AAIB September 2004

[Hilico]

MD902, NOTAR fan damaged, cause tba - report. (http://www.dft.gov.uk/stellent/groups/dft_avsafety/documents/page/dft_avsafety_030917.hcsp)

Ponsford Bensen B8MR autogyro, PIO / stability questions - report. (http://www.dft.gov.uk/stellent/groups/dft_avsafety/documents/page/dft_avsafety_030918.hcsp)

The latter report is particularly detailed and makes two safety recommendations that have been accepted by the CAA.

[pilotwolf]

Just read my copy of the AAIB report...

Just wondering if someone can enlighten me on a few tech points of the MD902 - just out of interest. Having never got to play with these machines!

Where does the airflow come from. Is it the direct exhaust of the engine or provided by a separate inlet and fan?

Reason for asking was the report doesn't make clear the amount of damage to the fan and I assume that the intake, if separate would have a coarse filter/grill to prevent large items being ingested. Or if the airflow is from the engine anything damaging the fan would have had to passed through the engine stages, which would have caused damage there too?

Or at risk of slandering the engineers, (but an excellent mechanic always told me your best preflight should be after the ship comes out of the shop), is it possible something could have been left in there during a the annual? But would have thought that would have caused damage during test flight.

[Hilico]

Don't know if it's anything like the MD520, but that has an air inlet just behind the MR (covered with a mesh) and the fan lives a short distance behind that.

Nice to see somebody taking notice of my monthly effort!

[pilotwolf]

Yeah that was my memory of them....

Would have replied earlier but my copy only arrived today :(

[SilsoeSid]

This seems to show what I think youre after.

http://www.geocities.com/pprunessilsoesid/AirlinersNetPhotoID533238.jpg airliners.net link not working.
by Derek Pedley

And the rest as per hilicos decription.

[pilotwolf]

Great! Thought as much but tried googling without much luck.

So assume the airflow is isolated from the engine(s) airflow? If you were unfortunate enough to suffer blockage or fod to the notar fan it wouldn t affect the engines? (I know the chances are slim to get fod that selective!)

For example if you were unlucky enough to get a plastic bag blocking the intake is there an alternate intake or would you lose yaw control?

[SilsoeSid]

Full tech description at MDHelicopters website (http://www.mdhelicopters.com/rotorcraft/models/MD900_Technical.htm)

Yes, airflow is isolated from engine airflow as can be seen in the photo. All is explained at the tech link above, however, briefly;

"The enclosed variable-pitch composite blade fan produces a low pressure, high volume of ambient air to pressurize the composite tailboom. The air is expelled through two slots which run the length of the tailboom on the starboard (right) side, causing a boundary-layer control called the “Coanda Effect.” The result is that the tailboom becomes a “wing,” flying in the downwash of the rotor system, producing up to 70 percent of the anti-torque required in a hover.
The balance of the directional control is accomplished by a rotating thruster. In forward flight, the vertical stabilizers provide the majority of the anti-torque, however directional control remains a function of the jet thruster."

Hope that helps.

[pilotwolf]

Bloody Google - why couldn't I find that!

Thanks for explaination - vaguely recalled how it worked but couldn't remember where the thrust was generated.