Operational Performance Comparison: Viper, Beagle and Stubby

[element1loop]

So, the question is how easy is it for an F-35 to hit that top speed? Does it take max AB to sustain it? Or can it reach that speed and pull back a little to sustain it?

That is a cracker question given how clean it will be and how little extra degree AOA required. If it's not engine speed-limited, as appears to be the case, after acceleration to M=1.6, yes, it should be able to throttle back some on fuel rate and just sit there. The software should automatically do that for the pilot to keep it in envelope, and thus extend the time available at or near to maximum speed part of envelope for altitude and weight, @ ISA.

[johnwill]

Modern designs are intricately woven balances that ideally are right on target. If not then the design is bad.

The easiest example- weight and structural life. In fact the latest reports of three times life on the test article for the F-35 tells me one thing. THE F-35 DESIGN MAY BE TOO HEAVY! If it doesn't break then it's too heavy. It could be made lighter and have the desired life. That's the interrelationship of design elements to performance.

MHO,
BP

Of course you are correct, it may be too heavy. The question arises, what do you do about it? Do you go back and scrape a few hundred pounds off the structure, then reanalyze and retest a new light weight airframe for two lifetimes, at considerable cost and schedule delay? Or do you lug around the extra weight and accept a tiny performance penalty? Another important factor, especially for F-35, is the verified three lifetime durability test allows longer inspection intervals for operational airplane structure, with a huge potential cost savings, considering how long the airplane is planned for service.

Also, having the extra structural margin allows for inevitable future gross weight increases from system upgrades. Remember the F-16 grew about a pound a day in its first ten years of service.

[blindpilot]

... Or do you lug around the extra weight and accept a tiny performance penalty? Another important factor, especially for F-35, is the verified three lifetime durability test allows longer inspection intervals for operational airplane structure, with a huge potential cost savings, considering how long the airplane is planned for service.

Also, having the extra structural margin allows for inevitable future gross weight increases from system upgrades. Remember the F-16 grew about a pound a day in its first ten years of service.

As an old pilot of the "707 type" I enjoyed the security of the extra weight. After the Lockheed Electra experience, Boeing was terrified not to keep over building their new jet. And so 6 decades later the KC-135's are still trucking along. (hopefully not for too much longer ) There are certainly advantages! I simply use that as an example that the various performance elements are very much interrelated. So usually a design spec is on target.

MHO,
BP

[Corsair1963]

https://youtu.be/O_b6vCOLLz8

[steve2267]

F-35B issues forced the SWAT weight reduction stand down. They shaved weight off the Bee like there was no tomorrow (because there wasn't). I would not be surprised to learn the A model is slightly heavy because it either uses a lot of B parts, or the "cousin A" part to the B part was scaled on some basis and did not undergo full analysis (to save analysis / design dollars). But this is pure conjecture / supposition on my part. Would be neat to read comments from an engineer or engineering manager in charge of that process and why the A ended up slightly heavy.

[ricnunes]

1- I also don't think that the F-35 will be cleared (if possible) to fly above Mach 1.6 while carrying it's full internal weapons loadout of 2x2000lb (usually GBU-31s) plus 2xAMRAAMs but how about when carrying 4xAMRAAMs (only)? Or only 2XAMRAAMs or even clean (although this last one - clean - is kinda useless in the real world).

If there's no weight or ISA info it's all guessing.

I'd default presume no internal weapons in that case, not the other way.

Not sure if I'm misunderstanding your post/point but if you're presuming that the F-35 top speed of Mach 1.6 isn't with full weapons load (internal) than please take a look at this (from LM):
https://a855196877272cb14560-2a4fa819a6 ... s9-183.pdf

It clearly says that the F-35 top speed of Mach 1.6/~1200 MPH is with with full internal weapons load which in the case of the F-35 is 2x2000lb air-to-ground stores plus 2xAMRAAMs.

But and in case I misunderstood your post, please disregard...

[ricnunes]

@blindpilot, steve2267 and sprstdlyscottsmn,

First of all thanks for the replies, they make sense.

