Airfield Question

[Zipper730]

I remember looking at footage of WWII and it seemed that you generally had fighters taking off on grass fields routinely, bombers taking off sometimes on grass-fields and other times on runway, but often taxiing on grass.

Why did they change this to operating on concrete always or minimally paved fields which are basically dirt?

 

[buffnut453]

The weight of aircraft increased dramatically from the mid/late 1930s to around 1942. The Wellington was originally designated a "heavy bomber" but by 1942 was considered a medium bomber, with the likes of the Lanc and Halifax being "true" heavy bombers. With this increase in aircraft weight, grass runways were no longer tenable because the aircraft just sank into the dirt.

In addition to the above, the drive for more airfields sometimes led to them being built in areas that were suboptimal from a drainage perspective, hence the use of concrete operating surfaces which allowed for continued operation even when the surrounding land was sodden.

 

[Zipper730]

The weight of aircraft increased dramatically from the mid/late 1930s to around 1942. The Wellington was originally designated a "heavy bomber" but by 1942 was considered a medium bomber, with the likes of the Lanc and Halifax being "true" heavy bombers. With this increase in aircraft weight, grass runways were no longer tenable because the aircraft just sank into the dirt.

I've seen Lancs parked on the grass and taxiing onto concrete...

In addition to the above, the drive for more airfields sometimes led to them being built in areas that were suboptimal from a drainage perspective, hence the use of concrete operating surfaces which allowed for continued operation even when the surrounding land was sodden.

So that's why minimally paved dirt and pierced plates are used?

 

[buffnut453]

Plus "perfection is the enemy of 'good enough'". If an airfield can be used with some areas still grassed, others minimally paved or using PSP, then most front-line operators will say "Bring it on! Let's get the job done!" rather than wait for all planned construction work to be completed. Also, weather plays a big part in this. I doubt you'd see a fully-laden Lanc parked on grass during or following heavy rainfall. An empty Lanc is a different matter entirely weighing as much as 22,000lb LESS than a fully loaded machine.

 

[pbehn]

I've seen Lancs parked on the grass and taxiing onto concrete...
So that's why minimally paved dirt and pierced plates are used?

It wasn't only bombers that got heavier, all aircraft did. The Typhoon had issues with tyre shimmy and blowing tyres on take off and landing, with all its armour fuel and weapons it was a light bomber on a fighters undercarriage.

 

[Shortround6]

I remember looking at footage of WWII and it seemed that you generally had fighters taking off on grass fields routinely, bombers taking off sometimes on grass-fields and other times on runway, but often taxiing on grass.

Why did they change this to operating on concrete always or minimally paved fields which are basically dirt?

Early airfields were grass. A lot of the later ones, at least US and allies, used metal matting but that was often covered with a thin layer of dirt (or coral or????)
to provide a bit of cushion between the metal and the tires, but not often.

Mention has been made of the Lancasters. Pre war the British had a requirement that an aircraft could NOT use tire pressures higher than 38lbs (?) to avoid putting ruts in the airfield. This was far all aircraft, fighters, bombers, recon, transport, etc. However this also leads to large tires which have to be housed in large nacelles or wheel wells. I am sure other countries had other requirements.

He 177

Note that the inner wheel retracted towards the fuselage and the outer wheel retracted into the wing between the engine nacelle and the oil coolers.

If your tires are sinking several inches into the dirt trying to take-off it lengthens the take-off run as you are trying to take off "up hill", climb out of the rut.
Easier to do with high power to weight ratio machines.

Many manuels will give take-off distances with different types of surface. such as a light B-26 (26,000lbs ) needs (with zero wind) 990ft of pavement, 1030ft of sod/turf and 1140ft of "soft" runway, however at 38,000lbs it needed 2390ft of pavement, 2540ft of sod/turf and a whopping 3040ft of "soft". now add distance required from wheels in the air to clearing a 50ft obstacle which is pretty much the same regardless of runway type.