Frum wrote (see)

Copied from your reference (above):

"Having an air foil shape on both the top and bottom of a wing now means airplanes and helicopters can fly upside down. By changing the angle of attack or pitch to negative when upside down, the rotor now produces lift in the opposite direction – pretty neat."

Did you miss these bits then Frum?

The Air Foil

All things that fly, from birds to supersonic aircraft and yes helicopters too - rely on air foils to create lift. An air foil (the shape of all wings if looked at from the edge) creates lift by producing lower air pressure on the top of the wing than the bottom.

Angle Of Attack

The other component of lift is angle of attack or in helicopter control terminology “PITCH”. If you angle the rotor blade or wing up (leading edge higher than the trailing edge) you get even more lift.

It might seem you could just use a flat board for a wing and just angle it upwards to get lift, but there would be so much drag and turbulence produced, the lift would be minimal for the amount of power that is being used.In fact you could keep adding more and more power and the only result would be more and more turbulence and drag acting against the lift produced.

Air foils are very efficient at creating lift with limited drag and turbulence - that is why they are used.

cysgod-du (Grand Slam 2008) wrote (see)

I was going to add that in a fixed wing you change the aerofoil shape and thus the differing speed of airflow over upper and lower surfaces of the aerofoil with the flaps, and it only needs s,all adjustments to do that.

Not forgetting this bit too!

"Certainly not all rotors have symmetrical air foils – some have semi-symmetrical or flat bottomed air foils depending on how efficient the rotor has to be. Symmetrical air foils are not nearly as efficient at producing lift as a flat bottomed air foil shape using equal amounts of power.

This is why birds don’t have symmetrical shaped air foil wings. The amount of energy to fly would be too great. I guess that is also why I have never seen a bird flying upside down."

cysgod-du (Grand Slam 2008) wrote (see)

Did you miss these bits then Frum?

No, they were explaining the background in simple terms before getting to the bit I quoted.

Where's Mal ?  It was his blox that started this.

Yes Parky, it is called "auto rotation," and having experienced it in the Air Ambulance, (Pilot exercise, so we recovered before the ground!) it ain't pretty"

(You actually use reverse collective to gain rotor speed as you decend and then pull up the collective to positive pitch which then generates the lift, slowing the decent, but the timing has GOT to be spot on!)

You pre-emted my edit above. It is the PITCH that is reversed as I described in my edit!

(And yes, it is during a power failure, although it would be rare for both engines to fail simultaneously)

cysgod-du (Grand Slam 2008) wrote (see)

Yes Parky, it is called "auto rotation," and having experienced it in the Air Ambulance, (Pilot exercise, so we recovered before the ground!) it ain't pretty"

(You actually use reverse collective to gain rotor speed as you decend and then pull up the collective to positive pitch which then generates the lift, slowing the decent, but the timing has GOT to be spot on!)

And bugger it, my flight tomorrow is off, the Jetranger has a turbine fault that wont be fixed until Monday, too late for Weston Helidays, Still better the fault came to light now rather than 2000 feet above the Bristol Channel, auto rotation ain't so clever into deep water!

Will have to wait for a couple of weeks now and fly into the Weston Helicopter museum instead!

Metric Kate wrote (see)

I spoke to Peter Snow on the phone once when his Battlefield Britain programme was in pre-production. He's as manic on the phone as he is on tv!!

When I lived in London, a few years back (about 2003), Peter Snow and his family (including now famous son) were sat at a 'pavement table' outside a pizza place on Regent St. (the bit north of Oxford Circus, towards BBC Broadcasting House).  I only noticed them because as I walked past, Peter was giving his order to the waiter, and he managed to order pizzas in exactly the same way that he describes a 4% swing to the Conservatives on election night.  He made ordering pizza seem very exciting and unpredictable, as if anything could happen at any moment.

Funnily enough, I was walking past said pizza place having just left a pub around the corner from BBC Broadcasting House, in which I saw Steve Lamaq and Des Lynham (not together).  Steve Lamaq was counting 'shrapnel' out of his pocket to buy a pint of cider, and Des Lynham ordered a cheese toastie at the bar.

I kid you not.  Three famous peeps in about 15 mins, and all of them ordering food or drinks.

For those that are interested, the pub was the Stag's Head on New Cavendish St.  If you're in the area, I recommend popping in - it's a small pub, but you're almost guaranteed to see somebody famous in there, due to its proximity to Broadcasting House.

Frum,

Here is a Youtube video of an almost perfect autorotation exersise (Which all pilots have to practice each year to regain thier rating.)

You can see clearly the moment the pilot pulls up the collective to positive pitch just about the time the helicopter reaches the tree line.

Great approach!

Flying hedgehog missile

But what it really needs is a way to hover and fire it's quills as harpoons - hmmm, the 'Black Hawk Hedgehog', I reckon it'd be a winner