PSA: F-14 Performance/FM Development Status + Guided Discussion

[eatthis]

5 hours ago, Baz000 said:

Got 2 words, motive flow

Precisely, the aircraft that is heavier is at a disadvantage because it needs to do more "work" but under the parameters of that theoretical question it can't change any parameters to do more "work"

the question statres 2 effectively identical ac doing th esame thing. 1 has less power than the other, so surely the 1 with less power loses

[draconus]

4 minutes ago, eatthis said:

1 has less power than the other, so surely the 1 with less power loses

but one weighs less

[Victory205]

What are the instantaneous total energy states of the two aircraft?

If you did the maneuver at zero thrust, does that change anything?

[Victory205]

The F14B configured as described, picks up a ~1500 fpm descent rate when rolled into a 30 AOB. After about a 400 foot descent, it slowly levels and pitches back up, demonstrating positive dynamic stability. Are you familiar with phugoid oscillations?

You were doing so well, writing at a far higher level than most, and the you just had to misspell “lose”. I was devastated.

I wouldn’t waste time flying too much with the SB in and DLC disengaged. I’d get familiar with power response and power settings in the landing config. I would be quick to say that they are about to change for the better, so get familiar, just don’t write the numbers in stone.

My top end velocities in the F14B-

F14B max mach at Max AB with 4x4 and 55K on fuel vs H-M Diagram Pg XI-9-3 Fig 9-2 Cross referenced to Maneuvering Diagram at corresponding altitudes-

Alt - Actual/Target

SL - 1.10/1.07
5K - 1.227/1.22
15K - 1.449/1.44
25K - 1.705/1.72
35k - 2.045/1.95

Mil power

15K - .985
35K - .974

All level accelerations as per the chart methodology with unlimited fuel. Understand, the width of the Ps=0 lines is approximately .01 to .02 Mach

Edited November 4, 2021 by Victory205
Typo at 35K

[cheezit]

2 hours ago, Victory205 said:

My top end velocities in the F14B-

F14B max mach at Max AB with 4x4 and 55K on fuel vs H-M Diagram Pg XI-9-3 Fig 9-2 Cross referenced to Maneuvering Diagram at corresponding altitudes-

Alt - Actual/Target

SL - 1.10/1.07
5K - 1.227/1.22
15K - 1.449/1.44
25K - 1.705/1.72
35k - 2.045/1.90

Mil power

15K - .985
35K - .974

All level accelerations as per the chart methodology with unlimited fuel. Understand, the width of the Ps=0 lines is approximately .01 to .02 Mach

I wonder if part of the discrepancy between your target numbers and Hummingbird's is the version of the charts you're looking at.  My assumptions are that you've got the final version of the charts while Hummingbird is looking at the (now cleared for open publication? certainly floating around the internet ) version from 15 September 1990, although of course I lack a palantir and cannot tell with certainty what anybody else is looking at.

 

That September 1990 version, unless I am reading it wrong, shows the same numbers that you listed for 4x4 and GW of 55,620 lb with max A/B per figure 9-2 (Sheet 1 of 12) on page XI-9-3 (note the chart is dated September 1987 despite the first page after the cover being dated September 15th 1990) at SL, 5k, 15k and 25k, but at 35k feet the chart shows Mach 1.97 which is the same number that Hummingbird got.

 

Nb. I get the same numbers as seen on Figure 9-2 when I cross-reference with Figure 9-5 (5k chart on page XI-9-29, 15k on XI-9-30, 35k on XI-9-31) by tracing a horizontal line at 1g on the Y-axis to its rightmost intersection with the Ps=0 line, and then from that point tracing a vertical line down to the TMN on the X-axis.  Not sure if this is the right way to try to cross-reference, and of course Figure 9-5 doesn't have any data for SL or 25k feet.

 

Another couple of curiosities I see in the September 1990 charts: the 2x2x2 loadout seems to give up basically nothing on the top end compared to 4x4, with a top end speed of maybe Mach 1.94 or 1.95 instead of 1.97 despite being 1500 pounds heavier (cf. XI-9-34), and even slapping on tanks with a bunch of drag and a further gross weight increase of ~2800 lbs still gets you a pretty respectable top end of 1.80 or so - that's actually a fair bit faster than some newer fighters can go when clean, if I'm not mistaken.  Also there is a dotted "structural limit" line  and a solid "projected structural limit" line at what looks like a +1g offset from the "structural limit" line, for some reason that I am ignorant of.

