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No cats and flaps ...... back to F35B?

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No cats and flaps ...... back to F35B?

Old 9th Jun 2012, 13:12
  #1041 (permalink)  
 
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Milo,

The article in 'Sharkey's world' is accurate - but then I would say that as I contributed the technical piece for it at his request.

I stand by my assessment on Typhoon and STOBAR - the launch issue revolves around how fast it can accelerate (with a heavy payload), how fast it can enter the ramp, and then how slowly it can fly away. Without vectored thrust (and that thrust operating throughout the CG) flying a Typhoon away from the ramp would be an interesting exercise. It really needs a reaction control system (which BAE proposed), and that would take more thrust from the already hard worked engines. At any realistic combat payload, a Typhoon launch would require very high end speeds. I'm not at all sure it can get there in a short deck roll.

The recovery issue is just as demanding - how do you get the aircraft to fly a good 30 to 40 its slower than a normal runway landing, catch the wire and then stop? BAE's ideas involved sprung decks and RB211s to generate an artificial upwind, as they knew that getting the necessary landing gear strength for a normal 'trap' would severely compromise the airframe. Trying to catch a wire flying some sort of 'dynamic false' manoeuvre is, in my view, a non-starter. And we haven't even mentioned the structure needed for the all new hook system. Typhoon is a very weight sensitive aircraft, as it should be to achieve its shatteringly good air to air performance.

I would think that any 'Sea Gripen' would encounter the same issues.

LO, very hard to answer your question without adding a lot of detailed assumptions about launch methods and performance calculations that I can't do without data. However, I would take a hefty bet that even from the same land runway, F-35A, B or C would all outperform Typhoon or Gripen in a strike role. That's because the F-35 is optimised to perform in the strike role - internal weapons bays deliver a massive range boost, and it has a very large fuel fraction. All its sensors (like EOTS) are already built in. Typhoon has to carry all that stuff (fuel, weapons, pods) externally. Typhoon is optimised for the air combat role, and very well optimised too - but that large wing and high thrust to weight ratio degrade performance in the strike role.

I spent a few years on the T-45 Goshawk programme, and that experience of modifying a very good light training aircraft to operate from a ship does, I admit, colour my opinion.

This issue has been around the buoy a number of times now, always happy to respond, though. In short, if you want a world beating land based air to air combat aircraft, buy Typhoon. If you want a ship based strike aircraft, don't.

Hope this helps,

Engines
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Old 9th Jun 2012, 13:38
  #1042 (permalink)  
 
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MM - Ward is a bit behind the times on the Seaphoon proposal, which is now based on thrust vectoring to reduce Vapp without an extreme angle of attack (which in turns means that the pilot can see the deck). He's also a little unclear on how a non-STOVL jet can benefit from a ski-jump - the physics are the same as STOVL although the speeds are higher. And the reason you don't have ski-jumps on land is that you would thereby make the runway one-ended, and unusable for landings.

[Engines posted while I was writing this. I don't see reaction control systems in the latest Seaphoon proposals. I am not a big fan of Seaphoon, anyway.]

As for Gripen, the pitch (which I am not endorsing, just conveying) is that the existing jet is already designed for STOL, so it has low Vapp (125-160 kt), good low-speed handling, inherently precise approach, and the structure for no-flare landings; the E/F's new gear and centersection is being designed so that a higher-sink-rate version can be generated quite easily; and that it can be STOBAR or CATOBAR according to choice.

Also, some expeditionary services might care to note that the Gripen will fly happily all day long off an 800 m runway, which is shorter than what they expect to use for F-35B. And I would love to see what an F-35A would do on an 800 m SCREECH CRASH BANG road base.

I expect that F-35A should haul its internal load further than most things from an unrestricted runway. What I was speculating about was whether a STOBAR fighter, particularly F-35B-sized, could match its 3000 lb/450 nm HHH from a realistic deck run.

Last edited by LowObservable; 9th Jun 2012 at 13:47.
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Old 9th Jun 2012, 15:42
  #1043 (permalink)  
 
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LO -

Thanks for coming back. The Typhoon proposal has always (to my knowledge, but happy to be told wrong) included thrust vectoring. I'm not clear how applying thrust vectoring at the aft end of the fuselage can help with the approach, but clever flying controls are probably being suggested.

Sorry to disagree, but the physics of a non-STOVL STOBAR launch are not the same as for a STOVL aircraft using a ramp. There are important differences.

