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Post by racket on Mar 1, 2015 20:30:48 GMT -5
sweet :-)
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Post by michaelgolden on Aug 25, 2015 23:34:30 GMT -5
New pics. Will report back once running with some numbers.
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Post by Johansson on Aug 26, 2015 4:13:51 GMT -5
Wow! Really interesting project you are working on Michael, keep the updates coming!
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gtbph
Veteran Member
Joined: August 2013
Posts: 101
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Post by gtbph on Aug 28, 2015 14:53:11 GMT -5
Hi Mike, Nice work! I'm trying to make something similar, did you design it yourself, or is it a scaled existing design? Alain
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Post by michaelgolden on Oct 6, 2015 19:07:23 GMT -5
Hey guys, finished the ducted fan recently. Happy with the results. Ready to move onto a bigger project. I've veered away from the axial flow compressor because I have a really good grasp on the subject now. I would like to build a very high bypass turbofan capable of 100lbs or so thrust. Maybe someone can recommend a supplier for large turbochargers at a reasonable cost. Here's some more videos of the completed axial flow fan. http://instagram.com/p/8UZKgaAZwX http://instagram.com/p/8KUGFVgZ21
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Post by michaelgolden on Oct 6, 2015 19:12:16 GMT -5
Hi Mike, Nice work! I'm trying to make something similar, did you design it yourself, or is it a scaled existing design? Alain Hey Alain, the design is completely scratch built and designed by myself.
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Post by racket on Oct 6, 2015 23:46:47 GMT -5
Hi Mike
Sweet :-)
What are your plans for the 100 pounder , what do you need ??
Cheers John
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Post by michaelgolden on Oct 7, 2015 0:31:58 GMT -5
Hey John, I'm very interested in the Martin Jetpack lift fans. I would like to nail down the science of high bypass lift fans and build one myself. Right now im looking into high velocity / massflow rates at lower densities generated by a single bypass fan. While keeping an eye on Reynolds number and blade stall. Someone mentioned one of the limiting factors in a ducted fan is the suction created in the duct. But I haven't found anything on the subject yet. Its also hard to find information on high velocity low pressure fans, as everything in terms of research papers is geared toward high overall pressure ratios because in a traditional turbofan, high velocity flow is seen as a large loss when trying to achieve high compression in the coming stages. Although when driven with an electric motor, that high pressure isnt as valuable as the velocity of the flow is in terms of; massflow =(density)*PI()*(RadiusT)^2*(1-(RadiusR/RadiusT)^2)*(velocity) and specific thrust =(velocity)+(1/(density*velocity))*(P03-Pa)*10^5 and Required energy = massflow*enthalpy*1.005 .. neglecting losses or maybe im wrong and its unreasonable to try and design a fan with low pressure ratio / high velocity. idk Also, I've seen the German jetpack "monocopter" www.technologie-entwicklung.de/Gasturbines/Monocopter/body_monocopter.html and it looks like he is using a good size turbocharger. A KKK brand. Any idea what size or what that may be rated at? www.technologie-entwicklung.de/17-wheels.jpg I read his engine weighs about 30lbs. Pretty cool! I'm looking for something similar but actually a bit smaller. Price will be the determining factor anyway. A prototype is the main objective. Once I decide on some numbers, I'll create a new build thread here for discussion.
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Post by racket on Oct 7, 2015 1:00:44 GMT -5
Hi Mike Have you considered mine/tunnel ventilation fans www.cbifans.com/en/products_axial.htm , I was looking at these some time ago, for some reason I've forgotten about right now :-) It depends what you call high velocity and low pressure ratio , a velocity of say 500 ft/sec is the same as a 2 psi pressure rise , you need to look at the total energy in the flow , the pressure rise obtained if that high velocity flow is brought to a standstill , its stagnation pressure . For a lift fan as with a prop on an aircraft , the best "thrust" for least horsepower is obtained with relatively low velocity change . More info please . Yep , the monocopter is a nice bit of kit , the turbo bits used are easily found Cheers John
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Post by michaelgolden on Oct 7, 2015 18:58:18 GMT -5
Hey John, I cleared it up this afternoon. It all comes down to aerodynamic limits dictated by cascade tests.
Something like the General Electric GEnx fan is what I had in mind.
Updates when I get it all sorted out.
