LO's F-15 vs. the F-15 Streak Eagle

[D-Scythe]

It could... if you can place it vertically at low alt with the speed it can be controllable. When you turn the nose to 90 deg pitch you: perform high-G maneuover (and add the great amount of drag) and gain the alt so you become at 90 deg pitch at the alt where thrust already less than your weight.

 

Can you post a track or some screens or something? Some of us tried, without success.

 

And do you have anything comment on the issue that, although the climb performance of the F-15 in Lock On matches that of the F-15's manual, that it STILL cannot accelerate vertically when it supposedly can?

[GGTharos]

Look up Streak Eagle time to climb records and P-42 time to climb records. They differ by a rather small percentage. WHoever wrote the data you posted is absolutely cracked.

 

BTW, the F-15 took the MiG-25's records ... FYI ;)

 

Wikipedia Ha-Ha-Ha laughable ahahahahahahaha................................... ha!

 

I am a NATO member I AM FROM BELGIUM!

I am a western fanboi TOOOOOOOOOO…

 

Pleeeeeeaaase help me because I find all these numbers all over the net on WESTERN websites confirming that Russian planes climb better!

 

Please confirm by posting a couple of links that the F-15C has a 1000ft/sec climb rate because ME TOO I am freaking out!!!!!!!!! :D

[S77th-GOYA]

It could... if you can place it vertically at low alt with the speed it can be controllable. When you turn the nose to 90 deg pitch you: perform high-G maneuover (and add the great amount of drag) and gain the alt so you become at 90 deg pitch at the alt where thrust already less than your weight.

 

If that is true, at what altitude does thrust match your weight?

[EvilBivol-1]

Can you post a track or some screens or something? Some of us tried, without success.

 

And do you have anything comment on the issue that, although the climb performance of the F-15 in Lock On matches that of the F-15's manual, that it STILL cannot accelerate vertically when it supposedly can?

 

I think you misundersood. Yo-Yo was saying that the F-15 can accelerate vertically in theory, i.e. if you could start at low altitude and already going straight up. In reality, the process of having to pull the nose from horizontal to vertical eliminates this possibility because by the time you reach 90 deg., you are already too high for the positive thrust to weight ratio, not to mention the G and drag caused by the maneuver.

 

Yo-Yo, I think the argument is that while LO seems to match whatever chart you guys are using in the studio, there appears to be a lot of data contradicting that. So perhaps your charts are somehow misleading?

 

I don't know either way, just clearing things up.

[D-Scythe]

I think you missundersood. Yo-Yo was saying that the F-15 can accelerate vertically in theory, i.e. if you could start at low altitude and already going straight up. In reality, the process of having to pull the nose from horizontal to vertical eliminates this possibility because by the time you reach 90 deg. you are already too high for the greater thrust ratio, not to mention the G and drag caused by the maneuver.

 

Eh, I think a bunch of F-15 pilots (as well as a lot of documented evidence) would disagree with that.

 

I know, I know, you're just clearing things up ;)

 

Yo-Yo, I think the problem is that while LO seems to match whatever chart you guys are using in the studio, there appears to be a lot of data contradicting that. So perhaps your charts are somehow misleading?

 

The charts are misleading.

[GGTharos]

Are we watching airspeed when climbing straight up? ...

[Pilotasso]

I just tested the F-15 ingame. I went vertical straight off the runway with 30% fuel clean config. It does accelerate verticaly for about 800 feet.past 1300 feet it will bleed off speed. Its still under what we should see but its not terribly off as I thought.

 

Also did high altitude zoom climb in AB and managed to accelerate with dry thrust at 35000 feet level flight. I usualy take the standard missile load and just 1 tank and perfomance difference is apalling.This leeds me to conclude that the only thing that makes it sluggish and causing the horrible underperfoming F-15 we see in missions are the weapons and drop tank drag factors. I had no idea how badly they were overestimeted untill today, even sparrows in smi-receded hardpoints will PWN the perfomance figures. Im am now very convinced that it beats for ED to change these drag values and we are set for high altitude cruise without afterburner all the time.

