Why the F 35 C?

Discuss the F-35 Lightning II
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aquietguy

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Unread post11 May 2016, 20:06

I'm a long time reader. Just joined up. The question I have is about Navy's variant. I know the Navy likes planes with good slow speed handing for carrier landings. But isn't the F 35 A model supposed to have great high alpha maneuvering? So why even design a C model which will be more expensive?

To the best of my knowledge.

Benefits of C model:

Bigger wings equal larger fuel storage and better range.
More lift.

Draw backs of C model:

Heavier(should mostly be balanced by more lift).
More expensive.
Lack of internal gun to save weight.

Correct me if I'm wrong but looks like the Navy would have been better off strengthening the air frame of the A model.
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basher54321

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Unread post11 May 2016, 20:33

aquietguy wrote:Correct me if I'm wrong but looks like the Navy would have been better off strengthening the air frame of the A model.


Hi - pretty sure the C came last and they did essentially strengthen the A/B - but then they needed to add bigger wings for carrier ops.

Unique features of the CV variant include a wing with approximately 35% greater area than that on the other two variants, larger tail surfaces, and ailerons on the trailing edges of the wings. These features were added to improve the slow-speed performance and flying qualities required for carrier landings. Additionally, landing gear and other main structural components have been strengthened to withstand shipboard launch and recovery. A launch bar and arresting hook are incorporated to allow catapult takeoff and arrested landings.

The Influence of Ship Configuration on the Design of the JSF( Ryberg Eric S , 2002)
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Unread post11 May 2016, 20:55

Thanks 'basher54321' :mrgreen: That PDF/article is a great resource and should answer all questions regarding why the F-35B/C are different for shipboard deck operations. viewtopic.php?f=61&t=26629&p=282930&hilit=Ryberg#p282930 & viewtopic.php?f=61&t=26629&p=282901&hilit=Ryberg#p282901 & viewtopic.php?f=22&t=26708&p=282596&hilit=Ryberg#p282596 & a bazillion more including: viewtopic.php?f=22&t=20426&p=274027&hilit=Ryberg#p274027 wherein the PDF is attached as

The Influence of Ship Configuration on the Design of the Joint Strike Fighter Mr. Eric S. Ryberg 26-27 Feb 2002 COMPLETEpp15.pdf

download/file.php?id=19105 (PDF 1.1Mb)
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Original Resource: http://handle.dtic.mil/100.2/ADA399988 (1.1Mb PDF)

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Unread post11 May 2016, 21:03

aquietguy wrote:Correct me if I'm wrong but looks like the Navy would have been better off strengthening the air frame of the A model.

Welcome to the boards! You are wrong however. The wings, and thus the lift they can make, are not a little bigger. They are much bigger. This means the F-35C can fly slower approaches at lower angle of attacks even with the extra weight.

If the LM had just strengthened the body of the A to handle the cats and traps then the "C" would be heavier than the current A still. This means higher approach speeds and more strain on the arresting gear and violating the Navy approach speeds requirements. So you would have to increase the lift generation anyway via larger wing. Much of the weight increase is in the big wing.
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XanderCrews

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Unread post11 May 2016, 21:31

as others have said Its not the Alpha, its the approach speed that matters. 8)
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geforcerfx

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Unread post11 May 2016, 22:08

Didn't the bring back requirements require the larger wing design as well? Thought I read that at some point and time.
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Unread post11 May 2016, 22:24

aquietguy wrote:So why even design a C model which will be more expensive?


Landing aboard a carrier is very demanding. Getting the speed down acceptably low, while still being able to see the carrier on approach is a difficult design task and one that limits how much alpha you use without having the pilot's view obscured by the aircraft structure. Also, you don't want to be "right on the edge" performance-wise, as you need margin to deal with gusts and bumping through the turbulence generated by the large moving structure beside and underneath your landing strip.

