patrickjp93
Posts: 389
Joined: Thu Aug 22, 2019 12:00 pm

Re: What's next for mainstream jet engines?

Sat Oct 05, 2019 12:44 am

Faro wrote:
Given the present issues dogging certain engine manufacturers...any significant engine innovation will have to have some very very serious durability/reliability testing done...

That in itself may become an industry innovation...


Faro

Or just trim out the fat and let GE and CFM buy out their lesser competitors.

/sarcasm.
 
User avatar
lightsaber
Moderator
Posts: 18275
Joined: Wed Jan 19, 2005 10:55 pm

Re: What's next for mainstream jet engines?

Wed Oct 09, 2019 1:39 am

kitplane01 wrote:
lightsaber wrote:
kitplane01 wrote:

First, love this post.

Second, how about variable pitch fans? Would eliminate the need for reversing buckets. I assume right now fans are pitched for optimum cruise, and therefore variable pitch fans would help most during takeoff and climb and descent. Might they even reduce noise levels during takeoff, if just by allowing a shorter roll and steeper climb???

I'd love to hear more about variable pitch fans.

I forgot variable pitch fans. Improved thrust at takeoff, improved climb and cruise fuel burn, about 2% in climb, maybe 0.6% in cruise (I am less familiar with test data, so please understand that is a SWAG).

The big benefit of variable pitch is reduced wear during climb. It allows efficiency gains and adds about 20% to the cycle life of the engine. Maybe 25%.

The simplified nacelle pays for the variable pitch. Small noise reduction, but since at where the ground absorbs, it doesn't effect the outside the airport noise profiles.

It is good tech.

I'm sure I forgot other stuff.
Lightsaber



Much of what you wrote surprises me. If fans are optimized for cruise conditions, why would a variable fan improve cruise? Are normal fixed fans set to a compromise between climb and cruise?

Any why would a variable fan reduce wear during climb? I imagine you'd run the core at some reasonable maximum thrust with either a fixed or variable fan pitch, and take the better climb performance with the variable pitch. The core would see a similar work load in both cases, but less time of climb in the variable case. (I'm not stating a fact, I'm asking if this is true).

I missed your excellent questions.

A fan must have surge margin at takeoff. At cruise that surplus surge margin is wasting fuel. Yes, the fan is optimized as best as possible for cruise, but it will meet the requirements for all opperating conditions, for a fan surge is a bad day.

During climb, the turbine powering the fan is going too slow. The fan is demanding far too much horsepower. By reducing fan pitch, the low spool goes faster during the slow climb phase. Once the plane turns over for cruise it accelerated up to an optimal fan RPM which is really optimal Mach #. The durability during climb is by increasing the RPM/Mach number on the fan, you have more thrust. The aircraft climbs faster. This allows the low compressor (aka booster compressor) to reach a higher pressure. This results in more pressure drop for the combustor and turbine cooling. Every about 50F drop in Nickel temperature doubles service life.

The above is why RR was sold on the triple spool.

The important time in climb is the end of climb scortch. The turn over to cruise is absolutely scortching on the combustor and high turbine (highest metal temperature). If the high turbine isn't the cycle limiting part, as the most expensive part of the engine, send the designers back to engine basic design class.

This is why the LEAP and GE9X have variable turbine cooling. High during takeoff, climb, and a few other conditions. Low turbine cooling for cruise.

Lightsaber
IM messages to mods on warnings and bans will be ignored and nasty ones will result in a ban.
 
patrickjp93
Posts: 389
Joined: Thu Aug 22, 2019 12:00 pm

Re: What's next for mainstream jet engines?

Wed Oct 09, 2019 9:33 am

lightsaber wrote:
I missed your excellent questions.

A fan must have surge margin at takeoff. At cruise that surplus surge margin is wasting fuel. Yes, the fan is optimized as best as possible for cruise, but it will meet the requirements for all opperating conditions, for a fan surge is a bad day.

