fixed Mosquito landing gear strut incorrect operation..

[Yo-Yo]

On 4/30/2024 at 9:46 PM, Lixma 06 said:

I can't realistically land with a lower sink rate than this...

...and yet the plane rebounds into the sky like an electric shock, and thus begins the inevitable rodeo session.

I can only say that attempts to 2-wheel landing with full fuel load from ME will not be successful. The landings you see in videos are performed for much lighter planes. I think, that I have not to explain, why GW is directly affects the pitch-up torque t touchdown.
The second thing that is important: stabilized low vertical speed and IAS. IAS is important to be sure that the desired low vertical speed is the same up to the moment of touchdown.
In this video the speed just before the touchdown lowers from 208 to 200 kph that means that the plane lost about 8% of lift, and the vertical speed increased. As you can see, g-meter shows 0.9 g instead of 1 just before the touchdown.
And the third thing:  small forward moving of the stick JUST AT THE MOMENT of touchdown . Not before and not too late, both cases worsen the situation, but if it is done in time it really works.
 

In this video one can see constant vertical speed and the almost constant IAS before touchdown. Anyway, small forward stick was used as well.

[Yo-Yo]

So, the initial procedure for good 2-wheels landing:
1. 10-15% of fuel, no bombs.
2. VSI zero mark area is visible (adjust camera position left, but only to see this area, not more)
2. Maintain 210-220 kph at normal stabilized approach.
3. As the wheels is about 2-3 m from the ground, start lowering VS to 50-100 fpm watching steady IAS app. 200-210 kph.
4. As the new VS is established do not touch the throttle, use only small stick deflection to maintain VS.
5. Wait.
6. As you feel ground, move the stick forward a bit as a mongoose and fix 2-wheel attitude.
7. Slowly retard both throttles. (Slowly forward throttles and go-around, if the airfield fence is too close). Freeze the stick and enjoy, you are cool. 
8. Wait for the tail lowering itself.

[Holbeach]

@SMH

"So it turns out the Mosquito's struts do compress as the aircraft weight increases, just not by much. (Which I think is probably correct for this rubber block type of suspension.)

That's right. Adding say, 4000lb. fuel and water should compress about 1''  of tube.

BUT:

You have to start with about 16000lb. of airplane already sitting on the struts, so you should start loading at about 2/3 inside the strut, not 8'' exposed.

..

[Holbeach]

2 hours ago, Shibbyland said:

I don't feel too bothered about the visual compression or lack thereof but I do find the Mosquito in particular not very nice to land, far too firm on the ground. 

 

To me visual is very important. If I lower the flaps 40 deg, I don't want to see 20 or 30 deg, I want to see 40 deg.

If the srut should be 2'' I want to see 2'' not 8'' and a strut like a Stork legs.

If it don't look right, it ain't right.

..

[Yo-Yo]

Anyway, the manual contains just terminal compressions for fully degraded rubber blocks. It means that physical parameters of the rubber degraded. But the initial compression is not available.
But, I am not sure I see this information here, in this degraded conditions the manual directed to replace half-size block to full-size. This can add about 20 mm to the numbers specified in the table, and this is what we can do for the struts in DCS. So, the strut will be authentic for refurbished one.

[Holbeach]

2 hours ago, Yo-Yo said:

Anyway, the manual contains just terminal compressions for fully degraded rubber blocks. It means that physical parameters of the rubber degraded. But the initial compression is not available.
But, I am not sure I see this information here, in this degraded conditions the manual directed to replace half-size block to full-size. This can add about 20 mm to the numbers specified in the table, and this is what we can do for the struts in DCS. So, the strut will be authentic for refurbished one.

Full load 20500lb (22500lb in DCS) minimum is 1.75 inch. Plus 20mm is 2.6 inches of tube showing. I'll take that.

Min load 14000lb (16000 in DCS) minimum is 3.0 inch. Plus 20mm is 3.79 inches of tube showing. I'll take that.

..

[Yo-Yo]

6 minutes ago, Holbeach said:

Full load 20500lb (22500lb in DCS) minimum is 1.75 inch. Plus 20mm is 2.6 inches of tube showing. I'll take that.

