A Technical History of the General Electric GE36 Propfan

[@basilb4733]

Thanks a lot! These detailed informations are - to my knowledge - nowhere else available.

[@AEHSvideo]

Thanks for that. More to come...

[@Xsiondu]

30 seconds in it's an instant subscribe

[@Xsiondu]

That was an excellent presentation. I forgot how loud those were.

[@AEHSvideo]

Thank you for your comments.

[@osmanfb1]

Thanks for the trip back into the 80s. I worked on this engine until it was cancelled. Interesting times. Engineering problems could have been solved but regulatory ones like the creating new regulations for the unducted fan blade out, might have been hard. But now it is all in a museum :-)

[@AEHSvideo]

Thanks for your comments and I hope the video was an accurate representation of the 578-DX history.

[@terencewong-lane4309]

I loved the prospect of the GE36!

[@malcolmmoy]

I've found you! I was a subscriber to the quarterly magazine, and hadn't realised you were now on KZbin. Great to have you here.

[@AEHSvideo]

Thanks. The AEHS is trying to expand its footprint through You Tube videos of original content.

[@jeylful]

Hi Tom, Thank you for your presentation. Very interesting concept indeed and even more after watching your video on the Allison 578-DX. On that video I commented on the complexity of subjecting the blades to the very hot air and freezing exhaust (expansion, different fatigues, etc) and when compared with this system now I realise the advantages of the Allison and its passively cooled blades.All jet engines use bled air for cooling but this engine uses almost 20% for the different blade mechanisms/turbines and it sounds so taxing! Sounds like great fuel efficiency can be achieved if another cooling mechanism or system that needs less cooling is devised! Cheers mate.

[@AEHSvideo]

The gearless GE36 propfan was the engine that required the large cooling flow at takeoff to keep the propulsor within temperature limits. Another compromise of the GE36 was the sub-optimal, but design-constained, turbine rotor speeds. The net combined +/- 3,780 rpm is pretty low for efficient turbine operation, thus the large diameter of the power turbine, the multiple stages, and contra-rotation. The gear-driven PW-Allison 578-DX demonstrator had issues with keeping the oil cool enough for safe operation but proved that passively cooled blades could survive the exhaust stream.

[@mlehky]

Fantastic video, thanks for posting. I never had a chance to see the GE36 in action, but did see the PW-Allison 578-DX doing low approach’s at KBDL. Although I don’t believe it was loader than a contemporary engine of that time it had a higher pitch that certainly did make it more annoying. It will be interesting to see how the RISE addresses noise issues since in order to be accepted it not only need to meet regulatory noise thresholds, but need to be at least as quiet as todays contemporary engines. I’ve lived under the approach path to a major international airport since 1996. In 96 my rear deck was basically unusable with the noise of common aircraft of that time. Today most aircraft overfly me with barely noticeable noise levels.

[@AEHSvideo]

Thank you for your comments. SAFRAN made remarkable progress in reducing noise on their contra-rotating open rotor engine run on the test stand, so I expect the noise signature of the RISE engine will be very satisfactory.

[@Deviation4360]

After seeing this video outlay in fantastic detail the pros and cons of this type of engine I still feel that a resurgence in diesel 2 cycle piston engines could be a solution. My bet is on 16 cylinder axial piston engines (the CW R-3350 radial engine data inclusion was a great comparrison) using exhaust energy for either additional input or for forced induction. The same cowling shapes would be possible and approx overal powerplant weight. 10,000hp is definitely in reach with way more torque for those values. No labrynthian air impingment and exotic metalurgical tricks needed accept in lightening the relatively simple axial piston engine internals. I know I will provoke objections from prestigious and notable pin-wheel heads, but I know the real reason all the focus is on gas turbines is the patent space and cubic meters of money that is demanded for all the fuss.

[@AEHSvideo]

Thanks for your comments. Likely the most recently certified diesel aircraft engine, albeit a 4 cycle, is the RED V12 (red-aircraft.de/) of +/- 600 hp. I would expect it to be a Herculean task to get 15-fold that horsepower from a reciprocating engine in a compact, light, and reliable package. If optimistically you could get 1 hp per 0.75 pounds of engine weight, that makes 7,500 pounds for the engine alone. Add in a 3,200 pound geared propulsor, and you have a 10,700 pound propfan propulsion system which is at least 20% heavier than the demonstrator propfans of the late 1980's.

