Operational Performace Comparison: Viper, Beagle, and Stubby

The F-35 compared with other modern jets.
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Dragon029

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Unread post08 Jun 2015, 14:40

Perhaps, but we also have this document saying that (when you do the maths) that the F-35 at Mach 0.75 and 40,000ft can fly for around 4 hours and over 3000km:

Image

Perhaps the official 2200km range for the F-35 is just rubbish and it can fly more than 3000km at Mach 0.94 (similar to the "over 18,000lb" payload; where the hardpoints are rated for a total of 22,300lb or more and loading ~22,000lb of payload is the only way that you could achieve an F-35A's MTOW of 70,000lb).
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Unread post08 Jun 2015, 16:25

fuel burn figures are VERY weight dependent, especially for Max Endurance.
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Unread post15 Jul 2015, 18:20

Spurts someone else in keypub who also study aerodynamic, response to your analysis :D, so what do you think ? is he right? , is he wrong?
Andraxxus wrote: []Well his work seems thorough and accurate in method, I don't share his assumptions, and accuracy of calculations. Let me put a wall of text and some data to point out his mistakes or areas I don't agree.

F-15

F-15 doesn't have fixed 27% MAC stability, its limited between 22-29,9% and typical CG travel during a mission is as follows;

Image
Its reasonable for any maneuvering is required in mid mission, so I assume CG distance is at 24% MAC, and working from wing area and Mean chord length, it translates to 3,632 feet, not 4.

At landing CG detrimental, so that aircraft will not roll back to its rear end, I assume 10 degree AOA at landing, working from wikipedia 3-view drawing and moving backwards from 22% MAC gives CG to be roughly at the 2/3 of the F-15%'s airbrake. (too lazy to draw it and upload it here)

This means distance from the center of the elevators to CG is 7,63 meters or 25,03 feet.

So for X amount of lift, 0,1451X or counter-lift from elevators is required, so roughly 85% of the lift is used.

F-15 Flight manual gives stall speed at 30000 lbs exactly at 110 knots. Calculating Clmax from these gives us Clmax=1,2028 .

Incedentally, F-15's maneuvering Clmax is given by Soviet booklet is 1,0. My calculation gave (1-0,147)*1,2028 = 1,02; not too bad.

F-16

He explains CAT-I limiter well, but its implacions not. We are looking for maneuvering conditions, not stall, so whatever Clmax he found from CFD is irrelevant. AOA@G limitation is there for structural reasons and will change the REAL Clmax of the maneuving aircraft. For example, we know F-16's turn rate, speed and altitude conditions is from its flight manual. F-16 Clmax for M0.4, M0.5 1,3991, 1,5687 respectively. For 9G at 10000 feet, its 1,1.

As for his CFD work; an F-16 blk50 at 36000lbs DI-0 stalls at exactly M0,2 at MIL thrust (according to flight manual). 78kN MIL thrust, 25 degree stall AOA, stall speed, altitude etc are all sufficent to calculate Clmax, which equates to 1,5827.

So F-16's clmax is ballpark around 1.6 for stall and around 1.3 when maneuvering due to CAT-I and 1.1 at 9G ITR turns. Of course that is if we are talking about subsonic only.

F-35

"I estimate clmax of F-35 to be 1.8" No offense to the author, thats utter nonsense, and clearly not good enough.

Typical 64A204 F-16 uses tops out at clmax = ~1,1. F-16 adds to that primarily with LERX vortices and LE flaps to delay the stall and as a result achieves Clmax = ~1,6

What if an aircraft didn't have LERX and LE flaps? Well F-15 uses very similar but thinner 64A203 airfoil. Despite wide body, and 64A006 wing roots, It barely manages to get around Clmax = 1,2

1.8?? Lets see the ONLY competitive aircraft: Su-27 has LERX, le flaps, and achieves Clmax = 1.85 with this THICK airfoil:
Image
And remember, this airfoil more or less makes up the whole Su-27, from lerx to tail, excluding nacelles. Even area from nose to stinger is shaped as a supercritical airfoil, with nose look slightly downwards to improve lift in the "tunnel". As for F-35, such lifting body design is not present on F-35 to any degree (its more like F-15's body lift than Su-27 with lifting body), has no lerx to make airflow stick to wings, and my mk1 eyeball inspection tells it uses MUCH thinner wings than the profile above. (Abominal extensions below wing roots don't count as wings)

