Aerodynamics, F15E sustained AOA 25deg limit (F15C had 35deg)

[razo+r]

41 minutes ago, xrx said:

drag force is measured inside wind tunnel static bolt on and has no matter how much frame weights, it can be hollow box or heavy metal filled box, drag force on object is the same

 

That is what's called parasite drag, which is made out of Form drag, Friction drag and Interference drag. But the drag of an aircraft is not only the parasite drag, but it's the combination of induced drag and parasite drag.

Induced drag depends on lift and for straight unaccelerated flight Lift equals weight.

 

[xrx]

21 minutes ago, razo+r said:

That is what's called parasite drag, which is made out of Form drag, Friction drag and Interference drag. But the drag of an aircraft is not only the parasite drag, but it's the combination of induced drag and parasite drag.

Induced drag depends on lift and for straight unaccelerated flight Lift equals weight.

 

"drag [due] to lift" - additional drag force induced the way the shape creates a lift force and turbulences that come with it affecting initial drag itself - two of them affect each other, known - Thanks

Edited October 31, 2023 by xrx

[xrx]

On 10/23/2023 at 10:57 PM, Rainmaker said:

What your point with this?  There was literally a SEEK Eagle program dedicated to departure prevention.  The E model has a digital system and is smarter than a legacy as well.

You are trying to nit-pick things and you are lacking a lot of knowledge base here.  

Enjoy the sim and go fly.  This is literally the wrong way to try and justify things.

I'm out!

 

 

 

as you can see flat spin smoke to nose angle 60-80deg, and thats due to elevator authority to get it there, which get AOA way past 35deg 

Edited October 31, 2023 by xrx

[Rainmaker]

33 minutes ago, xrx said:

as you can see flat spin smoke to nose angle 60-80deg, and thats due to elevator authority to get it there, which get AOA way past 35deg 

 

If you haven't noticed, I am ignoring your posts as its just drawn out nothing. I’ve said all I’m going to say about the matter. You have two choices, fly it or don’t.  If you are expecting things to happen the way you want them to happen, you are going to be sadly disappointed for a very, very long time. 

[xrx]

9 minutes ago, Rainmaker said:

If you haven't noticed, I am ignoring your posts as its just drawn out nothing. I’ve said all I’m going to say about the matter. You have two choices, fly it or don’t.  If you are expecting things to happen the way you want them to happen, you are going to be sadly disappointed for a very, very long time. 

(expected bit more from you, but ok)

I tried to bring issue upfront, now you know exactly whats it about, and the choice is yours, everyone will agree if things are right - Thanks again for good work

Edited October 31, 2023 by xrx

[Akrescue130]

2 hours ago, xrx said:

(expected bit more from you, but ok)

I tried to bring issue upfront, now you know exactly whats it about, and the choice is yours, everyone will agree if things are right - Thanks again for good work

 

I understand the point you’re trying to make and I with my limited knowledge can’t give you the answer you seek. In the 93’ -1, it talks about stall and departure warnings with units of aoa, and those audible warning are accurate from the documentation to the sim. As far as the aoa sustaining 25 degrees (~35 units) the only thing I can think of is BECAUSE of the heavier nose and much further forward CG in the E model, the elevators either just flat out don’t have enough authority for another 10 degrees, or the ability to pull that nose high was reduced in order to subdue negative flight handling and departure characteristics with the CFT’s installed and the changes of hardware/avionics. 

[Rainmaker]

2 hours ago, xrx said:

(expected bit more from you, but ok)

I tried to bring issue upfront, now you know exactly whats it about, and the choice is yours, everyone will agree if things are right - Thanks again for good work

 

Then show up with something more credible than the ‘The DCS C model does X…’. If you enjoy the C’s ability to sit at 45* CPU post stall maneuvering, then fly the crap out of it and enjoy it. Just don't expect someone to listen when that’s all you have to offer as information/data. 

