DCS: F-15C

[streakeagle]

1 hour ago, Buzz313th said:

Is this a hunch?  

Aerodynamic coefficients are a product of the physical shape of the aircraft. There is almost no difference in the physical shape and dimensions of an F-15C and an F-15E other than the presence or absence of the CFTs, the shape of the canopy, and some minor changes like the ECM antenna pods. So, no, it is not a hunch. It is physics. The F-15E gained some weight. So for a given angle of attack, the forces of thrust, lift and drag will be proportionally lower. But at the exact same gross weight and having the same presence or absence of the CFTs, the only differences will be in the center of gravity and inertia, and even those shouldn't be significantly different.

The key difference would be the engines. But most F-15Es originally had the same engines as the F-15C. So the main thing bogging the F-15E down was the weight gain from structural reinforcement to handle higher gross weights (especially the landing gear) and having the CFTs installed the majority of the time.

Edited December 5, 2023 by streakeagle

[Buzz313th]

19 minutes ago, streakeagle said:

Aerodynamic coefficients are a product of the physical shape of the aircraft. There is almost no difference in the physical shape and dimensions of an F-15C and an F-15E other than the presence or absence of the CFTs, the shape of the canopy, and some minor changes like the ECM antenna pods. So, no, it is not a hunch. It is physics. The F-15E gained some weight. So for a given angle of attack, the forces of thrust, lift and drag will be proportionally lower. But at the exact same gross weight and having the same presence or absence of the CFTs, the only differences will be in the center of gravity and inertia, and even those shouldn't be significantly different.

The key difference would be the engines. But most F-15Es originally had the same engines as the F-15C. So the main thing bogging the F-15E down was the weight gain from structural reinforcement to handle higher gross weights (especially the landing gear) and having the CFTs installed the majority of the time.

 

So how much difference do you think 3000 lbs makes on a given aoa throughout the flight envelope?  How about at altitude?  If there is a substantial relative change in aoa, how much difference do you think it might make regarding aerodynamics?  And if aerodynamics changes, to add just 10% drag in level flight somewhere in the envelope, then what happens when that increase in induced drag  is increased as the pilot loads the aircraft up in a turn?  How much of a difference do you think an increase of 10% of weight makes to critical aoa?

The decrease in performance of increased weight is exponential as G load increases and as pressure altitude drops.  The C does its best work up high and if it closes to the merge it works best around 8g with brief pulls to 9G

 

I think people are assuming that 3000lbs,  about 10% increase in empty weight is not enough to affect aerodynamics.

 

[Buzz313th]

Furthermore, we know the "E's" engines are rated at higher thrust than the "C's", but at what altitude?  Engines are designed to perform best at a particular point in the flight envelope that matches the aircrafts intended mission profile.  I would guess that the "E's" engines are designed to perform best at medium to low altitude.  This educated guess is due to the addition of the CFT's, more gas needed for the "E's" designed mission profile as a striker, not a mission where there is any need to loiter, unlike a CAP.  The "E" was designed to strike a predefined target and then get the hell out.  This makes me believe that the "E" was designed to go low and fast on ingress and egress burning loads of gas after wing tanks are dropped. The "C's" engines are probably tuned for performance at higher altitude.  How might this affect the difference in performance between the "C" and "E" in the "C's" designed mission profile? 

Even if you matched the two aircraft's at the same takeoff weight, the "E" without CFT's will have less gas than the "C", and with a higher burn rate.  

You can argue that most of the added empty weight of the "E" is probably engines.  This means that the CG might have traveled aft, but possibly negated by a heavier radar on the nose, more avionics in the bay, plus the extra pilot and life support equipment, possibly moving the CG forward within designed weight and balance.  So now we have potentially more weight at the tail and at the nose of the aircraft.  With most of the weight added as far away from the CG as you can get, what do you think this does to the pitch authority of the "E" compared to the "C"?  If the "E" pilot pulls harder to get the same pitch rate at the same weight as the "C", then what happens to the lift to drag ratio as the instantaneous alpha spikes on the "E" higher than it would in the "C" for the same maneuver?  What about if done at FL350 where the air is super thin and outside of the "E's" best engine performance?  Maybe a larger loss of velocity for the "E"?  Then the "E" pilot pushes the throttle into burner using more gas than the "C" pilot, plus the "E" is slower after the turn.  If all this happens at altitude during BVR, then the "E" starts losing kinetic energy, burns even more gas and AMRAAM range drops as the "E" pilot loses the initiative.  What about during a visual engagement?