During climb, the turbine powering the fan is going too slow. The fan is demanding far too much horsepower. By reducing fan pitch, the low spool goes faster during the slow climb phase. Once the plane turns over for cruise it accelerated up to an optimal fan RPM which is really optimal Mach #. The durability during climb is by increasing the RPM/Mach number on the fan, you have more thrust. The aircraft climbs faster. This allows the low compressor (aka booster compressor) to reach a higher pressure. This results in more pressure drop for the combustor and turbine cooling. Every about 50F drop in Nickel temperature doubles service life.

The above is why RR was sold on the triple spool.

The important time in climb is the end of climb scortch. The turn over to cruise is absolutely scortching on the combustor and high turbine (highest metal temperature). If the high turbine isn't the cycle limiting part, as the most expensive part of the engine, send the designers back to engine basic design class.

This is why the LEAP and GE9X have variable turbine cooling. High during takeoff, climb, and a few other conditions. Low turbine cooling for cruise.

Lightsaber

Well, at least we have a workaround in case the variable pitch fan idea never comes to fruition in a HBT. CMC compressor parts can also withstand higher temperatures in general, so the service life curve of the affected parts should be effectively reset.
 
gloom
Posts: 324
Joined: Thu Jun 30, 2016 4:24 pm

Re: What's next for mainstream jet engines?

Wed Oct 09, 2019 9:44 am

lightsaber wrote:
Turboprops are efficient, but limit cruise to Mach 0.6 or so


Not really, higher can be easily achieved. NK-12 on Tu95? TP400 on A400M?

I guess the problem is not the speed itself, but rather noise.

Cheers,
Adam
 
GalaxyFlyer
Posts: 3874
Joined: Fri Jan 01, 2016 4:44 am

Re: What's next for mainstream jet engines?

Wed Oct 09, 2019 2:23 pm

lightsaber wrote:
kitplane01 wrote:
lightsaber wrote:
I forgot variable pitch fans. Improved thrust at takeoff, improved climb and cruise fuel burn, about 2% in climb, maybe 0.6% in cruise (I am less familiar with test data, so please understand that is a SWAG).

The big benefit of variable pitch is reduced wear during climb. It allows efficiency gains and adds about 20% to the cycle life of the engine. Maybe 25%.

The simplified nacelle pays for the variable pitch. Small noise reduction, but since at where the ground absorbs, it doesn't effect the outside the airport noise profiles.

It is good tech.

I'm sure I forgot other stuff.
Lightsaber



Much of what you wrote surprises me. If fans are optimized for cruise conditions, why would a variable fan improve cruise? Are normal fixed fans set to a compromise between climb and cruise?

Any why would a variable fan reduce wear during climb? I imagine you'd run the core at some reasonable maximum thrust with either a fixed or variable fan pitch, and take the better climb performance with the variable pitch. The core would see a similar work load in both cases, but less time of climb in the variable case. (I'm not stating a fact, I'm asking if this is true).

Fans are optimized for cruise, but then compromises on stall margins.

During climb the fence Lowe's the Lowe's spool down too much. This means there is not sufficient pressure ratio for cooling. a low pressure ratio means the engine is also struggling to provide the thrust so there is a lot more turbine wear. turn climb the court is starved of turbine cooling cuz you have lots of heat but is not as much pressure to remove the heat. by having a variable pitch fan you can increase the RPM in there for the loading of the loads will which increases the pressure ratio which gives the high school more air to burn so you're not burning his Rich so you're not burning as hot.

Lightsaber


Sir, could correct or explain that post especially “Lowe’s “, please? The Passport on the G7500 is amazing, 10% lower fuel burn than BR710 powered G6000 at the same Mach number with a 10,000 heavier and larger airframe. Optimum altitude off a MTOW take-off starts and F410. Sure, wing improvements have their contributions, but engines are the main factor.

GF
 
User avatar
kitplane01
Posts: 1354
Joined: Thu Jun 16, 2016 5:58 am

Re: What's next for mainstream jet engines?

