Groppotrail - Folding Wings

[kasper]

I think whilst it may be possible getting controls to auto disconnect to facilitate a folding mechanism, getting that certified would be difficult without some kind of non automated fail safe.. I am not an aircraft designer so I am not sure but certainly in the GA world flight controls need at least 2 locking mechanisms which is usually the torque of the nut and a split pin or lock wire. It could be feasible to use a self locking nut (nylon or metalock) but I think most people are most comfortable with something that has no possibility of unwinding under vibration. In GA it is not difficult to get an authorisation to remove dual controls in helicopters provided that no hand tools are required so I don't see why that wouldn't or couldn't apply to flight controls in a recreational aircraft.

Disassembly of primary control runs where they are designed to be taken apart as part of the usual operations of the aircraft currently does require even an L1 RAAus authority and that from the RAAus tech on clarification of trikes where almost every primary control is taken apart when putting one one/off a trailer. BUT ... and it’s a big BUT ... RAAus and the tech office do seem to be rather reg happy and freedom light in their attitude to RAAus members and touching their aircraft so I’m sort of with HITC on this one

 

 

[Head in the clouds]

I think whilst it may be possible getting controls to auto disconnect to facilitate a folding mechanism, getting that certified would be difficult without some kind of non automated fail safe.. I am not an aircraft designer so I am not sure but certainly in the GA world flight controls need at least 2 locking mechanisms which is usually the torque of the nut and a split pin or lock wire. It could be feasible to use a self locking nut (nylon or metalock) but I think most people are most comfortable with something that has no possibility of unwinding under vibration. In GA it is not difficult to get an authorisation to remove dual controls in helicopters provided that no hand tools are required so I don't see why that wouldn't or couldn't apply to flight controls in a recreational aircraft.

With respect I think you miss the point.

 

There are numerous means of having auto-connect/disconnect controls which cannot, under any normal circumstances, come undone. They don't employ loose nuts or whatever you have in mind. For one easily researched example have a look at the paddle system that is used for Sonex to fold their wings. My own project uses a 'dog-bone and socket' system (imagine a tube with a slot cut into the end of it and the mating half is a rod with a cross-pin), controls lightly sprung to centre when disconnected they must engage when the wings are unfolded and there is nothing to come loose, in fact all parts on each side are welded together ...

 

Then there's the type of articulated system used for aileron connections when, for example, the wings of a Kitfox/Skyfox are folded, they just accommodate the geometric change as the wings fold, they are never disconnected or re-connected, they always stay connected whether the wings are folded or not.

 

Then there's the Pylon 500 hinge mechanism which allows the horizontal stabilisers/elevators to be folded up when the wings are folded, making a still smaller package, and the controls always remain connected - it's just simple geometry and a clever idea, thanks again Pylon!.

 

As far as removing/replacing duals on helicopters is concerned, I was a career comm heli operator and did get my own Approvals to remove/install them on several types, but that has nothing to do with it. Removing/fitting a set of duals doesn't have anywhere near the risk we're talking about here. Duals are just that ... Duals ... the primary controls don't get interfered with at all. In fact there's more risk with the common practice of turning the H369/MD369 pedals back onto each other to lock the pedals (due to the risk of not properly engaging them again, than there is with adding/removing duals.

 

You may not be aware of the not-inconsiderable number of fatal incidents, in Australia and Globally, immediately following re-rigging of sport aircraft types from a folded/trailerable condition? The problem is that in some cases it's not easy to determine whether connections have actually been correctly made prior to flight loads being applied, and by then it's already too late.

 

'Auto-connect or no folding' is already well along the way into regulation in both Europe and USA, and has been since the Ark for Type-Certified, so if you're planning to distribute these types I'd think it's something you'd do well to look at from a litigation-avoidance aspect if nothing else.

 

 

[Groppo Australia]

With respect I think you miss the point.There are numerous means of having auto-connect/disconnect controls which cannot, under any normal circumstances, come undone. They don't employ loose nuts or whatever you have in mind. For one easily researched example have a look at the paddle system that is used for Sonex to fold their wings. My own project uses a 'dog-bone and socket' system (imagine a tube with a slot cut into the end of it and the mating half is a rod with a cross-pin), controls lightly sprung to centre when disconnected they must engage when the wings are unfolded and there is nothing to come loose, in fact all parts on each side are welded together ...

 

Then there's the type of articulated system used for aileron connections when, for example, the wings of a Kitfox/Skyfox are folded, they just accommodate the geometric change as the wings fold, they are never disconnected or re-connected, they always stay connected whether the wings are folded or not.

 

Then there's the Pylon 500 hinge mechanism which allows the horizontal stabilisers/elevators to be folded up when the wings are folded, making a still smaller package, and the controls always remain connected - it's just simple geometry and a clever idea, thanks again Pylon!.

 

As far as removing/replacing duals on helicopters is concerned, I was a career comm heli operator and did get my own Approvals to remove/install them on several types, but that has nothing to do with it. Removing/fitting a set of duals doesn't have anywhere near the risk we're talking about here. Duals are just that ... Duals ... the primary controls don't get interfered with at all. In fact there's more risk with the common practice of turning the H369/MD369 pedals back onto each other to lock the pedals (due to the risk of not properly engaging them again, than there is with adding/removing duals.

