Me 262 Mach tuck

[R33GZ]

I suspect this is a stupid question.... but, is there any way to prevent Mach tuck at high speeds?

 

Finally getting the beast started after multiple engine fires, I took her up to 10k and initiated a split s dive, which turned my jet into an extremely fast coffin. No dive brakes, flaps don't work, can't bail out at warp factor 10 Mr Sulu.

 

I'm guessing the answer is just "don't go that fast" ?

[AndyJWest]

Avoid Mach tuck? Yup, don't exceed the critical Mach number...

 

This is a fundamental physical/aerodynamic effect, in the real aircraft, and others that followed. It took time (and a few dead test pilots) for aircraft designers to figure out solutions, and until they did, the only safe way to fly was to avoid it. If IL-2 GB makes recovery difficult or impossible, it is getting it right.

 

 

Edited January 1, 2023 by AndyJWest

[R33GZ]

Still learning this beast. Took me about half hour to not turn it into a burning wreck on the apron ?

 

I noticed also that I flamed out the engines when attempting to reduce throttle in the dive. I hadn't reduced by much, but unsure exactly how much... probably more than I thought. Any idea what the flight idle RPM is? 

[migmadmarine]

Generally keep the throttles above 6,000 rpm as I recall, as that is the threshold over which where you can slam the throttles forward without fear of igniting the engines. Preventing flaming out when pulling the throttles back is not a result of pulling them back too far, but too fast. You need to be very, very slow on your throttle reductions. 

[Yogiflight]

9 hours ago, R33GZ said:

I noticed also that I flamed out the engines when attempting to reduce throttle in the dive. I hadn't reduced by much, but unsure exactly how much... probably more than I thought. Any idea what the flight idle RPM is? 

In high altitudes, the problem is the temperature. If it falls below 450°C (I hope I remember the temperature correctly), your engines die. You first have to go to a lower altitude and wait for the engine temperature to rise again before you can throttle down.

[Thorne]

The Split-S of doom has happened to all of us at some point - and the crazy part is you don't even need to be transonic in a 262 to experience it.

 

A helpful hint, the missing and critical component to your meteoric fall has a lot more to do with our throttle position than I think you realize, I can almost assure you that your throttle was open a little too far when attempting the ill fated Split-S, which coupled with your high airspeed at the time was a death sentence. You'll find that moving your throttle to idle before inverting, and then pulling a fair amount of G through to the other side will mitigate hazardous acceleration even if you're already at a very high airspeed. It will also reduce the diameter of your downward arc, further protecting you against unwanted acceleration and altitude loss, finally you'll be able to get guns on faster.

 

Try it out again both ways (open and closed throttle) to diagnose the problem - you'll be happy you did. 

Edited January 2, 2023 by Thorne

[R33GZ]

Thanks for the info gents ?

[Verbum_Vincet]

Don't forget the trim tabs! As the others have said, best practice is to avoid exceeding critical mach but it is easy to get distracted in the heat of battle. Using the 262's electric trim controls, I've occasionally managed to avoid getting too far into mach tuck and/or pulled out just in time by cranking to full tail-heavy and holding full back pressure on the stick.

[Yogiflight]

10 hours ago, Verbum_Vincet said:

Don't forget the trim tabs!

You mean the trim lever. But you are right about the effectivity. The elevator doesn't have that much effect in high speeds, the stabilizer trim is much more useful here.

[Guest deleted@50488]

Which brings a question I was willing to ask:

 

- does IL-2 Flight Dynamics Model calculate the effects of wing sweep on the Coeficients of Lift and Drag, as well as in Total Drag, near the Critical Mach and through transonic regime?

 

I am referring to, ss an example of what can be found from many sources over the Internet:

 

https://aerodyn.org/sweepback/

 

https://www.boldmethod.com/learn-to-fly/aerodynamics/wing-sweep/

 

Is the cosine rule applied, or even better, one of the variants that takes into consideration the fact that wings are finite and spanwise flow can also create lift, thus reducing the impact by the square root or even the 3/4 power of the cosine ?

Edited January 3, 2023 by cagarini

[[CPT]Crunch]

Does it also model tail plane blanking when trying to pull at or near compression, cause that tail sits slightly above the wing plane.  Other planes in similar configuration suffered the same effects like Starfighter's and Voodoo's.  Pretty much  figured it out and eliminated it with the F-4 Phantoms angled stabulators, they tend to put the angle up top now days such as Hornets, Felons, and Raptors. 

[AndyJWest]

4 hours ago, cagarini said:

Which brings a question I was willing to ask:

 

- does IL-2 Flight Dynamics Model calculate the effects of wing sweep on the Coeficients of Lift and Drag, as well as in Total Drag, near the Critical Mach and through transonic regime?

