Does the B737 MAX use pickle-forks?

[MickG0105]

In a story on the B737 NG pickle fork problem Bjorn Fehrm of Leehamnews.com reported that

The affected 737 types are NG only; the MAX and Classic have a different wing attachment design.

Can anyone familiar with the MAX comment on the wing attachment design used in that aircraft?

[Dave Therhino]

The max uses pickle fork fittings that are machined from the same forging that the NGs are made from. The machining is different, so they aren't interchangeable.

[MickG0105]

Originally Posted by Dave Therhino

The max uses pickle fork fittings that are machined from the same forging that the NGs are made from. The machining is different, so they aren't interchangeable.

Thanks for that, Dave. Do you know what the design differences are between the NG and MAX pickle forks?

[Dave Therhino]

I don't know the differences at the detail level.

[MickG0105]

Originally Posted by Dave Therhino

I don't know the differences at the detail level.

Thanks Dave.

[VinRouge]

Originally Posted by MickG0105

Thanks Dave.

Not a definitive, but bearing in mind the Max was re-engined (possible weight increase?) together with the increased torsional load at max power from these donks, (think Thrust x Distance from the donk thrust line to the centre of torsion of the wing structure), one would expect the pickle fork design will have been beefed up to cope with these additional stresses. This considers the static case.

There may may have also been different dynamic/vibrational characteristics (mindful that aeroelastic flutter has much to do with the coupling of torsional and bending characteristics of the structure) which may have resulted in an increase In the beefiness of the structure.

Changing something as simple as a winglet can have a massive impact on the torsional and bending loads placed on the root of the wing, as the pressure distribution is significantly changed.

[ampclamp]

one would expect the pickle fork design will have been beefed up to cope with these additional stresses.

Beefed up before the current NG problems were found, perhaps expecting the NGs were adequate and would never likely have a cracking problem in that area?

I understand the PFs were supposed to be a life of airframe part of the structure. Beefed up enough? Time will tell.

It may pose some questions in future for the Max, but right now it is the least of their concerns

[VinRouge]

Originally Posted by ampclamp

Beefed up before the current NG problems were found, perhaps expecting the NGs were adequate and would never likely have a cracking problem in that area?

I understand the PFs were supposed to be a life of airframe part of the structure. Beefed up enough? Time will tell.

It may pose some questions in future for the Max, but right now it is the least of their concerns

beefed up in relation to increased loads. What is frustrating with airframe structures is the difficulty of protecting structure from cyclic stresses (dynamic case) which are more difficult to model. You could build the structure up significantly but still come up against high cycle fatigue if there is a vibrational mode that you haven’t modelled correctly. Aeroelastics are another significant complication (together with Aeroservoelastics) which are rarely encountered in other engineering fields. The compromises to provide economically competitive structures vs aircraft with a reliable long term structural integrity are as old as aviation. This issue has been spotted now and something is being done about it, which is the key differentiator between this and the MCAS issues.