, and this carburetor works with static air, In the photo is together with the engine stop mechanism. Independently of the speed of flight they are normally about 250 300 km / h. In certain models it is not necessary but in our case, the engine stopped abruptly in this type of maneuvers.
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Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Wed Jan 10, 2018 9:38 am

hectmarr, can you post a bigger picture and maybe a link to some reading of this "static air bell" because Google does not seem to find anything relevant.
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Re: Noise cannon for RC planes

Unread postAuthor: hectmarr » Wed Jan 10, 2018 10:09 am

Ok I'm looking for some info and I'll add it here. But the "idea" is very basic. You just have to avoid the direct entry of air with a stopper that should let air in only on the sides. You can test with the air of a compressor. You must determine approximately the speed of your model, and simulate that speed with compressed air, and see if you stop having that problem. I imagine it will be solved.
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Re: Noise cannon for RC planes

Unread postAuthor: hectmarr » Wed Jan 10, 2018 10:26 am

In figure 1 is the fully open admission of the pulsorreactor.
In figure 2, it is with the obstruction system, which I added to you.
In figure 3, an old, real drone apparently with the system incorporated.
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Re: Noise cannon for RC planes

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Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Wed Jan 10, 2018 10:31 am

Is this the way the air moves, some of it into the holes for the intake and some moves past the holes?

I have ordered some barometric air pressure sensors on ebay, with those I can log the pressure in different locations, and I plan on using them with a WiFi module, then I can see the pressure in real time from my mobile phone. But it takes 4 weeks for them to arrive.
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Re: Noise cannon for RC planes

Unread postAuthor: hectmarr » Wed Jan 10, 2018 11:59 am

It is right. The dynamic pressure of the air does not directly affect the air intake. This allows any system to work with "calm" air. You can, if necessary, make a hole or some, in the cover, to achieve calibrate the system with precision. I have the Castle Creature pitot tube and it works properly. Measures the differential pressure and the maximum, is recorded in the on-board indicator. To have patience until the sensors arrive. :)
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Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Wed Jan 10, 2018 2:37 pm

Thanks, I'll keep this in mind.

I went testing tonight, and my sound cannon is very sensitive to air blown into either the output or input. I have a few ideas to check out to fix this, but now I need to concentrate on fixing my exhaust and hope for good weather for more in-flight testing.
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