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

[Rhen]

....

 

I would agree, not only for this chart, but also for others in the Dash-1. The low-altitude lines all look like someone took a ruler and just drew a stright line through (0,0) - without any regard for what this physically means. That's the whole point I'm trying to make - to Yo-yo, to Rhen, to anyone who is interested. The Dash-1 contains some data that is too approximate for our use.

 

No, you're still not understanding that the straight line you're having so much trouble wrapping your mind around merely states that AT 5,000 FT and BELOW, the distance it takes to get to 5,000ft, between a HEAVY and LIGHT Eagle, is NEGLIGABLE. Let me state this in terms I've previously used - NEGLIGABLE = within accepted variations in pilot technique.

 

The charts are based upon flight data, derived from the flight profile within the Dash 1, and compiled from several test pilots.

 

Back up a bit, I think you have misunderstood the order of cause and effect that I'm trying to present:

 

(1) By F=m*a, I have established, beyond any reasonable doubt, that the sea level thrust of the F-15C in Lock On does not exceed 34,000 lbf.

 

(2) Despite this, the sea level performance of the F-15C in Lock On matches the Dash-1.

 

(3) Therefore, the Dash-1 does not describe the sea level performance of the 47,000 lbf F-15C correctly.

 

(3) follows from (1) and (2), not the other way around.

:huh:

 

Non-sequitur! I can do that too!

 

(1) The 220 pushes out about 24k, which is a helluva lot of horsepower.

(2) It's on the viper (f-16)

(3) The other viper (dodge) has much less weight and horspower.

(4) In a viper vs viper ground race, the viper will be marginally faster. :P

(5) The Dodge can keep up with (or surpass) the LM in the first 1/2mi.

(6) Therefore the STREAK Eagle is a better comparison with the LOMAC F-15 than the F-15 Dash 1. :megalol: :smilewink:

 

In the first 1/2 mi or the first 5,000ft, WEIGHT'S NOT MUCH OF A FACTOR at sea level to 5,000 ft, and any variations in multiple data sets is within a standard deviation which can't be ruled out to being attributed to individual pilot technique.

 

Perhaps this is what you might have logically concluded, had you been using someone elses cranium. :smilewink: :smartass:

 

(1) By F=m*a, I have established, beyond any reasonable doubt, that the sea level thrust of the F-15C in Lock On does not exceed 34,000 lbf.

 

(2) Despite this, the sea level performance of the F-15C in Lock On matches the Dash-1.

 

(3) The Dash-1 DOES INDEED represent actual REAL LIFE AIRCRAFT PERFORMANCE AS LONG AS IT'S FLOWN USING THE DASH 1 PROCEDURE.

 

(4) Therefore, there is a problem with how I flew the aircraft to derive the comparison data (did not conform to the Dash 1 climb technique), what Lock On is purporting the mass of the aircraft, the drag indices - to include ground friction, or engine thrust curve with respect to speed and altitude, or is using an inappropriately derived equation simulating this, or all the above. (Sorry Yo-Yo, no offense meant, merely arguing a point). Either that or I must revisit my first premise....

 

Trouble is, do we know what the mil power thrust is supposed to be?

Much easier to analyze max power, I think. That thrust evel is published in many places, and is more easily verifiable.

 

Walk before we run.

 

-SK

Mil power thrust can easily be determined by use of either the DASH 1 or reputable sources elsewhere. We spend MORE TIME in MIL than in MAX, so NO! MIL is VERY IMPORTANT also.

 

Why is it so hard for you to understand that the data from the Dash 1 and the STREAK Eagle BOTH come from pilot flight data and LOGICAL extrapolations of that data?:(

[Yo-Yo]

I brought this up before - in the "real" top speed chart, the F-15's top speed shown (around Mach 2.3-4ish) is an airframe limit, not a performance limit - extended flight times beyond Mach 2.3 is not really friendly to the airframe. The curve literally looks like it hits a wall, with basically the F-15's envelope past that speed being truncated out.

 

However, Lock On's curve looks like it takes it as an ACTUAL performance limit. It tops off at Mach 2.4, WITHOUT the wall. That's probably another indication of the lack of acceleration/thrust at altitude.

 

 

If you take into consideration that the speed curve for the real F-15 above extends to Mach 2.5+ above, than the F-15C *severely* underperforms at altitude (specifically, between 38 - 50 000 ft).

