Forum: F-35 Lightning II

LMAggie wrote:

habu2 wrote:

LMAggie wrote:

I think composites tend to shatter rather than shred.

...or not...

Maybe the definition of composite blades need to be a little more refined as there ate MMC blades as well as MFC blades I understand but the MMC blades have been the only guys put into real turbines and the MFC guy's the last I heard Kawasaki HI had a test engine running. MMC= metal matrix composite and MFC = metal fabric composite.

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F16JOAT wrote:

Looks like RR took a little time to catch on to the GE blisk game!

GE were first in the game with blisks in the T700 helicopter engine. Materiel factor considerations, rim stresses and containment issues restricted the blisk concept to small engines for many years.

In the 1980's Rolls-Royce and MTU developed a production cost effective method of automated friction welding to attach the blade airfoils to the disk cores. This allowed larger repairable rotors to be produced.

The latest designs of blisks are not produced as near net forgings and finished on five axis automated milling machines. By making the blades integral with the hub them the friction welding technique can be used for repair.

asiatrails wrote:

F16JOAT wrote:

Looks like RR took a little time to catch on to the GE blisk game!

GE were first in the game with blisks in the T700 helicopter engine. Materiel factor considerations, rim stresses and containment issues restricted the blisk concept to small engines for many years.

In the 1980's Rolls-Royce and MTU developed a production cost effective method of automated friction welding to attach the blade airfoils to the disk cores. This allowed larger repairable rotors to be produced.

The latest designs of blisks are not produced as near net forgings and finished on five axis automated milling machines. By making the blades integral with the hub them the friction welding technique can be used for repair.

You know, the engine FF diameter is way smaller on the T700 than the F110-132 and making those big blisk's fans at larger diameters is getting harder to keep the mid to tip deflections down to nothing. It would be interested to see the GE90 blisk fans deflection curves, its a MFC - metal-fabric- composite construction I understand. The diameter of that monster is 134-135 inches depending on the model. That's big !!!!

F16JOAT wrote:

asiatrails wrote:

F16JOAT wrote:

Looks like RR took a little time to catch on to the GE blisk game!

GE were first in the game with blisks in the T700 helicopter engine. Materiel factor considerations, rim stresses and containment issues restricted the blisk concept to small engines for many years.

In the 1980's Rolls-Royce and MTU developed a production cost effective method of automated friction welding to attach the blade airfoils to the disk cores. This allowed larger repairable rotors to be produced.

The latest designs of blisks are not produced as near net forgings and finished on five axis automated milling machines. By making the blades integral with the hub them the friction welding technique can be used for repair.

You know, the engine FF diameter is way smaller on the T700 than the F110-132 and making those big blisk's fans at larger diameters is getting harder to keep the mid to tip deflections down to nothing. It would be interested to see the GE90 blisk fans deflection curves, its a MFC - metal-fabric- composite construction I understand. The diameter of that monster is 134-135 inches depending on the model. That's big !!!!

The GE90 Fan has individual blades, it is not a blisk. You usually find blisk designs in core compressors.

Newbie Joined: May 03, 2008 Posts: 7 Status: Offline

That_Engine_Guy wrote:

More LiftFan info I've found...

The clutch sounds amazing!? Cool

Quote:

High power rapid-action closed-loop dry-plate clutch. This massive clutch unit incorporates drive surfaces provided by Goodrich, based on carbon-brake technology. It has to accept a near-instantaneous input of some 21,600 kW (29,000 HP), and accelerate the large counter-rotating fans up to maximum speed in about two seconds

29K Horsepower in 2 seconds!? WOW! Shocked

Not quite.......it's unlikely that the LiftFan would (or could) ever be accelerated up to full power over that short a time period. Full speed, yes, but not full power.

Besides the heat rejection and stress levels that the clutch would be required to cope with, plus the effect on the main engine of such a transient load increase on the LP turbine, you can imagine the huge pitch moment that such a manoeuvre would induce on the airframe?

