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Wheels dig into tarmac when taxiing


Jacodv201

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There seems to be a problem with the mig21 when you taxi. When you turn the wheels dig into the tarmac as if the tires have almost no air in them. When you straighten out after a couple of meters they pop out of the ground again.

 

I have tried this on all maps, all airfields, problem persists across all states. I attached 2 track files, one with full pylons and one with a empty plane, when weight is added it is much worse. I have re downloaded DCS and all modules and I use no mods. No other plane I own does this.

 

 

 

To recreate the problem load in the mig with some bombs, and turn while taxiing.

MIG21noweight.trk

MIG21withweight.trk

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  • 2 weeks later...

Same issue here on Open Beta.

Intel i7-12700K @ 8x5GHz+4x3.8GHz + 32 GB DDR5 RAM + Nvidia Geforce RTX 2080 (8 GB VRAM) + M.2 SSD + Windows 10 64Bit

 

DCS Panavia Tornado (IDS) really needs to be a thing!

 

Tornado3 small.jpg

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I believe this was a recognized bug in a thread not too long ago, in relation to the nose wheel digging in. In that thread, I mentioned the mains were digging in as well, and Hiromachi acknowledged it was being worked on.

 

I’ve noticed that the mains dig in on the takeoff run as well (full internal fuel, with no stores). They dig in enough that burst tires tend to happen more frequently than before. The new suspension system and taxying on grass is WIP, so hopefully improvements will include tires.

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  • 4 weeks later...
Can confirm the shimmy and sinking, though it's worth noting that the manual states a 10km/h limit for turns when taxiing, which explains all the weight tipping onto one wheel and potentially popping it.

 

 

 

 

Attaching the JATO rockets will make the Mig 21 lean to one side...

 

 

Yep...the suspensions need work and at time its very wobbly..

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  • 4 weeks later...

Yes, there will be some update to the front gear in the next patch.

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Thrustmaster TPR Pendular Rudder Pedals / Audio Technica ATH-MSR7

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  • 1 month later...

Problem still exist in current openbeta. If you load a heavy payload(2xtanks for example) mig have a tendency to sink one of the wheels under tarmac when turning while taxing. In external view I can see sparks and it the cocpit I hear scratch sounds...


Edited by Virun

Активно летаю на: F/A-18 | F-16 | Су-27 | МиГ-21бис



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Alright, I'm going to look into that and forward to Novak.

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AMD Ryzen 5900X @ 4.95 Ghz / Asus Crosshair VII X470 / 32 GB DDR4 3600 Mhz Cl16 / Radeon 6800XT / Samsung 960 EVO M.2 SSD / Creative SoundBlaster AE-9 / HP Reverb G2 / VIRPIL T-50CM /
Thrustmaster TPR Pendular Rudder Pedals / Audio Technica ATH-MSR7

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Indeed. Last night I tried a mil-power takeoff and got the shimmy at about ~150 km/h. A few seconds later either the tyre exploded or the front landing leg got bent (couldn't tell for sure, no external views) and I had to skid to a stop...

DCS module wishlist: F-104S ASA-M Starfighter / F-111F Aardvark / F-4E Phantom II / J 35F2 Draken / J-7M AirGuard / Kfir C.2 / MiG-17F / MiG-21 Bison / Mirage F1 / Su-17M4 / Su-24M / Yak-9U

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The nosewheel shimmy on landing rollout can be pretty brutal too, especially with the chute still attached.

 

 

 

 

The problem still exists despite the latest patch quoting its fix. Also the Front wheels still kinda wobble sideways.

 

 

 

I feel as if nothing has changed on Mig 21...:noexpression:

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  • ED Team

It seems that there are 2 problems with the suspension as it is, one is that the rate of spring on all 3 struts seems to be too low, while at the same time they are overdamped, causing them to slowly sink all the way to full deflection even in relatively slow turns. Then it seems to proceed to sink further until the rim starts seemingly scraping on the surface below, as if the tyre deflated (tyre pressure too low?). Same happens when running up engine on brakes, the nose strut fully deflects (damping coefficient appears to be lower on the nose strut though) and then the tyre itself fully deflects. Not sure why it was tuned that way but I won't believe that's how it was in real life, it would be an insult to the designers of the aircraft. It seems like the general model for the suspension is pretty realistic, but the individual parameters for both the tyre and the strut itself are wrong.

