On Sat, 21 Mar 2020 01:37:35 -0700, Tango Whisky wrote:

Absolutely. On a modern glider, this slope goes through zero at the
angle of attack of best L/D (zero lift = minimum drag). Below that
speed, the tailplane produces lift, above it produces downward force.

At a slight tangent:

If you're in a COVID-19 lockdown and need something to do with your
hands, you can do a lot worse that teach yourself some basic flight
stability rules while having fun making stuff.

All you need is:

- a copy of "Circular Airflow" by Frank Zaic ABE Books
https://www.abebooks.com
have a few copies if you don't have one (and you won't unless you were
a keen FF model flyer). Other second hand bookstores should also have
copies

- a sheet or two of 1/16" balsa

- modelling clay or electrical solder to use as nose weight

- some glue (white PVA, cellulose cement or a decent brand of
cyanoacrylate such as Zap)

- a suitable knife. I like the snap-off blade sort you can find in DIY
stores.

- maybe some glass-headed pins to hold stuff in place while glue dries

The section of the book called "Spiral Stability Demonstration" (starts
on page 49 in my copy) shows how to make very simple hand launch gliders
and use them to see the effect of side area, vertical and horizontal tail
size, etc. The models are small, light and slow enough to be flown in any
reasonable sized room or in your garden on a calm day. Its easy enough to
extend this to an investigation of CG position relative to wing chord and
the associated up or download on the tailplane.


Couple of other links:

- if you liked experimenting with the Zaic test models, you might like
Easy Mini, a small, light catapult launched balsa glider. Its interesting
because, when correctly set up, that same fixed trim works at high speed
in a spiral climb and equally well after it slows down into a slow
floating glide. You can lose these upwards of you fire them into a
thermal. They are suitable to use with scout groups, after-school hobby
groups, and, of course, young gliding club associates.

https://www.gregorie.org/freeflight/easymini/

- a debunking job I did to prove that an ancient Egyptian wooden bird was
probably a kids toy or a decoration and certainly not anything that
actually flew. Proving that was a lot of fun:

https://www.gregorie.org/freeflight/saqqara_bird



--
Martin | martin at
Gregorie | gregorie dot org