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Shipboard Rolling Vertical Landing - The saviour of Dave-B?

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Shipboard Rolling Vertical Landing - The saviour of Dave-B?

Old 5th Sep 2008, 16:51
  #81 (permalink)  
 
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Mr-AEO,

The driver for SRVLs is not deck erosion. Deck erosion is an issue, but it's not the reason SRVLs are being looked at. The real reason is the UK desire to get back to the deck carrying more at higher temperatures.

Don't think I ever said that SRVLs will be as safe as a purely VL. I don't know what the relative safety analyses say. Al I do know is that the team will not recommend SRVLs unless they can be made sufficiently safe. Oil on the deck -yes, absolutely a problem. That's why the USN take severe pains to get rid of them ASAP. They are a problem for CVN arrested landings as well.

Best Regards as ever

Engines
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Old 8th Sep 2008, 20:18
  #82 (permalink)  
 
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Engines. Many thanks for the reply.

Noted that we are trying to recover the hot/heavy capability, but is SRVL a critical go/no-go factor in the decision for a STOVL jet (i.e. a Key User Requirement) or have we passed that point already by selecting a certain flavour of CVF? Ipso Facto, we get what we get and if it is able to meet the requirements safely using the SRVL then even better.
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Old 9th Sep 2008, 09:58
  #83 (permalink)  
 
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AIUI, we're not committed yet, but are certainly on the vinegar strokes / got the Jesters toes......

It will probably be too late to get cat n trap into QE before her first refit, but the possibility remains for PoW to enter service fitted for Dave C - particularly given that QE will still be operating GR9 until 2017/2018, which is broadly the IOC for Dave B. Switching to Dave C might knock that back a bit, but ain't a show-stopper yet.

Either way, decision must be made before the end FY at latest.
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Old 9th Sep 2008, 11:55
  #84 (permalink)  
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As ever, very interesting. The V-22 idea was debated here sometime ago, and IIRC there was also an issue with the lack of pressurisation and, cost. Which was reputedly massive. (Mahoosive, in fact). For a maximum of 12 aircraft, getting the altitude performance and radar integration work done seemed to provide a range of numbers from the shockingly high to the truly absurd. However, if we could expand the customer base, then at least the engineering amortisation would be spread further
From aviation week, USMC and TOSS

...couldn't find mention of this earlier in the thread.

WRT Dave B and SRVLs, is the degree of difficulty increased by Dave B's unconventional flying controls when hovering and the transition thereto?
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Old 9th Sep 2008, 14:46
  #85 (permalink)  
 
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Vitamingee

seems to me you're on a safe bet re. software...

'Engines' will know a lot more about it, but given the basically non-vectoring thrust of the F-35B, it takes a whole new load of software to allow a SRVL.

Why this wasn't an initial requirement still hasn't been explained in words to get into my thick skull, nor has the reason why a ski-ramp isn't of use.

For reference ( of a sort ) we at BAe Dunsfold - no amount of money could seduce talented software guys to the northern slums of Wart On - had a whole, large building especially made housing over 200 people to solely write the control laws for the Eurofighter /Typhoon, they were particularly wary after the first Gripen's disaster ( how the Test pilot survived is still regarded a miracle ).

It would seem the only way the F-35B can slow down is to pitch up, but god knows what the computers make of that !

Last edited by Double Zero; 9th Sep 2008 at 15:18.
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Old 9th Sep 2008, 17:51
  #86 (permalink)  
 
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Sorry Double Zero but you're a bit off beam.

What makes you think F-35B won't do a ski-jump? Do you think CVF has a bow ramp simply for fun? F-35B most certainly has thrust-vectoring and most certainly uses it.

Many years ago, enlightened souls convinced the MoD to put its hand in the taxpayer's pocket and fund an experimental programme to answer the question "Yeah, but what has active-control-technology ever done for V/STOL?". "Well, there's autostabilisation". "Obviously, but apart from autostabs etc etc". Anyway, the point is that XW175 has tested, ashore and at sea, some pretty fundamentally different ways of doing the V/STOL thing. The option judged to be the best (not by everyone, not without reservations, not without some serious discussions) has been selected as the basis for how F-35B does it. Of the options I've seen (and indeed flown), I happen to agree with that selection. One legacy of all the effort is that UK happens to have pretty much the right tool for the job of actually going to sea and having a look at how something that flies like an F-35B would actually do an SRVL. So we did. Last year on the Charles de Gaulle, with our software tweaked to make XW175 as good a match for the rather heavier F-35B as we could (and if you do ever get to look in XW175's rear cockpit, you'll note it has un-Harrier like things like a sidestick and a whopping-big linear-slidey left-hand "make plane go fast now" control, plus a thing that sayeth "It is now safe to switch off your computer" upon its screen. Verily, I kid you not).

