Wheel Base and Track

[Boyington]

Can someone throw some light on the influence of wheel base and track on turning radius particularly on narrow taxi tracks.

[DaveReidUK]

Some good stuff here on the 747:

http://nicmosis.as.arizona.edu:8000/ECLIPSE_WEB/ECLIPSE_03/BOEING_747_SPECS/7474sec4.pdf

in particular about the difference in the turning characteristics made by the body gear steering.

[underfire]

What are you looking for, aircraft specific tracking/turn rad or in general?

There are a few Autocad based airport planning design tools...one can lay out the track, and simulate different ac running the track.

Wheel base, nose gear, tire slip...all sorts of fun variables

Generic slideshow on design: http://www.slideshare.net/pedrohectorcarreonazcue/geometric-design-taxiways

[Intruder]

"Influence"? Wider track and longer wheelbase generally mean larger turn radius. Is that not intuitively obvious? The absolute limiting factor in the turning radius of the wheelset is the track: With a locked wheel, radius ~= track width (e.g., tailwheel airplane with castering tailwheel and little resistance to turn).

[WeeJeem]

"Influence"? Wider track and longer wheelbase generally mean larger turn radius.

Am with you so far.

Is that not intuitively obvious?

"Intuitively obvious", eh? That's rather a dangerous phrase.

The absolute limiting factor in the turning radius of the wheelset is the track: With a locked wheel, radius ~= track width (e.g., tailwheel airplane with castering tailwheel and little resistance to turn).

Not in the taildraggers I fly, it isn't.

A locked wheel, fully-castoring tailwheel turn in a 'dragger would have me watching my tailwheel, not my other main; so my limiting factor would be wheelbase, not track.

[AerocatS2A]

Am with you so far.



"Intuitively obvious", eh? That's rather a dangerous phrase.



Not in the taildraggers I fly, it isn't.

A locked wheel, fully-castoring tailwheel turn in a 'dragger would have me watching my tailwheel, not my other main; so my limiting factor would be wheelbase, not track.

Assuming you can pivot on the inside main, the minimum strip width required for a turn will be track + wheel base. Whether it is a tail dragger or tricycle undercarriage will affect the technique you use to ensure all of the wheels remain on the runway at all times but not the strip width itself.

[underfire]

You cant use simply the track and wheelbase, as the center of the turn radius is not always the inside set due to wheel drag, ie the inside wheels dont pivot on the axis, but the theoretical center of turn is inside this, sometimes very far with multiple sets. There is also the max angle the nose gear can turn, which varies significantly by aircraft. On the 773 wheels are 5.5m from centerline, so turn center pivot point is about 10m from the gear...

Also depends on what the OP meant for taxi ways, and associated turns on those...

http://i64.tinypic.com/i35hzl.jpg

[Intruder]

Not in the taildraggers I fly, it isn't.

A locked wheel, fully-castoring tailwheel turn in a 'dragger would have me watching my tailwheel, not my other main; so my limiting factor would be wheelbase, not track.
OK. Then define the turn radius you want: main gear, all gear (ground radius), fuselage, entire airplane (gross radius)...

Assuming no skidding, the gross turn radius for the entire airplane will be approximately the distance from the innermost main wheel to the furthest outside point on the airplane (could be wingtip, tail, horiz stab...) PLUS the min turn radius of that wheel from the center of the turn. The turn radius of that inner wheel will depend on the nosewheel caster limit and drag of other gear, and could be near zero (maybe the width of the tread) for a fully castering nose/tail wheel and a simple tricycle gear arrangement. OTOH, the center of turn for a 744 is approximately at the leading edge of the wing, just outboard of the inboard engine nacelle.