....
... hence why and probably the main reason why I'm "speculating" if the F-35 could have its top speed increased/expanded...

Let's look at the phrase "if the F-35 could."

There is a difference between what the design on paper could be adjusted to, and what the aircraft built and coming off the assembly line, can be made to achieve. Even the F-16 when given the bigger engine, had to have it's "Big Mouth" inlet redone ... in the design and manufacturing. Without that change the "Big Mouth" F-16 would not have seen a performance enhancement from the "MO POWER !" engine. (which coincidentally had to be installed at the assembly line.)

Modern designs are intricately woven balances that ideally are right on target. If not then the design is bad.

The easiest example- weight and structural life. In fact the latest reports of three times life on the test article for the F-35 tells me one thing. THE F-35 DESIGN MAY BE TOO HEAVY! If it doesn't break then it's too heavy. It could be made lighter and have the desired life. That's the interrelationship of design elements to performance.

So - "could it?" Probably so at the margins. But if it does, then that part of the design is "bad." The design targets are the exact performance desired. If you want something else. Ask Lockheed. They can do Mach 2, or even Mach 3, or hypersonic. The customer seems to be getting exactly what they asked for with the F-35, according to test reports. That on it's own is remarkable for a fighter aircraft design.

MHO,
BP

You make some excellent points above.

However I would urge/ask you to take a look at the points that I mentioned just before the "...hence why and probably the main reason why I'm speculating if the F-35 could..." and give me your feedback?

[steve2267]

<snip>

You make some excellent points above.

However I would urge/ask you to take a look at the points that I mentioned just before the "...hence why and probably the main reason why I'm speculating if the F-35 could..." and give me your feedback?

You know, this is a real pain in the a$$. You refer to questions saying "that I mentioned just before the ..." I had to go back two pages to this post here. Did I get the correct post? I hope so.

We've been beating this dead horse for a while now. So, I'm taking out my 1911, and hopefully I can put the summbitch out of its misery with a few headshots.

Yes, some of you have definitely far better knowledge than I have about aerodynamics (and as such thanks again for your replies), so I guess you'll have to excuse be if I'm being a bit of a "pain in the a$$" about this subject (and as such not "giving this a rest", just yet ) but I have the following point/question which I would like to address (and for which I would really appreciate a reply on your part) which BTW was a point/question that I probably should have mentioned earlier:
- Yes, it's indeed a fact that the F-35 was designed with a top speed of Mach 1.6 in mind and as such I understand the designer/manufacturer when developing an aircraft will design it for such top speed and likely not more.
However, isn't the top speed of Mach 1.6 for the F-35 a top speed with full internal weapon which is a quite heavy payload of 2x2000lb (usually GBU-31s) plus 2xAMRAAMs?

Yes, I believe that to be correct: The 1.6 Mach top end design specification speed for the F-35 was with two AIM-120 missiles and two 2,000lb bombs. [BANG]

This I believe, is my main point for "keeping up" this subject. Yes, I understand that weapon payload is internal and as such shouldn't produce Parasitic drag but it adds weight and as such should produce lift-induced drag, right?

Yes, lift-induced-drag increases with lift. By carrying two AIM-120 missiles and two 2,000lb bombs, the F-35 weight is increased by nearly 5,000lb, so yes, lift-induced-drag would be higher compared to an F35 not carrying any weapons. [BANG]

Even thou the lift-induced drag is reduced at higher speeds, it should still be present (namely around Mach 1.6-1.8 ), no?

Yes, lift-induced-drag is still present at 1.6-1.8 Mach as long as the aircraft is generating lift (e.g. not flying a 0g parabolic arc, but a 1g level flight path). [BANG]

I guess that my point/question above could be "subdivided" into the next two "sub-points":
1- I also don't think that the F-35 will be cleared (if possible) to fly above Mach 1.6 while carrying it's full internal weapons loadout of 2x2000lb (usually GBU-31s) plus 2xAMRAAMs but how about when carrying 4xAMRAAMs (only)? Or only 2XAMRAAMs or even clean (although this last one - clean - is kinda useless in the real world).

