Sukhoi Su-57 / T-50 / PAK FA - flight testing and development Part II [2012-current]

[wasp850]

Can the plane pull 9G at 70 deg. bank angle at high speed without any stability issues and in perfect control at such a high AoA?

Above about 25 AoA, the F-15's handling degrades, as do probably all aircraft of that generation, including the Su 27 and MiG 29.
How much speed do you mean ? From about 1.5M the roll speed is reduced by the flight system.

 

[wasp850]

For example, Su-27 at 20 tones (with 4 missiles) can sustain 9G at 10000ft, but the clean F-15C with F100-PW-220 and 16,7 tones can't (it can sustain around 8,5G's).

Maximum operational overloading with the estimated gross weight of 21400 kg:
G max = 8,0 with [M]≤0,85
G max = 6,5 with 0,85<[M]≤1,25
G max = 7,0 with [M]>1,25
For the weights, which differ from estimated gross weight, the g-force is established from the detachment:
G max = const = of 17100 kg with [M]<0,85, but not more than 9,0 G
G max = const = of 13900 kg with 0,85<[M]≤1,25, but not more than 7,0 G
G max = const = of 15000 kg with [M]>1,25, but not more than 7,5 G




The table shows the sustainable limits of 8G for 50% fuel and 4 missiles. The dashed line is for
overloads exceeding the limits g max=8 at M<0.85; max=5.5 at M≥0.85




In the real world the Su 27 had a significant maneuverability advantage at low speeds, from 375 knots to about M 0.85 they were surprisingly close and at higher speeds the F-15 had the edge ( the Eagle was built according to EM theory with an emphasis on M 0.6 - 1.6 maneuverability ).

Below 375 knots the Su 27 had a big advantage in just about everything, here the F-15 would only win if its pilot was significantly more experienced.

 

[Galaxy]

How many pages of F-15 vs SU-27 dick measuring will there be before mods delete that off topic junk?

 

[RadicalDisconnect]

It is obvious that the F-15 can't pull 9G at 600 km/h, so the plane must fly at a higher speed to achieve 9G. Based on calculations (made by other people, I don't have the necessary data for that), that speed is between 700-740 km/h (depending on the F-15C version and weight), which translates to about 24-25 deg/s ITR. At that speed, the F-15 doesn't need to have the same Clmax as the Su-27 to to be able pull 9G, and at the same time, it is flying at a much lower AoA than 40 deg. , so the drag is in orders of magnitude lower, making that ITR practically achievable.

So the question still stands: is pulling 9G at 40 deg AoA at around 700-740 km/h a permissible flight condition for the F-15C?

F-15C manual doesn't have ITR charts but McDonnell Douglas did publish papers from flight tests proving you wrong, see attachment.

https://www.f15sim.com/files/Eagle%20Talk%20Vol%20IV.pdf

The F-15C at 10,000ft and 37,000lbs weight can pull over 8g at even lower speed of 305 knots or 565km/h, which throws your whole rant out the window. In fact, looking at the turn graph where Cl_max curve intersects with g-limit curve, it happens at about 310-320 knots KCAS, or about 575-593km/h.

So you find the data that shows McDonnell Douglas is wrong about their own aircraft.

The answer is obvious, you can't make any practical use of the Clmax for the max ITR in the F-15.

Again, the data shows that Cl_max is usable for the F-15. The formula from AOA units to degrees is:
AoA[units] = AoA[Degrees] + 11
So at 305 knots, 51 AOA units means 40 degrees AOA.

his is the loading and performance data for various flight profiles and missions for the F-15C with 220 engine.

We can see that the ferry range with 3 EFT is 1933 nm, or around 3518 km. The total amount of fuel in this configuration is 25350 lb, or around 11483 kg.
Su-27 combat range with four air-to-air missiles that are launched halfway is around 3,600 km (the Su-27's actual ferry range when clean is longer, but I’ll stick with the 3,600 km).

So, in typical mission where F-15 is not dropping the EFT, the plane can cover 3518 km with 11483 kg of fuel.
Su-27 on the other hand can cover 3600 km with significantly less fuel (9400 kg).
Based on the ferry range, when the EFT are dropped when empty, we can calculate the max range for the F-15C just on internal fuel.

Since the max internal capacity accounts for the 53% of the total amount of fuel (internal plus 3 EFT), we can calculate that the max range on internal fuel is around 2067 km.

Your numbers are questionable because the calculations are completely messed up. I see that you calculated range on internal fuel by applying the percentage of internal fuel vs total fuel, to the ferry range. In fact, you made it a bit lower, since 53% of 2,144nmi is 1136nmi or 2,104km.
Yet this is completely wrong because it ignores the added weight and drag of the 3 EFTs, which have total DI of 23.2, and looking at fuel burn at 480 knots you can see fuel burn is over 10% higher with DI=20, not to mention the higher weight causing more fuel flow. So in fact, the range on internal fuel must be higher than 53% of ferry range with 3 EFTs.

In fact, with 13,455lbs of internal fuel and assuming that 3,500lbs are consumed on takeoff climb and landing (very pessimistic assumption for F-15), then even with 10,000lbs or 4,545kg of internal fuel left, the F-15 will still travel 2,300km at 480 knots, using the fuel flow at 40,000lbs as an average.

At that weight Su-27 is carrying 3700 kg of fuel, it can cover 1415 km, and can sustain 9G at 10000ft.
At 16761 kg F-15 is carrying 3050 kg of fuel, it can cover 1034 km, and can sustain 8,5G at 10000ft.

And then you make the very same mistake a few lines later! Assuming that halving the fuel will half the range, when that's clearly not the case (just check the Breguet range equation where range is logarithmic with regards fuel fraction).

In other words your numbers are totally off.

You're probably using the wrong polar for the F-15. The AGARD data isn't accurate. This is a good match.

It looks like you beat me to the punch in finding the McDonnell Douglas paper, looks like we have the same documents.
However, do you know where this is from? The AGARD data is from flight testing so I think it's trustworthy. So PeregrineFalcon has been denigrating the F-15 with inaccurate data, but I think this chart looks too optimistic.

 

[wasp850]

It looks like you beat me to the punch in finding the McDonnell Douglas paper, looks like we have the same documents.
However, do you know where this is from? The AGARD data is from flight testing so I think it's trustworthy. So PeregrineFalcon has been denigrating the F-15 with inaccurate data, but I think this chart looks too optimistic.

The AGARD report was written at a time when it was not a good idea to publish the exact performance of the F-15, so its author deliberately stated some things a bit falsely.

The polar comes from a document which I can't track down right now, I have over 20 gb of pdf files on the F-15 but I'll search it over time.

The polar aproximatly corresponds to this somewhat simplified one, which is from the author of the AGARD document, Jack Abercrombie.
1,6 between +-25-40 AoA, depends..

 

[Scorpion82]

WHAT THE HELL HAS THIS DISCUSSION TO DO WITH THE SU-57!!!???