F-15 to ED

[JACN]

Hi,

 

When I´ve started flying the "eagle" (previously only used Su-25/T) first I thought: what a beast! Plenty of power excess, Mach 2.4+, 8 AA weapons...radar...well, a whole different world compared with the "frogs". I really enjoy flying it.

 

But, aside of all things mentioned in this forum regarding to eagle avionics simplification and lack of AFM...blablabla...I´d like to mention/question one thing about its FM I´ve found and think has been said before in this forum:

 

- The eagle seems to match quite accurately (at least for me) its real Flight Envelope, well, but taken into account that FE´s right-hand limits are given (in LO) by engine thrust limitations (max. reheat) we could consider that the modelized thrust(max. reheat)-drag relation is well done throught the whole envelope.

But, once the engines are set in any other position below "max. dry" problems appear.

I´ve found the LO´s F-15 unable to maintain horizontal straight flight level at 35k ft. at nearly below "Max. dry" thrust in a 3 fuel drops(half cap.)+6 AMRAAM+2 Sidewinders stores config.

I hardly believe the real eagle C behaving this way when E version, aside of fuel tanks, is able to carry a REAL heavy AG store config (+some AA).

In spite of trying a lighter config in terms of weight and drag, I´d say IMHO (always) either the actual LO F-15 thrust curve is not accurate under reheat or drag (stores drag?) overmodelled...perhaps both.

 

Please, ED, take a look in your next patch. I don´t think fixing it implies a AFM for the eagle (may I be wrong...?)

 

Thanks,

[MBot]

Don't know if it is of any use, but I have read that Strike Eagles have to engage afterburners with bombs loaded to keep up with a tanker at 35k ft.

[britgliderpilot]

I´ve found the LO´s F-15 unable to maintain horizontal straight flight level at 35k ft. at nearly below "Max. dry" thrust in a 3 fuel drops(half cap.)+6 AMRAAM+2 Sidewinders stores config.

I hardly believe the real eagle C behaving this way when E version, aside of fuel tanks, is able to carry a REAL heavy AG store config (+some AA).

In spite of trying a lighter config in terms of weight and drag, I´d say IMHO (always) either the actual LO F-15 thrust curve is not accurate under reheat or drag (stores drag?) overmodelled...perhaps both.

 

I need to check, but I think the real Eagle suffers the same sort of thing.

 

I've seen the same Strike Eagle quote as MBot, and think I've seen something similar for the F-15C. Will see.

[britgliderpilot]

Quoted from PapaDoc's Real Life page

 

Doubting Thomas appears to be a forum poster, replier is a Strike Eagle jockey.

 

>First off, do you really really think that a real life 737 can actually

>outclimb a real life F15E? You must, or you wouldn't have "thought about

>bringing up..." that bit about wing designs. You know how long it takes me

>to get a 737 up to FL330 with a full load? About 25 minutes if I'm lucky,

>closer to 30 is more likely, and I have seen 35. Don't you think that you can

>get an E model up there in less time? Surely you can do better than 1000 fpm

>all the way up.... And before you interject that fully loaded you can only go to

>this altitude or that, then let's make it 10000' or something else. The fact is

>no 737 is going to outclimb you.

 

I do not have any data on a 737. I do know for a fact that even a fairly

heavily loaded KC-135 will kick our asses unless we are in max AB and do our

best climb profile. Even then, the KC-135 will have a better climb angle so

we couldn't "hang with it". In mil power even when not too heavily loaded,

from 20,000 ft on up, our climb angle is only around 5 degrees nose high.

At 30,000 ft with 2 empty external fuel tanks and 2 500 lb bombs, mil power

is barely enough to stay in level flight. Turns greater than 20 degrees of

bank require AB. Again, with -229 engines, this whole picture changes for

the better, but with -220 engines, it's the sad reality.

 

>And that's the whole point of the original poster, and who I agreed with:

>the Jane's realistic flight model has so much drag on the it that it would

>allow a 737 to outclimb it. YOU then swallowed something and actually believed

>that since some yahoo says it's so, then it must be. A lot of people in this

>group take your word on a lot of things, especially dealing with Jane's game.

>In fact, it made me laugh when several people automatically believed you when

>you insinuated that it was wing design that allowed an airliner to outclimb a

>fighter/bomber, and the airline pilot who said the real world thrust to

>weight ratios would not let this happen was ignorant of aerodynamics. First of

>all, airline jets cannot outclimb military fighters! Or military ground attack

>fighters. Hell even a slug A7 would outclimb an airliner.