Neither the JPO nor any operator (USAF, USN, USMC, RN/RAF, RAAF etc etc etc) has made a requirement, nor even suggested a requirement, that the design specification top speed of the F-35A/B/C be increased above 1.6 Mach. [BANG]

So, this question is moot. That being said, I do not believe the theoritically, maximum possibly attained Mach is affected much by four AIM-120s vs two AIM-120s and two 1000lb (Killer Bee) or 2000lb bombs.

I have seen no one here on this forum even hint that such an increase has been suggested or discussed, let alone teased.

2- My second point which in some part is related to the points above, is that with previous fighter aircraft generations the top speed requirement was for a clean aircraft like for example Mach 2 for the F-16 or Mach 2.5 for the F-15 or Mach 1.8 for the F/A-18, etc... (but again please correct me if I'm wrong). So in case I'm not wrong, when the JSF/F-35 was designed it's maximum speed was for a full internal weapons load (albeit internal) which was kinda the opposite when compared to previous generations of fighter aircraft hence why and probably the main reason why I'm "speculating" if the F-35 could have its top speed increased/expanded since there's still a room for lower/lighter internal weapons load? (this is more a question than an affirmation, BTW).

Yes, IMHO, the design of the F-35A appears to have sufficient margin that the top end speed placard of the aircraft could probably be increased. This is just a SWAG on my part: 1.8 Mach is probably not a problem from a thrust / drag perspective. John Will's comments would suggest that structure / controls are probably not a problem. 2.0 Mach is probably even attainable, maybe even up to 2.2 Mach, but this is conjecture on my part. As you start to exceed 2.0 Mach, however, air intakes either have to be designed for a specific Mach requirement, or the aircraft requires variable geometry inlets, or some other means, most probably mechanical in nature, to control the location of the shock in the fuselage air intake inlet. [BANG]

Having said all this, it is purely conjecture on my part. LM may have an idea how fast the design can really go from CFD calculations. But since it was not a program requirement, I doubt they even ran the wind tunnel much past 1.6 Mach. When they tested their large models in the AEDC 16T (16'x16') transonic wind tunnel, that tunnel probably could not get much past 1.6 Mach anyway, owing to the amount of blockage the model presented to the tunnel. If it could, maybe they got some test points at 1.7 or 1.8 Mach. (Why would they have done so? Well, flight test reportedly went up to 1.67 Mach, so to avoid bad surprises during flight test, might as well get some WTT data points at 1.67 Mach or slightly higher just to avoid nasty test flight surprises which have killed test pilots in the past.)

Finally, someone also brought up the intakes. But regarding this, I think that the difference between Mach 1.8 and Mach 1.6 (or Mach 1.67 tested) isn't that big so I'm a bit skeptical on the impact that the F-35 intakes may have on preventing the F-35 to reach Mach 1.8. Besides, wasn't a F-16 tested with DSI and it still managed to reach Mach 2.0 (basically it's top speed or very close to it, this without DSI)?

Yes, the Block 30 F-16 used to test the DSI reached a maximum speed of 2.0 Mach:

JSF Diverterless Supersonic Inlet
By Eric Hehs Posted 15 July 2000

<snip>

The flight tests covered the entire F-16 flight envelope and achieved a maximum speed of Mach 2.0. The modified aircraft demonstrated flying qualities similar to a normal production F-16 at all angles of attack and at all angles of sideslip. Lockheed Martin test pilots performed two inflight engine restarts and 164 successful afterburner lights, with no failures. Fifty-two afterburner lights were performed during hard maneuvers. No engine stalls or anomalies occurred during the test flights.

<snip>

http://www.codeonemagazine.com/article.html?item_id=58

[BANG]

The devil lives in the details. From an engine thrust perspective, the F135 probably has plenty of power left. The F-35 design is pretty damn clean, so there is probably not a drag issue. The inlets are fixed, however, so the inlets probably will have a top end, limiting Mach. Structurally, it would seem, based on John Will's comments, that there are no show stoppers, but analysis would still be required. Control issues, again based on John will's comments, would probably need to be carefully considered / analyzed / tested etc.

