AoA

[David Smith]

I have been watching this thread for several days,
we are not going to get practical AoA displays for
gliders in the near future so how is the best way to
get it right as often as possible?

We have the ASI, Attitude and Feel and I guess that
we all use some combination of all 3 to fly efficiently,
so what is efficient?
Is it Best L/D or Min Sink or in between or in a flapped
glider the same AoA with a different flap setting?

For circuit and landing it cannot be Min Sink that
is much too close to stall speed so circuit AoA would
have to be different to thermaling AoA at the same
flap setting.

Any comments

Dave

[Martin Gregorie[_1_]]

David Smith wrote:
> I have been watching this thread for several days,
> we are not going to get practical AoA displays for
> gliders in the near future so how is the best way to
> get it right as often as possible?
>
> We have the ASI, Attitude and Feel and I guess that
> we all use some combination of all 3 to fly efficiently,
> so what is efficient?
> Is it Best L/D or Min Sink or in between or in a flapped
> glider the same AoA with a different flap setting?
>
Depends what you're doing.

- min.sink is best for climbing in weak lift, not so important in
strong lift, and terrible if you're trying to cover ground.

- best l/d is really only useful if you're stretching glide in
neutral or very weak conditions. If you're flying between
thermals in conditions when you're using a non-zero MC setting
then best l/d is too slow.

- flaps don't change the min.sink and best L/D speeds. Only
ballast does that. At least, that's true for an ASW-20. You
memorize the recommended speed ranges for different flap
settings and work to those, remembering that the flap
setting also affects Vma and Vne.

> For circuit and landing it cannot be Min Sink that
> is much too close to stall speed.
>
Efficiency is unimportant at this stage unless you've screwed up and are
too low. For starters, the wheel should be down and that destroys glide
efficiency. If you can't easily fly a planned circuit from high key and
use half brake for most of finals then you've misread the conditions
and/or forgotten how to plan a circuit. For a normal circuit I'd say not
slower than best glide after high key and not below 50 kts + 1/2 wind
speed on base and finals.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Sarah Anderson[_2_]]

Hi David,

As one lurker to another then..

Why won't we get practical AoA displays for gliders? People are thinking about it.

Although, I see in the current Sailplane & Gliding, ( pp20-21, the "Idaflieg summer
meeting") pics of an AoA probe that is nearly a meter long duct-taped to the nose of a twin Astir!
OK, maybe that isn't practical. I'm also not excited about the flightsafety AoA price or the installation -
I understand it requires cutting a hole in the fuse.

David Smith wrote:
....
> so what is efficient?
> Is it Best L/D or Min Sink or in between or in a flapped
> glider the same AoA with a different flap setting?

Optimal speed ( best L/D or whatever ) depends on what you want to do, cruise, climb..
Independent of that best speed theory, the polars for a flapped glider at various settings should be in
the POH. So for a given speed, you could see what flap setting would give you the best L/D or least
sink speed ( depending on what you want to do ).

I have also seen drag rake suction probes on flapped gliders, on the trailing edge.
These were supposed to be indicate on a meter the "amount of drag", and you set the flaps to
minimize this. Does anyone have any positive or negative experience with these devices, or a source?

--Sarah