Lockheed: Many F-35B landings won’t be vertical

Discuss the F-35 Lightning II
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quicksilver

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Unread post11 Jun 2011, 00:29

spazsinbad wrote:Thanks for further explanation quicksilver, apparently the SHAR had better waveoff performance in this situation. It will be good to be able to have a similar level of knowledge about the F-35B one day.


Actually not. Same performance factors that give one more VLBB, also enhance wave-off margin. AV-8B was/is considerably better than SHAR. Even at just KPP performance, F-35B is better than AV-8B.
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Unread post11 Jun 2011, 00:43

quicksilver, yes I understand about better VLBB for F-35B compared to Harriers. The apparent lack of VLBB in hot windless conditions for the SHAR killed it eventually. I don't really claim to know much about Harriers in general, especially the USMC versions and operating conditions as explained in the very long thread. I'd like to know more about the F-35B as this is the F-35 forum. I'm always glad to gain more general knowledge though, so I'm not complaining. This is why I am here. :D
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Unread post11 Jun 2011, 03:17

Well, it's clear that general knowledge about STOVL matters is limited outside those who might have flown them, built them, or studied them. Thus, the Harrier discussion. Cutting to the chase --

For a given landing configuration and load, a STOVL jet (take your pick) in semi-jetborne or jetborne flight is going to have a higher fuel burn rate than that same STOVL jet flying conventionally. Why? Because you're running the engine at a higher power setting to create lift by means of propulsion. Thus, claims that a STOVL jet burns less fuel landing vertically is false. F-35B is no different in that regard.

AIUI, the performance margins assumed for F-35B STOVL max performance calculations are the same as Harrier. However, as is the norm for flight test of any aircraft, additional margin might be assumed/required for a given test point or block of test points.
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Unread post12 Jun 2011, 04:22

quicksilver wrote:Well, it's clear that general knowledge about STOVL matters is limited outside those who might have flown them, built them, or studied them. Thus, the Harrier discussion. Cutting to the chase --

For a given landing configuration and load, a STOVL jet (take your pick) in semi-jetborne or jetborne flight is going to have a higher fuel burn rate than that same STOVL jet flying conventionally. Why? Because you're running the engine at a higher power setting to create lift by means of propulsion. Thus, claims that a STOVL jet burns less fuel landing vertically is false. F-35B is no different in that regard.

AIUI, the performance margins assumed for F-35B STOVL max performance calculations are the same as Harrier. However, as is the norm for flight test of any aircraft, additional margin might be assumed/required for a given test point or block of test points.


Here's the key: The relevant period to calculate is from the point the STOVL starts its conversion to shutdown. If a STOVL is brought in using conventional procedures (which may be the norm for peacetime use) it's going to have a higher fuel burn than if it takes advantage of its capabilities. There may be reasons to do this in peacetime. What remains, though is that the STOVL can afford to come back wth a lot less fuel than the CTOL and still operate safely. Aboard ship, you want your fighter/attack to arrive overhead the ship with 25% fuel still aboard to allow for pattern, waveoffs, bolters and foul deck. Those aren't factors for STOVL.

Another interesting calculation is the amount the two types use on takeoff, from the ramp to the point where the STOVL would be fully wingborne.

Something else that may also figure in is that although it'll be easier and probably safer to operate, the F-35B, with its more complex operation may not have all the flexibility of the Harrier in this mode.
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Unread post12 Jun 2011, 04:28

aaam said: "Something else that may also figure in is that although it'll be easier and probably safer to operate, the F-35B, with its more complex operation may not have all the flexibility of the Harrier in this mode." Do you mean in takeoff mode or VL or...?

Seems to me that the F-35B beats the Harrier in every way in general terms. What flexibility does the F-35B lack compared to the Harrier? Thanks.
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Unread post12 Jun 2011, 04:47

spazsinbad wrote:aaam said: "Something else that may also figure in is that although it'll be easier and probably safer to operate, the F-35B, with its more complex operation may not have all the flexibility of the Harrier in this mode." Do you mean in takeoff mode or VL or...?

Seems to me that the F-35B beats the Harrier in every way in general terms. What flexibility does the F-35B lack compared to the Harrier? Thanks.


VIFFing?
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Unread post12 Jun 2011, 05:35

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Unread post12 Jun 2011, 10:30

spazsinbad wrote:PoPcorn: This? :D http://www.youtube.com/watch?v=khskxgRRFPY


What the.. :shock:

:D :D :D
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Unread post12 Jun 2011, 17:57

popcorn wrote:
spazsinbad wrote:aaam said: "Something else that may also figure in is that although it'll be easier and probably safer to operate, the F-35B, with its more complex operation may not have all the flexibility of the Harrier in this mode." Do you mean in takeoff mode or VL or...?

Seems to me that the F-35B beats the Harrier in every way in general terms. What flexibility does the F-35B lack compared to the Harrier? Thanks.


VIFFing?


I read about that back in the day but then heard they quite using it for one reason or another. Anybody have further info on that?
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Unread post12 Jun 2011, 18:28

A (very) last ditch way to force an overshoot vectoring the nozzles as a brake I understand and lose all your energy - not generally a good idea.