A STOVL aircraft can leave the end of the ramp below wingborne flying speed. That's because it can vector its thrust through its C of G to help maintain flight. It can also control itself below wingborne flight speeds using either reaction controls or its thrust effector (F-35B uses both). A non-STOVL aircraft can't do either, so its ramp end speed would have to be much higher, and wing loading lower, to maintain controlled flight. Look at the weapon loads being carried in Russian STOBAR ops - all appear very light.

On Sea Gripen, I am sorry, but anyone who says that they could 'easily generate a higher sink rate version' of an aircraft structure is either badly informed or being economical with the actualite. The loads generated in a normal trap landing (including hook loads) are simply huge and don't exist in a non-maritime aircraft. You can't 'beef up' structure that's not there in the first place. Same for landing. The speeds required for trap operations are around 20 to 30 knots below any normal land based aircraft. No one, and I have a great deal of regard for the Swedes, ever goes out and designs an aircraft to do this unless the aircraft absolutely has to. I have no doubt that a Gripen can operate off an 800m long road - the Swedes are absolutely outstanding at this sort of stuff. But I bet you a lot of kroner that it can't do it with anything like a full payload, or on a hot day, or at altitude.

So, to answer your well phrased question - no, I don't thank that any conventional (ie non-STOVL) aircraft using STOBAR could match F-35B off a 550 ft deck run and a ski jump. Doesn't make them bad aircraft - just not designed for the particular task being faced.

Best Regards as ever

Engines
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Old 9th Jun 2012, 17:24
  #1044 (permalink)  
 
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Engines - A couple of clarifications:

The VT idea is to vector the nozzle downward and balance that with nose-up trim on the canard. Hence less wing lift required and lower alpha for same weight and speed. Should not have to be too fancy as the VT is for trim and the canards and TEs are providing fine-tune control.

If the STOBAR aircraft has to be at flying speed when it leaves the ramp, then what is the benefit from the ramp, aside from a little more time to go OH EJECT EJECT if something goes wrong? Surely (from a lift viewpoint) the STOBAR can leave the ramp below flying speed, on a ballistic trajectory, as long as it can accelerate and reach level flying speed at or close to the top of the arc?

And since modern fighters can remain under control at alphas much greater than those at which they can land (see slow pass at any air show), don't they have control authority to spare?

On the Gripen structure: I could have been clearer. My understanding is that the new stuff for the JAS 39E/F (including all the bulkheads, MLG and support structure) is being designed with a CV variant in mind, rather like the Rafale. The trick is to balance weight-optimization, on the one hand, with the goal of concentrating the extra beef in the smallest number of different parts, on the other. On the Rafale, this was one of the earliest CATIA party tricks.

As for the MTOW from 800 meters, I'm not sure what the limitations are - but I would think that 3000 lb of weapons fuel for 450 nm would be less than MTOW.

Last edited by LowObservable; 9th Jun 2012 at 17:24.
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Old 9th Jun 2012, 17:28
  #1045 (permalink)  

Do a Hover - it avoids G
 
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Chaps

Just to tidy up what happens off a ski-jump:

You can run a car up one and it will stay airborne (thanks to Mr Newton) for a length of time that depends on both the exit speed and the ramp angle.

You can run a MiG29/Su27 (or any other conventional non thrust vectoring jet) up one and it will fly for longer than the car because it has SOME wing lift. Clearly the extra time benefit will depend on the actual L/W ratio at exit. All you have to do after exit in this case is to be accelerating at enough kt/sec such that at the end of the number of seconds the ramp provides you have reached normal flying speed for your weight This is the ‘runway in the sky’ notion. (on an airfield the undercarriage holds you clear of the ground and allows you the number of seconds needed to accelerate to flying speed).

BUT- and it is a big but - the pilot must be able to control the attitude after exit while the aircraft accelerates to flying speed. This is what the MiG29/Su27 could do because they have aerodynamic flying controls that are effective well below normal flying speed. Without such controls you are going to have to enhance the V squared stuff with some sort of reaction control system.
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Old 9th Jun 2012, 18:14
  #1046 (permalink)  
 
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LO,

Thanks again for coming back, and always a pleasure to hear wise words from John Farley. As he so rightly points out, one has to look at the L/W ratio at launch - with a proper combat load. Modern fighters can do all sorts of ritzy stuff at low weights - it's a fully loaded combat launch that matters, though.

The Typhoon VT solution is one I'd guessed at, as there's no other way to balance out the pitching moment from the engine nozzles other than using the canards. But one has to wonder how much lift the canards are going to deliver at low landing speeds with an acceptable control margin. I'm sure the clever gents at BAE have worked it out, plus of course how having the engines vectored downwards is going to square with use of thrust control on the approach (this is a primary control for carrier traps). Don't forget that the carrier approach not only has to deliver a low landing speed, but also extremely precise handling qualities to give acceptable hook trap rates.