 

With all due respect, you make a very good argument, but you're only looking at it from the surface.

 

We know very little of the real specs..  Best bet to answer this question is to hopefully get a true answer from a test pilot who has flown both models.  Personally, from the little I understand about aviation, I would assume, the performance difference between the "C" and "E" in the "C's" mission profile is greater than we might think.

Edited December 5, 2023 by Buzz313th

[draconus]

2 hours ago, streakeagle said:

But at the exact same gross weight and having the same presence or absence of the CFTs, the only differences will be in the center of gravity and inertia, and even those shouldn't be significantly different.

It strikes me that you never heard of the heavy nose, limited alpha and lateral instability at high AoA in the B, D and E Eagles.

[GGTharos]

4 hours ago, streakeagle said:

Aerodynamically, the F-15E and F-15C are nearly identical. The only difference is the internal equipment which affects both total weight and weight distribution. Lift and drag coefficients would be virtually identical. The only changes should be modest changes in center of gravity, inertia, and total weight. If an F-15E has the CFTs removed and burns off enough fuel to weight the same as the F-15C, they should have near identical performance. Likewise, and F-15C with CFTs should fly near identically to an F-15E at the same weight. The only significant aerodynamic difference is the canopy shape, which doesn't dramatically impact overall performance.

I stand by what I said. 

[Exorcet]

5 hours ago, streakeagle said:

Aerodynamic coefficients are a product of the physical shape of the aircraft.

 

They are, but these things can be very sensative. Airfoil profile, relative to the rest of the shape of the plane is extremely minor, yet can be the difference between being able to exceed Mach 1 or not, or the ability to fly at 10 alpha or not. The canopy shape difference can't be dismissed purely visually.

[henshao]

the charts exist for the E without CFTs with both -220 engines and -229 engines, and they're right next to the charts with CFTs, but we are straying a little bit. I would agree with the general notion that the two-seat Eagles handle differently but it's not a completely different jet either. I mean the flight model changes every time you fire a missile or drop a bomb this isn't some impossible task

[Rick50]

 

Is there different types of CFT's for the Eagles ??

I mean, they probably all have the same shape... but are there different configurations? One version  that only  carries fuel. Another that allows for many 500lb class ordnance. And yet another that maybe has hidden capabilities built in? I ask because I'm realising it's been a very long time since the first CFT's and the Strike Beagle was teh hotness!!

[Exorcet]

4 hours ago, Rick50 said:

 

Is there different types of CFT's for the Eagles ??

I mean, they probably all have the same shape... but are there different configurations? One version  that only  carries fuel. Another that allows for many 500lb class ordnance. And yet another that maybe has hidden capabilities built in? I ask because I'm realising it's been a very long time since the first CFT's and the Strike Beagle was teh hotness!!

This was planned, but never done. Ideas included gunpods, refueling pods, rocket propulsion pods, and more.

[GGTharos]

4 hours ago, Rick50 said:

 

Is there different types of CFT's for the Eagles ??

I mean, they probably all have the same shape... but are there different configurations? One version  that only  carries fuel. Another that allows for many 500lb class ordnance. And yet another that maybe has hidden capabilities built in? I ask because I'm realising it's been a very long time since the first CFT's and the Strike Beagle was teh hotness!!

http://aviationarchives.blogspot.com/2015/05/more-f-15-with-conformal-tanks.html

Edited December 7, 2023 by GGTharos

[henshao]

There are two categories of CFTs in existence for the F-15, fuel-only tanks (with missile hardpoints to replace the ones on the fuselage) and bomb-rack CFTs. You can most often see Israeli F-15's carrying the former, US Eagles based in Iceland would often carry them as well. the E and EX carry the latter

[Buzz313th]

11 hours ago, GGTharos said:

http://aviationarchives.blogspot.com/2015/05/more-f-15-with-conformal-tanks.html

 

I like the gunpods...

