Low Observability of the F-135 engine

[spazsinbad]

POP STALL not mentioned in this F-35C Catapult Overview by USN F-35C Test Pilot (first arrest ever on a CVN way back).

F-35 Carrier Suitability Testing
17 May 2018 Tony Wilson

"...F-35C Control Laws
The F-35 uses non-linear dynamic inversion control architecture that is operated in three redundant Vehicle Management Computers (VMCs) to provide fly-by-wire control. The Control Laws (CLAW) that augment aircraft dynamics and provide stability are common amongst the three variants; however, each variant’s CLAW has been optimized and contain advanced features to reduce pilot workload and provide carefree handling for specific task (i.e. hovering in an F-35B). For the F-35C, these optimizations include, but are not limited to, shipboard launches and recoveries.

A shipboard catapult launch can be divided into three distinct phases: acceleration, rotation, and flyaway. The launch starts with an acceleration. The aircraft is attached to a shuttle on the deck by a launch bar on the nose strut. The shuttle, attached to a steam powered piston under the deck, provides the motive force to accelerate the aircraft to a safe flyaway speed. During this phase, the CLAW prepositions the control surfaces to provide aircraft rotation upon shuttle release. The horizontal tail is scheduled to achieve roughly 12.5 degrees per second of pitch rate at operationally representative aircraft weights, Wind Over the Deck (WOD), and energy imparted on the aircraft by the catapult. Next, the launch bar is released from the shuttle at the end of the catapult stroke; stored energy in the nose strut and aerodynamic moments generated by pro-rotation control surfaces (symmetric horizontal tail trim, symmetric ailerons and toe-in (trailing edge inboard) rudders) combine to provide a smooth and quick aircraft rotation. Finally, during the flyaway phase, the CLAW transitions from pro-rotation to pro-lift to optimize lift and minimize sink once airborne. The pro-lift control surfaces are symmetric trailing edge flaps (TEFs) and symmetric ailerons.

The catapult launch control law logic is evoked when the launch bar is commanded down while the aircraft is on deck; positioning the control surfaces for pro-rotation based on gross weight and the aircraft’s CG. The pro-rotation configuration is designed to achieve a positive flight path as quickly as possible following catapult launch in order to minimize sink. Additionally, catapult launch logic causes a 30-pound throttle detent to engage at the 100 Engine Thrust Request (ETR) MIL gate, Nose Wheel Steering (NWS) is disengaged, and engine AB Limit (ABLIM) is activated. The ABLIM feature is designed to reduce thermal heating of the tail boom, empennage structure, JBD panels, and flight deck. If throttle position is set for ETR > 122% during the catapult launch sequence, ABLIM control logic will automatically limit ETR to 122% power prior to launch. When a catapult launch is declared or longitudinal acceleration (Nx) > 0.5 g, the ABLIM feature will clear, allowing thrust to increase up to the commanded power setting during aircraft acceleration down the catapult track. The Flight Control System (FLCS) uses multiple sensor to provide feedback to the CLAW to declare a catapult launch:

1) ETR ≥ 95% and longitudinal acceleration (Nx) > 2 g or Calibrated Airspeed (VCAS) > 100 kts
or
2) ETR < 95%, wheel speed > 20 kts, and Nx > 2 g or VCAS > 100 kts

As the launch bar leaves the shuttle, the pro-rotation control surfaces begin to be removed as Angle of Attack (AOA) or pitch rate increase to protect from over-rotation. The control system commands 20 degrees AOA initially but backs off to 15 degrees as AOA passes through 14 degrees AOA. This command is then blended back to zero once a one-degree flight path (gamma) is achieved. If AOA and pitch rate do not increase prior to the aircraft rolling off the deck edge, the pro-rotation aids are removed quickly once weight-off-wheels is sensed and replaced with pro-lift aids. Once airborne, catapult launch mode is disabled. The control law reschedules surfaces from pro-rotation to prolift positions in order to minimize sink and to enhance fly-away characteristics.

The CLAW also augments the roll axis during catapult launches. Roll rates and bank angles induced by asymmetries and crosswinds at the deck edge are removed via a launch roll trim mode that commands differential flaps and ailerons during a catapult launch. Launch roll trim activates when VCAS exceeds 100 knots and is reset as the aircraft leaves the deck. Additionally, a bank assist was added to hold wings level on flyaway. Bank assist activates at Weight off Wheels (WoffW) and attempts to maintain a wings level attitude (zero degrees bank angle) during flyaway for 10 seconds. The pilot may override bank assist at any time with a lateral stick input...."

