Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 47 users online :: 5 registered, 0 hidden and 42 guests


Most users ever online was 218 on Wed Dec 07, 2016 6:58 pm

Registered users: Bing [Bot], Exabot [Bot], Google [Bot], Google Adsense [Bot], Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

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.
Sponsored 
  • Author
    Message

Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Tue Jan 03, 2017 6:04 am

I have just discovered that the telemetry sensor data protocol for my radio system is published documentation, so I can make use of my radios built-in telemetry functions to monitor stuff like propane pressure and temperature, heating battery voltage and so on. Most sensors are even associated with an alarm so I can have my transmitter beep or vibrate when a sensor limit is reached, like empty heater battery or empty propane canister.

This is so cool :D
  • 0


Futterama
Corporal
Corporal
 
Posts: 75
Joined: Sun Oct 11, 2015 1:19 pm
Country: Denmark (dk)
Reputation: 3

Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Sat Jan 07, 2017 2:21 pm

I did a destructive test today.

When searching for information on propane/butane canisters and refill of those, many people state that the cans can't hold up to the pressure of pure propane. So I took a look at the datasheet on my foam filled canisters from Express:

http://www.guilbert-express.net/product ... 44-76.html
http://www.guilbert-express.net/mediath ... 4_indF.pdf

It says: 18 bar steeel case...

So I bought myself a 25 bar gauge, hooked it up to a 444 canister with heater wires mounted, put it in a foam box, wrapped the canister with old fabric around it, including a piece of some pants and tried to secure it best as possible.
I hooked a thermometer to the can and used a long wire for the heater.

I took the box to the garden and secured it with a wheelbarrow ect. and aimed some cameras at the pressure gauge. I had a wireless video feed from an old smartphone pointed at the thermometer.

And so I started heating the can with the same battery I plan on using in the RC plane.

I feared a massive explosion when the canister would give in (no fire of course, just escaping pressure), but hoped for the best :D
The result is that the canister can take upwards of 20 bar before failing. The first failure was the concave bottom that went convex, it is seen as a drop in pressure and heard as a puff. Seconds later, the canister shoots out the bottom. No total destruction of garden or surrounding houses :lol:
It did however rip open the pants and filled the box with foam pieces, but it didn't even break a box made from stiff foam for putting up posters.

The temperature reading was 65°C when I last checked, but I was handling the zoom camera when the fun part happened and didn't have enough cameras to record the temperature reading, and the battery was disconnected from the thermometer when the canister failed. But with the speed of temperature increase in mind, I would suspect the canister to be somewhere around 75-80°C when it failed.

I made a video :albino:

With this result in mind, I have no trouble putting one of these canisters filled with propane in my RC plane.

Someone asked what would happen if my heating controller would just keep heating the canister. It would blow within 8 minutes. So I will monitor the temperature and make sure I get an alarm soon enough to be able to land the plane and remove the heater battery. Or I could make a safety function that activates the valve servo without activating the HV modules, so as to be able to empty the canister in-air in case of emergency.

  • 0


Futterama
Corporal
Corporal
 
Posts: 75
Joined: Sun Oct 11, 2015 1:19 pm
Country: Denmark (dk)
Reputation: 3

Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Sat Jan 14, 2017 10:09 am

I started building the controller for the sound cannon. This one can control up to 6 cannons.

PCB ready for soldering 8)
  • 0

Attachments
DSCF4333.JPG

Futterama
Corporal
Corporal
 
Posts: 75
Joined: Sun Oct 11, 2015 1:19 pm
Country: Denmark (dk)
Reputation: 3

Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Sun Feb 19, 2017 11:43 am

The controller board takes a lot of time to build. Probably because I want all the bells and whistles I can get :lol:

So I was wondering:
Question 1: How hot does the sound cannon parts actually get when shooting?
Question 2: How hot can I allow the sound cannon to get inside the wing of the RC plane?
Question 3: How many shots can I do or how long can I shoot before needing a cooling break?
Question 4: How long does it need to cool before next round of shots?

