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F-15 Performance


Ranchgrom

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Are any of us going to be flying the F-15 anymore? haha

Actually yes.

Me too. I just can't figure out if the current Eagle's popularity is driven by it's greatness or the simple fact that it's the only "easy" American fighter available.

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If I remember correctly, the Harrier does hold the time-to-altitude record for 15,000ft.

The Mirage with old flight model had indeed superior supersonic acceleration compared to the F-15, but that was fixed with the new flight model.

 

It was fixed? Read again some more. It still beats the F-15 between some IAS airspeed ranges and at altitudes above 11000meters, besides that it outclimbs the F-15C in every way.

 

Check these threads latest news and get convinced:

https://forums.eagle.ru/showthread.php?t=197059

https://forums.eagle.ru/showthread.php?t=199528

 

The Mirage is still a WIP.

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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It was fixed? Read again some more. It still beats the F-15 between some IAS airspeed ranges and at altitudes above 11000meters, besides that it outclimbs the F-15C in every way.

 

Check these threads latest news and get convinced:

https://forums.eagle.ru/showthread.php?t=197059

https://forums.eagle.ru/showthread.php?t=199528

 

The Mirage is still a WIP.

 

As I asked you in the Mirage forum... The tracks please. Even your engineer collegues would agree that fancy graphs without supplemental raw Data are not worth the paper they are printed on.

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...

Missiles, fuel + 1 bag puts you at 50000lbs, thrust is 47000. That's before we account for the store drag.

 

...

Wrong technique. To get maximum thrust out of the engines (installed thrust is 80% of rated, typically) you need to get moving. If you want to accelerate straight up you need 500kts before you pull up. You'll accelerate for a short time, as you'll soon reach a density altitude where again you're not ramming enough air into the engines to maintain all this thrust.

 

Just 80% of 23500 (47000 / 2), which makes 18800lbs? Is that what you try to say? That in DCS, the F-15C has 18800lbf at FULL AB on each engine? At 500kts it's capable to have a T/(W+D) higher than 1? If it's KIAS, then I don't know if the engines (although indeed their thrust increases with dynamic pressure or IAS) would be capable anymore to generate a total thrust higher than the weight + drag in order to accelerate on X-axis at higher than 1G, if this is what you say!

 

 

...

The F-15 is fine. It might be the other aircraft that need some adjustment ;) OTOH the Harrier shouldn't have anywhere near the performance of an eagle at medium to high altitude, and neither should the mirage. Down low it's another story.

 

Also, the mirage is light. Very different airframe.

 

The Mirage is light, but it doesn't make any sense to beat the F-15 in horizontal acceleration and climbout (only between some IAS and altitude ranges after latest updates, but still not correct) giving their real T/W ratio. Even by neglecting the drag, the T/W ratio difference is colossal, so it doesn't matter if it's light if by performance isn't that capable. The lift force of the Mirage is also found to be exaggerated. It can't fly in reality as slow as it does now in the sim.

 

Regards!


Edited by Maverick Su-35S

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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Does any of this matter once the F-18 comes out? Are any of us going to be flying the F-15 anymore? haha

 

You think? The best F-18 pilot would get beaten everytime by the best pilot flying the F-15 or Su-27. The F-18 lacks the T/W that the Su-27 and F-15 have. Although in reality it outturns any fighter we have in DCS at instantaneous turn rate, it's engines won't help it win in sustained turn rates and climb.

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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... what about the negative g push-over? :D

 

You think? The best F-18 pilot would get beaten everytime by the best pilot flying the F-15 or Su-27. The F-18 lacks the T/W that the Su-27 and F-15 have.

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Just 80% of 23500 (47000 / 2), which makes 18800lbs? Is that what you try to say? That in DCS, the F-15C has 18800lbf at FULL AB on each engine? At 500kts it's capable to have a T/(W+D) higher than 1? If it's KIAS, then I don't know if the engines (although indeed their thrust increases with dynamic pressure or IAS) would be capable anymore to generate a total thrust higher than the weight + drag in order to accelerate on X-axis at higher than 1G, if this is what you say!

 

Yep, installed thrust is typically around 80% of bench thrust. I don't know how much speed you need to bring in up to rated (and you can probably exceed rated, but I don't actually know) but if you're starting from 'not moving', you're suffering.

As for accelerating at 'higher than 1g', which acceleration chart shows that? I mean I have my own suspicions, but I don't feel like doing the conversions right now.

 

The Mirage is light, but it doesn't make any sense to beat the F-15 in horizontal acceleration and climbout (only between some IAS and altitude ranges after latest updates, but still not correct) giving their real T/W ratio. Even by neglecting the drag, the T/W ratio difference is colossal, so it doesn't matter if it's light if by performance isn't that capable. The lift force of the Mirage is also found to be exaggerated. It can't fly in reality as slow as it does now in the sim.

