Hey all, I don't recall if this was discussed in Roskam or Raymer, but didn't see it at a glance.
Once concern in choosing ground angle for a tricycle gear aircraft is avoiding the nose wheel touching down first. No one wants to be a Cessna 182 or similar.
What is the appropriate critical case to consider for this?
Obviously, the least-critical case is a nicely flared, near-stall landing, where vertical velocity goes to zero just as the pilot greases it in, so flight path is at a 0° angle relative to runway path, and CL at landing is close to CLmax. If CLmax is at a wing AoA of, say, 15°, it's easy to see how this would have the nose well up in the air.
It seems like a sane critical case is a pilot who sets up a stabilized Vref approach at CL of CLmax/1.69, along a 3° approach path, and just takes a nap from there -- flies it into the ground at this angle, and without flaring. If this CL is achieved at a wing AoA of, say, 9°, this combines with the approach path to mean that the wing angle relative to the ground at touchdown is only 6° -- substantially less than above.
And of course steeper approaches are possible, and approaches at more than Vref...
It's easy to come up with a design where either of the above is fine, so maybe this isn't a common topic; but then, C182s sure do land nose-first a lot, and that 6° number that I pulled out of my imagination hole isn't that far off from the ground angle of a C182.
So: Informed statements or (even better) references as to what condition should be considered here requested!
Once concern in choosing ground angle for a tricycle gear aircraft is avoiding the nose wheel touching down first. No one wants to be a Cessna 182 or similar.
What is the appropriate critical case to consider for this?
Obviously, the least-critical case is a nicely flared, near-stall landing, where vertical velocity goes to zero just as the pilot greases it in, so flight path is at a 0° angle relative to runway path, and CL at landing is close to CLmax. If CLmax is at a wing AoA of, say, 15°, it's easy to see how this would have the nose well up in the air.
It seems like a sane critical case is a pilot who sets up a stabilized Vref approach at CL of CLmax/1.69, along a 3° approach path, and just takes a nap from there -- flies it into the ground at this angle, and without flaring. If this CL is achieved at a wing AoA of, say, 9°, this combines with the approach path to mean that the wing angle relative to the ground at touchdown is only 6° -- substantially less than above.
And of course steeper approaches are possible, and approaches at more than Vref...
It's easy to come up with a design where either of the above is fine, so maybe this isn't a common topic; but then, C182s sure do land nose-first a lot, and that 6° number that I pulled out of my imagination hole isn't that far off from the ground angle of a C182.
So: Informed statements or (even better) references as to what condition should be considered here requested!