Two 30mm and a 20mm all at the same time would be "Sick"... 

 

[Exorcet]

1 hour ago, Buzz313th said:

I like the gunpods...

Two 30mm and a 20mm all at the same time would be "Sick"... 

 

I think they'd be nice additions to DCS, for both the C and E. They were never built, but DCS is fine for exploring what ifs. I'd also like to see the option to remove/add the existing CFT's to be added to the E someday, and a C module should we ever get one.

[Beirut]

1 hour ago, Buzz313th said:

I like the gunpods...

Two 30mm and a 20mm all at the same time would be "Sick"... 

 

 

Yes! More guns is good guns. 

[Buzz313th]

4 minutes ago, Exorcet said:

I think they'd be nice additions to DCS, for both the C and E. They were never built, but DCS is fine for exploring what ifs. I'd also like to see the option to remove/add the existing CFT's to be added to the E someday, and a C module should we ever get one.

I'm ok with hypothetical as well..  It's only a game.

Might be interesting to get some fictional aircraft based completely on theoretical concepts that are proven technology.

[draconus]

2 hours ago, Exorcet said:

They were never built, but DCS is fine for exploring what ifs.

I can take "never used operationally" but "never built" is way over the DCS line.

[Raven (Elysian Angel)]

10 minutes ago, draconus said:

I can take "never used operationally" but "never built" is way over the DCS line.

Absolutely! The F-14 with Zuni rockets for example is about the maximum most people will accept: it's nice for gameplay but not completely unrealistic  

[Tank50us]

2 hours ago, Buzz313th said:

I'm ok with hypothetical as well..  It's only a game.

Shh... The super-sim nerds will start seething enough to boil the oceans

2 hours ago, Buzz313th said:

Might be interesting to get some fictional aircraft based completely on theoretical concepts that are proven technology.

I completely agree. Though it would be nice if the teams could get more aircraft out in a more rapid time frame to make this viable. For example the F-15 ACTIVE as a combat aircraft instead of a tech demo, or the Super Tomcat '21 project. But, the main problem will forever be those that demand the sim stick to only the aircraft that were built and saw active service... and the unit in question has all of the relevant data available to the public blah blah blah....

To them I say: Just because it's a simulator, doesn't mean it has to stick to only one set of aircraft.

[Rick50]

 

Well, if we ever get an A or C Eagle, we could hope that it included an optional "Streak Eagle"  for those just wanting to punch holes in the skies like the test pilots did, maybe even one set up like that ASAT with an appropriate missile and maybe a satellite target too? It would be awfully "niche",  but one can dream! 

 

[Dragon1-1]

Eh, the ASAT one was a modified test aircraft, so I wouldn't expect that particular mission. That said, a clean A or C would still be a pretty solid contender in the hole in the sky field.

Edited December 7, 2023 by Dragon1-1

[GGTharos]

3 hours ago, Rick50 said:

 

Well, if we ever get an A or C Eagle, we could hope that it included an optional "Streak Eagle"  for those just wanting to punch holes in the skies like the test pilots did, maybe even one set up like that ASAT with an appropriate missile and maybe a satellite target too? It would be awfully "niche",  but one can dream! 

 

You would basically have to fly a specific profile with very specific timing and launch the ASAT.   You wouldn't have any weapon systems interaction or anything like that - no radar lock and whatnot.  ASAT was a test against a known target, nothing like today's air to space weapons.

[Exorcet]

10 hours ago, draconus said:

I can take "never used operationally" but "never built" is way over the DCS line.

I think if something was mature in design and documentation, but not built it can still fit DCS pretty well. You can do a lot of work without actually building a physical example. There are of course uncertainties that need to be acknowledged, but that's the case even with existing weapons in the sim.

20 minutes ago, GGTharos said:

You would basically have to fly a specific profile with very specific timing and launch the ASAT.   You wouldn't have any weapon systems interaction or anything like that - no radar lock and whatnot.  ASAT was a test against a known target, nothing like today's air to space weapons.