Not severely. All you noticed really present in th FM. And it was necessary to make impossible for users override the limitations. I think that all of you clearly understand that if they could they would. We are not so cruel to explode aircaraft because of overspeed.

But it is not a big problem because of very low level of excessive power in the "upper-right region" of the flight envelope. Some time ago I explained that in this region thrust and drag curves intersect at very low angle: 1 % changing in the thrust causes 10% changes in max speed while the acceleration and dHe/dt stay almost the same.

MiG-29 was cut at the same way at low level for example...

[GGTharos]

You should be so cruel! :)

 

You should make it take some random amount of time, with accumulating damage - you should start to see the canopy melting, the pilot say 'damn it's getting hot in here' or something like this - then you would have warning :)

 

Not severely. All you noticed really present in th FM. And it was necessary to make impossible for users override the limitations. I think that all of you clearly understand that if they could they would. We are not so cruel to explode aircaraft because of overspeed.

[Yo-Yo]

We will think...

[GGTharos]

Ehh, you're not talking about a piper here - you're talking about an aircraft made of honeycomb and structural components which will be more resistant to this problem than the canopy.

[Trident]

I'm actually not sure the aircraft would be an outright loss if it went beyond it's rated top speed. The canopy would be affected by the friction heat (it's made of stretched acrylics, IIRC) due to it's non-ideal shape for supersonic flight (bubble canopy) and the engines might suffer as well, but a crash would be unlikely, IMHO. However, the airframe might be unsuitable for future use without major repairs, something that could be considered almost as damning as a loss in a wartime setting. Unfortunately it would be hard to simulate this realistically in a PC sim.

 

I also don't subscribe to the idea that the Dash-1 data isn't good enough for us - a sim is about the piloting experience first and foremost, if it's good enough for the real pilot's it should most certainly be good enough for us. The only issue I can see that the declassified data might be altered to hide certain performance characteristics?

[aimmaverick]

Not severely. All you noticed really present in th FM. And it was necessary to make impossible for users override the limitations. I think that all of you clearly understand that if they could they would. We are not so cruel to explode aircaraft because of overspeed.

But it is not a big problem because of very low level of excessive power in the "upper-right region" of the flight envelope. Some time ago I explained that in this region thrust and drag curves intersect at very low angle: 1 % changing in the thrust causes 10% changes in max speed while the acceleration and dHe/dt stay almost the same.

MiG-29 was cut at the same way at low level for example...

 

So Yo-Yo why doesnt this apply to russian aircraft as well? Why have they higher top speed than stated but Eagle has it lowered? Whats up with that? Dont the same limitations apply to russian airframes or are they made from super strentgh materials? Why dont you(ED team) just admit that everything russian in this game- from ground units to air-air missiles is overmodelled so it always comes out better than western stuff?:thumbdown:

[GGTharos]

^^^^

 

Now that was useless and unnecessary. Perhaps you haven't been playing the same game everyone has been playing. The problem of bias is minor and is a reflection of old code. All missiles are pretty equally porked, same with all the avionics, etc, etc.

[SwingKid]

(Sorry to skip ahead, I'll probably reply to other stuff later)

 

I also don't subscribe to the idea that the Dash-1 data isn't good enough for us - a sim is about the piloting experience first and foremost, if it's good enough for the real pilot's it should most certainly be good enough for us.

 

Out of curiosity - how do you resolve the apparent contradiction that the Lock On SFM follows the Dash-1, the Dash-1 is good enough for the real pilots, but the Lock On SFM is not good enough for the real pilots?

 

-SK

[TucksonSonny]

Good observation. But, Rhen ain't gonna be going beyond open source in this discussion. ;)

 

Get the hffms manual (130 pages) and you will get answers for all your MIL/AB thrust questions and more ;)

Of course it is for the viper but for all your thrust questions about MIL thrust /AB power it is very simple: just multiply the numbers with 2 for the F-15.

[Trident]

Out of curiosity - how do you resolve the apparent contradiction that the Lock On SFM follows the Dash-1, the Dash-1 is good enough for the real pilots, but the Lock On SFM is not good enough for the real pilots?

 

Well, there doesn't seem to be much of a contradiction in that particular part of the envelope, does there? Where the crux of the problem (and there does seem to be one) with the thrust numbers and at high altitudes lies is another issue entirely - as Rhen points out there is any number of possibilities in this regard. That the Dash-1 is so grossly inaccurate would be the least likely of them IMHO, unless said inaccuracy is deliberate, as pointed out above.