There wont be any complaints about SFM then. :)

 

 

tracks are included for the 2 test flights I described:

[S77th-GOYA]

This is the old track I made when we had this debate before. It shows an F-15 weighing in at 34926 lbs taking off at full AB and immediately climbing full vertical. Acceleration stops before it reaches vertical and at only ~1200 feet. Yes, 1200, not 12,000. The max KTAS acheived is 234. NASA's EngineSim gives the net thrust for the F100 engine at 1200 feet and 234 knots as 27670 lbs. Doubling that for the F-15 gives 55,340 lbs of thrust.

 

http://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.html

 

Please note that the plane weighs 34,926 lbs and its thrust is 55,340 lbs. That's an excess of more than 20,000 lbs of thrust.

 

So let's talk about drag. Using a drag coefficient of .15 and 234 knots and 1200 feet the drag force comes to 2320 lbs.

 

 

D = .5 * .0023 * 395.226^2 * 86.111 * .15 = 2320 lbs

 

Granted, the F-15 in the track is not at 0 AoA so the Cd is higher than .15. (AoA is around 10 degrees in the track) But even if the Cd was 1.0, the drag force would still only be 15,468 lbs and the F-15 would still accelerate.

 

Also, I believe EngineSim to be modeling the higher output version of the F100. But that difference still doesn't explain LOMAC's modeling.

straightup.zip

[GGTharos]

People will complain -less- about SFM at that point, sure.

I'm pretty sure the Flanker's payload also drags it down significantly, IIRC ... on the other hand, a MiG-29 doesn't seem to suffer quite as much ...

 

I had no idea how badly they were overestimeted untill today, even sparrows in smi-receded hardpoints will PWN the perfomance figures. Im am now very convinced that it beats for ED to change these drag values and we are set for high altitude cruise without afterburner all the time.

There wont be any complaints about SFM then. :)

[S77th-GOYA]

Addendum:

 

To remove increased drag from AoA let's look at the point in my track where the plane is vertical and AoA is 0. That is 3400 feet @ 219 KTAS. EngineSim gives a net thrust of 25,747 lbs per engine and that speed/altitude. The plane has burned 404 lbs of fuel at that point and has a net weight of 34,522 lbs. compared to a net thrust of 51,494 lbs. Drag at that speed and altitude is less than it was in the earlier calculation which still leaves a LOT of excess thrust. (~15,000 lbs)

 

Yo-Yo?

[SwingKid]

SK could you post minimum sustained speed in level flight per altitude charts?

I think that would be enlighning as well. Believe me.

 

Is this what you're looking for?

 

http://www.ecf.utoronto.ca/~pavacic/lomac/scan0184.JPG

 

-SK

[SwingKid]

Just to stop speculations about F-15 "underpowered", etc.

I took the chart for maximum thrust climb (MAX, not MIL) and found that the time to get 25000 with 39000 lb initial weight for DI = 0... 40 (there is no valuable dependance on DI while this kind of klimb is performed) .

The result (please believe me :) ) was 1.1 minute + 0.5 minute to get the climb speed, i.e. 1 min 36 s.

The speed direction is 350 knots till 0.95M then 0.95M.

Though I am not SFM fan :) I managed to hold 350+-10 kts and the total time was 1min 32...33 s.

Any comment, gentlemen?

 

It bothers me that the "0.5 minutes" claimed on the Dash-1 climb chart is regardless of aircraft weight - and this grossly approximate and obviously unreliable number makes up 30% of the proof.

 

Meanwhile, my opposing finding is using a reference measured accurately to the individual second and pound, and over a more tightly defined altitude band, where errors have less chance to "smooth out" by averaging.

