Viper with the Hornet's slow speed handling?Possible or not?

Unread postPosted: 23 Apr 2019, 14:49
by Patriot
I just have a simple question or at least theoretically.
Would it be possible to add to the existing Viper the slow handling characteristics close or equal to what F/A-18 have? What would it eventually take? A software changes or design changes would be needed as well and if.. how deep that changes would have to be to achieve Hornet slow flight abilities? And if so, could it be done without sacrificing Viper legendarny well-established high speed, high energy, high rate, high g performance or virtually there is no such thing as mastering the entire envelope in aerospace business and there's always a tradeoff... so you get certain abilities at the expense of others abilities?
Here Im thinking about the Eurofighter Typhoon that seem to be actually good on both ends of the envelope. Flies good slow, low, fast and high.

From my own little understanding.. the higher the AOA gets the lowest the stability capacity becomes in all three axis, x, y and z. So to make Viper better at low speeds the effort would have to be put to increase Viper's stability at high AOA and probably enhance it's roll/pitch authority?

Re: Viper with the Hornet's slow speed handlin? Possible or

Unread postPosted: 23 Apr 2019, 14:58
by sprstdlyscottsmn
Well, even the Typhoon is not a master of all. The Typhoon is closer to a Viper in that it rules the high speed low AoA game. The AMK modification will improve it's low speed game, but that has not been ordered yet IIRC. The Viper has inherently too little stability. Go to high AoA and the nose won't come back down without rocking back and forth. You would need larger/further aft horizontal tails to increase the nose down pitch moment available. It may also require twin tails, not sure. So in short, I do not think a SW update would give the Viper airframe as is the low speed high AoA ability of a Hornet.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 23 Apr 2019, 15:14
by Patriot
I see. So the changes to the airframe would have to be considerable and that would likely mean more mass/drag so that would likely (I guess) undermine the well-established sustained turn/high g/superb acceleration characteristics that Viper own.


So, where exactly Viper outperforms Typhoon? Sustained turn rate @ 400-500 knots speed range, better g-/energy conservation, better acceleration @ low alts?

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 23 Apr 2019, 15:36
by sprstdlyscottsmn
I've heard that under 10-15,000ft the Viper can match the Typhoon. Above that the thrust advantage of the Typhoon must help greatly. I don't think the Viper has any true EDGE over the Typhoon. I was just saying that the Typhoon is not a Hornet like low speed machine.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 23 Apr 2019, 17:23
by Patriot
So the Viper moves arround within the preset limit of 26° AOA.
Lifting this limit to say 35° AOA wouldnt help improve slow speed handling? or maybe 35° is way beyond natural stability treshold of the Viper which sits arround that 26°? I just wonder if this would work if the flight control software would be altered to allow 35° AOA when slow - anywhere below 300 indicated?

And if talking Eurofighter. I think its superiority really comes down to 2 things: 1. excess power 2. big wings/small wing-loading. The sheer thrust just eliminates most if not all of negative side effects of its delta-ish wings (deltas naturally lose energy quickly) and the induced drag corelated with having big lifting surface area as well as big wings help to stick well to the air on high alpha and in thin air up high.

I still think, as you said, below 15K and the lower the better Viper still turns better even if the difference is marginal.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 23 Apr 2019, 17:58
by f-16adf
Lift limit for the F-16 is about 35 AOA. Beyond that it loses directional stability. And above 50+ AOA is deep stall territory. The Limiter on the F-16 is placed there for energy conservation.


I'm guessing even if they would of put 2 vertical tails on the F-16, it would not really have mattered because GD wanted the limiter there in the first place (for energy conservation, --that is what separates the F-16 from the other teen series). 2 tails would have meant more weight and cost vs single tail.


Interesting YF-16 video at various AOA:
https://www.youtube.com/watch?v=nrc5M0S ... e=youtu.be




For what it's worth, I have an old issue of WAPJ. And it says Eurofighter at 20,000ft and about Mach .9 can out turn all previous jets, ....except F-22 Raptor.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 23 Apr 2019, 18:07
by sprstdlyscottsmn
pitch-moment.jpg


Here are the actual curves for the F-16. You can see that at 35AoA the tails will be working to hold the nose down and have limited authority to reduce AoA. Also, the F-16 is only allowed 25AoA at 1G due to the CAT-1 schedule. There is no flying around pulling 5-9G at 25 AoA in an F-16.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 23 Apr 2019, 18:54
by Patriot
Great infos guys. :thanks:

sprstdlyscottsmn wrote:There is no flying around pulling 5-9G at 25 AoA in an F-16.

So what is the AOA when the Viper is turning low to the ground at 450kts/9g at its apex rate of 25degs/s?

