Helicopter take-off

[Prudie]

When a helicopter is running and on the ground what happens to it physically to make it take off? Presumably the rotor speed is increased but is that all, do the blades alter angle (like flaps)? Just wondering.

[Philtaz]

Yes, Prudie, the angle of the blades is altered.

[TheWinner]

Hi Prudie,
I have recently been at an event where a chinook helicopter was.
I was filming it taking off, and the down draught threw me to the floor, and it was if someone had thrown a shovel-full of grit in my face.
It was unbelievable!

[Prudie]

Thanks Philtaz and hi The Winner, Now a Chinook is one thing I really don't understand how they stay up. Actually I don't know how any helicopter stays up. This has sparked a bit of a discussion - my OH says a plane revving along a runway will take off on its own just based on speed but I think the change of wing shape is required too (the flaps!) to make it lift.

[jackthehat]

The blades on a Chinook are immense and can be angled to take such huge 'bites' out of the air that the aircraft itself has no need to tilt.

[Philtaz]

I've been in quite a few helicopters when I served in Northern Ireland and there is no feeling like it.
One of the units I worked in had a Major from the Army Air Corps as its head and on the day I left he organised a flight for me with one of his colleagues in a Gazelle. I was taken on a hedge hopping flight around South Armagh which was finalised by the pilot completing a wing-over (apparently quite dangerous in a heli), which was exhilerating and terrifying at the same time!

[TheWinner]

Philtaz, you went in a gazelle? OMG!

[Philtaz]

Gazelle, Chinook, Puma and Lynx. Lynx was my favourite, awesome bit of kit.

[Philtaz]

Have to say the Gazelle flight was special because I was in the co-pilot seat, plus it is literally like being in a goldfish bowl.

[jackthehat]

My boy is currently under-going his CTT, after getting his wings......he was hoping for the Lynx but, as they will be being phased out shortly, he's got the Bell 212.

[Philtaz]

Forgot about the warhorse, the Wessex too.

[Prudie]

Good for him jack, bet your proud.
Philtaz that sounds a great memory. I would be very nervous in a helicopter (I figure if the engine fails you drop like a stone). I live near to a RNAS and see them over my house daily. They do an exercise that looks like hovering in the air but with the nose pointed down not far off vertical - it terrifies me to watch.

[Philtaz]

Not sure that's possible methyl. I believe the blades change their angle at the same time and cannot be altered independently. The rotors on the chinook may differ (front to back and vice versa) but not the individual blades, though I may be mistaken.

This may explain it a bit better:
https://www.youtube.com/watch?v=cf5iG299hzk

[Philtaz]

Not too sure Prudie. I was also based near where they trained RAF helicopter pilots (RAF Shawbury at the time, don't know about present day) and they used to practice engine cut-out drills, which was jaw-dropingly frightening, but only from a certain height, speed and flight direction.

Despite your fears, if you ever get the chance to fly in one go for it, there is nothing like it.

JTH, best wishes for your lad, hope he makes it.

[AlBags]

I know .. but I haven't the time right now!
I have done tip checks on a few helicopters (holding a stick and paper up into the rotors whist running) scary : )

Collective and Cyclic pitch are two ways of altering AOA on rotor blades. Check it out.
The weight of the AC is carried/moved along by upward lift through rotor head .. if this angle is a small amount forward of vertical, ac will gain forward speed quite easily.

[jackthehat]

My boy did most of his training in Squirrels at Shawbury......and some down at Middle Wallop, too.
I've already told him that I'll never fly with him. I'm a nervous flyer, anyway, and the temptation for him to terrify his mother would just be too delicious for him to resist........:o)

[sherrardk]

I've been in a Lynx - it was brilliant (although I didn't organise it properly so the school I was working at was besieged by phone calls asking if the school was under some sort of attack - not my best day).

[Andyvon]

Hi Prudie,

When a helicopter is on the ground with the blades idling they are exatly edge on to the air. When the heter wwants to tae off the pilot operates a control (cyclic) that increases the rotor speed and the angle of the blades causing them to 'push' more air downwards. The cross section of the blades also causes lift which assists take-off. Most modern helicopters are powered by a jet engine or two which power the rotor and the exhaust is directed back to form forward thrust moving the helicopter forwards. A Chinnok has two jet engines mounted on the rear fuselage. Helicopters steer to left or right by increasing or decreasing the speed of the tail rotor which keeps the machine going straight rather than spinning around it's own main rotor as it would if no tail rotor were fitted (or the linkage breaks).

There are variations such as older helicopters having piston engines and a few having a jet exhaust instead of a tail rotor, but that's generally how helicopters take off, hover and move forwards.