It would still be an interesting mission to include with the module, scored on how close you were to the planned profile, even if the actual weapon was just a visual prop more than anything else.

[mkellytx]

On 12/4/2023 at 2:36 PM, Buzz313th said:

It doesn't need to because it's primary design adaptation was not to be our air superiority fighter, the F-22 owns that role.  Just like the F-15C before it.  Just like the F-15E is our premier "MudMover". 

I doubt the F-22 was "Excused" from having the "9X" and the JHMCS simply because they didn't see the need for the 22 to close to the merge.  Lets not forget the thrust vectoring nozzles on the 22 as well.   

 Read on below regarding why the 22 might be limited with the "9X"....

I do believe that for the Aim9x or any "Heater" for that matter to be effective, that the "IR" seeker on the nose of the missile needs to be slewed to the IR source for a lock.  This means that to get a lock, the seeker would need an unobstructed view of the IR source.   With the 22 and 35 carrying most of their weapons in the bays, to get a lock (Target designation) for a heater outside of the radar gimble range (Off Boresight) would require the heater to be lowered outside of the bay, or mounted externally before a lock can be achieved.  

With that being said, I highly doubt that the 22 and obviously the 35 don't have the full ability to use the "9x" or the helmet.  I think it's just a matter of what gets put on the aircraft for a particular mission.  I think I heard that both aircraft can mount external pylons for weapons, I don't know if either of the two aircraft have the ability to lower or expose missiles from the bays before they take a shot.  I would guess that they cannot, since the physical engineering used to lower a weapon from the bay would take up precious space that can be used to carry more weapons.

Considering the HMCS is not only a targeting device, but also an SA device, I highly doubt the 22 drivers aren't wearing JHMCS.  

 

But I do appreciate your tenacity on trying to get me say in so many words that nowadays, systems are more important than performance...

 

Bravo...

 

So here' the deal, JHMCS doesn't fit in the F-22 cockpit for all pilots.  That's why Scorpion helmet mounted display was evaluated for Raptor (not sure if it was ever integrated).  Back in '08 or '09 when I was at Eddy's patch the -9X was integrated into Raptor.  FWIW, I saw the accident A/C takeoff that crashed on a -9X sortie that killed the test pilot, so the missile has been integrated for some time.  The HMD functionality has not been since USAF thought the LO capabilities of the Raptor were good enough not to require the need of a HMD.

[Vampyre]

15 hours ago, mkellytx said:

  Back in '08 or '09 when I was at Eddy's patch the -9X was integrated into Raptor.  FWIW, I saw the accident A/C takeoff that crashed on a -9X sortie that killed the test pilot, so the missile has been integrated for some time. 

 I remember this crash. I was the platoon commander for China Lakes Auxiliary Security Force at the time. We were tasked with responding to any aircraft/weapons incidents within 100 miles of NAWS China Lake to provide security to the areas/assets affected. It was early 2009 if I remember correctly. The jet crashed almost vertical and piled into a big crater. The pilot ejected out of envelope and ended up hitting the ground near the crater. The NAWS CO had us stand down after our initial surveillance of the area and we ended up having the Air Force take responsibility for the security of that one.

[mkellytx]

8 hours ago, Vampyre said:

 I remember this crash. I was the platoon commander for China Lakes Auxiliary Security Force at the time. We were tasked with responding to any aircraft/weapons incidents within 100 miles of NAWS China Lake to provide security to the areas/assets affected. It was early 2009 if I remember correctly. The jet crashed almost vertical and piled into a big crater. The pilot ejected out of envelope and ended up hitting the ground near the crater. The NAWS CO had us stand down after our initial surveillance of the area and we ended up having the Air Force take responsibility for the security of that one.

That would be the one.  It was an out of envelope ejection, the wind blast mortally injured him.  He was alive when the helo picked him up but died on the way to the hospital.  That SIB out brief was a mandatory all air crew call, where they made us listen to the cockpit recording.  That one stuck with me for a while.  Most of the details are covered by privilege, but the AIB should fill in enough to get the general idea.  Anyhow, enough off topic.