Need info on LTE for a simulator

[Simon853]

Hi All,
It's been a while since I've posted here when I had to stop my training a couple of years ago due to illness.

Anyway, since then I've been involved in the desktop simulator scene. These days I'm writing a program that runs alongside Microsoft Flight Simulator and augments the flight dynamics, adding torque yaw, LTE, improved low speed instability, control sensitivity and whatever else I can find ways of making it do. My aim is to make Flight Sim that little bit more representative of the control inputs required to fly a helicopter. Initial feedback from folks who still fly has been positive.

What I'm looking for at the moment is information on LTE. i.e. Assuming a helicopter is hovering, at what windspeed would you begin to encounter main rotor vortex interference on the tail assuming the wind was from about 300 degrees on a counter-clockwise rotor, and at what windspeed would a wind from 270 degrees put a tail rotor into vortex ring state?

I realise this is all platform specific. I'm just after some ballpark figures for say a 206 or R22, as my software allows the user to adjust all the parameters to suit a particular model.

Best regards,

Si

[NickLappos]

Simon,
ALL helicopters show signs of a reduction in TR thrust during some low speed flight regime, the effect of some nasty wash or rotor tip vortex hitting the tail rotor. This reduction seems to be about 5% of the available thrust. Call this the "relative wind thrust reduction".

Where does this thrust reduction occur? On Comanche, you could see the yaw control shift and hear the fan sing at a hovering azimuth of 45 degrees (right of the nose). On an S76, the TR pedal shifts about 5% when the wind is from about 60 degrees relative (right). On the plots provided for the B206, it is from about 90 to 135 degrees from the left.

What does this thrust reduction do? On a helo with a TR that is sized to suffer this small loss of thrust and still do its job, nothing. This situation is true of perhaps 95% of the helicopters built. On a helo that has almost NO TR thrust margin to spare, the loss of thrust causes loss of yaw control.

LTE is the resultant of that problem, and is not simulatable unless you first "build" a TR that is very small, and that has little excess thrust, and then also build in a reduction in thrust at a specific azimuth.

LTE has nothing to do with a pilot who pulls too much power, reduces rpm, runs out of yaw control, and then blames LTE.

[Simon853]

Thanks Nick. Much appreciated.

Si

[delta3]

Nick

why this assymetry ?

Just looking from above the MR-super vortices can as will interfer from the right (say 45-60 degrees) and from the left.

d3

[Charles du Plessis]

Hi my name is Charles and I am involved in building rotary wing part task trainers. I would be most interested in talking to you about what you are doing. I am fairly new to PPrune and do not want to infringe any of the protocols so if you can contact me on my e-mail address at [email protected].

Kind regards

[plaskon]

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/aba9e26c4d43dfab862569e7007463bf/$FILE/ac90-95.pdf