Fri Oct 11, 2019 5:27 pm

patrickjp93 wrote:
lightsaber wrote:
I missed your excellent questions.

A fan must have surge margin at takeoff. At cruise that surplus surge margin is wasting fuel. Yes, the fan is optimized as best as possible for cruise, but it will meet the requirements for all opperating conditions, for a fan surge is a bad day.

During climb, the turbine powering the fan is going too slow. The fan is demanding far too much horsepower. By reducing fan pitch, the low spool goes faster during the slow climb phase. Once the plane turns over for cruise it accelerated up to an optimal fan RPM which is really optimal Mach #. The durability during climb is by increasing the RPM/Mach number on the fan, you have more thrust. The aircraft climbs faster. This allows the low compressor (aka booster compressor) to reach a higher pressure. This results in more pressure drop for the combustor and turbine cooling. Every about 50F drop in Nickel temperature doubles service life.

The above is why RR was sold on the triple spool.

The important time in climb is the end of climb scortch. The turn over to cruise is absolutely scortching on the combustor and high turbine (highest metal temperature). If the high turbine isn't the cycle limiting part, as the most expensive part of the engine, send the designers back to engine basic design class.

This is why the LEAP and GE9X have variable turbine cooling. High during takeoff, climb, and a few other conditions. Low turbine cooling for cruise.

Lightsaber

Well, at least we have a workaround in case the variable pitch fan idea never comes to fruition in a HBT. CMC compressor parts can also withstand higher temperatures in general, so the service life curve of the affected parts should be effectively reset.



I don't think that's true.

CMC can either be used to run the normal temps at higher margin and therefore higher lifespan, or at higher temps and therefore better fuel efficiency. I'm guessing we'll see #2.

Besides, I think the really scary temps are on the turbines just downstream of the combustion, and not in the compressor at all.
 
patrickjp93
Posts: 389
Joined: Thu Aug 22, 2019 12:00 pm

Re: What's next for mainstream jet engines?

Fri Oct 11, 2019 5:42 pm

kitplane01 wrote:
patrickjp93 wrote:
lightsaber wrote:
I missed your excellent questions.

A fan must have surge margin at takeoff. At cruise that surplus surge margin is wasting fuel. Yes, the fan is optimized as best as possible for cruise, but it will meet the requirements for all opperating conditions, for a fan surge is a bad day.

During climb, the turbine powering the fan is going too slow. The fan is demanding far too much horsepower. By reducing fan pitch, the low spool goes faster during the slow climb phase. Once the plane turns over for cruise it accelerated up to an optimal fan RPM which is really optimal Mach #. The durability during climb is by increasing the RPM/Mach number on the fan, you have more thrust. The aircraft climbs faster. This allows the low compressor (aka booster compressor) to reach a higher pressure. This results in more pressure drop for the combustor and turbine cooling. Every about 50F drop in Nickel temperature doubles service life.

The above is why RR was sold on the triple spool.

The important time in climb is the end of climb scortch. The turn over to cruise is absolutely scortching on the combustor and high turbine (highest metal temperature). If the high turbine isn't the cycle limiting part, as the most expensive part of the engine, send the designers back to engine basic design class.

This is why the LEAP and GE9X have variable turbine cooling. High during takeoff, climb, and a few other conditions. Low turbine cooling for cruise.

Lightsaber

Well, at least we have a workaround in case the variable pitch fan idea never comes to fruition in a HBT. CMC compressor parts can also withstand higher temperatures in general, so the service life curve of the affected parts should be effectively reset.



I don't think that's true.

CMC can either be used to run the normal temps at higher margin and therefore higher lifespan, or at higher temps and therefore better fuel efficiency. I'm guessing we'll see #2.

Besides, I think the really scary temps are on the turbines just downstream of the combustion, and not in the compressor at all.
Which is fine, CMC turbine blades are already on the cards.

Who is online

Users browsing this forum: N766UA and 94 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos