Operational Performace Comparison: Viper, Beagle, and Stubby

The F-35 compared with other modern jets.
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sprstdlyscottsmn

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Unread post09 May 2018, 22:53

viper12 wrote:
sprstdlyscottsmn wrote:There IS a 1,000kg ton (tonne, long ton, or metric ton) which is 2,200 lb.


Just to nitpick a bit, a long ton is actually different, being the heaviest of all tons around ; it's 2,240lb = 1,016kg : https://en.wikipedia.org/wiki/Long_ton

I did not know that. Thanks! I love learning new random bits.
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Unread post10 May 2018, 02:29

The most evident proof of F-35's maneuverability limitation in 2015:
Pilots complained about F-35's pitch rate.
Now, who complains F-35's pitch rate? Those airshow moves clearly contradicts that.
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Unread post11 May 2018, 10:23

Spurts, thank you very much!

Do you mind if I repost your explanation elsewhere?
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sprstdlyscottsmn

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Unread post11 May 2018, 14:20

By all means, do.
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Unread post14 May 2018, 20:52

Further question; why would the F-35 be weaker in the 20-25 AOA range where the F-16 dominates? Is there anything to the idea that the F-35 was optimized for instantaneous turn rate while the F-16 was optimized for sustained turn rate?

Thank you for clarifying the issue of fineness ratio vs area ruling.

F-35C vs F-35A is interesting. The F-35C lacks the little wing root vortex generators that the A has. Presumably it has to generate a lot of lift at a fairly low AOA for carrier operations. Which makes me wonder; what would happen if you put an F-35C wing on an F-35B? STOVL operations require quite a bit of low-airspeed lift too.

One of the things I remember when I read earlier drafts of the operational performance comparison is that the F135 engine has surprisingly uninspiring specific fuel consumption. Given that it's a generation newer than the F100/F110, it should have a higher overall pressure ratio and a hotter turbine inlet temperature. It's also got a rather high bypass ratio. All else being equal, those things should make it an exceptionally efficient engine. But it isn't.

What is your guess as to why that is? I was thinking that the LO features of the nozzle trade away a bit of SFC. But that's just a guess. Could it be something else? Could the compressor have a rather low isentropic efficiency in exchange, say, for compactness, light weight or good throttle response?
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sprstdlyscottsmn

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Unread post14 May 2018, 21:55

collimatrix wrote:Further question; why would the F-35 be weaker in the 20-25 AOA range where the F-16 dominates? Is there anything to the idea that the F-35 was optimized for instantaneous turn rate while the F-16 was optimized for sustained turn rate?


We cannot draw the conclusion that the F-16 was also using 20-25 AoA. At no point does the test report indicate the regime the F-16 was using. If anything, we can conclude the F-16 was at less than 25 degrees as that only allows 1G in the CAT-I configuration while 20 degrees is around 7G IIRC.

The F-16 was optimized to reduce speed lost in a max pull. The F-35 is optimized to lose and gain speed as needed.

collimatrix wrote:F-35C vs F-35A is interesting. The F-35C lacks the little wing root vortex generators that the A has. Presumably it has to generate a lot of lift at a fairly low AOA for carrier operations. Which makes me wonder; what would happen if you put an F-35C wing on an F-35B? STOVL operations require quite a bit of low-airspeed lift too.


The F-35C also has full span flaps/flaperons and a large lifting tail. I expect its lift curve looks very different than the F-35A. As for a STOVL C (or big wing B) I doubt it would even be able to operate. Adding 160ft^2 of wing and likely another 60ft^2 of tail is going to add a lot of weight. The C is the heaviest variant and it isn't all in the landing gear and longerons. Think instead of it this way, the difference in weight from the A to the B is all STOVL requirement, now add that weight to the C. It would also then be too wide to operate from small deck carriers.


collimatrix wrote:One of the things I remember when I read earlier drafts of the operational performance comparison is that the F135 engine has surprisingly uninspiring specific fuel consumption. Given that it's a generation newer than the F100/F110, it should have a higher overall pressure ratio and a hotter turbine inlet temperature. It's also got a rather high bypass ratio. All else being equal, those things should make it an exceptionally efficient engine. But it isn't.


There are a LOT of systems on the F-35. That requires a LOT of power. That power comes from the gearbox on the F135. It takes fuel to keep that gearbox adequately powered. I agree that on the surface I would expect the F135/F119 to have a better TSFC than the F100/F110 line. I don;t have enough info here to give a better answer.
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Unread post15 May 2018, 05:18

zero-one wrote:
sprstdlyscottsmn wrote: Also, the F-35C still has enough "oomph" to break Mach 1 with six one-ton JDAMs and four A-A missiles. How many navy planes can even carry that load? (F-35C only) How many fighter aircraft in the world can even carry that load? (F-35A, F-35C, F-15E) And how many of those are single engine? (F-35A/C only)


Hi sprst, Im curious about this line? Its amazing, but were Flankers and other European fighters also taken into account?

Also when we say six 1 ton JDAMs are we talking tonnes 1,000 pound Jdams or tonnes 2,000 poud JDAMs. cause I tried to convert and it seems that there are a few different kinds of tonnes. 1 is equivalent to around 1k lbs and the other is around 2k lbs


6 2k lb JDAMS
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sprstdlyscottsmn

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Unread post29 May 2018, 17:08

With my new sheet I'm taking another look at how I was going to be scoring the aircraft. I decided to make a scaled effect list for ECM and a radars ECCM as well as working an assumption of tracking range vs detection range based on advancement of radar technology.

Previously it was a generic "if the radar can detect you then it can track you, and if the ECM can detect the radar in can jam it. Jamming reduces detection range by 50%" I never liked how that was very cut and dry and didn't play in to the intricacies of modern radar and ECM at all. I spent a few days pouring over garrya's blog until I came up with something that I feel better approximates reality but is still simple enough for me to implement.

I know 100% that what I do here is not correct as the truth about ECM and ECCM is extremely classified and anyone who knows how my analysis is wrong will not be allowed to tell me how to make it right.
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Unread post29 May 2018, 19:43

Actually tonnes/tons should be generally either 2,000 pounds or 1,000 kilograms.
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sprstdlyscottsmn

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Unread post04 Jun 2018, 18:36

For the sake of everyone understanding the accuracy that I drive toward for my modeling I am showing the calibrations I used for the Strike Eagle (-229). Clean here refers to no ordnance or CFTs, AA refers to 8 missiles, CFTs, and LANTIRN (configuration found in -1 and also used in actual combat)

I used the clean 40,000ft accelerations to make sure my actual excess thrust is in the correct ballpark.
Mudhen Cal Accel Clean 43-600.PNG


I used the AA 40,000ft accelerations to make sure my supersonic drag model for ordnance is in the correct ballpark.
Mudhen Cal Accel AA 60-700.PNG


I then use the flight envelopes to make sure that my thrust values at key speeds are correct.
Mudhen Cal Env Clean 40-000.PNG

Mudhen Cal Env AA 55-000.PNG


I use the AA STR plot to make sure my thrust values at 20,000ft are calibrated with my dynamic Oswalds Efficiency Factor.
Mudhen Cal Sust AA 55-000.PNG


And I use Max End fuel flows and Max Range Opt Cruise values with AA loading across almost the entire fuel range to calibrate my induced drag and my dynamic fuel flow model.
Mudhen Cal Fuel AA.PNG


Once I get my model to this level of calibration I am confident that I can simulate a wide range of performance parameters including those not found in the FM.
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Unread post05 Jun 2018, 08:51

I really like your approach sprts! :D

This is really educational, thanks a lot!
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Unread post05 Jun 2018, 10:31

sprstdlyscottsmn wrote:
collimatrix wrote:I am curious if you would be willing to make a post giving your interpretation of the design priorities and general capabilities of the F-35.

When I read your first work in this thread, I had come away with the following impression of the F-35:

-The F-35 doesn't compare so well to the best fourth gen fighters in a guns only dogfight if both are clean and at half fuel.

-Part of this is because the F-35 carries a ridiculous amount of fuel, and because it has internal weapons bays. If the two fighters are given equal internal fuel endurance, and an actual air to air weapon load, the F-35 quickly pulls ahead.

-Still, all those weapons bays and all that fuel have to fit somewhere. The F-35 is a rather stubby, tubby plane with a shape that works very well for stealth and reasonably well for subsonic flight efficiency. However, the F-35 has somewhat unavoidably high wave drag because it just isn't that long and pointy, so its transonic and supersonic performance are less impressive.

I was curious if you might confirm or dispel those general conclusions, and what your overall take on the F-35's aerodynamic priorities is.


The F-35A is the most "empty" fighter aircraft... possibly ever. With an empty weight of 29,300 lb and a total internal load of 23,500lb (weapons and fuel) and having it's length dictated by the LHA/LHD elevators, it certainly had to make concessions.

Wave drag can be thought at a very high level as fundamentally coming from Area Rule and Fineness Ratio.