Cheers
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Post by racket on Oct 7, 2015 19:52:20 GMT -5
Hi Mike The GEnx fan will be a high pressure ratio fan , much higher than you require for a monocopter, theres a lot of wasted energy having an airflow of several hundred feet/second from a vehicle travelling at a fraction of that speed . Theres an interesting set of "numbers" in au.trapletshop.com/the-model-turbo-prop-engine-for-home-construction-by-kurt-schreckling for thrusts from various sized "props" . At say a 2 Kw power supply ,a 20 cm prop will produce ~3kgs of thrust , a 50cm prop ~8kgs , whilst a 160cm heli "prop" ~13 kgs , naturally the small prop could be spun faster and would probably be able to produce a faster airflow , but the larger props will produce more static thrust from a lower airflow speed increase across the prop . Unless you intend traveling at high speeds a high velocity airflow is only wasting a lot of energy . Unfortunately for a backpack fan, size limitations apply to keep the whole unit compact , so you'll be needing a higher than necessary efflux velocity to produce sufficient lift . Assuming a 1.2 PR from the fan , this will produce an air velocity of ~500 ft/sec , now if you need say 300 lbs of thrust , you'll be needing a flow of ~20 lbs/sec , now to compress 20 lbs/sec to a 1.2 PR at say ~80% effic , you'll be needing ~240 HP ...............jet nozzle size ~0.5 sq feet or ~10 inch diameter . Cheers John
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Post by michaelgolden on Oct 8, 2015 0:28:47 GMT -5
Hey John,
Tonight I ran some numbers of my own and decided upon a fan of around 10 inches or less. Except in order to get the thrust I require from the smaller diameter I'll need to experiment. I can't get enough efflux from a single stationary fan. I'm currently looking into the velocity that can be achieved by adding a second counter rotating fan.
I should also mention I'm looking into 150lbs total thrust for this project.
Also, thank you for the numbers.
~Mike
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Post by racket on Oct 8, 2015 4:00:26 GMT -5
Hi Mike
A single stage fan should be able to provide your thrust requirement with a fan of less than 10" dia .
I have a first stage transonic axial compressor fan from a T700 engine ,~ 10 lbs/sec at ~44,000 rpm at 7.725" inlet tip dia , root 3.925" , outlet tip dia 7.430" , root 4.325 " .
Doing inlet velocity triangles with the T700 fan at a reduced 33,000 rpm , the design speed of the turbine wheel I was going to use to power the fan , indicate an inlet air speed of ~600 ft/sec is ideal ,
Even with the usual losses etc etc , it'd produce your 150 lbs of thrust , but horsepower requirement would still be near 150 HP as the mass flow would be down a bit requiring a higher pressure/velocity than ideal
I'd be looking at the largest diameter fan that you can fit into the design to maximise the airflow so as to minimise the pressure rise/velocity and horsepower requirement , creating higher pressure/velocity requires too much power , even a 1.1 :1 PR ( 1.5 psi) at 80% efficiency produces a 10 deg C temp rise requiring ~6 HP/lb of mass flow , so 60 HP for 10 lbs/second , and ~440 ft/sec jet velocity for ~135 lbs of thrust
With ~100 HP and a 10 inch fan , it should be relatively easy to produce your 150 lbs. :-)
Cheers John
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Post by michaelgolden on Nov 15, 2015 15:12:13 GMT -5
Hey so I wrote a new spreadsheet to compare the number of blades to the kW usage and thrust gained. I found maximum efflux velocity is not the most efficient but actually a lower efflux velocity and additional blades beats it out. Comparable to going with a larger size fan which makes sense. And instead of building a 10" fan I have been focusing on one of 14". I was eager and cut out half the blade length needed and will stick this into a homemade wind tunnel and test it for stall from root to mid blade span. I've already adjusted the angles for the next one before even testing it. But its sort of an evolving project. Here's some pics of the variable pitch test blade for wind tunnel testing and the motor I will be initially testing two blades with to the mathematical model. The motor has a maximum speed of 25,000rpm and 22kW. Although I wont be running it that hard initially. And will most likely be winding my own with twice the torque, seeing as how expensive they are. The final rendition of the blades not shown here, will most likely look like a smaller subsonic version of the genx/HF120 with fewer blades.
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Post by michaelgolden on Dec 15, 2015 2:03:03 GMT -5
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