[BoneCollector]

Airbus is planning to test a new engine type for the successor of narrow body A320s towards the end of this decade. It's an open fan blade design and will be run on the A380 test bed.

Link

[Jeroen]

Thanks for sharing.

Open fan technology itself is not new. I seem to recall a short hype about two-three decades ago? I recall seeing them on planes like the MD80. But it never delivered on its promises I think.



Several aircraft engine manufacturers are pouring serious resources into it currently.

E.g. https://www.geaerospace.com/news/pre...l%20efficiency.

Not sure what break through was required. Material? I seem to recall issues around noise, vibration and concern of bits flying off and penetrating the cabin. Not sure what the real reasons were for not becoming successful

They are supposed to be considerable more fuel efficient. I have seen figures upwards of 20% compared to regular bypass jet engines I don’t quite understand how that is achieved.



I will be at the Paris airshows in a little while for a couple of days. Finished my trip and show bookings last night. I’ll probably be able to see one of these up close. Should be interesting.

Jeroen

[FlankerFury]

Originally Posted by BoneCollector

It's an open fan blade design and will be run on the A380 test bed.

Originally Posted by Jeroen

Open fan technology itself is not new. I seem to recall a short hype about two-three decades ago? I recall seeing them on planes like the MD80. But it never delivered on its promises I think.

Could someone help me understand how an open fan engine differs from a turboprop?
At a quick glance it looks very similar to a regular turboprop.

[Jeroen]

Originally Posted by FlankerFury

Could someone help me understand how an open fan engine differs from a turboprop?
At a quick glance it looks very similar to a regular turboprop.

They do look very similar. It has been suggested the name open fan is more of a marketing trick as it really is very similar to a turbo prop.

There is a huge difference in application though. Turbo props are best for relative slow flying. Mach0,4 thereabouts. For all kinds of reasons they don’t work very well at higher air speeds.

The open fan rotor has many more blades than a turbo prop. Different shape too.
This is where the open fan technology comes into its own, which operates at its peak efficiency around Mach 0,8-0,85 which is the cruising speed of most jet airliners.

So even though they might look very similar there is a fundamental difference as to how they can be used most effectively.

Jeroen

[V.Narayan]

Originally Posted by FlankerFury

Could someone help me understand how an open fan engine differs from a turboprop?
At a quick glance it looks very similar to a regular turboprop.

If you ignore the propeller devices then the two - Unducted Fan {UDF} engine and a turboprop are similar. A turboprop has roughly 5% to 8% of its thrust coming from hot gases exiting fast from the exhaust while the UDF has that number down to 3% or so. A modern day turbofan would have that number at around 20%. All numbers are approximations to give a general idea. Where the UDF hoped to make a mark in the 1980s/1990s was in fuel efficiency through superior variable pitch rotor blade design. But at the same time the efficiency and reliability of high bypass ratio turbofans {the ducted variety} moved so well and so fast that any benefit of fuel efficiency got left by the way side.

I'm no expert but the way fluids move the kort nozzle effect does improve thrust and a ducted turbofan is just that - a kort nozzle simplistically speaking. I don't see the UDF replacing the turbofan anytime soon.

The other two disadvantages of a UDF that were discovered during testing was - (A) noise levels being too high even for the more lenient standards of the 1980s (B) the diameter of the blades was found to be almost 2X, power output for power output, compared to a traditional turbofan. This latter point #(B) caused design issues of fitting the engines under the wings - not enough ground clearance. That is why we see photos of the UDF fitted at the aft on the tail area.

It is good to see Airbus experimenting with newer options but UDFs are still in the future.

Originally Posted by BoneCollector

Airbus is planning to test a new engine type for the successor of narrow body A320s towards the end of this decade. It's an open fan blade design and will be run on the A380 test bed.

Thank you for sharing this.



A GE UDF on a McDD-80 airframe, 1988.



To best of my knowledge the only UDF or Propfan to enter service was the Russian Progress D-27 powering the Antonov An-70 military/civilian freighter - albeit this was only at the prototype stage. Thrust was in the order of 12,000 kgf. The An-70 did not sell following the collapse of the USSR. The D-27 at cruise had a fuel sipping specific fuel consumption of consumption of 0.31 lbs/hp/hour which is significantly better than a high speed turbocharged ICE diesel! One could argue if this is a true UDF or a super duper contra-rotating turboprop {like the ones on the Tu-142M}. The question highlights the fact, going back to Flanker Fury's question, that the lines of demarcation are thin.

