A new F-35 topic (if it's allowed....)

[PR19_Kit]

Having trawled all the way through this area of the Forum reading every F-35 topic there is (was...) I find that the only ones that are general enough in nature have been closed down for 'political' reasons, so the only answer is to open a new one. 

Ten years ago I mentioned that in one vid of RAF/USMC F-35Bs :-

In the daylight shots they're landing with the weapons bay doors open, I wonder why?

Our much missed mate Brian Kitnut617 replied that it may have been some sort of intake flow diverter, which made some sort of sense to me. Since then, and mostly today while waiting for putty to dry on my F-35D, I've watched dozens of F-35 vids and it seems that the -Bs open their inner weapons bay doors, the ones that carry the AIM-120 Slammers, as they come into the hover, and close them once the exhaust nozzle starts to return to its normal position. The doors are never open on take-off, and on the approach, even a VSTOL approach, they stay closed until the nozzle goes into the vertical and the airrcaft drops below a certain speed.

So was Brian's answer correct? Neither he nor I knew for certain why they do it, we just took an educated guess.

Anyone else any other ideas?

And PLEASE don't thread drift this topic into another 'F-35 Bashing Thread', it's too late now, we've got them and so have lots of other people.

[jcf]

Robert  was most likely correct, and it may also be a matter of the doors helping to contain and direct the flow from the lift-fan and aid in preventing reingestion of the hot air from the vectored nozzle.

[Steel Penguin]

like wot JCF and Robert  said, i know on the Harriers they had either the gun pods, or a set of strakes  on the belly to help with air flow when hovering and prevent hot air re-ingestion, and that the also helped hold a " bubble" of air under the plane to aid lift.   

[Dizzyfugu]

... it may also be a matter of the doors helping to contain and direct the flow from the lift-fan and aid in preventing reingestion of the hot air from the vectored nozzle.

Not an F-35 nerd, but I assume that this is the technical background. Rigid air dams are not a true option for stealth technology, and the weapon bay doors are a great fallback choice to prevent exhaust gas circulations close to the ground. I do not think that there is any connection between the bays and the main air ducts?

[PR19_Kit]

. I do not think that there is any connection between the bays and the main air ducts?

If the model is anything to go by, no, there's no ducting through to the intake plenum chamber.

That all makes sense, thanks gentlemen. I'd forgotten the strakes they fitted to the GR5 Harriers for just that reason. As the aircraft approaches the ground the exhaust flow has nowhere else to go but out and around in all directions as it's 'squashed' by the airframe itself, and they sure don't want that going back into the intake!

[jcf]

... it may also be a matter of the doors helping to contain and direct the flow from the lift-fan and aid in preventing reingestion of the hot air from the vectored nozzle.

Not an F-35 nerd, but I assume that this is the technical background. Rigid air dams are not a true option for stealth technology, and the weapon bay doors are a great fallback choice to prevent exhaust gas circulations close to the ground. I do not think that there is any connection between the bays and the main air ducts?

"Directed" in a passive sense rather than being ducted. 

Coralled rather than being forced through a chute. 
😉