 

Regards!

 

The M2K has plenty of TWR when not full fueled and only hauling a pair of heaters or nothing. We don't have good documents on it, but the truly suspicious stuff (F-22+ performance) has been fixed.

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The M2K has plenty of TWR when not full fueled and only hauling a pair of heaters or nothing. We don't have good documents on it, but the truly suspicious stuff (F-22+ performance) has been fixed.

 

Well, it does have a higher T/W ratio when lightly loaded, but all other fighters do the same, so the M2k isn't proving anything magical, in real life I mean, not as it does right now in DCS.

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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Yep, installed thrust is typically around 80% of bench thrust...

 

So again, sorry to bother you with this so much, but until you assure me I kind of feel it hard to believe...! You tell me that the engines on the F-15C (in real life as well as in DCS) develop only 18800lbf (which is 0.8 * 23500) at FULL AB at around sea level at zero IAS (static thrust)? Is this the truth? If not please then, tell us what would that value be in these conditions (static FULL AB at sea level)!

 

Thanks!

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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(Good) Estimated thrust charts (not F-15) for the PW-220 put it just under 20,000lbs at 0KIAS SL rising to a peak of ~32,000 lbs thrust at M1.1. SL. The F-15 would have different curves but probably similar in places.

 

Note all jet engines manufacturer thrust figures are normally 0 KIAS uninstalled on a test bench (not associated with an aircaft) - same applies for any SNECMA (whatever) ratings for the the Mirage I expect.

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Sorry, I don't have material to link you to - but yep, that's the deal. As mentioned above, thrust depends on intakes etc. So bench thrust is not installed thrust.

An Airshow eagle loaded with 6000-8000lbs of fuel can do wonderful things at slow speed, but the TWR might not be as high as you believe. Speed up and things change very quickly.

 

Getting back to the Mirage, you're right, it's not 'proving anything', however I'd like to point out that you're more likely to encounter it in 'racecar' condition, than not. It's all about average combat weights.

 

So again, sorry to bother you with this so much, but until you assure me I kind of feel it hard to believe...! You tell me that the engines on the F-15C (in real life as well as in DCS) develop only 18800lbf (which is 0.8 * 23500) at FULL AB at around sea level at zero IAS (static thrust)? Is this the truth? If not please then, tell us what would that value be in these conditions (static FULL AB at sea level)!

 

Thanks!

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I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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Sorry, I don't have material to link you to - but yep, that's the deal. As mentioned above, thrust depends on intakes etc. So bench thrust is not installed thrust.

An Airshow eagle loaded with 6000-8000lbs of fuel can do wonderful things at slow speed, but the TWR might not be as high as you believe. Speed up and things change very quickly.

 

Getting back to the Mirage, you're right, it's not 'proving anything', however I'd like to point out that you're more likely to encounter it in 'racecar' condition, than not. It's all about average combat weights.

 

Thanks all you guys for making this think clear known, that the manufacturers can only tell at what thrust force their engine peaked during bench testing and indeed the demonstrated output on an aircraft depends on the geometries that will eventually affect it's thrust, so that 80% is what the engine generally remains with due to airflow problems and not because someone reduces their thrust to 80% on purpose. These are things that few of the majority here know about so it was important;).

 

Cheers!

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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I suspect you already know that some intakes are better at recovering thrust due to altitude and speed also :)

 

Eg - F-15 has very complex ramps and thus tends to have higher thrust available than say, an F-16 at higher altitudes.

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I think the Mirage 2000 also has variable inlet cones which probably account someway for the top end speed at altitude - there seems to have been some requirement for a high altitude interceptor there.

 

But yes the F-16 design team decided to ditch that inlet type and save weight instead - but still met the M2 requirement.

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I suspect you already know that some intakes are better at recovering thrust due to altitude and speed also :)

 

Eg - F-15 has very complex ramps and thus tends to have higher thrust available than say, an F-16 at higher altitudes.

 

Yes and a reason why the F-16's maximum Mach limit is 2.15, is not because of pressure recovery limitation of the inlet as it is due to a shock reflection down the inlet above that, otherwise it's said that the engine still has enough gathered thrust to push the F-16 beyond 2.2.

 

As someone mentioned about the variable inlet cones on the M2K, yes they work as any other inlet spikes in order to control the normal shock's position down the inlet to give maximum pressure before entering the compressor, but still, I find the M2K's actual acceleration quite exaggerated in DCS atm. Hope RAZBAM will investigate and correct the thrust tables with altitude.