[@Deviation4360]

@@AEHSvideo There you go. Its not impossible 😉, it's just there's no incentive $$$$. A 2 cycle diesel more likely wouldn't need the unwieldly gearbox in the 1st place (comfortable @ max power between 1,000 to 2,000rpm). Thank you for the intelligent reply though as most of the time I get responses (to this kind of statement) that refer to the 50's state of recip engine developement. Or "That won't go fast enough" responses. I'm sure you know of the efforts of Napier, RR Crecy, Stewart Tressilian etc. That was 1950 achievements. The RED diesel is a tentative feeler to avoid being swatted by GE/P&W/RR Et al.

[@AEHSvideo]

@@Deviation4360 , the certified, modern, twin-turbo, intercooled RED AO3 makes 550 hp from 790 lb dry weight, so no better than 0.7 horsepower per pound of dry weight. For high horsepower applications, I'd guess that ratio would have to almost triple. That is a tough mechanical mountain to climb. Pun intended.

[@Deviation4360]

@@AEHSvideo I don't think the RED engine example is at all the optimal layout and therefore a poor example in recip future development. I would revisit the Napier Nomad/ Deltic (originally Jumo 223 inspired) trail and include construction advances from F1 engine development (most development inherited from late 40's recip engineering) and think very much more laterally in between. Like I originally stated my money is on the Axial piston engine with all the above goodies thrown at it, very much like the Tresilian X-16 concept but even more compact in axial piston engine form. The RED engine is a safe Grandma bet and far too contemporary to be breaking into any new ground for this "Mountain of horsepower" you feel is so illusive. Just for reference the Napier Nomad was capable of 1.43 HP/lb in its final developments, with no prop gearbox at all accept a clutch for the turbo recovery input, and with reduced efficiency but never the less test cell proven in 1950.

[@imano8265]

Wow! Fantasic! Its a pitty that these fuel saving engines never came to fruition, for both economical and ecological reasons. It seemed that we had further progress then. So we can really say that the future ist the past .I always had the feeling that the real reasons for turning them down kept hidden. They say they were to loud etc, but as your video prooves, they were not, and it could have been managed to bring them into a allowed level. Of course in the late 80s the prices went down again, so that for economical reasons they were no longer needed. But what a shame to be on such a high level and then making a step backwards. I think the main reason for that ist that the industrie and the airlines were worried wether their customers would accept theese engines or not. When people see such a engine tey think of "propellers" and all combined prejudices. So for the industrie they got the task to develop a prop-fan engine and selling it as a jet-engine: thats exactly what happened since the 90s. Thank you for your very detailed video. The best I found .. I appreciate it very much I´m a fan ...... a propfan!!!

[@AEHSvideo]

Thank you for your comments. The groundbreaking technology (composite blades, advanced airfoils, gearbox technology) of those times can be found in the high bypass turbofans of today. The SAFRAN RISE engine is the likely future of propfan technology: kzbin.info/www/bejne/gpbKin6il8qbp5Y

[@SteveMcD-w4c]

Your presentation was truly enjoyable. Thank you! I often wonder, with many prototype designs, what would it be like today if development had continued.

[@AEHSvideo]

Thank you for your comments. SAFRAN built an Open Rotor demonstrator which ran on the test stand a few years ago (facebook.com/watch/?v=1598258160237345) but SAFRAN has since moved away from the CRP to a tractor propfan design with non-rotationg, variable incidence swirl recovery vanes (kzbin.info/www/bejne/pZu5f4KgYtZmibM)

[@olegadodasguerras3795]

NICE vídeo

[@AEHSvideo]

Thank you for your comment. Check back quarterly for more!

[@Metrallaroja]

Great video! Keep it up :)

[@AEHSvideo]

Thank you for your comments. More videos to come.

[@rickgrear8270]

I like the look of the Ge36. They should equip blended wing design with this engine. It's strange seeing an Md80 make that sound taking off

[@AEHSvideo]

Thanks for your comments. Contra-rotating propellers and propfans work best with undisturbed, clean air into the rotors for minimum noise, vibration. and blade stress. A blended wing pusher configuration means dirty air into the rotors that is made even worse in maneuvering flight (takeoff, turns, landing). I suspect all future propfans, if there are any future propfans, will be tractor installations.

