F-35 Cancelled, then what ?

[Courtney Mil]

The whole "creeping and rolling" thing needs to be understood for what it is. It's this simple, the jet can do VL, BUT it can do damage to surfaces that aren't prepared to accept it. This is important as it's another piece of F-35 capability creep (in reverse). "Yes you can land vertically as long as you don't hang around over the same piece of landing surface too long, so move around a bit."

[John Farley]

LO

I know you realise this but others may not.

There are two basic types of landing:
1 where you can hover
2 where you are too heavy to hover

With 1 you may not necessarily choose to land vertically. If you can hover but you choose to move forward for the touchdown then you are doing a rolling vertical landing. An example would be when you do not wish to make the surface hot. We must always remember that heating effects depend on both temperature and residence time. The pilot has no control over the temp element but he has total control over the residence time. Even walking pace forwards makes the residence time negligible. (I am not talking about blast effects just temp ones). Of course residence time can be high if people insist on landing on a specific spot to show how good they are or because (say) the deck is painted that way. Another reason for having forward speed is if the surface is loose and will blow about. In this case you need to move forward sufficiently fast that the bow wave of debris (be it stones, earth, water, snow or sand) stays just behind the intake. With the Harrier family this required 50 kt ground speed in still air. Clearly a good head wind helps to reduce this speed. I don’t know what it is for the B but it will be determined by the fan efflux since we already know that the fan efflux prevents the hot stuff from spreading forward.

With 2 you are doing what is properly called a slow landing. With the Harrier I wing you needed some 90kt before you carried much extra weight in. With the Harrier II wing 50kt – 60kt really helped.

The B produces real lift at low speeds hence the business of "shipboard rolling vertical landing". Which if you strip the politics out of it is of course no such thing - it is just a very slow slow landing.

[Engines]

Lone,

We can actually both be right here - there was certainly a great deal of political attractiveness in 'Joint' solutions' (the F-22 was originally pushed as joint programme, with Lockheed claiming it could operate off a carrier!), which the programme architects certainly wanted to exploit. The DoD sources I knew (fairly highly placed) were ready to share with the UK the very large amount of technical study they had done to indicate that a single engined single seat solution was practical. I'd suggest the two came together to produce the programme.

LO, again I'd like to suggest that we may both be right. The F-35 has a spec sortie to be able to deploy to a 1500 foot bare strip, shut down and wait orders to launch for a sortie, do the job and then recover to the ship. You might think that's a rubbish scenario - hey, we can all have opinions, that's a good thing. But the fact is that you need just 1500 feet to 'operate' an F-35B in that particular scenario. More if you use another one.

I'm glad you're interested in the improvised-base ops demos - so am I. One thing to note, that builds on JF's excellent post. This aircraft has a level of stability and control in the hover and transition that is a whole generation on from the Harrier. There are a variety of potential landing and takeoff modes that the test team are working through, with the able assistance of some excellent Brit TPs. I'm sure that the USMC will find ways to exploit them.

On the prepared surfaces stuff - I had a great time managing a whole set of surface erosion trials at Warton. These were far beyond anything ever attempted for Harrier, and delivered a ton of data to the programme. happy to give more info over PMs if anyone's interested.

Best Regards as ever to those fine STOVL folk

Engines

[John Farley]

Tha advantages of landing from a hover

In my experience the interests of the squadron pilot are not always given the priority they deserve when it comes to procuring the aircraft they will use to fight wars on our behalf. I would like to discusses some piloting factors during takeoff and landing that I feel should be taken into account when choosing a combat aircraft. In particular I will try to explain the limited potential of Slow Landing to provide safety and operating site flexibility. In concentrating on these piloting issues, I fully accept no account has been taken of such matters as inter-service rivalry, company self-interest, industrial partnerships or politics. While history shows there are good reasons for supposing that such non-piloting matters are likely to seriously effect the acquisition of an aircraft, surely that is no argument why all concerned should not clearly appreciate what is at stake for the pilots if such considerations are allowed to unduly influence matters

A case can be made that future landing needs would be satisfied by providing a conventional or slow landing capability on land or an arrested landing at sea. There are piloting reasons why this view should be questioned. To clarify this, the advantages that result from being able to hover before landing are listed below. The reasoning behind these points is explained later. It is important to note that the term "hover" has a specific meaning here. It refers to a hover in free air outside ground effect. It should not be taken as necessarily implying that a vertical landing or vertical takeoff capability also exists, or indeed is needed for the hover under discussion to be worthwhile. Following such a hover, the pilot may choose to step forward into a ‘rolling vertical’ landing at low forward speed to avoid hot gas recirculation, foreign object damage (FOD) or damaging the surface with the exhaust efflux.