[xrx]

its your/ED product and I'm not the one to offer data, why you asking me questions, I asked for ref tables with ignored answers

manual doc doesn't have even basic maneuverability section

undocumented implementation product - buy or fly, all I can say, thx

Edited November 1, 2023 by xrx

[Ramsay]

On 11/1/2023 at 7:37 AM, xrx said:

I asked for ref tables with ignored answers

undocumented implementation product - buy or fly, all I can say, thx

Razbam's F-15E has been built using as much documentation as is publicly available and tuned using SME's (pilots and maintainers) who have flown/worked with the real.

Most of what you ask for IS available on the internet, however, you won't get links here as forum rule 1.16 prevents the sharing of such

Quote

1.16 Posting of screenshots, images, file links, file sharing links, and copying and pasting information is prohibited if the source document has a limited distribution statement or it is classified.

However, the F-15E's AoA limits are discussed in detail in a 2011 Accident Report (where a load imbalance caused the mishap aircraft to spin out of control and crew eject) which I'll quote

Quote

The basic empty F-15E is laterally imbalanced with a moment of 1,850 ft-lbs right-wing heavy due to the internal gun and other aircraft installed equipment. A moment is a measurement used in calculating aircraft weight and balance.

Loading of external stores has a marked effect on the aircraft’s lateral asymmetry depending on the configuration loaded. Using the known stores configuration at the time the MA launched, it was possible to calculate the take-off lateral imbalance of the MA at 8,168 ft-lbs right wing heavy.

With fuel in the external fuel tanks and/or air-to-ground stores loaded, the F-15E is limited by technical order to a maximum angle of attack (AOA) of 30 cockpit units (CPU).

AOA is the angle between the relative wind direction and the aircraft wing cord line. The F-15E does not directly display AOA. Instead, it displays AOA as CPUs, which is actual AOA plus 10 degrees.

The aircraft has a programmable high AOA warning tone the pilot can set from 20 to 45 CPUs. The default setting is 30 CPUs. The warning tone beeps to cue the aircrew when the programmed AOA is exceeded. The aircraft can attain AOA in excess of the maximum displayed 45 CPUs. Normal manoeuvring range is from approximately 8 to 30 CPUs. High AOA is considered to be above 30 CPUs.

The F-15E’s 30 CPU restriction was put in place to mitigate the risk of departure (uncontrolled flight path change) due to imbalanced fuel in the external fuel tanks.

This Spin Stability AoA/load imbalance table was generated using a F-15E Simulator at Lakenheath when investigating the root cause of the accident.

Original Sources

https://aviation-safety.net/wikibase/121265
https://www.airandspaceforces.com/PDF/AircraftAccidentReports/Documents/2011/032111_F-15E_Libya.pdf

Edited November 7, 2023 by Ramsay
Spelling

[jaylw314]

On 11/1/2023 at 3:31 AM, Ramsay said:

Razbam's F-15E has been built using as much documentation as is publicly available and tuned using SME's (pilots and maintainers) who have flown/worked with the real.

Most of what you ask for IS available on the internet, however, you won't get links here as forum rule 1.16 prevents the sharing of such

However, the F-15E's AoA limits are discussed in detail in a 2011 Accident Report (where a load imbalance caused the mishap aircraft to spin out of control and crew eject) which I'll quote

This Spin Stability AoA/load imbalance table was generated using a F-15E Simulator at Lakenheath when investigating the route cause of the accident.

 

Original Sources

https://aviation-safety.net/wikibase/121265
https://www.airandspaceforces.com/PDF/AircraftAccidentReports/Documents/2011/032111_F-15E_Libya.pdf

Nice!  TIL that CPU is simply AOA + 10!  I always thought it was some arbitrary and fancy conversion 

Edited November 2, 2023 by jaylw314

[draconus]

6 hours ago, jaylw314 said:

Nice!  TIL that CPU is simply AOA + 10!  I always thought it was some arbitrary and fancy conversion 

It's simplification and can work for most common cases to get you a ballpark number but it's not really that simple. It may even not be linear but I have also found this equation:

AoA[Units] = 0.7728*AoA[Degrees] + 12.22

[jaylw314]

10 hours ago, draconus said:

It's simplification and can work for most common cases to get you a ballpark number but it's not really that simple. It may even not be linear but I have also found this equation:

AoA[Units] = 0.7728*AoA[Degrees] + 12.22

Arrrgh.  You burst my bubble