I had opportunity to see first official flight of Albi. My impressions?
Airplane looks very cool
Takeoff has been long and noisy = ducted fan has much lower efficiency at low speeds.
Noise has been higher (in compare with prop airplanes) even during flight.
When you compare performance of airplanes with prop and Rotax 915i (JMB VL3, TL Strem, Shark etc.) you can see that is possible to achieve better performance.
Albi and Dreamer are using 200hp+ engines and performance is still lower than prop airplanes. Seems that ducted fan small prop has significantelly lower efficiency at speeds where most of LSA airplanes are operating. In my opinion both this projects would work better with small turbines - for example from PBS
I know - than is not possible LSA registration. However Albi (even Dreamer) would be beautifull experimental jet. Maybe could be altrnative for "Beast one project"![]()
Aircraft Engines | Turboprop/Turboshaft & Turbojet | PBS
Hitech products and technology..www.pbs.cz
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=iff involve EJECTOR nacell,ruway can be shorter...
=iff CRDiff. syxstem=+30 % thrust !
Yea: Though LSA weight and having a claimed 193 HP engine, she has a rate of climb that makes a Quicksilver looks like an F-15.Wow. Must be doing almost 100 MPH.
Having a bunch of flames shoot out the back of a cylinder doesn't indicate meaningful thrust is being produced.
At each point in the fluid flow aft of the ducted fan (or, aft of the compressor in a jet engine), the pressure must decrease (else the flow would reverse direction). For any ducted fan that can provide meaningful, practical thrust in manned aircraft using a piston engine, the relatively low pressure aft of the fan puts a significant cap on any potential for producing thrust from an afterburner. Now, factor in the fuel burn needed to achieve any "afterburner" (?) thrust and we can pretty much put the idea to bed.
Another idea that is frequently mentioned but which is impractical is use of hydrogen as a fuel for aviation internal combustion engines. Check out the problems/weight of storing it, the practical implications of making it, and the challenges of moving it. Hydrocarbon fuel can be "greener" and much more practical.
And, then there's hydrogen embrittlement. Hydrogen doesn't weaken all materials, but a lot of common, useful ones. It's just not a very practical fuel, but it has some ardent boosters who keep dreaming the dream.Storing hydrogen is a major problem. Since hydrogen atoms are so tiny, they can leak ... permeate ... thorugh most conventional pressure cylinders. This requires specialized storage facilities. Even so, some hydrogen will leak out after a few days ...
Storing hydrogen is a major problem. Since hydrogen atoms are so tiny, they can leak ... permeate ... thorugh most conventional pressure cylinders. This requires specialized storage facilities. Even so, some hydrogen will leak out after a few days ... forcing you to top off hydrogen tanks just before every flight.
Hint: Hans von Ohain only burned hydrogen in his first jet engines, but quickly switched to petroleum. Old Hans might have known a thing or two about jet engines ... back during the 1930s ....
And, then there's hydrogen embrittlement. Hydrogen doesn't weaken all materials, but a lot of common, useful ones. It's just not a very practical fuel, but it has some ardent boosters who keep dreaming the dream.
The early high bypass turbofan called the Astafan is nearly a ducted fan with a jet core. The ducted fan had a variable pitch design for optimising thrust at different speeds ie idle takeoff vs cruising.
The document is 'Ducted fans', by Hovey. I purchased a copy from Zenith Aviation books, no longer operating. Booklet seems out of print, you can look for it at sites as Abebooks, Amazon, eBay, libraries, or try finding something similar. Blessings +May I inquire what document those pages are from and if you might share? Thanks!
The document
The UL39 ALBI is indeed going to be powered by a turboshaft version of the PBS-TJ100. In some ways it is closer to a high-bypass turbofan. The best engine for it would have been the DGEN 380 or 390 with about 600 to 900lbf thrust.
It's the version called UL-39 ALBI II M DUCTED FAN TRAINER
Can variable blade pitch be used on piston-powered Ducted Fans to increase their efficiency across a broader flow regime?
Or what about a variable nozzle at the exhaust end of the duct? Can that help?
Can variable blade pitch be used on piston-powered Ducted Fans to increase their efficiency across a broader flow regime?
Or what about a variable nozzle at the exhaust end of the duct? Can that help?
Variable inlet vanes would be very useful. They would act much like having a variable pitch prop on a conventional aircraft.All this will help, but at what complexity and cost? This will make it "million dollar" aircraft that nobody can afford for privet use...
Variable inlet vanes would be very useful. They would act much like having a variable pitch prop on a conventional aircraft.
Vince Homer
Martin Hollmann wrote a book about ducted fans & props. He shows how the drag on a duct becomes so high above 100 mph that it’s no longer tenable above 130 mph. I asked Moeller about this and he walked away in silence (I guess he was an early proponent of “alternate facts”). Given this limitation, your YT follower should consider alternate propulsion configurations if he desires to travel faster than 100 kts...
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