Min load 14000lb (16000 in DCS) minimum is 3.0 inch. Plus 20mm is 3.79 inches of tube showing. I'll take that.

..

Yes, we changed it, and it will merged sooner or later.

 

[Holbeach]

One thing I can't find, is any kind of damping system for the strut.

Maybe the rubber deforms and reforms slowly, but there is no dedicated system, such as the Ferodo friction damper, seen in the tailwheel, which also has rubber blocks, (5).

Here's what my WW2 pilot says about his first flight in a Mossie.

 

 

 

This is represented quite well, according to goggles wearers, but as an unpleasant experience.

 

 

..

Edited May 2, 2024 by Holbeach

[Slippa]

On 4/30/2024 at 2:34 PM, Lixma 06 said:

Not sure how your setup works - but I just use Radeon Adrenalin's native recording thing.

Win 10 has it's own version (this is from a Google search)

I tried these today. I have Radeon Pro software so thought it'd be easy enough. Adrenalin isn't part of what I have so tried downloading it. It threw me an error, said I didn't have Radeon bits etc. so I read a bit. I don't think I can install it without removing drivers and reinstalling and even then... So I went the gamebar route. Can't have that either . Being a Mac, I can't upgrade so short of getting really creative with crayons I'm still trying to work it out.

Cheers anyhow .

[Slaobladder]

The landing gear, tailwheel and brakes are borked. There is zero give in the main struts or tyre as you touch down causing the excessive pitch up which is contrary to real life where the spin up of the main gear and aircraft deceleration should promote a tail rise and nose down effect. The tailwheel again appears to have zero damping causing constant bouncing and will break even when taxiing the aircraft, which again is contrary to real life as the tyres on main and tailwheel should smooth out the harshness. The braking is also an issue and seems to either have over heating/fade to high or the braking effectiveness not high enough, the aircraft even when taxiing doesn't seem to respond enough to differential braking, even when cold, it's almost impossible to centre the aircraft post landing sometimes. The pre Christmas aircraft was more realistic on landing/taxiing, both undercarriage and braking. 

[SMH]

15 minutes ago, 4eyes said:

I was hoping for a fix in todays update 

Yeah we were promised one. I wonder if it snuck in without mention in the Changelog as happens far too often?

Checking for new content... the .dll and manifest files always change for every aircraft with every update so those don't necessarily mean anything. Though that .dll also contains the flight model so, hard to say.
 

Edited May 3, 2024 by SMH

[Holbeach]

I would say It's a bit soon to expect an update, so here's a quick video for future reference.

Strut position before expected update. (For the record).

T/O with 100% fuel.

 

 

Showing 3 inches. Measured against 16 inch wheel rim.

..

Edited May 6, 2024 by Holbeach

[Slippa]

Funny, though it is a bit early for much change, I’d imagine, I checked the page wondering if we’d got anything new for the Mos too.

At least it’s being looked at again, finally. 

[Holbeach]

Watching the gear landing animation. 50% fuel. 18667 lb. Reference, v.2.9.4.53990..

Whether it be steel, pneumatic, or rubber block struts, they will all compress under load, in the Mossie case, about 5 inches.

In the DCS case, it starts at 8 inches and ends at about 7.5 inches under load. There is barely any difference. (The width of the white mark).

 

 Made for the DCS bug thread. This shows the high rigidity of the landing gear strut and the lack of compression when static and under full load..

..

Edited May 10, 2024 by Holbeach

[Terry Dactil]

Here is how a real landing gear works.

Note the long compression stroke and then the very small and highly damped (slow) rebound stroke.

It does not work like a spring!

[SMH]

13 hours ago, Terry Dactil said:

Here is how a real landing gear works.

Note the long compression stroke and then the very small and highly damped (slow) rebound stroke.

It does not work like a spring!

Springs compress under constant pressure, so it does work like a spring. It just has dampening so it doesn't bounce too much.

The Mosquito's suspension is just a stack of rubber blocks though. (See all the excellent photos and diagrams posted above.) And what your video shows here is pretty much the same as what the P-47 and P-51 are doing. (Except the P-51 is too soft and bouncy.) 

