Landing Gear Suspension too stiff

[Nealius]

That's also a D model, which had a higher max trap than As and Bs, didn't it? I know the max trap was increased a few times for the Tomcat but I thought the A and B remained somewhat lighter than the D.

[Smith]

10 hours ago, JupiterJoe said:

I'm not sure the mains should be bottoming out at max trap weight.  There should still be something in reserve, otherwise it'd be a hell of an impact on the airframe, not to mention the crew.

 

Sorry, in my video i should have written "Almost full compressin of main landing gear". Of course i don't want it to bottom out on every carrier landing. But from what you can see on the blury real life video, the main landing gear uses like 95% of the suspensiontravel on touch down and settles at about 70% compression. It looks like on carrier landings there is only like 5% left from bottoming out. This is what i tried to achieve with modifying the config file.

A carrier landing is the hardest landing the plane can do without taking damage, so for this landing you need all the travel of the suspension that is available. When you land even harder than the allowed max sink rate it should bottom out and the airframe and landing gear should take damage.

[Despayre]

52 minutes ago, Smith said:

Sorry, in my video i should have written "Almost full compressin of main landing gear". Of course i don't want it to bottom out on every carrier landing. But from what you can see on the blury real life video, the main landing gear uses like 95% of the suspensiontravel on touch down and settles at about 70% compression. It looks like on carrier landings there is only like 5% left from bottoming out. This is what i tried to achieve with modifying the config file.

A carrier landing is the hardest landing the plane can do without taking damage, so for this landing you need all the travel of the suspension that is available. When you land even harder than the allowed max sink rate it should bottom out and the airframe and landing gear should take damage.

Also note, despite how much compression the gear goes through, that plane is almost clean, nowhere near max trap I wouldn't think...

[draconus]

2 hours ago, Despayre said:

Also note, despite how much compression the gear goes through, that plane is almost clean, nowhere near max trap I wouldn't think...

That's the problem with videos - you never know the fuel state, so you can't tell anything about the weight, only educated guess.

[Nealius]

True, however the assumption in USN practice is that the fuel ladder is calculated so that you trap at max trap weight to maximize fuel. 

Edited May 17, 2023 by Nealius

[Smith]

9 hours ago, Despayre said:

Also note, despite how much compression the gear goes through, that plane is almost clean, nowhere near max trap I wouldn't think...

What is the max weight of a F-14 doing a carrier landing?

[Despayre]

7 hours ago, draconus said:

That's the problem with videos - you never know the fuel state, so you can't tell anything about the weight, only educated guess.

You can tell there's just about zero weapons onboard. So even assuming all the tanks are full, I think we can safely assume we're thousands of lbs under max trap in that demo. 

I believe the Phoenix is about 1000 lbs, and we know we can carry 6 of them, so, right there, that's 6,000 lbs under max trap, minus the weight of whatever that pod attached under the wing is, is that a single dumb bomb, or something else under the right wing, not sure, but I'm guessing it doesn't weigh 6000 lbs, and while you're right, that's just an educated guess, I think we can get close enough for lawn darts. (old expression meaning close enough that it counts, even if it's not perfect... explained for the young ppl who never saw the bloodsport known as lawn darts in the 80's... )

50 minutes ago, Smith said:

What is the max weight of a F-14 doing a carrier landing?

54,000 lbs

[sLYFa]

2 minutes ago, Despayre said:

You can tell there's just about zero weapons onboard. So even assuming all the tanks are full, I think we can safely assume we're thousands of lbs under max trap in that demo. 

The empty weight is about 44000lbs, the rails and adapters you see in the video add about another 1000lbs-1500lbs. That leaves about 9000lbs of fuel left to stay below 54000, which is less then half of what the Tomcat can take. So we cannot assume anything safely. During normal cyclic ops, aircrews tend to recover with max trap weight but that doesn't always happen. As long as they are above 3000-4000 lbs of fuel they can take shot at recovery before going to the bolter tanker.

[Despayre]

5 minutes ago, sLYFa said:

The empty weight is about 44000lbs, the rails and adapters you see in the video add about another 1000lbs-1500lbs. That leaves about 9000lbs of fuel left to stay below 54000, which is less then half of what the Tomcat can take. So we cannot assume anything safely. During normal cyclic ops, aircrews tend to recover with max trap weight but that doesn't always happen. As long as they are above 3000-4000 lbs of fuel they can take shot at recovery before going to the bolter tanker.

Hrrm, Google says the weight of an F-14 is 40,100... I think even re-calculating for that, your point still remains though... but I think we can still agree, that whatever the weight is in that video, that suspension is pretty clearly close to, if not actually, maxing out in terms of flex. If it does that when it's not at max trap, max trap is gonna be an awfully hard feeling landing (and maybe it was!).

[sLYFa]

IIRC the earliest As where around 40k empty but Bs and Ds sit around 44k. In any case, I dont think a couple of thousand pounds will make much of a difference anyway so its safe to say that the main gear should compress a lot on touchdown which the modified config replicates nicely.

