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

The F-35 compared with other modern jets.
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gta4

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Unread post23 Nov 2016, 20:11

First thing first, Su-27 has only a usable Clmax of about 1.6.
1.83 is when tailing edge flaps are deployed (for low speed level flight).

The highest Clmax is probably super hornet, which is near 2.0.

F-15 also has a max Cl of about 1.6 (I can prove that with NASA test reports) and F-15 has lower wing loading, so F-15 has better Cl/wing loading ratio, which gives it a better instantaneous turn rate than Su-27. Surprise? :mrgreen:

TsAGI underestimated F-15's Cl to be 1.08 (rather than 1.6), which significantly underestimated F-15's instantaneous turn.

And again, in your figure Su-27 sustains a 20.8deg/sec in 18920kg flying weight, which is with 2000kg fuel. F-15 could achieve similar AB duration with 1800kg fuel and that is 13600+1800+174=15574kg (34325lb) flying weight. According to F-15 flight manual, it could sustain 20.5 deg/sec with 37000lb flying weight, so if we convert it to 34325lb (normal load factor is inversely proportion to flying weight, making the conversion pretty easy), the sustained rate of turn is 22.1deg/sec
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garrya

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Unread post23 Nov 2016, 20:38

gta4 wrote:First thing first, Su-27 has only a usable Clmax of about 1.6.
1.83 is when tailing edge flaps are deployed (for low speed level flight)

I think Mach 0.5 is fast enough speed for dogfight TBH

gta4 wrote:F-15 also has a max Cl of about 1.6 (I can prove that with NASA test reports) and F-15 has lower wing loading, so F-15 has better Cl/wing loading ratio, which gives it a better instantaneous turn rate than Su-27. Surprise? :mrgreen:
TsAGI underestimated F-15's Cl to be 1.08 (rather than 1.6), which significantly underestimated F-15's instantaneous turn.

I dont think F-15 CL can reach 1.6 , it lacks most criteria for high CL value like LERX or LEF or Negative stability. CL of 1.6 looks like something belong to F-16 instead , and it only reach that vale below a certain G load

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gta4 wrote:And again, in your figure Su-27 sustains a 20.8deg/sec in 18920kg flying weight, which is with 2000kg fuel

Their figure is taken when Su-27 is at 50% fuel IMHO
i concluded that from their ITR value
Lift = 1/2*V^2*reference wing area*air density *CL

Take for example when speed is mach 0.5 ( about 164 meters/sec) => CL is 1.85
air density at sea level is about 1.2kg/m3
Su-27 wing area is about 62m2
so total amount of lift is 1.85 * 1/2 * 1.2 * 164.8^2 * 62 = 1879085N
Su-27 empty weight is 16380 kg, max internal fuel is 9400 kg, Su-27 with 50% fuel will weight about 21080 kg
max G it can pull based on lift generated is 1879085/9.81/21080 =about 9G. That seem to fit with value in the graph
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Unread post23 Nov 2016, 20:52

Sorry, man, you made two mistakes:

1) When calculating the centripetal force, you forgot to add the component of thrust of AL-31F. It is huge to multiply 25000kg with sin 24deg. You will find the Clmax=1.6 if you do this compensation.

2) The 18920kg flying weight is claimed to be the calculation standard in TsAGI report. (305*62=18920. Cl max=1.6)
3.jpg

For early Su-27s, 18920kg is with 50% fuel (50% * 5270kg, not 50% * 9400kg. Please check with Sukhoi website). But now Su-27 is much heavier. Even the lightest Su-27SK has an operating weigh of more than 17400kg. So if you want to maintain 18920kg flyin weight, you have to sacrifice some fuel.

3) For F-15 cl max: I will show you the proof afterwards.