[Yo-Yo]

14 hours ago, Terry Dactil said:

Here is how a real landing gear works.

Note the long compression stroke and then the very small and highly damped (slow) rebound stroke.

It does not work like a spring!

Do you see a difference between rubber blocks and gas-oleo struts?

[Holbeach]

Whether it be steel, pneumatic, or rubber block struts, they will all compress under load, in the Mossie case, about 5 inches.

In the DCS case, it starts at 8 inches and ends at about 7.5 inches under load. There is barely any difference.

Moved vid.

Edited May 9, 2024 by Holbeach

[Terry Dactil]

1 hour ago, Yo-Yo said:

Do you see a difference between rubber blocks and gas-oleo struts

Yes I do.   The way the rebound gets damped.

The whole point of a shock strut is for it to rebound much more slowly than it compresses.

The Oleo strut does this with different one-way restricting orifices controlling the fluid flow past the piston.  With the Mosquito, if the hole in the rubber block is tapered  then the sliding resistance on the tube will be more in one direction than the other. Same effect. It stops the strut being just a spring.

 

 

 

Edited May 8, 2024 by Terry Dactil

[SMH]

Looks like only a few inches. (You can see the part of the strut that's extended as a darker color in that first shot.)

[Slippa]

I know it bounces as he turns here but it looks like a softer bounce to me.

There’s a walk around video he does as well as another of him getting it out to his place. YouTube has more of the Mossie in New Zealand knocking about. I’m sure most are aware but for those interested, ya know.

 

[SMH]

Yeah, doesn't look like a lot of compression. (That's the bomber variant but I suspect the gear are exactly the same. The fighter/bomber was an afterthought - explaining why many of our instruments are behind our gunsight!)

And it also shows just how much shock the tires take up. What are they inflated to? How's that compare to P-47/P-51 tire pressures? I'm guessing a lot less.

And surely there's a maintenance manual somewhere that says exactly what compressions we should expect on the struts under what weight conditions. 

[Yo-Yo]

8 hours ago, SMH said:

Yeah, doesn't look like a lot of compression. (That's the bomber variant but I suspect the gear are exactly the same. The fighter/bomber was an afterthought - explaining why many of our instruments are behind our gunsight!)

And it also shows just how much shock the tires take up. What are they inflated to? How's that compare to P-47/P-51 tire pressures? I'm guessing a lot less.

And surely there's a maintenance manual somewhere that says exactly what compressions we should expect on the struts under what weight conditions. 

Except the fact that the manual gives the numbers for fully dead rubber stack.

[Slaobladder]

This is the original video from December release post regarding the Mossie clearly showing near zero retraction and a fully extended strut....

[Yo-Yo]

12 hours ago, Terry Dactil said:

Yes I do.   The way the rebound gets damped.

The whole point of a shock strut is for it to rebound much more slowly than it compresses.

The Oleo strut does this with different one-way restricting orifices controlling the fluid flow past the piston.  With the Mosquito, if the hole in the rubber block is tapered  then the sliding resistance on the tube will be more in one direction than the other. Same effect. It stops the strut being just a spring.

 

 

 

 

The only problem is that in fact rubber blocks, as the drawing shows, have no friction contact with the case or any fixed part of the strut. Energy is absorbed using internal friction of rubber that is symmetrical during a compression cycle. And it is absolutely right approach to do it. Friction in this case  is the worst way for it because the heat can not dissipate from the contact zone and rubber will burn and wear every time the strut is used. The energy at the touchdown can be estimated as 4500*1^2/2 for 1 m/s strike velocity that gives up to 5-7 kW of power concentrated at the surface.  Remember, how rubber belts smoke and fire in seconds as the pulley is jammed even at small engines. Moreover, as you are trying to use friction for the stack, you will see that only lower block moves full travel, while the majority of blocks move much less or simply stays in place, and provides no significant work at all.

Any rubber details has its internal energy dissipation, otherwise your garden wheelbarrow would bounce for minutes as you drop it. It stops bouncing after several times. But if it had a oleo-pneumo strut it would react exactly as in your video.