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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Yes and a reason why the F-16's maximum Mach limit is 2.15, is not because of pressure recovery limitation of the inlet as it is due to a shock reflection down the inlet above that, otherwise it's said that the engine still has enough gathered thrust to push the F-16 beyond 2.2.

USAF Block 40/42 circa 2012

Maximum operating airspeed is 800

knots from sea level to 30,000 feet MSL. Above 30,000 feet

MSL, the aircraft is limited to 2.05 mach.

One of the main limiting factors is the canopy.

 

[ATTACH]178008[/ATTACH]


Edited by mvsgas

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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USAF Block 40/42 circa 2012

 

One of the main limiting factors is the canopy.

 

[ATTACH]178008[/ATTACH]

 

Sorry, yeah, it's 2.05, not 2.15 and indeed I forgot the canopy's problem becoming opaque due to temp, yet we were generally discussing the engine's inlet geometry which also affects the Mach limit.

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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NASA has flown their F-15B to M2.69 IIRC.

 

The acceleration graphs in the -1 tend to stop at an acceleration of 0.03g - so obviously you can go faster, it's just low payoff.

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  • 2 weeks later...

I read the entire thread and I am sure this is well explained but I just wanted to explain a few things if you guys don't mind.

 

One thing you should keep in mind is the fact that on the testbench, the engines have a bellmounth inlet installed. Which prevents inlet depression. And improves the airflow to the engine.

 

As for the speed and thrust relation, yes the engine loses thrust because of the difference between the V1 and V2 velocities. V1 is the velocity at which the air enters the engine, and V2 is the exhaust gas velocity. If the values are the same, no thrust can be made. And that's called Ram drag. Ram drag is introduced when the aircraft has forward speed. On take-off this is generally ignored though, so we can use gross thrust in that case. Not the data from the testbench though.

 

Formula for this would be Ms (V2 - V1) / g

 

So let's say an engine has a mass flow of 250 lbs/s and the exhaust gas velocity is 1,800, so using the formula above 250*1,800= 450,000/32.2= 13,975 we can see that the gross thrust is 13,975 lbs of thrust. That would be the engine on the ground, standard day conditions. No forward speed.

 

When you add forward speed (V1) to this equation, the thrust decreases because the difference between V1 and V2 is reduced. And now, it's called Net thrust.

 

So let's say the same aircraft is flying at 450 miles per hour (660 ft/s).

 

Since the aircraft is flying at 660 ft/s, we can add this V1 number to the equation, which is 250 (1,800 - 660) / 32.2. The V2 is subtracted from the V1, so again, the difference between V1 and V2 is greatly reduced.

 

Considering that the mass flow and exhaust gas velocity stay the same (which they won't in this case due to ram/pressure recovery), we can see that the thrust being developed is 8,850 lbs of thrust. A lot less compared to the engine running on the ground.

 

This is a rule for most of the subsonic aircraft, at sonic and supersonic speeds, these aircraft generally have a complex inlet system which makes a great use of the Ram effect, so with forward speed, it's possible that the aircraft will eventually overcome this negative effect, which is the ram drag.

 

For instance, the Viggen engine at Mach 1.1 produces around 164kN, 36,000 lbs of thrust. On the ground it produces 115kN (25,853). So forward speed can either be a good or bad thing for the airframe. It all depends on what the aircraft needs.

 

 

LPDNBts.jpg

 

 

Heatblur recently released an update showing the progress on the F110-GE-400 engines, and one of the graphs shows the engine making 133kN at Mach 0.9. That's probably the highest thrust this engine can make though, from that point, thrust is going to decrease, because of the inlet efficiency. Mach 0.9 is probably the optimum speed for the Tomcat, in terms of thrust at least. Keep in mind that Ram drag wasn't modeled here.

 

With that said, gross thrust and net thrust are completely different. So they can't be compared, you shouldn't say that the Eagle produces the same thrust as the engine on the testbench. Because it doesn't. Unless the aircraft is flying at a specific speed where the Ram recovery is great enough that the engine can recover some of that thrust.

 

Unless you have an inlet system that is capable of diffusing the supersonic air (which increases static pressure), you won't be able to get that thrust back. With no augmentation obviously. :)

 

About the thrust being lost because of the intake ramps and all that stuff, let's use the MiG-21 as an example, the MiG-21 has a moveable spike in the nose, and a 'tube' that extends all the way back to the engine, throughout the fuselage. It's quite long, and not quite efficient, efficiency is lost due to the air viscosity and friction between the air and the walls of the tube. So you could say that these engines on the testbench aren't suffering from that, on the contrary, they have a device called bellmounth inlet which helps the engine as I said above.


Edited by Vitormouraa
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I read the entire thread and I am sure this is well explained but I just wanted to explain a few things if you guys don't mind.