More likely you'll see the LiftFan brought up to full speed but at reduced thrust (hence lower power) during the first moments of the transition for a vertical landing. Once the clutch is fully engaged, thrust could then be increased as the aircraft decelerates from wing-borne to jet-borne flight, maintaining lateral stability (balance) with thrust from the main engine via the 3BSM as it translates from full aft to vertical thrust.

Newbie Joined: May 03, 2008 Posts: 7 Status: Offline

Oh, and cool site by the way Smile

Looking forward to browsing through the huge number of topics and gaining some insight into a number of interesting subjects.

Pecker wrote:

That_Engine_Guy wrote:

More LiftFan info I've found...

The clutch sounds amazing!? Cool

Quote:

High power rapid-action closed-loop dry-plate clutch. This massive clutch unit incorporates drive surfaces provided by Goodrich, based on carbon-brake technology. It has to accept a near-instantaneous input of some 21,600 kW (29,000 HP), and accelerate the large counter-rotating fans up to maximum speed in about two seconds

29K Horsepower in 2 seconds!? WOW! Shocked

Not quite.......it's unlikely that the LiftFan would (or could) ever be accelerated up to full power over that short a time period. Full speed, yes, but not full power.

Besides the heat rejection and stress levels that the clutch would be required to cope with, plus the effect on the main engine of such a transient load increase on the LP turbine, you can imagine the huge pitch moment that such a manoeuvre would induce on the airframe?

More likely you'll see the LiftFan brought up to full speed but at reduced thrust (hence lower power) during the first moments of the transition for a vertical landing. Once the clutch is fully engaged, thrust could then be increased as the aircraft decelerates from wing-borne to jet-borne flight, maintaining lateral stability (balance) with thrust from the main engine via the 3BSM as it translates from full aft to vertical thrust.

TEG its an amazing design.

For pecker, I don't understand your last comment, the lift fan is a cold fan so speed = power. It has to get up to power quickly to minimize the pitching moment during transition and avoid the VAK-191B "coffin corner"

Elite Joined: Dec 14, 2005 Posts: 586 Status: Offline

The LiftFan's "extra power" would be very similar to the "fuel bias valve" for the JFS in a Viper. (For all you well versed JFS mechanics out there...) Simply: The moment the clutch is engaged, extra fuel is poured into the starter to compensate for the additional torque of starting the engine.

Quote:

If the clutch, connecting the engine to the LiftFan®, is engaged at the same time as the fuel flow is increased, the additional power can be used to accelerate the LiftFan®, instead of the engine. By selecting the fuel flow to match the power produced by the turbine to the power required to drive the LiftFan®, the engine speed can be held constant. The process is similar to depressing the gas pedal in an automobile with a manual transmission. With the clutch disengaged, stepping on the gas causes the engine to accelerate. Engaging the clutch, at the same time as you depress the gas pedal, transfers the power to the drive wheels, so that the engine does not accelerate.

This Thesis sums it up quite well.
Ref: https://dspace.lib.cranfield.ac.uk/bits ... 0final.pdf

The turbine will extract more energy from the exhaust gases as needed when torque is extracted. (Especially if more fuel is added to compensate for the increased load.) The net result is reduced thrust from the exhaust stream. This all depends on the stall margin of the turbine as well. Extract too much and slow the turbine below the stall limit, and no more horsepower. The nozzle will most likely open somewhat as well. PW engines typically use Aj (Area, Jet or "nozzle area") to regulate Fan (N1) RPM by controlling back pressure through the engine. This would further serve to reduce the load on the N1 spool that provides power to the LiftFan system.

Lets also not forget the N1 turbine and shaft supplying the power to the LiftFan will be already spinning as it is part of the engine's own fan spool. You don't see Vipers "torque" over like drag-racing cars when the engines are snapped from Idle to MIL on the runway during take-off. Turbine engines don't make torque that way.

I will add other sources that say this about clutch engagement time...

Quote:

The clutch is designed to engage in 3-7 seconds. With the variable geometry vanes closed and the engine speed reduced to 80-85%, horsepower during engagement is reduced to about 4,000 hp. After engagement, it transmits approximately 28,000 hp at 8,500 rpm.

