Key Publishing

engineerK

Forum Replies Created

Viewing 13 posts - 1 through 13 (of 13 total)

Author

Posts
November 27, 2016 at 6:42 pm in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2142112

engineerK
Participant

Isn’t it a bit strange that they write CL but under that write coefficient of drag ?????

Please read the full caption. It is Cd as a function of Cl and Mach number. The graph is a surface instead of a curve.

November 27, 2016 at 2:08 am in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2142348

engineerK
Participant

1) I have a report from MIT that also proves F-15 has a CL of 1.6:
[ATTACH=CONFIG]249926[/ATTACH]
Russian TsAGI estimates F-15’s CL to be 1.08 and significantly underestimated its turning performance.

2) The airshow flight instruction of F-22 shows that F-22 performs the show with full fuel, does low speed pass at 75knots, 40deg AOA, with less than military power.
The low-speed pass is the 6th maneuver out of all 10 maneuvers, by this time the F-22 consumes at most 2 tons of fuel. At this low speed the total air pressure recovery of any air intake is at most 0.9, meaning that the useful thrust from the engine should have a 15% deduction (1% loss in total air pressure recovery gives 1.5% deduction in thrust). The military thrust of F119 is 105~110KN. From this we have the equation:

Lift+component of thrust=weight

0.5*CL*1.225*(38.5)^2*78+2*105000(or 110000)*0.85*sin(40deg)=(19700+8200-2000)*9.8

CL=1.9 or 2.0

November 25, 2016 at 7:52 pm in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2143637

engineerK
Participant

And I recently got the proof that F-22 has a maximum Cl of at least 1.9-2.0. Surprised?

November 25, 2016 at 4:59 am in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2143985

engineerK
Participant

How to calculate acceleration from climb rate graph? and can we see the graph?

climb rate=SEP=(thrust-drag)*speed/(weight*g)=acceleration*speed/g

So:

acceleration=climb rate*g/speed.

November 25, 2016 at 4:37 am in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2143989

engineerK
Participant

Ok Andraxxus, if you were correct, let’s verify you idea using this data set: M0.2, 21400kg, 2.3G

0.5*Cy*1.225*(0.2*340)^2*62=2.3*21400*9.8;

Cy=2.6

Are you saying the maximum Cl at M0.2 is 2.6?

Afterall, why are you even trying to find and prove a Clmax value that contradicts the flight manual? Its clearly written there as 1,85 at M0,5… You can easily use google translate for the texts below to check it yourself; only unclear thing you would be facing is “АБСП”, you could insert the the long version as I’ve typed above.

“Cl for level flight is 1.85” does not contradict “Cl in high g maneuver is 1.6”.

You can not deploy full trailing edge flap in high g turn. It will break.

I have plenty of TsAGI documents supporting the idea that the maximum Cl=1.6 in high g maneuvering.

Anyway, if Su-27 could use Cl=1.85 in 9G turn, it could easily exceed 30deg/sec in instantaneous turn, under 21400kg. But Sukhoi only advertises Su-27 to have 27-28 deg/sec instantaneous turn rate under 18920-19000kg. This is a huge contradiction.

http://www.f-16.net/forum/download/file.php?id=23822&t=1&sid=6a7ddf5e67e6b87b72ff684bf0c2d60c
http://www.f-16.net/forum/download/file.php?id=23823&t=1&sid=6a7ddf5e67e6b87b72ff684bf0c2d60c

November 25, 2016 at 4:07 am in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2144007

engineerK
Participant

Thank you for supporting the acceleration estimation in the first post and providing useful opinion on the source of estimation errors.

However, the main source of the estimation error (the change in air density causes induced drag to change) will only make F-35’s acceleration even better at low altitude, or in other words, this estimation is rough, but it only underestimates F-35’s performance. That’s why I think this estimation is solid and reliable.

