F-35B/C and the Ski-Jump?

[spazsinbad]

Just following on from 'madrat' statement: 'It's not like the B model is going to use its lift fan on a ski jump.' Went looking for a video with first effort not clear on this point. Clearly in this X-35B video clip (despite the heading) we can see a short takeoff being performed - shown side on to aircraft:

http://www.youtube.com/watch?v=Dz5I8o9k6Xg

[madrat]

I like this concept of using landing gear doors as a blast trap on the F-35B and as air strakes on the A and C models. You don't need the extra drag at higher speeds, being deployed when you need them for low speed handling. I wonder if the shaping of the gear housing will help with a ski jump effort.

[spazsinbad]

md, here is an explanation of some of the magic in the STOVL version which is probably more important:

From Supersonic to Hover: How the F-35 Flies By Chris Kjelgaard 21 December 2007

http://www.space.com/businesstechnology ... works.html

Extra thrust for hovering
But, for hovering, the F-35B can rely on 40,000(+) pounds of thrust without having to use reheat. The F135's full-authority digital engine control (FADEC) software runs the engine at a higher temperature for hover flight than it does during conventional flight, producing more "dry" thrust than the engine normally develops without activating its afterburner.

"We de-rate for CTOL (conventional take-off and landing)" operations, explained Dan Tennant, Pratt & Whitney's F135 system demonstration and development program manager.

When the F-35B is hovering, all 40,000 pounds of thrust is directed downwards, not backwards. It also can be directed anywhere in between, and even slightly forwards, said Tennant.

How the F-35B achieves all this involves a complex fusion of software, precision engineering and materials technology. The F135 is designed to be completely interchangeable with any other F135 or F136 in any of the three versions of the F-35 Lightning II, two of which won't land vertically. However, in the STOVL F-35B, the engine's design also allows for a forward-leading shaft to be coupled to the spool driven by the F135's low-pressure turbine.

The F-35B's lift fan
This spool drives the main fan that pulls air into the engine to allow combustion to take place. But when the spool is coupled (near the main fan) to the shaft, the spool/shaft arrangement also drives a twostage, vertically mounted "lift fan" situated just behind the pilot's cockpit.

In hover mode, the F135's low-pressure spool imparts 28,000 shaft horsepower to the shaft, said Tennant. This is then converted to vertical thrust in a 90-degree gearbox located behind the cockpit. In this gearbox, a clutch engages a horizontally mounted pinion gear on the shaft to drive two vertically mounted bevel gears, one above and one below the pinion gear.

The two bevel gears rotate in opposite directions, each gear driving a short vertical shaft. These shafts power the two counter-rotating fan stages of the lift fan, Tennant explained. Doors in the fuselage above the lift fan open to provide an auxiliary air inlet and the fan forces air downwards to produce 20,000 pounds of vertical thrust. The air exits through a "variable area vane box nozzle" (VAVN) situated in the bottom of the fuselage directly underneath the lift fan.

"It allows us to control (vertical) thrust ... magnitude and direction," said Tennant. The VAVN "looks like a set of Venetian blinds. When it's somewhat closed, thrust can point somewhat aft to somewhat forward, or straight down."

Pitch and roll control while hovering
While the lift fan is providing downward thrust near the front of the aircraft, an amazing assembly called the "three-bearing swivel duct" produces another 20,000 pounds of downward thrust from the engine's exhaust at the rear of the aircraft, and controls the aircraft's pitch attitude.

The swivel duct is composed of several attached, overlapping pieces that swivel at angles to each other with the aid of ball bearings. It can direct the engine's exhaust air anywhere in a 105-degree continuous range from straight back through directly down to slightly forward, said Tennant. Pointed downwards, the duct looks like a stubby elephant's trunk.

When hovering, the F-35B also relies on two "roll post ducts," downward-pointing nozzles located in the root of each wing.