The air show slow pass is just that - an air show slow pass. Typhoon can't land using it as the pilot can't see over the nose, and the gear has to be up, as I understand it. Plus, of course, this sort of thing is done at low weights. As John so properly points out, controlling an aircraft at ramp exit speeds demands specially designed controls plus low launch weights so as to get to the speeds at which even these work.

Once again, my honest opinion, for the avoidance of doubt. If you want to have an effective carrier borne combat aircraft, you either go for cat and trap, and design the aircraft to do it, or use powered lift (STOVL). That allows the aircraft to stop and then land, and also to use powered lift to help it get off the deck without a catapult. I honestly don't think STOBAR is the way forward, and by the way, the clever guys at Dstl who can do the physics agree. I sincerely hope that the Indians don't do a 'Cameron', change tack and go for 'Seaphoon' - they would certainly regret it.

Hope this helps - interesting discussion...

Engines
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Old 9th Jun 2012, 19:24
  #1047 (permalink)  
 
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Originally Posted by Engines
I sincerely hope that the Indians don't do a 'Cameron', change tack and go for 'Seaphoon' - they would certainly regret it.
Forgive my warped sense of humour but this remark had me choking on my coffee with horrible visions of the head of a horse tickling my feet as I am laying here reading the messages!

I am guessing the Russians would NOT appreciate India breaking its contract to buy a full wing of Mig 29 aircraft! Why am I hearing the theme from 'The Godfather'?

India might scrap that carrier but they have signed a contract to buy 'x' number of aircraft and it would take a foolish person to renege on it!
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Old 9th Jun 2012, 19:55
  #1048 (permalink)  
 
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because they have aerodynamic flying controls that are effective well below normal flying speed
I've always been aware of that John, but why is that so? Is it a 'slab' effect, a draggy thing, or what?
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Old 9th Jun 2012, 21:39
  #1049 (permalink)  
 
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Engines -

Actually, we're not far off agreement. Particularly if EMALS matures into what it could potentially be - a low-maintenance and scalable catapult - CATOBAR is the way to go, because STOBAR does little for you except eliminate the cat, while (at the best of times) taking more deck space.

Sea Gripen, by the way, is taking the agnostic approach and is being offered with or without a cat-compatible nose gear and loadpaths. It's more realistic than Seaphoon, I think, particularly for smaller navies.

The question with the B is how much you're paying for STOVL and how much for stealth. Somehow I think it ought to be possible to build an aircraft with 43000 pounds of thrust and have it do STOBAR with more than 3000 lb/450 miles....

JF - Re the car off the ski-jump, that's basically what this guy did, except on two wheels...

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Old 9th Jun 2012, 23:33
  #1050 (permalink)  
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Just to confirm John's point, it has been tried with a car over a ski-jump and the results are below. The car unfortunately has no propulsion after it leaves the ramp and not much in terms of aerodynamic lift. Not sure I would like to take off in a 30 ton jet without buckets of lift This is why the F35B will have to you use the lift fan for take off. The lift fan door looks awfully flimsy. I hope LM have done all the stress tests on it. I must make an impact on take off speed because the a/c is effectively trying to take off with an airbrake deployed. It just looks very odd to me.

Good to see Invincible and the Shars once again. All gone.


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Old 10th Jun 2012, 07:37
  #1051 (permalink)  
 
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Looks odd to me as well navaleye...originally the fan doors were very different (X35) but they were redesigned for the F35,as you so rightly say the door/actuator/mounting structure is going to take some hammering in service...does not look right at all...

X35 vid clip (fan doors at 3.00 )




Last edited by longer ron; 10th Jun 2012 at 07:38.
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Old 10th Jun 2012, 08:49
  #1052 (permalink)  
 
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Milo

We went back to them to the USA after Skybolt, no?

They are the only show in town after all.............
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Old 10th Jun 2012, 08:54
  #1053 (permalink)  
 
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Longer Ron,

As you say, the doors were redesigned however my understanding was that is was due to adverse intake flow down into the lift fan during deceleration to the hover. Hence F-35B has the large flap lid rather than the french shutters you see in your linked X-35 clip.

