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

[GGTharos]

Funny guy ;) .... 199 posts to go ;)

 

Actually my data shows the same thing anyway.

 

Rhen - the times and distances you cite from the "Dash-1" don't match my own, since they were measured from brake release. Didn't you suggest the Dash-1 data is only valid from the moment of reaching 350 kcas, starting the climb? Would it be difficult for you to revise your table, subtracting out the take-off run data? I think that it will still show, what you want it to show - it will just save us another 200 GGTharos posts if we all do what he says. :rolleyes: ;)

[GGTharos]

Never mind, I'm blind! :D

 

Yo-Yo, may you please also investigate Su-27? Similar problem as the F-15. MiG-29 might be a -little- overpowered, but I don't really know.

 

Also, I will try to remember to do a test with stores on tonight - I think the stores are too draggy - nevermind, I know they are ... as there is no way to reach Mach2 in level flight with stores onboard, IIRC. I will try to present findings ASAP.

 

I understand if you wish to deal with one thing at a time though.

[S77th-GOYA]

I performed the test at MIL to 40000 (39000 lb airplane)

 

Why 39,000lbs?

[britgliderpilot]

And finally.... I must say that Rhen is right - after I perform the detailed investigation I've found F-15 at MIL is slightly overpowered at low alt and slightly underpowered at 40000 and higher.

So I promise to fix these items.

 

. . . . has everyone else missed this so far?

 

 

Looks like we're getting a tuned-up F-15 :)

[Pilotasso]

we hope to see the same for Su-27/33.

[Kula66]

. . . . has everyone else missed this so far?

 

 

Looks like we're getting a tuned-up F-15 :)

 

The keyword is 'Slightly'!

[Rhen]

Yo-Yo,

 

Thanks for being opened-minded about changing "your baby" of all these years to reflect reality. You're willingness to change your opinion speaks volumes about ED and where you're heading. Thanks!

 

@ Kula:

 

Just to visually point out what "slightly" looks like Here's a graph. I just got around to plotting the data vs the Dash1:

 

 

This is a chart of Distance (in NM) vs Altitude (Ft) comparing the Dash1 data (expected performance) vs LOMAC's F-15 at MIL power and 40,000Lbs, clean aircraft.

 

The lines should mirror each other if the simulation meets expected Dash1 performance. It's a better way to show where the discrepancies lie.

 

As you can see, performance begins to diverge at 10,000ft (+/-1500ft) and the LOMAC aircraft becomes quite underpowered.

 

The other area of concern is below 5000ft. This area appears underpowered as well, which mirrors my qualitative analysis that in the pattern, the aircraft doesn't perform as it should either.

[Trident]

And finally.... I must say that Rhen is right - after I perform the detailed investigation I've found F-15 at MIL is slightly overpowered at low alt and slightly underpowered at 40000 and higher.

So I promise to fix these items.

 

Thank you, I'm sure the community greatly appreciates this decision!

[S77th-GOYA]

The keyword is 'Slightly'!

 

More importantly, the undermodeling of power for any altitudes under 40,000ft has not been admitted.

[Kula66]

This is a chart of Distance (in NM) vs Altitude (Ft) comparing the Dash1 data (expected performance) vs LOMAC's F-15 at MIL power and 40,000Lbs, clean aircraft.

 

Very interesting stuff Rhen - well done Sir!

 

Wow ... so, a 15 should get to 40k' in about 60% of the distance when flying the -1 profile.

 

It'll be interesting to see how this 'slight' change pans out when flying at 40k' in terms of available power ... where I tend to play despite the problems with TWS.

 

Yo-Yo ... Given your work on this I hope ED go far!

[GGTharos]

And this thing won't even let me hand out rep to all the people who did hard work, and to Yo-Yo for working with us!

[TucksonSonny]

How about modeling the F-15A Streak Eagle in Black Shark?

Why not? The F-16 and the Mig29 have already both A and B model!

 

Give me a Streak Eagle with a couple of 229-engines in RL and I would go vertical against an F-22 and beat it…

........ 30 pages without the f-22 word (no way) :D

 

 

Anyhow Su-30MKK/Mig29k/F-18E/F is also Ok for me… (Even as a no flyable):P

[ViperEagle]

An F-15A with Dash 229's was actually already done. By some accounts, it actually had to throttle BACK because the windscreen started to melt (Mach 2.6+)

[rogue_blade]

sweet so is there a conclusion i previously asked about! i cant read this much

[D-Scythe]

An F-15A with Dash 229's was actually already done. By some accounts, it actually had to throttle BACK because the windscreen started to melt (Mach 2.6+)

 

Apparently it was pushing Mach 2.8 when the canopy started to melt.

 

And this thing won't even let me hand out rep to all the people who did hard work, and to Yo-Yo for working with us!

 

Yeah, I can't rep them enough either.

[SwingKid]

Rhen,

 

How is your Dash-1 giving you 376.8 seconds (> 6 minutes) to 40,000 feet? Do we have contradicting Dash-1s? Unless I'm reading it wrong, my own says 296 s (less than 5 minutes):

 

 

i.e. your Dash-1 says it takes 124 seconds to go from 30,000 to 40,000 - -mine says only 52 seconds, less than half? This may be important to resolve before Yo-Yo starts making changes. I notice that you also seem to have data for 2,500 feet and 7,500 feet also. Different version?