An aircraft that can hover offers the following advantages:

(a) Operating site choices are increased on land and at sea increasing operational flexibility and effectiveness.

(b) Peacetime landings provide valid training in the event that restricted site operations become necessary in wartime.

(c) Weather is less of a problem on the approach.

(d) The landing surface can have standing water, ice or snow that would preclude a safe short landing.

(e) A landing can be made with aircraft defects that would require ejection in the absence of a hover capability.

(f) The landing is easier for the pilot.

An examination of the reasons underlying these assertions involves the following topics:

Pilot workload
Size of operating site
Weather effects
Training
Aircraft defects and combat damage
Operational flexibility
Safety

I am happy to put these up (perhaps one at a time as I dunno wot a max length a post should be?)

[GreenKnight121]

Originally Posted by Engines

And the F-35B's replacing the AV-8Bs first, as far as I understand the programme.

That USED to be the plan, but thanks to the gift the UK gave us* (USMC) we can now keep the AV-8B around for far longer than originally planned.

Thus, the USMC is now replacing its Hornets first.

http://www.pprune.org/military-aircr...go-2030-a.html
US Marine Corps studying Harrier enhancements
USMC hopes new method for tracking fatigue life will help extend Harrier to 2030

Originally Posted by LowObservable

Also, while F-35B is sold as maintaining the Marines' sea-based air and their ability to operate off any 3,000 foot stretch of runway that has a 100-foot-square slab of continuously reinforced refractory concrete next to it, it's actually replacing the F/A-18 Classics first.

And for LO... what in this in any changes or invalidates the plan for the F-35B to maintain the USMC/s ability to operate off LHA/LHDs and short runways?

To me, this actually means that it will enable the USMC to strengthen that capability faster than originally planned, by getting rid of the strike fighters that couldn't do those things first!



* 72 complete Harrier II aircraft with more remaining airframe hours than the average USMC Harrier II, plus the RAF's entire stock of spares, for a bargain-basement price.

[John Farley]

PILOT WORKLOAD

A slow landing differs from a conventional landing in that ground roll is greatly reduced however important piloting problems remain so long as the aircraft cannot hover. During the approach to a slow landing, the following constraints apply:

(a) A minimum speed set by limits of lift or control.

(b) A maximum speed set by stopping ability and the strip remaining at touchdown.

(c) The approach path angle must be within narrow limits.

(d) The track over the ground must be accurately aligned with the strip in the final stages or the aircraft will leave the side of the strip shortly after touchdown.

(d) In order to avoid an undershoot or an overrun, very little height variation is allowable as the strip is reached.

Considerable pilot effort and skill can be necessary to fly within these constraints. This workload increases rapidly as the landing strip dimensions are reduced towards those needed by the aircraft when it is flown perfectly.

We all know that an inability to stop, whether on foot or in any vehicle, brings with it a fundamental need to plan ahead. In the case of an aircraft, any minimum flying speed limit requires the provision of overshoot and diversion procedures, together with the fuel reserves to carry them out. These procedures bring air traffic control problems and lead to repositioning sorties and logistic complications.

Because of these issues, pressure on the pilot is further increased at the very time that he is expected to perform at peak skill levels leading to the possibility of reduced accuracy and increased risk of failure. Even worse, the pilot may continue towards an inevitable accident because, under this pressure, he subconsciously rejects all options other than the approach in progress, despite the fact that the approach is beyond his capabilities or those of his aircraft.

Given a hover capability, these demanding requirements do not apply and the pilot just needs to establish a hover with the landing spot in view. This fundamental change reduces his workload for several reasons:

(a) The approach speed can be varied to suit external factors such as poor visibility or the need to fit in with other aircraft in the air or on the ground.

