Someone please help me with the blade-out requirements for open rotors.
I always assumed that open rotors would be certified as propellers, which do not require armor for the case of blade failure. But many posters assume they will be certified as turbo-fans, which do require such armor. Has the FAA or EASA spoken or written about which way they will certify open rotors?
The source documents are hard to understand, but EASA has worked on that subject under rulemaking task RMT.0384(MDM.092). The rules don't appear to be finished, though.https://www.easa.europa.eu/sites/default/files/dfu/ToR%20RMT.0384%20%28MDM.092%29%20Issue%203.pdf
(9 pages - 2/20/2017)https://www.easa.europa.eu/sites/default/files/dfu/NPA%202015-22.pdf
(96 pages - 12/21/2015)
What is there to keep Airbus to attach a UDF on a resigned A320 based airframe? Design a new wing, possibly elongate the landing gear for slightly more clearance, though I doubt that'd be needed. The SAAB 340 and 2000, as well as the Ilyushin Il-114, work well with a standard wing configuration and a decently low wing to the ground. Though I'm not an engineer. Is there a specific benefit to the shoulder mounting I'm missing?
Not that I mind it per se, but I think it would reinforce for ordinary passengers that the aircraft is "a dinky prop" if it looks like an ATR. A fine aircraft that I personally I love flying on, but from a public perspective that I gather is slightly more... negatively tinted... I think a low set wing would reinforce "same, but different"
Thinking about it... would the UDF impart the same blown surface benefit as an ordinary prop? Or would the airflow be negatively impacted by the peculiarities of the UDF?
WRT re-engining an A320, I asked about turboprop wing-mounting issues
in the Embraer New Turboprop Aircraft News and Discussion Thread. The helpful responses from mxaxai
explain how there's more practical flexibility in where you mount the engine onto the wing (top/bottom/in between) for a turboprop/open rotor compared with a turbofan. So I don't think wing-mounting and ground clearance are the biggest issues with an A320 open rotor. I'm guessing the main problem might be aerodynamics; the airflow effects of a large open rotor on the wing might not be compatible with the existing empennage. So maybe the A320 would have to have major changes to the tail (like making it a T-tail), which might mean that an open rotor A320 couldn't be certified as a plain old derivative. (Updating the A320 wing to a top-mounted open rotor may break the grandfathering by itself, for that matter. I don't know - I gave up trying to follow the changes in the post-MAX regulatory landscape a long time ago.)
I think the open rotor does help with airflow above and below the wings. The variable pitch fans by themselves reduce the takeoff distances and short-range fuel consumption by large double-digit percentages.