Proof: F-35 has good sustained rate of turn. Same A/B time

The F-35 compared with other modern jets.
  • Author
  • Message
Offline

gta4

Forum Veteran

Forum Veteran

  • Posts: 918
  • Joined: 17 Oct 2010, 19:10

Unread post25 Mar 2017, 16:06

inst wrote:Your calculation is overly generous, which is just short of being dead wrong.


Too gennerous?
Please, do not cheat again.

If 2000 kg fuel is too generous for F-35, then your figure is way too generous for Su-27.
The turn rate chart you cited is TsAGI report (I have the Russian full version), where the total flying weight for Su-27 is only 18920 kg! The corresponding internal fuel was only 1500kg, considering the fact that nowdays Su-27 is much heavior, even the lightest Su-27 single seater weights 17400 kg empty. Check Sukhoi official website.

18920 kg flying weight for Su-27 in that report:
http://s14.postimg.org/nkknvh56p/Su-27_acceleration.jpg

And, in 1989 le Bourget, Sukhoi and TsAGI distributed performance brochure for Su-27, the total flying weight was also 18920 kg: (rounded to 19000 kg)
Image

Admite the fact: F-35 has better sustained turn rate under the sam A/B duration. Peroid.
Offline

castlebravo

Active Member

Active Member

  • Posts: 231
  • Joined: 08 Feb 2011, 19:10

Unread post25 Mar 2017, 16:21

gta4 wrote:
inst wrote:
castlebravo wrote:here's a graph of the Su-27 and F-15's STR. At the same level the OP is inflating the F-35 to 13 degree/sec, the Su-27 and F-15 are showing slightly over 16 deg / sec STR turn rates. As I mentioned earlier; it doesn't matter, in a realistic engagement the Su-27s would be wiped out by AIM-120s from extended range.

https://forums.eagle.ru/showthread.php?t=159251


Cheater, you are cheating again: comparing turn rate at 3000 m with that at 4527 m (15000 ft)!

Trt not to fool us when you can not out-smart us.


Good catch, but I didn't write that.
Offline

gta4

Forum Veteran

Forum Veteran

  • Posts: 918
  • Joined: 17 Oct 2010, 19:10

Unread post25 Mar 2017, 17:11

castlebravo wrote:
Good catch, but I didn't write that.


Sorry about an error in HTML code editing. It definitely was not you who wrote that. Corrected.
Offline

inst

Active Member

Active Member

  • Posts: 110
  • Joined: 04 Jul 2015, 01:58

Unread post26 Mar 2017, 02:27

Castlebravo didn't catch that, but neither did I. 3000m is not 15000 feet, it's 9840 feet.

You're also misinterpreting your document, the Su-27 is a high fuel fraction fighter, like the F-35, with about 40% of its weight, fully-loaded, dedicated to fuel. The figure given above is closer to the tested weight, but the Su-27 actually has a higher combat radius than the F-35 by about 300 km, so if you discount its fuel fraction to account for range, the tested 50% would be correct. Other figures also state that the Su-27 has roughly a 16500 kg empty weight, so your figures on the second document seem to be instead for empty weight, 50% weight, and fueled weight.

Here's a chart with the Su-27 at 5000m, or roughly 16000 feet.

http://forumimage.ru/uploads/20110308/1 ... 004937.jpg

Here, the Su-27 calculates roughly out to 13.6 deg / sec, but you can't inflate your F-35 STR because both are medium-range high-fuel fraction fighters. It then comes out to 10.8 vs 13.6, giving the Su-27 a 25% superiority.

What you can do, however, is compare the F-35 to the Su-35 instead, which is about 10% heavier loaded, but has superior ITR compared to the base Su-27. Using the thrust change / weight change squared formula, you get about a 6% decrease in sustained turn rate, dropping you down to a 18.7% STR superiority.
Offline

gta4

Forum Veteran

Forum Veteran

  • Posts: 918
  • Joined: 17 Oct 2010, 19:10

Unread post26 Mar 2017, 03:15

inst wrote:Castlebravo didn't catch that, but neither did I. 3000m is not 15000 feet, it's 9840 feet.

You're also misinterpreting your document, the Su-27 is a high fuel fraction fighter, like the F-35, with about 40% of its weight, fully-loaded, dedicated to fuel. The figure given above is closer to the tested weight, but the Su-27 actually has a higher combat radius than the F-35 by about 300 km, so if you discount its fuel fraction to account for range, the tested 50% would be correct. Other figures also state that the Su-27 has roughly a 16500 kg empty weight, so your figures on the second document seem to be instead for empty weight, 50% weight, and fueled weight.