[Callsign JoNay]

2 hours ago, Despayre said:

You can tell there's just about zero weapons onboard. So even assuming all the tanks are full, I think we can safely assume we're thousands of lbs under max trap in that demo.

I think you need to check your math. A Tomcat with full tanks is several thousands of pounds over max trap weight even without bringing back any stores.

Edit/Add: Yes the Tomcat could carry six Phoenix, but it can't trap with them. Max takeoff weight and max trap weight are not the same thing.

Edited May 17, 2023 by Callsign JoNay

[Despayre]

Just now, Callsign JoNay said:

I think you need to check your math. A Tomcat with full tanks is several thousands of pounds over max trap weight even without bringing back any stores.

Edit/Add: Yes the Tomcat could carry six Phoenix, but it can't trap with them. Max takeoff weight and max trap weight are not the same thing.

 

That's not a math problem, that's a lack of knowledge problem. My math is just fine. But thanks for pointing that out.

[HavaFaza]

On 5/16/2023 at 10:47 AM, Despayre said:

There might be a little left in reserve, or possibly a variable thickness coil (or equivalent) requiring more force to bottom out the suspension, but if you look at Smith's video above, that shows a real Tomcat landing, and at about the 22 second mark, that looks pretty darn close to bottoming out to me... Also, there's a reason there's a max trap weight, it's the max!

Oleo struts have a tapered metering pin (or similar) that increases damping as the strut compresses. The pin is thicker at the bottom than the top and is attached to the lower piston. As the strut compresses, it passes through an orifice that restricts how much fluid can pass between the upper and lower cylinders, decreasing its area and increasing the strut's damping. Ideally, the strut's damping maxes out before the strut can bottom out, so heavy impacts will get very close but not quite to bottoming out.

[Smith]

With the new Update Heatblur changed a lot in this config file. I tried to make the suspension bouncy again and it worked with the main gear, but the nose stays very stiff no matter what values i change. Maybe with the new file there are other values relevant that i don't know at the moment. With the old config file it was very easy to change the spring and damping values and i could see the change take effect in the game. With the new file i can't change the spring and damping values of the nose gear. So i think i will wait until they finish the suspension update and then check it again for realisitc suspension behavior.

Until then i will use the config file that fat creason postet with my tweaks for a bouncy  main landing gear:
Config.lua

The changes i made to his file are:

1. Line 94: I lowered the damping value of the main gear a lot, so that at touch down the suspension compresses almost fully like in the video I posted. I checked it with ACLS carrier landings and at about 54000 lbs weight. If i lower this value more the suspension will bottom out. If i raise this value the suspension will not compress like in the video.

   Line 94 Original:
   amortizer_direct_damper_force_factor	= 160000 * 0.6,
   
   Line 94 Tweaked:
   amortizer_direct_damper_force_factor	= 160000 * 0.13,

2. Line 96: I raised the rebound damping value a bit, so that the plane doesn't bounce back in the air after touch down.

   Line 96 Original:
   amortizer_back_damper_force_factor		= 160000 * 0.20,
   
   Line 96 Tweaked:
   amortizer_back_damper_force_factor		= 160000 * 0.3,

    

3. Line 155: This change is very important to achieve the behavior in the video fat creason postet. In this video when the pilot brakes, the nose suspension first dives in very far, and when the brakes are released it moves out again until it tops out and the wheels lift of a bit. There you can see that there is almost no weight on the nose wheel and the suspension stays almost toped out when the wings are swept back. The lower this value is, the more the front suspension is topped out.

   Line 155 Original:
   amortizer_reduce_length					= 0.1,
   
   Line 155 Tweaked:
   amortizer_reduce_length					= 0.03,

    

4. Line 163: This value for the rebound damping is a lot to low. I think Heatblur wanted to achieve with lowering this value to 0.012 that the nose lifts off a bit after braking, but as i mentioned in point 3 this is because the front suspension is almost topped out and not because the rebound damping value is so low on the real plane. On planes you want a softer compression damping value so that the touch down is not to hard on the airframe. After the suspension absorbed the shock of the touch down you want a higher rebound damping value, so that the plane doesn't jump back in the air again.

   Line 155 Original:
   amortizer_back_damper_force_factor		= 152000.0 * 0.012,
   
   Line 155 Tweaked:
   amortizer_back_damper_force_factor		= 152000.0 * 0.18,

    

So, as you see, its not difficult to make the suspension behave more like the real deal. The damping values should just not be too high. I hope Heatblur is adapting these ideas to the official update.

Maybe someone finds out how to make the nose bouncy with the new update. I will continue trying to find a solution for this.

[FZG_Immel]

that is awesome. where is this file located ?

 

found it :

 

C:\Program Files\Eagle Dynamics\DCS World OpenBeta\Mods\aircraft\F14\Entry

Edited May 24, 2023 by FZG_Immel

[MadManCLC]

Awesome stuff!!

[Smith]

Found a nice video where you can see what i m looking for. At 19:55 you can see how a suspension should look when landing. The suspension of a lot of planes in DCS look like that (Su-25/27/33, MiG-29, A-10, KA-50) but not the F-14 and F-18 at the moment.