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Smoke for Electric RC Planes - Experiment

colorex

Rotor Riot!
Mentor
#1
Some time ago I posted a photo on the FliteTest Facebook page about trying to make a smoke system for any electric plane. It can't be liquid fuel - as it's either too big or too expensive. But there is a relatively cheap solution: homemade smoke bombs.



So I started off doing the research. I learned that you use sugar and potassium nitrate to make homemade smoke bombs, and that they are relatively efficient.

Now potassium nitrate (KNO[SUB]3[/SUB]) doesn't sound like something you can get over the counter. Well I can. But for you in other places, look in your gardening department for stump remover - which is said to be 99% KNO[SUB]3[/SUB].

Now I tried several different methods proposed on the web, and they didn't quite work out. I tried it dry, compacted, molten together, packed into a big carton, tin can, etc. Nothing nice. Turns out I was using powdered sugar to make my mix - and I always got remains of the sugar as all of it didn't burn. Sometimes molten sugar turned off the reaction.

Here are the failed attempts with powdered sugar - also contained in aluminum foil.



But I finally got a successful formula. This time I used grain sugar - and a yellowish type, meaning it hasn't been whitened with chemicals (which also means it's healthier). I used 5 tablespoons of KNO[SUB]3 a[/SUB]nd 5 tablespoons of sugar.
  1. First get your ingredients and the mold ready. Use a tall tin can and a wooden stick if you don't want to clean up when you're done.
  2. Now put just enough water to cover the bottom of the tin can. Turn the heat up high, let it boil.
  3. Pour in the sugar and turn the heat down. Start stirring.
  4. When the sugar has dissolved, pour in the KNO[SUB]3 [/SUB]into the tin can. From now on watch your heat.
  5. Stir, keep stirring. Don't let the sugar burn.
  6. Keep it on low heat until the water has evaporated and you have a paste that is about as thick as ketchup.
  7. Turn off the heat and pour the stuff into the mold. Try not to mess around with it too much, try to get it right on the first pass. Don't make layers of the stuff as it'll get brittle.
  8. Let it cool.
  9. Take it out of the mold.
  10. Light a small piece on fire outside and check the result!
The thing should burn and sound like a match head. And produce a grayish white smoke. The smoke isn't toxic, but don't go breathing it all day long.

So why does it work? This is what happens: Sugar is combustible, but only at high temperatures. It also needs more oxygen than the air can provide. So we use potassium nitrate which has 3 atoms of oxygen in it to give it the oxygen supply it needs. Potassium and Nitrogen are also quite reactive and burn nicely. The smoke is basically burnt sugar.

---------------------------------------------------

To apply these concepts into a plane, we need to think of our needs.
  • We need to have smoke that lasts for more than a minute.
  • We need to have relatively thick smoke.
  • We need to mount the smoke on the plane.
  • We need to protect the plane from the heat.
So first - we need to have long-lasting smoke. This is done by making the mixture into a long stick - my mixture burnt at an average rate of 5-10 seconds per centimeter (15-25 seconds per inch). So a nice 10 cm bar will burn for about 50 - 100 seconds, which sounds great for me.

Then how much smoke do we need? The amount of smoke is determined by how much you burn at the time. If you start at the middle of the bar, it will burn toward the edges - double the smoke in half the time. So we need do determine the thickness of our bar in the balance between effectiveness and weight. My experience suggests that about 1 - 1.5 cm diameter should be enough smoke.

Now we need to mount the bar on the plane. My super idea for this is to put a piece of piano wire into the bar - making a way to mount it and something to strengthen it as well. Piano wire can be easily stuck into a piece of plywood taped to a wing.

Now we don't want hot sugar ashes on our nice and clean plane. So we just mount it far out on our wingtips, behind the wing. Shouldn't be a problem. Otherwise, two layers of aluminum foil will also work.

SAFETY

My dad watching me make my smoke, neighbors are paranoid:



I'm not responsible for the uses you give to this information. Etc etc etc.

Be careful. When this mix burns it burns hotter than a matchstick, and probably hotter than a soldering gun. While the flame isn't longer than half your thumb, it can still catch anything on fire pretty quick. Be sure you know how to control a model with this kind of stuff. If you crash, report to the crash site immediately to stop any fires.

The stuff is relatively safe away from fire. Keep it in a cold, cool place as it is sugar and warmth makes it messy. It's hard to get it on fire, but it's also hard to stop it. CO2 EXTINGUISHERS WON'T WORK directly on the paste - the oxygen is contained in the potassium nitrate, so you need a bucket of water to turn the stuff off. However, an extinguisher can put out a fire initiated by a smoke system mishap, so keep one handy.

The flame can and will spew hot ashes as it burns. While this isn't a problem in the air, as the ashes cool down quickly as they fall, it can be a problem for hand-launched planes. So use a fuse if you want, this will make it safer. I can't get hold of fuses here, so I have to light them directly.

Notice the size of the fire - compared to the KeyRing LED flashlight. Also notice the black pieces of ash that spewed from it.