[hrman]

This looks like the current ultra short haul or private aircraft like Bombardier and Embraer. In recent trips to tier 2/3 cities these definitely cause more noise due to the open design.
Noob question, will this result in lesser damage due to bird hits, thereby better safety?

[fhdowntheline]

Wasn’t there a luxury executive jet Piaggio Avanti with the rear prop fans that had a relatively high speed for a prop jet?

[Jeroen]

Originally Posted by fhdowntheline

Wasn’t there a luxury executive jet Piaggio Avanti with the rear prop fans that had a relatively high speed for a prop jet?

Yes, there was. Some 250 were build.

https://en.wikipedia.org/wiki/Piaggio_P.180_Avanti

But this is not an inducted fan. It is more or less a regular turbo prop in a push, rather than pull configuration. Four blade, constant speed prop.

I seem to recall there was at least one other, pretty similar design too?

Jeroen

[Random_Alien]

As a person with a lot of interest in aircrafts, i always had a question in mind- why don't open fan aircrafts use electric motor that is powered by an efficient turbine (similar to APU) like the way honda civic hybrid works?

Wouldn't it be better since the turbine can run at max efficiency and electric motors being torque-y and quick to spool up and down would add to performance and efficiency? Sure, the weight of aircraft would increase but the thrust can more than compensate for that isnt it?

[ads11]

Originally Posted by Random_Alien

As a person with a lot of interest in aircrafts, i always had a question in mind- why don't open fan aircrafts use electric motor that is powered by an efficient turbine (similar to APU) like the way honda civic hybrid works?

Wouldn't it be better since the turbine can run at max efficiency and electric motors being torque-y and quick to spool up and down would add to performance and efficiency? Sure, the weight of aircraft would increase but the thrust can more than compensate for that isnt it?

Looks like the Swedish firm Heart Aerospace have kinda gone this way with their 4 prop airframe, with the two inboard props being electric whilst the outer pair are conventional turboprops.

https://www.youtube.com/watch?v=zeYySXlo8js

By the way, in the product video below you can see them mocking up the engine on a variety of configurations (traditional underslung wing mounted, high mounted wing based, and rear fuselage mounted).

https://www.youtube.com/watch?v=nHBYcIvHHZM

This thread reminded me of a decent primer I'd noted on Twitter years ago. Managed to find it, sharing it below.
https://x.com/Jordan_W_Taylor/status...05868852514816

As the above and the posts prior point out, open fan engines aren't quite the panacea yet. For starters I don't think there are easy engineering solutions to the noise issue on contra rotating propellers (ask Tu-95 pilots and ground crew for feedback), plus the shape of open fans would require clean sheet airframe designs given their issues with conventional turbofan mounting configurations. But given their vastly more efficient fuel burn in the take off part of the cycle, it's hard to overlook their potential benefits to high frequency, short routes. I could easily picture something in the A220 air or CRJ frame class with open fans.

NOTE: I should add that it looks like the RISE engine isn't contra rotating, instead that rear set of rotors are static. Not sure what that does - though I'm sure someone will chime in to clarify

[Jeroen]

Originally Posted by Random_Alien

As a person with a lot of interest in aircrafts, i always had a question in mind- why don't open fan aircrafts use electric motor that is powered by an efficient turbine (similar to APU) like the way honda civic hybrid works?

Wouldn't it be better since the turbine can run at max efficiency and electric motors being torque-y and quick to spool up and down would add to performance and efficiency? Sure, the weight of aircraft would increase but the thrust can more than compensate for that isnt it?

It doesn't work like that. Weight, as you undoubtedly know, is always a huge factor in planes. A turbine doesn't run efficient by itself. It all depends on the loading of the turbine and a bunch of other factors. (e.g. temperature, density (altitude), humidity and so on.

Hybrid solutions, e-motor with an engine running a generator, are not an efficient way in general.

They can be efficient in certain applications. Where you have a lot of different power/torque settings. E.g. Modern tugboats, cruise ships and so on. Cruise ships tend to have multiple diesel engines with different power ratings, so they can optimise the required horsepower over different diesel configurations. So the optimise the number of diesel engines, versus the electrical power requirement of the electric propulsion system.

Doesn't work like that in aviation, by a long shot!

The reason we see them on trains/locomotives was more a limitation in the diesel drive train set-up than anything else.

