Takeoff roll

[baobab72]

Hi folks
Still tryi g to figure out the takeoff technique and the inputs i have to apply to keep the darn ship straight!!
At the beginning of the run, cyclic froward to redirect some total lift forward - namely thrust - to induce a forward motion.
As the helicopter accelerates maintain ground path with pedals.
At 10 kts or so transverse flow will cause the front portion of the rotor to move into cleaner more horizontal air, reducing the vertical component of the induced flow, resulting in a greater aoa for the same pitch and thus in a greater lift, than the rear portion of the rotor. Due to gyroscopic precession, the max increase in lift occurs 90 degrees away which translates in a tendency of the helicopter to turn right which must be compensated for by applying left cyclic.
Between 16 to 24 knots the disk will move away from its downwash, the resultant relative wind will become more horizontal, greater aoa for the same pitch, lift increases which reflects in a tendency of the heli to baloon up if nor compensated for by a forward motion of the cyclic.
The tail rotor operates in cleaner air as well, resulting in an increase in side thrust and thus a tendency to yaw to the left which must be compensated for by right pedal.
At 50 kias release the pressure on the cyclic, allowing the helicopter to rotate to 60 kias attitude for the climb, eventually increasing power to takeoff power if any available with respect to hover power, not to exceed limited to power - mcp plus 0.9 for the r22. Apply left pedal to maintain trim.
At 300 ft agl turn crosswind continuing climbing and set mcp from the placard.
50ft prior to tpa apply fwd cyclic to accelerate to 70kias, upon reaching 70kias adjust collective as required - 21"MAP roughly.

Are the above considerations correct or i have the sequence of events messed up?

Many thanks

Baobab72

[misterbonkers]

Maybe you're thinking about it too much?

Just try ignoring the ASI, look forward out of the windshield and apply control inputs required to keep the aircraft where it's going - as hopefully demonstrated by your instructor!

It wont be EVER be perfect - it will just improve with experience.

[RVDT]

Still tryi g to figure out the takeoff technique and the inputs i have to apply to keep the darn ship straight!!
At the beginning of the run, cyclic froward to redirect some total lift forward - namely thrust - to induce a forward motion.
As the helicopter accelerates maintain ground path with pedals.
At 10 kts or so transverse flow will cause the front portion of the rotor to move into cleaner more horizontal air, reducing the vertical component of the induced flow, resulting in a greater aoa for the same pitch and thus in a greater lift, than the rear portion of the rotor. Due to gyroscopic precession, the max increase in lift occurs 90 degrees away which translates in a tendency of the helicopter to turn right which must be compensated for by applying left cyclic.
Between 16 to 24 knots the disk will move away from its downwash, the resultant relative wind will become more horizontal, greater aoa for the same pitch, lift increases which reflects in a tendency of the heli to baloon up if nor compensated for by a forward motion of the cyclic.
The tail rotor operates in cleaner air as well, resulting in an increase in side thrust and thus a tendency to yaw to the left which must be compensated for by right pedal.
At 50 kias release the pressure on the cyclic, allowing the helicopter to rotate to 60 kias attitude for the climb, eventually increasing power to takeoff power if any available with respect to hover power, not to exceed limited to power - mcp plus 0.9 for the r22. Apply left pedal to maintain trim.
At 300 ft agl turn crosswind continuing climbing and set mcp from the placard.
50ft prior to tpa apply fwd cyclic to accelerate to 70kias, upon reaching 70kias adjust collective as required - 21"MAP roughly.

Are the above considerations correct or i have the sequence of events messed up?

Bao72,

No disrespect at all but do yourself and others a favour -

Easy reading and the man is a true icon and gent. Very little formula.

Will most definitely answer all your queries above. Get your head around it and you will as expert as most if not more.

Helicopter Aerodynamics #1
by Ray W. Prouty (http://www.actechbooks.com/products/act531/)

Helicopter Aerodynamics #2
by Ray W. Prouty (http://www.actechbooks.com/products/act534/)

Part with a bit of cash and all will be revealed.

You will get 20 different and possibly incorrect answers here.

[Aucky]

At the beginning of the run, cyclic froward to redirect some total lift forward - namely thrust - to induce a forward motion. yes, and usually raise collective a little to maintain height (counter loss of ground cushion) in light winds, with a touch of left pedal (in CCW rotating helis).

As the helicopter accelerates maintain ground path with pedals. Actually you fly the 'path' with the cyclic, but keep the skids straight with the pedals.