Now I would think that if there were something horrifically wrong with how the F-35B control strategy deals with SRVLs (we did NOT change the strategy from the "Unified" control scheme), we'd have noticed it at some stage in the process of preparing for that activity (or perhaps even in the trial, because if you knew exactly what was going to happen in a flight trial there would be no point going would there? Apart from the food and climate obviously). I might be wrong of course, but "Unified" to me seemed to be pretty much just the job for SRVLs, as of course its originators back in 1980 or so knew it would be (and they'd never heard of SRVLs, but they knew about V/STOL and fundamental pilot-throttley-rudder-stick-stuff and were also a bit clever, which makes the job of those that followed-on, like me, rather easier).
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Old 9th Sep 2008, 18:26
  #87 (permalink)  
 
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Okay Novhoverstop,

You've flown it ( or rather the prototype / simulators ) and I certainly won't; but when I say ' no vectored thrust ' I know that aft nozzle vectors a bit, but not as in the 98.5 degrees - all combined - like the Harrier.

As for ski-ramps, well it seems any decent fighter - as in Mig 29 on the Russian carrier- can do it, but without vectored thrust the launch/ bring back penalty is considerable.

- Yes I've heard at least the first of the CVF's is getting a ramp, but made out to be a hang-over from Harrier times - remind me again about delivery dates & delayed expiry dates ?!

Despite the obvious advantages of STORL / STOVL ( if the kit allows ) the U.S. Marines don't seem to be driving the project along, hence the flat rather than ramped decks of their carriers - they put up with whatever they're given.

Last edited by Double Zero; 9th Sep 2008 at 18:39.
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Old 9th Sep 2008, 18:42
  #88 (permalink)  
 
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We're still missing the fundamental problem with SRVL here. FCS is an issue but not a show-stopper. The real problem with SRVL is that once you're committed to touch down, you are totally reliant on the brakes. The throttle will have to be brought to idle, otherwise you're p1ssing away your braking power. If you spool the engine down, there is unlikely to be sufficient time to get sufficient power back on to do anything - that's why boltering is not an issue - if something bad happens you just can't do jack-sh1t about it. I may be missing a trick here and it may be possible to spool up again in the 200m or so between touch-down point and the bow (inc ramp), but then you're into a number of undesirables, like ramp entry speed, a further margin of fuel to allow a (very) abbreviated go-around with consequent impact on the bringback issue that we're trying to fix, and the huge swathe of deck 280m x 18-ish that would then have to be kept clear. Plus, if "something" does go wrong, it is likely to involve lateral forces which will tend to make the cab go anywhere but straight ahead. With VL, the relative velocity is unlikely to make you hit anything, with CV, you're pointed away from the deck park and going so fast that if something does happen you're still unlikely to cause any unpleasantness (except to yourself). SRVL doesn't appear to allow either of those.

Once again, I have no doubt that SRVL can be done - and with a "reasonable" interval between something going wrong. It's just that when the "something" is aboard an operational deck crammed with bombed up, fuelled up aircraft, it might end in tears.

Last edited by Not_a_boffin; 9th Sep 2008 at 19:04.
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Old 9th Sep 2008, 18:56
  #89 (permalink)  
 
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What is the potential for UAV/UCAV operations from CVF?

I assume the maturity of any potential solution is currently so low and that there is no programme geared for CVF which would influence the cats/traps vs STOVL/STORL debate for the long term?

Can CVF (HMS QE) retain the ramp but be fitted with a cat along the angled deck (a la Nimitz class)? Whilst this would give a really good cross deck potential and allow for a mixed fleet (training issues noted!!) I assume that Dave-B and Dave-C are now very different from a logistics footprint (compared to the original intent of JAST to achieve a "common" platform with service variations).
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Old 9th Sep 2008, 19:10
  #90 (permalink)  
 
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You could do it, but why would you want to?

