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Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 06:06
by garrya
what is F-15 CFT DI

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 19:50
by gta4
It's a bit off-topic. You can open a new thread about this.

First of all, it's not fair to consider DI of CFTs, because aircrafts are supposed to remove CFTs before air combat missions.

CFTs do create less drag but they have their own weight, so turning, climbing and acceleration performances are dropped significantly.

You would be surprised how draggy the pylon/launcher combo under F-15 wings are. One pylon/launcher combo has a DI of almost 10. Two combos under two wings give a DI of 20, which is bigger than a giant 300 gallon tank, or is twice as draggy as a small central line tank (the one that Mig29 carries)

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 20:15
by XanderCrews
sferrin wrote:
eloise wrote:would you mind if i took this to Keypublishing?


Probably get more useful answers by taking it to the playground at the local elementary school.


indeed, most elementary school kids are open minded

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 21:24
by eloise
sferrin wrote:
Probably get more useful answers by taking it to the playground at the local elementary school.

Some keypub member like Andraxxuss is very good with aerodynamic

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 21:29
by basher54321
garrya wrote:what is F-15 CFT DI



Been discussed before - very little drag increase - an F-16 with CFTs has the same drag index as without.

I think F-15s have a different drag index system but F-15E CFTs with pylons have a lot of drag (more than 2 drop tanks IIRC) - but the basic CFTs are less draggy.

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 21:38
by basher54321
gta4 wrote:First of all, it's not fair to consider DI of CFTs, because aircrafts are supposed to remove CFTs before air combat missions.



Doubtful - especially with the F-16 - the extra fuel, less drag and lower profile is far more beneficial.
and the things are a nightmare to remove and put on again if you read the crew comments on here.

F-15Es would always fly with them (very rarely take them off for check flights according to pilots) - USAF F-15Cs got round the issue by mostly not using them at all.

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 22:37
by gta4
During India MMRCA competition, India official made an notorious decision: they let F-16 go through flight tests with CFTs. This decision was complained by LM but indian didn't listen to it. The F-16 was ranking top during the initial maneuverability test, but with CFTs equipped, it dropped to the bottom. This caused F-16 to be knocked out.

From this we know LM does not recommend carrying CFTs to perform air dominance missions.

Also, during the korean F-X competition, F-15K went through the performance test without CFTs and achieved astonishing energy performance (exceeded the climbing threshold by 50%). From this we also know that Korean are not against the idea to strip CFTs before going air dominance.

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 23:24
by steve2267
gta4 wrote:During India MMRCA competition, India official made an notorious decision: they let F-16 go through flight tests with CFTs. This decision was complained by LM but indian didn't listen to it. The F-16 was ranking top during the initial maneuverability test, but with CFTs equipped, it dropped to the bottom. This caused F-16 to be knocked out.

I don't have a clear picture of how the CFT-equipped F-16 and competing aircraft were configured for this maneuverability test(s).

For the maneuverability test, were the competing aircraft required to carry fuel tanks under their wings? Or were they flown clean? For the F-16 with the CFTs, was it able to fly without any additional underwing fuel tanks?

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 22 Nov 2016, 23:38
by basher54321
gta4 wrote:During India MMRCA competition, India official made an notorious decision: they let F-16 go through flight tests with CFTs. This decision was complained by LM but indian didn't listen to it. The F-16 was ranking top during the initial maneuverability test, but with CFTs equipped, it dropped to the bottom. This caused F-16 to be knocked out.

From this we know LM does not recommend carrying CFTs to perform air dominance missions.

Also, during the korean F-X competition, F-15K went through the performance test without CFTs and achieved astonishing energy performance (exceeded the climbing threshold by 50%). From this we also know that Korean are not against the idea to strip CFTs before going air dominance.


The F-15E is a stellar performer without CFTs on those check flights - other airforces may use them without CFTs or may not I guess.

If that was the only deciding factor why the F-16 lost (don't think it was) then it might explain to some extent why the MMRCA was such a farce (How many Rafales did they end up with again?) if they haven't got a clue what they are doing.

Maybe LM should have offered the jets without CFTs :D

Of course LM would be stupid to offer the same jet again some years later wouldn't they?

“Under our current proposal, Lockheed Martin is offering India the exclusive opportunity to produce, operate and export F-16 Block 70 aircraft,” he said. “We also foresee significant Indian participation in the F-16 supply chain based on Indian industry’s capacity to offer best-value F-16 supply chain options.”

http://www.defensenews.com/articles/deb ... india-trip

If there is as you assume a recommendation from LM to not use CFTs I guess they left it out of the manuals (silly them!) - but regardless of all that I would expect to see CFTs used for most missions including A-A.
Shame Poland didn't do BAP with their F-16s so we could see for certain what they might turn up with - but there are plenty of photos with them in training A-A with CFTs.
Obviously if you go on an A-G mission you might have to do A-A anyway (oh no) - and this notion of degraded agility with full CFTs is no more ridiculous than that of a fully fuelled Su-27 at takeoff!

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 23 Nov 2016, 00:39
by gta4
http://carnegieendowment.org/files/Deco ... cision.pdf

I believe the test was carried without drop tanks but with some AA missiles, because the threshold is "to sustain 16 deg/sec at 5000ft." India atmosphere is hotter which will cause some performance loss (but not huge), I don't think any jet could achieve this sustained rate of turn with drop tanks. However, some powerful jet such as typhoon, which should have easily exceeded this threshold (I believe tyohoon could sustain more than 18deg/sec a 5000ft), achieved only 16.2deg/sec, so I believe some A-A missiles are carried.