(b) Any descent path angle can be used so long as it is above local obstacles.

(c) The direction of the approach is not linked to the landing.

(d) Aircraft height at the end of the approach needs only to be above any obstacles and below any cloud.

(e) Because it is easy to adjust position over the surface once in the hover, acceptable position limits for the end of the approach can be measured in hundreds of metres to the left, right, forwards or backwards.

It is important to note that any trial results aimed at comparing pilot workload during different types of landing will only be valid if the landing sites chosen are equally limiting. Vertical landings on the small aft platform of a ship or in an urban car park may only be properly compared with slow or conventional landings made on a strip with a bomb crater or other genuine limit at each end. It is misleading to rely on measured short landing data obtained on a runway that is much wider and longer than aircraft performance alone would dictate. As discussed later, peacetime flying from an oversize runway is also inadequate training for any wartime restricted strip case.

[John Farley]

SIZE OF OPERATING SITE

Since the area required for a landing from the hover is small, it is clearly easier to provide or find suitable locations for this as opposed to a short landing strip. However, it is sometimes suggested that, because a short takeoff strip has to be provided for a VSTOL aircraft to take off at max weight, then the existence of this takeoff strip means that it can be used for short landing and hence STOL is all that is necessary. This view takes no account of several reasons why an STO, even at maximum weight, can be safely carried out from a much shorter and narrower strip than is acceptable for a slow landing even at a lighter weight. First consider factors affecting strip length:

(a) An aircraft can be positioned for takeoff at the very beginning of the strip and the subsequent ground roll required to unstick can be very accurately predicted (as a function of weight and thrust), making it acceptable to plan to unstick close to the end of the strip. On the other hand, some distance will be needed for a landing at both ends of the strip to allow for scatter in touchdown position and stopping performance.

(b) The acceleration available for takeoff may well approach 1g and be unaffected by a wet or icy surface but it is difficult to design for a similar level of deceleration throughout the ground roll when landing, even in good conditions. Given slippery conditions, wheel braking effects can all but vanish.

(c) The use of full power on takeoff maximises the lift effect of thrust, reducing the speed needed to fly at a given weight. However, in order to have a go around capability when landing, some power margin must remain at touchdown. This results in a reduction of the lift element from thrust on a slow approach, compared to that available during a STO. Replacing this powered lift with V squared aerodynamic lift can need a surprisingly large increase in V at the lower approach speeds of short landing aircraft, countering the advantage to be expected from reduced weight at the end of the sortie.

A narrower strip is acceptable for takeoff compared to landing because:

(a) An aircraft can be lined up very accurately before a takeoff, whereas there is a need to allow for lateral scatter when landing.

(b) Direction can be controlled relatively easily during the slower first part of the takeoff ground run and then the quality of aerodynamic directional control improves as speed increases. The opposite applies when landing and the use of brakes, aerodynamic devices and reverse thrust all tend to degrade directional control and stability. This stems from the use of large forces to slow down quickly on the ground and so quite minor asymmetries in those forces can cause the aircraft to veer. Experience shows that such asymmetries can also result from crosswinds interacting with the complex flow patterns around an aircraft using high power or aerodynamic devices for deceleration.

Provision must be made at the end of a strip used for landing for the aircraft to turn round and backtrack or clear the strip at the side, whereas places for landing from the hover can be provided some way away from the short takeoff strip, thus easing flow control on the ground through the land/hide, replenish/takeoff sequence. When the same strip has to be used for both takeoff and landing, a larger and more complicated site layout becomes necessary. Even in the orderly peacetime world of civil aircraft operations, the advantages and smooth traffic flows that result from using different runways for takeoff and landing are apparent for all to see.

[Squirrel 41]

Mr Farley -

Fascinating, very many thanks.

S41

[John Farley]

My pleaure Squirrel 41

A couple more sets of reasons...

WEATHER EFFECTS

In the absence of full autoland, pilots need time to make final visual corrections to an instrument approach before landing. The length of time taken to carry out these corrections can be shown to depend on the size of the approach error, the manoeuvrability of the aircraft, pilot skill, ground speed, crosswind, turbulence and the accuracy of touchdown required. Provision of this time interacts through any minimum speed of the approach to determine the lower limits for cloud base and visibility. The greater the time needed then the higher the cloud base and the better the visibility must be.