One cat = one point of failure and low launch rate. You could put two in the waist, but it's very cramped. You're also then compromising one of your prime parking positions for STO, in addition to needing the full angle for a CV recovery.

One or t'other. Otherwise you end up like a STOBAR carrier, with a relatively tiny deck park due to the large launch and recovery areas needed.
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Old 9th Sep 2008, 21:11
  #91 (permalink)  
 
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N.A.B - nice post, and I quite agree!

Whilst there are obviously no Cat's, does anyone know if CVF are considering a Trap to catch SRVL overshoots? What if the jet has no brakes because of an in-flight emergency? I guess the option there is to dump as much fuel/ordnance as possible and recover light, thereby allowing a STOVL approach?
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Old 9th Sep 2008, 23:43
  #92 (permalink)  
 
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Despite the obvious advantages of STORL / STOVL ( if the kit allows ) the U.S. Marines don't seem to be driving the project along, hence the flat rather than ramped decks of their carriers - they put up with whatever they're given.

They'd get a ramp if they wanted one. The ski jump has disadvantages. For one thing, it gets in the way of rotary wing operations.

You've flown it ( or rather the prototype / simulators ) and I certainly won't; but when I say ' no vectored thrust ' I know that aft nozzle vectors a bit, but not as in the 98.5 degrees - all combined - like the Harrier.

For slower, heavier takeoffs and touchdowns, the aft nozzle needs to be able to vector upward to offset the nose down moment due to full[er] flaps.
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Old 10th Sep 2008, 03:40
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Wrong to say slower takeoffs. I should have said "shorter."

How about this?:

SUCCESFUL ESTOL LANDINGS WITH THE X-31A
By Karl Schwarz

„It was the high point of my career as a pilot,“ said Rüdiger Knöpfel of the Bundeswehr Aircraft Test Center (WTD 61) with enthusiasm, as he looked back on the first landing with the X-31A in extremely short take-off and landing (ESTOL) mode. In the critical minutes of the flight he had had virtually nothing to do, as it is only thanks to the unbelievably accurate position finding and automatic control functions of the complex software that the German-American experimental aircraft is able to perform extremely short landings.

...

„You don't have time to be nervous,“ adds Rüdiger Knöpfel, although the manoeuvre is extremely risky. „If the computer reduces the angle of attack too early, the nose landing gear could buckle under; if it acts too late or too little then the tail could hit the ground.“

Neither occurred, a major success for the small test team, which had to contend with a very tight budget. But what was the point of all this expenditure? On the last test flight the landing speed was 121kt (224km/h), down 31% from the normal 175kt (324km/h). Whereas on a normal conventional landing the X-31 requires some 2,400m of runway to come to a halt, all it requires now is 520m.

Such figures naturally depend on the aircraft type, but have the attraction of making landings on short temporary airstrips feasible. The reduction in landing energy is important for aircraft carrier-based operations. The aircraft structure could be lighter or it would be possible to set down with greater fuel reserves remaining or with unused weapons without overstressing the airframe. Again, the requirements regarding headwind on the deck would be less stringent if planes could land at a lower speed.

...

FLUG REVUE July 2003: X-31A demonstrates ESTOL landing





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Old 10th Sep 2008, 16:53
  #94 (permalink)  
 
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Modern Elmo,

I certainly wasn't suggesting 'upwards vectoring' though I suppose it would give a specific deck spot to keep clear of !
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Old 11th Sep 2008, 14:46
  #95 (permalink)  
 
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A bit!

I know that aft nozzle vectors a bit
YouTube - f-35 Thrust Vectoring

Might help if you define 'a bit'
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Old 11th Sep 2008, 21:04
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NoHoverstop's post sets the stall out here, and very well too.

The F-35B can do SRVLs. It's designed to do land based short landings, and the changes needed to get the SRVL optimized for CVF use aren't, I believe, too significant. For those in the programme, the 'unified' control system they have adopted seems to work OK.

The issue Not a Boffin identifies is very real - stopping safely after touch down, or executing a bolter. My view is that a bolter is really a must, and the CVF has the space to adopt an 'angled deck' layout for SRVL recoveries.