 

You may not be aware of the not-inconsiderable number of fatal incidents, in Australia and Globally, immediately following re-rigging of sport aircraft types from a folded/trailerable condition? The problem is that in some cases it's not easy to determine whether connections have actually been correctly made prior to flight loads being applied, and by then it's already too late.

 

'Auto-connect or no folding' is already well along the way into regulation in both Europe and USA, and has been since the Ark for Type-Certified, so if you're planning to distribute these types I'd think it's something you'd do well to look at from a litigation-avoidance aspect if nothing else.

Your point is well taken and I appreciate the input. As I said I am not an aircraft designer nor am I a very avid follower of recreational aviation, although it is something I learn more about every day. I understand your point with regard to the Groppo's folding wing and the connection of flight controls, however, the manner in which the ailerons are connected and disconnect is really quite foolproof and if one were to mess it up I would seriously consider their ability to safely navigate the skies.

With regard to helicopter dual controls, which really is beside the point I suppose, I have yet to see a helicopter who's dual controls are not directly connected to the primary controls so to say the primary controls don't get interfered with is not really an accurate statement because if the dual stubs get jammed on something then the primary controls are jammed too.

 

With regard to the fatal accidents due to re-rigging of the flight controls, I am not aware of the numbers but being that the Trail is push/pull tube aileron and elevator control, rigging is not really an issue in this instance.

 

The folding wings you mention that have "been around since the ark" I am not sure have ever been prevalent in commercial aircraft. Most certainly such iconic machines as the F4U, A-1, F6F and most carrier borne aircraft to this day sport such features but I am not sure if it would really work in a high winged aircraft. I may be totally wrong (as I often am). Either way, as our Trail is currently under construction, it is hard for us to know what will be an issue and what will be a selling feature. But most certainly it is a robust and well designed little machine.. will keep you posted on how it goes when its flying

 

 

[pylon500]

Hi HITC.

 

Yeah, don't know how much things have changed from my days, but most gliders have 'auto couple' controls, which anyone could rig, the usual thing was to then have someone double check before signing the DI sheet.

 

I can't remember if that was our club policy or GFA policy?

 

Probably more complex today...

 

As for the Trail, I thought it looked the part (mainly because it looked like my Stollite), and even managed to have a look at it at Oshkosh back around 2013.

 

Even showed the designer photos of my Stollite!

 

The only thing that concerned me a little (and I can't remember if I mentioned this before, or just refrained), but I was a little worried about the top end wing/strut attach point..

 

Most aircraft set the attach systems up to use bolts in shear, as does the Trail for most of the wing, except the top of the strut.

 

To facilitate the folding system, a bolt is used in tension, and it is used through two diaphragms (technically).

 

It's OK if this is done with a complete 'overkill' of materials and hardware, but from memory, it just looked like a 3/8th bolt through two pieces of 1/8th plate just under an inch square, welded to support brackets.

 

 

 

Probably well strong enough, just left me a little concerned.

 

 

[Head in the clouds]

Hi HITC.Yeah, don't know how much things have changed from my days, but most gliders have 'auto couple' controls, which anyone could rig, the usual thing was to then have someone double check before signing the DI sheet.

I can't remember if that was our club policy or GFA policy?

 

Probably more complex today...

 

As for the Trail, I thought it looked the part (mainly because it looked like my Stollite), and even managed to have a look at it at Oshkosh back around 2013.

 

Even showed the designer photos of my Stollite!

 

The only thing that concerned me a little (and I can't remember if I mentioned this before, or just refrained), but I was a little worried about the top end wing/strut attach point..

 

Most aircraft set the attach systems up to use bolts in shear, as does the Trail for most of the wing, except the top of the strut.

 

To facilitate the folding system, a bolt is used in tension, and it is used through two diaphragms (technically).

 

It's OK if this is done with a complete 'overkill' of materials and hardware, but from memory, it just looked like a 3/8th bolt through two pieces of 1/8th plate just under an inch square, welded to support brackets.

 

[ATTACH=full]52749[/ATTACH]

 

[ATTACH=full]52750[/ATTACH]

 

Probably well strong enough, just left me a little concerned.

Hi Pylon,

 

Yes I think you mentioned the diaphragms/bolt-in-tension thing. As you say, it's probably well strong enough though it doesn't look ideal.

 

The bolt-in-tension aspect is fine, in fact bolts seem to be used in shear mostly on aircraft and similar structures, but they actually have a higher rating in tension than in shear. These days my day job is in structural steel and whenever lifting lugs are attached to anything the bolts are always arranged in tension, so I'd say that's probably the best way to go about it even if it doesn't 'feel' quite right. The benefit of using bolts in shear for aeroplane struts is that it provides a good start for adjusting/setting dihedral and other wing rigging.

 

Down the track I'd expect that Groppo might develop machined parts for their top strut fitting, rather than fabricating them, for better looks and structural consistency if nothing else, and especially if it makes the customers happy ... My DooMaw has wings that fold similarly, except they hinge at the rear spar for a less tall folded package (though it has the penalty of being longer), so I also needed a 'wrist' mechanism at the top of the strut. I machined mine from 6061T6 billet. As a one-off set it was quite a time-consuming business but for a production aircraft kit using a multi-axis CNC milling machine it would probably be a lot quicker than fabricating them.

 

Pic of my strut fittings, also the second and third pics show a 'dogbone' arrangement, one of many ways to have auto-connect controls -

 

 

 

 

 

[farri]