Ref: http://www.vtol.org/Lockheed.htm

When talking almost 30K HP, there isn't much difference between 2 or 3 seconds, and even at 7 seconds that clutch is amazing to absorb and transmit THAT much horsepower!?! Shocked

Quote:

Goodrich's Santa Fe Springs, California-based high temperature composites team will provide a clutch pack for each JSF STOVL propulsion system. The clutch pack transmits the torque from the engine to the LiftFan to allow vertical takeoff, and then disengages when wing-borne flight is underway. The engine initially transfers the equivalent power of three train locomotives through the clutch, and the rapid engagement results in extremely high heat generation. Goodrich's composite materials are tailored to provide the right amount of friction while absorbing that heat.

AT has it right on the power/speed issue; there is no heat to the lift fan, whatever air volume is moved through it at a given velocity is what you get for power/thrust. No thermal loss

Newbie Joined: May 03, 2008 Posts: 7 Status: Offline

asiatrails wrote:

I don't understand your last comment, the lift fan is a cold fan so speed = power. It has to get up to power quickly to minimize the pitching moment during transition and avoid the VAK-191B "coffin corner"

It's not quite as simple as 'speed = power' (things never are, much as it challenges the gray cells!).

If the Liftfan were a fixed geometry device then, yes, you would be correct, but there's the matter of variable inlet and exhaust geometry to consider.

On the concept demonstrator, LiftFan thrust at a speed was modulated by variable inlet guide vanes. Altering the angle (closed - open) reduced/increased fan flow as required (flow = thrust = power). Thrust vector control was by means of a D-shaped duct that could 'swing out' to vector thrust aft.

For the next phase, a variable area nozzle has been developed. This allows further control of thrust by increasing Liftfan pressure ratio (higher PR= greater thrust = more power please!).

Thus, it is possible for clutch engagements to be conducted with the variable geometry configured for minimum thrust levels, hence minimum power and an easier time for the clutch.

Things can always get complicated.

A two-stage low-pressure turbine in the engine delivers the horsepower to drive both the engine fan and the STOVL Lift Fan. The contra-rotating Lift Fan provides about 20,000 lb of thrust, using variable inlet guide vanes to modulate the airflow and therefore the thrust. The Lift Fan has a clutch that engages for STOVL operations and a telescoping "D"-shaped nozzle to provide thrust deflection. When operating at normal speeds, the Lift Fan is capable of supporting nearly half of the weight of the airframe.

The engine exhaust is through a three-bearing swivel nozzle that can deflect the thrust from horizontal to just forward of vertical. Two roll ducts supplied by engine fan air provide roll control. Yaw control is through swivel nozzle yaw. Pitch control is done using the Lift Fan/main engine thrust split.

For conversion to short take-off mode, the Lift Fan inlet and exhaust doors open, the inlet guide vanes are closed down to minimize air flow, and the clutch is engaged. As the clutch plates synchronize, the Lift Fan gear drive accelerates up to the input shaft speed. A mechanical lock-up device then assures that the clutch does not slip once the Lift Fan is fully engaged. Initial rig testing of the concept in 1997 demonstrated an excellent clutch plate wear rate during high-speed clutch engagements that were representative of the expected operating conditions.

The inlet guide vanes are then opened to bring the Lift Fan up to speed and the D nozzle is rotated down to vector the Lift Fan thrust aft this, together with the main engine thrust, accelerates the aircraft through the transition.

After transitioning to wing-borne flight, the inlet guide vanes are again closed down to reduce the airflow through the Lift Fan, the clutch is disengaged, the nozzle is retracted, and the inlet and exhaust doors are closed.

For the conversion to vertical landing mode, the aircraft decelerates and the Lift Fan inlet and exhaust doors open. The Lift Fan is then brought up to speed as described above, but the D nozzle is left retracted in its fully vertical position.