What I wonder about, though, would be thermal effects. Does the increased aero heating have any issues on canopy structural integrity? What about structural integrity, durability, and reliability of the various stealth compounds that are being used? Are there any potential issues regarding increased engine wear?

And if one part of the design has to be changed to meet some mythical, higher-than-originally-designed Mach number, there is a high probability that change cascades somewhere else and forces other design changes. All which have to be verified still meet all other specifications, either by analysis, or by flight test, or both. Which all costs money.

So I ask you, ricnunes, do you want to see an $80M F-35A? Or would you rather dump a LOT of extra development money into re-design / analysis / flight test to see a possible increase in top end Mach of a few tenths?

Now, before you ask, how many tenths more do you think you can get, I will say I already gave you a fuzzy answer above. if you want a harder number, I am going to ask for your Visa or MasterCard number. I will cut you a break and only charge $100(US)/hr. However, I will caution you that first of all, Lockheed Martin is probably unwilling or unable to give me the necessary hardware CAD files or flight test data or CFD results thus far. I also doubt a Freedom of Information Request will pry the prerequisite hardware geometry loose from the government. So I will have to CAD everything up from scratch with a lot of what-if's and thumb guesses. Then I will model the aircraft using OpenFOAM, maybe NASA's OverFLOW if I'm feeling jiggy. Of course, I have no test data to anchor my CFD results, so... they will be a SWAG too, but a CFD swag, which we all know will be correct, because, well... CFD! I estimate a minimum starting cost of $10,000 to begin such an analysis? Do I have your permission to proceed? [BANG]

In summary, can the F-35 potentially exceed 1.6 Mach? Yes, it appears it can. By who much? (What is your Visa/MC # again?) 1.8 - 2.0 Mach seems reasonable to guess, but the devil lives in the details. The -A model will most probably be fastest -- smaller wing than the -C, more gas than the -B and no lift fan "shoulders." [BANG][BANG]

I'm out of rounds. Is the poor horse dead yet? Can we move on?

[element1loop]

1- I also don't think that the F-35 will be cleared (if possible) to fly above Mach 1.6 while carrying it's full internal weapons loadout of 2x2000lb (usually GBU-31s) plus 2xAMRAAMs but how about when carrying 4xAMRAAMs (only)? Or only 2XAMRAAMs or even clean (although this last one - clean - is kinda useless in the real world).

If there's no weight or ISA info it's all guessing.

I'd default presume no internal weapons in that case, not the other way.

Not sure if I'm misunderstanding your post/point but if you're presuming that the F-35 top speed of Mach 1.6 isn't with full weapons load (internal) than please take a look at this (from LM): ...

That's what I made clear here:

viewtopic.php?p=401986#p401986

… With the F-35A you don’t have that problem at all, it’s a very clean lift-body with clean short wings. So even if you added maximum internal payload of 5,700lb, that weight increase is still only 8.14% of the total 70,000 lb MTOW (my figures are about 2 to 3 years old here, I need to update the spreadsheet).

In that state TOW is 52,949 lb with 17,051 lb payload available.

So the AOA increase for the High-High area of the envelope is still going to be just a very small fraction of 1 percent [1 degree ... it was bed time] AOA increase, at that higher speed. Thus the F-35A will still be able to use 100% of its speed envelope, given it's not being limited by drag or by the engine (the envelope makes clear it is not engine speed-limited). …

[basher54321]

Ran into this from an F-5E case study but only from [cough] 100,000 M2 capable Jet sorties but might be representative.

Vietnam Combat Speeds

[marsavian]

In Tom Cooper's F-14 book there were claims of Tomcats chasing Foxbats at over Mach 2. These days it would be Mig-31s which would be going at these speeds maybe armed with hypersonic attack missiles. Mach 1.6 just is not going to cut it for intercepting these unless it's heading your way.

