Duct fan propulsion?

[BiGH]

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just strap a jet engine and be done with it



here's a video of one going really slowly:
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edit: one more casuse its a diy from a turbo!
[youtube]ej-2VQPzdSc[/youtube]

 

[Canis Lupus]

just strap a jet engine and be done with it

Love those videos. Wouldn't it be great to take off from lights making that sound on your bicycle or trike. For once it would be worth being pulled over by the police just to watch the look on their face as they try to work it out where it fits with the law. The radio call back to base would be interesting, "We've got a cyclist here with a couple of rocket engines, possible terrorist suspect ... "

 

[BiGH]

just strap a jet engine and be done with it

Love those videos. Wouldn't it be great to take off from lights making that sound on your bicycle or trike. For once it would be worth being pulled over by the police just to watch the look on their face as they try to work it out where it fits with the law. The radio call back to base would be interesting, "We've got a cyclist here with a couple of rocket engines, possible terrorist suspect ... "

jay leno has a production jet bike called the Y2k or something. He says its great, but has the tendancy to melt plastic bumpers at the lights behind them.

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[TylerDurden]

Spaces in the BBcode need to be removed:

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EDIT: all good now... fun clips.

 

[BiGH]

Spaces in the BBcode need to be removed:

oops....

drunk posting = fail.

 

[EVTodd]

How about DUCK fan propulsion?

 

[jag]

That was with the discharge end nearly sealed off, but yes, 0.4psi. The moment you let the discharge end up off the desk a smidge, the pressure drops right off to less than half of the obstructed pressure. This is because obstructed, it's not doing useful work, it's just applying a force, and the useful efficiency is 0%, and it would be useless for moving a scooter. Stacking a bunch of them in series would also be useless for moving a scooter. You would want them as unobstructed as possible, hopefully with nicely radiused inlets, and put units in parallel to gain useful thrust.

The engine I wish to supercharge is only drawing ~400 hundred CFM peak, and around 300CFM average, which is why it acts like an largely obstructed discharge nozzle for a device that would otherwise be moving >5,000CFM unobstructed.

Stacking the fans seems like the right idea. The compressor of an axial turbojet engine has stacked counter rotating compressor stages (like fans, but with different blade geometry). Now there are a few hitches trying this with RC motors and ducted fans intended for model propulsion. First with the small diametre (compared to an aircraft turbojet) rpm will have to be very high. Second, the successive stages in a turbojet compressor are sandwiched with near zero clearance between the blades, so intuitively air cannot leak/shortcircuit backwards around the blades. Third, compressing air to meaningful pressures heats it up. Plastic blades will melt. Even choosing the metal alloys and getting the crystalline structure right in compressors is tricky business.

Garrett/AIResearch proposed the solution to your problem about a decade ago: Sandwich a high rpm motor between the exhaust and intake side of a regular radial turbo. The motor spins the turbo when exhaust energy is insufficient and it regens energy back during high load, when exhaust energy is high. I'm not sure if their prototypes ever made it to sales though... But I think the idea is sound. Compressing the intake air to some noticable pressure (10psi) and volume takes serious power. The battery, motor and controller system required to do this in continuous operation is likely much bigger and heavier than a conventional turbo charger. The KKK turbo on my VW 4 cyl is not much bigger than a grapefruit, yet pumps air with a power equivalent to probably a 10hp motor and battery. If you could get a 100-150,000 rpm motor you could drive the compressor stage of a conventional turbo, but the resulting size and weight of the system would be much bigger than just leaving the turbo alone.

I'm curious to what your exact problem is? Trouble keeping turbo pressure/rpm up at starts? Shifting? Maybe some other modification to a conventional turbo install would do what you want?

PS google garrett electric turbo and you get some hits to info on their proposed hybrid system.

 

[TylerDurden]

 

[ptd]

methinks this is what wil e coyote would do if he lost his rocket r&d grant from acme... love it, lol

 

[Whiplash]

i'm wondering if it would be possible to do a micro rc friction drive on those heely's?

it would be fun to race my dogs in the park.

DUDE! That would be AWESOME! LOL!!

 

[bobc]

regarding stacking fans - last century (!) I did a test with cooling fan stack for a travelling wave tube amplifier. I managed to find 2 types of 6" mains fans with RH and LH blades, so sequential fans were contra-rotating. If you do this the pressures from all the fans add up. If you have all the fans turning the same way you can have 3, 6 or 8 fans, you'll only get the pressure of just one.
The stacked fans had sufficient pressure & flow for the job but were not used in the end - too 'radical' for the project leadership, one big centrifugal fan & lots of metalwork used instead.
I did originate what became an official NATO flow rate test on that job though - timing the inflation of a big bag to measure total airflow rates (I remember recieving emails from contractors around the world saying "we now have a big bag like yours & now agree with your results......")