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 23 Apr 2019, 19:23
by sprstdlyscottsmn
Patriot wrote:So what is the AOA when the Viper is turning low to the ground at 450kts/9g at its apex rate of 25degs/s?

The AoA limit for 9G is 15 degrees.

F-16CD AOA-G Limiter Function (Cruise Gains).gif

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 15:27
by Patriot
f-16adf wrote:Lift limit for the F-16 is about 35 AOA. Beyond that it loses directional stability. And above 50+ AOA is deep stall territory. The Limiter on the F-16 is placed there for energy conservation

However the F-16 with MATV nozzle demonstrated directional stability up to 120° of AOA 8)

https://youtu.be/dj8OJs6E3JM

So from the energy conservation standpoint the 25 degree limit is optimal. Im guessing that if the limit would be set to 28 or 30 (still below 35) degrees the Viper could have better instaneous turn capability and could achieve more g but the energy conservation and thus the sustained turn rate would suffer?

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 17:18
by sprstdlyscottsmn
Peak ITR in the Viper occurs at around 8G due to the Cat-I limiter, so thats only 18 degrees AoA. Even if they opened it up to 25 degrees across the G range you would see more ITR and much more deceleration.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 17:20
by basher54321
From what was released and demonstrated in A-A the MATV added low speed capability far better than the legacy FA-18 and more towards the F-22. (if not better). Cold War budgets ended that luxury add on like a lot of things.

TV provides the required directional stability and control the normal surfaces cannot at the higher AoA and likely eliminated Deep Stall.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 17:35
by sprstdlyscottsmn
basher54321 wrote:From what was released and demonstrated in A-A the MATV added low speed capability far better than the legacy FA-18 and more towards the F-22. (if not better). Cold War budgets ended that luxury add on like a lot of things.

TV provides the required directional stability and control the normal surfaces cannot at the higher AoA and likely eliminated Deep Stall.

Correct. When the MATV style nozzle was put on the F-15 SMTD to become the F-15 ACTIVE, well the results cannot be publicly discussed, but let's say it would be jaw-dropping. All that I can definitively say is that the engines on the ACTIVE were "better" than -229/-129 class.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 20:28
by Patriot
What you guys would say on this comparison? Looks nice but is it legit?

https://youtu.be/B8CAQ2HQQiw

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 20:55
by sprstdlyscottsmn
Falcon 4 BMS 4.33 is wthout a doubt the most accurate performance model of an F-16 available to the public. It does not hold that claim for the F/A-18C. THAT goes to DCS. So the F-16 performance you see may be within an acceptable margin of error from reality, but the F/A-18 is likely not. The margin of error on the DCS F/A-18C Block 20 is likely smaller than the margin of error for a BMS 4.33 F-16C Blk50/52.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 21:04
by Patriot
Roger copy.

Btw, Ive never up until now heard of "paddle switch" that is attached to the stick in the Hornet. I guess the MPO switch in the Viper cannot be used for augmenting manuverability in combat, only to do a post-stall recovery, right?

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 21:23
by sprstdlyscottsmn
Correct

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 21:28
by Patriot
So, what would have happen if Id flip the MPO switch while being in the middle of 9g turn in the Viper? Can it be activated from the HOTAS or a pilot can enable it only by reaching out to the cockpit?

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 22:15
by sprstdlyscottsmn
I know it is not a HOTAS control, but AFAIK all you would do is rapidly enter a deep stall. You would have no way to manage your AoA.

Think of it this way, the control logic would toggle from "Give me whatever tail deflections are needed for me to be at nine-g right now (tails level to slightly trailing edge up based on the pitch moment chart)" to "Give me full trailing edge up range of motion on the horizontal tail and do it right now". The result would be uncontrollable pitchup well past stall AoA.

Not only does the F-16 have a high nose up pitch moment at "Stick Full Back" at 0-15 AoA, but it only gets greater until past 25 degrees AoA. Not only does your pitch increase, but the rate at which your pitch increases keep increasing until this point. By 50 degrees AoA your rate of pitch increase has slowed to what it was when you hit the switch, but it still going up rather fast. By the time the rate of pitch increase has slowed to where you realize what happened you are likely already at 60 AoA and deep stalled. The good news here is that you already hit the MPO switch so you can begin trying to rock yourself out of the stall, but your position in the fight is lost.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 22:40
by ricnunes
A "Viper with the Hornet's slow speed handling"?

Well that would be a F-35A :wink:

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 23:18
by sprstdlyscottsmn
ricnunes wrote:A "Viper with the Hornet's slow speed handling"?

