multi-gear bogie configs ?? 2

[rb1957]

attached are some screen grabs from a YT video, showing different a/c with multiple MLG with different "relaxed" bogie positions.

On all (?) the wing mounted gear bogies position fwd wheel up,
but the fuselage mounted gears are any which way ... fwd up, flat, fwd down.

Thoughts ?
One consideration would be the relative heights ... the wing mounted gear have longer strokes and so are lower and so impact the ground first with the more natural aft wheel contacting first.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

Landing gear arrangement and design is all about efficient energy absorption... for best strength-to-weight ratio, for all sizes and 'mission' requirements.

Optimum design ensures no potential 'waste' for potential to absorb energy absorption... unless there is a more urgent/critical design necessity.

Energy transfer between aircraft and solid surfaces [landing] begins the instant EACH tire [or tyre if You prefer] contacts the ground and goes from a round inflated/cold state... thru tread shear-scuffing and carcass compression and centrifugal tire 'spin-up' to rolling speed [kick/torque].

The 'bogy arrangement' is intended to spread-out these tire contact forces in relation to angle of attack, sink/descent rate, side-drift, over-an extended-time, etc...

Then the bogy progressively absorbs the compression and rolling drag kick/torque forces thru rocking motions until tires are in solid/deformed/rolling contact and the shock-strut begins to absorb compression load-energy thru the length of the stroke.

All this orchestrated energy absorption... this cascade of reactions/movement/burning rubber/etc... occurs and is directed directed thru the landing gear to the structure... in the span of just a few seconds. Then the tires/brakes/bogies/drag-and-side braces/shock-struts endure the undulation/strain associated with full transfer of weight/drag/side-slide, from wing-lift, solidly to the gear/supporting structure.

OH-YEAH... and ALL of this crazy loading, as described, occurs under ideal circumstances... over-weight emergencies, severe directional winds/turbulence, variable runway conditions [rain/snow/ice/slush/debris/rubber-build], tire/wheel/brake failures, leaking/flat shock-strut and bogy shock and leveler-components, extreme heat or extreme deep-cold, etc... all add into the chaotic and conflicting elements influencing landing gear design.

Uhhh my head-hurts, just describing this.

NOTE1. This description^^^^ is related to the main-gear: I have not really mentioned the nose gear. It doesn't include braking... but does include tire/shock/compression/side-load effects [due to steering and compression/pitching, braking-drag, etc]. AND, of course, it has 'a significant other design factor' related solely to ground-operations: 'towing' loads.

NOTE2... when I worked on fighters... One added problem, that was insidious, was 'empty and flight-weight creep', due to modifications and mission changes... which had significant effects on taxi, takeoff and TO abort. Yes everything stayed in 'design ranges'... but the heavier configurations always took a toll by shortening tire, brake and landing gear life. Example: avionics/antenna/wiring mods [weight/cg changes]... and changes to mission[sortie] duration [increasing, for fewer flights] by going from 1-to-2-to-3 external 500-gallon fuel tanks. Ughhhh... The unique problems they have. Worst case I ever encountered was an F-15D, 2-crew, max external ordnance, max fuel... then abort at take-off speed, using the tail-hook and cable-barrier. Lots of components affected/changed.

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]