Ducted Fan propulsion

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John.Roo

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Oct 8, 2013
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Letohrad / Czech Republic
Dear Ross,
just to precede misunderstanding – UL-39 is not my project.
Robert Theiner is my friend and I like work of his team
J
I can see that “ducted fan propulsion system” requests large development team and access to aerodynamic tunnel for precise measurements.
Far away from my possibilities….
I really wish to see UL-39 in the air this year.
Best regards!

Martin
 

Aircar

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Feb 20, 2010
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Melbourne Australia
Thanks for the clarification Martin I understand the team approach -it is a very nice development in any case -just downloaded the two papers to read later (and thanks Henryk again.)
 

Xanadrone

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Nov 24, 2011
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195
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Bucharest Romania
Outstanding initiative indeed - and one of the few, if not the only truly professional approach in this field (ducted fans for ultralights).
And a big A+ for Henryk too, who brought us this valuable information.

I wonder though why a 10-years old variant of the Yamaha R1 engine (slightly detuned from 179 HP/12,500 rpm to 150 HP/10,500 rpm) was preferred instead of more modern motorbike engines.
Anyway, the positive results of preliminary dynamic tests (175 kgf static thrust - a good value for a 58 cm diameter ducted fan at over 6,000 rpm) show that the usual issues of overheating, seizing etc. are not at all insurmontable.

P.S. I’m still not convinced that a CLmax. of 2.61 - needed for the 450 kgs MTOW, 8.5 mp wing area and the 65 km/h mandatory stall speed - would be achievable in that (very sleek and aesthetic anyway) L-39 configuration.
 

Xanadrone

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Bucharest Romania
Impressive data for a RC-ducted fan, but let's not forget that those 23-24 kgf thrust are obtained with the price of over 15 kWh absorbed (310 Amps at +50 Volts = 14S LiPo) - so, the "usual" ratio of approx. 1 kgf static thrust per e-HP remains the same.
And there's no need for complex explanations, those RC-ducted-fans being in fact simple cylinders, without any performance enhancement-study involved (maybe just a little bit in designing the fan-blades).

Your previous L-39 UL example shows the good path to follow - also a more complicated one -, although I still believe that ducted fans remain only a "compromise" sollution for swift homebuilts, especially when the designer doesn't want (or doesn't succeed) to find enough prop-clearance.;)

P.S. I’m still not convinced that a CLmax. of 2.61 - needed for the 450 kgs MTOW, 8.5 mp wing area and the 65 km/h mandatory stall speed - would be achievable in that (very sleek and aesthetic anyway) L-39 configuration.
 
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henryk

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Mar 8, 2010
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krakow,poland
Henryk -- are you asking for a translation of your link ? (ubersetzung?) -- the idea of a flow mixing ejector is used on several VTOLS to increase exhaust momentum and lift in a somewhat similar fashion , maybe this is related to that . The idea of an internal ducted fan is interesting in the context of replica jet fighter/trainers -- and even maybe for some roadable designs so this thread ought to be followed up when your friends get their Russian fighter style ducted fan aircraft flying --and any technical links to the design would be appreciated I am sure.
http://www.reaa.ru/yabbfiles/Attachments/P2280755__Large_.JPG

http://www.reaa.ru/yabbfiles/Attachments/P2280755__Large_.JPG

=PJ-II=one step forvard,two steps back...
 

Floydr92

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Aug 13, 2013
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357
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Scotland
not worth starting a new thread but on the same subject....

am i missing something here?

E-flite Delta V electric ducted fan for rc planes -
69mm fan
2.8 lbs static thrust
644w = 0.858hp

= 3.26lbs static thrust per hp ... seems pretty good to me?

from what i've read most prop setups would give between 2-2.5lbs static thrust per hp
 

BBerson

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Props on full scale pull about 5 to 6 pounds per horsepower. ( depends on the airplane and prop, of course)
A .40 size OS glow fuel model engine is listed at 1.0 hp and will pull 4.5 -5 pounds ( straight up in a hover.)
 

TFF

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Apr 28, 2010
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Memphis, TN
In the rc ducted fan world, electric has helps reliability a bunch. The orginal glow DF started running .45s at about 30,000 rpm on hot fuel. 12 lb planes. Reliability was terrible so they started stuffing .91s into the same spot also running crazy rpms but they were down enough to help reliability. When the real jets hit, it transformed the planes. Now you have the same diameter engine but now it could turn 100,000 rpm and it made the planes so much better to fly. The glow planes always felt like they were dragging around even at a 120 mph; the jets just feel like the could "get on step." Glow is pretty much gone in the rc jet world. The electrics can be run close to the turbine rpms for the thrust; the problem is battery lasts about 5 min for an equal turbine like setup. The smaller fans flying the 3 lb foamies fly for a lot longer, but fly 1 min longer than needed, and you cooked a $150 battery.
 

Steve C

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Oct 6, 2008
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Lodi, CA
Sounds like you don't really know that much about models. The 91 glow engines turned about 24,000 rpm and some of those had planes going 200 mph. I've seen guys with well tuned motors start them by flipping the starter wand by hand. Reliability had a lot to do with the operator apparently.

Electrics don't turn the kind of rpm that turbines do. 50k would be a lot for EDF and turbines turn anywhere from 120 to 200,000.

It will be interesting to see if this UL-39 works out. I've done some work on a similar project I wanted to do. I like motorcycle engines as well, but the clutch and transmission is built in, so I wonder how they will deal with that. There's a BMW twin that comes apart from the transmission, but it doesn't have as much power as the latest superbike engines.

Steve
 
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