F-35C design changes from -A

Unread postPosted: 28 Jan 2017, 19:45
by steve2267
The design changes from the F-35A to the F-35C to support carrier ops are substantial. Larger wing to enable lower approach speeds, larger control surface to increase control at those lower approach speeds, beefier landing gear, beefier structure in general to handle shock / impact / vibration loads of arrested landing etc.

My specific question: Can someone estimate the weight of the changes required to support EMALS catapult assisted takeoff, but nothing else. I'll break the question in two:
  1. How much weight would you have to add to an F-35A to support an EMALS CATO in conventional configuration? (I realize this may not be possible with the -A's smaller wing.)
  2. How much weight would you have to add to an F-35B to support an [b]EMALS/b] CASTO where you are launching the -B in a STO mode using the liftfan / vectored main engine and you only need to get it to ~80 knots?

Are we talking 500lbs of extra structural weight? 1000lbs?

EMALS is a smoother acceleration compared to a steam cat, at least from what I've read. Combined with only having to accelerate a -B to 80kts, I would think the additional structural weight would be minimized.

Obviously extra weight in a -B reduces its bring-back capacity, but I am curious nonetheless.

Re: F-35C design changes from -A

Unread postPosted: 20 May 2019, 06:36
by spazsinbad
Regarding Q.2: An F-35B is able to STO from 300 feet [length of CVN EMALS] AFAIK with a useful fuel load - there are always whatevers regarding WOD Wind Over the Deck and air temperature. May one be curious to know: WHY 80 cannots?

Re: F-35C design changes from -A

Unread postPosted: 20 May 2019, 15:32
by sprstdlyscottsmn
That was my first thought as well Spaz. The Killer Bee already STOs in the distance of a cat shot, so if you are trying to CATASTO then go for 120kt at max weight.

Your real question is "how much structure is needed to fling a 30 ton aircraft at 4 G by the nose wheel and do it thousands of times without fail?"

Re: F-35C design changes from -A

Unread postPosted: 20 May 2019, 16:45
by steve2267
Wow, this is a thread from the past.

I do not recall entirely where the 80 kannohts came from. I am thinking I may have read somewhere that the rotation / takeoff speed for a Killer Bee was 80kts.

At that time period... I may have been playing around in my head with how small could one make a ship to fling Killer Bees off the front end and vertically recover them on the back. At one point, I had hair brained ideas of destroyer-sized ships where the Killer Bee cat shot may have started from within the superstructure, launching ala Battlestar Galactica. Then vertically recovering on a largeish landing area at the rear of the ship. But then I got edjeemukated on the dynamic movement of a small boat and that if helos have a challenge recovering to frigates and destroyers, Killer Bees recovering in sea states of varying nastiness is not smart. Plus there's the whole WOD thing, especially as it relates to superstructure wake turbulence etc. My original idea was spun off a what-if question having to do with dispersing Killer Bees across a wide area... so the enema would have a harder targeting problem, and would not know from where the next attack was coming.

I think the original question was an attempt to swag the weight required for a CASTO and whether it would kill your vertical recovery weight.

I came to the conclusion the smallest ship that would be potentially useful as a small aircraft carrier would be between 10,000 and 20,000 tons (ish), and potentially be able to embark between 10 and maybe up to 20 Killer Bees. Of course, we have other threads to discuss light carriers, and various nations are potentially interested in LHA / lightning carriers.

Best I can recall my thinking behind this old thread from the past.

Re: F-35C design changes from -A

Unread postPosted: 20 May 2019, 21:36
by spazsinbad
:crazypilot: :devil: It was a good zombie thread (unanswered) to resurrect but.... F-35B is amazing - as it is. :mrgreen: 8)

Re: F-35C design changes from -A

Unread postPosted: 20 May 2019, 23:23
by steve2267
:cheers:

Re: F-35C design changes from -A

Unread postPosted: 20 May 2019, 23:25
by sprstdlyscottsmn
By nearly any metric it is the "least capable" but it is by far the one that impresses me the most.

Re: F-35C design changes from -A

Unread postPosted: 20 May 2019, 23:36
by steve2267
I guess it depends on your metric.

The ability to STO with a decent payload, accelerate supersonic, conduction mission, RTB and VL is quite a capability. In fact, no other aircraft in the world can accomplish it. As I recall, that capability won the JSF team the Collier Trophy a while back.

