Re: ARC radius airfoils question....long

From: Nick Ray <lasray_at_gmail.com>
Date: Wed, 30 Oct 2013 11:58:02 -0400

Ren,

I think I was being more cryptic than I intended to be. An LPP flies at a
near constant velocity. So if we assume everything is the same except the
camber. Three major things change as camber is changed.

 First the as Mike stated, lift increases and drag increases as camber is
increased.

Second, the moment or the aerodynamic balancing point of the model changes.

If the wing airfoil camber is increased then the coefficient of lift of the
stab decreases.

If the stab airfoil camber is increased then the coefficient of lift of the
stab increases. Because the stab is now doing more of the total lifting,
the wing's contribution to overall lift of the model is proportionally
reduced.

Third, as Mike deduced the model becomes more stable and also more draggy
as the camber is increased. The drag is important in a practical sense
because the model is flying slightly faster at the beginning of the flight.
When you move a high camber airfoil off of its optimal design point the
drag tends to dominate. That means that the model will not climb quite as
high. In events where VPs are ban you get the effect of being able to
launch on slightly more power without climbing as high. Then, you get the
extra lift as the model slows slightly and moves back on to the design
speed.

I hope that helps more than my first post.

Nick


On Wed, Oct 30, 2013 at 11:03 AM, William Gowen <wdgowen_at_gmail.com> wrote:

> **
>
>
> My answer is I use the same airfoil for all ceiling heights.
>
> On 10/30/2013 11:02 AM, nmonllor_at_tampabay.rr.com wrote:
>
>
>
> AArrg!
>
> 3 replies and still no answer to the question, dang it!
>
> Yes Gary, I should have said camber and not hump. I must have camels on
> the brain today or I'm just getting old, sorry.
>
> It's nice to know that I'm not the only one who finds this worthy of
> question.
>
> If anybody can come up with the answer, I'd really appreciate it.
>
> Thanks,
>
> Ren
>
> ---- Warthodson_at_aol.com wrote:
> >
> > Ren,
> > That is an interesting question. Sorry I do not have the answer, but I
> will add this to your question: Assuming one of the two airfoils will have
> a better L/D ratio, I would think the better L/D ratio would be the best
> choice for both a low & a high ceiling.
> >
> > Also, I do not understand your statement below. A 6% arch has a higher
> camber than a 4% arch. Is that what you are refering to? If not, what did
> you mean?
> >
> > Gary H
> >
> >
> > A smaller percentage would create a higher hump in the air foil
> increasing lift according to Bernulli, but yet it is suggested for a lower
> cieling. Whyis this?
> > What am I not seeing?
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
>
>
Received on Wed Oct 30 2013 - 08:58:03 CET