[Trident]

So Yo-Yo why doesnt this apply to russian aircraft as well? Why have they higher top speed than stated but Eagle has it lowered? Whats up with that? Dont the same limitations apply to russian airframes or are they made from super strentgh materials? Why dont you(ED team) just admit that everything russian in this game- from ground units to air-air missiles is overmodelled so it always comes out better than western stuff?:thumbdown:

 

The problem seems to affect ALL (as in, including the Russian aircraft) SFM player aircraft in the game to some degree, so stop spoiling for a fight.

[britgliderpilot]

Get the hffms manual (130 pages) and you will get answers for all your MIL/AB thrust questions and more ;)

Of course it is for the viper but for all your thrust questions about MIL thrust /AB power it is very simple: just multiply the numbers with 2 for the F-15.

 

If it was accurate for the F-16, it'll most likely be inaccurate for the F-15.

Biggest difference is the intake system - big difference at high mach nos, less so at lower numbers.

 

The zero forward speed/zero altitude case is still interesting, though. Below 20,000lbs thrust in the HFFMSMSfufflemumble F-16 as well as according to SwingKid's numbers . . . . .

 

Where are the HFFMS numbers coming from, out of interest? I assume they're the ones from the Falcon flight model . . . . but what source did they use?

[hitman]

Correct me if Im wrong, but doesnt the F-16 utilize the exact same engine the -15 uses?

[britgliderpilot]

Correct me if Im wrong, but doesnt the F-16 utilize the exact same engine the -15 uses?

 

The same engine doesn't automatically mean you'll get the same performance from the engine. The intake system can make a BIG difference - especially comparing the fixed geometry intake on the F-16 to the variable geometry intake on the F-15.

 

The intakes on Concorde and the Blackbird were absolute works of art - they were the single biggest thing allowing the performance of those two aircraft.

 

 

There'll be differences in static thrust and at low Mach numbers due to differences in the ducting systems as well . . . . those aren't so big, but you can pretty much guarantee they'll be there.

 

Just as an example - observe pressure recovery curve comparing the intake efficiencies:

 

[SwingKid]

Well, there doesn't seem to be much of a contradiction in that particular part of the envelope, does there?

 

If you feel this way (and I have a lot of respect for you as a "voice of reason"), then it seems that the discussion has moved well past what the title of the thread, and the first post in it, have anything to do with - without ever having solved the basic discrepancy exposed in post #145.

 

In that sense, I think it's appropriate now to ask D-Scythe what exactly he feels he accomplished by starting this topic at all, and dragging my good name into it. :)

 

 

"Are you not entertained??"

 

-SK

[hitman]

The same engine doesn't automatically mean you'll get the same performance from the engine. The intake system can make a BIG difference - especially comparing the fixed geometry intake on the F-16 to the variable geometry intake on the F-15.

 

Technically not the point I was getting at, but merely a point that if it is indeed the same engine then perhaps bench thrust will both be the same, and still have the same numbers pop up on the charts regarding to engine performance. Sorry Im not exactly a physicist and I dont even know how to interpret 99% of the stuff posted on this thread. :smartass:

[SwingKid]

For the F100-PW-200 version,

...maximum thrust of 14,670 pounds at full

military power. Maximum afterburning thrust is 23,830 pounds.

 

Since the afterburning thrust is similar to the 23,450 lbf of the F100-PW-220, we'll assume that the military thrust is also similar.

 

Based on that, I have found the following result for maximum military thrust:

 

Lock On F-15C: ~23,100 lbf thrust

Real F-15C: ~29340 lbf thrust

Lock On F-15C underpowered in military thrust by: 21.3%

 

Note that from post #145, we found that in the afterburning regime, the Lock On F-15C was underpowered by 27.5%. So, it would appear that at sea level, max thrust is actually significantly more wrong than mil thrust in Lock On.

 

I've also tried to fly Rhen's test of a climb to 40,000 feet at mil power. I seriously doubt the precision of this kind of test, since it relies on maintaining a speed of Mach 0.9 by watching a Mach meter that is graduated in units of 0.5. The KCAS dial also reads a different value than the HUD, calling into question the claim that one is "maintaining 350 KCAS." The whole test seems to mainly involves holding a pitch of around 6.5 degrees for about 6 minutes, and feels extremely "mushy." If I wasn't at 0.9 Mach like I thought, then over six minutes, huge errors are going to appear in my measurement, and the whole test is worthless.

 

That being said, my result was:

Time to 40,000' in Lock On: 7:07 min

Time to 40,000' by Dash-1: 4:30 min

Lock On climb performance underpowered by: 58%

Distance to 40,000' in Lock On: 55.3 nm (corrected 2007/04/30)

Distance to 40,000' by Dash-1: 38 nm

Lock On climb performance underpowered by: 46% (corrected 2007/04/30)

 

-SK

[Rhen]

SwingKid,

 

I don't mean to get personal with you... If you derived that from my posts, I sincerely apologize. We're both on the same team here - in that we think there's something wrong with the performance of the aircraft in LOMAC. We're both trying to get to the same point - a fix. We're just arguing about the 'what's' and 'why's' of the matter.

 

Only hope the two of us, in explaining the matter of poor performance with respect to the real aircraft (or in the case of the Fulcrum - its abuse of steroids) can hopefully convince Yo-Yo to address our concerns.

 

Although the FM for anything flyable except the frog is simplified, I still enjoy flying LOMAC for its ability to give me the "feel" of flight. Where the SFM fails to convince me is at either end of it's spectrum. The high AOA, low speed envelope, and the high-speed, low AOA portions, just lose that ability to convince me that I'm flying something - let alone an Eagle.

 

While I'd much rather have an AFM for all flyables, I'd be happy if those two realms, but even more importantly, the MIL power aspect and drag indices are addressed. Bump up the thrust here (the simple fix) and it would approximate an Eagle more readily than it already does.

 

People who tend to fly around in MAX all the time and then tell me that the FM is appropriate aren't looking at the entire picture. I've got the feeling the drag is a problem.... Regardless of the matter and Yo-Yo's need to quantify things, when stuff's hanging off the jet the turn performance is a bit off. In my experience corner velocity in the LOMAC Eagle appears higher than the real thing, at least to get the same turn for the same airspeed loss. That's all I'll say without making Yo-Yo happy with quantifiable numbers.

 

I'm hoping that you'll see that the Dash-1 is the way to go. It's what we use to flight plan, and attempt to determine what kind of time, fuel, distance we'll use up in a sortie - at least without using our "rule of thumbs." Regardless of whether I convince you of this or not, we can agree (hopefully) that the Eagle's performance appears less than "advertized" when it comes to demonstrated ability.

[Rhen]

I've also tried to fly Rhen's test of a climb to 40,000 feet at mil power. I seriously doubt the precision of this kind of test, since it relies on maintaining a speed of Mach 0.9 by watching a Mach meter that is graduated in units of 0.5. The KCAS dial also reads a different value than the HUD, calling into question the claim that one is "maintaining 350 KCAS." The whole test seems to mainly involves holding a pitch of around 6.5 degrees for about 6 minutes, and feels extremely "mushy." If I wasn't at 0.9 Mach like I thought, then over six minutes, huge errors are going to appear in my measurement, and the whole test is worthless.

 

That being said, my result was:

Time to 40,000' in Lock On: 7:07 min

Time to 40,000' by Dash-1: 4:30 min

Lock On climb performance underpowered by: 58%

Distance to 40,000' in Lock On: 125 nm

Distance to 40,000' by Dash-1: 38 nm

Lock On climb performance underpowered by: 229%

 

-SK

 

That's another problem with the LOMAC Eagle - avionics, as IguanaKing's said. Nevertheless, as long as we agree on an instrument - the HUD, let's stick with that. Once airborne, hit the "2" key and you'll get a mach readout on the HUD. Follow the climb profile per Dash 1. The MIL thrust performance of the Eagle is indeed weak.

[SwingKid]

Thanks for the response Rhen.

 

The high-altitude, mil-power regime is obviously important to you, and for this case I agree the Dash-1 figures are the way to go.

 

The low-altitude, max-power regime is of more interest to me, because it lets me isolate a few parameters at a time for testing, without worrying about ram drag or other complications. I still believe that unless we get the low-altitude, max-power regime correct, there is no way to "bump up the thrust" at higher altitudes. That is basically a hack - it might make connecting to the tanker easier, but things like that can throw off the whole balance in air combat. And for the low-altitude, max-thrust regime, the Dash-1 lets me down in precision of langugage, by interchanging "1 nm" with "negligible," and other approximations. For low-altitude, max-power, the Streak Eagle records are IMHO a much better reference, and that is what I considered this whole thread to be about.