The F135 is a low-bypass turbofan engine: Some of the air pulled in by the fan at the front doesn't go into the engine core to be mixed with fuel and burned, but bypasses it to flow outside the casing.

During hover, some bypass air is directed into the roll post ducts to give the F-35B roll control stability while performing a vertical take-off or landing. (Although the F-35B needs a short take-off run when fully loaded, it produces enough vertical thrust to take off vertically when lightly loaded.)

FADEC software varies the thrust through each roll post duct independently to ensure the pilot has complete roll control over the aircraft while hovering, said Tennant.

Four FADEC systems
In its F-35B partnerships, Rolls-Royce is responsible for the lift fan and its associated drive shafts, gearbox and clutch, as well as the swivel duct and the roll post ducts. In the F135-equipped F-35B, Pratt & Whitney provides the engine itself, its stealth-optimized exhaust nozzle and, most importantly, the FADEC software.

Uniquely, the F-35 features not one but four FADEC systems -- two for the main engine, to ensure complete redundancy of operation, and, likewise, two for the lift-fan system.

"The software is a big piece of the technology that makes the STOVL work," said Tennant.

The FADEC software is so complex that it runs through a high-speed databus that P&W developed specifically for the F-35's propulsion system. This databus is linked by means of a firewire-like system to the high-speed databus developed by Lockheed Martin to control the aircraft's other systems.

[spazsinbad]

And from recent pilot experience here is some more (worth reading all of it):

Piloting the Joint Strike Fighter

"Testing of the Lockheed Martin F-35 Lightning II (joint strike fighter) is well underway. Ian McInnes catches up with Graham "GT" Tomlinson, BAE Systems' lead test pilot for the STOVL variant, to find out how it flies. Date: 26 May 2010

http://www.airforce-technology.com/feat ... ture85998/

"All STOVL aircraft encounter non-linear behaviour close to the ground, caused by hot air bouncing back up and interfering with aerodynamics and propulsion characteristics. I'm greatly encouraged that our experiences of this so far have been as good as we could have hoped; it is far more benign than in the Harrier family. It will undoubtedly remain an area of interest as we expand the wind envelopes for low speed take-offs and landings.
&
It also surprised me that the aircraft copes so well with the airflow disturbances created by the huge door above the lift fan, which generates destabilising airflow for the rudders and tails. The upside of the door is that it scoops flow into the lift fan intake and adds significant thrust. The downside is the non-linear flow over the rear of the aircraft at conventional speeds where we convert from a conventional aircraft into a STOVL aircraft. The compromise seems to have been made just about right, as we retain satisfactory control through the conversion process (opening the doors and spinning up the lift fan). This will be another area of interest as we expand the
conversion window from our initial heart-of-the envelope speeds.
&
It is when you sit back afterwards that you realise what fun it is, how lucky we are as individuals to be involved at this early stage of testing and how the UK's heritage of STOVL aircraft has propelled us to the forefront of testing of this latest incarnation."

[bjr1028]

bjr1028, nevertheless the ski jump trials were done and information gained.

Before the era of precision guided weapons, either a salvo of dumb bombs rippled at 45 degrees to runway heading to ensure hits or specialised semi precise 'concrete dibber' weapons were used against runways for 'runway denial'. Sure in todays world precision guided weapons make targeting a runway obsolete perhaps.

[EDIT] Always useful to deny runways (and not just one) to enemy aircraft airborne - then where do they go - even if they can take off with a ski jump. Aaahhh this is where carrier aviation is most useful and of course let us not forget STOVL unless the conventional aircraft can not only take off from a ski jump from a damaged/unusable runway but also land back on the ski jump in reverse. Geez I'd like to see that.

Runway denial isn't very effective. Repairing the runways are too easy.

[spazsinbad]

bjr1028, I'm not interested in land base use of ski jumps but shipboard use. Without actually getting the USN to install a ski jump on a ship the only way to test them in the US to date has been land based. And they are effective as illustrated.

