Is there any formula or rules for the length of landing gear struts?  I know the Corsair had gull wings to lengthen the landing gear because of it's large propeller.  But what determines the length of a landing gear strut?

Noel

 

1 hour ago, birdguy said:

Is there any formula or rules for the length of landing gear struts?  I know the Corsair had gull wings to lengthen the landing gear because of it's large propeller.  But what determines the length of a landing gear strut?

Interesting question and not one with a simple answer. While there is no formula, there are certain basic considerations, the main one relating to clearances. This could be for prop blade clearance, or for underslung jet engines, particularly in the event of a heavy landing. Wing position is significant, especially with tricycle undercarriages.  If the gear is wing mounted, then higher wings mean longer landing gear. Longer main legs mean more twisting forces applied to the pivot points and more stress on the locking struts. This is allowed for at the design stage.

Larger aircraft need special consideration of compression forces when landing and the amount of gear travel required to absorb them, without having to make the gear too bulky or heavy. The gear travel required directly affects the main landing gear length. Another clearance requirement is for long body varients of many airliners. To achieve the optimum angle of attack for takeoff brings the increased risk of a tail strike. The answer in some cases is to increase the length of the main gear, but this has design complications because the wheel bays may need to be extended, or the leg may have to be compressed on retraction. Neither is a simple prospect. 

A prime design factor is which way the landing gear needs to retract. Inwards, outwards, or in some cases backwards or forwards, with or without complex folding mechanisms. Longer landing gear requires more space. This in turn is related other factors like wing thickness and components within the wings, like tanks or wing spars, and in the case of older warbirds the need to fit in multiple guns and their ammunition boxes. Thin wings may necessitate more complicated gear retraction systems, but that can increase the risk of faults. The EE Lightning had quite long outward retracting main gear and thin wings, but it could use a straightforward retraction method because it had very high pressure tyres which were quite narrow, so they could still be accomodated without added complication.

Aircraft track (distance apart of main wheels) is another consideration. Narrow track aircraft can be pigs to land safely in gusty crosswind conditions. Think F104 or the F16. And powerful single props like the Spitfire need very careful power handling on takeoff because swinging also creates a rolling effect,  In the case of the Corsair the gull wing allowed the gear struts to be shorter than they would otherwise have to be for prop clearance and also provided the bonus of a wide track. Both factors were beneficial for carrier operations.

Edited September 25, 20232 yr by Biggles2010
accuracy

Thanks John for a clear and authoritative answer.

Noel

46 minutes ago, birdguy said:

Thanks John

Noel, I'm sure there are other things I have missed, but in writing about this it made me think about the 737 Max8  accidents. The clearance for the bigger engines could have been dealt with by extending the undercarriage which could have avoided moving the engines forward with the need for changes to the trim system and the fatal consequences. However it was not practical (read too expensive) to implement the changes to the wheel wells and gear mountings which would be needed. Despite the safety mods, I still feel uncomfortable flying in a Max8.