Operational Performace Comparison: Viper, Beagle, and Stubby

The F-35 compared with other modern jets.
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mixelflick

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Unread post28 Apr 2019, 14:03

curious... why hasn't the USAF re-engined its F-15C's with engines developing 29,000lbs of thrust? Would it not give it a thrust to weight ratio making it a better dogfighter? Or interceptor? Or all around air superiority aircraft?

The margin of superiority between it and the J-10C, SU-35 etc seems too close for comfort. This would give the Eagle something that could make all the difference in air to air combat, yes?
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mikemag

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Unread post28 Apr 2019, 14:22

All very true, but with large numbers F-35s and a few raptors operating in the battle space the F-15’s thrust to weight ratio just isn’t as important as it once was. In the world of stealth 5th gens, the F-15C gets relegated to the AMRAAM truck role. So whatever an engine upgrade would cost for the F-15 fleet, that money gets you more warfighting capability if invested elsewhere.
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Unread post28 Apr 2019, 14:42

mixelflick wrote:curious... why hasn't the USAF re-engined its F-15C's with engines developing 29,000lbs of thrust?


Reasons could include a drop in Range/endurance to go with the increased costs and you might find they would take range over a bit more thrust. Existing engines are probably fine considering they normally only do A-A configs without CFTs.
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f-16adf

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Unread post28 Apr 2019, 15:39

1. Cost aka budget.

2. Why waste money on F-15s that have FY 80-86 stamped on their tails. And many have easily 10-12k hrs on their airframes.

3. Better to use those funds on the F-22 mlu or F-35. The Eagle is a tired old bird.
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mixelflick

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Unread post29 Apr 2019, 15:25

f-16adf wrote:1. Cost aka budget.

2. Why waste money on F-15s that have FY 80-86 stamped on their tails. And many have easily 10-12k hrs on their airframes.

3. Better to use those funds on the F-22 mlu or F-35. The Eagle is a tired old bird.


I agree with all of these points. I was wondering more along the lines of why weren't they re-engined in the 90's, vs today. Up-rated Pratt and Whitney along with GE engines were available then. 5th gens didn't come along until 2005, and even then in small numbers.

I suppose they had their reasons. Right now, I just wish they'd get their act together on stamping out more F-35's and making clear to everyone it's a better air to air machine than any F-15 could ever be..
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Unread post29 Apr 2019, 17:50

Maybe if the Cold War/USSR had not ended, they would have put -229's in the A/C Eagle. But in reality with the Soviet Union gone by 1992; And with Bill Clinton and Les Aspin in control by Jan 1993 ...it didn't have a chance.
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Unread post05 May 2019, 04:48

sprstdlyscottsmn wrote:
marsavian wrote:The Meteor max range is classified but if it is that good why hide it ? I was expecting Phoenix type performance from an AMRAAM sized missile so your numbers look in that ballpark. Out of interest what is the max range at the best loft angle ?

So, my model uses a 19 degree loft angle for the AIM-120D currently. Fired from 36,000ft and 1.00M it can physically reach 94nm at 36,000ft before falling below 1.00M. It has a peak alt of just under 82,000ft and a top speed of 4.99M with a 17s motor burn time (3s boost 14s sustain).

Not to give you an example of what I mean by "I can make the max range be whatever I want"
Currently the boost stage lasts 2 seconds and the throttle-able sustain lasts 90s at full power. Minimim thrust is 1/3 of max thrust. Let's leave that be.

Zero loft results in the Meteor unable to reach 94nm. It flies at just above 2.0M at a mid-range throttle setting for 73nm and falls out of the sky around 85nm.

Loft of 3 degrees. Climbs to just over 61,000ft 80nm out before bunting over. At the bunt the missile has accelerated to 3.3M. It was able to fly faster at the minimum thrust rating because of how much thinner the air was. The motor is still burning and increases to maximum thrust as it dives on the 94nm "target" hitting it at 3.72M. It is able to have a 1.0M intercept of a target up to 154nm away after peaking at just shy of 73,000ft and 3.97M.

19 degrees of loft and it goes too high to be able to turn down and intercept (195,000ft at 92 miles at 5.7M, it is unable to pitch down)

Hmm, throttle is adjustable 10:1, not 3:1.