 

I wonder whether any of this survived to later versions of the charts based on what I assume is more and better testing.

 

In any case, thanks for putting in the time and effort dusting off the old charts to ensure that ill-informed and obnoxious pedants such as myself enthusiasts and consumer simmers get a super high-fidelity version of the Tomcat in all its glory.

Edited November 4, 2021 by cheezit

[Victory205]

I don’t know what Hummingbird or others are doing, what they are looking at, why some seem obsessed with testing at SL where there are no references, there is ground effect modeled who knows how by DCS, nor have I seen any method to validate performance “interpolation” whatsoever.

It’s quite easy to just replicate the conditions portrayed on the H-M and Maneuver charts, and then fly those profiles. If someone is going to make up the targets, then proof of methodology to include supporting documents of both references and results are required. Otherwise, it simply an irrelevant opinion. 

Until valid answers are provide in a demonstrative paper, I’d simply ignore it. Especially since the outcomes are frequently not in line with what you can see by doing it yourself.

[Baz000]

4 hours ago, Victory205 said:

What are the instantaneous total energy states of the two aircraft?

If you did the maneuver at zero thrust, does that change anything?

The way I understand it is that the one 20% heavier needs to fly with more power(thrust) added to maintain stable formation with the other, so technically speaking the one that is heavier is actually flying at a higher thrust output than the other. The difference is the relative positioning and closure between the two cancel out because of the added power compensating for the added weight.

So, right from the beginning the two aircraft are not equal in performance... What is happening however is the forces are balancing relative between the two so they are able to maintain stable formation... But, with that said one aircraft compared to the other is already starting off at a greater power setting if you look at it comparing the two in just engine performance right off the gate.

With that said however, at the start of the maneuver even if they both had zero thrust so they start at a truly equal state in engine performance alone... The overall result still doesn't change, one aircraft vs the other has to fight more to climb and it is due to the additional magnitude of the downward vector from the 20% increase in additional gross weight, this same effect also causes the climb to be at a slower rate in comparison to the lighter aircraft, given the parameters set in the theoretical example.

In regards to phugoid oscillations- its oscillations in the longitudinal axis (tho it can happen laterally as well) which can be both short and long term, it depends on aircraft design how "stable" the aircraft oscillates but this is where the aircraft passes the point of trimmed equilibrium in how I can best describe as a porpoising motion where the aircraft will climb and descend... Usually with a constant AOA but with changes in airspeed and altitude. Am I understanding the aerodynamics correctly? Also, when experiencing such it is possible to have the pilot enter into PIO by unintentionally overcontrolling the aircraft... In this case, freezing control input to the aircraft and allowing it to stabilize generally will allow such oscillations to diminish and return the aircraft to a state of equilibrium.

I hope i'm understanding that correct.  

Edited November 4, 2021 by Baz000

[Hummingbird]

My targets are, as always, pulled directly off the available documentation.

 

5 hours ago, Victory205 said:

F14B max mach at Max AB with 4x4 and 55K on fuel vs H-M Diagram Pg XI-9-3 Fig 9-2 Cross referenced to Maneuvering Diagram at corresponding altitudes-

 

Sorry but I'm using the same reference, and I am not seeing the same number for 35 kft.

It's M 1.97 @ 35 kft according to Pg XI-9-3, not 1.90.

Same on all the other charts for that configuration, and corroborated by Pg.XI-9-61 with M 1.95 @ 1.1 G  

 

Just to prove I'm not talking smack (Screens from XI-9-3 & XI-9-61):

Spoiler

 

Finally there are references that show performance for SL & up within four load factors, they are on Pg.XI-9-4 for 3 G, Pg. XI-9-5 for 5 G and finally Pg. XI-9-6 for 6.5 G. (XI-9-3 from above is for 1 G, i.e. level flight)

That's where these targets come from:

M 0.34 (225 KTAS) = 3.0 G Pg. XI-9-4   vs   3.2 G DCS (+0.2 G overperformance)

M 0.46 (304 KTAS) = 5.0 G Pg. XI-9-5   vs   4.8 G DCS (-0.2 G underperformance)

M 0.62 (410 KTAS) = 6.5 G  Pg. XI-9-5   vs   6.5 G DCS (spot on)

 

Finally I did find a reference for level speed clean, with only stub pylons left (the SAC docs), which lists top speed clean 50% fuel (as I ran it) as 1196 kts @ 35,000 ft. Which is M 2.073. So a M 0.1 improvement vs the 4x4 load out:

Edited November 4, 2021 by Hummingbird

[Victory205]

I changed the typo at 35K, the aircraft overperforms at Vmax all but one altitude.