Given a hover capability, speed on the approach can be reduced to suit the visibility, avoiding a minimum visibility cut off below which a landing will not be possible. Similar relaxations apply to cloud base considerations with the additional advantage that a hovering aircraft need not be constrained to a shallow approach path angle but can descend more steeply once it has passed obstructions in the chosen approach sector. Indeed the approach sector may be deliberately chosen to avoid obstacles as the aircraft is not constrained to line up the approach with any ground roll.

Crosswind is of little concern to an aircraft that can hover because it can be yawed around in the hover to point into wind for the actual touchdown. If a rolling touchdown is required, then the optimum starting position can be set up accurately while in the hover, before stepping forward for the landing. This avoids approach errors caused by crosswind being carried forward into the ground roll on a narrow strip.

Turbulence has adverse effects on the stability and control of all aircraft. Because the extent of these effects depends on the ratio of the local gust velocity and the aircraft lifting system velocity, the lower the lifting velocity the greater the distortion of flow around the aircraft for a given gust. In the case of a jet lift aircraft in the hover, the lifting system velocity is that of the jet efflux. Since this velocity is very high when compared to gust velocities, the hovering jet lift aircraft hardly reacts at all to turbulence levels that seriously degrade the control of other fixed wing aircraft and helicopters.

Water, snow, ice or sand contamination of the landing surface causes fewer problems for aircraft that can hover because of the slower nature of their touchdowns. In addition, such aircraft do not have to rely on surface friction for control of direction and speed on the ground but have reaction controls and reverse thrust to back up brakes and nosewheel steering. In many cases jet lift aircraft can use their own efflux to clean an area before takeoff or landing.

An example of poor weather capability if you can hover was provided during the Falklands war when Sea Harriers crawled up the wake of their ship in poor visibility and very low cloud base just by following flares thrown onto the water, indicating the way to the deck (like a motorist in fog lucky enough to have cats eyes leading to his garage). In this case, the only flight path limits that had to be observed were to remain above the sea, below the cloud and clear of obstacles. Since the ship was an obstacle, the top of which was in cloud, the landing pilots kept to port of the flare centreline and corrected to the landing spot once in the hover alongside the deck. Put even some of these circumstances, let alone the radio silence needed because of the submarine threat, into the recovery of conventionally arrested naval aircraft and it becomes likely that some, or even all, would have been lost when operating non-diversion.

TRAINING

Because of the scatter in conventional landing performance (whether this scatter is caused by aircraft characteristics, pilot performance or ambient conditions is immaterial), operators only clear aircraft to land routinely on runways that are much wider and longer than perfect performance requires. An acceptable peacetime accident rate is quoted as the reason for this conservatism. Common sense in the face of reality would be another way of putting it. What price the landing accident rate for the Hawk and Tornado, the F-16 or the MiG-29 if the runway width and length normally available was only that needed with man, machine and the elements all on top form?

In some quarters (although not crew rooms), it is felt that things will be routinely achievable during war without constant practice in peacetime or that accidents would be the least of people’s worries. Put another way, attrition in war will only occur due to the additional element of enemy activity and that an unacceptable peacetime accident risk will not carry over to wartime.

In fact nothing could be further from the truth. If a procedure is unacceptable in peacetime due to the risk of accident and attrition, then in war it carries an even higher risk due to the extra pressures present during hostilities.

Because of the increased chance of an accident, there is no precedent in RAF or RN operations for conventional fast jet operation into limiting sized landing sites other than with the use of arrester gear or when the aircraft can hover. It is not clear what aspect of a short landing capability is going to change this in the future but, without such a change, where will be the peacetime training of the wartime case? Only a hover capability can permit this critical training.

[John Farley]

Last lot.