 

I am referring to, ss an example of what can be found from many sources over the Internet:

 

https://aerodyn.org/sweepback/

 

https://www.boldmethod.com/learn-to-fly/aerodynamics/wing-sweep/

 

Is the cosine rule applied, or even better, one of the variants that takes into consideration the fact that wings are finite and spanwise flow can also create lift, thus reducing the impact by the square root or even the 3/4 power of the cosine ?

 

You could ask the developers, but I doubt they'd give an answer that satisfied you - they don't seem to see the need to discuss the inner workings of their flight modelling, when it is the results that matter in IL-2 GB. 

 

With regard to the Me 262, the 15° or so of wing sweep from the engine nacelles outboard only isn't going to have much aerodynamic effect. The wings weren't swept because of Mach effects, they were modified from the original unswept design because of CG problems.

[Verbum_Vincet]

13 hours ago, Yogiflight said:

You mean the trim lever. But you are right about the effectivity. The elevator doesn't have that much effect in high speeds, the stabilizer trim is much more useful here.

 

Thanks, good looking out! Been a while since I flew the 262, but I believe it's the lever to port with the red circular knob on the end and activated via trim key. Controls tailplane incidence, like on 190A's and 109's. Gotta love that German engineering! I recall reading they trained Turboflieger using Bf-110's with throttles locked in one position. Never tried it in sim, though.

[Avimimus]

On 1/1/2023 at 5:26 PM, R33GZ said:

I suspect this is a stupid question.... but, is there any way to prevent Mach tuck at high speeds?

 

At least one Me-262 test pilot is suspect to have died on account of exceeding the VMax and encountering this... so it seems to be historical (and I'm glad you were just flying a simulator)!

[AndyJWest]

A nice video showing what happens to airflow around an airfoil as it reaches critical Mach.

 

[Crocogator]

5 hours ago, Verbum_Vincet said:

 

Thanks, good looking out! Been a while since I flew the 262, but I believe it's the lever to port with the red circular knob on the end and activated via trim key. Controls tailplane incidence, like on 190A's and 109's. Gotta love that German engineering! I recall reading they trained Turboflieger using Bf-110's with throttles locked in one position. Never tried it in sim, though.

Here it's a yellow port side sliding lever. The stabiliser basically saves you in the 262. Set it to a lever or wheel on your throttle and you will wake up after most blackouts just rolling around in the sky, rather than lawn-darted and buried.

[AndyJWest]

Wandering a little off topic, I've just come across an interesting article on why a poor choice of propeller aerofoil may have crippled the high-altitude performance of the Westland Whirlwind.

 

WHEN THE WIND WON'T WHIRL - OR THE REAL REASON THE WHIRLWIND SUFFERED AT HEIGHT

 

Yup, it's a Mach-related issue again. The propeller blades were reaching Mcrit well before they needed to, due to their thickness. And it appears that the issue was well-enough understood, though nobody seems to have told Westland. And then Westland went on to design the high-altitude Welkin, which would have performed a whole lot better with a thinner wing, even if they had to reduce the aspect ratio substantially. Like the later U-2 spyplane, it found itself in 'coffin corner' at altitude, with only a few knots between Mach-induced shock stall and its conventional stalling speed. Just about acceptable in a recon aircraft, but not something you really want in a high-altitude interceptor.

 

 

 

[Holtzauge]

A lot of interesting info in this thread! In particular the films @AndyJWest linked to were very instructive and especially interesting I think. Not often you can see such a good explanation of Mach effects like that.

 

Some Il-2 history to go along with the theme of this thread:

 

While I don't know the inner workings of the current IL-2 flight model when it comes to compressibility effects, I do know that this was missing in the earlier releases: As the attached picture shows, this was a problem a number of us forum users identified at the time since we noticed that the aircraft in-game were attaining speeds far greater than they would have been able to IRL since in-game measurements like the P-51 example below, showed that the drag rise when approaching transonic Mach numbers was simply missing.

 

The curves from my C++ simulation and the measured speed are slightly offset due to the starting point of the dive being slightly different, but if you move back the red curve as measured in Il2 about 2.5 s (shown in black), you can see that the two simulations are very close to each other for the first 20 s. However, at this point the Il-2 model kept on accelerating due to the Cdo being constant.

 

This has since been fixed in Il-2, and if someone has the time and inclination to redo the test it would be interesting to see how this is now modelled in IL-2.

 

 

PS: If you want to know more about the C++ simulation model, I have described it on this page on my website.

 

[FeuerFliegen]

On 1/3/2023 at 5:29 AM, Yogiflight said:

You mean the trim lever. But you are right about the effectivity. The elevator doesn't have that much effect in high speeds, the stabilizer trim is much more useful here.