[@BlitzvogelMobius]

Holy crap I never knew the GE36’s cruise TSFC was THAT good. I figured in the .400s, not .24……. I wonder where PW/Allison was with the benefit of gear reduction. Granted the big gain in TSFC came with sizable reduction in cruise Mach.

[@AEHSvideo]

The 578-DX will be the subject of a future video. For a number of reasons the 578-DX did not get as much development and flight time as the GE36 before the program(s) ended.

[@BlitzvogelMobius]

@@AEHSvideo Awesome! Looking forward to it.

[@TairnKA]

I once lived near the flight route into Boeing Field and one day I heard a strange (and loud) sound? From my balcony I saw a Boeing 727 and realized it must have been the Unducted fan testbed I had read about in the "Boeing News".

[@AEHSvideo]

It would be interesting to see the flight logs for the 727 UDF test bed, see where it's been.

[@williamhickey1058]

I’d love to have a copy of the slides used in the video and or references for the info!

[@AEHSvideo]

The references are listed on a slide towards the end of the video. Pause the video at that time, take a screenshot, then paste that into a program such as Word or Powerpoint to save. There are a number of free video downloaders available to download the video to your computer. The primary source document on the GE36 can be found here: ntrs.nasa.gov/api/citations/19900000732/downloads/19900000732.pdf

[@jimmydesouza4375]

Sorry if you answer this in the video, but I am pausing it half way through to watch the rest later and am curious. I have seen a couple of things about these prop fan engines, but what is the difference between a propfan and a turboprop? They seem like the same thing to myself (though I am not very knowledgeable on the subject).

[@AEHSvideo]

Thanks for your comments. Back in the early days (late 1970's-1990), a propfan was defined as having multiple, swept, thin, composite blades that were very highly loaded. These days there are a dozen criteria for the definition, but certainly the Airbus A400 and the An-70 qualify as a propfan. The C-130 upgraded with the 8-blade NP2000 propellers is close to being a propfan, but the blades are only moderately loaded. Hope this helps.

[@rEdf196]

The GE36 had similarities to the General Electric CJ-805-23s proto turbofan jet engine that powered the 1960's era Convair 990. basically a ducted J79 turbojet with a added secondary turbine driving a rear turbofan. It made the CV 990 the fastest subsonic jet but the plane was noisy and inefficient.

[@AEHSvideo]

Thank you for your comments and that is an interesting comparison. The CJ-805-23 had a bypass ratio variably reported as 1.46 or 2.2, with a sfc of 0.56, the latter being quite good for the times.

[@ronaldgreen5292]

😎 cool design and love the sound it makes on power! But, it looks like a giant food processor!😁😁

[@AEHSvideo]

Thanks for watching! It was an amazing engine.

[@briansilcox5720]

I read a story this morning in Aviation week, CFM and GE partnering to develop a new prop fan engine. Seems that now, instead of oil prices driving technology, it is a “climate initiative.” The CFM RISE program will bring forward the GE 36 data. They state that prop blade containment is among the top regulatory issues, along with noise, which tests indicate has been improved upon.

[@AEHSvideo]

Thanks! While SAFRAN and partners built and ran a contra-rotating, gear-driven, ducted-exhaust Open Rotor engine a few years ago, the consortium has opted for a single rotor propfan with downstream, variable-pitch, but non-rotating swirl recovery vanes. www.aviationtoday.com/2021/06/21/ge-aviation-safran-see-sustainability-key-next-gen-cfm-engine/

[@rafaelwilks]

The reason the Piaggio Avanti is so loud is because the exhaust gases hit the propeller blades, resulting in a higher volume than ambient air hitting the blades. As I was watching this video, it suddenly occurred to me: the contra-rotating UDF sounded a lot like a Piaggio, and if the high-velocity exhaust gases hitting the propellers in the Piaggio make a lot of sound, like the GE36, then the sound of the GE36 is due to a set of blades getting hit by high-velocity air from the blades in front of it, just like the high-velocity exhaust gases hitting the propellers of the Piaggio. But the propfan needs to harness some of the energy coming from the fan blades in order to be more efficient. What to do? This, I figured, is the genius of the CFM RISE: the stator vanes behind the fan harness the energy from the fan and make it efficient, without sounding like a Piaggio. (Of course, personally, I love the sound of the GE36 and any propfan, contra-rotating or not, but it obviously wouldn't permit it to be used commercially) Awesome video!

