Garrett GT6041 powered kart

[Johansson]

Bummer.

I am actually starting to think about the next build and got inspired by what you said earier about making a turbofan engine, how much thrust would it be possible to get out of a TV94 powered turbofan?

One very wild idea is to make a hollow shaft gas turbine with DIY rotor parts and a turbofan in front driven by a shaft inside the gas producer shaft, ball bearings throughout the entire engine.

It would sure make an interesting secondary project to work on, the turbine bike development will always come first but how fun is it to only have one build going?

[racket]

Hi Anders

You won't get as much thrust from a fan as you will from a tire on tarmac , probably 300-350lbs -150 kgs from the fan ..................with afterburn in the fan discharge, ~250 kgs .

The fan will be producing fairly high airspeeds , much higher than the vehicle speed so a poor conversion of energy whereas the tire on tarmac will be "geared" to produce the maximum "thrust" at your terminal velocity . ...................nothing "left over".

Cheers
John

[Johansson]

I didn´t intend to use it on the bike, more like an oversized sled engine for the ice race here in Sweden.

[racket]

Hi Anders

Well now , thats a suitable scenario :-) , ............... better to aim for a larger but slower mass flow to maximise thrust , but that then entails a gearbox , whereas a direct coupled fan to a freepower is relatively simple , .........just a big "turbo" , .....build it with brass bushes.

Or you could use your bikes freepower stage to drive the fan , just a "coupling??" onto the pinion end .

LOL, we may need to do some PMs on this :-)

Cheers
John

[Johansson]

Might just have to do that.

[smithy]

Nov 1, 2011 19:30:58 GMT -5 racket said:

Hi Smithy

Heh heh , having seen "inside" your 1/4 scale afterburning jet dragster and the degree of sophistication needed to have it operate at the levels it does , I can't wait to see what you'll be doing with the kart ................I'm excited :-)

"so should be a reasonable candidate for an electric start system , the "bull nosed" comp hub is just asking to be used for a "micro style" starter to lock onto , ....... using that big electric motor in your "speed machine" maybe ??

Hi John,
I've made a "test/prototype" starter coupling with a thick "O" ring for the electric motor and ramped it up using a servo tester and my 150 amp controller. I just applied it by hand to the "nose" of the comp wheel.... the little electric motor has more than enough grunt to do the job...nearly twisted my wrist off..! LOL..!

I used a 3s Lipo battery which should give my 1580kv electric brushless motor a free rpm of ~17,500rpm. Assuming the rotor load I'd suggest I'm getting in the range of ~ 1/2 that rpm or close to it, even with the 70+ psi oil pressure, looks very promissing indeed. I can run up to a 6s Lipo with my controller, should be plenty..! Just have to think of a good way to mount it to the engine now, I'm open to suggestions.!

I may have to apply some form of "roughness" to the comp nut though, it takes quite a bit of force to eliminate the initial slippage, but once the rotor is turning it's not too bad.

I'm in the process fitting a "momentary" switch to the steering wheel for the A/B, similar to the one I have on my little jet dragster.... I don't think I like the idea of reaching through or around the steering wheel to the dashboard to activate it. I'll post some pics when I'm finished.

Cheers,
Smithy.

[racket]

Hi Smithy

Do you think its possible to mount the starter onto the bellmouth like a normal micro starter ??

I had the 10/98's "automotive" starter motor mounted on the outer rim of its bellmouth and I'd imagine it was applying a huge amount of torque to it .

Is the A/B switch going to be in conjunction with the pressure switch or just have it "independent" as on the dragster ?

Something familiar is always the safest option


Heh heh , how did you like the potential terminal velocity numbers I PM'ed you .

I'll add it here in the Thread for the guys to checkout .

Looking forward to the pics :-)

Cheers
John

[racket]

Hi Guys

Heres some potential speed numbers ..............


The 80cc gearboxed Kart Class , (which the kart was originally built for, it came with a "bored out" 110cc engine) now runs engines turning out powers of 28 hp and doing speeds up to 190 kph -118mph - 173 ft/sec ,

Now Horsepower is equal to ...........

resistance (drag) X feet per second
---------------------------------------------
550

so 28 hp X 550 divided by 173 ft/sec , this comes out at ~89 pounds of "resistance" at terminal velocity , or in other words, it'll only need 89 pounds of "tire to road thrust" to achieve this terminal velocity , no wonder my old freepowered kart with 160 lbs of static drawbar "thrust" was still accelerating like mad at 120kph-75mph when I had to lift the throttle on that rough bit of road I was using for a test track


Now the International Superkart Class with twin cylinder 250cc engines running 90 hp are getting around 260kph - 161mph - 236 ft/sec

so, 90 hp X 550 divided by 236 = 209 lbs of resistance/drag ..................heh heh , this is just about what the Green Beast should produce with A/B at full song

Acceleration will naturally be much slower than the IC engined kart with its gearbox , but terminal velocity should be the same.

Power required goes up at the cube of the speed , 161mph divided by 118mph = 1.36 , ...............1.36 X 1.36 X 1.36 = 2.51 ..............2.51 X 89 lbs of thrust = 223 lbs for the higher speed , mmm , only 7% off the 209 lbs calculated theoretically ..................close enough allowing for "class differences" .