 

One thing you should keep in mind is the fact that on the testbench, the engines have a bellmounth inlet installed. Which prevents inlet depression. And improves the airflow to the engine.

 

As for the speed and thrust relation, yes the engine loses thrust because of the difference between the V1 and V2 velocities. V1 is the velocity at which the air enters the engine, and V2 is the exhaust gas velocity. If the values are the same, no thrust can be made. And that's called Ram drag. Ram drag is introduced when the aircraft has forward speed. On take-off this is generally ignored though, so we can use gross thrust in that case. Not the data from the testbench though.

 

Formula for this would be Ms (V2 - V1) / g

 

So let's say an engine has a mass flow of 250 lbs/s and the exhaust gas velocity is 1,800, so using the formula above 250*1,800= 450,000/32.2= 13,975 we can see that the gross thrust is 13,975 lbs of thrust. That would be the engine on the ground, standard day conditions. No forward speed.

 

When you add forward speed (V1) to this equation, the thrust decreases because the difference between V1 and V2 is reduced. And now, it's called Net thrust.

 

So let's say the same aircraft is flying at 450 miles per hour (660 ft/s).

 

Since the aircraft is flying at 660 ft/s, we can add this V1 number to the equation, which is 250 (1,800 - 660) / 32.2. The V2 is subtracted from the V1, so again, the difference between V1 and V2 is greatly reduced.

 

Considering that the mass flow and exhaust gas velocity stay the same (which they won't in this case due to ram/pressure recovery), we can see that the thrust being developed is 8,850 lbs of thrust. A lot less compared to the engine running on the ground.

 

This is a rule for most of the subsonic aircraft, at sonic and supersonic speeds, these aircraft generally have a complex inlet system which makes a great use of the Ram effect, so with forward speed, it's possible that the aircraft will eventually overcome this negative effect, which is the ram drag.

 

For instance, the Viggen engine at Mach 1.1 produces around 164kN, 36,000 lbs of thrust. On the ground it produces 115kN (25,853). So forward speed can either be a good or bad thing for the airframe. It all depends on what the aircraft needs.

 

 

LPDNBts.jpg

 

 

Heatblur recently released an update showing the progress on the F110-GE-400 engines, and one of the graphs shows the engine making 133kN at Mach 0.9. That's probably the highest thrust this engine can make though, from that point, thrust is going to decrease, because of the inlet efficiency. Mach 0.9 is probably the optimum speed for the Tomcat, in terms of thrust at least. Keep in mind that Ram drag wasn't modeled here.

 

With that said, gross thrust and net thrust are completely different. So they can't be compared, you shouldn't say that the Eagle produces the same thrust as the engine on the testbench. Because it doesn't. Unless the aircraft is flying at a specific speed where the Ram recovery is great enough that the engine can recover some of that thrust.

 

Unless you have an inlet system that is capable of diffusing the supersonic air (which increases static pressure), you won't be able to get that thrust back. With no augmentation obviously. :)

 

About the thrust being lost because of the intake ramps and all that stuff, let's use the MiG-21 as an example, the MiG-21 has a moveable spike in the nose, and a 'tube' that extends all the way back to the engine, throughout the fuselage. It's quite long,and not quite efficient, efficiency is lost due to the air viscosity and friction between the air and the walls of the tube. So you could say that these engines on the testbench aren't suffering from that, on the contrary, they have a device called bellmounth inlet which helps the engine as I said above.

 

Thanks for the informative post. Forward speed seems to be a good thing for net thrust on the F-15

Source:

ilmd95W.jpg

 

“The faster you go, the faster you go faster” :thumbup:

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USAF Block 40/42 circa 2012

 

One of the main limiting factors is the canopy.

 

[ATTACH]178008[/ATTACH]

 

MV what is that article from? Code One magazine?

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MV what is that article from? Code One magazine?

 

Code one magazine, SemperViper series of articles

To whom it may concern,

I am an idiot, unfortunately for the world, I have a internet connection and a fondness for beer....apologies for that.

Thank you for you patience.

 

 

Many people don't want the truth, they want constant reassurance that whatever misconception/fallacies they believe in are true..

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Thanks for the informative post. Forward speed seems to be a good thing for net thrust on the F-15

 

Source:

 

ilmd95W.jpg

 

 

 

“The faster you go, the faster you go faster” :thumbup:

 

 

 

Yup, that's really awesome. I was looking for a chart like that for the Eagle. Thanks for sharing!

 

You should see the Blackbird, the pressure in psi at 85,000 ft is around 0.3 and the inlet system can rise that all the way up to 14, 16 psi! With forward speed and ram recovery.

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