[@AEHSvideo]

Thanks for your comments. The other factor with the Piaggio (Beech Starship, B-36) is the wake turbulence from the wing hitting the prop blades which creates cyclical variations in blade loadings and airflow patterns depending on the position of the blade(s) relative to the wing. This creates noise and vibration that needs to be managed. Propellers, especially contra-rotating propellers, prefer undisturbed airflow into them.

[@rafaelwilks]

@@AEHSvideo wow I would probably have never guessed that! Good to know!

[@markzhangMA261]

Thanks for the excellent video. However, the cruise SFC of the GE36 is still too good to be true. Are you sure the 0.24 lb/lb/hr is the crusie SFC and not the takeoff SFC?

[@AEHSvideo]

Thanks for your comment. The 0.24 SFC is specifically quoted in the video published by General Electric at 20,000 lbs of thrust on the test stand, so presumably a cruise setting.

[@markzhangMA261]

@@AEHSvideo based on the test stand video shown, it appears the engine was exposed to conditions similar to the standard atmosphere. If this is true, the result of 0.24 should be resemble the “takeoff” SFC, where there are simply much more air for the engine to bite at lower altitude (sea level). It might be possible to replicate cruise atmosphere conditions (temp, density, pressure) in an advanced wind tunnel, but I don’t see any source of evidence from your / GE’s video suggesting that was the test case. Based on the source (Air Transport World. Vol. 21, 1997) cited in Wikipedia about GE36, the GE engineers were estimating the cruise SFC would be around 0.41-0.4, which is a far more believable cruise SFC value.

[@AEHSvideo]

@@markzhangMA261 , thank you for your comments and the reference. The GE video did not specify under what conditions that the test stand 0.24 TSFC of the GE36 was achieved, and I'm not aware of any published data for in-flight TSFC. Cruise TSFC is the more relevant efficiency metric for commercial transports. As a frame of reference, the CFM56 takeoff TSFC is +/- 0.35 while cruise TSFC is +/- 0.55 according to Wiki: en.wikipedia.org/wiki/CFM_International_CFM56

[@Mark_Ocain]

Wow they got a bark up, didn't they...really a rowdy engine LOL. This concept is still in play with the engine manufacturers though, which is kind of cool.

[@AEHSvideo]

As development engines they were loud, but not quite as loud as people think. Significant progress was being made on reducing their noise signature, but there was insufficient development time and money towards the end while risk remained high and commercial interest waned.

[@PilotGigi]

Amazing, but it looks very complex

[@AEHSvideo]

It is a simple in concept, but the execution of that concept was extremely complex.

[@joaoalbertodosanjosgomes1536]

🇺🇸🌎👍❤

[@Sacto1654]

I think with better engine technology now and better blade design, the GE36 propfan could have worked in 2024. Interestingly, the CFM RISE technology demonstrator uses a lot of research used by the GE36.

[@AEHSvideo]

Thank you for your comment. GE is a 50/50 partner in with SAFRAN in the CFM RISE project. The gearless (multi-stage, large-diameter, contra-rotating turbine) GE36 system is likely a dead end, and with Pratt & Whitney flying turbofan gearboxes capable of handling 40,000 horsepower, I suspect all future propfans will be using a gearbox.

[@arthurmario5996]

comparing unducted fan specific thrust to reciprocating bsfc not helpful.

[@AEHSvideo]

Thanks for your comment.

[@jasperzanjani]

wow this is a pretty deep dive.. KZbin recommended your video to me after searching for CFM Rise, which is by far the most popular video on the Mentour Now! channel. I think if you got together with some content creation guys you could really flog this topic and become the Internet's propfan guru

[@AEHSvideo]

Thank you for your comments. The AEHS (www.enginehistory.org) has some amazing material. There will be additional videos, 4 per year, and eventually the 578-DX will receive similar treatment as the GE36. Stay tuned.