I haven't gotten to make the final application for the plane yet - but I will. When I do, I'll post an article about it.
I hope you enjoy and learn from this. I did.
 

colorex

Rotor Riot!
Mentor
#4
Cool idea, Andre! Have you worked out how to mount it on a plane and ignite?
Yeah, probably with a piece of plywood stuck to the wing and piano wire... Ignition would be on the ground - as I don't have a Rx channel switch to use David's ignition system with overheating a resistor.
 

colorex

Rotor Riot!
Mentor
#6
Coul you try adding food colouring to change the color of the smoke...?
Yeah. It doesn't quite work like that. Food coloring will probably not work - but I will try adding aniline based coloring.

This kind of smoke can't be "colored". But you can make it disperse fine dust particles of color powder into the air as it burns. Will try soon.
 

colorex

Rotor Riot!
Mentor
#7
Oh, and I need to point out that you shouldn't leave it out in humid areas - mine got all messy overnight. Harder to light, but still burns, though.
 

Carbon

Elemental Madness
#9
Guess what, I know how to make these!
I knew my research would come in handy. So about 2 years ago my dad and I started working on kno3 and sorbital rocket motors and this is what we ended up with this:
[video]http://s1204.photobucket.com/albums/bb416/CarbonEvergreens/?action=view&current=ToRussiaWithLoveV2Launchemail.mp4[/video]
it flew sideways because the motor slipped out of the mount

anyway! after some experimenting we came up with a very smokey, firery mixture that when lit burns super hot and gives off thick white smoke. I thought about putting it on a plane but here is the problem:

KNo3 is an oxidizer that burns at over 1500 degrees, therefor, it can burn through just about anything on your plane....
When we did one of our tests, the tin can the mixture was sitting it glowed red hot and then started to melt...

smoke bomb formula

65% kno3
35% sorbitol

plus about a tablespoon of baking soda to slow down combustion.
Cook and put into cylindrical mold- let cool in freezer
ready to light in 2 hours- also, use a firework fuse or something, we bought cannon fuse...
if you are doing a dry mixture, make sure to dry out you potassium nitrate because it collects water from the air(wont light) I use my oven- set to low and spread it out on a baking sheet

oh, and about color- potassium chlorate is what is typacally used to achieve a good smoke bomb. You can add a mineral based dye such as cement dye (carefull, that stuff is super concentrated) and it will change the color like in this video: http://s1204.photobucket.com/albums...iew&current=ToRussiaWithLoveV2Launchemail.mp4
 
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colorex

Rotor Riot!
Mentor
#10
KNo3 is an oxidizer that burns at over 1500 degrees, therefor, it can burn through just about anything on your plane....
When we did one of our tests, the tin can the mixture was sitting it glowed red hot and then started to melt...

smoke bomb formula

65% kno3
35% sorbitol

plus about a tablespoon of baking soda to slow down combustion.
Cook and put into cylindrical mold- let cool in freezer
ready to light in 2 hours- also, use a firework fuse or something, we bought cannon fuse...
if you are doing a dry mixture, make sure to dry out you potassium nitrate because it collects water from the air(wont light) I use my oven- set to low and spread it out on a baking sheet
Oh yeah, it does burn hot! But I think I can figure something out for the protection of the plane.

My plan is to use a 1/2" round aluminum pipe IF I can figure out a way to get the hot mixture in there. Otherwise I'll just roll it around a steel wire kind of like a sparkler for kids. Maybe roll it into aluminum foil for humidity protection.

I have to get some fuses as well.

I learned the humidity factor pretty quick - a humid mixture tends to be harder to light, but it still burns, and makes darker gray smoke (personal experience).
 

Carbon

Elemental Madness
#14
I have a huge roll of aviation "tape" my dad used in the military. It is used to patch up bullet holes in planes to keep the pressure. Basically, it is aluminum tape, very cool stuff. I bet if you covered parts of the plane with that it would reflect some of the heat..
 

colorex

Rotor Riot!
Mentor
#15
I have a huge roll of aviation "tape" my dad used in the military. It is used to patch up bullet holes in planes to keep the pressure. Basically, it is aluminum tape, very cool stuff. I bet if you covered parts of the plane with that it would reflect some of the heat..
I was thinking on mounting them behind the tip of the wing - so the plane should be quite safe.

Can't use hotglue, though.
 

Carbon

Elemental Madness
#16
how's the experimenting coming? I am interested to see how this turns out...
btw, due to the 4th of july, I bought 30 smoke bombs....
 

Carbon

Elemental Madness
#18
I feel like that all the time! That's why I got am one of the only 15 year olds I know that has a job (you have to be 16 to get a real job). Also, I started a website where family and friends can donate to my projects.
 

colorex

Rotor Riot!
Mentor
#19
I feel like that all the time! That's why I got am one of the only 15 year olds I know that has a job (you have to be 16 to get a real job). Also, I started a website where family and friends can donate to my projects.
Good luck on the fundraising!