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

[xrx]

why F15E has lower AOA limit than F15C - technically its same avionics other than more fuel weight.

10 deg difference results in way much lower G limit, no wonder it flies sluggish. 

also there is no way to do get f15e into flat spins at this lower aoa /elevator limit.

Please increase/update.

Thank you

Edited October 31, 2023 by xrx

[Rainmaker]

No bugs there.....

[xrx]

could you point out public aerodynamics ref tables that you modeling F15E against, raw tables or analytical curves, would be more valuable to believe so

[xrx]

F-15 Upright Spin Flight Test with aircraft audio

 

 

 

 

 

[Rainmaker]

2 minutes ago, xrx said:

F-15 Upright Spin Flight Test with aircraft audio

 

 

 

 

 

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!

 

 

 

[xrx]

AOA limit depends on elevator up range is same 30deg - assuming same aerocenter and CG for both F15 aircrafts

in that case we missing additional 10 deg on AOA limit at least 

not looking into digital AOA limiter, would like to see what FBW does direct input without nanny cushioning (not sure if f18 ever implemented it)

again whats your source tables on AOA limits at various IAS? can you provide specific public pdf documentation?

[Rainmaker]

27 minutes ago, xrx said:

AOA limit depends on elevator up range is same 30deg - assuming same aerocenter and CG for both F15 aircrafts

in that case we missing additional 10 deg on AOA limit at least 

not looking into digital AOA limiter, would like to see what FBW does direct input without nanny cushioning (not sure if f18 ever implemented it)

again whats your source tables on AOA limits at various IAS? can you provide specific public pdf documentation?

You are the one that said it was wrong there guy.  Where is your data at?  And no, using the C does not count.  By the way....not 30*....or how that works either.

Also...still no

Didn't even try that hard.

[xrx]

didnt say elevator angle relates to aoa, just saying elevator up range angle is not any lower than f15c, so aoa max limit should be nearly same

 

also I see you got 30deg aoa(40* points) at 200kn turn (but this is max instantaneous, not sustained AOA)

why then i cant get same aoa - simply during flat sink, flat spin, or tight loop? nose doesnt go up much, it locks into 25deg (35*) aoa, induced pitch yank doesnt help either

Edited October 29, 2023 by xrx

[Deano87]

@xrx Razbam have multiple real F-15E aircrew as SMEs for both the flight model and the systems. Can you please stop posting things based on feelings of how the F-15E compares to the C model. They are different aircraft.

[draconus]

On 10/29/2023 at 1:33 AM, xrx said:

just saying elevator up range angle is not any lower than f15c, so aoa max limit should be nearly same

No, because it's different aircraft - E has CFTs, heavier nose and different CG.

[Sarge55]

I think we’re being trolled…

[Moosemermaid]

STOP TRYING TO TURN THE E INTO A DOGFIGHTER! 

But seriously, I dont know how many times I need to say this. If you want C performance, just fly the C model. Its in the game. Or if you want to drop bombs and then go to the merge and dominate your opponents, learn the Viper. 

[SloppyDog]

On 10/23/2023 at 9:52 PM, xrx said:

why F15E has lower AOA limit than F15C - technically its same avionics other than more fuel weight.

10 deg difference results in way much lower G limit, no wonder it flies sluggish. 

also there is no way to do get f15e into flat spins at this lower aoa /elevator limit.

Please increase/update.

Thank you

Ok, I'll chime in. Don't face it as I'm trying to berate you. I am, as everybody else is, trying to help you and others. 

I believe, or I'm convinced of, that you bought a product expecting something and when playing/flying it got something else entirely, and it brought you a lot of frustration.

So, based on that belief, I don't want to assume that you are a troll trying to have a good time at the expense of others. However, I'm assuming that you are confused by what you have on your hands and is not entirely convinced about it.

So, here we go: 

It is clear that you are a big fan of the F-15C, and I believe that you expected the F-15E to be a full fidelity version of the F-15C.

As many stated here, and in other topics, they are not the same aircraft. Not at all. The F-15C was designed to counter the Mig-25. Big, powerful, air superiority fighter.

The F-15E, on the other hand, was designed to replace the aging F-111. Low-level penetrator/interdiction/strike aircraft. Totally different mission sets.  

Yes, they look alike. Yes, the F-15E can carry air-to-air missiles and a has a powerful radar. And that where the similarities end.

I strongly recommend that you read the companion book to the F-15E: "Be Afraid of the Dark". It can be found on your Doc folder inside the F-15E main folder.

In there you will have lots of information about what the F-15E is and how it become to be. I'm reading it and it is a great book. 

