Revolutionizing Flight! The Amazing Potential of the CFM RISE Engine.

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Even if you could find a former Tu-95 pilot to ask him what that plane was like to fly, he wouldn't be able to hear you asking the question . . .

I am a retired Boeing engineer here who worked on 7J7 program when I first hired into the company in 1985. This is a good summary of what happened. But one thing which is left out is the generally unforeseen business success of the 737-300 using the CFM-56 engine and the use of hub-and-spoke. With both low fuel prices and the success of the 737-300, there was not need for the technology of the 7J7 to meet the requirement of Delta's RFP for a 150 passenger aircraft. There was quite a bit of government and industry focus on fuel efficiency in the 1970s due to the oil crisis. Methods of design and certification of advanced composite materials, which would have been used on the 7J7, were initial researched during this time as part of NASA's effort to reduce fuel use. The use of composite materials in primary structure on 7J7 was pursued in fact to address the high sonic environment of the unducted fan. One other reminder is that the cruise speed of the 737 Classic family of aircraft (737-300, -400, and -500) is between M = 0.74 - 0.78. So the lower cruise speed of a CFM RISE engine is not that out-of-the-ordinary in comparison.

It’s worth noting that the US tried their hand out at supersonic propellers as well with the XF-84 “Thunderscreech”. That plane was also ridiculously loud

25 years ago I discussed why the Propfan didn't get any traction with a dear friend who was a professor at a aviation college. He said the biggest thing that killed the Propfan wasn't only the noise. It was the marketing focus groups. The public was turned off by the appearance of the open fan blades which made the aircraft looked like the one that that parents and grandparents flew in. I remember at the time there were designs floated around that had a massive duct around the fan with the core of the out in front for underwing widebody plane i.e. the 747 to give Propfans a more "jetlike" look.

I never really had an interest in flying, but I'm an engineer who has spent more than 30 years solving problems - it's my passion - so I have always loved videos about aircraft accident investigations, so I started watching your videos, and now I am fascinated by the airline industry as a whole, which is my round-about way of saying that your videos are fantastic - Thank You - and are so good that you have converted someone who had no interest, and no intention of becoming interested, in the topics you discuss. That's how brilliant your videos are... Keep up the great work!

I didn't know the Tupelov Tu-95 Bears were noisy because of the tip speed, I always thought it was a straight fluid dynamics issue. After the end of the cold war, the American Navy admitted they could identify them with submarines in the Arctic Ocean with Sonar microphones. An aircraft so loud they could hear it at cruising altitude from below sea ice.

Around three decades ago I was a student at Embry-Riddle Aeronautical University. We were shown a video of the "un-ducted fan engine" and it sounded promising. I always wondered what happened to it. Now I know. Thanks for this video.

As a young engineering working at Pratt & Whitney Aircraft back in the late 1980's & early 1990's, I sat in a presentation from the President & CEO of P&W revealing how the engineering efforts were going to be totally dedicated to developing the counter rotating fan engines. Extensive work had already been done on blade and gearbox development. It was an exciting time to be working on the projects to support this effort. The Applied Mechanics lab an experimental engine development was running wide open and the test cells were always running full scale tests around the clock. However, world economics (as mentioned) and the Desert Storm conflict brought all the development (and the commercial aircraft industry in general) to an abrupt halt. It amazed me to observe how this effort disappeared almost overnight. Flight testing was well underway and there were talks about achieving FAA certifications and establishing goals to meet them. Great video!

This episode hits home! In 2013-2014, I worked on the design of the engine mount system for that Safran SAGE2 open rotor engine demonstrator under Cleansky EU initiative. I learned a lot as a younger Aerospace Stress Engineer. Proud to have been part of it 🙂

2 things not mentioned here: 1- The casing also adds drag. 2- These new-generation open rotor engines moved the rotor to the front (they are puller rather than pusher). Pusher propellers (or rotors in this case) are much noiser because they encounter uneven "dirty" air. Uneven because the engine must be supported somehow and that creates an area of "shadow". And dirty because they are in the wake of turbulent boundary layers at least from the engine and from the pylon. Puller props on the other hand receive a very even flat and laminar profile of oncoming air, which makes them less noisy. 1 thing mentioned here wrong: Turboprops are not required to keep a severed prop blade from penetrating the fuselage. And they don't. In every instance where a prop blade separated at operating RPMs and flew in the direction of the fuselage, they penetrated the fuselage, sometimes killing people, some times damaging critical systems (like control cables or hydraulic lines), and sometimes even exiting the fuselage at the opposite wall.

The Russian "Bear" bomber is exceptionally loud, but is also a really cool looking aircraft. When I was stationed on the USS Carl Vinson in the early to mid 80s we had to intercept a Bear bomber with F-14s and "escort" them around the fleet. They were allowed to pass close by, but not directly over the fleet, so they were quite close and easy to see from the flightdeck.

My main concern about this type of engine is blade containment - or lack there-of. In the 1990s I was heavily involved in fan blade containment tests at Rolls-Royce when we were testing the use of a Kevlar bandage as a lighter alternative to a metallic casing. It was successful but the destructive potential of a free blade (which we blew off with an explosive charge at the appropriate speed and position for the high speed film cameras to capture) was chilling to watch. I wrote the s/w and designed the electronic h/w that controlled the test. I was also involved in the design of the h/w and s/w to measure blade untwist which needed probes fitted in the casing. Presumably these blades untwist under load too but positioning the probes might be a challenge :) My only aviation interest after retirement is model aircraft. It's considered that fewer blades in a propeller are the most efficient (in fact speed control line models have single blades with a balance weight). I wonder how that affects the oddly shaped blades on these engines.

I saw this propeller design in the mid-late 80s, probably in Popular Mechanics. I've thought about it many times. It's been a long wait to see it in action.

Being an engineer I give you kudos for saying “0.xx”. Whether written or spoken it is a good example of minimizing potential errors. Well done.

I love, LOVE how quiet the leap engines are. So I hope things just continue to become quieter.

I remember sitting through my A&P classes learning about the inducted fan design and thinking about how much further along most companies are in their R&D than their current products would indicate. It's interesting to learn what factors ultimately decide if and when those new technologies and techniques get introduced to the market. Thank you for your video!

Hey Mentour. Lifetime airhead, here. I've enjoyed most of your videos on crash investigation, and still will, if you continue with these, I'm sure. However, I must really give you kudos for your new line of videos, where you explore technologies and the business, in general. Highly instructive, even for an armchair expert, like me ;-) Thank you and keep the blue side up, as the other guy would have it

Very interesting developments. Lots of clever aerodynamics going on to permit a tipped fan blade to derive thrust at mach 0.8 without punishing noise problems...

This is really fascinating and exciting to see, with a beautiful new design and significant improvements in fuel efficiency. btw. watch out for Scott Manley who it branching out from space into aviation. I think there is space for both of you excellent producers!