 

:dunno:

 

-SK

[Rhen]

SwingKid,

 

You've GOTTA read the notes man! :book:

 

NOTES:

1. Time is from brake release to indicated altitude, Distance is from brake release, Fuel is from 350KCAS.

2. Fuel under Dash-1 is fuel from 350KCAS, fuel depicted below that includes, run-up, takeoff, and climb to 350KCAS, thus the apparent discrepancy.

3. If the Dash 1 number falls between the numbers, then there's no statistically significant difference between LOMAC and the Dash-1. If it doesn't... well then, obviously there's only a 1 in 20 chance that LOMAC is correct.

 

I've got a physical product, so it's pretty easy for me to use a ruler to follow the lines with appropriate spacing to interpolate data for 5k and 7.5k. You must also take SOME amount of drag into account. I used a default 10 Drag index for the pylons still hanging off the aircraft. Just removing the turkey feathers makes the starting drag index 3.7, then add the pylons LAU-114s, etc. and you'll get somewhere around 8, so 10 should suffice.

 

I double checked the values I got from the Dash-1, but feel free to recheck things. A second set of eyes is always a good thing.

[SwingKid]

SK, first of all - ground effect was modelled in LO even in SFM.

 

"Где доказательство?" ;)

 

It would have been good to say that so clearly, two years ago:

 

http://forum.lockon.ru/showthread.php?t=7066&page=3&highlight=%FD%EA%F0%E0%ED%ED%FB%E9+%FD%F4%F4%E5%EA%F2

 

...because then, we could discuss it.

The Russian testers in that topic found no detectable evidence of a ground effect in Flaming Cliffs AFM, and neither did I when I made my own tests.

 

I defer to Rhen's opinion on this one though - is the ground effect properly modeled for F-15 landings?

 

It increases CL and L/D by decreasing induced drag.

 

These are two different things - can you clarify?

Decreasing induced drag will increase L/D, that I understand - but I don't understand how decreasing D would increase CL.

 

In my experience, both as pilot and observer, the fighter plane will often "bounce" from the ground effect as it tries to land, because it's so strong - and the pilot reduces the engines to idle power in order to land gently through it while decelerating. This is very different from what I'm accustomed to in Lock On.

 

-SK

[Rhen]

I defer to Rhen's opinion on this one though - is the ground effect properly modeled for F-15 landings?

 

I don't really notice that there is ground effect in LOMAC... :huh: Came as a surprise to me as well. The aircraft should balloon during the flare if there's any excess airspeed crossing the threshold.

 

These are two different things - can you clarify?

Decreasing induced drag will increase L/D, that I understand - but I don't understand how decreasing D would increase CL.

 

-SK

 

Ground effect shifts the top of the curve up and to the left, thus increasing the lift coefficient and decreasing the angle of attack - which decreases induced drag.... IIRC my aero.:smilewink:

[S77th-GOYA]

Yo-Yo, your track in post 275 doesn't appear to play back correctly in 1.12a. It spirals to the left and never even reaches 30,000ft.

[SwingKid]

I double checked the values I got from the Dash-1, but feel free to recheck things. A second set of eyes is always a good thing.

 

Yes, I made another math error; good to check twice. In fact, our figures seem to agree well.

 

Not enough sleep. :doh: Thanks for patience.

 

-SK

[SwingKid]

If you fly the appropriate profile, it takes about 28.8 - 31.4 sec to accelerate to 350KCAS in a MAX takeoff, and 58.5-59.3 sec in MIL, so the difference is negligible. However, I have no problems with that if you want to execute the timing from that point.

 

Rhen - where are these numbers coming from? Is this what you measured in Lock On?

 

In Lock On, my 40,000 lb F-15C takes only 37 seconds to reach 350 kts under mil power. By my estimate, the real jet should take only 30 seconds. This seems to be giving us disagreement in our other numbers, when measuring from brake release.

 

Yo-Yo, how much time did it take for you to reach 350 kts in your track, from brake release?

 

-SK

[Yo-Yo]

Yo-Yo, your track in post 275 doesn't appear to play back correctly in 1.12a. It spirals to the left and never even reaches 30,000ft.

 

Sorry... it was recorded in 1.1 but was tested in 1.12 I have. Ok, I'll try to record it in 1.12.

[Yo-Yo]

Ground effect shifts the top of the curve up and to the left, thus increasing the lift coefficient and decreasing the angle of attack - which decreases induced drag.... IIRC my aero.:smilewink:

 

 

The origin is INDUCED DRAG decreasing though.... induced airflow gets slower and your geometrical AoA must be reduced to maintain the actual flow AoA... but for practice it does not matter - L/D and CL rizes.

[Yo-Yo]

Rhen - where are these numbers coming from? Is this what you measured in Lock On?

 

In Lock On, my 40,000 lb F-15C takes only 37 seconds to reach 350 kts under mil power. By my estimate, the real jet should take only 30 seconds. This seems to be giving us disagreement in our other numbers, when measuring from brake release.

 

Yo-Yo, how much time did it take for you to reach 350 kts in your track, from brake release?

 

-SK

 

41 s.

 

To check your estimation and LO model you can check takeoff distances with -1. But please first read the notes and pre-charts directions... :)