So for F-35, Clmax = 1.4 is most reasonable assumption to me, as its right between F-15 and F-16; with # of aerodynamic features is also 0 for F-15, 1 for F-35, and 2 F-16, i just take the middle: (1,6 + 1,2) / 2. This is also ballpark similar to MiG-29 and F-18, and I assume F-35 wont have AOA limitations of F-16, which is unique to that aircraft. So;

And by that, "CL*A" of these aircraft should be as follows (I am also writing in feet so that you can compare with his)
F-15E = 608*1,2*0,85 = 620 ft2 = 57,6m2
F-16C = 302*1,3 = 423 ft2 = 36,41 m2 and 332 ft2 =30,84m2 @9G
F-35A = 460*1,4 = 644 ft2 = 59,83 m2

With these Cl*A's known, we need weight to judge performance. Lets assume dogfight 500nm out take his range graph as accurate (I am also adding Su-27 as potential adversary, and just because I like Su-27)
F-15E = 58% fuel, = 18000kg
F-16C = 83% fuel. = 11735kg
F-35A = 57% fuel. = 18082kg
Su-27 = 40% fuel. = 20060kg (50% should easily reach

While all can pull 9Gs, their ITR will differ by speed;
F-15E = 17,17 deg/s @ 292 m/s,
F-16C = 16,07 deg/s @ 313 m/s,
F-35A = 17,6 deg/s @ 285 m/s,
Su-27 = 20,96 deg/s @ 240 m/s (Su-27's clmax @M0,75 = 1,51)

For STR we simply have insufficent data. Even we assume same Cd, we have to know exact Lift-drag to even make guesstimates about STR.

Lets go on with some other mistakes:

He is right about ANY payload attached to CFT limits F-15E to M1.4 but, again, his interpretion is wrong. To simplify, F-15E's CFT has 6 stations. Two rows are simply groupped as inboard and outboard in flight manual and these do limit to M1.4.
However, F-15 carries AIM-120s on stations 3C, 4C, 6C and 7C EVEN WITH CFT INSTALLED. (those stations extrude from inside CFT, between CT-1, CT-2 and CT-3 like this:
Image

So they are NOT CFT stations, and still subjected to general CFT limit of M2.0:

Image
As for the rest, he is making assumptions. This is his idea, I don't have a clue if they are correct or not.
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Unread post15 Jul 2015, 18:56

eloise wrote:Spurts someone else in keypub who also study aerodynamic, response to your analysis :D, so what do you think ? is he right? , is he wrong?



:D

I think Spurts comparison was done after Andraxxus posted a really simplistic comparison based on clmax and turn rate.

viewtopic.php?f=33&t=25718

But there have been some corrections since then - also see
viewtopic.php?f=46&t=27333&start=15
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Unread post15 Jul 2015, 20:49

Andraax has downloaded and pick his figures from flight manuals.
Both from F-15 and Su-27SK.

If you mean to say he just invent stuff, well just download the fligh tmanuals yourself and go through them.
And then come back and correct any mistakes he made..

About the F-35, ofcourse his figures are not correct, sinse there is no flight manual at this point.
Still i'd say his assumption are not far out eighter.. meaning they look plauseble.
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Unread post16 Jul 2015, 00:10

borg wrote:If you mean to say he just invent stuff, well just download the fligh tmanuals yourself and go through them.
And then come back and correct any mistakes he made..


No I didn't mean that at all..................perhaps you are better off on a non English forum where you might understand a bit more about what's going on yes!!

Spurts comparison was also done using the same manuals - which I also have.
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Unread post16 Jul 2015, 01:42

I appreciate Andraxxus time in going through my data. I certainly have it out there to be reviewed and anyone who can aid in the accuracy only increases the overall knowledge base. I have no way of knowing which version (I have four so far) of my analysis he was judging. My responses to his points are as such, and please go back and share my responses.

Of course the F-15 doesn't have a static MAC. 27% was not the best choice on my part and I have in my most recent version recanted the "Stable" part of that discussion as the Strike Eagle borders on neutral stability per other texts of the Manual.

For Strike Eagle max lift I used 40,000lb at sea level with power off for 125 kt, yielding which gives 1.24. With his 1.2028 I think we are splitting hairs. The reason it is much lower than the others is, in my opinion, due to the lack of full instability, LEF, and any LERX/chines.