 

Second issue is the shimmying of the nose strut during landing and take off run, especially on landing. The speed where it occurs is inconsistent, but is generally around 100-150kph. It would seem that either there is no shimmy damper at all (despite the aircraft having it in real life) the tyre parameters are wrong (which is likely the case based on the above), the damping coefficient is too low on the damper or a combination of the above.

 

Indeed. Last night I tried a mil-power takeoff and got the shimmy at about ~150 km/h. A few seconds later either the tyre exploded or the front landing leg got bent (couldn't tell for sure, no external views) and I had to skid to a stop...

 

150 km/h is where you should pull the stick to around 3/4th deflection and keep it there until the nose lifts off the ground, it won't prevent shimmy but it will prevent death, since you'll be shifting weight to main gear as you accelerate. In MiG-21 you don't just wait until rotation speed and then rotate in one swift motion, that's an easy way to collect tail strikes due to how low to the ground the nozzle is on takeoff, instead you pull the stick way before rotation speed, let the wheel slowly raise off the ground as you approach the rotation speed, and then stabilize around 5-10 degrees of pitch until the aircraft lifts off the ground on its own.

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@m4ti140, that seems like a fair assessment. IMHO the key factor here is that the springs are far too soft for this amount of suspension travel. As a result the plane effectively rides on the bumpstops when taking turns even at moderate speeds, thus causing the effective spring rate to skyrocket. It appears that DCS does not model low speed damping and weight transfer correctly, so instead of bouncing around like a 1970s American land yacht (losing its chrome hubcaps in the process) the tyre sinks through the ground, making the game engine think the plane is riding on its wheel rims, just like a car with a blown tyre. I suspect M3 modelled it this way in order to make the Fishbed capable of taking off from grassy airstrips (just like the real aircraft), even though the latter aren't used on modern maps.

 

Thanks for the tip, that's exactly how I take off in the 21. Glad to learn I'm doing it right. I haven't done many mil power takeoffs since the FM update, which is probably why that time I held too much weight over the front wheel for too long, not expecting the shimmy to be so severe.

DCS module wishlist: F-104S ASA-M Starfighter / F-111F Aardvark / F-4E Phantom II / J 35F2 Draken / J-7M AirGuard / Kfir C.2 / MiG-17F / MiG-21 Bison / Mirage F1 / Su-17M4 / Su-24M / Yak-9U

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The real question is why would you want to do a mil power takeoff? :D

 

The tyres are definitely clipping the ground/deflating - you can usually hear the rim scrape when the suspension bottoms out. Even clean, it's fairly easy to scrape in a turn, but with a moderately loaded aircraft it's even worse. Of course, as soon as this happens you lose almost all steering effort, so it's an easy way to end up in the grass and unless you keep your momentum up, it can be very hard to get back out of.

 

Would be nice if ED would share whatever magic attribute it is that allows the Hornet to offroad, since the 21 should be able to take off and land from a (somewhat prepared) grass or dirt surface, let alone taxi on it.

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The real question is why would you want to do a mil power takeoff? :D

 

Just wanted to save fuel. :)

 

Would be nice if ED would share whatever magic attribute it is that allows the Hornet to offroad, since the 21 should be able to take off and land from a (somewhat prepared) grass or dirt surface, let alone taxi on it.

 

I suspect there's no magic involved, more likely it's just a properly tuned suspension setup. Speaking of which, here's a video of Hungarian MiG-21bis squadron operating from a grass airstrip.

 

DCS module wishlist: F-104S ASA-M Starfighter / F-111F Aardvark / F-4E Phantom II / J 35F2 Draken / J-7M AirGuard / Kfir C.2 / MiG-17F / MiG-21 Bison / Mirage F1 / Su-17M4 / Su-24M / Yak-9U

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