Which Flight Model Does the F15 Use?

[henshao]

1 hour ago, wilbur81 said:

 Without a true FLCS or FCS, I'm sure the Eagle driver has to make all those stores/over-g calc's in his head as well.

 

 yes and no

 

 

I don't think the OWS accounts for every possible store configuration though

[henshao]

At what weight, speed, and g-load should an Eagle break, and what should the nature of the damage be?

[dundun92]

13 hours ago, gortex said:

now the Eagle is all by itself in not being susceptible to over g damage.

Lol, it literally just got added this patch, have you like done any testing? (I will grant it was stealth patched, but still)

Edited October 21, 2021 by dundun92

[henshao]

51 minutes ago, dundun92 said:

it was stealth patched

 

 please elaborate

[dundun92]

30 minutes ago, henshao said:

 please elaborate

It was added but not put in the patchnotes. Fairly common occurence in DCS

[henshao]

7 minutes ago, dundun92 said:

It was added but not put in the patchnotes. Fairly common occurence in DCS

Ok let me be more clear: Source?

[dundun92]

Just now, henshao said:

Ok let me be more clear: Source?

Boot the game and try it like I have ? I dont have a recording off hand

[draconus]

5 hours ago, dundun92 said:

Lol, it literally just got added this patch, have you like done any testing? (I will grant it was stealth patched, but still)

Wow, it really is implemented - Eagle is loosing the wings now!

[Cab]

Does anyone know the AOA limit for the F-15 in RL? In degrees, not units.

[GGTharos]

AoA limit for what exactly?  Normally up to ~25, but there are records of it doing 40+.  It depends on what you're doing.

[Cab]

The operational limit, I assume. Is there a published limit in the dash-1.

[GGTharos]

Just a warning that after 35CPUs (or less, depending on payload), longitudinal stability gets funky.

[Cab]

7 hours ago, GGTharos said:

Just a warning that after 35CPUs (or less, depending on payload), longitudinal stability gets funky.

Okay, thanks. No way to convert those to degrees, right?

 

[draconus]

10 minutes ago, Cab said:

Okay, thanks. No way to convert those to degrees, right?

Idk what CPU means here but the conversion for AOA to units in the Eagle is AoA[Units] = 0.7728*AoA[Degrees] + 12.22.

[Cab]

11 minutes ago, draconus said:

Idk what CPU means here but the conversion for AOA to units in the Eagle is AoA[Units] = 0.7728*AoA[Degrees] + 12.22.

Assuming CPUs are units, 35 units calculates to 39 degrees.

I had no idea the F-15 could do such high AOA with it's hard wing.

[GGTharos]

29 degrees (I assume that was a typo) and the highest spike I've read about was 54 CPUs or about 54deg in this case oddly enough.

[henshao]

27 minutes ago, Cab said:

Assuming CPUs are units, 35 units calculates to 39 degrees.

I had no idea the F-15 could do such high AOA with it's hard wing.

F-15 has a lot of subtle tricks up its sleeve. The wing is conically cambered, that is to say it reaps some of the benefit of a leading-edge slat design due to its curved shape:

 

The F-15's nodding intakes not only function somewhat like canards, adding or dumping lift ahead of the CG under some circumstances, but IIRC they also function somewhat as a LERX as well, in addition to their primary function of providing unrivaled pressure recovery to the engines at high and low AoA

 

Quote

https://history.nasa.gov/SP-468/ch11-6.htm

The wing planform of the F-15, shown in figure 11.36, suggests a modified cropped delta shape with a leading-edge sweepback angle of 45°. Ailerons and a simple high-lift flap are located on the trailing edge. No leading-edge maneuvering flaps are utilized, although such flaps were extensively analyzed in the design of the wing. This complication was avoided, however, by the combination of low wing loading and fixed leading-edge camber that varies with spanwise position along the wing. Airfoil thickness ratios vary from 6 percent at the root to 3 percent at the tip.

 

The F-15 can sustain some pretty ridiculous AoA.