 

Bullshit. A loaded F-15E is the worlds shittiest, draggiest, pig in space

known to mankind. At least with the -220 motors it is. Empty out all but

10k fuel and jettison everything that causes drag, and yea we can climb

pretty good... Using AB. You raise the bullshit flag about wing

efficiencies and drag, and I say you do not know what you are talking about.

For example, at 25,000 ft and 330 cal, an F-15E with 2 full external fuel

tanks and ZERO other stores takes 10,000 lbs/hr fuel flow just to keep from

falling out of the sky. The tanker which weighs 10 times as much and as you

say, has 10 times the frontal area, is burning about 8,000 lbs/hr (if I

remember correctly, haven't ridden a tanker in months). The tanker can gain

efficiency by slowing down another 50-100 knots, but at 330 knots fully

fueled we're actually 20-30 knots below our max range cruise AOA so slowing

down actually increases fuel burn. To stay on the refuelling boom at 27,000

ft once the wing tanks start filling up even with only 2 (count them, 2) 500

lb bombs on the plane required the use of up to stage 2 AB on one motor

while the other one is used just under mil power for small position

corrections. That burns well over 10,000 lbs/hr fuel flow while the tanker

is actually using LESS. That is called efficiency. The L/D curves for an

airliner wing are optimized for climb rates and cruise efficiency, while our

wing is optimized mainly for transsonic and supersonic drag.

Here's a little tidbit: Above about 1.3 mach, our maximum acceleration AOA

causes the plane to pull about 2.5 G's. That's right, the F-15 wing is

shaped so weirdly that our best acceleration is achieved while pulling G's

once we get going that fast. No shit.

Now tell me that an airliner's wing isn't better optimized for climb. While

you think about that, think about the last airliner you saw take off. Those

buggers have an initial climb angle of nearly 30 degrees...? Robey can fill

in what an airbus climbs like at takeoff power. A loaded F-15E in max AB

can't handle 25 degrees very long if it has -220 motors. One more tidbit,

our max range airspeeds are probably 100 to 150 knots higher than those of

airliners weighing 10 to 20 times our gross weight. That alone speaks

volumes about how the wings are optimized.

 

>Do you honestly think that if Iraq armed some 737s you would be outclimbed

>by them? That despite those incredibly powerful motors behind you that the

>granny riding in 1st class will reach altitude before you?

 

Yes. Actually, I think one of the best climbing aircraft in the world today

is the U2... One recently set an altitude record, although they've been

operationally flying that high for decades. That sucker sure isn't a

fighter, but it can outclimb us. It's design philosophy is much closer to

that of an airliner than it is to a fighter, and it's wing is optimized for

min fuel burn climb to altitude plus max cruise altitude with min fuel burn.

 

>I can have the best damn wing in the world but if I don't have the horses

>pushing me I ain't going nowhere. And, most importantly, give me the

>horses and I can kick anyone's ass.

 

Sigh... "enough horses" in the case of the F-15E is about 10,000 lbs of

thrust more than we have with the -220 engines. The -220 and -229 aircraft

perform dramatically differently. It's the extra drag of the CFT's and

LANTIRN pods that kills us, really. Except that I heard an F-15C guy

bitching once about a 135 that got a little too eager during a breakaway,

and left all the F-15's in the dust until it pulled it's power back...

 

The F-15C has the -220 engines still. Extra drag is impossible to gauge, but assume 3 external fuel tanks, 6x AMRAAM and 2x Sidewinder . . . .

 

Doesn't sound too far off.

[JACN]

I need to check, but I think the real Eagle suffers the same sort of thing.

 

I've seen the same Strike Eagle quote as MBot, and think I've seen something similar for the F-15C. Will see.

 

Ok, guys, may I be wrong and real Eagle is as modelized in LO, but I find hard to believe that two of the most powerfull engines available can´t stand an AA store config+fuel in any other throttle position than max-dry or above..:(

[britgliderpilot]

Ok, guys, may I be wrong and real Eagle is as modelized in LO, but I find hard to believe that two of the most powerfull engines available can´t stand an AA store config+fuel in any other throttle position than max-dry or above..:(

 

They are powerful, but more powerful engines exist. And you have to bear in mind that once you get up to altitude, the thrust produced differs significantly from uninstalled ground thrust due to a fairly large number of factors not usually considered.