About the performance of the -E compared to the -C, don't take my word for it. Below is the transcript of the book, from the test pilots flying it: 

Page 23, second and third column:

"We also wanted to look at the CFTs to see what
aerodynamic penalties we would pay for carrying
them. Did they put us at a big disadvantage in the
air-to-air arena? So, we flew air-to-air against as 

many types of adversary as we could. We did what I
would call VHNs – Very Heavy Nose – where you have
just come off a tanker and are full of gas. We then
reduced the weight to a half fighting load and then
further reduced it to an ideal fighting weight. We had
never flown this heavy before and I wanted to see
what would happen when we did.”

Page 23, end of third column, and Page 24:

"When we flew the air-to-air portion of the tests in a

VHN condition it did not perform like the C model – it couldn’t, it was just too
heavy. Once down to a half fuel load though, it would
start to fly like a C or D model."

 

[xrx]

"Once down to a half fuel load though, it would start to fly like a C"

so still holds water, you put same total weight 43k lb on both (read if need again), on nearly same frame (this is not entirely new aircraft/frame, just very minor mods), same wing foil spec, same elevator angle authority and area
- result is AOA will be same any speed, and will fly nearly same (limits and moments).
 

excluding the roll moment due to those CFTs, but thats least of focus for now. obviously you put extra 10k lb fuel it will be heavy, so is f15c with extra tanks.

 

Edited October 31, 2023 by xrx

[Akrescue130]

1 hour ago, xrx said:

"Once down to a half fuel load though, it would start to fly like a C"

so still holds water, you put same total weight 43k lb on both, on nearly same frame (this is not entirely new aircraft/frame, just very minor mods), same wing foil spec, same elevator angle authority and area
- result is AOA will be same any speed, and will fly nearly same (limits and moments).
 

excluding the roll moment due to those CFTs, but thats least of focus for now. obviously you put extra 10k lb fuel it will be heavy, so is f15c with extra tanks.

 

 

The CFT’s alone are 20.1 units of drag on top of a clean airframe, and weigh an additional 4400 pounds. If you want to try and “simulate” a similarity, take a C model give it 5,000 lbs more fuel than the E model, and add pylons and empty wing tanks. The wing pylons add 3.5 units of drag each, and the external wing fuel tanks add 7 units of drag each for a total of 21. 
 

On top of this the E model has a heavier nose due to the differences of avionics and radar, which makes it have a more forward center of gravity than the C model. There’s no way to really simulate this effect though, other than knowing that you reduce maneuverability when you pull the center of gravity away from the center of lift on the aircraft. 

[xrx]

drag has no units its a coefficient - get metrics straight

and drag has nothing todo with weight either

[jaylw314]

4 hours ago, xrx said:

"Once down to a half fuel load though, it would start to fly like a C"

so still holds water, you put same total weight 43k lb on both, on nearly same frame (this is not entirely new aircraft/frame, just very minor mods), same wing foil spec, same elevator angle authority and area
- result is AOA will be same any speed, and will fly nearly same (limits and moments).
 

excluding the roll moment due to those CFTs, but thats least of focus for now. obviously you put extra 10k lb fuel it will be heavy, so is f15c with extra tanks.

LOL, your response made me think of that movie line:

"What are the chance of a guy like me and a girl like you ending up together? ... One out of a hundred?"

"I'd say more like one in a million"

"So you're telling me there's a chance!" 

Edited October 31, 2023 by jaylw314

[draconus]

@xrx it's clear you're just trolling now. If you have some hard data (docs, manuals) that F-15E FM is wrong please provide it to the devs - we all want it to be as true to life as possible. Otherwise drop it.

[razo+r]

1 hour ago, xrx said:

drag has no units its a coefficient - get metrics straight

Drag index = drag coefficient * 1000. And since its not really a coefficient anymore, it gets the unit "units" added. 

1 hour ago, xrx said:

and drag has nothing todo with weight either

Lets see if that is true. 

Take a F-15C as an example, one basically empty and a second one fully loaded. 

In a straight and level flight, we know lift has to be equal to the weight. So the heavier one will naturally have to create more Lift than the light one. And if we now use the Lift induced drag formula, we see that the heavier one creates more drag because it is heavier. 

[Akrescue130]

1 hour ago, xrx said:

drag has no units its a coefficient - get metrics straight

and drag has nothing todo with weight either

It’s not a matter of coefficient in this sense…. That equation has already been done be engineers at McDonnell Douglas. They use units because most pilots are not going to sit down and figure out a plethora of coefficients and math out drag indexes for every single varying loading they may take. The units are simply a simplification. Just like how some aircraft report AoA as an actual degree, and some aircraft report AoA as. “Unit” of alpha. 
 