As TEG said earlier, the Lift Fan clutch is designed to engage in about 5 seconds. With the variable geometry vanes closed and the engine speed reduced to 80-85%, horsepower during engagement is reduced to about 4,000 hp. After engagement, it transmits approximately 28,000 hp at 8,500 rpm. The clutch plates absorb a lot of energy during engagement they dissipate it before the next engagement via forced cooling air.

The main engine nozzle, developed by Rolls-Royce, was patterned along the lines of the exhaust system on the Yakovlev Yak-141 STOVL prototype that last flew at the 1992 Farnborough air show. A US Navy program also developed swivel nozzles in the late 1960s and was proposed for a supersonic STOVL design by Convair in the early 1970s

The Shaft Driven Lift Fan was selected for three primary reasons:

1. The STOVL Lift Fan thrust can be de-coupled from the cruise engine, allowing the cruise engine to be sized for conventional flight.

2. The thrust augmentation obtained from the Lift Fan greatly exceeds the additional weight incurred

3. The lower exhaust jet temperature and pressures result in a more benign ground environment during hover than that produced by direct lift.

Both the lift fan and the main engine contra-rotate to minimize the precession effects in the hover and transition envelopes.

Have there been any other contra-rotating turbofans that actually went into production? That seems like a tricky bit of design in and of itself.

Newbie Joined: May 03, 2008 Posts: 7 Status: Offline

That's a pretty good summary there, Asiatrails. The only thing that has really changed is the introduction of the VAVBN (variable area vane box nozzle) in place of the concept demonstrators d-shaped hinged exit nozzle. One less thing hanging out into the airflow......

Guysmiley, i can think of one or two contra-rotating engines:

RR Pegasus (in all it's guises) to avoid gyro precession in VTOL mode
RR Trent 1000 series has contra-rotation, although only between IP and HP systems (Fan rotates in the same direction as the IP shaft).

Will rack my brains for other examples......

Pecker wrote:

That's a pretty good summary there, Asiatrails. The only thing that has really changed is the introduction of the VAVBN (variable area vane box nozzle) in place of the concept demonstrators d-shaped hinged exit nozzle. One less thing hanging out into the airflow......

Guysmiley, i can think of one or two contra-rotating engines:

RR Pegasus (in all it's guises) to avoid gyro precession in VTOL mode
RR Trent 1000 series has contra-rotation, although only between IP and HP systems (Fan rotates in the same direction as the IP shaft).

Will rack my brains for other examples......

The VAVBN was introduced during the weight saving exercise when the lift fan exhaust nozzle became an integeral part of the airframe structure.

Newbie Joined: May 03, 2008 Posts: 7 Status: Offline

There you go....weight savings and improved operability.

Who says that you can't have your cake and eat it too Wink

Elite Joined: Dec 14, 2005 Posts: 586 Status: Offline

Guysmiley wrote:

Have there been any other contra-rotating turbofans that actually went into production? That seems like a tricky bit of design in and of itself.

RR F402 (Pegasus)
PW F119
PW F135
GE F136

RR Trent 900
RR Trent 1000
Honda(GE) HF118
GE GEnx

I believe the PW GTF (Geared TurboFan) is also counter-rotational, and that Allison made a counter-rotating engine as well at one point.

The Textron Lycoming AGT-1500 engine of the M-1 series Abrams tank has counter-rotating low/high pressure compressors as well. What better to move a 70 ton tank than a 1100kw/1500hp gas-turbine engine!? Shocked

There may be some others, I'll keep it in my mind as I wonder the internet in search of further engine knowledge. Cool

History note:

Quote:

In the summer of 1939, Bramo was taken over by BMW, a complicated counter-rotating axial turbojet project from Helmut Weinrich was also begun under the designation P.3304 or 109–002. Even the conservative Daimler-Benz company had decided to enter the files with paradoxically, a complicated counter-rotating, ducted-fan turbojet (109–007).

Ref: http://www.xs4all.nl/~jqmgrdyk/jetpower ... er-p2a.htm

Forum: F-35 Lightning II

F135 blade failure could hold up STOVL JSF