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Nills Lagerbaak
17-08-2005, 10:56:26
http://news.independent.co.uk/world/asia/article306419.ece

Right, let's suppose for a second that this was true.
We all know that the lift achieved by a helicopter is proportional to the surface area of blades, speed of the blades and the air pressure.

What I don't know is the how much air there is on the summit of Everest, but it isn't enough to breath. I'm guessing the blades would have to turn at some rediculous speed to lift a copter.

Unless it's just the oxygen content that is lower up thre, but I think the air in general is of a lower pressure.


HELP!

protein
17-08-2005, 11:03:21
There's less air in general. Maybe they are really fat, very angled blades that go stupidly fast?

protein
17-08-2005, 11:07:23
http://www.eurocopter.com/site/FO/scripts/siteFO_accueil.php?lang=EN

Can't see anything helpful on the site. I assume that since it's a test flight it's a plane in development and not for sale yet.

Nills Lagerbaak
17-08-2005, 11:08:59
Well, let's assume they are angled for maximum lift (so they can only go up, never forward)

Very fat blades would have to be very strong (i.e. heavy) to reach the kind of speeds that would be required. I just can't see it happening myself. but I'd very much like to work out the speeds that wowould be required though. Might do it this evening (yes I'm that sad!)

Beta1
17-08-2005, 11:11:27
They claim to have flown the same helicopter at 29,500 ft in france which would be high enough to reach the summit. I don't see why its not possible.

The air pressure is lower so there is less lift - breathing thing is just that our lungs don't opperate efficiently at lower air pressures.

Beta1
17-08-2005, 11:14:18
according to the web (so it must be true) the greatest height achieved in a copter in flight is 40,000 ft (although the engine subsequently failed and the pilot also set the record for the worlds longest autorotation on the way back down.

Nills Lagerbaak
17-08-2005, 11:16:01
Originally posted by Beta1
They claim to have flown the same helicopter at 29,500 ft in france which would be high enough to reach the summit. I don't see why its not possible.

The air pressure is lower so there is less lift - breathing thing is just that our lungs don't opperate efficiently at lower air pressures.

Yeah, I guess a more pertinent question is how much less is the air pressure at that height? Are we as humans just a bit lame at breathing?

protein
17-08-2005, 11:20:46
Originally posted by Nills Lagerbaak
Well, let's assume they are angled for maximum lift (so they can only go up, never forward)

Very fat blades would have to be very strong (i.e. heavy) to reach the kind of speeds that would be required. I just can't see it happening myself. but I'd very much like to work out the speeds that wowould be required though. Might do it this evening (yes I'm that sad!)
I think you can change the angle of the blade on helicopters, that only effects the upward lift though. From what I understand, the angle of the rota disk compared to the body of the plane is what makes the thing go forward or backward or sideways, the slowing or speeding up of the tail rota and angle of the tail fin provides the left or right rotation. I don't know though, how does a helicopter dip it's nose?

Nills Lagerbaak
17-08-2005, 11:42:28
Yeah, exactly, but the angle for maximum life results in zero forward/backward motion. (so for this calc. we have to assume just lift)

I think a helicopter changes the angle of the blades (by a mechanism on the shaft) this results in a slight forward motion, and then two small airplane type "flaps" can be angled to dip the nose down.

Funko
17-08-2005, 11:50:45
Pressure decreases exponentially with height according to the hydrostatic equation.

Dp = -rgDh where p = pressure, r = density, and h = height.

Sea level pressure is approximately 1000 milibars.

Pressure at the top of Everest is roughly 1/3 pressure at sea level.

Funko
17-08-2005, 11:54:37
Lift in a helicopter is proportional to air density.

Air density is proportional to pressure so the lift of the helicopter is proportional to air pressure

ie the helicopter will have 1/3 of its lift at the top of everest, assuming the same power output of the helicopter.

However

The engines on the helicopter are probably fuel burning and the efficiency of their burning will decrease as they take in less oxygen, so not only will you have less lift due to less atmosphere but you'll also be producing less power to turn the rotors.

protein
17-08-2005, 12:00:45
Originally posted by Nills Lagerbaak
Yeah, exactly, but the angle for maximum life results in zero forward/backward motion. (so for this calc. we have to assume just lift)

I think a helicopter changes the angle of the blades (by a mechanism on the shaft) this results in a slight forward motion, and then two small airplane type "flaps" can be angled to dip the nose down.
No, that's assuming the helicopter is in motion. A helicopter can dip it's nose (which is how it goes forward) from a static hover. I think it's all to do with the angle of the rota disk in relation to the body of the plane (rather than the angle of the individual blades on the rota disk). I know the rota blades can change their angle but I'm not sure what for because the amount of lift can be changed by powering up or down and increasing or decreasing the rota speed.

protein
17-08-2005, 12:02:35
One would assume that the change in angle of the individual blades is for higher flight at lower air pressure so that there is a higher angle of attack on the blades against the air and therefore more downward thrust?