The FR is where the F-35 suffers compared to the F-22 (as a directly applicable example). They have similar body width yet the F-35 is a dozen feet shorter. Yet, despite being a dozen feet shorter with a similar body width and shorter wingspan the F-35A manages to have about 2,200lb MORE internal carriage (between fuel and weapons) because it only has a single engine to deal with.

Now, the Area Rule is how smoothly the cross section increases down the length of the plane. Look closely at the F-35A. As the peak of the canopy blends back toward the fuselage the pointed intakes begin. Once the intakes meet the center body the bumps for the A-G weapons bay begins. Once those bumps reach their peak the wing begins. Follow this thought process as you look at the side and bottom views of the F-35A and you will see that it appears to have near flawless area ruling. Look at the bottom. Why doesn't it have a flat bottom like the F-22? It would be cheaper to manufacture and make it roomier in the weapons bays right? Instead it looks like a river coursing over rocks. The lower surface is carefully sculpted.

This is why an F-35A can effortlessly exceed 1.6M if the pilot chose to ignore the limits. Evidence of this? The F-35C has been taken to 1.6M. It has the same engine. It has a much larger wing that contributes to a poorer wave drag (as evidenced by the transonic acceleration times). If the same engine can push the plane with much more wave drag to 1.6M then it can easily push the F-35A beyond that. Also, the F-35C still has enough "oomph" to break Mach 1 with six one-ton JDAMs and four A-A missiles. How many navy planes can even carry that load? (F-35C only) How many fighter aircraft in the world can even carry that load? (F-35A, F-35C, F-15E) And how many of those are single engine? (F-35A/C only)

The design priorities of the F-35 are to be the perfect plane for the actual missions the F-16 and F/A-18 do in real life. Even ignoring the stealth and systems side of it, just looking purely at payload and performance, it exceeds the capabilities of the teen-series by far.

A clean F-16 is a hotrod, but it is also useless. Send it out on a CAP mission and it sees an increase in form drag and weight from missiles, pylons, fuel tanks, and maybe ECM gear. Send it out for a strike mission and it sees a bigger increase in form drag and weight from bombs and targeting pods in addition to the missiles, pylons, fuel tanks, and ECM gear.

A clean F-35 is not quite as much of a hotrod. Send it out on a CAP mission and it sees the weight of the missiles, no form drag. Send it out on the strike mission and it sees the weight of the bombs, no form drag. No pylon drag, no fuel tank drag, no ECM drag, no targeting pod drag.

Before you even add in the VLO properties, the F-35 is one of the finest warplanes ever designed.

As to the F-16 "dogfight", I will get to that later.

*EDIT* Now it's later. The only people who believe the F-35 lost a dogfight to an F-16D with two empty gas tanks are those who only read the hit pieces and not the test pilots report on the encounter, that was attached to at least one of the hit pieces.

The test was a CLAW test of the AoA region between 20 and 25 degrees AoA. The F-35 in question was not 3F or even unrestricted 3i. What the test pilot commented can best be summed up in a few points.

1. The CLAW begins blending from low AoA logic to high AoA logic in the 20-25 degree region. This should be increased to 35 AoA as at 25 AoA the F-35 still flies as if its at low AoA.
2. At the specified test AoA, the F-35 cannot generate sufficient rate to achieve or maintain an offensive position on the F-16 target. The specified AoA also does not allow sufficient energy retention.
3. Overall control responsiveness felt sluggish, particularly in pitch and yaw. Previous flight tests on later CLAW builds (remember, test was not done using latest CLAW in test at teh time) already demonstrated the safe use of more rapid control deflections.

So to further summarize: Open up and adjust the CLAW, don't fight at 20-25 AoA.

Recall Dolby Hanche talking about how he can rake the nose hard in an F-35 to get angular position and then accelerate quickly to recover the lost energy, an acceleration he states the F-16 would have to drop it's nose to achieve.



I guess weasel1962 didn't read this thread....... :wink:
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Unread post05 Jun 2018, 13:03

So clean and without CFTs the -229 Eagle can supercruise at Mach 1.1 ?
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Unread post05 Jun 2018, 13:41

Yes, but that doesn't get you anything.
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Unread post05 Jun 2018, 19:33

marsavian wrote:So clean and without CFTs the -229 Eagle can supercruise at Mach 1.1 ?


I also doubt the fuel consumption is worth it. Aircraft designers tend to avoid having the cruise speed in the Mach 0.9-1.2 range IIRC because the fuel efficiency is relatively bad.
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