Several very successful aircraft have made the transition from carrier aircraft to land-based aircraft. (The Phantom II stands out, but there have been a reasonable number.) There have been only a few to go the other direction and none with great success. If you were going to skip a variant of the JSF, it would be the "A". With greater sales volume, the cost of the "C" model would drop. And I'm sure that LM could fit the internal gun as an option.
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Unread post11 May 2016, 23:13

To summarise some of the points made already: There are specific KPPs Key Performance Parameters for the F-35C in regard to CVN operations - maximum approach speed at the maximum bring back weight in a specific range of internal/external weapon load configurations. KPPs from SAR Dec 2015 for the F-35C: download/file.php?id=22832 (0.7Mb)

The F-35C must have excellent engine & control responses - also now there is Delta Flight Path or IDLC Integrated Direct Lift Control which with flaps/throttle moving automatically to keep the F-35C on speed and on glideslope the pilot can spend more time on accurate line up to arrest on target wire every time.

A bunch of quotes; whilst a tonne of info will be gleaned by searching the F-35 forum with Ryberg & RCLW separately.
F-35C Approach Criteria – Maximum Landing Weight, Optimum Angle of Attack & KIAS

"The C-model is as solid as a rock and pilots land at a much slower speed—high 120s to low 130s [KIAS]." http://www.codeonemagazine.com/f35_arti ... tem_id=110
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"The Navy has added approach speed as a service specific key performance parameter. The threshold for approach speed is 145 knots with 15 knots of wind over the deck. This must be possible at Required Carrier Landing Weight (RCLW). The RCLW is the sum of the aircraft operating weight, the minimum required bringback, and enough fuel for two instrument approaches & a 100nm BINGO profile to arrive at a divert airfield with 1000 pounds of fuel. The minimum required bringback is two 2000 pound air-to-ground weapons and two AIM-120s.

The Navy further requires that the CV JSF be capable of carrier recovery with internal and external stores; the external stations must have 1000 pound capability on the outboard stations & maximum station carriage weight on the inboard." http://www.f-16.net/f-16_forum_download-id-14791.html
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"The [F-35C] max trap weight will be around 46k lbs, with an empty weight of about 35k lbs. It will fly an on-speed AOA of 12.3° at 135-140 KCAS [Optimum AofA or Donut].

Due to the fact that flap scheduling is completely automatic, the cockpit was designed without a flaps switch.

Additionally, the tail hook retracts into the fuselage and is covered by hook doors that have an as-yet-to-be-determined airspeed limitation..." LT. Dan "Butters" Radocaj VX-23 Ship Suitability
http://www.hrana.org/documents/PaddlesM ... er2010.pdf
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Knowles [test pilot] says the [C] aircraft approached at 135 kt., compared with 155 kt. for the smaller-winged F-35A & B variants at the same 40,000-lb. gross weight. Takeoff rotation speed was 15-20 kt. slower, he says.
http://web02.aviationweek.com/aw/generi ... ht%20Goals
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Unread post12 May 2016, 01:30

Contrast 'how to land the F-35A' with some F-35C testing details. At 150 KIAS the F-35A is already too fast at ??? weight.
F-35 Achieves Three Major Flight Test Milestones On Same Day
29 May 2014 LM PR

"...The F-35C, designed for aircraft carrier operations, completed a landing at its maximum sink speed to test the aircraft’s landing gear, airframe and arrestment system at Naval Air Station Patuxent River, Maryland. “Five sorties were conducted, building up the maximum sink rate test condition of 21.4 feet per second, which represents the maximum sink speed planned for this test,” McFarlan said. During the tests, the F-35C did three arrestments, several touch and goes and one bolter. The landings were to demonstrate structural readiness for arrested landings on an aircraft carrier at sea..."

Source: http://www.lockheedmartin.com/us/news/p ... e-day.html

Shake Rattle and Roll
July 2014 Air International F-35 Special Edition

"...Shake testing includes catapults and arrested landings. Catapults build up in longitudinal acceleration up to 5.5g and include shots with the aircraft deliberately off the centre in the shuttle. Arrested landings include high sink rates up to 20 feet per second (1,200 feet per minute or about a 5-degree flight path angle), maximum deceleration points and free flight engagements.

“Here at the field we don’t have the ability to heave or roll the runway pitch like the boat does so we high sink the aircraft up to its limits and simulate a very hard landing. We come down at various roll and yaw attitudes, and a combination of both, to simulate pitching and rolling of the deck.

