Autorotation

[Brien]

What is the angle of the blade at the tip of a UH-1 in Autorotation. Is this
angle somewhat the same for most Helicopters?

[Steve R]

Which angle are you asking for?

Do you want to know what the blades actual AoA (angle of attack) is or do
you want to know what the blades angle of incidence is?

Steve R.


"Brien" > wrote in message
...
> What is the angle of the blade at the tip of a UH-1 in Autorotation. Is
> this angle somewhat the same for most Helicopters?
>

[Brien]

Angle of incidence?

"Steve R" > wrote in message
...
> Which angle are you asking for?
>
> Do you want to know what the blades actual AoA (angle of attack) is or do
> you want to know what the blades angle of incidence is?
>
> Steve R.
>
>
> "Brien" > wrote in message
> ...
>> What is the angle of the blade at the tip of a UH-1 in Autorotation. Is
>> this angle somewhat the same for most Helicopters?
>>
>
>

[Beav]

"Steve R" > wrote in message
...
> Which angle are you asking for?
>
> Do you want to know what the blades actual AoA (angle of attack) is or do
> you want to know what the blades angle of incidence is?

My guess would be he wants the angle as measured on the ground like we'd do
on an RC heli. So incidence, not AoA.

I'm willing to bet he's an RC flyer too coz they're the only ones who want
to know that info :-))

As it happens, I'd be interested in knowing what the incidence angle is with
the lever fully lowered and the heli sat on the floor. I know it's nothing
like as negative as we can usefully make use of on RC machines, but there's
probably an optimum static setting for each type of heli.


--
Beav

Reply to "beavis dot original at ntlworld dot com" (with the obvious
changes)

[Flyingmonk]

OK, I'll crank her up, you hold the tape measure. ; ^)

Bryan "The Monk" Chaisone

[Steve R]

"The OTHER Kevin in San Diego" <skiddz "AT" adelphia "DOT" net> wrote in
message ...
> On Thu, 8 Sep 2005 16:35:41 +0100, "Beav"
> > wrote:
>
>>
>>"Steve R" > wrote in message
...
>>> Which angle are you asking for?
>>>
>>> Do you want to know what the blades actual AoA (angle of attack) is or
>>> do
>>> you want to know what the blades angle of incidence is?
>>
>>My guess would be he wants the angle as measured on the ground like we'd
>>do
>>on an RC heli. So incidence, not AoA.
>>
>>I'm willing to bet he's an RC flyer too coz they're the only ones who want
>>to know that info :-))
>>
>>As it happens, I'd be interested in knowing what the incidence angle is
>>with
>>the lever fully lowered and the heli sat on the floor. I know it's nothing
>>like as negative as we can usefully make use of on RC machines, but
>>there's
>>probably an optimum static setting for each type of heli.
>
> I'd be interested in seeing this data measured at various points along
> the blade to get an idea of the twist various manufacturers employ to
> avoid tip stalls...

I've read that autogiros generally fly with a fixed incidence setting of +2
to +3 degrees. I'd assume that helicopters, in a steady state autorotation
would be somewhere close to that. However, autogiros do nothing but
autorotate so I'd think that their rotor blades would be optimized for that.
Since helicopters power their rotors, they use different airfoils and the
optimum pitch settings may be different.

As to collective full down incidence settings, I've been told that 0 degrees
is pretty much it. One person told me that some ships are set as low as -1
but that's only to assist in rpm recovery if the pilot gets sloppy and lets
the rpm's degrade to much. To hold that setting for too long would
overspeed the rotor system. I have no idea if any of that is true or not.

Kevin, I don't think that blade twist is used to prevent tip stalls. My
understanding is that having it improves the efficiency of the rotor system
at or near hover. The trade off is that it compromises cruise performance.
It all depends on what the machine is designed to do.

Do you have a reference on the tip stall point? I'd be interested in
learning more on that if I've got this wrong.

Fly Safe,
Steve R.

[Beav]

"The OTHER Kevin in San Diego" <skiddz "AT" adelphia "DOT" net> wrote in
message ...
> On Thu, 8 Sep 2005 16:35:41 +0100, "Beav"
> > wrote:
>
>>
>>"Steve R" > wrote in message
...
>>> Which angle are you asking for?
>>>
>>> Do you want to know what the blades actual AoA (angle of attack) is or
>>> do
>>> you want to know what the blades angle of incidence is?
>>
>>My guess would be he wants the angle as measured on the ground like we'd
>>do
>>on an RC heli. So incidence, not AoA.
>>
>>I'm willing to bet he's an RC flyer too coz they're the only ones who want
>>to know that info :-))
>>
>>As it happens, I'd be interested in knowing what the incidence angle is
>>with
>>the lever fully lowered and the heli sat on the floor. I know it's nothing
>>like as negative as we can usefully make use of on RC machines, but
>>there's
>>probably an optimum static setting for each type of heli.
>
> I'd be interested in seeing this data measured at various points along
> the blade to get an idea of the twist various manufacturers employ to
> avoid tip stalls...

I'm under the illusion that a twisted blade is twisted to allow lift to be
generated more evenly along the blade as opposed to most of it being created
by the outer 1/3rd. Could be ******** mind, but it makes sense to me.


--
Beav

Reply to "beavis dot original at ntlworld dot com" (with the obvious
changes)