What I find even more impressive, is even with design compromises forced by the STO and VL requirements... the Killer Bee can still (apparently) handily dispatch F-16's, F-18's, F-15's etc.

Re: F-35C design changes from -A

Unread postPosted: 20 May 2019, 23:49
by steve2267
Thinking about this a little more...

There have been endless debates here (and elsewhere) over E-M diagrams. I'll toss this idea out for debate: one of the (primary?) reasons the F-35 is so dangerous, is that it can slide left <--> right (e.g. velocity) faster than any other aircraft to date, save the F-22. That is, in totality, it can brake faster, accelerate faster, and perform maneuvers at high alpha better / faster than any other aircraft.

One might argue that the F/A-18 / Super Duper can fly at high alphas like the F-35, and it can slow down fast too... BUT... the F-35 can re-gain its energy faster than the F/A-18 / Super Duper. The Bug/Rhino can piss away its energy to perform magical butterfly tricks, but regaining that E is going to suck. On the other hand, the F-16 performs really well towards the right end of the E-M domain at high energy states. And from reading what Gum's has written, the F-16 can dump it's energy if the pilot wants via a bat turn. The F-16 can regain it's E (almost) like nobodies business... BUT the F-16 is alpha limited.

The F-35 is the first aircraft to be able to (out?) decelerate other aircraft, utilize the high-alpha flight regime to its advantage, but regain it's E quickly when it is needed.

How can a 7g limited aircraft like the Killer Bee kill Bugs / Rhinos / Vipers / Eagles etc? I think it is because it can take advantage of the high alpha regime when the situation calls for it, yet slow down to it's optimum turning speed (e.g. smaller radius + v. good rate) but with the power to either re-accelerate to get-out-of-dodge speed or power into the vertical. It's the combination of all these traits that make it so deadly.

Having said all that, yes, the F-35C and F-35A are more "capable", but the Killer Bee is still better than everything else out there save the F-22 (i.e. in an air-to-air role).

Back in the '80s, if you had asked someone how'd they like an F/A-18 Hornet that accelerates like a Viper, is invisible on radar, oh, and it can do that Harrier thing, yet have a top speed of 1.6 Mach... they'd probably look at you like you had just come from a Cheech and Chong party hosted by Saab... :devil:

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 00:48
by quicksilver
So, tell us again what your question might be...

I think you’re making waaay too much out of the structural load limit.

Wrt your scar weight question, there would be the difference in weight between the cat-capable nose strut; a different keel structure; and, given significant differences in load paths there is structure (like the keel) that has to be accommodated in the overall design. It’s not like there is a kit that could be created to do some kind of ‘conversion’. Johnwill would have the most insight on this topic.

The bottom line is it would kill your VLBB.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 02:46
by steve2267
quicksilver wrote:So, tell us again what your question might be...


I have no question.

In trying to recall why I made my origial post almost 2-1/2 years ago -- in my earlier posts of this resurrected zombie thread (tanks a lot Spaz! :shock: ) -- as best I can recall, I was a wondering how much additional structural weight would be required to be able to make an F-35B catapult-able on an EMALS catapult. I vaguely recall thinking that EMALS should result in far less shock loading on a catapulted aircraft, and thus, could the structural weight required be minized such that VLBB is not squooshed?

quicksilver wrote:I think you’re making waaay too much out of the structural load limit.

Wrt your scar weight question, there would be the difference in weight between the cat-capable nose strut; a different keel structure; and, given significant differences in load paths there is structure (like the keel) that has to be accommodated in the overall design. It’s not like there is a kit that could be created to do some kind of ‘conversion’. Johnwill would have the most insight on this topic.

The bottom line is it would kill your VLBB.


I never envisioned "a kit." I didn't fall off the Sprey-inspired turnip truck. But I was looking for a swag on how much additional weight would be required.

As became clear from other threads, it was a stoopid idea.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 03:18
by quicksilver
“I never envisioned "a kit." I didn't fall off the Sprey-inspired turnip truck. But I was looking for a swag on how much additional weight would be required.“

I wasn’t suggesting you did. But, your hypothetical comes near a too-common public perception that it’s relatively easy to make ‘other’ jets successfully cat/trap capable (eg APA and F-22). Thus, my query about what you were trying to resolve.