“And finally we do what we call ‘max Nx’ [maximum engagement speed] – really hit the gear hard to see the effects on the aircraft and the gear and whether we can get the hook to engage the wire prior to the aircraft coming down. “We do that in a very controlled manner. We call it a free flight [inflight arrest], to ensure that both the arresting wire and aircraft can handle the stress in the event that a pilot tries to fly away from the boat and grabs the wire while the ‘plane is either going straight [ordinary] or on an upward vector [inflight arrest].”….

Source: Air International July 2014 F-35 special edition

F-35 Lightning public debut shows the right stuff
04 Aug 2015 David Tulis

“...[Col. Chris] Niemi has eight years in the cockpit of an F-22 and is one of the few Air Force pilots who is qualified in both the Raptor and the F-35 Lightning II...." ...Niemi said typical approach speeds are 150 knots and strictly by a 13-degree angle of attack all the way to the ground. “It’s a real easy plane to fly and it has good powerful [air] [the author inserted "air" mistakenly – should read "wheel" brakes]. At 100 knots it will sit down pretty good,” he said....” [Pilot means 'powerful computer controlled wheel carbon brakes' used after initial 'aero braking' [nosewheel off] from 150 knots at touchdown, reducing during airbraking to 100 knots, then brake when three wheels are down on the runway.] - - [The benefits of approaching at a constant AoA is that as the weight decreases so will the airspeed. I cannot guess by how much however for F-35A...."

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Unread post12 May 2016, 01:56

I think it's backwards, Navy designs tend to become Air Force designs because the former tends to have a better grasp on future-proofing. C should become the common model
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Unread post12 May 2016, 01:59

madrat wrote:I think it's backwards, Navy designs tend to become Air Force designs because the former tends to have a better grasp on future-proofing. C should become the common model


Wut?
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Unread post12 May 2016, 03:19

XanderCrews wrote:
madrat wrote:I think it's backwards, Navy designs tend to become Air Force designs because the former tends to have a better grasp on future-proofing. C should become the common model


Wut?

A-7 and F-4 are examples what madrat is saying. But no, the F-35C has poor supersonic performance (which the Navy stopped caring about after they retired the F-14) so it does not meet the needs of the Air Force.
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Unread post12 May 2016, 03:50

Shaken wrote:Landing aboard a carrier is very demanding. Getting the speed down acceptably low, while still being able to see the carrier on approach is a difficult design task and one that limits how much alpha you use without having the pilot's view obscured by the aircraft structure.


I'm not saying this is wrong (I'm aware that in past aircraft this was a significant issue, leading to things like planes taking a gentle turn as their approach to the carrier, so the pilot can keep his eyes on the carrier as long as possible), but for the F-35, wouldn't the pilot be able to look "through" the aircraft due to the helmet and DAS? (I don't know if at close range i.e. carrier landing the angle difference between the DAS and the pilot's head is big enough to be noticeable). I would imagine that -- depending on the software -- the helmet could be doing something like projecting the carrier's outline as a wireframe, and show all the pertinent info the pilot needs to know (like if he's above or below the target glideslope) regardless of if the nose is in the way.

I always thought (and I may be wrong on this) the maximum alpha is due not only to the pilot's need to see the carrier on landing, but also things like the tailhook and to make sure the elevators and engine don't hit the deck (since a carrier's deck is not always horizontal, unlike a runway on land). At any rate (for the OP), yes the F-35C is needed because the bigger wings and other changes allow for better low-speed handling, the folding wing means it saves space in the hangar, etc.
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Unread post12 May 2016, 04:18

'vanshilar' IF you read the first referenced PDF by Ryberg you will understand about what is needed. Visual reference is required IF the HUD goes pear shaped. Then the pilot has a chance to recover visually OR probably he can recover Automatically via JPALs & Delta Flight Path / IDLC - under LSO supervision - however JPALS for the F-35C is not certified, nor installed as yet. An initial version of JPALS - OK for the X-47B - was installed on suitable CVNS however it ain't qualified for humans in Super Hornets or F-35Cs but soon will be (however long 'soon' may be). And yet that was a great demonstration of the future of Auto Landings if it all works out well. Graphic below is called 'Over-the-nose Field-of-View Approach Speed Criterion' on page 10-11 of my version of the PDF: download/file.php?id=19105 (PDF 1.1Mb)

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Unread post12 May 2016, 04:21

speaking of the hook...
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