Im sure Nigel Ward (FAA) also found another low speed thing the Harrier could do due to the air from the exhausts causing lift under the stabs.

Today I'm really not sure either have any practical application in a fight tbh or even if they had back in 82.
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Unread post13 Jun 2011, 00:24

popcorn wrote:
spazsinbad wrote:aaam said: "Something else that may also figure in is that although it'll be easier and probably safer to operate, the F-35B, with its more complex operation may not have all the flexibility of the Harrier in this mode." Do you mean in takeoff mode or VL or...?

Seems to me that the F-35B beats the Harrier in every way in general terms. What flexibility does the F-35B lack compared to the Harrier? Thanks.


VIFFing?


Operationally, the F-35B's capabilities definitely exceed that of the Harrier's. I was referring strictly to the engine-borne takeoff/landing phases. ON the F-35B the process is fully automated, more complex and you could almost think of the engine-borne mode as airborne landing gear. A STO takeoff in the AV-8 is nozzles aft, full power, when accelerated to the precomputed speed, nozzles to the intermediate stop selected, and you're airborne. Landing is slow to transition speed, nozzles down or slightly forward, power as needed until touchdown. F-35 is not that simple, and I'm not sure they'll have the ability to do all the Harrier can during those phases. However, that doesn't mean it won't work. Besides, this portion of a mission is a small percentage of the total flight.

VIFFing kind of faded away partly for the reasons that flighthawk mentioned, but also because it was overcome by technology. VIFF made it virtually impossible to get a gun solution on a Harrier, but in the age of modern missiles, who cared? You couldn't dodge them with VIFF, and once you did it you were low on energy. AFAIK, VIFF was not used in the Falklands War.
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Unread post13 Jun 2011, 01:28

aaam I don't follow your reasoning here why the F-35B is deficient, perhaps we need to be patient to see what it can do. "... [Harrier] Landing is slow to transition speed, nozzles down or slightly forward, power as needed until touchdown. F-35 is not that simple, and I'm not sure they'll have the ability to do all the Harrier can during those phases. However, that doesn't mean it won't work...."

A former SHAR pilot has told me that yes VIFFing is useless as described - especially when the actual effect is known by opponent but (when unknown by Argentinians) it was talked up during the Falklands War as a propaganda ploy about the 'black art of VIFFing possesed by the SHAR'.
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Unread post13 Jun 2011, 17:59

When the opposing pilot knows to look for VIFF, it just robs the Harrier of its momentum and makes it an easy target when the other plane comes back around.
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Unread post17 Jun 2011, 03:35

aaam said -- "Here's the key: The relevant period to calculate is from the point the STOVL starts its conversion to shutdown. If a STOVL is brought in using conventional procedures (which may be the norm for peacetime use) it's going to have a higher fuel burn than if it takes advantage of its capabilities."

I am working really hard to keep this respectful but that statement is 180 degrees away from the reality. I have no idea where you get that (goofy) idea but it is utterly untrue. The slower a STOVL jet flies, the more engine lift it has to create, and thereby it burns more fuel in the process. The fact that it has a much higher probability of landing once the intended landing area is in sight (boarding rates very near 1.0) certainly allows for far less recovery fuel. However, it does not diminish the fact that slower approach and landing speed equates to higher fuel burn rates for a given period of recovery. The offsetting benefit, of course, is that the probability of first pass recovery is far higher than conventional aircraft.
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Unread post17 Jun 2011, 05:35

The NAVY Jul-Sept 2008 Vol.70 No.3 - The Magazine of the Navy League of Australia —
How to Fly a Sea Harrier Part 3 – The Landing by Mark Boast [ex-A4G Pilot]
“...The aim of the Rolling Vertical Landing was to achieve a minimum distance ground run consistent with avoiding the possibility of foreign objext damage to the engine and aircraft inherent in the pure Vertical Landing. The desired fifty knot groundspeed (add the headwind component to get actual airspeed) was achieved by moving the nozzles slightly aft of the Hover Stop position. The remaining small amount of wing lift only added five hundred pounds to the “bring back” or fuel/stores weight of the Sea Harrier and therefore had limited usefulness. The much larger wing and flap on the later Harrier II (AV-8B)/GR-7/9 exploited this area and quite significant “bring back” advantages could be gained. The STOVL JSF programme is also looking at utilizing this same technique for landing on large carrier decks in order to exploit the “bring back” increase to cater for expensive weapons and fuel loads that may be required when working with larger air groups.

The Creeping Vertical Landing was a very slow forward speed landing used in locations where a vertical landing was required, but FOD damage likely. By moving forward the aircraft would be clear of the majority of ground debris which would be blown behind the engine intakes. This technique was not required on FOD free flight decks and therefore was not employed on the small UK carriers where space usually precluded landing with any forward speed.