 

If you want to be correct on terminology, it's not trim at all.   It's simply an adjustable stabilizer. 

[Yogiflight]

51 minutes ago, SCG_FeuerFliegen said:

adjustable stabilizer.

too long. I was out of letters, so I used trim instead

[[CPT]Crunch]

There's no reason they couldn't have put a trim tab on an elevator with a movable stab, it wouldn't be the first or only.  Plenty have both.

[Avimimus]

On 1/5/2023 at 2:26 AM, AndyJWest said:

Wandering a little off topic, I've just come across an interesting article on why a poor choice of propeller aerofoil may have crippled the high-altitude performance of the Westland Whirlwind.

 

WHEN THE WIND WON'T WHIRL - OR THE REAL REASON THE WHIRLWIND SUFFERED AT HEIGHT

 

Yup, it's a Mach-related issue again. The propeller blades were reaching Mcrit well before they needed to, due to their thickness. And it appears that the issue was well-enough understood, though nobody seems to have told Westland. And then Westland went on to design the high-altitude Welkin, which would have performed a whole lot better with a thinner wing, even if they had to reduce the aspect ratio substantially. Like the later U-2 spyplane, it found itself in 'coffin corner' at altitude, with only a few knots between Mach-induced shock stall and its conventional stalling speed. Just about acceptable in a recon aircraft, but not something you really want in a high-altitude interceptor.

 

This is also the reason why the British V-bombers were initially uninterceptable... they were much less prone to this issue than the interceptors that would be sent against them... a Vulcan could easily outturn a fighter 1/6th its size when at altitude.

[Cpt_Siddy]

set the stab trim to max up attitude and wish on the start really really hard

[Gort]

1 hour ago, Avimimus said:

 

This is also the reason why the British V-bombers were initially uninterceptable... they were much less prone to this issue than the interceptors that would be sent against them... a Vulcan could easily outturn a fighter 1/6th its size when at altitude.

 

Some of the claims about the beloved Vulcan are quite entertaining. 

[Avimimus]

23 minutes ago, Gort said:

Some of the claims about the beloved Vulcan are quite entertaining. 

 

I'd be happy to hear!

 

I do gather that this specific claim is more about Soviet anxiety regarding their interceptor fleet in the 1950s (Tony from Butler's "Soviet Secret Projects: Fighters Since 1945") but it does depend on the Vulcan's huge wings and overall altitude performance.

[Rjel]

On 1/2/2023 at 7:20 PM, Verbum_Vincet said:

Don't forget the trim tabs! As the others have said, best practice is to avoid exceeding critical mach but it is easy to get distracted in the heat of battle. Using the 262's electric trim controls, I've occasionally managed to avoid getting too far into mach tuck and/or pulled out just in time by cranking to full tail-heavy and holding full back pressure on the stick.

Same for the P-51. It has a very high dive speed which locks the elevators but using the trim tabs will bring the nose up even when diving in excess of 550mph.

Edited January 7, 2023 by Rjel
Locks the elevators.

[Han]

As far as I know - it is. One of the reasons why 262 development was not easy thing ))

[Hoots]

On 1/7/2023 at 7:56 PM, Gort said:

 

Some of the claims about the beloved Vulcan are quite entertaining. 

My dad flew F4s, when we went to the RAF museum and saw the Vulcan, he said exactly that. At altitude the vulcan could turn easily, the F4s couldn't maintain the lift in the same way.

[=621=Samikatz]

On 1/7/2023 at 8:22 PM, Avimimus said:

 

I'd be happy to hear!

 

I do gather that this specific claim is more about Soviet anxiety regarding their interceptor fleet in the 1950s (Tony from Butler's "Soviet Secret Projects: Fighters Since 1945") but it does depend on the Vulcan's huge wings and overall altitude performance.

 

I imagine some of it comes from the results of Sky Shield II in the early 60s, where eight Vulcans were used to simulate Soviet high-altitude bombers and did manage to penetrate the American air defence network

[Wardog5711]

A pretty good article on Sky Shield II.

https://vulcantothesky.org/articles/operation-sky-shield/

[Holtzauge]

Flying in with bombers at 56,000 ft may have been viable in the 1960's. Doing so in the late Cold War period would have been suicide.

 

By this time both fighter and missile technology had reached such a state of development that this was not an option against a foe with the technological level of the Warsaw Pact.

 

And yes, you can rely on ECM to some extent, but the only way you would send in bombers at high altitude is after you had successfully suppressed the enemies air defenses. And by that I mean the hard kill method, not EW suppression.

 

As far as I know, RAF Vulcan doctrine during the late Cold War called for low level tactics. In fact, they planned on crossing Sweden at tree top level on their way east to avoid radar detection and being intercepted.

 

How accommodating the Swedish Air Force would have been we thankfully never had to find out.