Aeroplanes fly at cruise altitudes within a narrow range of throttle settings. Take-off power settings tend to be higher, but only for a very short while. And both engines on either side of the cabin/wing/tail need to produce the same amount of power all the time!

At the end of the day, the spooling up of an emotor that is driven by a generator-turbine combination is still limited to how quickly the generator-turbine can produce that power. Yes, you might have it running at constant speed, but you will still need to throttle up speed/torque-wise. That always takes time; the larger the jet engine, the longer it takes.

I don't want to oversimplify matters, but on aircraft, you can more or less assume a direct correlation between power/torque (correlated to the amount of fuel you inject) and thrust.

Adding an e-motor and a generator doesn't produce more thrust. If anything, there are additional efficiency losses you need to overcome.

So, such a solution adds weight and a lot of complexity. Let's not even begin to discuss the time and cost to get such a concept validated and approved.

Jeroen

[Random_Alien]

Originally Posted by Jeroen

It doesn't work like that. Weight, as you undoubtedly know, is always a huge factor in planes. A turbine doesn't run... ...

Make sense now, thanks a lot for the insight! Maybe I underestimated the fuselage strengthening and wing span requirements for having such a setup, not to mention the cost of developing such a thing.

I would still love to see a prototype of such technology.

Originally Posted by ads11

Looks like the Swedish firm Heart Aerospace have kinda gone this way with their 4 prop airframe, with the two inboard props being electric whilst the outer pair are conventional turboprops.
https://www.Youtube.com/watch?v=zeYySXlo8js

By the way, in the product video below you can see them mocking up the engine on a variety of configurations (traditional underslung wing mounted, high mounted wing based, and rear fuselage mounted).
https://www.Youtube.com/watch?v=nHBYcIvHHZM

Very interesting!

Originally Posted by ads11

This thread reminded me of a decent primer I'd noted on Twitter years ago. Managed to find it, sharing it below.
https://x.com/Jordan_W_Taylor/status...05868852514816

I'll check it out in my free time.

Originally Posted by ads11

NOTE: I should add that it looks like the RISE engine isn't contra rotating, instead that rear set of rotors are static. Not sure what that does - though I'm sure someone will chime in to clarify

I believe this is because of something called destructive interference of waves. Basically, the rear blades oppose the sound waves produced by propeller in front by producing waves of same amplitude, but in opposite direction or phase. I suggest you read about this topic a bit, maybe a brief explanation by chatgpt to properly understand the application.

Note: this is completely my guess, i have no knowlege of the reason implementation of rear blades. Apologies if i get something wrong.

[FlankerFury]

Originally Posted by Jeroen

I seem to recall there was at least one other, pretty similar design too?

PimaAir.org | Beechcraft Starship

Wikipedia | Beechcraft Starship

Both this Beechcraft and Piaggio align with Burt Rutan's design philosophy of having canards upfront, a main wing in the middle, and an engine in a pusher configuration.

[Jeroen]

Originally Posted by FlankerFury

Both this Beechcraft and Piaggio align with Burt Rutan's design philosophy of having canards upfront, a main wing in the middle, and an engine in a pusher configuration.

Of course, Burt! Truly amazing guy.

Here he is arriving at Oshkosh last year in style!

https://youtu.be/QLqApU6VYZM?si=9HyjMFD14W2g2tMY

Slightly off topic, if you can attend only one air show on your whole life, make sure it is the EAA Oshkosh air show. Unbelievable event. And yes you can just bump into people like Burt.

I have had the pleasure attending three or four times. I had the opportunity to listen to astronauts from the Apollo program, U2 and blackbird pilots.

For a full week the busiest airport in the world. All VFR traffic is not allowed to talk on the radio. They have controllers on the ground along the approach route with binoculars. You will receive your instructions over the radio. To acknowledge you rock your wings. Three different touch down points on the runway to keep the landing sequence as short as possible. And several tens of thousand pilots watching you land. Talk about peer pressure!

Jeroen

[MyLife_MyCar]

Keeping the fuel efficiency and other benefits aside, what about the asthetic and traveller’s state of mind?

Personally, I didn’t the open fan design. Looks like something was left unfinished.

Secondly, since it’s open fan, then an engine failure will easily be noticeable (since the fan would stop rotating) and create (unnecessary)panic among the travellers and many would be shitting their pants!
Although this is nothing to worry about as aeroplanes can easily fly even on one engine, the current design with concealed fans surely gives more assurance!