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| Title: | Welcome To The Radio Control Conference |
| Notice: | dir's in 11, who's who in 4, sales in 6, auctions 19 |
| Moderator: | VMSSG::FRIEDRICHS |
|
| Created: | Tue Jan 13 1987 |
| Last Modified: | Thu Jun 05 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 1706 |
| Total number of notes: | 27193 |
1202.0. "Sailplane Design program" by CURIE::ANKER (Anker Berg-Sonne) Fri Apr 13 1990 15:09
The Sailplane Design program uses windtunnel airfoil data
to either give you lift vs angle of attach or Cl vs Cd plots for
the airfoils in the database. This is essentially the same plots
as you see in Soartech # 8, but the resolution is better because
you don't have the stupid squares and triangles covering the
graphs.
The other, infinitely more interesting, capability is to
predict and plot sailplane performance in the form of L/D vs
speed plots.
The program will work on just about any video monitor
with graphics capability, but in order to get hardcopy you need a
HP compatible plotter or the ability to print a hardcopy of your
graphics screen with the Print Screen key. The latter requires
either an IBM-compatible or Epsom-compatible printer and the
GRAPHICS program running.
The user interface is atrocious. All functions are
performed with function keys and there are 5 separate menus that
you continually cycle through. They are not hierarchical, but
cyclical instead and usually you will have to switch back and
forth between menus to perform even simple functions.
The airfoil data is hidden in four "datasets" and, of
course, the default one contains the least interesting data. I
almost gave up on the program before I discovered the hidden
airfoil data. If I had read the manual thoroughly I would have
discovered this, but who does?
To get you started on design they have design data for
about a dozen gliders, including Sagitta 900 and Windsong plus a
bunch of less interesting planes. A plane design is defined by a
number of parameters which are really complicated to enter. For
example, one that looks simple is elevator height over the wing.
But its not over the zero datum line in the airfoil, but over the
zero lift plane. So as you change airfoils you need to
take the airfoil data, find the zero lift angle of incidence,
then draw it onto a threeview and finally measure the tailplane
height. You can make it easier by pretending that you change the
angle of incidence as you "change" wings to keep the elevator
height constant. Entering a totally new design is a BIG job.
The real fun starts as you change airfoils on the designs
in the database. Using the Princeton data you can in a few,
confusing, keystrokes substitute a brand new airfoil or change
tripping, flaps etc, AS LONG AS the airfoil is in the database.
The program will allow the dimensions to stay constant.
Another piece of fun is to look at wings with up to three
different airfoils. Once again, you have complete freedom to
design your own airfoil.
You can also look at the effects of moving the CG. All
of this is displayed in L/D vs speed plots.
So what have I learned? Looking at the lift plots its
amazing to see how badly some airfoils stall. Also how the stall
gets less severe as Reynolds numbers increase.
Its also obvious that most of us fly much too slow. For
example an E214 has the optimal L/D (this is untripped and no
reflex) at about 20 feet per second. This is about 15 MPH, which
is quite fast.
CG placement has a surprisingly large effect on
performance. Probably because of the drag of the elevator as it
tries to keep the plane level.
Something I haven't done yet is redesign of some of the
standard planes. Seems like it will be tons of fun.
This disk is definitely worth the money. You can learn a
lot, even if you never get to designing an airplane.
Anker
Anker
| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1202.1 | Oh, I forgot | CURIE::ANKER | Anker Berg-Sonne | Fri Apr 13 1990 15:15 | 17 |
| Something important that I forgot. You can plot up to
three different airfoils at the same time on a L/D vs speed plot,
thus showing you what you have gained or lost by changing the
airfoil. For example, it will tell you where a reflexed flap
gives you an advantage.
It seems that a very valuable instrument for honing your
flying skills would be an airspeed indicator. With it, you could
trim the plane for optimal performance and go at the optimal
speed. For example, it you are hunting for thermals you would
reflex and then fly at the airspeed that gives you maximum L/D
for that configuration. Then, when thermaling, you would use the
standard configuration and then adjust your speed for minimum
sink rate. All of this can be read from a single plot. Really
neat!
Anker
|
| 1202.2 | But does it do... | K::FISHER | Stop and smell the balsa. | Tue Apr 17 1990 14:02 | 16 |
| Anker - can you for determine tip stall characteristics. For instance if
you have a constant cord wing with a certain airfoil then start a taper to
another airfoil. Such that the tip is a different airfoil and because of
the taper also a different renolds number.
__________--------------------------------------
__________---------- | | Root
Tip |Airfoil | Constant Cord Section |
|B |Airfoil |Airfoil
----------__________ |A |A
----------______________________________________
Bye --+--
Kay R. Fisher |
---------------O---------------
################################################################################
|
| 1202.3 | Yes and no | CURIE::ANKER | Anker Berg-Sonne | Tue Apr 17 1990 14:11 | 16 |
| Re: <<< Note 1202.2 by K::FISHER "Stop and smell the balsa." >>>
Kay,
The program knows how to deal with such a configuration,
but it doesn't give you stall characteristics for a plane. You
need to look at the lift plots for the two airfoils separately,
and using the mean cord for each determine whether the tip stalls
before the root.
One thing the program doesn't take into account at all as
far as I remember is different angles of incidence at the root
and tip. I believe it assumes the incidence is constant over the
entire airfoil.
Anker
|