Thanks Cheezit!

 

Edited November 4, 2021 by Victory205

[eatthis]

7 hours ago, draconus said:

but one weighs less

i misremembered the question. same power different weight. the same applies though doesnt it??
a vulcan bomber has 80k lb of thrust at full chat but has way less than 1:1 p/w an f16 has less than half that power but id bet it would climb vertically MUCH better than the bomber, same physics apply dont they?

[Victory205]

Think in terms of total energy. Don’t get bogged down in thrust to weight. We’re not adding power in the zoom.

Simple concept, too many are rushing down rabbit holes.

[Baz000]

same physics apply, yes but the aircraft are getting lift in 2 primary ways, one is from the shear brute force of the engines and the other is the lift from the wings and other lift producing surfaces (like pancake on F-14)

my guess in your bomber v F-16 the bomber could get to a much higher max altitude than the F-16 but the F-16 will climb much faster but stop at a lower altitude.

My reasoning is, a Vulcan bomber has huge wings compared to an F-16 but alot of weight which will reduce its acceleration performance in a climb. Mind you this is not taking into account engine limitations or pilots needing pressure suits.

Also, F-16 pilots don't like to cruse above 30k because the wings have such reduced lift to them if they are loaded up with junk on the wing pylons that they have to travel faster to make up for the loss of lift, they prefer to be around 25k-20k.

for the cute bunny to come out of the rabbit hole

also, have you guys heard of the "coffin's corner" when it comes to flying? It is more of a problem in airliners than fighters.

Edited November 4, 2021 by Baz000

[Victory205]

How in the world do you go from energy state comparison to Vulcan Bombers? Are you British?

First things first, how do you spell the word “lose”? Two “o’s” or one?

You must work on a Rabbit Farm!

Edited November 4, 2021 by Victory205

[draconus]

37 minutes ago, eatthis said:

i misremembered the question

Then go read it again:

 

[Baz000]

30 minutes ago, Victory205 said:

How in the world do you go from energy state comparison to Vulcan Bombers? Are you British?

First things first, how do you spell the word “lose”? Two “o’s” or one?

You must work on a Rabbit Farm!

 

 

58 minutes ago, eatthis said:

i misremembered the question. same power different weight. the same applies though doesnt it??
a vulcan bomber has 80k lb of thrust at full chat but has way less than 1:1 p/w an f16 has less than half that power but id bet it would climb vertically MUCH better than the bomber, same physics apply dont they?

well, he was talking about a Vulcan bomber vs. a F-16 in a climb... I thought i'd provide some answer to him i'm guessing he must be a Brit if he randomly throws out the Vulcan bomber out there

vs. this

oh, he said "full chat" that was a dead give away to me that he must also be a Brit too.

Edited November 4, 2021 by Baz000

[draconus]

11 hours ago, Baz000 said:

Wanna know what rate of decent to use to loose that 200 ft downwind after your level overhead break?

Seems it was you...

[Baz000]

Ah, thats that stupid Kindle for yah... It has a mind like HAL thanks for pointing it out tho really didn't realize it. It always wants to write fpm as rpm too!

Yeah, my apologies about that normally I spell it as "lose" with one O meaning to not be a victor in a battle as an example.

"loose" spelled with two Os meaning to have something not tight.

Edited November 4, 2021 by Baz000

[Victory205]

You can’t see what you write? I’d throw that Kindle away if it won’t let you see mistakes and allow you to change them before you hit send. Get your money back.

Come back down to earth, consider the problem. Note that I didn’t specify aircraft type at all. Think only about the problem. That’s the point.

[Baz000]

On 10/28/2021 at 11:34 AM, Victory205 said:

Which aircraft climbs quicker and attains the greater height?

I'm sticking with my original answer of the lighter aircraft... Final answer, I'm very confident about it.

[Victory205]

Even if it’s a Vulcan Bomber?

Very confident you say?