One thought on the safety issues - we did takeoffs from the very small CVS for some years, and as far as I know never lost an aircraft or a person to the aircraft running laterally off the very small runway. SRVLs present a similar issue, in controlling a maneuver (in this case decelerating) down a deck. The speeds involved are actually lower for SRVLs. And losing an outrigger tyre would be every bit as bad as losing an F-35B main wheel.

Not trying to be glib, but I trust the team who are working this at Warton and in Fort Worth. They are committed to a safe solution - and I think they'll get there.

Best Regards
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Old 11th Sep 2008, 22:19
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Engines - the bolter is irrelevant (although missed approach is not). I may be wrong, but would have thought that on touchdown, the engine will be immediately brought to idle (otherwise you're negating your braking effort) which means if something goes wrong on deck, you have no time to spool back up and regain any sort (wing or thrust-borne) of flying speed off an angle. It's been a while since I checked the distances, but assuming a touchdown point 60-80m forward of the round-down, the size of CVF and probable angle gives you around 120m-ish to play with before you hit the deck edge. At 40 knot relative, thats 6 seconds maximum to get back your rpm, probably a bit less if you factor in things going wrong slightly after TD rather than on it, plus an "oh-sh1t" factor and thottle lag. As if thats not bad enough, if you've done any of the hard braking necessary, your actual speed will be WoD plus about 20kts at best.......

An angle should prevent the deck park having a bad day, but I should have thought we're looking at a very wet and scared pilot and a certain requirement for a plane guard (damn - I knew I shouldn't have mentioned that!).

The STO vs RVL comparison isn't necessarily valid - for a kick off, on launch there are minimal vertical loads on the gear compared to a 3-4 degree glideslope and instantaneous frictional contact with the deck on recovery.

I don't doubt Warton & FW are looking very hard for a safe solution - my concern is that they are looking in a very small box from absolute necessity rather than exploring options for "extra" performance.
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Old 12th Sep 2008, 04:38
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Mr. 0^2:

To perform a conventional landing or a short rolling landing or a roll until something stops you landing, one doesn't try to level the aircraft with respect to the surface on final approach. Instead, the nose is pitched up somewhat. The higher the angle of attack on final approach, the less kinetic energy the aircraft's center of mass will have at touchdown, other things being equal. Why? Because both lift and drag increase as aoa of the lifting airfoils increase, until stall.

This is the case whether the aircraft is CTOL or a Harrier or an F-35B.

The point is, one doesn't use thrust vectoring merely to push the aircraft upward or backward, if the goal is a minimum kinetic energy rolling landing. In addition, some thrust vectoring should should be used to rotate the airplane to a higher aoa than could be achieved without thrust vectoring.

The question is, can this attitude control be done without automation?
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Old 12th Sep 2008, 15:17
  #99 (permalink)  
 
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N-a-B...
That would be my view too. And add to that the fact that there is a hell of a lot of rotational inertia in that propulsion system, and it is not going to come to full power like switching on a light.
Another aspect: if SRVLs (as Engines has said) will only be needed on a a Royal Navy Hot Day (as opposed to a Marine hot day, the Marines having the ability to control the weather) with weapons on board, does that mean that everybody (pilots, deck crew) will train for both? Or will SRVL become standard, in order to eliminate double training? And does that affect parking, recovery and sortie rates?

ME...
Good question. In a VL, wing lift doesn't matter - so it's not surprising that the F-35 appears to be designed to land with next to no AoA at the wing. But even at 60 kt (airspeed for a SRVL) that eedy-beedy thin wing is going to need some alpha to produce some lift (I should think). While the integrated controls should handle this, it does mean that the landing will be mains-first, derotate, throttle back, brake...
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Old 12th Sep 2008, 18:01
  #100 (permalink)  
 
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LO

I think if it became SOP then you've negated the reason for doing it in the first place - namely bringback, aka recovery weight. If you plan to do it on a routine basis, you'd have to be a dribbling idiot not to include a fuel margin for a very short go-around, even if that go-around included hitting the emergency ditch everything button (which come to think of it won't be easy with internal weapons carriage). Additional fuel margin = additional recovery weight, which reduces your bring-back etc....

The more you scratch, the less sensible it looks.
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