So if the worst case happens and in 2013 the -B is cancelled? How much would it then cost to go back to Carrier Alliance and ask them to switch again to the CATOBAR design yet fit both QEC and POW with EMALS (which I presume would be preferred over a steam device for a number of good reasons...), buy F/A-18E to perhaps acquire F-35C later? Not an inexpensive option I fear and to make it worthwhile you'd have to buy quite a few more F/A-18E for the same effect you'd have gotten with the F-35B (that's been proven btw). Granted that with Super H our Navy would have power projection from the sea against all but the anticipated Russian/Asian threats next decade though, until we acquired F-35C of course but then would we have the numbers?

That's the only reason why I can see a situation in SDSR 2015 (drafting now) in that we still don't have the money needed to cope with the above situation if it were to happen. I could see the Govt opting to sell both carriers in order to cut its losses and a phased-in procurement option for JSF transferring to the RAF as a Tornado replacement post-2018. This could be F-35C (range for deep strike) or F-35A (why not, there is no carrier requirement in this scenario now). F-35A range is only a few miles shorter than F-35C but it is a lighter platform, allowing more growth potential with less risk through-life.

Again, let me re-iterate that the above musing is unlikely, unless the F-35B is abandoned altogether. USMC lobby will prevent that IMHO.
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Old 10th Jun 2012, 09:13
  #1054 (permalink)  
 
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Navaleye,
I was onboard at the time and we had a couple of laughs because firstly, the handbrake was left on by the special effects man so the pneumatic ram didn't send the car anywhere near as far as it should. Secondly, the ship's AEO in charge of salvage had a whole exercise based around recovering the car after the event (it had flotation added), only for the thing to sink like a stone. Matelots do love it when a plan doesn't come together! (chuckle)

Cheers now
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Old 10th Jun 2012, 09:46
  #1055 (permalink)  
 
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Yes ICBM...thanks - I can see why they have gone for that design of door - it just looks like such an obvious problem area for the future,at MTOW speeds the door and support structure are going to take a hammering

rgds LR
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Old 10th Jun 2012, 10:18
  #1056 (permalink)  
 
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@ engines

Modern fighters can do all sorts of ritzy stuff at low weights - it's a fully loaded combat launch that matters, though.
yep!



Would you like to discuss the varying levels of "stealth" capability now that it has been recorded that there will be a disparities in capability across the build?
Not that I blame them mind, we did the same as well with some of our export "stuff"

Last edited by glad rag; 10th Jun 2012 at 10:20.
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Old 10th Jun 2012, 10:27
  #1057 (permalink)  

Do a Hover - it avoids G
 
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jindabyne

Controls not only have to overcome aircraft inertia and aerodynamic damping in the axes concerned - both of which naturally resist the pilot’s demands for manoeuvre – but they also have to deal with the inherent stability of the wing concerned and the way that the wing pitching and rolling moments will vary with changes to angle of sideslip and angle of attack. In the case of the MiG29/Su27 wings (designed by the same two blokes) they have clearly achieved a better than average optimisation of the many factors involved, resulting in unusually good attitude control being available at much less than normal flying speeds.

Last edited by John Farley; 10th Jun 2012 at 10:28.
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Old 10th Jun 2012, 13:40
  #1058 (permalink)  
 
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Longer Ron

at MTOW speeds the door and support structure are going to take a hammering
The door opening is scheduled with airspeed to help with adverse flow and the drag it inevitably causes when deployed. If you are doing a STO, and therefore using the lift fan, the sort of MTOW speeds we're talking about won't cause the hammering you suggest. They will be around 100-120kts - the lift fan door deploys at a much higher speed than this when decelerating from conventional flight into the hover for instance, so it can cope with 'airspeed' loads quite well. I'm sorry but I can't remember the speed limit on it now but it has a good margin. To put it into perspective, unless you are getting airborne off the QEC or doing a STO for periodic handling currency at home base (not the hardware store) you wouldn't routinely deploy the doors and engage the lift fan; you'd take off and land conventionally like a Tornado, Typhoon or F/A-18 does day-to-day.

The point of the extremely well-designed flight controls is that currency requirements for F-35B in the hover or for STO are not akin to the VSTOL handling requirements needed on the SHar or GR7/9 where a lack of recency/competency would result in a near or actual death experience...

Last edited by ICBM; 10th Jun 2012 at 13:42.
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Old 10th Jun 2012, 15:21
  #1059 (permalink)  
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I seem to remember 165kts as being the airspeed for deployment/retraction of the lift fan door.
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Old 10th Jun 2012, 16:01
  #1060 (permalink)  
 
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Does the F35 require a targeting pod (litening/sniper/whatever) or is that already integrated?
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