Nills Lagerbaak
17-08-2005, 12:27:51
Originally posted by protein
No, that's assuming the helicopter is in motion. A helicopter can dip it's nose (which is how it goes forward) from a static hover. I think it's all to do with the angle of the rota disk in relation to the body of the plane (rather than the angle of the individual blades on the rota disk). I know the rota blades can change their angle but I'm not sure what for because the amount of lift can be changed by powering up or down and increasing or decreasing the rota speed.


They change the angle of the rota disc (the imaginary disc swept out bt the blades) in relation to the body by physically angling the shaft. (wish I could draw a piture)

What makes it more complicated is that to get 100% lift and no forward motion, the blades are angled any way. You only get forward motion by angling the same lifting force so that a component of it is in the forward direction which is why powering up and down can control purely forward speed too.

Nills Lagerbaak
17-08-2005, 12:29:10
Originally posted by Funko
Lift in a helicopter is proportional to air density.

Air density is proportional to pressure so the lift of the helicopter is proportional to air pressure

ie the helicopter will have 1/3 of its lift at the top of everest, assuming the same power output of the helicopter.

However

The engines on the helicopter are probably fuel burning and the efficiency of their burning will decrease as they take in less oxygen, so not only will you have less lift due to less atmosphere but you'll also be producing less power to turn the rotors.

Aha, so it is feasible. I would have thought that it would have been less than a third though, but you can't argue with the hydrostatic shiznit.

Nills Lagerbaak
17-08-2005, 12:31:08
I can see why the confusion might arise though. The blades are not purely for keeping it up, and then another system to make it go forward.

Although to add further compication you can have jet engine helicopters (like airwolf) that can do this!

protein
17-08-2005, 12:33:27
Originally posted by Nills Lagerbaak
They change the angle of the rota disc (the imaginary disc swept out bt the blades) in relation to the body by physically angling the shaft. (wish I could draw a piture)



Yeah. We're talking about the same thing then. Additionally to that, the angle of the individual blades can be changed - say from 30 degrees to 40 degrees - which changes the lift.

protein
17-08-2005, 12:34:33
The nose doesn't dip from any fins or anything, it dips because of the angle of the rotor "disk".

Nills Lagerbaak
17-08-2005, 12:37:26
Nothat wouldn't dip the nose by itself though. It would result in a horizontal helicopter rising up and going forward. That on its own will not cause the nose to dip. I think it's the "flaps".....will do some investigation.

protein
17-08-2005, 12:41:24
I believe that it has something to do with gyroscopes or gyroscopic principals. You definately hear the term "gyro" when people talk about helicopter controls.

Nills Lagerbaak
17-08-2005, 12:44:42
Aha, you are correct! I was forgetting that if you angle the rotor, not only do you get a forward component of the lift, but also more lift at the back, thereby tilting the machine forward)

From wikipedia, and excellent definition, from which a sample follows:

"For pitch (tilting forward and back) or roll (tilting sideways) the angle of attack of the main rotor blades is altered or cycled during the rotation creating a differential of lift at different points of the rotary wing. More lift at the rear of the rotary wing will cause the aircraft to pitch forward, a increase on the left will cause a roll to the right and so on."

It is indeed a complicated beast

Nills Lagerbaak
17-08-2005, 12:47:39
Jesus, I wouldn't want to be responsible for one of these:

The cyclic changes the pitch of the blades cyclically, causing the lift to vary across the plane of the rotor disk. This is how the pilot causes the aircraft to tilt, and the helicopter to move. The cyclic is usually controlled by the stick in front of the pilot. The stick controls the swashplate, which has a number of rods each connecting to a blade from the front. When the swashplate is not tilted, the blades are all at the collective angle. When it is tilted, the rods give a pitch-up at some azimuthal locations and a pitch-down at some others, hence create a non-uniform distribution of blade geometric angle of attack. This allows the rotor to tilt, in the way the stick is tilted. So the pilot can push the stick forward, and the rotor tilts forward, and the rotor produces a thrust in the tilted direction (forward in this case).

MoSe
17-08-2005, 12:53:56
Originally posted by Nills Lagerbaak
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We all know that the lift achieved by a helicopter is proportional to the surface area of blades, speed of the blades and the air pressure.

Just offhand at first sight: isn't it proportional to speed SQUARED?

Nills Lagerbaak
17-08-2005, 12:55:49
No lift is proportional to relative wind speed. Drag is proportional to relative wind speed squared.

MoSe
17-08-2005, 13:09:08
ah, um, OK.

after reading the whole thread, I am now figuring blades angled on one part of the turn and almost flat on the way, back, much like the rows in rowing...
:clueless:

what's the standard/average blades rpm we're talking about in a copter?

Nills Lagerbaak
17-08-2005, 13:13:40
It's all in the wikipedia definition, apparantly operating RPM has only 2% error margin!

I'm guessing 3000 at least.

Have you seen the twin blade helicopter (on the same shaft spining in oposite directions). This does away with the need for a tail rotor. CRAZY!!!

Beta1
17-08-2005, 13:16:44
think thats mad - the other week I saw a later model spitfire - that had two props turning in opposite directions on the front.

Apparently it had something like three times the HP of the 1 bladed version and had held the air speed record several times.