At 10 kts or so transverse flow will cause the front portion of the rotor to move into cleaner more horizontal air, reducing the vertical component of the induced flow, resulting in a greater aoa for the same pitch and thus in a greater lift, than the rear portion of the rotor. Yes

Due to gyroscopic precession, the max increase in lift occurs 90 degrees away which translates in a tendency of the helicopter to turn right which must be compensated for by applying left cyclic. To be a pedant, gyroscopic precession only truly describes the (similar) behaviour of a solid object with rigidity, such as a wheel, gyro, or arguably a rigid rotor head, however in any other system that allows flap and coning it's down to aerodynamic forces... It's the disc flapping to equality: You are only describing the short period of time in the early acceleration where there is a big difference in AOA at the front and back of the disc due to 'transverse flow effect'. During this short time, a blade that is moving from the 3 'o' clock towards 9 'o' clock (CCW rotating head) is experiencing an above 'average' AOA so it flaps up, with it's maximum rate of flap-up at the 12 'o' clock position after which it continues to rise but the rate of upwards movement is reducing, until it reaches it's high point at the 9 'o' clock. The opposite blade moving from the 9 'o' clock to the 3 'o' clock is experiencing a below 'average' AOA and so flaps down, with it's maximum rate of flap down in the 6 'o' clock to a low point at the 3 'o' clock position. The fact the blades are flapping up and down, means they modify their own AOA, and the lift produced across the disc finds a new equilibrium, but at a new disc attitude which will in turn effect the fuselage attitude... If we don't correct this with left cyclic we would roll right. By correcting with left cyclic we increase the pitch angle at the 6 'o' clock, and reduce the pitch angle at the 12 'o' clock, evening out the AOA differential across the front and back halves of the disc, which will flap back towards a level disc attitude. It's easy to call this gyroscopic precession, but it's not strictly true :ok:

Between 16 to 24 knots the disk will move away from its downwash, the resultant relative wind will become more horizontal, greater aoa for the same pitch, lift increases which reflects in a tendency of the heli to baloon up if nor compensated for by a forward motion of the cyclic. Yes, especially when transitioning in light wind conditions where it is very pronounced, ALSO throughout the transition you must also overcome flap back from the increasing disymmetry of lift as you accelerate. Similar to the transverse flow effect aerodynamically, but starts 90 degrees earlier in the blades rotation. The blade on the advancing side (6 'o' clock to 12 'o' clock) produces more lift (initially) than on the retreating side due to differential in 'V squared' over the airfoil on each side of the disc, so the advancing blade starts to rise, but in doing so reduces it's AOA (due to an increase in induced flow). The retreating blade produces less lift initially, starts to fall, but in doing so increases it's AOA, so the disc has stability and has flapped to a new position of equality but in a new disc attitude. Result is blade high at 12 'o' clock, blade low at 6 'o' clock, which if uncorrected for will pitch the nose up. It must be countered with some forward cyclic.

In essence, as you accelerate you push the cyclic forwards and slightly left in a CCW heli, however manufacturers build in a little phase angle offset into the head knowing that disymmetry of lift is predictable, so you don't have to move the cyclic very far to the left as you continue to accelerate through the flight envelope.

The tail rotor operates in cleaner air as well, resulting in an increase in side thrust and thus a tendency to yaw to the left which must be compensated for by right pedal. Yes, and the vertical stabiliser starts to 'work' as airspeed increases, producing an increased thrust in the same direction.

At 50 kias release the pressure on the cyclic, allowing the helicopter to rotate to 60 kias attitude for the climb, eventually increasing power to takeoff power if any available with respect to hover power, not to exceed limited to power - mcp plus 0.9 for the r22. Apply left pedal to maintain trim. Yes - but, if you do still have power in hand to pull at the point of reaching 45-50 kts remember your nose will pitch-up as you pull in the remaining power so you may even need a little forward cyclic to avoid pitching higher than the 60kt attitude.

Sounds like you got it to me :ok:

You will get 20 different and possibly incorrect answers here. Number 1 in the list of BS answers :E

[RVDT]

Aucky,

No. 1 - check.

Re-read your answers after you have read the books! :rolleyes:

[Aucky]

:( oh well... always worked for me :ouch:

[AnFI]

Aucky was so humble and stated the established thinking with clarity - i 'thort' - that was a pretty inappropriate firm put down RDVT ?

Obviously it doesn't actually work like that. If you've seen Those Magnificent Men In their Flying Machines you'll know that you can't actually fly a flying machine by knowing each effect (even if you do actually catch them all) and responding in anticipation of them occurring. You actually need to look out of the window and respond with the appropriate control to maintain each parameter where you want it to be. Feedback loop - respond to the feedback to be in control.

[Ascend Charlie]

Try balancing a broom handle on your fingertip.
Then try to describe what you are doing with your finger while it is happening - you can't.

You just do whatever you have to do with your finger (working the cyclic) to make the top of the broom handle (the attitude) stay steady.

Don't over-think it, just do whatever is needed to hold the attitude steady, whether it is a flat attitude (cruise, climb, hover) or leaning to one side (turning).:8

[baobab72]

Hi guys
Thanks for your answers!
I am aware of the fact that you can not think about all the events that are taking place as they are unfolding during the takeoff roll, however i would like to have a grasp on the reason why those inputs are needed, even though with the right amount of practice they should become second nature to you, as you consolidate your muscle memory.

I have been flying jets for the last 20 years and it is a bit frustrating to me ignoring the reason behind an input even though i dont think it over, but at least i have to understand to manage that energy!

Many thanks

Baobab

[RVDT]

B72,

Try starting off from OGE hover. Much easier.

Answers on the back of a postcard to........................................:E