Well that would be a F-35A :wink:

Yeah, I went out of my way to not go there and stick with the issues of the F-16 airframe.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 24 Apr 2019, 23:43
by Patriot
I personally still have a hard time to understand how in the world this obese flying concrete mixer (bomb) truck with its tiny wings and huge wingloading can have better slow speed autorithy / high alpha stability / handling properties than the sleek sexy Viper.. :doh:

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Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 25 Apr 2019, 01:01
by madrat
The F-35 looks like a v-hull boat whereas the F-16 looks like a catamaran with thin hulls.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 25 Apr 2019, 01:54
by johnwill
Patriot wrote:So, what would have happen if Id flip the MPO switch while being in the middle of 9g turn in the Viper? Can it be activated from the HOTAS or a pilot can enable it only by reaching out to the cockpit?


If you could do that, you would almost certainly be faced with instant disintegration of the airplane. If you have the airspeed for 9g (probably above 400kt), wing/fuselage lift and down tail load will rapidly increase AoA, g, and structural load, resulting in rapid disassembly of the airplane.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 25 Apr 2019, 10:30
by Patriot
Roger that John. That make sense. The loads raise exponetially with speed so the aoa and likewise turn rate at some point have to be limied more and more so the loads wont kill the plane and the pilot.

What if Id do the same at lower speed.. at arround 250-350kts when pulling say 4-6gs? That's the speed range where Hornet or Raptor does their vertical takeoff consisting of massive onset of turn rate. Does in the Viper a momentary increase of max stab deflection by let's say 50% would help in moving the nose effectively at an adversary aircraft (lag pursuit ---> pure/lead pursuit) or help do similar vertical takeoff without loss of control?

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 25 Apr 2019, 16:05
by johnwill
Cannot really say. You're trying to do something the airplane wasn't designed for. To be safe, you'd need to do a complete analysis of tail loads, wing loads, fuselage loads, pitch acceleration, internal equipment loads, etc.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 25 Apr 2019, 16:28
by sprstdlyscottsmn
johnwill wrote:Cannot really say. You're trying to do something the airplane wasn't designed for. To be safe, you'd need to do a complete analysis of tail loads, wing loads, fuselage loads, pitch acceleration, internal equipment loads, etc.

This is the part I focused on. The F-16 was not meant to fly without the computer. The MPO was for deep stall recovery only as the plane was already not flying at that point.

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 25 Apr 2019, 23:09
by marsavian
Patriot wrote:I personally still have a hard time to understand how in the world this obese flying concrete mixer (bomb) truck with its tiny wings and huge wingloading can have better slow speed autorithy / high alpha stability / handling properties than the sleek sexy Viper.. :doh:

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Looks can be deceiving ;). This has been discussed many times before on this forum especially in the F-35 vs Rafale thread but basically at the front end the F-35 has a lot of features that keep generating vortex lift at very high AoA, lerx/strakes/chines, while at the back the big twin tail surfaces give great directional authority at this high AoA. The end result is that it points very well and can extricate itself from this extreme pointing with no stalling or energy deficiencies i.e. quickly. It's actually a very clever design to get such a short boxy stubby shape to maneuver so well at all AoA especially when it is primarily optimized for stealth !

https://www.quora.com/How-is-the-aerody ... ogfighting

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Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 26 Apr 2019, 19:42
by Patriot
Good post. Thank you.
So aerodynamically it looks like the low wingloading is the least important factor for the ability to fly slow (up until recently I thought rather otherwise). It looks to me like F-35 thanks its slow speed controlability to the huge stabs and to the fact its tail has roughly 2x the surface area of the F-16 tail. Big stabs, big tail, big rudder working together = lots of directional authority almost like with TV nozzle

Re: Viper with the Hornet's slow speed handling?Possible or

Unread postPosted: 26 Apr 2019, 23:57
by marsavian
Low wing loading gives you better sustained turn rates and high thrust/weight ratio gives less energy bleeding in an instantaneous turning state. Low wing loading does help you fly slower but only in a sustained state which is why the F-35C has the bigger wings. High AoA ability is about generating vortex lift over your wings after the main wing has stopped producing most of its lift in a raised state so usually canards, strakes, chines, leading edge root extensions and other forward protuberances.

Alternatively you can just cheat like the Russians do and have TVC nozzles which provide angled thrust instead of lift however without lift all you are doing is pointing while you are falling. Having big widely spaced twin tails then help you control direction at high AoA. The F-16 is primarily a high energy sustained turner and its FCS has deliberately left a little AoA/instantaneous ability on the table to deliver this goal optimally as it will never match a Hornet or F-35 in AoA ability so doesn't bother trying to by hampering its main strength, continuous turning. At sea level the best sustained turner even now is either an F-16 or Flanker depending on fuel load. F-16 also accelerates and climbs very well, it's a classic hotrod.