[Baz000]

On 10/28/2021 at 11:34 AM, Victory205 said:

Two identical aircraft are flying in formation

So aren't they identical airframes and loadout configurations? 

the only difference is 20% increase in gross weight, yeah?

yeah even if its 2 Vulcans haha

Edited November 4, 2021 by Baz000

[Hummingbird]

Different set of figures for sea level @ M 0.46 (304 KTAS) target speed using the script kindly provided by Cpt.Dalan:

 

F-14B, 55,620 lbs, 4xAIM9 + 4xAIM7, Std. day 15 C, unlimited fuel:

SCRIPTING: TR: Counter, Alt(m), GS(km/h), GS(Mach), Turn Rate(deg/s)

2021-11-04 22:54:09.060 INFO    SCRIPTING: TR: 3 /  23 / 562 / 0.460 / 16.9 = 4.80 G  
2021-11-04 22:54:14.264 INFO    SCRIPTING: TR: 4  / 28 / 560 / 0.457 / 16.9 = 4.78 G
2021-11-04 22:54:42.550 INFO    SCRIPTING: TR: 5  / 36 / 563 / 0.460 / 16.8 = 4.78 G
2021-11-04 22:54:47.752 INFO    SCRIPTING: TR: 6  / 44 / 563 / 0.460 / 16.6 = 4.72 G
2021-11-04 22:54:52.958 INFO    SCRIPTING: TR: 7  / 40 / 565 / 0.462 / 16.8 = 4.79 G

 

Backs up my previous figures.

 

Note: Attempt nr.6 was actually my best turn, which I held very steady for a long time with no alt gain/loss, and it read 4.7 G.

 

FYI; According to Pg. XI-9-5 (5 G Ps diagram) in the performance manual, the F-14B should be hitting 5 G @ M 0.46.

Spoiler

 

So if the test figures are accurate (again HB will know) we're missing between 0.2-0.3 G here, which is upwards of 1.5 DPS.  

Hence that's the improvement in performance we can expect once the FM is done (although note performance at M 0.34 is +0.2 G according to my earlier tests, so here you should expect less perf, albeit that's rather non-consequential considering you don't fight at that speed)

 

Edited November 5, 2021 by Hummingbird

[captain_dalan]

8 hours ago, Victory205 said:

The F14B configured as described, picks up a ~1500 fpm descent rate when rolled into a 30 AOB. After about a 400 foot descent, it slowly levels and pitches back up, demonstrating positive dynamic stability. Are you familiar with phugoid oscillations?

You were doing so well, writing at a far higher level than most, and the you just had to misspell “lose”. I was devastated.

I wouldn’t waste time flying too much with the SB in and DLC disengaged. I’d get familiar with power response and power settings in the landing config. I would be quick to say that they are about to change for the better, so get familiar, just don’t write the numbers in stone.

My top end velocities in the F14B-

F14B max mach at Max AB with 4x4 and 55K on fuel vs H-M Diagram Pg XI-9-3 Fig 9-2 Cross referenced to Maneuvering Diagram at corresponding altitudes-

Alt - Actual/Target

SL - 1.10/1.07
5K - 1.227/1.22
15K - 1.449/1.44
25K - 1.705/1.72
35k - 2.045/1.95

Mil power

15K - .985
35K - .974

All level accelerations as per the chart methodology with unlimited fuel. Understand, the width of the Ps=0 lines is approximately .01 to .02 Mach

 

Very close to my own tests so far, at least for the two altitudes i have tested. 

[Victory205]

Those are simple Vmax values, not the times associated with them. Level accels, windup turns, sawtooth climbs, pull up push over, even split S’ are used to obtain data that is then reduced mathematically construct the various Energy charts.

While it may be fun to compare, it should be obvious that the information is mathematically derived (there is no “unlimited fuel/constant weight” setting), due to cost, time and sometimes the danger involved, and a 3% accuracy result is considered outstanding.

[Hummingbird]

Well I mean that goes for any aircraft, so I think we should strive to match the charts precisely, as it's by far the most accurate source we have and it's what is done for the other modules; Also esp. since it can be done, as we see at M 0.62 where we're spot on at 6.5 G.

If we don't conform to some sort of std., the aircraft won't compare accuraretly with each other in the sim. 

E.g.: One aircraft that pulls 1 dps too little matched with one that pulls 1 dps too much according to RL available data, and suddenly you have a 2 dps difference (very noticable in a two circle turn fight) that simply aint there IRL.