MiG-25RBs participated in the first Iraqi air offensive against Khark Island, which was launched in August 1982. Operating at high speeds and altitudes, they proved exceptionally difficult to intercept. For even
the best and most aggressive IRIAF Tomcat crews, a successful ‘Foxbat’ interception was the ultimate exercise in precision flying and high-speed operations, causing heavy cockpit workload. Yet, like all IRIAF pilots,
those of the 8th TFW were eager to attempt an engagement. This eagerness intensified after September 1982, when IrAF MiG-25RBs started flying missions deeper into Iran, striking civilian targets and causing dozens of deaths. Iraqi ‘Foxbat’ operations grew to
such a degree that F-14As deployed at Mehrabad had to conduct 24-hour CAPs over the Iranian capital. During these difficult times, patrols were limited to nocturnal hours or during Friday Prayers. CAPs were initially
conducted at 30,000 ft, but when a MiG-25 was detected, the F-14s would climb to 40,000 ft and accelerate to Mach 1+. The ‘Foxbats’, however, usually operated at between 60,000 and 70,000 ft and flew between Mach 1.9 and 2.4.

They proved evasive targets, and it took the IRIAF some time to learn how to intercept them – mainly by changing patrol altitudes, positions and speeds. F-14A crews would also occasionally act as fighter-controllers, directing other fighters to intercept Iraqi MiG-25s, as well as Tu-22B, Tu-22KD and Tu-16 bombers.

It is not known exactly when the IrAF lost its first ‘Foxbat’ to IRIAF Tomcats. On 4 May 1982, an IrAF defector explained to his Syrian interrogators that Iraq had lost 98 fighters and 33 pilots to Iranian F-4s and F-14s. This total included a MiG-25 to an F-14-launched Phoenix missile. The Iraqis were not likely to reveal such details without good reason. What is confirmed, however, is that it came when the ‘hunting season’ for Iraqi MiG-25s was opened by the IRIAF’s 8th TFW.

At 1240 hrs on 16 September 1982, two F-14As on a CAP between Bushehr and Khark were advised by GCI of a single contact approaching Khark at 70,000 ft and travelling close to Mach 3. The Tomcats turned
into the threat and the leader’s RIO activated his AWG-9 to start the interception of what was clearly a MiG-25RB. After few minutes the target was acquired. The AWG-9 established a targeting file and a single AIM-54A was fired from a range of over 100 km (60 miles). There was no reaction from the Iraqi MiG, and the missile swiftly cut the distance to the target and slammed into it, creating a giant ball of fire. The pilot was reported to have ejected over the sea, but he could not be found by Iranian helicopters – the shark-infested waters of the Persian Gulf were never a promising area for search and rescue operations.

According to Iranian sources, this was the first confirmed kill of an Iraqi ‘Foxbat’ by IRIAF F-14s, although the Iraqi defector had claimed that one had been lost prior to this date. The victory confirmed that the AWG-9 and AIM-54 could engage and destroy MiG-25s flying at almost Mach 3. There would be other successes too, but the IrAF remained defiant. On 22 September a MiG-25RB roared high over Tehran. Clearly, the IRIAF could not tolerate such Iraqi missions over the Iranian capital. Therefore, F-14As of the 72nd TFS, deployed at Mehrabad, were always well supplied with AIM-54s, as these offered the best chance of intercepting Iraqi aircraft operating in the area.

Additionally, three F-14As normally used for testing and training purposes had their AWG-9s and communication equipment modified to allow them to operate as ‘mini-AWACS’. These jets not only provided early warning coverage for the Tehran area, but also guidance for other
fighters – particularly F-4Es from TFB 1 – intercepting Iraqi bombers. Their patrols frequently lasted 12 hours, during which time they would refuel from a KC 707 up to five times.