For Viper lift, he goes on about how G, speed, and altitude matter. That was not the purpose of this section. I was trying to demonstrate the highest Clmax the F-16 could generate 9G with as that will give the "best" turn, even though the CAT-1 limited gives a best turn rate at ~8G and best radius at ~3G. You cannot use mil thrust as a stall indication as installed dynamic thrust does not equal (is less than at stall speeds) rated thrust.

As for the F-35, it has Chines which perform the same action as the LERX as evidenced by the vortexes they generate so I did not penalize it. The F-35 also has LEF, so again I am not penalizing it. What he is not bringing up is that both of these aircraft are fully unstable. This means the horizontal tails make lift. This added lift "adds" to the "reference" CLmax the same as a LERX does. Relatively speaking, the F-35 has a MUCH larger tail and it is deflected at least as much as the F-16 tail if not moreso when under similar circumstances. This means that that the tail of the F-35 has to make proportionally more lift than the tail of the F-16, so I gave it a higher Clmax. If he wants to disagree on this point he is certainly allowed to, the actual value will not be known to the public for decades to come.

For ITR he seems to take each of them to 9G and calculate ITR for the speed required by his ClMax analysis. I went a different route and showed what their ITR would be at the cruise speed for the mission based on the Manual (F-15E and F-16C) and my CLmax analysis (F-35A). So his is not wrong per say, just different.

STR is given in both Manuals for F-15E and F-16C so there is not a lot of guesswork involved.

For the F-35 I have to generate a model of dynamic thrust and work backwards through the induced drag equation to estimate the extra Cl available. This is, I admit wholly, the least accurate part of my analysis as it requires the most assumptions.

On to the payload. He is using an F-15A-1 not an F-15E-1. The F-15A-D are cleared to 700/2.0M with CFT/Fueselage mounted missiles. The SAME PAGE of the F-15E-1 lists 660/1.4.

Send him my regards, I appreciate the review.
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Unread post16 Jul 2015, 01:49

borg wrote:Andraax has downloaded and pick his figures from flight manuals.
Both from F-15 and Su-27SK.

If you mean to say he just invent stuff, well just download the fligh tmanuals yourself and go through them.
And then come back and correct any mistakes he made..

About the F-35, ofcourse his figures are not correct, sinse there is no flight manual at this point.
Still i'd say his assumption are not far out eighter.. meaning they look plauseble.


I don't know if you have read my analysis in the first place, but I also used the F-15E flight manual. I have the Su-27SK manual and the only meaningful performance you can get from it is the V-n diagram (G for speed and weight) and the Cl-alpha to get ClMax. I wish there was more that you could get from it like the F-16 manual gives. Like my last post said, I appreciate his review and "counter analysis" if you will. He has a good technical approach. Peer review is what it is all about.
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Unread post16 Jul 2015, 03:00

Yes I agree. I was merly addressing some other members whom seems to cast doubts about andraxx way of work, which b.t.w. I find very helpfull.
Anyway, I meant no disrespect towards you sprst@
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Unread post16 Jul 2015, 03:22

None taken borg. Other than the use of the F-15A-1 for the weapon limitations there was nothing inherently wrong with his analysis. He made assumptions and gave his reasons for doing so. They are different than mine based on my different assumptions.
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Unread post16 Jul 2015, 05:51

Hello Guys Long term reader, and frequent visitor.

I would like a laymans explanation on How the super hornet thrives in BFM, and at High AOA.
Since the F-35 seems to look more like a hornet in close, and will exploit peddal turns and probably
Pirouette type manuvers. How can this be exploited? I was never a Big Super hornet fan, so Im very curious.
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Unread post16 Jul 2015, 06:06

sprstdlyscottsmn wrote:I appreciate Andraxxus time in going through my data. I certainly have it out there to be reviewed and anyone who can aid in the accuracy only increases the overall knowledge base. I have no way of knowing which version (I have four so far) of my analysis he was judging. My responses to his points are as such, and please go back and share my responses.

Of course the F-15 doesn't have a static MAC. 27% was not the best choice on my part and I have in my most recent version recanted the "Stable" part of that discussion as the Strike Eagle borders on neutral stability per other texts of the Manual.

For Strike Eagle max lift I used 40,000lb at sea level with power off for 125 kt, yielding which gives 1.24. With his 1.2028 I think we are splitting hairs. The reason it is much lower than the others is, in my opinion, due to the lack of full instability, LEF, and any LERX/chines.