Here's a chart with the Su-27 at 5000m, or roughly 16000 feet.

http://forumimage.ru/uploads/20110308/1 ... 004937.jpg

Here, the Su-27 calculates roughly out to 13.6 deg / sec, but you can't inflate your F-35 STR because both are medium-range high-fuel fraction fighters. It then comes out to 10.8 vs 13.6, giving the Su-27 a 25% superiority.

What you can do, however, is compare the F-35 to the Su-35 instead, which is about 10% heavier loaded, but has superior ITR compared to the base Su-27. Using the thrust change / weight change squared formula, you get about a 6% decrease in sustained turn rate, dropping you down to a 18.7% STR superiority.


Don't know if you are trying to cheat, but you are making a mistake again:

In Su-27 flight manual, the horizontal axis is not true airspeed (or mach number), but indicated airspeed (or mach number). The latter is always smaller than the former. If you do not do the conversion, you will sure over-estimate the turn rate.

I will explain the reason and show the proof.

Reason why indecated airspeed is always smaller than true airspeed:
The pitot tube uses dynamic pressure to caculate airspeed. But when the airplane is flying with some angle of attack, the incoming airflow is deflected inside the pitot tube and thus decelerated, resulting in less dynamic pressure. The viscous force of the wall of the tube also slow the airflow down. That is why the indicated airspeed is always smaller than the true value, even at sea level.

Proof: this is a chart from Su-27 flight manual, Su-27 at 21400kg could pull 2.5G at indicated mach number of 0.2. But given the fact that Su-27's maximum lift coefficient is smaller than 1.9, there is no way it could pull 2.5G below Mach 0.25. There is an 20% deviation. This is not considered an error because that is how a pitot tube works. Each pitot tube has its own convertion table, but that is not always available in flight manuals.
Su-27-indicated speed.jpg


If you don't do the convertion, you will definitely over-estimate Su-27's turn rate significantly. TsAGI has already done the conversion, and showed a sustianed rate of turn of 21deg/sec at sea level, 18920kg. You can ignore the convertion and try the figures on Su-27 manual, you will definitely find something greater than 21deg/sec.
Offline

gta4

Forum Veteran

Forum Veteran

  • Posts: 918
  • Joined: 17 Oct 2010, 19:10

Unread post26 Mar 2017, 03:32

To inst:

You are trying to cheat again, cheater. You are comparing two combat radius of different flight profies. Soviet advertisements tend to use less strict mission profile and thus making the range and radius more pretty, while western standards are far more strict.

Here is a proof:

Mig-29 is advertised to have 2100km range and 710km combat radius with one tank. But after being test by Western contries, the combat radius is only 278km with one tank. And, if you use the specific range given by the western tester, Mig-29's range with one tank is less than 1800km. Look at how soviet's advertisement exagerates their jets:
29 radius.jpg
Offline
User avatar

count_to_10

Elite 3K

Elite 3K

  • Posts: 3300
  • Joined: 10 Mar 2012, 15:38

Unread post26 Mar 2017, 04:45

gta4 wrote:Reason why indecated airspeed is always smaller than true airspeed:
The pitot tube uses dynamic pressure to caculate airspeed. But when the airplane is flying with some angle of attack, the incoming airflow is deflected inside the pitot tube and thus decelerated, resulting in less dynamic pressure. The viscous force of the wall of the tube also slow the airflow down. That is why the indicated airspeed is always smaller than the true value, even at sea level.

I thought the IAS/TAS difference was just due to the change in air density with altitude.
Einstein got it backward: one cannot prevent a war without preparing for it.

Uncertainty: Learn it, love it, live it.
Offline

sprstdlyscottsmn

Elite 4K

Elite 4K

  • Posts: 4783
  • Joined: 10 Mar 2006, 01:24
  • Location: Phoenix, Az, USA

Unread post26 Mar 2017, 07:02

That's the biggest factor, yes. IAS and CAS differ only by pitot issues
"Spurts"

-Pilot
-Aerospace Engineer
-Army Medic
-FMS Systems Engineer
Offline

inst

Active Member

Active Member

  • Posts: 110
  • Joined: 04 Jul 2015, 01:58

Unread post26 Mar 2017, 13:31

Actually, let me put this out, I think you're trolling. And I appreciate it, while to be honest, I don't have the time for this, it's lots of fun handling your trolls. First, regarding your CAS / IAS argument, it's irrelevant because if you look at the Su-27 diagram 1100 km/h provides the same sustained turn rates as around 900 km/h.

Second, for your weight, look up the T10-1. The figures you're giving are actually for the lighter prototype of the Su-27, which notably was lesser-powered, having only a 100 kn engine, as well as being smaller in dimensions. This is somewhat akin to a comparison between the F-18 and F/A-18E.