Answer 1: I borrowed a thermal imaging camera from my workplace and went out shooting. It can get REALLY hot if I just keep shooting, but with the weather we have here now, it cools very rapid too. But inside the wing, it won't get nearly as much cooling.
I also wanted to know which part of the sound cannon got hottest. The thermal imaging helped figure out the hot spots but they are not 100% accurate due to the mild wind during the testing. I didn't have a wind-free area to test, but I think I got the big picture.
I have added some temperature sensors to my controller, they can measure up to 150°C. These should be located at the hottest parts of the sound cannon, so the controller can prohibit shooting when temperature is too high.

Answer 2: I would have to look at the materials used to build a plane wing. The most sensitive material would probably be the balsa wood, as it ignites at 200°C according to what I found online. The covering film can withstand 250°C, but the glue actives at 92°C, but the film will have all the cooling from the airflow over the wing. I don't know about the wood glue, but I won't be gluing the sound cannon in place, I will use some metal standoffs bolted in place.
Then there is the temperature sensors, so I definitely won't go above 150°C on any part of the sound cannon.

Answer 3: I let the sound cannon cool way down, and fired it for 10 seconds at 250 shots/min. The hottest place was just below 100°C.
10 seconds would be a long time to shoot during flight as the plane would pass in just 5 seconds at full speed (I checked one of my videos). And you don't attack a target flying slow, do you? :wink: So I don't think it would be any problem to fire the sound cannon for the duration I would desire during flight as long as the sound cannon gets to cool down.

Answer 4: In open air, with a bit wind, less than 1 minute. Inside a plane wing, probably with still air around it, I have no idea. Only time will tell.
If cooling takes forever, I could add some forced cooling. I could have a servo operated hatch behind the air intake that would close when shooting, letting pressure rise around the gas mixer, which helps to flow the gas the right way into the sound cannon and not out the intake. The hatch would then open after shooting, letting the airflow from the speed of the plane both push air into the sound cannon barrels, but also suck air out of the intake and out the hatch. On the P-51 Mustang, the air intake and adjustable air scoop outlet is scale, but on my current plane, it would not be scale, but I don't mind that right now.

How cool are those pictures, huh? :alien:
  • 0

Attachments
IR_0517.jpg
Cold sound cannon
IR_0517.jpg (50.61 KiB) Viewed 106 times
IR_0518.jpg
Cold sound cannon
IR_0518.jpg (54.06 KiB) Viewed 106 times
IR_0521.jpg
Hot spot seems to be the front of the initiator chamber
IR_0521.jpg (50.73 KiB) Viewed 106 times
IR_0522.jpg
A hard to cool spot where the silicone tubing joins two pieces of tube
IR_0522.jpg (49.68 KiB) Viewed 106 times
IR_0527.jpg
Just below 100°C after 10 seconds of shooting = around 40 shots
IR_0527.jpg (48.34 KiB) Viewed 106 times
IR_0529.jpg
Long time shooting, like 30 seconds or so
IR_0529.jpg (42.52 KiB) Viewed 106 times
IR_0536.jpg
Tube can get really hot if something isolates it from the cool weather like a leather glove
IR_0536.jpg (45.16 KiB) Viewed 106 times

Futterama
Corporal
Corporal
 
Posts: 75
Joined: Sun Oct 11, 2015 1:19 pm
Country: Denmark (dk)
Reputation: 3

Re: Noise cannon for RC planes

Unread postAuthor: Futterama » Sun Feb 19, 2017 2:32 pm

More update!

I made a neoprene jacket for the gas canister. The idea is to keep the excess heat from the heating wire close to the gas canister. Another feature is the canister will now be mounted with vibration dampening material.

The blue lead is for the heating wire that's wrapped around the canister. The other lead is for a temperature sensor glued to the bottom of the canister for monitoring it's temperature.
  • 0

Attachments
DSCF4327.JPG
Gas canister without label
20160516_193724.jpg
Wrapped with kapton tape and heater wire
DSCF4296.JPG
DSCF4350.JPG
DSCF4352.JPG
DSCF4351.JPG

Futterama
Corporal
Corporal
 
Posts: 75
Joined: Sun Oct 11, 2015 1:19 pm
Country: Denmark (dk)
Reputation: 3

Previous

Return to Combustion Cannon Discussion

Who is online

Registered users: Bing [Bot], Exabot [Bot], Google [Bot], Google Adsense [Bot], Yahoo [Bot]

Reputation System ©'