I never said drag has anything to with weight. I’m simply saying that the cft’s installed add an additional 4400 lbs of weight to the airframe empty. 
 

you can use the “units” of drag in this case scenario BECAUSE the airframe is technically the same and the math works. That’s why I suggested using a C model with empty wing tanks and adding 5000 lbs more in fuel to “simulate” having CFT’s installed to let you do some research on how much it affects the airframe. Will it ever be a true like for like? No not at all. Could it get you in a reasonable ballpark? It could, if both flight models are made fairly accurately. 
 

it seems that there is either somewhat of a language barrier here, or you are in denial about a lot of facts that people are supplying. I’m all for testing, finding bugs, and making sure things are correct, however throwing out blanket statements with any amplifying detail or background research to support your argument won’t get you anywhere.

 

That being said, I’ll go ahead in some free time and see how those to setups compare. It will never be apples to apples, but it could be interesting 

[xrx]

8 hours ago, draconus said:

@xrx it's clear you're just trolling now. If you have some hard data (docs, manuals) that F-15E FM is wrong please provide it to the devs - we all want it to be as true to life as possible. Otherwise drop it.

I want the same, would like to take a look first what ED has as a ref tables modeling into DCS 

Edited October 31, 2023 by xrx

[xrx]

6 hours ago, razo+r said:

Drag index = drag coefficient * 1000. And since its not really a coefficient anymore, it gets the unit "units" added. 

Lets see if that is true. 

Take a F-15C as an example, one basically empty and a second one fully loaded. 

In a straight and level flight, we know lift has to be equal to the weight. So the heavier one will naturally have to create more Lift than the light one. And if we now use the Lift induced drag formula, we see that the heavier one creates more drag because it is heavier. 

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

drag coefficient (could be percentage) is measured as part(or in relation) to frontal cross section, or also as part of wing area, if that is

coefficient is under or above 2.0 in relation to flat plate depends on object convexity, by definition of the drag formula

[draconus]

22 minutes ago, xrx said:

would like to take a look what ED has as a ref tables modeling into into DCS first

You've already been told - devs don't share their sources. If you have hard data that does not match with what is modeled, please, share it with the devs. Otherwise you have to trust that it's correct until you can prove otherwise.

[xrx]

7 hours ago, Akrescue130 said:

It’s not a matter of coefficient in this sense…. That equation has already been done be engineers at McDonnell Douglas. They use units because most pilots are not going to sit down and figure out a plethora of coefficients and math out drag indexes for every single varying loading they may take. The units are simply a simplification. Just like how some aircraft report AoA as an actual degree, and some aircraft report AoA as. “Unit” of alpha. 
 

I never said drag has anything to with weight. I’m simply saying that the cft’s installed add an additional 4400 lbs of weight to the airframe empty. 
 

you can use the “units” of drag in this case scenario BECAUSE the airframe is technically the same and the math works. That’s why I suggested using a C model with empty wing tanks and adding 5000 lbs more in fuel to “simulate” having CFT’s installed to let you do some research on how much it affects the airframe. Will it ever be a true like for like? No not at all. Could it get you in a reasonable ballpark? It could, if both flight models are made fairly accurately. 
 

it seems that there is either somewhat of a language barrier here, or you are in denial about a lot of facts that people are supplying. I’m all for testing, finding bugs, and making sure things are correct, however throwing out blanket statements with any amplifying detail or background research to support your argument won’t get you anywhere.

 

That being said, I’ll go ahead in some free time and see how those to setups compare. It will never be apples to apples, but it could be interesting 

there is no blanket statements and dont drag this sideways

to reiterate this topic is not about CFTs, engines power, or what we know about each

topic is about AOA limit, that clean same total weight F15C & F15E, should have same sustained AOA limit, at least in subsonic range

how much those CFTs proportional to entire frontal cross section add drag coefficient at 200-400kn? - marginal, drop it. It only adds drag quadratically due to speed at supersonic speeds (another thread on speed limit, which is another prob, dont try explain as nine grader know hows there is ways to test max altitude speed from max speed at sea level).

what is frontal drag coefficient on entire airplane? With and without CFTs. Not even concerned, since it doesn't contribute a lot on AOA limit itself.

AOA limits is driven by elevators spec - area and angle.

 

stop sticking nonsense statements troll n sh, everyone did their homework, we just need to agree upon if numbers are right 

 

Edited October 31, 2023 by xrx

[xrx]

1 hour ago, draconus said:

You've already been told - devs don't share their sources. If you have hard data that does not match with what is modeled, please, share it with the devs. Otherwise you have to trust that it's correct until you can prove otherwise.

understood, will take it as-is

as I said without you guys giving ref tables (and sources) what you modeling flight dynamics into DCS, hard to tell and make sense - aerodynamics I assume not the edge aspect of the sim, hence its called combat sim (schematic some might say), not flight dynamics sim in true aerodynamics form, alot of advanced aerobatics maneuvers bit iffy (due to local lift/drag extrapolated from orthogonal refs which are within aoa low -10..+30deg - thats where tests done most/not full spherical), but again, dont have to agree 

 

Thank you, its been well done to what it is right now

Edited October 31, 2023 by xrx