[spazsinbad]

Quote about 'short takeoff performance' fully combat loaded (but no mention of wind strength or ambient temperature which always have an effect on takeoff performance for any aircraft): "Tomlinson said that a fully combat loaded F-35B will take-off from a small unimproved airstrip in less than 1200ft." This is where point a ship into wind to get a good WOD helps heaps.

http://www.examiner.com/x-5411-Military ... st-fighter

[spazsinbad]

X-35B Mission X pilot (then) Major Tomassetti describes a short takeoff:

http://www.airspacemag.com/military-avi ... ion_X.html

"Once in position for takeoff I moved the Thrust Vector Lever (TVL) back about an inch, initiating the process of converting the aircraft from CTOL mode to STOVL. Behind the cockpit, four sets of doors were opening. This would allow air to flow through the lift fan and enable the vectoring rear nozzle to move through its full range of travel. While the doors were opening, the clutch was engaging, transferring power from the engine to the lift fan. The only noticeable change in the cockpit was an increase in noise as the lift fan spooled up."
&
"...at 80 knots, after only 200 feet, I vectored the thrust to 60 degrees and the aircraft leapt off the ground. I completed the post-takeoff checks, climbed through 5,000 feet, and converted the aircraft from STOVL mode back to CTOL ..."

[spazsinbad]

3rd video in an illustrated list (below main screen on page - OR - click on the 3rd text link on right ) shows an:
F-35B Short Take Off test:

http://article.wn.com/view/2010/06/15/F ... h_fighter/

"F-35B JSF Short Take­off Test" 0:35 seconds. Note rotated rear nozzle from beginning.

[spazsinbad]

Lockheed Martin rebuts F-35 critics on cost, progress By: Chris Pocock July 19, 2010

http://www.ainonline.com/news/single-ne ... ess-25359/

"...The first F-35B arrived last November, and by early January began testing of the conversion from wingborne to jetborne flight, following rigorous testing over a hover pit.

“We built down in small steps,” said Tomlinson, “starting with increasingly slower landings before progressing to vertical landings and short takeoffs.” The first fully vertical landing was made on March 18.

When asked how the F-35B compared to the Harrier in terms of ease of takeoff/landing, Tomlinson replied: “It’s chalk and cheese–and so it should be! This is a single-button operation with no special controls–much easier than the Harrier. For short takeoffs you just power up; the system takes care of everything else. On the ski-jump, for instance, the system detects the change in deck angle and doesn’t apply any rotation as it would on a flat deck.”

The recent arrival of F-35 BF-4 is a milestone, as this is the first aircraft equipped with a mission system, including the APG-81 AESA radar. The first three F-35Bs are aerodynamic/aircraft systems testbeds, with BF-1 bearing the brunt of STOVL trials, and BF-2 handling speed/ load testing. It was this aircraft that achieved Mach 1.07 last June.

Testing has revealed a few minor problems. Some work was necessary to “tweak” the tail controls for optimum effect in the disturbed air caused by raising the forward lift fan door. Generally the team is ahead of schedule, and completed 155 flights against a planned 107 last year.

Trials with a ski-jump are expected to begin by the end of next year, the ramp having been built in the UK for installation at Patuxent River. This will be a crucial step for the F-35Bs destined for the Royal Navy. Perhaps more challenging from a testing standpoint will be the trials of short takeoffs from the flat-deck “Wasp” class LHDs from which the F-35B will operate in U.S. Marine Corps service.–David Donald"

[spazsinbad]

FWIW GoogleErf has an updated overhead of NAS Patuxent River dated 20 Oct 2013 so I'll post a few pics for posterierority. CLICK on the thumbnails pics to see more detailed BIG pic..... SCALE on Pics also....

SKI JUMP YELLOW LINE DISTANCE is 908 feet from what I guess is the start after the Square with 'H' on it from right to left.

