Mini Thermojet

[Eric]

I have decided to make another alternative to the spot welded thermojets on ebay. This one is a mini thermojet, not quite as small as the ones Steve Wallington has made, but they come in at 13.5" long and less than 3/4 of a pound with the injector setup. Its all 20 gauge stainless to stand up to long static tests.

Its incredibly loud and suprizingly powerful for the size, scaled down from the modified thermojet that I made for Jim, this one has proportionately much larger diameter intakes. To scale it should produce about 1.4 lbs thrust.

The most suprizing part was the initial test to play around with a single injector and get a feel for how it behaved, with 80 psi air and high fuel flow rate it was producing rapid fire machine gun shots in sync with the model T coil, the flames shooting out were close to 2 feet long, and extremely loud sharp cracks like a machine gun.

The throttle range is excellent, I could throttle it even lower if I had a needle valve with better control, throttle response is great too.

Eric

[Jim Berquist]

The Thermojet LIVES!

Cool stuff Eric. Do I see what I think I see?

On my monitor I see what appears to be Blue Banding within the exhaust flames.

The little Beast you built for me produces a much rounder exhaust flame.

This one is producing a much more linear flame, banded with shock-wave formations within it!!!!!!!!!! POWER!!!!!!!!

Jim

[Eric]

Heres a video clip, anyone got a high / low frequency reading?

Eric

[Mark]

That was a funny video. Very entertaining.
Mark

[Eric]

Glad you like it. I have another video clip that I need to prepare of me grabbing a chunk of snow, and holding it behind the engine on low throttle, and just raising my hand into the exhaust and having it get blown away, and then dropping some snow chunks into the exhaust.

Eric

[Jim Berquist]

Eric:

I see banding within the flame front on your second photo! .

What changes did you make to the little Thermojet other then the shorter exhost tube and larger intakes turned outward?

That one looks like it could fly!!!!

Jim

[Eric]

I cant see much with my lcd monitor's contrast ratio, not quite the same as a good CRT, but its flat and I have about 20" more desk space :)

Sometimes with the pulsejets I think I see shock discs or mach diamonds, but with them pulsing unless it does it in the same spot for a majority of the time you cant see anything, the only thing I was absoltely positive that there were mach diamonds in was the TP-180 pulse-ram exhaust.

I dont doubt this little guy could fly, other than the intakes being larger in diameter it is otherwise to scale with your little thermojet. The intakes turned in was just to make it feasible to weld, but it also should provide a more unified fuel air charge, so maybe a bit more power is being developed in that way.

I think with yours having a smaller intake : tailpipe ratio yours is breathing in through the tail a lot more, which causes the flame to be big and fat, with a narrow waist where you can see the fresh air is flowing into the pipe. Its definately not a bad thing, it means that more cool air at a higher density is filling the pipe and being shot out, for more efficient production of thrust.

Eric

[milisavljevic]

Hello Eric --

Sweet little thermojet, dude! During the first 18 seconds of audio (from the video clip that you have provided here),
your mini-thermojet resonated at 386-387 Hz (F1). I did not check for the frequency later in the video (Sorry! =).

The spectrum was characteristically closed-pipe, as one would expect from a thermojet, and with very little
acoustic energy distributed in the upper harmonics. It looks better than its sound looks, so to speak. =)

You are going to start selling these little gems on eBay, or what?

Cheers!
M.

[Eric]

Yep, tomorrow I am going to update my site and add them as a new "in stock" item and just always keep a few around, and put them on ebay.

Eric

[milisavljevic]

Hi Eric --

Care to post the dimensions (or drop a copy off in my inbox)? It would be interesting to model the performance.

Cheers,
M.

[craigclavin]

yey! Dimensions sound good!

[Mark]

Congratulations on the new non-drill ignition system Eric. If you don't want to lug a battery around, you can use a small plug in the wall transformer if you are near an outlet, I use a 12 volt, 800ma phone transformer, it's about a 2 X 2 X 2 cube that plugs in an outlet.
I love those Model T coils, they are real workhorses and entertaining if you shock yourself.
Mark

[Irvine.J]

This thing is totally awesome. Love your work Eric!
Would a 24V 1000ma cordless drill batttery recharger do the same job as that phone transformer? Nice new setup Eric.

[Mark]

I wouldn't go over 12 volts, lest it arc over internally. If you don't give the spark a place to go you can damage your buzz coil with normal voltage, it can arc internally I have read.
They are made to run on 6 volts and an amp or two. Some of my transformers are 6 or 9 volts but don't have enough milliamps to get it to run. For me I like to run it on the least it needs just to be on the safe side.
Mark

"Many people have told me that I should not operate my coils on 12VDC as it will harm them, but I've also had an equal number of people tell me that nothing goes wrong. I personally favour the 12VDC camp as you get a better spark, and unless the insulation in the coil is dangerously close to breaking down the extra voltage will not hurt it (especially when you consider that the higher the voltage the less current it will draw - the exact same amount of energy will travel through the wires in the primary coil)."
http://www.steamengine.com.au/ic/engine ... index.html

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"The top and bottom post are primary, + and -, doesn't make any difference which way. The center button is secondary, be sure you have a wire with a 1/4 to 3/8" gap for the spark to jump. Letting it buzz wqithout a place for the secondary to go is asking for trouble, it will find a path inside the coil and burn the insulation. 12 volts won't hurt it, just don't leave it buzzing, when running it only see's momentary contact."
http://www.smokstak.com/forum/showthread.php?t=9970

[Eric]

Hahahaha thanks Mark, I have had model t based ignition for a while, its just people keep on buying them from me with their engines and I have to get a new one, this is #3 for me. :)

I need to get some switches so I can box it up in another nice tight feild unit, with a tiny ATV battery to go along side it.

Eric