Despite the Tehran overflights, the next engagement with ‘Foxbats’ took place near Khark. On 1 December 1982, an F-14A flown by Maj Shahram Rostami was on a CAP between Khark and Bandar-e-Khomeini, covering a convoy of merchant ships en route to Bandar
Abbas. After two hours on station, and shortly after refuelling from a KC 707, Rostami was alerted by GCI of a single contact approaching from the north at 70,000 ft and Mach 2.3 – a MiG-25. Rostami’s F-14A was at 40,000 ft and flying at only Mach 0.4 at the time. GCI control warned him that the bandit was rapidly closing to 113 km (61 miles), so the crew had to work fast. While Rostami accelerated, his RIO tried to acquire the target, but his efforts were briefly hindered when the MiG pilot activated his own ECM systems and swiftly closed to 71 km (38 miles). Despite the jamming, Rostami’s RIO was
able to obtain a positive radar lock-on and fire a single AIM-54A in a snap-up engagement from 64 km (34 miles) as the F-14A accelerated to Mach 1.5 and climbed to 45,000 ft. The missile separated properly, the engine ignited almost instantly and the hefty Phoenix thundered away trailing white smoke. After the launch, Rostami turned his Tomcat slightly to the west and reduced speed and altitude to avoid approaching the MiG too fast. He held the target just inside the radar envelope. As time passed, and the MiG continued to cut the distance, Rostami turned back to starboard. Just then, the computer-calculated time-to-impact on the weapons panel counters reached zero. The hit symbol
illuminated on the radar screen, and moments later ground control confirmed that the Iraqi fighter had disappeared from their radar scope.The MiG-25RB crashed into the sea. The pilot could not be found
despite an intensive IrAF SAR operation.

The Iraqi/Soviet ‘Foxbat’ community vowed to take revenge after this loss, and on 4 December two MiG-25PDs penetrated the airspace over northern Iran and tried to intercept an airliner flying from Turkey as it
passed over Tabriz. While searching for a target, the MiGs separated. Unknown to them, the IRIAF had vectored a single 81st TFS F-14A, flown by Maj Toufanian, into the area. His AWG-9 was on standby, and
only the ‘Combat Tree’ equipment was being used in his approach to minimum AIM-54 firing distance. As soon as the radar was activated, the ‘Foxbat’s’ on-board RWR warned the pilot of the F-14’s presence and the
MiG-25PD immediately accelerated. The Tomcat crew watched in awe as their target attempted to out-turn the AIM-54 that they had fired at it. This time, the Phoenix malfunctioned. It missed, passing behind the ‘Foxbat’, but Maj Toufanian, who was one of the first, and most
uncompromising, Iranian F-14 pilots, powered his jet up to Mach 2.2 and went off in pursuit. After the first Phoenix had missed, the Iraqi pilot slowed down, obviously feeling safe. But he had effectively signed his owndeath warrant, for a second AIM-54 blew the ‘Foxbat’ out of the sky.

[castlebravo]

In Tom Cooper's F-14 book there were claims of Tomcats chasing Foxbats at over Mach 2. These days it would be Mig-31s which would be going at these speeds maybe armed with hypersonic attack missiles. Mach 1.6 just is not going to cut it for intercepting these unless it's heading your way.

Your own data shows examples of Migs going Mach 2.5+ being killed by Tomcats that stayed under Mach 1.6. The one instance of a Tomcat going Mach 2+ was only after the first missile (fired within parameters from a much lower speed) malfunctioned and missed. While it is certainly great that the Tomcat was able to catch up to and kill the Mig with a second shot, it had already achieved a "mission kill" with the first missile.

[F-16ADF]

The Six never served in Vietnam, the Deuce did.

[steve2267]

The bags of gas the F-35 carries internally should give it very useful loiter times if used for a CAP.

Perhaps spurts might be able to give us acceleration times from 0.8 Mach to 1.6 Mach for the F-35 as compared to the teen series aircraft. If the F-35 gets to 1.6 Mach considerably quicker, the need to go faster would seem to be greatly reduced. Of course, this is probably born out in the 1.6 Mach max speed requirement anyway. But we are also talking about interceptor missions, which I do not believe were primary in the JSF requirements.

[basher54321]

The Six never served in Vietnam, the Deuce did.

Yes to much faith in the AIAA - however it was also from 1978 so don't know whether the info was lacking.