Re: A Waikerie slip up?

[Vassilios Mazis]

One thing is for sure, the climb gets no better.
But there is an interesting effect that few people are aware of:
Higher speed means higher Reynold's numbers accross all of the wing,
in direct proportion. Higher Reynold's number generally means higher
efficiency. Therefore, there may be some small improvement in the
glide angle.
I recall vaguelly that some model of the Ventus is quoted with an
extra 1/2 point of L/D max at maximum ballast.

regards

Vassilios Mazis

Greece

[Philip Plane]

In article >,
Vassilios Mazis wrote:

> Higher speed means higher Reynold's numbers accross all of the wing,
> in direct proportion. Higher Reynold's number generally means higher
> efficiency. Therefore, there may be some small improvement in the
> glide angle.
> I recall vaguelly that some model of the Ventus is quoted with an
> extra 1/2 point of L/D max at maximum ballast.

That's the case with the DG1000. From memory it's 45 and a bit dry
and just over 46 fully loaded.


--
Philip Plane _____
|
---------------( )---------------
Glider pilots have no visible means of support

[George William Peter Reinhart]

Wet Or Dry?
Nimbus 2C factory polar shows 47.5 @ 95 kph dry and 49@116 kph wet.
Cheers!

[Vassilios Mazis]

(Michael) wrote in message >...
> Vassilios,
>
> Do you want to say I cannot reach higher speeds with a dry glider?
>
> Cheers
> Michael
> ================================================== ===============
>
> > One thing is for sure, the climb gets no better.
> > But there is an interesting effect that few people are aware of:
> > Higher speed means higher Reynold's numbers accross all of the wing,
> > in direct proportion. Higher Reynold's number generally means higher
> > efficiency. Therefore, there may be some small improvement in the
> > glide angle.
> > I recall vaguelly that some model of the Ventus is quoted with an
> > extra 1/2 point of L/D max at maximum ballast.
> >
> > regards
> >
> > Vassilios Mazis
> >
> > Greece

Errr, No, you can reach whatever speed you like*, flying unballasted,
but your average X-country speed will drop relative to the theoretical
maximum. Improving glide speed is is the first-order effect of
increasing the Wing Loading (shifting the "polar"). The Reynold's
number effect (improving the best glide angle)is the secondary
side-effect and much smaller. It is also the reason why designing
winglets can be tricky.

You better rephrase your question though.


* NB perhaps it would be interesting to discuss the effect of ballast
in
Rough Airspeed limits, ride quality and flutter, but that is a
completely different story.

Vassilios

[Jim]

On Tue, 22 Jul 2003 11:59:12 -0400, Todd Pattist
> wrote:

>mosquito > wrote:
>
>>What is the effect of water ballast on: (a)stall speed,
>>(b)climb performance and (c)glide angle?
>>
>>In their answer on page 4, they say "The stall speed and glide angle are
>>increased..."
>>
>>AFAIK, the glide angle ISN'T increased - with increased weight, you just
>>travel down the same glide angle, but faster.
>
>You are correct that for a constant glide angle, the speed
>at which that glide angle occurs increases as you add
>ballast. Thus, if they had asked about the effect on
>maximum glide angle, their answer would be wrong and yours
>correct. However, they didn't ask about the effect on
>maximum glide angle, nor did they specify a constant glide
>angle.
>
>Instead of assuming a constant glide angle, we could equally
>well assume a constant airspeed. For a constant airspeed,
>the effect varies. At speeds above the ballasted max glide
>angle, adding weight increases the glide angle. At speeds
>below the unballasted max glide angle, adding weight
>decreases the glide angle. There's a crossover somewhere in
>between those two speeds.
>
>
>Todd Pattist - "WH" Ventus C
>(Remove DONTSPAMME from address to email reply.)

I don't quite follow what you say in your second paragraph.
Do I understand your point if I make the following changes?

"At speeds above the ballasted max glide angle, adding weight
SHALLOWS the glide angle. At speeds below the unballasted
max glide angle, adding weight STEEPENS the glide angle."

Or is this still not right?