[spazsinbad]

Allowing for being able to line up under own power etc. the approx. take off distance from stern to end of ski jump will be 850 feet on CVF. BIG PIC: http://farm8.staticflickr.com/7369/9929 ... 94ae_o.png

[spazsinbad]

This LM promo fillum from recent Singapore Air Show shows the centrefield at PAXriver with an F-35B nose. Screenshot to follow....

Aeronautics in the Asia-Pacific Region 13 Feb 2014

"Why is the Asia-Pacific region so important to Lockheed Martin? George Standridge, Vice President, Lockheed Martin Aeronautics Business Development, talks about aeronautic capabilities and partnerships locally and worldwide."

[spazsinbad]

Interesting factoid about hi speed data buses for the FADECs about midway up the page.

"...The [F-35B] FADEC software is so complex that it runs through a high-speed databus that P&W developed specifically for the F-35's propulsion system. This databus is linked by means of a firewire-like system to the high-speed databus developed by Lockheed Martin to control the aircraft's other systems."

Anyway here is something relevant to JUMPdeSKIs from CVFs anyways - from a chap who should know - but may not if he is a CRAB!

And for something completely different - another factoid about the thread topic title question?

ETS winter 2012_13 LIGHTNING STRIKES

"...Onboard the Queen Elizabeth aircraft carriers, the aircraft would take off at its maximum weight of nearly 27 tonnes using a UK-developed ski-jump, and land either vertically or using the novel UK-developed Short Rolling Vertical Landing [SRVL) technique. This would enable the jet to land at a much higher weight than is possible in a purely vertical Landing.

[2204.62lbs = 1 tonne | 59,535lbs = 27 tonnes] (F-35B is in the 60K weight class)

Wing Commander Hackett explained: "SRVL is under development for the carriers. but it means the aircraft would fly in at around 60 to 70 mph and then brake to a stop on the deck, without the need for any costly arrester gear. It will be able to land up to 1.8 tonnes (4,000lbs [3968.32072 pounds]) heavier than would otherwise be possible, meaning unexpended weapons can be brought back to the ship."

SOURCE: http://content.yudu.com/A219ee/ETSWin12 ... ces/20.htm

[zerion]

Pax readies F-35B ski jump

http://www.dcmilitary.com/article/20140 ... i-launches

By Sarah Ehman

Atlantic Test Ranges Business Communications

Thanks to a partnership between the Atlantic Test Ranges (ATR) and the F-35 Lightning II Pax River Integrated Test Force (ITF), the Joint Strike Fighter took one step closer this Spring to making its debut on international ships.

The Pax River ITF partnered with ATR’s Geomatics and Metrology team to perform a high fidelity survey of the shore-based ski jump at Naval Air Station Patuxent River’s center airfield. The survey is a prerequisite to future F-35B flight testing by the Pax River ITF, the United Kingdom and Italy.

The shore-based ski jump at centerfield was built in the United Kingdom, divided into sections, then transported and reassembled at Pax River.

“Launching off our Pax ski-jump paves the way to F-35Bs launching off our international partner ships that feature ski-jumps,” said Bob Nantz, the Pax River F-35 ITF external environment and performance lead. “The significance of the Pax ski-jump shape is connected to aircraft loads and performance modeling. Ideally, the loads will never limit the launch weight or speed, thus allowing the maximum performance benefit.”

Together, Fred Hancock, Sung Han and Warren Kerr, each with ATR Geomatics and Metrology, employed electronic differential leveling and total station measurement techniques to check for drift in construction and determine precise deviations in both vertical and horizontal components of the ramp.

“We captured hundreds of elevation readings, determining the relative vertical difference between points,” Hancock said. “We also obtained precise angular distance measurements to determine if the ramp edges were parallel to the center line. This helped us to know whether the ramp was at all skewed.”

Hancock noted that the team achieved readings accurate to within one millimeter — approximately the thickness of a credit card.

“The razor-sharp accuracy of the Geomatics team’s survey is a key part of the process leading to future ski-jump operations at sea,” Nantz said.