The other matter in ANY weight addition to the B is location of that weight relative to thrust split between the lift fan and the main engine.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 04:23
by spazsinbad
Given all we know with posts about how NAVAL AVIATION Aircraft are designed & TESTED (SHAKE & ROCK & ROLL!) is this:

Navalising the F-22 Raptor 23 Feb 2009 Chris Mills: http://www.ausairpower.net/APA-NOTAM-230209-1.html

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 06:13
by steve2267
The memory jogs once more.

The other idea that had been bouncing around my head was to fling a modified F-35B (F-35BC ?) off the ship with an EMALS catapult, with the idea, that again, an EMALS system would have less of a weight impact to the "BC" structure. Then leverage the STOVL mode 4 of the Killer Bee to do SRVL recovery on the boat... negating the need for an arresting gear system. I seem to recall thinking that the EMALS could maximize the load carrying capacity & range of the Killer Bee (Cat) -- i.e. enable an aircraft to carry more on a catapulted Bee than the max you could get on a STO.

Having said all that... the KISS solution is a ramp at the front of the boat, then architect the boat to maximize aircraft flow: launch, recovery, re-arm, re-fuel etc. The new Queen Elizabeth class probably has that all figured out. None of the boats in development now, with possible exception of one of the Italian boats, in the 20-30,000 ton class seem to be optimized for F-35B operations. They seem to be more LHA adapted to be able to conduct F-35B ops. But that is probably all best for another thread.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 06:58
by johnwill
Using the EMALS system to launch an F-35B from a deck seems really impractical to me, considering all the weight and cost needed to strengthen the airplane. Not just the landing gear and fuselage backup structure, but every piece of internal equipment (systems, weapons, engine, lift fan, etc. would have to be re-qualified to the new conditions. But there is a possibility to develop an EMALS-assisted launch capability, using only a fraction of EMALS capability. The idea would be to conduct a thorough analysis and test program to determine how much added launch thrust from EMALS could be accommodated without any structural changes other than a launch bar on the nose gear.

Why do it? Increased gross weight takeoff, reduced WOD requirement, reduced lift thrust from engine and lift fan for increased life, less deck space required, etc. Would I try it? Absolutely not. And if anyone says I suggested it, I'll deny it.

Back to the bicycle shop!

Added:
Steve I see you added a post whilst I was pecking away at my keyboard. Seems we are thinking along the same lines. By the way, you will never get an arresting hook installed on a B.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 11:40
by quicksilver
https://images.search.yahoo.com/images/ ... r2=piv-web

Note differences betwixt a B strut and that of C in this pic (and others on Interweb). I believe the mechanism aft of the strut is called a ‘drag brace.’ Where would that go on a B given the lift fan? Additionally, imagine a redesign of the whole forward fuselage to accommodate the size and weight of that strut in a B vs the existing gear. Now, add an entire (soup to nuts) test program to qualify said aircraft.

Use the existing strut? Using what device to attach said strut to the cat shuttle?

As you finally concluded, ‘crank up the WOD and/or add a ramp to the ship’ is the right answer.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 12:04
by quicksilver
sprstdlyscottsmn wrote:By nearly any metric it is the "least capable" but it is by far the one that impresses me the most.


Just off the top of my head, the (six) exceptions to your ‘any metric’ are subsonic accel, transonic accel, max Mach, unassisted STO, VTO and VLBB.

And, STO, VL (and VTO) are not ‘compromises’; they are monumental achievements that expand the amount of tacair (5th Gen, no less...) that allied nations can put to sea in defense of their national interests.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 15:18
by sprstdlyscottsmn
quicksilver wrote:
sprstdlyscottsmn wrote:By nearly any metric it is the "least capable" but it is by far the one that impresses me the most.


Just off the top of my head, the (six) exceptions to your ‘any metric’ are subsonic accel, transonic accel, max Mach, unassisted STO, VTO and VLBB.

STO, VTO, and VLBB are not metrics used by anything other than the AV-8B and the F-35B. You are correct that it can out accelerate the C and that it has the same max speed across the board. But is slower in acceleration than the A. It has less payload than the A/C, it has less range than the A/C, it has a lower G limit than the A/C.

You seemed to miss what I said next though. It is, BY FAR, the one that impresses me the most. I never said a single word about STOVL being a compromise.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 15:54
by quicksilver
You made the statement about metrics; someone else mentioned ‘compromise.’ Both are worthy of alternative views.

