Johanssons Jet-Cart

[JW]

wow that looks great! I wonder what the glowing material was that shot out of the engine in the end of the clip.... :wink:

[Johansson]

Thanks!

Don´t worry, it was most likely something from my quickly welded-together flameholder in the afterburner that came loose from the heat...

//Anders

[JW]

yeah, I've had the same with some small leftover metal scrapnel (from drilling holes) in the flame tube, gives a nice show.

[thecheat]

this is quite nice! ok a quick question, how much have you spent on this, how loud, and when do we get to see it move? :) I'll probably never be able to build this type of thing but it would be pretty sweet! and is it normal for the flame and the "exaust pipe" to glow purple?

[Johansson]

Lets see. The cart frame cost me 5000 Swedish kr, the turbo 5000, the pumps and oil cooler with connections 4-5000, gauges 2-3000, the steel tubes and flanges 500, brakes and the other stuff costs about 1000. Roughly counted I will have spent 25000 Skr when the cart is finished, a bit over 3000 USD. Well worth every cent!

How loud the engine is in dB I do not know, but my father who I talked into being the cameraman doesen´t even hesitate using the angle-grinder for several hours without ear protection, and he started screaming after a few seconds with the afterburner lit so it must be quite loud... *LOL*

The flame from the exhaust pipe is diesel fuel burnt in the afterburner, the purple colour indicates that the combustion is "complete" with no fuel left unburnt. Had the flame been yellow then there would not have been enough oxygen available for the amount of fuel injected. The pipe glows yellow from the heat, and that is normal.

"Everyone" can build an engine like this, you just have to read lots about the theory and see how others have built their engines first. It took me 4 years of dreaming and reading (and a couple of failures...) before I made this engine, so take your time and don´t rush to get it running before the weekend or so...

//Anders

[thecheat]

heh first I gotta build my pulse jet, though, as it seems you know what you're doing making this for a go kart, what do you I would need to power a 8ft by 4ft hovercraft?

PS: sorry dragging from the subject but how low can you build one of these for and where are the plans? I've looked all over the place and can't find them (free ones)?

[thecheat]

well, it's not like I ever follow plans closly. (unless it's needed of course), so where a good couple page thing on the theory and such of the mecanics of the gas turbine? (I just love how that afterburner looks on that go-kart, and I will say that thing is going to go)

[Johansson]

Here is a quick drawing of the afterburner. The flameholder has the form of an X and sits about one decimeter after the flange so it won´t create too much back-pressure by restricting the exhaust flow. The AB would probably have worked reasonable well without the flameholder, but from one of the videos you can see that the exhaust flame gets much more concentrated and stable after a few seconds when the flameholder is red hot.

As you may have noticed I have a separate ignition circuit for the afterburner which is coupled over the fuel pump so the spark is on when the pump is running, without this I would have to jazz the throttle to get it lit and it would probably flame out easily before the flameholder starts to glow...

[Johansson]

The flameholder is not used anymore, I found out that it restricted the exhaust flow too much. The afterburner works fine without it, but the heat-pattern is now very different with the entire pipe glowing from a point 10cm after the point where it gets wider and all the way to the exhaust cone.

Something must have happened with the propane injector since it has suddenly become much harder to start, I will have to disassemble the engine and check it out before running it again...

One good thing is that I measured a thrust of 16kg with the afterburner lit, so I might get some decent speed readings next summer!

//Anders

[Tom]

I'm sure it's been mentioned before, but please, stick a grille over that intake, my hair cringes at what could happen lol.

[larry cottrill]

Johannsen -

Pretty shots of a beautiful piece of work. Man, it would be exciting to see that thing roll out!

I'm always amazed that people want to build afterburners but nobody wants to build motorjets. To me, a turbo with afterburner is just a motorjet with a very expensive front end. (This is NOT meant as some kind of put-down - I just really am utterly surprized that nobody cares to try the concept and at least see what it will do.)

Good luck with driving that beast!

L Cottrill

[racketmotorman]

Hi Larry
LOL... you're not the only one who wonders why guys spend so much time and effort lovingly making afterburners .
I've been attempting to convince the GT guys (for what feels like years), to try putting freepower turbines on them instead of afterburners , unfortunately without success :(
That beautiful big turbo of Anders ( nice kart Anders :D ) could produce something like 60 or more shp from a freepower and make that kart go like a scalded cat and with only a quarter of the fuel burn rate .
I guess guys just love the sreaming sound of a big A/B pushing them along rather than the whine of another turbine. :?
Cheers
John

[serverlan]

Hey John,

If I made something similar and used a freepower turbine to drive a propellor, I could presumably replace my 50 HP rotax on the gyro.

Or I could make several and push them through the one freepower.

Two of the issues with multiple engines for light aircraft ( a gyrocopter)
is that more parts mean more failures,
but if it can fly on one engine, then thats ok.
The other problem is combining the power of the engines.
using a single freepower turbine of appropriate size might solve this second problem. If one cuts out, no problem, just less power.

What about fuel consumption?

Or, as Larry might suggest,
use multiple small Rotax as an air pump to compress a motorjet,
or just drive a turbine.
What would be the efficiency of a freepower turbine?

What sort of air compressor would be suitable for a 50 hp rotax?
Some sort of smallish supercharger?
Efficiency?

Argh. Too many options.
How about a pulsejet (valveless) driving a freepower turbine?
Would the sound reduction be significant?

Don

[Bruno Ogorelec]

How about a pulsejet (valveless) driving a freepower turbine?
Would the sound reduction be significant?

Yes.

[racketmotorman]

G'day Don
Nice to see another aussie on here , where abouts in Oz are you , I'm on the mid north coast of NSW .

Your 50hp Rotax is probably going to give you the best fuel burn rates , small turbines generally give poor consumption .

But if you want something different , then a turbines the way to go :D

Have you seen the vids of my freepower efforts on Nick Haddocks site ?
http://www.nickhaddock.co.uk/jetgallery.htm
about 3/4 the way down his page.

I'd definately suggest two seperately systemed gas producers flowing thru a single freepower turbine , you simply need to "split" the NGV set , exactly like they do with the large axial turbined turbos on large diesel engines , that way if "one engine out" you still produce reasonable power for an emergency landing in the paddock of your choosing .
For aircraft use it would probably be better to make a couple of the larger "model" turbine engines to feed a single freepower , the weight will be significantly less than using turbos .

As for what happens when a PJ is flowed thru a freepower driving a "fan" , I'll let you know in a coupla days time when I fire her up , just a few last minute bits to fit and she'll be ready .

Cheers
John