 

I do believe that ED used the best data that was available when the F-15 SFM was first developed. However, I don't believe that the Dash-1 climb chart can any longer be considered the best reference for our purposes today.

 

To say that we did the best we could at the time, and nothing can be done about it now, and ED is working on Black Shark - I would agree, and am happy to drop all argument about the F-15 performance.

 

But to say that the Lock On F-15 is producing the correct thrust, and the Dash-1 climb chart is proof of that, and the Streak Eagle records are less useful than the Dash-1 climb chart - it's a belief I had myself in the past, and was forced to reject by the evidence. I invite anyone to reconsider.

 

Kuky, I rep you for your independent experiment. But - what was your speed, at 25,000 feet?

 

-SK

[GGTharos]

I don't think it should be dropped; it will probably not be fixed for Black Shark (though it would be nice if it was) however this topic ought to be brought back at least during the fighter project - it shouldn't be forgotten.

 

Besides it is both an interesting and useful discussion :)

[Kuky]

Kuky, I rep you for your independent experiment. But - what was your speed, at 25,000 feet?

 

I can't recall as I didn't pay attention to this... I'll try again later this evening when I get home.

[Kula66]

I had no idea how badly they were overestimeted untill today, even sparrows in smi-receded hardpoints will PWN the perfomance figures.

 

At 40k+ you get a noticable jump in perforance when you drop the tank ... I wonder how well those semi-recessed AMRAAMs are modelled compared to AA-10/12s on wing/under fuse hard-points which look as draggy as hell!

[Pilotasso]

Is this what you're looking for?

 

http://www.ecf.utoronto.ca/~pavacic/lomac/scan0184.JPG

 

If the smaller curves represent minimum-maximum sustained level flight in military thrust then yes. Notice how 4 Sparrows impact so little, when I get home I will do some more testing with the same weights, dont empty your attatchments yet.

[Yo-Yo]

Can you post a track or some screens or something? Some of us tried, without success.

 

And do you have anything comment on the issue that, although the climb performance of the F-15 in Lock On matches that of the F-15's manual, that it STILL cannot accelerate vertically when it supposedly can?

 

I can not too.... and I have very strong feeling that nobody can. :). SwingKid if I was told yesterday prooved that F-15 CAn NOT accelerate vertically.

The main reason is that it can not position itself at the altitude where its thrust is more than weight at 90 deg pitch. Sic.

[Pilotasso]

I posted a track showing you CAN but under 1300 feet starting verticaly straight off of the runway and with 30% fuel only.

 

The worst problem though is weapon drag, they are all so draggy it feels like flying with a drag shute open in mid flight. Thats why you have to afterburn at high altitude.

[Yo-Yo]

Addendum:

 

To remove increased drag from AoA let's look at the point in my track where the plane is vertical and AoA is 0. That is 3400 feet @ 219 KTAS. EngineSim gives a net thrust of 25,747 lbs per engine and that speed/altitude. The plane has burned 404 lbs of fuel at that point and has a net weight of 34,522 lbs. compared to a net thrust of 51,494 lbs. Drag at that speed and altitude is less than it was in the earlier calculation which still leaves a LOT of excess thrust. (~15,000 lbs)

 

Yo-Yo?

 

I am afraid Engine Sim is very optimistic... :) What sim did you use?

[britgliderpilot]

I am afraid Engine Sim is very optimistic... :) What sim did you use?

 

Given that it's predicting 28,000lb thrust for the F100 at sea level, zero forward airspeed, I'd agree with that.

 

 

PA, if you can tweak the EngineSim model so it'll give the advertised F100 thrust levels, and then repeat . . . . that'd be interesting.

 

My guess would be they've not included duct losses or have overestimated efficiencies - but I'm just guessing.