The ‘A’ is the “least capable” at landing on a ship. The ‘C’ was ‘compromised’ by scar weight/features necessary to land on the CVN.

So what metrics are most important? What you see depends on where you stand. :wink

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 16:14
by sprstdlyscottsmn
quicksilver wrote:The ‘A’ is the “least capable” at landing on a ship.

Nah, it can do it just fine.... Once. :whistle:

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 16:40
by quicksilver
It is almost ‘ritual’ (to be flattering) to talk about the ‘B’ using those two descriptives — ‘least capable’ or ‘compromised.’ I clearly don’t subscribe to those conventions, nor to the idea that the ‘B’ is some kind of ‘improvement on Harrier’ (see the thread about first ‘B’ combat sorties elsewhere). IMNSHO, some (many who frequent this site excepted) still haven’t gotten their head around the package of capabilities that is “F-35” — which includes how/where they takeoff and land.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 16:49
by quicksilver
sprstdlyscottsmn wrote:
quicksilver wrote:The ‘A’ is the “least capable” at landing on a ship.

Nah, it can do it just fine.... Once. :whistle:


Note that I said ‘least capable’ as opposed to ‘not capable.’ :wink:

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 18:20
by steve2267
I used the word "compromise." Perhaps I should have written trade-off instead. I believe either is an accurate term to use from where I stand as an engineer. I (pithely speaking on behalf of LM aircraft design engineers) could give you the same range as the F-35A by stuffing more gas in there... BUT... you either have to give up internal stores capacity, OR the airframe has to grow larger (cannot store gas where the fan goes, after all), which means more structural weight, very probably a decrease in kinetic / maneuver performance, AND you probably lose your VL or severely restrict your VBB weight. I could give you a 9g airframe... but the increased weight is going to kill your VL / VBB performance. So compromises had to be made. If you don't like the "c" word, call it a trade or trade-off.

But in the binary metric of STO / VL / VTO (re-positioning) / VBB / ability to operate out of a 1000ft (or shorter?) strip when all AF base runways have been cratered, or CVNs sunk or driven out of the AO... it gives you a bright shiny "1", where everyone else, save the Harrier, gets a dull, dark "0."

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 19:25
by sprstdlyscottsmn
Heh, my favorite "that would be neat, but stupid" thought experiment is a Typhoon sized and shaped SSCVN. Instead of ballistic missile tubes, a small Hangar deck. An elevator right in front of the conning tower to get the F-35B to the launch deck. Have the top hatch that opens be the JBD and have the elevator treated for heat resistance. STO right off the elevator and VL right back on it.

Yes I already know it's stupid and would never work in reality, but its still fun from a Sci-Fi kinda perspective.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 21:14
by quicksilver
Steve, some understand that ALL aircraft designs are an amalgam of trade-offs between a multiplicity of competing requirements. Most do not.

‘Compromise’ in reference to F-35 (...in general, and F-35B most often) is used in its pejorative, i.e. to “accept standards that are lower than is desirable.” Hence, in my view, its use tends to perpetuate the negative rather than accentuate the positive. Some would say that’s splitting hairs; so be it. Engineers will understand that precision. :salute:

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 22:09
by johnwill
quicksilver wrote:Note differences betwixt a B strut and that of C in this pic (and others on Interweb). I believe the mechanism aft of the strut is called a ‘drag brace.’ Where would that go on a B given the lift fan? Additionally, imagine a redesign of the whole forward fuselage to accommodate the size and weight of that strut in a B vs the existing gear. Now, add an entire (soup to nuts) test program to qualify said aircraft.

Use the existing strut? Using what device to attach said strut to the cat shuttle?

As you finally concluded, ‘crank up the WOD and/or add a ramp to the ship’ is the right answer.


The drag brace on the C is aft of the gear and on the A and B it is forward of the gear. No interference with the lift fan.

Adding a launch bar was mentioned as a necessity for cat shots. Could it be done? Maybe. Should it be done? No.

I don't claim to be an expert on this topic, but I was the General Dynamics structural engineer on F-111B carrier suitability tests at Pax River in 1968 and for F-16 arrestment tests in 1979 at EAFB.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 22:23
by quicksilver
“The drag brace on the C is aft of the gear and on the A and B it is forward of the gear. No interference with the lift fan.”

The point I was trying to make from the pic of the ‘C’ was that to put a ‘C’ strut on a ‘B’ would require accommodation of the drag brace in space/structure that is occupied by lift fan. Is that incorrect?

