NTSB Recommendation re Airbus Rudder Travel Limits

[protectthehornet]

if one could ''right'' a plane in wake turbulence just using aileron/spoilers and not rudder...one would do that

and if that was insufficient, rudder would be used.

anyone remember the DC9 that couldn't pull out of the wake and was lost?

[glad rag]

Why is the Airbus fin attached with an alloy fitting down one side and a direct
composite fitting down the other-

Where's the HF shunt (antenna) fitted on these aircraft?

[protectthehornet]

and how long is the nelson river bipole?

[DozyWannabe]

anyone remember the DC9 that couldn't pull out of the wake and was lost?

Yes, and the AA training that indicated rudder could be used was based on the DC-9 series - in fact the video of the training session shows the instructor using a DC-9 model to illustrate the technique. That technique did not or should not apply to the A300 series - in fact any large-wide-bodied airliner, because the surface area of the rudder is so much larger. Larger airliners tend to have less severe reactions to wake vortex encounters because their momentum/inertia is so much greater - as such, ailerons should be more than sufficient.

I know one DC-9 was lost on a training flight after encountering the wake vortex of a DC-10, and I think it was either a DC-9 series or a bizjet that was lost in the wake of a 757 - which led to the 757 getting a special classification in ATC separation, because the design of it's wing generated wake vortices considerably larger than those generated by any other aircraft of it's size.

[protectthehornet]

dozzywannabe

the size of the rudder and vertical stabilizer are based more on the need of the rudder to counter an engine out situation...as the DC9/MD80 series has engines close together, there is less need for a big rudder than the traditional underwing mounted engines like on the A300.

so, this makes my case that the DC9/MD80 is a stronger plane than the A300?
;-)

[DozyWannabe]

It's like comparing an articulated semi to a (US) full-sized sedan in terms of the amount of air displacement required to affect it's direction of travel, as well as the amount of air displacement it leaves in its wake.

Also, the smaller a hollow object is, the greater structural rigidity it tends to have, presuming the thickness of the material is roughly equal - that and the difference in the volume of air contained when such a hollow object is pressurised is why data from a decompression event in a narrow-body like a 707 cannot reliably be extrapolated to a widebody like a DC-10 (or an L-1011, or an A300 for that matter) - something the industry found out the hard way in the mid-70s.

The DC-9 is therefore structurally marginally more rigid than a widebody, but the flipside of that is it's relative susceptibility to extreme upset in a wake vortex encounter.

[Graybeard]

HF Antenna

Glad Rag:

Where's the HF shunt (antenna) fitted on these aircraft?

HF currents causing VS damage was my initial thought on this accident back then. Other HF knowledgable guys have agreed, but we don't have any details from this accident. Neither do we know if HF currents were even addressed in the investigation.

It's in the leading edge of the vertical fin. Transmitting HF generates up to hundreds of amps which must pass through the VS to the fuselage, as the entire airplane is the antenna. The connection must be clean, or heat will be generated. Carbon is a resistive conductor that would heat up if current passed through it.

The antenna spec for the DC-10, the standard of good HF antenna design, is 8 milliohms maximum. Boeing didn't know what it was doing when it put HF shunt antennas in the 767, and it showed in poor performance. I don't know if Airbus was any better.

FWIW, the guy who designed the DC-10 HF antenna was an ex-pat Brit.

GB

[PA-28-180]

"I think it was either a DC-9 series or a bizjet that was lost in the wake of a 757 ".......

It was a bizjet following the 757 that was lost due to wake turbulence....happened in Southern (?) California.

[Piper_Driver]

It was a Westwind biz jet that crashed on approach to John Wayne airport in 1993. the Westwind did have a wake turbulence encounter with a 757 that it was following. The CEO of In-N Out Burgers was killed on the flight.