AIRCRAFT DEFECTS and COMBAT DAMAGE

A landing from the hover is tolerant of many defects that make a forward speed landing hazardous. Indeed, where the option exists, it is the landing of choice in the event of any malfunction or suspected problem with gear, brakes, steering, tyres and flaps. There have been several cases of wheels up vertical landings in Harriers with only cosmetic damage and none with any injury to the pilot. This fall out from a vertical landing capability becomes a significant force multiplier and cost saving in the real world of operating aircraft.

All systems associated with deceleration and steering of a short landing aircraft on the ground have to be fully serviceable to achieve minimum distances. The operation of some of these (e.g. lift dumpers, reverse thrust, parachutes, tyres and auto configuration changes dependent on weight on wheels switches) cannot be fully checked in flight before landing. The need to rely on such systems is one of the reasons why commanders will not approve routine training into performance limited sites unless the aircraft can hover.

In the limit, the pilot of a Harrier (not an F-35B of corse) only needs power, a variable nozzle angle and reaction controls to come to the hover.

Therefore, as soon as combat damage is suspected and, while remaining at cruise speed, the ability to land vertically can be confirmed by simply opening the throttle to check rpm response, momentarily pulling the nozzle lever back to check nozzle rotation and by moving the stick and rudder with the nozzles deflected to check reaction control response. As previously mentioned, flaps, airbrakes, gear, steering and tyres are not necessary in order to carry out a safe landing. No other type of fast jet can offer such damage tolerance and still land safely.

OPERATIONAL FLEXIBILITY

In addition to the operational flexibility that stems from being able to operate from smaller sites, the ability to hover provides further operational advantages.

Such an aircraft can, if required, operate in the VTOL mode. Whilst restricted in payload/radius of action, the VTO mode is always the ultimate in flexibility so far as dispersal, quick response time to airborne or even ease of moving aircraft between theatres are concerned, for example, Atlantic Conveyor in the Falklands.

These days Commanders rely on flight refuelling to give them operational capability in many roles from air defence to tactical strike. Few would disagree with this point of view which is why flight refuelling close to base following VTO provides a unique flexibility of operation.

Some proposals exist based on short landing aircraft being able to return to base and land between the craters. How will the length of these strips be ascertained by the pilots? How will they be defined? Will they land between the craters regardless of FOD from small debris or just on the clean areas? How will they be marked so that the pilots can identify them? Will they be able to taxi from the isolated strip to the hide/dispersal/hardened aircraft shelter (HAS) or will they be on the ground exposed and unable to taxi due to having no safe route?

A hovering capability eliminates all these problems as it allows an aircraft to land at the entrance of any serviceable HAS. When required it can also emerge from a HAS, VTO at once and deploy to the nearest available weapons or fuel if the HAS cannot be supplied for any reason. Only such an aircraft can take itself to supplies or engineering resources that have become trapped in the rear echelons. This sort of flexibility provides a force multiplier factor that is beyond value in times of disarray and tactical confusion.

SAFETY

Easier tasks tend to produce fewer mistakes so the reduced pilot workload when landing from the hover can be expected to result in fewer pilot error accidents during the landing phase, in both the lack of skill and error of judgement categories. However, if a landing accident should occur despite this, the situation is inherently safer than during a short landing because the energy remaining at touchdown is less. (The dents, scratches and lost pride associated with car accidents at city centre speeds compare favourably in most people’s minds with the aftermath of high speed motorway pile ups.)

Safety also reduces attrition and the exchange rate between attrition and operational cost effectiveness is a high one.

CONCLUSION

To land from the hover offers many piloting advantages compared to doing a short, arrested or conventional landing.

[MSOCS]

LO,

The 3000ft strip length is the minimum to operate the C-130 for sustained FOB/FARP CONOPS istr. Previous comments saying STOVL can use much less are entirely accurate; load-dependent of course!

[SpazSinbad]

ship was an obstacle :-)

Thanks 'John Farley' for your knowledgeable input and for this quote: "...Since the ship was an obstacle, the top of which was in cloud, the landing pilots kept to port of the flare centreline and corrected to the landing spot once in the hover alongside the deck...."

[Stuffy]

John Farley,

Interesting input. Unfortunately, this forum won't hear you dropping a brick into a tin. To wake up the snoozers.

Are you endorsing the F-35B as a good option and probably the best one ?

How does the F-35B's slow handling compare to the Harrier? ( The ones we virtually gave to the USMC).