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 22:42
by steve2267
quicksilver wrote:Steve, some understand that ALL aircraft designs are an amalgam of trade-offs between a multiplicity of competing requirements. Most do not.

Compromise’ in reference to F-35 (...in general, and F-35B most often) is used in its pejorative, i.e. to “accept standards that are lower than is desirable.” Hence, in my view, its use tends to perpetuate the negative rather than accentuate the positive. Some would say that’s splitting hairs; so be it. Engineers will understand that precision. :salute:


Your beating is finally getting through. Keeping in mind a wider potential audience than just other technically astute individuals is smart, and something to bear in mind. Thank you.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 23:45
by quicksilver
sprstdlyscottsmn wrote:Heh, my favorite "that would be neat, but stupid" thought experiment is a Typhoon sized and shaped SSCVN. Instead of ballistic missile tubes, a small Hangar deck. An elevator right in front of the conning tower to get the F-35B to the launch deck. Have the top hatch that opens be the JBD and have the elevator treated for heat resistance. STO right off the elevator and VL right back on it.

Yes I already know it's stupid and would never work in reality, but its still fun from a Sci-Fi kinda perspective.


Neat but (goofy)? Try this on for size —
https://www.secretprojects.co.uk/thread ... rier.2372/

Or how about a people pod?
https://theaviationist.com/2013/12/06/e ... ng-pods-2/

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 23:53
by sprstdlyscottsmn
Oh yeah! I remember reading about that system. Supposed to be gyro stabilized so that the Harrier only needed to hover and the arm would grab it. Good times.

Re: F-35C design changes from -A

Unread postPosted: 21 May 2019, 23:58
by quicksilver
Ponder for a moment the ejection envelope...(under the skyhook apparatus).

Re: F-35C design changes from -A

Unread postPosted: 22 May 2019, 02:56
by spazsinbad
Ah Da SkyHooks (famous Oz band in the 1970s) but also plenty of HOKiness on this forum searching on dem SKYHOOK:

viewtopic.php?f=61&t=52576&p=357975&hilit=skyhook#p357975
& download/file.php?id=23940

Image

Re: F-35C design changes from -A

Unread postPosted: 26 Jun 2019, 14:02
by mixelflick
spazsinbad wrote:Ah Da SkyHooks (famous Oz band in the 1970s) but also plenty of HOKiness on this forum searching on dem SKYHOOK:

viewtopic.php?f=61&t=52576&p=357975&hilit=skyhook#p357975
& download/file.php?id=23940

Image


Other than the Goblin fighter trapeze in the B-36, this might well exceed it in danger. At least with the Goblin if it missed the hook, it had enough altitude to recover.

Not so here!

Re: F-35C design changes from -A

Unread postPosted: 26 Jun 2019, 15:59
by SpudmanWP
It's no more dangerous than a STOVL landing at sea today, in terms of fuel & altitude for recovery... well, maybe just fuel :roll:

Re: F-35C design changes from -A

Unread postPosted: 26 Jun 2019, 16:58
by quicksilver
Ejection envelope in any kind of sea state apart from ‘calm’ would be interesting to see — even with a stabilized crane system. It would also be interesting to understand the degree of precision required in both the crane and the cockpit for ‘capture’ of the aircraft by the crane.

Re: F-35C design changes from -A

Unread postPosted: 26 Jun 2019, 17:10
by SpudmanWP
The F-35's ejection envelope is 0/0 with auto-eject in STOVL mode.

mk16_f-35[1].pdf
(471.84 KiB) Downloaded 48 times

Re: F-35C design changes from -A

Unread postPosted: 26 Jun 2019, 17:18
by quicksilver
Dude, you have an obstruction near or above the seat’s pathway out of the jet (the crane). You also have a very restrictive wind envelope given the turbulent flows that are going to come off of the ship, which will further complicate safe ejection probabilities.

Re: F-35C design changes from -A

Unread postPosted: 26 Jun 2019, 17:43
by quicksilver
SpudmanWP wrote:The F-35's ejection envelope is 0/0 with auto-eject in STOVL mode.

mk16_f-35[1].pdf



I would also point out (wrt f-35) you have the AAI/doors in the fuselage structure where this device would nominally capture the jet. Reminder at the link —

https://images.search.yahoo.com/images/ ... r2=piv-web