[JACN]

Quoted from PapaDoc's Real Life page

 

Doubting Thomas appears to be a forum poster, replier is a Strike Eagle jockey.

 

 

 

The F-15C has the -220 engines still. Extra drag is impossible to gauge, but assume 3 external fuel tanks, 6x AMRAAM and 2x Sidewinder . . . .

 

Doesn't sound too far off.

 

Ok, but I think Strike Eagle has a far greater drag profile.All in all, thanks, this info is enough for me.:icon_jook

 

Cheers,

[JACN]

They are powerful, but more powerful engines exist. And you have to bear in mind that once you get up to altitude, the thrust produced differs significantly from uninstalled ground thrust due to a fairly large number of factors not usually considered.

 

Yes, I do know...;)

[britgliderpilot]

Ok, but I think Strike Eagle has a far greater drag profile.All in all, thanks, this info is enough for me.:icon_jook

 

Cheers,

 

Just one more thing here - how fast were you flying at the time?

 

The Eagle and it's clever shiny variable geometry intakes essentially mean that the faster you fly, the more thrust you get . . . . at higher speeds it's as much ramjet as it is turbojet. If you're trying to cruise below Mach 0.85 or thereabouts, you may be suffering unduly as a result.

 

Will go and fiddle with it in a bit, I'm getting interested in the performance now.

[MBot]

Except that I heard an F-15C guy bitching once about a [KC-]135 that got a little too eager during a breakaway, and left all the F-15's in the dust until it pulled it's power back...

 

Hehe, you got to love that :)

[JACN]

Just one more thing here - how fast were you flying at the time?

 

The Eagle and it's clever shiny variable geometry intakes essentially mean that the faster you fly, the more thrust you get . . . . at higher speeds it's as much ramjet as it is turbojet. If you're trying to cruise below Mach 0.85 or thereabouts, you may be suffering unduly as a result.

 

Will go and fiddle with it in a bit, I'm getting interested in the performance now.

 

I think oblique shock waves effect on the diffusor wouldn´t be noticed until mach well above 1,0...say 1,5+? so cruise at any mach below it has little or no benefit in thrust terms.

[britgliderpilot]

I think oblique shock waves effect on the diffusor wouldn´t be noticed until mach well above 1,0...say 1,5+? so cruise at any mach below it has little or no benefit in thrust terms.

 

. . . Lemme find the quote . . . .

 

As the Mach number increases at a given altitude, the thrust of the afterburning turbofan also increases. For example, the thrust of the F-15 engine at sea level and Mach 0.9 is nearly twice the sea-level static value.

 

Not necessarily shockwave interaction that's causing the extra thrust ;)

 

 

Just been experimenting - the Eagle will cruise at altitudes higher than 35k feet at max dry thrust with 3x fuel, 6x AMRAAM, 2x Sidewinder, for not that much fuel burn penalty over, say, 90% throttle.

 

I'd be relatively happy with cruising at max dry thrust :)

 

 

Yet another thing that's occurred to me is that ED have the F-15A flight manual - and the F-15A was fitted with the F100-PW-100 engine.

 

Nominal dry thrust is about 500lbs MORE than the -220, speculate freely about effects at altitude etc.

[JACN]

 

Not necessarily shockwave interaction that's causing the extra thrust ;)

 

You suggested it:

 

"The Eagle and it's clever shiny variable geometry intakes essentially mean that the faster you fly, the more thrust you get . . . . at higher speeds it's as much ramjet as it is turbojet. If you're trying to cruise below Mach 0.85 or thereabouts, you may be suffering unduly as a result."

 

;)

 

And, yes, increased mass-flow means "extra-thrust"

 

 

I'd be relatively happy with cruising at max dry thrust :)

 

 

Me too.

[D-Scythe]

Quoted from PapaDoc's Real Life page

 

Doubting Thomas appears to be a forum poster, replier is a Strike Eagle jockey.

 

 

 

The F-15C has the -220 engines still. Extra drag is impossible to gauge, but assume 3 external fuel tanks, 6x AMRAAM and 2x Sidewinder . . . .

 

Doesn't sound too far off.