The pure Vertical Landing was set up by entering a stabilised hover over the touchdown point on land, or abeam the carrier landing spot (there were a number to choose from) at sea. The nozzles were left in the Hover Stop position for manoeuvring in the hover and the aircraft was either tilted in the pitch and roll by the control stick, or rotated in yaw by use of the rudder pedals. To assist the pilot there were low authority autostabilisers for pitch and roll and a yaw stabiliser that primarily sought to avoid dangerous sideslip. A rudder pedal shaker also warned the pilot of high sideslip rates. A very useful device in the Sea Harrier that was not incorporated in the other Harriers was the “nozzle nudge” facility that used the speed brake switch on top of the throttle to select the nozzles either ten degrees forward or aft. This useful tool enabled the pilot to move forwards or backwards without having to tilt the aircraft in the hover excessively and therefore complicate the situational awareness challenge. It also helped when matching the ship’s speed when hovering alongside.

A rate of descent was established by a slight reduction of thrust and a constant descent rate was maintained through to touchdown. At touchdown (and not before!) idle power was rapidly selected to avoid “bouncing” on the efflux that rapidly built up between the aircraft and the ground or deck surface, and the nozzles selected aft to avoid heating up the surface and [with?] engine exhaust. Whilst this technique sounds simple on paper, in practice it was moderately difficult due to the piloting tasks and situational awareness challenge of flying a pure vertical descent. Unlike a helicopter which is very responsive to control inputs in the hover, the Harrier has a sluggish response due to its relatively high mass. The pilot also has very little downward vision and therefore has to rely on both fore/aft and lateral references that can be some distance from the landing point. For this reason it was often said by some that it was easier to land on the ship due to the easily seen visual references. On a calm day with no ship movement and no one else on the deck — maybe! But the very close proximity of superstructure, other aircraft, and above all, people, never induced an air of languor in my experience.

So why have I made so much about situational awareness? As in all naval aviation, success comes down to the ability to conduct embarked flying operations not only in good conditions, but also in poor weather and/or at night. The transition from instruments to a visual hover alongside a ship is very different from the transition for a conventional landing ashore. Whilst the ship itself provides potentially excellent visual cues of direction (ship centreline) and height (masts and superstructure), the sea conditions often cause the ship to heave, roll, and sometimes weave. As the Harrier’s hovering characteristic was determined by its mass, it was very unwise to “chase” the ships motion. As the thrust requirements were already very high, any unnecessary bleeding of compressor air to feed the reaction control system for control inputs, or extra demands by the throttle to climb and descend around a moving hover point, would use up the remaining thrust available. This could mean only one thing!

The answer was straightforward and largely relied on the Sea Harrier’s very effective Head Up Display and reliable inertial attitude system. Pilots were taught to establish a stable hover at approximately 90ft (forty to fifty feet above deck height) above the water alongside the landing spot, transition laterally whilst maintaining altitude, stabilise in the hover about forty feet above the landing spot, and then descend vertically. No external commands were involved with the pilot making all decisions. Some coaching or advice was usually available from a duty pilot in the Flying Control position but usually reserved for initial deck qualifications and emergencies. An abbreviated and informal flow of “patter” was used by an experienced pilot in Flying Control to assist those making night approaches as the ships visual cues for establishing a visual hover didn’t appear until quite late in the approach. Affirmation of a good final approach through closure rate (“fast, slow, looking good”), height above the water (“high, low, looking good”), and deck issues such as movement and landing spot availability were the most frequented topics.

The Sea Harrier always flew a common visual and instrument straight in approach at night despite various attempts to devise a safe night visual circuit. The critical piloting task was to judge the point at which to commence the final deceleration to the hover. Too early and the aircraft could be left too far behind the ship with insufficient visual cues to maintain a safe hover. Too late and the aircraft would be ahead of the ship with no visual reference whatsoever! This latter error was jocularly termed an “anchor inspect-ion”. In real life it was hardly jocular and if sever required a nerve wracking transition back to wing-borne flight for a very abbreviat-ed second approach with minimum fuel. The final Hover Stop selection point was hard to reliably achieve from the curving/des-cending final approach of a visual circuit, so the best technique was to come straight in and take advantage of the relatively stable aircraft parameters to exploit information from the aircraft’s own radar and range calls from the ships approach radar controller.

To provide a solution to night and poor weather approaches, a unique approach system was installed on aircraft and carriers. Microwave Assisted Digital Guidance Equipment, or MADGE as it was called by its friendly acronym, was a digital range and azimuth finding system based on a ship based active antenna for aircraft interrogation and a passive angle measuring antenna. Aircraft were equipped with complementary avionics including backup indicators on the conventional secondary flight instruments. Developed originally as a system for helicopter approaches in poor weather and night to tactical landing sites in the land environ-ment, this system provided very accurate ILS like information including a very accurate range for deceleration cues. Additional benefits were the exchange of aircraft information such as Call-Sign, fuel weight, angle of attack and altitude to the Flying Control position. As far as most of us pilots were concerned, the other big benefit was that only the aircraft carrier had this system....”

The 'Fixed Nozzle Slow Landing' and the 'Fixed Throttle Slow Landing' for the SHAR are described in the attached PDF also. I'll look to see what else is in the USMC NATOPS about these landings.
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