4) This was the brochure distributed by Sukhoi at airshow to promote flankers. Note the performances are calculated under 19000kg weight.
4.jpg

5.jpg
Last edited by gta4 on 23 Nov 2016, 22:10, edited 1 time in total.
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Unread post23 Nov 2016, 21:17

Another mistake:
Your Cl curve is not for F-16, but for an experimental model for LWF development.
F-16 has a Cl of 1.7 at 25deg, M0.9.
(I will show you the proof later, maybe tonight when I get access to my laptop)
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garrya

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Unread post24 Nov 2016, 01:58

gta4 wrote:1) When calculating the centripetal force, you forgot to add the component of thrust of AL-31F. It is huge to multiply 25000kg with sin 24deg.

25000kg*sin24 = about 10.000 ( so that about 0.5G for a loaded Su-27). Moreover, shouldnt that be the case for all aircraft at high AoA ?

gta4 wrote:For early Su-27s, 18920kg is with 50% fuel (50% * 5270kg, not 50% * 9400kg. Please check with Sukhoi website). But now Su-27 is much heavier. Even the lightest Su-27SK has an operating weigh of more than 17400kg. So if you want to maintain 18920kg flyin weight, you have to sacrifice some fuel.

From sukhoi website
http://www.sukhoi.org/eng/planes/military/su27sk/lth/

Su-27SK carry 9400 kg fuel
gta4 wrote:3) For F-15 cl max: I will show you the proof afterwards.

Iam looking forward to that. Never expected F-15CLmax to get that high tbh
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Unread post24 Nov 2016, 05:12

From sukhoi website
http://www.sukhoi.org/eng/planes/military/su27sk/lth/

Su-27SK carry 9400 kg fuel

Please read the webpage carefully: The take-off fuel is not 9400kg, but 5270kg. So the half fuel is not 9400/2=4700, but 5270/2=2635.

I think I have given enough evidence to show that TsAGI uses 18920-19000kg as flying weight standard to calculate performance. Doesn't this number remind you of something? Hmmmmm.....

18920=16000(back in the days when Su-27 was light)+2635(the "half fuel of 5270kg")+2 R73 missiles. A typical air combat weight calculation.

But now Su-27 is much heavier, even the lightest Su-27sk. If it continues using 18920kg as performance standard, fuel weight must be sacrificed.
Last edited by gta4 on 24 Nov 2016, 05:37, edited 1 time in total.
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Unread post24 Nov 2016, 05:16

Iam looking forward to that. Never expected F-15CLmax to get that high tbh


https://www.nasa.gov/centers/dryden/pdf ... H-1243.pdf

F-15 has a Clmax of 1.6.

I have a similar wind-tunnel test result from a MIT report. If you want I can dig it out, will take some time though.

This is because F-15 uses a thick, round, and twisted leading edge which acts somehow like a fixed-angle leading edge flap. Russian didn't expect that so they used their experience on Mig-25 to estimate F-15's aerodynamic performance. Some performances are significantly underestimated.
Last edited by gta4 on 24 Nov 2016, 06:01, edited 1 time in total.
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Unread post24 Nov 2016, 05:54

To Garrya:

For F-16 aerodynamic curves, please Google:
Correlation of F-16 Aerodynamics and Performance Predictions with Early Flight Test Results," AGARD CP-242, by TS Webb, DR Kent, JB Webb

You will find F-16 has very steep lift curve slop (around 0.08), steeper than Su-27 (0.066). Your Cl curve could not be F-16's :mrgreen: Anyway, it never claims to be F-16's.
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garrya

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Unread post24 Nov 2016, 06:17

gta4 wrote:https://www.nasa.gov/centers/dryden/pdf ... H-1243.pdf
F-15 has a Clmax of 1.6.
.