Now with the 3 degree loft it climbs at 2.0M for 100+nm where it is light enough and high enough that it accelerates for the next 40nm on minimum throttle. At 140nm it bunts from 80,600ft and 2.3M and throttles up, peaking at 3.5M. It hits the 154nm target now at 3.47M. Theoretical 1.0M intercept flight range? 250nm.

No loft still has the same result as before.

So, with one set of engine parameters and only changing loft, we have max ranges at which the missile flies 1.0M between 79nm for 0 degree loft and 250nm for 3 degree loft. I clearly have to change something to get a reasonable value.

Oh, BTW, my model shows a corner velocity at 36,000ft of 2.61M. With no loft the Meteor can still top out at that speed (accelerating on acquisition) to hit a 72nm target. Only 7nm difference between "NEZ" and "Rmax".

Like I said, I need to choose what I think a reasonable Rmax is and chose how I want to get there.

Is it reasonable to assume the engine of Meteor can last 90 seconds at max throttle? As far as i know even AIM-54 motor only last for 27-30 seconds
From the kinematic stand point, do you think Meteor is better than AIM-54 ?
http://media.heatblur.se/AIM-54.pdf
I also want to point out that AIM-120 from C-4 onward use full boost motor without sustain stage.
According to this study
http://www.zaretto.com/sites/zaretto.co ... t-rev2.pdf
Aim-120 motor burn time is 7-8 seconds
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sprstdlyscottsmn

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Unread post05 May 2019, 05:26

Because the meteor is airbreathing it does not carry oxidizer. For that reason it has been stated that the ISP of the Meteor motor was three times higher than traditional rockets. Since it is also a larger missile than the AIM-120 I estimated it to have a larger motor. Since it doesn't need that great of speed I figured that the long burn time would come at the cost of reduced max thrust.

Also, going 7-8 seconds boost only does not sound like the right formular for long range, and the C-7 has more range than the C-5, and the D has more range than the C-7. That study is on the C-5 only.
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Unread post05 May 2019, 05:44

sprstdlyscottsmn wrote:Because the meteor is airbreathing it does not carry oxidizer. For that reason it has been stated that the ISP of the Meteor motor was three times higher than traditional rockets. Since it is also a larger missile than the AIM-120 I estimated it to have a larger motor. Since it doesn't need that great of speed I figured that the long burn time would come at the cost of reduced max thrust.

What is the common ratio of fuel to oxydizer on AAM?
Is it 50:50 or is it 30:70? I understand Meteor not having to carry oxydizer will give it more fuel than AIM-120 use, however 90 seconds of burn time at max throttle is 11.6 times better than AIM-120C-5 and 3 times better than AIM-54? That sound a little too good to be true?
Last but not least, the diameter of Meteor body (not include inlet) is the same as AIM-120
sprstdlyscottsmn wrote:Also, going 7-8 seconds boost only does not sound like the right formular for long range, and the C-7 has more range than the C-5, and the D has more range than the C-7. That study is on the C-5 only.

I could be wrong but from what i remember C-5, C-7 and C-8 use same motor and the range improvement come frombetter trajectory ?
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Unread post05 May 2019, 09:44

mixelflick wrote:curious... why hasn't the USAF re-engined its F-15C's with engines developing 29,000lbs of thrust? Would it not give it a thrust to weight ratio making it a better dogfighter? Or interceptor? Or all around air superiority aircraft?


I agree with this.
Of course the common rebuttal is that close range combat will be rare in any future conflict and any dog fighting that will occur will be handled by the Raptor first the F-35 second before ever getting close to the F-15s which will be behind, relegated at the back as an AMRAAM truck.

However I think this is only applicable in an all out war scenario. Recently, enforcing no fly zones with very strict ROEs and very high tolerance against bandits are the ones that end in WVR with a high probability of turning into a dogfight.

The Superhornet is arguably the most capable 4th gen in avoiding dogfights (reduced RCS, high SA, AESA) but still ended up WVR against a Su-22. The F-15 is just as likely to end up in the same scenario given the same circumstance. What if its not a Su-22 on the other end this time.

