Balloon burners as thermojet?

[pezman]

I was reading up on how burners for hot-air balloons work (trying to figure out how to proper carburetor for a big valveless). It turns out that the use liquid propane fed through a venturi system (like a giant bunsen burner) and then use the resulting flame to heat the coils that carry the LP in order to make the vapor a little more "peppy". Kind of like a gluey or a thermojet.

It looks like you can occasionally get them for under $200 used.

Some of the fancier, super high-flow versions seem to use air-amplifiers rather than a conventional jet-in-a-tube carburation (they mention "coanda effect" and "foil" in the description).

The BTUs (per hour? forgot to look at the time units) that they put out are rated in the 10's of millions.

If you want to get an LP fed system w/o risking your life ot your engineering/fabrication prowess. it might be worth looking into.

[Bruno Ogorelec]

I have long wondered at the possibility of using a pulsejet in ballooning instead of the usual burners. After all, not only is the pulsejet a more efficient heater, it is also safer (having the combustion encapsulated, rather than out there in the open), easier to run on liquid fuel and also easily convertible to a propulsion engine when you want your balloon to move somewhere where the wind does not happen to be blowing.

However, the noise would be a big deterrent.

[larry cottrill]

I have long wondered at the possibility of using a pulsejet in ballooning instead of the usual burners. After all, not only is the pulsejet a more efficient heater, it is also safer (having the combustion encapsulated, rather than out there in the open), easier to run on liquid fuel and also easily convertible to a propulsion engine when you want your balloon to move somewhere where the wind does not happen to be blowing.

However, the noise would be a big deterrent.

Bruno, I've thought the very same thing. Having a built-in air mover is highly useful - when they start up hot air balloons now, they always need a huge fan to direct the hot air into them while they're lying flat on the ground, and it's quite an effort [like a 3-man job] to get the initial fill. The idea seems promising to me.

The burners themselves are awfully loud already. And, the use of an augmentor might be advisable anyway, which would apparently take some of the noise out of your pulsejet heating rig.

L Cottrill

[Bruno Ogorelec]

when they start up hot air balloons now, they always need a huge fan to direct the hot air into them while they're lying flat on the ground, and it's quite an effort [like a 3-man job] to get the initial fill.

Larry, you are right. I haven't even thought of that. It's a major pain in the... er... back to have to run the big blower. A simple pulsejet with an augmenter would replace all that.

Hey, this is the biggest commercial idea in pulsejets in a while. The market is BIG -- those balloons are _everywhere_ and everything connected with them is horribly expensive. We can undercut everyone and still have a big profit margin on a piece of equipment that will work better than anything they have at the moment.

My only real concern is noise. Yes, the balloon burners are noisy but pulsejets... well, pulsejets are really something else. And, the one that would fill a hot air balloon effectively will have to be pretty big. A case for ducting it, perhaps? Not just to shield from heat and noise but also to pump still more air. I am very excited by this.

[Ogge]

Only problem I can see is that the exhaust gasses may be too hot for the material of the balloon. I would think you would have to have a large thrust augmentor to allow enough cooling.

[marksteamnz]

Back up a bit here. The big fan is to blow COLD air into the balloon at the start to form large enough (house sized) air bubble so when you start heating the burner doesn't scorch the balloon fabric. There has been a big effort to product burners that have two stages, one vapourising burner for major and instant heating (The one everyone has seen and heard) and a quieter but less powerfull liquid propane burner for crusing and to reduct annoying the /farmer/sheep/horses etc.
Thrust on a balloon may work but you do have a vehicle with a mass of over 1 tonne (The air inside the enveolpe has to be counted) with the air resistance of a clipper ship

[Bruno Ogorelec]

I see no problem with the heat of the output. A proper augmenter mixes a lot of fresh air into the hot gas. Look at the Lockwood illustration showing that within 8 feet of the engine exhaust, the temperature is down to mere 140 Fahrenheit.

As for thrust, perhaps I was not clear enough. I am only thinking of having emergency power and steering. Using the engine for propulsion would spoil the essential charm of the ballooning.

[Bruno Ogorelec]

Let me add that the Lockwood was optimized for thrust. In this application, one would optimize for volume of hot air (and perhaps low noise level). I think that we can safely think in terms of a low-load valved pulsejet running on gasoline or diesel fuel, rather than a propane-burning valveless.

[Stephen H]

dont forget the problim of starting it, dont really wanna have to carry around a bottle of compressed air!!

[Bruno Ogorelec]

Stephen, when you look at the equipment balloonists need to start a balloon, our need for compressed air becomes laughable. They need a big trailer full of equipment and at least three people working on the thing for at least half an hour to be able to start. Most pulsejets will easily start on air provided by a spare tire. Well-designed big pulsejets don't even need starting air. A balloon wilkl need a _big_ pulsejet. The only really serious problem I can see here is noise.

[Viv]

some one must have been reading my marketing file again:-) we have all ready looked in to this one for product placement, sorry to piss in your bonefire:-)

But don't forget guys you want to heat the air in the balloon envelope not blow it out with thrust from a pulse jet!

Air blowers are only for starting as has been pointed out.

Viv

[marksteamnz]

Stephen, when you look at the equipment balloonists need to start a balloon, our need for compressed air becomes laughable. They need a big trailer full of equipment and at least three people working on the thing for at least half an hour to be able to start. Most pulsejets will easily start on air provided by a spare tire. Well-designed big pulsejets don't even need starting air. A balloon will need a _big_ pulsejet. The only really serious problem I can see here is noise.

Sorry Bruno. Yes the towing and trailer rigs nowdays are very impressive but most of this stuff is comfort and add ons.
If the balloon has it's tanks fueled and strapped in the basket with flying lines set up to a correctly stowed envelope in its bag (Which it should be it you packed it up correctly from a previous flight and refueled on the way to the launch) from stopping the trailer, two people can flake out the envelope, drop the basket on the ground, hand flap the air into the envelope (Yes, no fan and yes it is hard work) and have the balloon up right and ready to fly in 15 minutes.
This requires the two people to be one a really good pilot and two a crew person who has done it a few times.

I spent 2 years about 20 years ago crewing on NZFBI a 4 person Cameron flying over the Canterbury plans and we did the above when pushed. Plus in 1999 I was at the New Mexico balloon Fiesta and watched 800 balloons mass launch. In a hurry with big fans balloons were going from arrived to up ready to fly in 10 minutes. The Balloon and a fan was all the gear people needed

What you do not want is heavy bulky kit over your head as the mounts for the burners are only semi ridgid. If the PJ burner is heavier or bulkier than the existing burners I doubt it will find a market.

[Mark]

I use to crew on a hot air balloon. I remember the owner said one time he took off out of his backyard all by himself. We used a fan of course when we went out on jobs. It was a gas motor with wooden prop shielded in a cage to cold inflate the balloon first.
Mark

[Mark]

I remember holding a sign on the runway for my balloonist boss who was also an X fighter pilot in Vietnam. He would take off in a Stearman painted with the 7-Up logo and tow the sign over Pensacola Beach. He use to do skywriting/advertising over the beach too for the summer crowds. He would always say if he ever got in trouble for something, "What can they do, send me to Vietnam?" As if the stress of bombing runs were the ultimate punishment.
For all I know he is probably dead by now, he was very overweight when I knew him.
Mark