DrivingAloft

Hey guys.. I'm sure most of you heard about this type of engine: the propfan or unducted fan engine. For those of you who haven't, it's basically a mix of turboprop and jet engine. Biggest advantge is that has the fuel economy of a turboprop with the efficency of a jet at high speeds. This technology came up in the late 80s and basically didn't develop further due to the cost of fuel being very cheap, and the fairly high development costs. Off course, that was back when the jet fuel was about 1$/gal. We all know that even though the oil of barrel price went down this year, it is still not cheap and it could go up again. Remember that when the global economy crisis ends, economies like China, India and other SE Asia will resume, and demand will increase dramaticaly.
Why haven't this engine design come back? Fuel consumption is between 25-40% less than a turbofan. That was with 1980s technology, these days they could probably improve it even further.

This video is from 1989, and they keep talking about this engine as the future for comercial jets. If this engine would been in service last year with airplanes like the md-90, b717, or even 737 "NNG", I'm sure the oil crisis wouldn't have hit us so hard, specialy in the domestic market.

YouTube - Ultra High Bypass Jet Engine Green Technology Airline Flight Test

Rightseat Ballast

I also remember noise being a big drawback for the unducted fan engines.

III Corps

Noise and vibration.

On the ground it was not that bad. McDoug took the UDF to Paris and did a demo and the takeoff/landing noise footprint did not seem that much different in total noise footprint. Just a different sound.

DrivingAloft

MD put first class seats in the back of their MD-94X for company execs. to get a feel of the engine, and apparentely it was very decent. I mean, won't be as quiet as a turbofan, but won't be as noise or "shaky" as a plain Turboprop.

rickair7777

There is currently a battle raging amongst the engine mfgs for the future direction of turbofan engines. There is an urgent need to reduce fuel consumption and noise for economic and environmental reasons...

Pratt is going with the geared turbofan...basically similar to what we have to today, except the fan is geared down 1-to-3 for increased efficiency and quieting (maybe 20% better). The only catch is that you need a gearbox...this has GE and others scared off, but Pratt has a bit of experience with gearboxes so they are already off and running. Their GTF will be used on the Bombardier C-series and the MRJ. They are also developing a narrowbody GTF for the 737/A320 replacements...this would have a higher gear ratio for more efficiency.

GE and I think Rolls are experimenting with open rotors. These have the potential for more efficiency gains (30%+). There are some problems though...

- They are loud for obvious reasons.
- There are certification issues with fan containment (obviously)
- The engines cannot be underwing mounted since the the rotors are larger than traditional fans and unprotected from FOD...they would need to be tail or possibly over-wing mounted.

The open rotor would be a significant design factor for the airframe, it is not a bolt-on solution. My guess is the next-gen narrowbodies will use the GTF, and maybe we'll see open rotors on blended body-wing designs at some point after that.

forgot to bid

Embraer toyed with this before the ERJ-145 was developed. In fact, if you ever look at some part numbers on the ERJ-145 there are EMB-123 part numbers on them. Evidently the engine mount is.






Maybe Embraer ought to drag out of Rolls Royce a pusher prop version of the AE3007 that can be installed on existing ERJs. It'd probably cut the range but so be it. Maybe add canards to make it that much cooler.

Dirtdiver

Hmmm,

I've got 2500 hours in the Herc, 5 engine shutdowns, all for gearbox problems.
This is also what worried me about the Osprey. They put a connecting shaft to cover an engine failure, but the reduction gearbox is what's gonna kill you.

hindsight2020

What he said^^

Gearboxes are for trucks.... I want direct drive baby!

I do see the shelling issue and customer apprehension towards turboprops as major items to de-myth before such an application can be made mainstream. I do think the economic savings and cost-efficiency in present day toilet paper money America would automatically be there on the medium sized jets, at least on the non-gearbox conceptualization of the unducted turbofan. If anything, it'd give us some to do other than attempting to shuffle paper as a means of wealth creation, meh manufacturing on these thing will probably be outsourced before it hit the CAD scope....never mind

rickair7777

They are certainly not as reliable as direct-drive, but we have plenty of gearboxes in airline service right now. They are not falling out of the sky. Of course they are not maintained by teenagers in a sandstorm either.

cal73

Money talks.

At CAL 737 routes went to RJs

then RJ routes went to Dash-8 T-props.

Noise apparently wasn't that big of a deal for that. Gimme da CASH!!!

Ground personnel watch out!!!