There shouldn't be a large deviation from "normal" kart frontal area/drag coefficient , so even allowing a 20% buffer for unknowns, its potentially got a fairly high top speed with a sufficient length of tarmac to wind her out

Cheers
John

[smithy]

Nov 8, 2011 23:43:42 GMT -5 racket said:

Hi Smithy

Do you think its possible to mount the starter onto the bellmouth like a normal micro starter ??

I had the 10/98's "automotive" starter motor mounted on the outer rim of its bellmouth and I'd imagine it was applying a huge amount of torque to it .

Is the A/B switch going to be in conjunction with the pressure switch or just have it "independent" as on the dragster ?

Something familiar is always the safest option


Heh heh , how did you like the potential terminal velocity numbers I PM'ed you .

I'll add it here in the Thread for the guys to checkout .

Looking forward to the pics :-)

Cheers
John

Hi John,

Yes, I believe the starter can be mounted to the inlet bellmouth, I was a bit aprehensive about mounting it there as the bellmouth is not part of the housing, but if you believe it's "robust" enough, I'll give it a shot. The torque required to turn the rotor will be substantially lower than the 10/98 I suspect/hope.!!....and the brushless motor only weighs ~200grams.

The main reason I'd like to do this is due to lack of space for the blower with the seat installed, plus I wish to be able to start the engine from the seat. The little brushless starter motor fits in this area nicely...plus I can mount all it's "gubbins" on the main engine frame you have made, should fit easily, the whole package should weigh less than 1kg.

With the momentary switch for the A/B, it will be wired via your relay system and P2 pressure switch as originally designed, all I've done is extend the wiring from the dashboard to the steering wheel, simple. I'll have a push-in stereo guitar lead plug so it can be disconnected easily if the steering wheel has to come off.

Cheers,
Smithy.

[racket]

Hi Smithy

LOL, the 10/98 needed half a foot pound of torque to get it to move , it hurt the finger just turning it , the 6041 is a dream to turn by comparison , it'll actually continue spinning after giving the comp a flick with the finger :-)

A 1580 Kv motor with 100 Amps should turn out 0.44 ft /lbs of torque , the ~2650 Kv Mamba Monster motor I used was only turning out ~0.26 ft/lbs on 100 Amps , it needed ~200 Amps to "unstick" the 10/98's rotor and get it moving at even modest rpm , I guess thats why the controller packed it in :-(

If the bellmouth can't cope with the starter (I'm pretty certain it will ) , it should be possible to drill through it and fit mounts to the exterior of the comp housing snout , I'd be going for the bellmouth first , its pretty solid , the times I've tried to push it into place , its required a bit of force , maybe some extra silicone around the joint to give a bit more strength for the axial starter forces.

A/B switch mods make sense.................heh heh , electrics are not my thing :-( .......... you know more about whats needed than I do ...........go for it :-)

Cheers
John

[smithy]

Just a little update.....Things are moving along nicely. Haven't finished the electric starter system yet though, it's a few weeks away yet, still procrastinating about the bendix drive for it, the electric motor mount is done, as is the electronics to control it.

Have bought a cheap laser-tacho which I will dis-assemble and then mount the laser/sensor on the inlet and the readout on the dashboard....I like to know what's going on as far as rpm goes, P2 pressure is nice but it's not always an exact science as far as rpm is concerned. I'll now be able to adjust maximum fuel flow to give me the correct 77,000rpm maximum I wish to achieve. It will of course be adjustable to suit ambient conditions but I'm pretty close to sea level so it shouldn't need too much in the way of adjustment either way.

The kart itself is ready to run now thanks to John's great work, The seat is finally fitted and I've "notched" the top-rear of the seat to allow the use of the blower if required, I actually fit in ok which is a surprise. Have purchased a new propane BBQ bottle and connection line, modified to allow enough starting flow of course. I've done a couple of "dummy light-offs" and she lights off every time. John's ignition system works a treat, thanks mate.

That's enough for now,
Cheers,
Smithy.

[racket]

Hi Smithy

Heh , good one , can't wait to see her on electric start , she'll sound awesome spooling up without that noisy two stroke blower

LOL, went "the notch" eh , I'm glad you were able to decide on a mounting methodfor the seat , I was in two/three minds which way to go ....................and you got your fat arse into it as well , even better ;-)

She's going to be one very sophisticated lady by the time you're finished with her , a perfect blend of DIY turboturbine and aero micro technology ......................you'll set a benchmark that will be hard to beat :-)

Cheers
John

[smithy]

Dec 8, 2011 16:37:55 GMT -5 racket said:

Hi Smithy,

......and you got your fat arse into it as well , even better ;-)

Yeah...thanks for that....I think..!!

Dec 8, 2011 16:37:55 GMT -5 racket said:

......................you'll set a benchmark that will be hard to beat :-)

Pfffttttt...!!!! Surely you jest...! ;-) I've got nothin'...

BTW....I've got another car show on this coming Sunday down at Kiama, Black Beach, near the lighthouse and blow-hole, hopefully the weather will be kind to us..! It's already been postponed once due to inclement weather. The litte jet dragster is certainly earning it's keep..!! ;D

Cheers,
Smithy.

[enginewhisperer]

let me know if you guys want to offload the leaf blower - I need a big one like that to spin my big turbo (which is still a lot smaller than the GT6041!)

[racket]

Hi Smithy

All the best for Sunday ...............its been nothing but wet weather here for weeks , seems like we've had 2 nice days in a month .

......your jet dragster has done a lot of "road miles" , she's a popular exhibit , and rightly so :-)

Cheers
John