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

Patriot · by **Patriot** » 23 Apr 2019, 14:49

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?

sprstdlyscottsmn · by **sprstdlyscottsmn** » 23 Apr 2019, 14:58

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.

Patriot · by **Patriot** » 23 Apr 2019, 15:14

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?

sprstdlyscottsmn · by **sprstdlyscottsmn** » 23 Apr 2019, 15:36

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.

Patriot · by **Patriot** » 23 Apr 2019, 17:23

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.

F-16ADF · by **F-16ADF** » 23 Apr 2019, 17:58

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.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 23 Apr 2019, 18:07

: pitch-moment.jpg (30.56 KiB) Viewed 12930 times

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.

Patriot · by **Patriot** » 23 Apr 2019, 18:54

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?

sprstdlyscottsmn · by **sprstdlyscottsmn** » 23 Apr 2019, 19:23

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.

Patriot · by **Patriot** » 24 Apr 2019, 15:27

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

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?

sprstdlyscottsmn · by **sprstdlyscottsmn** » 24 Apr 2019, 17:18

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.

basher54321 · by **basher54321** » 24 Apr 2019, 17:20

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.

sprstdlyscottsmn · by **sprstdlyscottsmn** » 24 Apr 2019, 17:35

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.

Patriot · by **Patriot** » 24 Apr 2019, 20:28

What you guys would say on this comparison? Looks nice but is it legit?

https://youtu.be/B8CAQ2HQQiw

sprstdlyscottsmn · by **sprstdlyscottsmn** » 24 Apr 2019, 20:55

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.