BTW, So glad to see a super hornet is 93% as good as a typhoon in terms of sustained turn :mrgreen:

— until then, among the world’s most
wickedly agile air combat platforms —
with conformal fuel tanks (CFTs). These
CFTs, which can be removed between
missions but not jettisoned in flight,
extended the F-16’s already impressive
reach, but at the cost of robbing it of its
renowned sprightliness.

With its CFTs, the F-16IN’s handling
and sustained turn rates — which otherwise
rank among the world’s best —
dropped to the bottom relative to the
other MMRCA competitors and thus
provided the final strike against its inclusion
in the shortlist. The fact that the
CFT-equipped F-16IN would be less manoeuvrable
compared to Pakistan’s F-16
Block 50/52s made the Super Viper’s exclusion
from the MMRCA shortlist virtually
a foregone conclusion.

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 23 Nov 2016, 01:09
by basher54321
Not a bad article that - don't completely agree with some of writers thoughts but at least gives an idea of where the issues were:

- the IAF did put the aircraft through its paces. At the end of the day, however, it was found ‘noncompliant’ — a term indicating that the aircraft did not meet certain technical criteria in the IAF’s Air Staff Quality Requirements (ASQRs) — in five areas, some of which were of critical importance to the service: growth potential; carefree handling (and automatic sensing of external stores); sustained turn rate; engine change time; and assurance against obsolescence over a 15-year period.

The F-16IN Super Viper is already a mature aircraft and while it is likely to evolve further where its sensors and weapons are concerned — especially for foreign markets — it is unlikely to remain the premier dogfighter it was
when first introduced into the United States Air Force. Since the IAF was looking to acquire an aircraft that would remain competitive over the next 30 years, the F-16IN appeared like a poorer choice relative to the competition in both growth potential and assurance against obsolescence. Although the IAF’s judgment on both these counts can be debated by airpower specialists, even the most ardent supporters of the F-16IN would find it difficult to claim that this legendary airplane would remain the world’s most nimble closein combatant or its premier multirole combat aircraft in, say, 2030. The F-16IN’s failure to meet the IAF’s standard where engine change time was concerned was due largely to an idiosyncratic mishap during the field trials. It is certain that if the trials were to involve multiple stochastic demonstrations of engine change, the F-16IN would have easily made the mark. Unfortunately, second chances are sometimes not available, and the IAF, for its own reasons, chose not to accept Lockheed Martin’s subsequent evidence of being able to meet the engine change standards laid down in the ASQR.

---

Beyond these characteristics, the service also wanted a fighter that would be the newest of the new, something unmatched in the region, the latest of the available choices, and one with the greatest growth potential. The two American aircraft in the Indian MMRCA competition were deficient by some of these
yardsticks, when matched against the three ‘Eurocanards’: the Eurofighter, the Rafale, and the Gripen.



Agree on this (in perhaps a different context):

Obviously, this by itself did not make them inferior war-fighting machines. Far from it. Marginal differences in aerodynamic performance rarely affect combat outcomes and whenever such deficiencies exist, better sensors and weapons and advanced combat tactics can often serve to compensate.

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 23 Nov 2016, 16:05
by eloise
According to pilot, F-15C acceleration at subsonic speed is even higher than F-35.That is why it can dogfight with Su-27 despite lower turn rate. F-15 with F-110GE-132 would be unbeatable in vertical fight

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 23 Nov 2016, 16:41
by gta4
eloise wrote:According to pilot, F-15C acceleration at subsonic speed is even higher than F-35.That is why it can dogfight with Su-27 despite lower turn rate. F-15 with F-110GE-132 would be unbeatable in vertical fight

If you put on the "fuel for same AB duration" restriction, you will find F-15 is also better at turning, with a noticeable margin.

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 23 Nov 2016, 17:19
by gta4
It seems that the author's theory checks out. Someone verified it with F-15E data:

http://forum.keypublishing.com/showthre ... ost2358007


"
I checked the author's theory with F-15E data:
at 10000ft, the air density is 3 times as big as that at 40000ft, so the acceleration should be at least 200% better if the theory is correct.

from M0.8-1.0, at 10000ft, a 44000lb F-15E spends 7s in total, which is 9.37m/s^2.
from M0.8-1.0, at 40000ft, a 44000lb F-15E spends 20s in total, which is 2.95m/s^2. (remember, the speed of sound is different at higher altitude)

It is 217% better. Very good match indeed. The theory checks out.

By the way, it is also safe to assume that F-15E could easily out-accelerate Su-35 using this theory.
"

Re: Proof: F-35 can out-accelerate Su-27/35 in subsonic regi

Unread postPosted: 23 Nov 2016, 19:56
by garrya
gta4 wrote: If you put on the "fuel for same AB duration" restriction, you will find F-15 is also better at turning, with a noticeable margin.

That is unlikely IMHO
Su-27 has very big CLmax
Image
At Mach 0.5 its max AoA is 24 => CL is 1.85
At Mach 0.6 its max AoA is 23 => CL is 1.7
At Mach 0.7 its max AoA is 22 => CL is 1.58
At Mach 0.8 its max AoA is 20 => CL is 1.45

Image