The weight difference, consequently, is about 16.4%. But at the same time, wing area rose from 48 to 62 m^2. implying, from wing-loading only, an increase of 11% STR. From thrust to weight, ironically, the engine is uprated by about 20%, implying an increase in T/W of 4%. Using the same model I've been using previously, changing sustained turn weight based on change in wing loading * change in thrust, we get a 14% improvement over the existing T10-1 figures. How about that? Even if you factor in a fudge factor of about 5-10%, you'd still get figures superior to the F-16, and thus the F-35.

About speed misreadings, look at my graph again. Compare the turn rate at 1100 km/h with the turn rate at 900 km/h. The point is, if there's an IAS / CAS difference, it doesn't matter.

And about actual range vs advertised range, let's handle it next week when I have time. Toodles.
Offline

gta4

Forum Veteran

Forum Veteran

  • Posts: 918
  • Joined: 17 Oct 2010, 19:10

Unread post26 Mar 2017, 14:32

inst wrote: First, regarding your CAS / IAS argument, it's irrelevant because if you look at the Su-27 diagram 1100 km/h provides the same sustained turn rates as around 900 km/h.


Your math is terrible. If the sustained G is irrelavant of speed, your augument is correct. But this time it's not the sustained G, but the turn rate, which means Su-27's turn rate is poor regardless of the speed.

inst wrote: Second, for your weight, look up the T10-1. The figures you're giving are actually for the lighter prototype of the Su-27, which notably was lesser-powered, having only a 100 kn engine

The weight difference, consequently, is about 16.4%. But at the same time, wing area rose from 48 to 62 m^2.


Again, you are a terrible liar.

The TsAGI report states very clearly that the Su-27 data is retreived from Su-27 flight manual, with 62 m^2 wing area, 18920 kg flying weight, 305 km/m^2 wing loading (18920/62=305), and with 1.31 T/W ratio (25000/18920=1.31). The thrust and the wing area all match the final Su-27, not the smaller T-10.
tsagi su-27.jpg

Image
Last edited by gta4 on 26 Mar 2017, 15:00, edited 3 times in total.
Offline

gta4

Forum Veteran

Forum Veteran

  • Posts: 918
  • Joined: 17 Oct 2010, 19:10

Unread post26 Mar 2017, 14:46

OK lets give inst a math lecture, please take notes:

I have proven that the indecated speed (mach number) could be smaller than the true value by 20%. Let's be generous, we assume it is 15% smaller.

The flight manual shows a 6.5G sustained at indicated mach number 0.8 at 5000 m, so the true mach number could be mach 0.95, speed=304m/s, turn rate=6.5*9.8/304*57.3=12 deg /sec.
Offline

sprstdlyscottsmn

Elite 4K

Elite 4K

  • Posts: 4783
  • Joined: 10 Mar 2006, 01:24
  • Location: Phoenix, Az, USA

Unread post26 Mar 2017, 15:08

Actually Mach is always a true airspeed. The actual speed it is depends on local speed of sound but it is a true airspeed none the less. TAS/a.
"Spurts"

-Pilot
-Aerospace Engineer
-Army Medic
-FMS Systems Engineer
Offline

gta4

Forum Veteran

Forum Veteran

  • Posts: 918
  • Joined: 17 Oct 2010, 19:10

Unread post26 Mar 2017, 15:19

sprstdlyscottsmn wrote:Actually Mach is always a true airspeed. The actual speed it is depends on local speed of sound but it is a true airspeed none the less. TAS/a.


The indicated much number is also smaller than the true mach number, even though the deviation is smaller than CAS/TAS. Some pitots approximate CAS with IAS.

http://aviation.stackexchange.com/quest ... ach-number
http://www.pprune.org/tech-log/94319-in ... umber.html

When the Su-27 flight computer shows M0.2, it is already M0.25, as shown in previous replies. This devaition is higher when the aircraft maneuvers, because the angle of attack is significant.
Last edited by gta4 on 26 Mar 2017, 18:41, edited 1 time in total.
Offline

garrya

Forum Veteran

Forum Veteran

  • Posts: 849
  • Joined: 25 Dec 2015, 12:43

Unread post26 Mar 2017, 15:32

gt4 can you steer your photo horizontally please?
Offline
User avatar

spazsinbad

Elite 5K

Elite 5K

  • Posts: 24258
  • Joined: 05 May 2009, 21:31
  • Location: ɐıןɐɹʇsn∀¯\_(ツ)_/¯
  • Warnings: -2

Unread post26 Mar 2017, 15:37

Voila
Attachments
IdioticRussianSMALL.gif
A4G Skyhawk: www.faaaa.asn.au/spazsinbad-a4g/ & www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/videos?view_as=subscriber
Previous

Return to F-35 versus XYZ

Who is online

Users browsing this forum: No registered users and 12 guests