That interesting indeed , but that CL is at 40 degrees though ( while it is about 25 degrees for F-16 and 22.5 degrees for Su-27). Can F-15 even reach that AoA in high G turn ?
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garrya

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Unread post24 Nov 2016, 06:27

gta4 wrote:Please read the webpage carefully: The take-off fuel is not 9400kg, but 5270kg. So the half fuel is not 9400/2=4700, but 5270/2=2635

Iam under the impression that 50% fuel load mean 50% of maximum fuel load . Does it not ?. So if maximum internal fuel load of su-27 is 9400 kg , shouldnt 50% of that is 4700 kg ?

gta4 wrote:But now Su-27 is much heavier, even the lightest Su-27sk. If it continues using 18920kg as performance standard, fuel weight must be sacrificed.

Fair point
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Unread post24 Nov 2016, 15:20

garrya wrote:
gta4 wrote:Please read the webpage carefully: The take-off fuel is not 9400kg, but 5270kg. So the half fuel is not 9400/2=4700, but 5270/2=2635

Iam under the impression that 50% fuel load mean 50% of maximum fuel load . Does it not ?. So if maximum internal fuel load of su-27 is 9400 kg , shouldnt 50% of that is 4700 kg ?

gta4 wrote:But now Su-27 is much heavier, even the lightest Su-27sk. If it continues using 18920kg as performance standard, fuel weight must be sacrificed.

Fair point


Good question.

In fact, no one (including Sukhoi) has ever used 9400/2=4700 to calculate performance, because it will make Su-27 very underperformed.
Su-27 has two "internal fuel" standard. When Sukhoi calculate range or radius, it uses 9400kg. When it calculate T/W ratio, it uses 5270kg/2 (not 9400kg/2). The rest of the fuel (9400-5270=4130kg) is treated as undroppable fuel tank.

For the maximum AOA of F-15, I know F-15 could easily sustain at 35-37deg based on airshow HUD view, I do have read a high AOA test report that it could maintain control at 40deg AOA. In fact F-15 is the second best AOA performer (only inferior to superhornet) in 4th Gen.
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Unread post24 Nov 2016, 16:27

gta4 wrote:For the maximum AOA of F-15, I know F-15 could easily sustain at 35-37deg based on airshow HUD view, I do have read a high AOA test report that it could maintain control at 40deg AOA. In fact F-15 is the second best AOA performer (only inferior to superhornet) in 4th Gen.

Iam still wondering why Su-27 cant maintain same AoA and thus higher CL ? For F-16 case obviously its vertical stabilizers is the one getting in the way. But what stop Su-27 from getting to 40 AoA in a turn ? if it can get to higher CL than F-15 at 26 degrees then surely that value would be higher at 40 degrees ?
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Unread post24 Nov 2016, 16:34

Btw , this
Image
308 meters/second = about Mach 0.85 at sea level
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Unread post24 Nov 2016, 16:51

garrya wrote:
gta4 wrote:For the maximum AOA of F-15, I know F-15 could easily sustain at 35-37deg based on airshow HUD view, I do have read a high AOA test report that it could maintain control at 40deg AOA. In fact F-15 is the second best AOA performer (only inferior to superhornet) in 4th Gen.

Iam still wondering why Su-27 cant maintain same AoA and thus higher CL ? For F-16 case obviously its vertical stabilizers is the one getting in the way. But what stop Su-27 from getting to 40 AoA in a turn ? if it can get to higher CL than F-15 at 26 degrees then surely that value would be higher at 40 degrees ?


This is because Su-27 will lose lift rapidly once it exceeds 24deg. Its lift drops much faster than eastern jets.

By the way, according to F-16 test report by GD (the literature I recommended), F-16 could easily achieve a Cl of 1.7 at 24deg AOA, Mach 0.9. At lower subsonic speed I believe it could achieve it earlier.
Last edited by gta4 on 24 Nov 2016, 16:54, edited 1 time in total.
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Unread post24 Nov 2016, 16:53

garrya wrote:Btw , this
Image
308 meters/second = about Mach 0.85 at sea level


Sorry, man, that is not speed, but Wing Loading!!!! :mrgreen: :mrgreen: :mrgreen:

G/S, look at the unit, it is kg/square meters :D

and that is 305 not 308.

the total weight=305*62=18910kg for Su-27
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