Trying to understand incredible shake rattle and roll of T-Cat when pulling G with wings out.

[DmitriKozlowsky]

Why does it shake so violently? Seems the entire aircraft is about fly apart. Other air-air , high fidelity flight model aircraft don't do that, unless they are stalling.

[BreaKKer]

It's the buffet. It happens when the wing is close to a stall or stalling. The F-15 has something similar, but not present on the FC3 F-15. 

[Jackjack171]

You have to handle the Tomcat with respect! She will talk to you and tell you that she doesn't like it when you pull too hard, just like your lady! I have a blast flying her. She's the only thing I fly as of late. Lot's of ACM and pattern work!

[draconus]

9 hours ago, DmitriKozlowsky said:

Other air-air , high fidelity flight model aircraft don't do that

You're not comparing modern FBW to the AFCS Tomcat, are you?

[TLTeo]

FBW has little to do with how much the aircraft buffets at moderate AoA. Plenty of DCS modules with non FBW controls also have little buffet (e.g. the Sabre).

 

Ultimately, physical feedback from the airframe is something that is not easy to translate into a computer sim, and to some extent it's down to developer choice. According to SMEs, the Tomcat was one of the more communicative jets in that sen, so HB have settled on it being much more prominent than in other aircraft (like the Sabre I mentioned - although the Viggen and even Mig-21 are similar ish).

[wowbagger]

I find most of the modules don't give enough (barely any) feedback of this sort. They feel far smoother and less affected by aerodynamic forces than even any jumbo jet I've ever been on.

 

It's one of the things that sets the Tomcat apart from say... the Hornet. And I love this feedback. It feels much more like I'm in a real aircraft instead of just managing some video screens in a tiny office with too many beeps and bings.

[DmitriKozlowsky]

3 hours ago, draconus said:

You're not comparing modern FBW to the AFCS Tomcat, are you?

Well DCS: Mig-21Bis departs into spin or wackly pitch up when over-g, or held at high G for too long. A stall in level flight is preceded by buffet, but nothing like DCS: F-14B.

[BreaKKer]

24 minutes ago, DmitriKozlowsky said:

Well DCS: Mig-21Bis departs into spin or wackly pitch up when over-g, or held at high G for too long. A stall in level flight is preceded by buffet, but nothing like DCS: F-14B.

2 completely different aircraft with completely different designs

[DD_Fenrir]

My 2-cents:

 

At high AoA the stabilators and the vertical tail surfaces will be in the aerodynamic shadow of the "pancake" and will be subject to the turbulent airflow coming off it, plus the "pancake" is so large that it itself will be being hammered by the turbulence generated from the leading edges. The "pancake" is large so significant amounts of turbulent airflow will be generated and at anywhere above 15 units where the ratio of lift-drag starts to favour the latter, you will be generating a lot of turbulence.

 

Ref: the MiG-21 comment, I find it surprising that this needs to be asked; the MiG was designed 15 years before the Tomcat and represents the manned missile school of interceptors; the Tomcat represents one of the first 4th generation aircraft where consideration of high AoA controllabilty and agility was a major factor. The thing was literally designed to out-rate and out-radius the MiG-21 and F-4 - these two were used as benchmarks to improve upon as part of the design specification.

[DD_Fenrir]

BTW: if you're spinning at high AoA you've either:

 

1. Stayed beyond 15-17 units of AoA too long and let the speed get too low, or
2. You're trying to roll using lateral stick inputs above 20 units AoA, or
3. Both

Learn to dogfight keeping the AoA to 15-17 units and be patient. Also remember to coordinate rudder and lateral stick at this mark. Take brief excursions to the 20 and above mark if you must to defend or gain angles but regain the energy spent as soon as you can by unloading when possible. And if you must make rolling manoeuvers at anywhere above 20 units then DO NOT USE LATERAL STICK; keep it centered and work the roll using the rudders; there is significant roll inertia using pedals in this regime but you can get used to it. Use the stick and the spoilers will induce roll OPPOSITE to the way you wish to roll. Also if engaging in BFM it is advisable to disable the Roll Stability Augmentation System to help mitigate uncommanded roll inputs being generated by the system in it's attempts to keep up your inputs in the high AoA regime.

[GGTharos]

13 hours ago, BreaKKer said:

It's the buffet. It happens when the wing is close to a stall or stalling. The F-15 has something similar, but not present on the FC3 F-15. 

 

Yes it does, it's just not as servere.  Different aircraft, different handling.

 

2 hours ago, DmitriKozlowsky said:

Well DCS: Mig-21Bis departs into spin or wackly pitch up when over-g, or held at high G for too long. A stall in level flight is preceded by buffet, but nothing like DCS: F-14B.

 

Different aircraft, different developers.  In the end it's all about AoA.   Less AoA, less shaking.

Edited January 4, 2021 by GGTharos

[Skysurfer]

It's called vortex lift. The Hornet and F-16 buffet at high AOA as well. It's turbulent air hitting the wing and stabilators/tail.

[DmitriKozlowsky]

This vortex lift buffet, wreacks havoc on gun shot. That means also the seeker of AIM-9 is shuddering and gimbal has to compensate. 

[DmitriKozlowsky]

Trying similar turn rates and speeds in Viggen. There is also buffeting, and stall warnings, but nothing so violent. Now that I know what it is, I'll to work with it. One of my difficulties is performing a proper YO-YO. The up , then bank with rudder and little to no lateral stick, gets me every time. Aircraft doesn't quite is doing what I want it do. At the apogee is where I have problems, nose drops by itself without authority, and leaves in in low energy, and pointed at .. Well any number of directions except the enemy.  No wonder I prefer strike fighter missions.

[DmitriKozlowsky]

Buffet at high G, but NOE flight and no buffeting. However DCS may not support low level flight buffet. But it was issue with F-111, B-1B, BUFF, and Tornado. In Syria, when flying between mountains, and through valleys, shouldn't there be higher turbulence.

[RustBelt]

5 hours ago, DmitriKozlowsky said:

This vortex lift buffet, wreacks havoc on gun shot. That means also the seeker of AIM-9 is shuddering and gimbal has to compensate. 

Well, work on your lag turn so you're not so far up the AOA when you try to pull off a shot.