 

You're comparing how the F-15C should behave by referring to an F-15E? An F-15C with three external fuel tanks and 8 AAMs would still weigh less and at most have comparable drag than a clean F-15E with CFTs and LANTIRN.

 

Just felt like pointing that out ;)

 

Nominal dry thrust is about 500lbs MORE than the -220, speculate freely about effects at altitude etc.

 

A difference of 500 lb in one specific scenario/portion of the operating envelope is meaningless.

[cool_t]

Flight envelopes

 

""Scramble!!!!!

 

:icon_supe 3-26-06 12 kills 2 losses 1 sam site splattered with my guns the F-15 ROCKS!!!!!!!!!!!!!!!!

Torrey Spinelli "AKA Cool t"

[SwingKid]

Well, the real F-15C can accelerate straight up like a rocket with full internal fuel load, the one in Lock On cannot... That much at least should be easy to confirm, no?

 

-SK

[capttrob]

One thing that bothers me about the F-15 is acceleration in straight and Level at high alt. If i accelerate to say 500 KIAS on the deck, and pull into a 7G vertical climb with full AB, i'll level off at say FL250 (and it gets there quick which i like) at about 200 KIAS, i'll have to pitch down quite a bit to pick up speed with the burners lit and lose some altitude. If i level at FL250 and reduce to mil power, shes gonna stall if i dont get the nose down quick from level to pick up speed. I would think you should be able to accellerate (especially in AB) from 200 KIAS in level flight at 250 without sacrificing altitude. I seen an F-15 (not sure which model) accelerate away from us after mock intercept at FL250, 260 KIAS (Mach .64 roughly?), somewhere over Atlantic City NJ and this thing took off. It was gone within seconds (and no, it wasnt an ACY ANG F-16). I mean its not like we're talking about FL350 or 450 here.... edit: Basically it seems to behave at FL250 as if it were near its service ceiling. I find myself checking to see if i left anything "hanging out in the breeze" frequently in this game....

 

 

Either way, its still a blast to play.

[Hawg11]

Well, the real F-15C can accelerate straight up like a rocket with full internal fuel load, the one in Lock On cannot... That much at least should be easy to confirm, no?

 

That's the first I've ever heard about the F15 being able to do this with a full fuel load...Got a source by any chance?

The manufacturer doesn't mention fuel state for an accelerated climb, nor do they mention to what altitude.

http://www.boeing.com/defense-space/military/f15/

I always understood that the 1:1 weight ratio didn't include maximum fuel as part of the equation.

 

I just did a very quick check. The F-15 in lockon does accelerate in a climb. At 20 percent fuel load, starting from 50 ft at 450 kts (pulling max G to 90 degrees) I accelerated in the climb until I reached 6000 feet.

 

You cannot use the HUD or mach meter for your readings. The HUD shows Calibrated Airspeed. You must use the oustside view to get the TAS (True Airspeed).

 

NOTE: I fly 1.02, so results from 1.12a would be interesting to see...

[Bublik]

Made a quick test for LOF-15C at 100% fuel load, clean config, FL250 (actually it was 24500 ft to be precise), straight and level

 

 

Well, Vy around 270 KIAS looks plausible to me (in this particular setting). I cannot comment on 87% N1 though, don't have that kind of data on F-15s :)

[capttrob]

Thanks for the chart....

 

Edit: Anyone have access to the real F-15C L/D Max?

[Bublik]

What does that chart represent? power vs. airspeed? Cl vs. airspeed? Cd vs. airspeed? Altitude vs. airspeed?

 

Horizontal axis is KIAS, vertical is N1 in percent.

 

If its power vs. airspeed, are you telling me that the F-15 accelerates from 150 to 300 KIAS (doubles its airspeed) in straight and level flight with full fuel while reducing power from 96 to 87%? The F-15 doubles its airspeed by reducing power? what?

 

Yes.

Have you ever heard about the back side of the power curve and so-called 'mushing regime'? ;)

 

http://www.av8n.com/how/htm/power.html#sec-speed-change-back

[capttrob]

Yeah, its been a long night for me and i havent seen an L/D max in years...lol

 

Actually, my first reference was correct, although interpretation of the chart didnt "click" in my mind. The correct way of stating it for that chart is that as airspeed decreases more power is required, hence the back side of the power curve. Like i said, i had a long night... and mis-interpreted that chart. My bad. Although, labels would have helped. ;)

 

I edited my post...