November 25, 2016 at 3:32 am in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2144011

engineerK
Participant

As you can see, first condition (Clmax=1,85) is applicable up to M0,48 at sea level, where it will yield;

0,5*62*1,85*(343,1*0,48)^2 / 9,8184 = 193909 kg of lift. Divide that to 21400 kg as given in the manual its 9Gs.

Sorry but again I think you forgot to deduct the component of thrust. If you do that compensation you will find Cl=1.6, pretty close to TsAGI report. According to the manual, the maximum load factor at M0.48, 21400kg is 8G, rather than 9G.

[ATTACH=CONFIG]250069[/ATTACH]

(I am using a word version of the manual, bu I am sure you can find the same figure in your scanned version)

If you don’t have the thrust effect compensated, and use the maximum load factor at Mach 0.2, you will find a Clmax close to 3.0. That is absurd.

uses this data set: M0.2, 21400kg, 2.3G, and you will find a Cl close to 3.0. This is what happen if you don’t have the thrust effect compensated.

November 24, 2016 at 6:23 pm in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2144537

engineerK
Participant

You can verify Clmax=1.6 in high g turns by another page of the flight manual, if my memory serves, which shows a Su-27 under 21400kg weight could pull 8G at mach 0.48.

So:

Lift+Component of thrust=21400*9.8*8

1/2*Cl*1.225*(0.48*340.39)^2*62+25000*9.8*sin(24deg) = 21400*9.8*8

Cl=1.6

November 24, 2016 at 6:08 pm in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2144555

engineerK
Participant

If anyone who proficient in Russian can translate this ?

Iam wondering what is the real Clmax of Su-27 , is it 1.85 or 1.6 ?

The first one is Su-27 manual,
The second one is TsAGI report for Su-27/F-15 comparison. F-15 data are estimated.

1.85 is when tailing edge flap is fully deployed (level flight only), which could not be used in High G turns. The usable Cl in maneuvers is 1.6.

November 23, 2016 at 7:41 pm in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2145524

engineerK
Participant

drag drops with altitude, but so does thrust, and so does fuel consumption

Yes but as long as the “same AB duration” standard is applied on the same altitude, it would be verified for other altitude as well.

For instance: at sea level, a Su27 with 2000kg fuel would have the same AB duration as a F-15 with 1800kg fuel. So they will have almost the same AB duration on other altitudes (low to medium), because the AB thrust of Su27 and F15 both decay with almost the same rate as altitude increases (low to medium altitude)

November 23, 2016 at 4:01 pm in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2145743

engineerK
Participant

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.

November 23, 2016 at 3:50 pm in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2145774

engineerK
Participant

To haarvala:

Nowadays Su-27 is becoming heavier. If it wants to maintain 18920kg flying weight it must sacrifice some fuel, that is where the “2000kg” fuel comes from.

If Su-35 is carrying 3000kg fuel for perofrmance calculation, F-35 needs only 2400kg fuel for same AB duration, the average acceleration is at least 10.4m/s2 in this case, which is still better than Su-35.

I know this is not a good news for Russian jet fanboys, but this is life.

BTW, if we use “same AB duration” for all jets, you will find F15 and F16 could outperform Mig29 and Su27 in almost every aspect. I will write a thread for that.

November 23, 2016 at 3:45 pm in reply to: Proof: F-35A can out-accelerate Su-27/35 in subsonic region ? #2145778

engineerK
Participant

I have no means to challange this by equations. But we have andraax charts where it clearly shows the Mach figures with given altitude.
What is very clear in those is that the mach numbers increase from 1000m – 5000m – 10000m etc

So the point that loss of air density(Engine performance) is equal to drag(index1.44) is pure ********.

cruising at 5000m gives you a better acceleration vs cruising at 1000m. And that does not compute with the autor’s figures.
We need eighter F-35 charts at 1000m or Flanker at 5000m to get this right.

To haarvala:

Sorry, man, you are completely wrong. This is all about subsonic acceleration. At 1000m, the subsonic acceleration is definitely better than that at 5000m.
Author

Posts

Viewing 13 posts - 1 through 13 (of 13 total)