But I think the F-15 specially the X model will get 229 or 129 engines specifically because they don't make 220Es anymore,
however, I'm confused, the purpose of the F-15X buy is to replenish dedicated air superiority squadrons that fly the F-15C. But the F-15X is actually a variant of the F-15QA which is actually an upgraded F-15E strike platform. And in this thread it has been established many times that the F-15E is far heavier and less kinematically capable than the F-15C.

Is there a way to make the F-15X an upgrade of the F-15C instead of an upgrade of the F-15E?
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marsavian

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Unread post05 May 2019, 11:27

Is there a way to make the F-15X an upgrade of the F-15C instead of an upgrade of the F-15E?


Of course and Boeing proposed this, F-15CX. However the USAF did not want to spend the money and it's pretty obvious why because if they are replacing F-15C now, these same EX airframes may replace old F-15E in the strike role in the future if their ANG role is eventually taken over by F-35. Having one design allows that future flexibility.
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Unread post05 May 2019, 15:11

eloise wrote:I could be wrong but from what i remember C-5, C-7 and C-8 use same motor and the range improvement come frombetter trajectory ?

And from simulations I can tell you that isn't possible. Not the 50% increase from C-7 to D that is reported.
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Unread post05 May 2019, 17:32

sprstdlyscottsmn wrote:
eloise wrote:I could be wrong but from what i remember C-5, C-7 and C-8 use same motor and the range improvement come frombetter trajectory ?

And from simulations I can tell you that isn't possible. Not the 50% increase from C-7 to D that is reported.

I found the quote:
ATK (the only manufacturer of AIM-120 motors) only makes 2 kind of motors for the AMRAAM, the baseline unit and the 5+ inch (PEP motor) that was introduced in C5.
viewtopic.php?f=54&t=9416&start=450
Could that be the trajectory of previous version is incredibly inefficient?
I wonder why USAF didn't choose to develop and purchase something similar to Meteor
3 times better burn time than AIM-54 in a AIM-120 packet, what more can you ask for?
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Unread post05 May 2019, 17:45

sprstdlyscottsmn wrote:And from simulations I can tell you that isn't possible. Not the 50% increase from C-7 to D that is reported.


Due to drag or kinematics?
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Unread post05 May 2019, 19:06

madrat wrote:
sprstdlyscottsmn wrote:And from simulations I can tell you that isn't possible. Not the 50% increase from C-7 to D that is reported.


Due to drag or kinematics?

yes.

Okay, for the sake of discussion I will fire up my latest stable version of my missile guidance and performance simulator. For this discussion all shots will be head on at 36,000ft with shooter and target moving 0.9M.

I will start with the standard AIM-120C-5 Motor as I know it (135lb fuel, 265ISP) and give it an 8 second burn (gives 4,470lb thrust) and a 0 degree loft. (link to the atk site is a dead link, but with it having been referenced I will accept that it was true) I will check what launch ranges result in the missile still moving Mach 1+ at impact.

0 deg loft
a 41nm shot gives a final speed of 1.01M, peak speed of 4.85M, and a final distance of 28.4nm.

5 deg loft
a 44nm shot gives a final speed of 1.02M, peak speed of 4.87M, and a final distance of 31.5nm.

10 deg loft
a 53nm shot gives a final speed of 1.03M, peak speed of 4.85M, and a final distance of 38.2nm.

15 deg loft
a 71nm shot gives a final speed of 1.00M, peak speed of 4.84M, and a final distance of 51.0nm.

20 deg loft
a 95nm shot gives a final speed of 1.01M, peak speed of 4.81M, and a final distance of 68.7nm.

Well. I need to eat (my words/crow/humble pie).

The AIM-120D setup I was using was 150lb propellant, 3s boost (at 2.6:1 ratio) and 14 sec sustain with a 19deg loft. Using the above firing scenario gives a 124nm shot gives a final speed of 1.02M, peak speed of 4.92M, and a final distance of 92.5nm.

I was "calibrating" it with a 33,000ft shot from 1.02 to a 33,000ft 0.83M target (effectively the MINIZAP setup) which yielded a 111nm shot for a 1.0M finish (I was looking for a 1.2M finish in calibration).

Back to the drawing board. Thank you eloise for challenging my assertions and assumptions. Not only can max range drastically increase, but the range at which the missile still has high speed increases as well.
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