MoSe
17-08-2005, 13:30:59
will check wiki, thx

as the main purpose of the tail is to support the tail rotor, no need for a tail rotor means no need for a tail!

they could build a sphere (or a cube!) with a twin blade propeller!

MoSe
17-08-2005, 13:31:22
.

Nills Lagerbaak
17-08-2005, 14:01:10
Originally posted by MoSe
will check wiki, thx

as the main purpose of the tail is to support the tail rotor, no need for a tail rotor means no need for a tail!

they could build a sphere (or a cube!) with a twin blade propeller!

Where do I sign up for the test flight?

Funko
17-08-2005, 14:08:41
Awesome.

although twin rotored helicopters normally have tails so maybe there are some other control surfaces on the tail?

Nills Lagerbaak
17-08-2005, 14:10:55
Well, I'm sure it can be used to add tilt stability, but who cares, an massive flying dodecahedron would make my day, and I don't care if it's unstable :D

Funko
17-08-2005, 14:11:27
if you could find a suitably unstable pilot it'd compensate

Nills Lagerbaak
17-08-2005, 14:20:59
I've already requested an application form!

Beta1
17-08-2005, 15:52:49
you would keep the tail so you could tell which side was the back.

MoSe
17-08-2005, 16:01:15
GO BEYOND THE BACK!

er... :brwncard:

protein
17-08-2005, 16:10:13
So the individual blades tilt and then return to their normal position on each rotation?

Japher
17-08-2005, 16:11:19
That's Gilet Sensor Technology!

protein
17-08-2005, 16:13:51
Mach 3 Turbo!

Funko
17-08-2005, 16:13:56
Gillette.

Provost Harrison
17-08-2005, 16:35:02
King

Provost Harrison
17-08-2005, 16:35:24
Oh sorry, I thought this was word association :D

Nills Lagerbaak
17-08-2005, 16:39:40
Originally posted by protein
So the individual blades tilt and then return to their normal position on each rotation?

Yeah, depending on which side of the rotor the pilot wants more lift. It's totally crazy, such a complicated machine, I'm surprised there aren't more accidents!

protein
17-08-2005, 16:45:25
That is amazing! Presumably it isn't all done by computer - which makes it an engineering masterpiece.

Nills Lagerbaak
17-08-2005, 16:52:52
Indeed, very clever stuff! I might have to get me a radio controlled one (cheap indoor one of course!)

http://www.thaitechnics.com/helicopter/tg5/swash_plate2.jpg

King_Ghidra
17-08-2005, 16:54:59
Originally posted by Nills Lagerbaak
Indeed, very clever stuff! I might have to get me a radio controlled one (cheap indoor one of course!)


one word: robodog

Don't do it dude

Nills Lagerbaak
17-08-2005, 16:56:09
Ah, you mean Texter. Well, that was clearly a moment of other worldly detatchment. This time will be different......

Funko
17-08-2005, 17:04:13
Now you know how it works just get some meccanno and make your own.

Nills Lagerbaak
17-08-2005, 17:07:32
I think I could make the rotating shaft / swash plate part, but then I'd need a power source....hmm might have to dig out my old bike...

Funko
17-08-2005, 17:09:30
That's no way to talk about your mother.

Nills Lagerbaak
17-08-2005, 17:11:45
Your right! It'as the only way to describe your mum though.

Funko
17-08-2005, 17:12:43
Wacka wacka wacka (as both Fozzy Bear and a helicopter would say)

chagarra
18-08-2005, 01:41:44
Originally posted by Nills Lagerbaak
Have you seen the twin blade helicopter (on the same shaft spining in oposite directions). This does away with the need for a tail rotor. CRAZY!!!

See here.. http://www.airscooter.com/

Nills Lagerbaak
18-08-2005, 09:15:07
I ould love one of those! You need to have alarge expanse of open space, and ideally you'd want some interesting scenery to look at.

Funko
18-08-2005, 09:52:52
Wow. I want one so I can fly to work.

Nav
18-08-2005, 12:53:42
Originally posted by Nills Lagerbaak
Indeed, very clever stuff! I might have to get me a radio controlled one (cheap indoor one of course!)
I got an indoor one for christmas. Best Present Ever.

It has two main rotors one on top of each other that contra-rotate, and one small vertical rotor on the tail to do backwards and forwards motion..

SOoo much fun! :D

Nills Lagerbaak
18-08-2005, 12:56:00
Seroiusly?! Did you make it yourself (I think that's the best bit) Could you please send me a link to the one you have....


Anyway NAv, stop farting around in this thread and dish the dirt on what happens in the Funko's secret little boys grooming forum

MoSe
18-08-2005, 12:57:32
is it fitted with a camera? or a gun?

Beta1
18-08-2005, 13:15:33
how about one of these?

http://www.iwantoneofthose.com/XUFOFL.htm

Beta1
18-08-2005, 13:19:11
or this?

http://www.iwantoneofthose.com/BLARUN.htm

Nills Lagerbaak
18-08-2005, 15:39:33
Yeah, but are any of these self-assembly? I had such fun making the two differential gear boxes in my R/C car