[Kuky]

I did bit more testing and this time I recorded the track, 4 test in total and left framerate counter for timing purposes (please bare in mind the time/Indicated-speed/altitude valies are estimate)

 

Test 1:

11sec - Started on the runway

25sec - Gear up @ 250Mph (no flaps) and continued to accelerate level

35sec - Started 2.5G Immelman @ 480Mph

79sec - Completed Immelman flying level @ 370Mph @ 29,000ft

 

Test 2:

07sec - Started on the runway

17sec - Gear up @ 220Mph (no flaps) and continued to accelerate level

31sec - Started 2.5/3.0G Immelman @ 490Mph

74sec - Completed Immelman flying level @ 400Mph @ 27,500ft

 

Test 3:

10sec - Started on the runway

23sec - Gear up @ 250Mph (no flaps) and continued to accelerate level

35sec - Started 3.0G Immelman @ 490Mph

74sec - Completed Immelman flying level @ 410Mph @ 25,500ft

 

Test 4:

09sec - Started on the runway

20sec - Gear up @ 230Mph (no flaps) and continued to accelerate level

33sec - Started 2.5G Immelman @ 490Mph

77sec - Completed Immelman flying level @ 370Mph @ 29,000ft

 

I wonder exactly from what point does t=0 in this record?

[Kuky]

Here is one more (in this one I tried to keep as close as posssible to specified speed at the start of Immelmann and G value) and again I used 28% fuel which gives gross weight just about 31,900lb

 

Test 5:

07.6sec - Started on the runway

19.6sec - Gear up @ 230Mph (no flaps) and continued to accelerate level

32.6sec - Started 2.5G Immelman @ 495Mph (0.65mach)

76.6sec - Completed Immelman flying level @ 375Mph @ 29,000ft

 

Now I wonder how on earth do they achieve this kind of vertical turn with sustained 2.5G and starting speed of 495Mph and are able to complete the turn and get level within 56sec???? :huh: From my tests I don't see how this is possible... they would have to be pulling more then 3G to be able to complete the turn within 56sec. If I take the difference from time I raise the gear to time I am flying level that actually comes very close to 56sec, but it takes at least 10sec to get from stand point to getting airborne...

 

From this diagram I think they start timing from when the aircraft has accelerated to 0.65Mach and the point of 56sec is where the aircraft has completed the turn and flying level. The diagram also shows final speed at exit of Immelmann as 1.1Mach where as I only achieve about 0.55Mach. That doe not seem right. I think this would be bit of undermodelling in speed (maybe too much dragg calculated) in LockOn at medium to high altitudes for the F-15.

 

 

Anyway, If my assumption is right and they time from 0.65Mach (not standstill) then 29,000ft in 69sec is not so bad for LockOn "stock" F-15C and most definitely NOT 1/2 as people complain and way over claimed 18,000ft. The way I see it the way comparison test in LockOn was done with pulling much more then 2.5G (and it doesn't even say what starting speed was at the begining of turn.

 

So, to conclude on my part, surely LockOn is not maching this record especially in exit speed but hey, it's not supposed to as let me remind you again, this is a RECORD achieved once with airframe set up specifically for this. Oh and... I just remembered someone said the engines for the test airframe had modified engines (boosted) so I'm not surprised it achieved much higher exit speed. I wouldn't be surprised if that was fitted especially for better engine performance and higher thrust at higher altitudes.

[Yo-Yo]

Given that it's predicting 28,000lb thrust for the F100 at sea level, zero forward airspeed, I'd agree with that.

 

 

PA, if you can tweak the EngineSim model so it'll give the advertised F100 thrust levels, and then repeat . . . . that'd be interesting.

 

My guess would be they've not included duct losses or have overestimated efficiencies - but I'm just guessing.

 

What data did you feed this Sim? AIr flow, fuel flow to burner and afterburner, bypass ratio, pressure coefficients for compressors and turbines, efficiency numbers, etc?

[Pilotasso]

what is EngineSIM?

[S77th-GOYA]

what is EngineSIM?

 

 

http://forum.lockon.ru/showpost.php?p=320790&postcount=90