Operational Performace Comparison: Viper, Beagle, and Stubby

The F-35 compared with other modern jets.
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sprstdlyscottsmn

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Unread post15 Feb 2019, 15:32

There are many problems with using you-tube videos, so I will go over them here.

1: No air data available. We don't know the speed the aircraft are flying and we don't know the density altitude. I know from looking over the documentation for USAF demo routines that speed drops during these turns, and as such they do not represent sustained turn capability but average transient capability instead.

2: Perspective. As the videos are all shot from the ground we do not have accurate representation of when the flight heading of an aircraft reaches it's original course. All we can really see is nose/tail position relative to the camera. This only gets further confused as AoA changes throughout the turn. This is especially relevant to a half turn.

3: No vehicle data available: We don't know what these aircraft weigh in this moment.

Demos are fun, no doubt about that, and watching an aircraft turn tight and fast is always impressive. If you want to compare demo vids to see who puts on the best airshow turn, that's fine. I've done that myself. But no video only evidence will be sufficient to generate a performance model.

FWIW, I can promise you a Cessna 172 can perform a 180 degree heading change in 4 seconds at 7,000ft density altitude.
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Unread post15 Feb 2019, 19:31

sprstdlyscottsmn wrote:FWIW, I can promise you a Cessna 172 can perform a 180 degree heading change in 4 seconds at 7,000ft density altitude.


Isn't that close to the stalling speed ? I vaguely remember the G-limit on the 172P being 3G IIRC, and using that number, I get something like 68.7 knots TAS for that angular speed, in a horizontal constant speed turn.
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Unread post15 Feb 2019, 19:57

viper12 wrote:
sprstdlyscottsmn wrote:FWIW, I can promise you a Cessna 172 can perform a 180 degree heading change in 4 seconds at 7,000ft density altitude.


Isn't that close to the stalling speed ? I vaguely remember the G-limit on the 172P being 3G IIRC, and using that number, I get something like 68.7 knots TAS for that angular speed, in a horizontal constant speed turn.

G limit is 4.4, but there is no G readout in the plane. And while I did not lose altitude, I did lose airspeed. I went from 100KIAS to ~70KIAS. In losing speed I lost G. I was riding the stall horn the whole way around.
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Unread post22 Mar 2019, 17:27

I need to learn when to leave well enough alone. Decided to see if I could alter my missile sim to allow Meteor to be throttle-able. I got THAT to work... and somehow broke something unrelated. Max range is now truly insane. This may need some more tweaking.
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marsavian

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Unread post22 Mar 2019, 17:30

Max range is now truly insane.


Maybe you accidentally discovered the truth ! Lol :D
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Unread post22 Mar 2019, 18:01

marsavian wrote:Maybe you accidentally discovered the truth ! Lol :D

well the problem is that I can MAKE the max range be whatever I want my altering parameters. It's a balancing act to see if the parameters make sense and if the results make sense. If everything makes sense then I call it good. For example, if I say the Meteor has zero loft then it has a "90" mile max range, if I say it lofts to 3 degrees then it has a "160" mile max range. Granted that is in line with that once old document stating the yet to be developed MBDA missile that would become the Meteor was to have a 300km range, so I don't know.
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Unread post22 Mar 2019, 22:17

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 ?
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Unread post22 Mar 2019, 23:06

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.
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marsavian

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Unread post22 Mar 2019, 23:39

Very interesting set of results. Could you work back say from an assumption that Meteor NEZ is twice that of the AIM-120D to estimate the minimum/maximum throttle factor and then get the range ? Also from the perspective in this video the Meteor does appear to have a slight angle of climb/loft.

https://youtu.be/8dAmfVlcbp4?t=1m24s
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Unread post23 Mar 2019, 09:42

I've posted this before on another thread, but I personally think that absolute max range is not too relevant in BVR combat.
No one has ever shot down enemy aircraft from absolute max ranges, I think even the Iranian claims which are the furthest kills ever claimed were just around 50 NM which is well within the range of most BVR missiles.

BVR really happens within a 20 nautical bubble, whats important is what you can do inside that 20 nautical mile BVR bubble.
How effective are your ECM, ESM, sensors, data links and RCS, IR reductions within that bubble is what counts. So the Aim-120D carried by an F-22/35 is far more lethal than a Meteor carried by a Gripen.
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marsavian

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Unread post23 Mar 2019, 10:41

Both these missiles have two way datalinks so they can be guided in against countermeasures so the final energy state is important regardless of distance already travelled. Meteor's variability in that regard may change normal assumptions about decreasing lethality with missile range.
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Unread post23 Mar 2019, 14:34

Theoretically what is the loft angle that maximizes range? Is it 45 deg? Have been curious about this for long time. :mrgreen:
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Unread post23 Mar 2019, 15:57

gta4 wrote:Theoretically what is the loft angle that maximizes range? Is it 45 deg? Have been curious about this for long time. :mrgreen:

Closer to 20. You have to remember that a 45 degree loft means is the missile lofts for 20nm it also goes UP 20nm.
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Unread post23 Mar 2019, 19:06

Except with a sustainer motor you don't magically cut drag. Your loft would give a trajectory for optimal energy, so it's probably over 45 degrees for lonng distance shots, with a dive optimal for execution of an intercept. Missiles with no ability to sustain power have a range chart that looks like a mushroom. The same type of chart for the former (loft trajectory with sustainer motor) looks quite different.

/realizes I'm thinking SAM, not AAM
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Unread post24 Mar 2019, 01:25

madrat wrote:/realizes I'm thinking SAM, not AAM

Yes, when I was building S-400 missile models a 45 degree loft was optimal. Starting from "0-0" sucks.
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