Could the F-35B fly up the side of a Swiss Mountain ?

[ORAC]

Last part of the Time series on the F-35. Not exactly on the fence about it.....

On Final Approach to Fighter Fiscal Sanity

.......It is not unreasonable to expect the cost of future F-35s to be about where they are today, averaging more than $200 million per aircraft. It is also reasonable to doubt that F-35 unit costs—for a complete, operable F-35 force—will decline significantly, especially to a point anywhere close to the amounts currently projected for 2018 and beyond, pegged by Bogdan at $85 million. The history of combat-aircraft acquisition warns us that F-35 unit costs will be much higher than are currently projected by the Pentagon and Lockheed-Martin, and will remain well above what can be characterized as affordable.

The data reported to the public and Congress on F-35 costs and production, from the Defense Department’s comptroller, do not conform to the data in other Pentagon reports. Even the number of F-35 units authorized to be produced, and the number to be delivered, are in dispute.

Without a complete and independent audit of the F-35 program, including any costs that may not now be a formal part of the program as reported in Selected Acquisition Reports, it is impossible to discern which F-35 cost reports, if any, are accurate, and precisely what F-35 costs are today and will be in the future. The Defense Department’s SAR, and its seeming wishful declaration of the F-35’s total program costs coming down, should be audited by an independent and competent party. That GAO’s latest report on the F-35 has sided so clearly with the new hopefulness of program advocates for the F-35 calls into serious question whether GAO, or rather its current management, should be the party to such an accounting.

American taxpayers, the U.S. military services, and foreign purchasers — all of whom have been promised F-35 aircraft for as little as $85 million each — are in for a rude awakening. When real F-35 purchase prices unfold in the future, they may be as much as they are today—averaging more than $200 million per aircraft. It remains inevitable that as actual costs sink in, fewer aircraft will be purchased.

This toxic stew of the F-35’s high cost, abetted by concurrent production, lagging performance and continuing design problems, has put U.S. and allied air power into a dive. The dive will steepen so long as F-35 production at the currently-projected rates continues.

[glad rag]

@ JF re battle damage and vert landings

JF, thanks, as always, for your considerations.

BUT, I'm trying to work out how your description of the Harriers [fairly] simplistic nozzle system translates across to the F35b somewhat "transformer" like vertical landing conclusion

all the best

gr

[John Farley]

Stuffy

No I am not endorsing the F-35B in particular just trying to explain why I think there are many piloting advantages to being able to hover before landing.

The F-35B is a fly by wire aircraft so the handing is whatever the pilots want. The GR9 standard Harrier had better handling than the GR1 but in no way can it be compared to the immaculate standard provided by fly by wire.

I don't see why you would you want to fly an F-35B up a mountain. 42 years ago PR exercises were appropriate to show VSTOL to a world that was not aware of what it offered.

glad rag

In order to give the customer what he asked for (supersonics, stealth and a VL in one aircraft) the F-35B configuration is the best available. But it necessarily requires considerable complexity. Whether this leads to unreliability on the front line remains to be seen. Given modern engineering standards it may not- but clearly it could. Compared to the Harrier the complex systems necessary in the B clearly provide a different order of headache when it comes to combat damage. However the Harrier did not have any defensive aids untill well into its career - unlike the F-35B. As to handling at low speed (or any speed for that matter) the F-35B's handling will never be in doubt and removes at a stroke the Harrier selection, training and currency issues.

[Courtney Mil]

John F,

Thank you very much for your well written and well argued posts. I think you have put a lot of issues back into perspective and I hope other regulars here will take the time to read and consider what you have said. Again, thank you. You put a lot of effort into that and your experience shines through.

[Finnpog]

Thank you John F. Top posts and very informative.

[John Farley]

Thank you chaps for your kind words.

I have a confession to make. I wrote that 39 years ago (apart from the mention of the F-35B) but having read it again I saw no reason to change a word.

BTW it was not well received in 1984 by my employer whose centre of gravity had by then moved to Warton.

[JSFfan]

Thanks John, quality posts like yours, Engines and several others on different subjects is the reason I've been coming to Pprune for years as just a reader.