Wing folding/storing for large aircraft

[shin_getter]

With recent conflicts, it seems like hardened hangers is necessary for almost all expensive aircraft with military relevance.

So time to investigate this:

Which designs can practically have folding built into it, and which can not (how much can you fold a flying wing?)? How difficult to add folding features to converted civilian aircraft? Which aircraft would be made smaller instead of adding this complexity? What about V-22 style rotating wing, which aircraft would suit that design?

 

[red admiral]

You can fold pretty much at the wing root, but for wing mounted engines then you're probably looking at outboard of the engine nacelles. Something like a simple chord wise fold with pins should be a lot simpler and lighter than a rotating V-22 style wing.

It should be possible to retrofit to existing aircraft, but this is not a trivial exercise. It's time/money/effort rather than technical difficulty.

Probably also want to have a folding vertical tail to reduce height.

 

[jmspeedfreak]

You can fold pretty much at the wing root, but for wing mounted engines then you're probably looking at outboard of the engine nacelles. Something like a simple chord wise fold with pins should be a lot simpler and lighter than a rotating V-22 style wing.

It should be possible to retrofit to existing aircraft, but this is not a trivial exercise. It's time/money/effort rather than technical difficulty.

Probably also want to have a folding vertical tail to reduce height.

Is there a good resource on design details for wing fold mechanisms Red? As in US Navy practice?

 

[Scott Kenny]

My suggestion would be to use something similar to the old Grumman Sto-Wing, as used on E-2 Hawkeyes (etc): Wings rotate ~90deg and fold backwards towards the tail. Fold point would be just outside the engine nacelles or MLG bays.

 

[red admiral]

Is there a good resource on design details for wing fold mechanisms Red? As in US Navy practice?

This recent paper seems pretty reasonable in laying out a variety of approaches and non-structural factors to consider e.g. actuation

There's a few other papers available as well on other folding mechanisms

 

[Seragina]

It's not really a technical problem but an economic one. Is it worth for a company to design a less economic aircraft due to weight penalty for a military market of perhaps 200 verses a commerical market of 5000?
A blended wing design could reduce the aircraft size and make it more feasible because of higher efficiency range that could be traded of.

 

[Nicknick]

Liebherr is actuslly developing a wingtip folding mechanism for the Boing 777. Doing something similar at the wingroot would be much more complicate and add lot of weight.

Blended wing bodies might be one alternative, otherwise I would prefer a detachable parasol wing for transport planes. Here, the main wing wouldn't be integrated in the fuselage but connected with struts which could relativly easiely beeing detached and be hang up under the roof of the shelter. The design would be much lighter and simpler than folding wings and with the wings beeing stored under the roof the handeling wouldn't become very difficult. Of course, the fuselage needs to be able to be caried around on the gear, so that the planes could be stored very close to each other.

 

[jmspeedfreak]

This recent paper seems pretty reasonable in laying out a variety of approaches and non-structural factors to consider e.g. actuation

There's a few other papers available as well on other folding mechanisms

Thanks a lot.

 

[Scott Kenny]

It's not really a technical problem but an economic one. Is it worth for a company to design a less economic aircraft due to weight penalty for a military market of perhaps 200 verses a commerical market of 5000?

I mean, 777X is supposedly getting folding wingtips for clearance around lights etc on the airfield. There's not a lot of difference between "folding the outer 20ft of wing" and "folding the wing at the engine pylon".

You absolutely could fold the wings of an airliner just outboard of the engines. Or, if we're messing with that truss-braced wing, just outboard of the strut mounts.

 

[Foo Fighter]

What level of additional servicing would a wing fold entail? Worth it when a lot of operators appear over the last ten years, to have cut standard servicing to the bone and indeed beyond?

 

[Scott Kenny]

What level of additional servicing would a wing fold entail? Worth it when a lot of operators appear over the last ten years, to have cut standard servicing to the bone and indeed beyond?

It'd require some additional inspections. Locking blocks and pins, the hydraulics/electric motors.

 

[Foo Fighter]

It'd require some additional inspections. Locking blocks and pins, the hydraulics/electric motors.

Thanks, I was thinking that the forces would be somewhat greater than those on the engine mounts in standard pylons, 73/5/7/8 etc.

 

[ncc81701]

I mean, 777X is supposedly getting folding wingtips for clearance around lights etc on the airfield. There's not a lot of difference between "folding the outer 20ft of wing" and "folding the wing at the engine pylon".

You absolutely could fold the wings of an airliner just outboard of the engines. Or, if we're messing with that truss-braced wing, just outboard of the strut mounts.

There is A LOT of difference when you are the one that have to design the structure and mechanism to ensure the load path stays good and you still retain positive load margin when the wings are unfolded.

The further inboard you make the hinge, the greater the complexity and weight penalty of incorporating the folding wings. For a commercial operator where pennies per passenger-seat-miles is king, you’d want that hinge to be far outboard as you can get away with if you need a folding wing at all.

 

[Scott Kenny]

There is A LOT of difference when you are the one that have to design the structure and mechanism to ensure the load path stays good and you still retain positive load margin when the wings are unfolded.

The further inboard you make the hinge, the greater the complexity and weight penalty of incorporating the folding wings. For a commercial operator where pennies per passenger-seat-miles is king, you’d want that hinge to be far outboard as you can get away with if you need a folding wing at all.

Yes, for an airliner you want to avoid wing folds entirely if you can.

But military aircraft are now looking like they need to be kept inside an HAS when not flying, which likely means folding wings and possibly vertical stabilizers.

 

[Foo Fighter]

Just how much protection do the HAS provide? Having seen many instances where they may as well not be there I have to say I am uncertain as to the benefits/cost ratio.
Obviously direct hits and shrapnel from local near misses are different kettles of fish.

 

[red admiral]

Just how much protection do the HAS provide?

It depends on the threat type.

Generally you are invulnerable to many "cheap and easy" threats and so you drive a need to use "expensive and complex" threats like a cruise missile with specific penetrating warhead. These still may be available in large (absolute) numbers, but orders of magnitude lower relative to other threats like One-Way Attack drones.

 

[ncc81701]

Yes, for an airliner you want to avoid wing folds entirely if you can.

But military aircraft are now looking like they need to be kept inside an HAS when not flying, which likely means folding wings and possibly vertical stabilizers.

Yeah but that’s not a trivial change to retool the assembly of the wings to accommodate folding wings or designing one in the first place. The original response was to address the claim that there was not a lot of difference between folding the wings at the tip vs folding the wings just outboard of your engine pylon. I’m saying that that is absolutely not the case.

Even for an organization that is less cost sensitive like the military, it doesn’t change the physics that the further out you put the wing fold hinge line the lighter, simpler and less complex the mechanism and structure will be because there is less load on the outer portion of the wing. That weight penalty will be applied at every performance metric from TOFL, time to climb, to fuel burn (time on station), etc.

So if you tell me that the wing have to fold so it fits though the 140ft wide door of a harden shelter with no other constraints, I will put the hinge line so that I will only have 6inch of clearance on either side. Where you put the wing folding hinge line matters, and matters a lot was the point that I was trying to make.

 

[MadRat]

How about hinge mechanisms like on a glide bomb to symmetrically stretch out wings for takeoffs and landing, then folds back into a streamline storage for cruise? You would be able to engineer thinner, high aspect ratio wings for much lower speeds than cruise, to reduce weight.