For Viper lift, he goes on about how G, speed, and altitude matter. That was not the purpose of this section. I was trying to demonstrate the highest Clmax the F-16 could generate 9G with as that will give the "best" turn, even though the CAT-1 limited gives a best turn rate at ~8G and best radius at ~3G. You cannot use mil thrust as a stall indication as installed dynamic thrust does not equal (is less than at stall speeds) rated thrust.

As for the F-35, it has Chines which perform the same action as the LERX as evidenced by the vortexes they generate so I did not penalize it. The F-35 also has LEF, so again I am not penalizing it. What he is not bringing up is that both of these aircraft are fully unstable. This means the horizontal tails make lift. This added lift "adds" to the "reference" CLmax the same as a LERX does. Relatively speaking, the F-35 has a MUCH larger tail and it is deflected at least as much as the F-16 tail if not moreso when under similar circumstances. This means that that the tail of the F-35 has to make proportionally more lift than the tail of the F-16, so I gave it a higher Clmax. If he wants to disagree on this point he is certainly allowed to, the actual value will not be known to the public for decades to come.

For ITR he seems to take each of them to 9G and calculate ITR for the speed required by his ClMax analysis. I went a different route and showed what their ITR would be at the cruise speed for the mission based on the Manual (F-15E and F-16C) and my CLmax analysis (F-35A). So his is not wrong per say, just different.

STR is given in both Manuals for F-15E and F-16C so there is not a lot of guesswork involved.

For the F-35 I have to generate a model of dynamic thrust and work backwards through the induced drag equation to estimate the extra Cl available. This is, I admit wholly, the least accurate part of my analysis as it requires the most assumptions.

On to the payload. He is using an F-15A-1 not an F-15E-1. The F-15A-D are cleared to 700/2.0M with CFT/Fueselage mounted missiles. The SAME PAGE of the F-15E-1 lists 660/1.4.

Send him my regards, I appreciate the review.

thanks sprstdlyscottsmn, I found your and Andraxxus analysis very interesting, alot better than the common nonsense " F-35 suck because it look like a pig" or " bla bla... Carlos Kopp said so"
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Unread post16 Jul 2015, 08:50

BTW here is what he said about the LERX and vortex part :
Andraxxus wrote:If you are referring to the appearant vortex at intakes, its mostly useless, it will help reducing fuselage drag at best.

If you are referring to the canted area at wing roots, yeah it would produce a vortex which would actually be useful (and withness the benefits of CFD, no appearant body part, but airflow is still directed above wings with pressure differences). Still I would question the intensity of such vortex when compared to F-16/18.

F-15's LERX-like structure is a different -symetrical- airfoil (64A006). Its by definition not an extension of the wing's leading edge. It would of course produce a vortex, but again I would question the location and intensity of the vortex.

You have to understand LERX on F-16/18 Su-27 MiG-29 starts very well in front of the wings, even slightly in front of the cockpit canopy. By the time this vortex reach the main wings, it will be so large that entire wing wil be affected. This vortex is so dominant that a) airflows primary velocity is due to rotational action which makes small disturbances in early stall irrelevant, as with increased vortex intensity, air is fast enough reduce pressure further to increase lift. b) such velocity gives air higher inertia which helps delaying flow reversal.

Surely we are not living in 1960s. F-15's wing roots, F-22's chines, F-35's canted wings, Mirage 2000's and Typhoon's vortex generators, F-5E's and MiG-31's tiny root extensions all work in same very basic principle but size does matter here, and none of these can possibly approach 1/4 the intensity F-16/Su-27 achieve with their LERX (size relative to wing size of course). In fact, I would say, only method for improving vortex control even more is close coupled canards like on Rafale, and -if works as advertised- LEVCONs on T-50. For supersonics, Typhoons far positioned canards should work best as it allows distance for vortex intensity to grow
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Unread post16 Jul 2015, 12:24

sprstdlyscottsmn wrote: What he is not bringing up is that both of these aircraft are fully unstable. This means the horizontal tails make lift.


Hell, there are pics out there of the F-35 in a turn with the horizontal tails pointed down.
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Unread post16 Jul 2015, 14:18

Because of AoA and wing wash effects, you have no clue whether tail lift is up or down.
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