 

[Cab]

25 minutes ago, GGTharos said:

29 degrees (I assume that was a typo) and the highest spike I've read about was 54 CPUs or about 54deg in this case oddly enough.

No, not a typo but a mistake. I inserted the units into the formula where it should be degrees.

Math is hard, but luckily for me I have a lot more experience being wrong than being right. 

Incidentally, the reason I asked is I see F-15 routinely exceeding 30 degrees AOA in Tacview and had wondered about the accuracy of that. (Both the flight model and Tacview)

33 minutes ago, henshao said:

F-15 has a lot of subtle tricks up its sleeve. The wing is conically cambered, that is to say it reaps some of the benefit of a leading-edge slat design due to its curved shape:

Yes. I had originally typed "simple wing" but changed it to "hard wing" because I know the design itself is far from "simple".

[GGTharos]

Yeah my calc prof said 'never do arithmetic in public, it could be embarassing' ... do math instead, no one will be able to tell

Above 35CPUs (20-25 in some cases) the aircraft becomes very sensitive to yaw, which isn't really well represented in DCS.  Very high AoA excursions (like the 54 I mentioned) can then result in problems, in this case it was an accident due to a deformed nose cone, causing the aircraft to spin out because the moment arm is huge while stability is reduced.  So you can fly very high AoAs but you have to finesse it a lot.

[Cmptohocah]

2 hours ago, GGTharos said:

29 degrees (I assume that was a typo) and the highest spike I've read about was 54 CPUs or about 54deg in this case oddly enough.

It can do 54deg. without stalling? Did I get that right?

[GGTharos]

5 minutes ago, Cmptohocah said:

It can do 54deg. without stalling? Did I get that right?

54 deg was a spike in a defensive maneuver.  The book which describes the exact capabilities is nowhere to be found for the public unfortunately.

In other words I couldn't tell you that you can 'walk' the eagle at 54, and you probably can't.   Also as I said, that spike led to a spin due to asymmetric airflow over the nose cone combined with lack of longitudinal stability due to the high AoA (vertical stabs are washed out, low airflow, etc).

[Cmptohocah]

8 minutes ago, GGTharos said:

54 deg was a spike in a defensive maneuver.  The book which describes the exact capabilities is nowhere to be found for the public unfortunately.

In other words I couldn't tell you that you can 'walk' the eagle at 54, and you probably can't.   Also as I said, that spike led to a spin due to asymmetric airflow over the nose cone combined with lack of longitudinal stability due to the high AoA (vertical stabs are washed out, low airflow, etc).

Doesn't really matter how much it went as long as the wing is stalled. I mean, for example: if the max AoA is 30, it doesn't matter if the wing is at 31 deg or 131 deg, 'cause it's not producing any lift.

[GGTharos]

Couldn't tell you, all I can tell you is that this sort of maneuver is practiced and no one wants to stall so ... anyway, like I said the actual details exist but not in any document we can access.   Things like exact effect s of rudder - like say how fast cna you turn with just the rudder, assuming you use aileroon to remain level, the wing's critical parameters etc.   All that is not available to us.   Maybe if someone feels like it they could find some sort of FCF record or something that goes into testing high AoA handling.

[Cmptohocah]

We could do a flight test and measure the AoA at stall speeds. For example: idle power level flight, at 35k lb should stall at around 119 knots IAS. Then we can take the measurement of the AoA and this would be the AoA limit. I don't have access to DCS at the moment, so I can't test it my self.

[Exorcet]

51 minutes ago, Cmptohocah said:

Doesn't really matter how much it went as long as the wing is stalled. I mean, for example: if the max AoA is 30, it doesn't matter if the wing is at 31 deg or 131 deg, 'cause it's not producing any lift.

A stalled wing still produces lift, just less than the peak lift, and more drag. Anyway the peak recorded AoA isn't about stall. The plane can exceed critical AoA if it's stable enough, like the Su-27 performing the Cobra.