Source: download/file.php?id=27756 (PDF 3Mb)

[doge]

I found a B type photo, so I will post it.
https://www.instagram.com/p/BssIGDHgrvP/
(It's a photo by an aviation photographer, so It's thought that It's not a Collage or CG.)

[spazsinbad]

Pic Zoomed

[doge]

This is an A model.
It only looks a little bit. (almost! )

[doge]

It's A model of Paris AirShow 2019.
It looks faintly... (The whole is...Just a little more...!! )

[doge]

This is an A model.
I finally found the overall picture of the A model. (Almost the whole is visible.)
This completed the collection of the A, B, C, 3 type engines. (but, nevertheless, Perhaps I will continue to collect and search... )

[doge]

It's looking into this side from the shadow... ┃

[element1loop]

One thing that's perhaps being missed here is that it not only blocks the hot section exhaust from direct exposure (and as discussed an RCS reduction, plus augmenter) it will also induce a strong twist in the nozzle's air-flow, which then mixes the outer cold concentric bleed-air in with the central hot expanding core-air, thus rapidly reducing the NET temperature in a dry-thrust exhaust gas before it exits the end of the nozzle. Thereby reducing dry-thrust IR signature via both a direct shielding, and an indirect air-mixing means.

[doge]

Bokeh.

B of MCAS Miramar Air Show 2019.

Hello~. (Look in)

[doge]

This time, it's C.
On the web, there are almost no clear photos of inside the C's engine! (In the case of C, the first video is the clearest.)

Faintly...Wispy...I feel like I can see...

I peek into the darkness.

[jaws]

Eventually it will become declassified, but until then someone with a monster zoom lens needs to get us a shot inside that nozzle.

[eloise]

Found this tidbit on aircraft101, I must have missed it first time
The blocker is cooled.

[spazsinbad]

Thanks again 'eloise' - graphic text reproduced below (where is 'aircraft101' please?).

Transition to the JSF Program from 'aircraft101'
For the F-35, the Pratt & Whitney F135 engine and LOAN balanced the requirements of LO and efficient aeromechanical performance. It offered a lightweight (especially for the F-35B STOVL variant), low-cost configuration. The F-35A and F-35C variants use the same nozzle configuration. A shorter version was readily configured for compatibility with the F-35B STOVL 3BSM to meet ground clearance needs while landing vertically. Since the engine exhaust system is the primary contributor to aft sector infrared signature, engine and nozzle design needed to incorporate effective methods to reduce infrared emissions. This was accomplished using reduced radar cross-section-compatible techniques, including hiding, shaping, and temperature control. The F-35 exhaust system employs a cooled turbine face blocker, effectively eliminating the temptation to employ more impacting techniques like a serpentine exhaust duct. The F135 exhaust system does use a cooled nozzle to significantly reduce the aft sector infrared signature. With these techniques, the cooled blocker and nozzle tail-on infrared signature is significantly less than the signature of an uncooled exhaust system.
Approved for public release 5/8/18, JSF18-365

[eloise]

Thanks again 'eloise' - graphic text reproduced below (where is 'aircraft101' please?).

Transition to the JSF Program from 'aircraft101'
For the F-35, the Pratt & Whitney F135 engine and LOAN balanced the requirements of LO and efficient aeromechanical performance. It offered a lightweight (especially for the F-35B STOVL variant), low-cost configuration. The F-35A and F-35C variants use the same nozzle configuration. A shorter version was readily configured for compatibility with the F-35B STOVL 3BSM to meet ground clearance needs while landing vertically. Since the engine exhaust system is the primary contributor to aft sector infrared signature, engine and nozzle design needed to incorporate effective methods to reduce infrared emissions. This was accomplished using reduced radar cross-section-compatible techniques, including hiding, shaping, and temperature control. The F-35 exhaust system employs a cooled turbine face blocker, effectively eliminating the temptation to employ more impacting techniques like a serpentine exhaust duct. The F135 exhaust system does use a cooled nozzle to significantly reduce the aft sector infrared signature. With these techniques, the cooled blocker and nozzle tail-on infrared signature is significantly less than the signature of an uncooled exhaust system.
Approved for public release 5/8/18, JSF18-365

I was reading some old articles there to find references and photos
https://basicsaboutaerodynamicsandavion ... -benefits/

[lbk000]

Y'all a buncha perverts in here trading upskirt photos I say.