 

So in essence there seem to be two problems - one above Yo-yo's "sweet spot" of 10,000 feet altitude where everything magically seems to work out in his charts, and another one below. And they seem to affect all SFM aircraft, one way or another. The question is - having identified these problems, how does Yo-yo proceed to a solution? If you feel that the low-alt performance can be tolerated, and the high-alt thrust can just be "bumped up" to compensate even if the error is in drag or something else, then I guess we should just respectfully agree to disagree. Something as complex as a combat sim flight model does not lend itself well to quick-hack, end-of-pipe solutions, IMHO. The unforeseen consequences of such changes always seem enormous afterward - e.g. the "Tunguskas shooting down Mavericks" affair, when they tried to allow Patriots to shoot down ARMs. I want to know exactly what is causing the problem, and attack it at its source.

 

Cheers,

 

-SK

[D-Scythe]

In that sense, I think it's appropriate now to ask D-Scythe what exactly he feels he accomplished by starting this topic at all, and dragging my good name into it. :)

 

 

"Are you not entertained??"

 

Well, my bad for dragging you through the mud, but honestly, once you got in the thick of things, I don't think anyone would believe how much I enjoy reading your posts or Rhen's.

 

And really, I know there are a ton of other guys who feel the same way as well. You and Rhen make a solid case - besides Yo-Yo's "sweetspot" at 3050m, I don't think there is now any doubt that something's not quite right here with the Eagle's engines. I'm actually curious as to how Yo-Yo's going to respond to all of this.

[Yo-Yo]

I've also tried to fly Rhen's test of a climb to 40,000 feet at mil power. I seriously doubt the precision of this kind of test, since it relies on maintaining a speed of Mach 0.9 by watching a Mach meter that is graduated in units of 0.5. The KCAS dial also reads a different value than the HUD, calling into question the claim that one is "maintaining 350 KCAS." The whole test seems to mainly involves holding a pitch of around 6.5 degrees for about 6 minutes, and feels extremely "mushy." If I wasn't at 0.9 Mach like I thought, then over six minutes, huge errors are going to appear in my measurement, and the whole test is worthless.

 

That being said, my result was:

Time to 40,000' in Lock On: 7:07 min

Time to 40,000' by Dash-1: 4:30 min

Lock On climb performance underpowered by: 58%

Distance to 40,000' in Lock On: 125 nm

Distance to 40,000' by Dash-1: 38 nm

Lock On climb performance underpowered by: 229%

 

-SK

 

SK, for the God sake, if you are in doubt what gauge reading is wrong you can use F2 status bar speed to judge. Besides if M-meter at the board is to row you easyly can calculate your IAS vs altitude profile and then follow it. I am in doubt if you played my tracks.

 

Please, your "228%" can get somebody down... perform your tests very carefully so I have not to refute it. Really THERE IS NO evidences that LO F-15 is significantly out of the DAsh 1.

 

As an engineer you can perform your own investigation. The CG motion equation are very simple and you can find them in any aircraft dynamics book.

Draw you own thrust curve regarding the numbers you operate with, set your own CD_O , induced drag coeff, calculate turn rate/sustained G, derive dHe/dt from the accel Dash 1 charts, integrate the plane motion in climb within Dash 1 directions and have a good coincidence with Dash 1 results. As with the turn rate charts...

Besides your thrust curve must at least similar to typic AB and w/o AB curves.

 

And after this great work is finished we'l be glad to know for example max L/D of F-15...

[TucksonSonny]

 

Where are the HFFMS numbers coming from, out of interest? I assume they're the ones from the Falcon flight model . . . . but what source did they use?

 

Andre “Raptor One” Joseph / Mav-jp:

 

Data was calculated from NASA sources and a public domain simulation program that makes use of the same NASA sources.

Anyway the aerodynamic input data (Cl vs AoA and Cl vs Cd) was from the USAF and contained the full range of data from low subsonic to high supersonic.

Anyway I remember Raptor One bragging about (kind of) confidential documents/charts/tables in his possession…:D

[D-Scythe]

Andre “Raptor One” Joseph / Mav-jp:

 

Data was calculated from NASA sources and a public domain simulation program that makes use of the same NASA sources.

 

Anyway I remember Raptor One bragging about (kind of) confidential documents/charts/tables in his possession…:D

 

Well, it doesn't matter anyway. Even if the HFFM numbers are legit, they only apply to the F-16 - the fact that the F-15 uses a completely different, variable geometry intake changes the equation entirely.