Regards,
Charlie H.
Michael Selig wrote:
I have just added the Fokker Dr.1 triplane to the CVS. There are notes in the readme below about how to get a 3D model file. Unfortunately, I could not acquire one under the GNU GPL.
If I were going to be in a dog fight and had my pick of the Camel or Dr.1, the Dr.1 would be the weapon of choice. The Red Baron once said it "It climbed like a monkey and maneuvered like the devil." I concur.
Regards,
Michael
<pre>
======================================================
= Fokker Dr.1 =
= WWI Fighter =
= for FlightGear with LaRCsim and the UIUC Aeromodel =
= =
= Flight model by: =
= Michael Selig, et al. ([EMAIL PROTECTED]) =
= http://www.aae.uiuc.edu/m-selig/apasim.html =
======================================================
To run, try:
fgfs --aircraft=fkdr1-v1-nl-uiuc
Files and directory structure required in $FG_ROOT/Aircraft/ to fly the
model:
fkdr1-v1-nl-uiuc-set.xml
fkdr1/Sounds/uiuc/fkdr1-sound.xml
UIUC/fkdr1-v1-nl/aircraft.dat
UIUC/fkdr1-v1-nl/CDfa-03.dat
UIUC/fkdr1-v1-nl/CLfa-03.dat
UIUC/fkdr1-v1-nl/Cmfa-03.dat
UIUC/fkdr1-v1-nl/Cmfade-01.dat
These files above come with the FlightGear base package.
To add a 3D external model, read the file:
~/Aircraft/UIUC/beech99/README.beech99.html
as an example to follow. A Fokker Dr.1 model file that does work is
fokdr1m2.zip from http://www.flightsim.com. (The fuselage for this
model is too wide in the cockpit region.)
There are several variants of this which can also be used, namely
these files:
dr-1cfs.zip
dr1mp98.zip
dr1mpcfs.zip
fkdr1blk.zip
fokdr-15.zip
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Model description and updates:
11/10/2002 - First release: v1-nl
* Motivation: FGFS and the UIUC aero model were used to develop flight
models for both the Sopwith Camel and Fokker Dr.1 Triplane. These
models were then used in another simulation with a collaborator,
Brian Fuesz. In that simulation, guns, terrain, villages, multiple
planes, etc were added to simulate the last flight of the Red Baron.
This work was filmed for the Discovery Channel show "Unsolved
History: The Death of the Red Baron" scheduled to first air Dec 18,
2002.
* A weights and balance was performed to arrive at an allowable
c.g. location and from that data, mass moments of inertia were
calculated.
* Lift, drag and pitching moment data is modeled from -90 to +90 deg.
Because the aerodynamics are not modeled from -180 to +180 deg, the
aircraft will sometimes twitch when coming out of a tail slide as it
passed through 90 deg.
* In general, the aerodynamics are modeled using various sources.
* Apparent mass effects are modeled.
* Gyroscopic forces caused by engine rotation and aircraft rotations
are modeled. For an animation of how a WWI-type rotary engine
works, go here:http://www.keveney.com/gnome.html
An example of gyroscopic forces, are those forces produced when one
tries to rotate by hand a spinning bicycle wheel.
* Spin aerodynamics are not yet modeled.
* The simulation starts on the ground. Throttle up to take off or
alternatively, use Ctrl-U to jump up in 1000-ft increments.
* The Fokker Dr.1 did not have brakes. Application of brakes in FGFS
will cause the aircraft to promptly nose over. (I have added a fake
contact point ahead of the aircraft to avoid completely tipping
over.) The c.g. of the aircraft sits almost directly above the
wheel contact point. There is a reason for this. The aft fuselage
and tail were designed to be very light. Thus, the tail could not
support much load, so the weight of the aircraft largely rests on
the main wheels, which again requires the c.g. to be almost directly
above the wheels.
* WWI aircraft engines did not have a conventional throttle (at least
most did not). The engines were either on or off/idle using a
"blip-throttle". So it is not realistic to fly with a variable
throttle, which the current model allows.
* To modelers, I can provide a graphic showing the c.g. location.
* Something I have not yet modeled is rudder ineffectiveness on roll
out and touch down. When the aircraft is sitting on the wheels and
tail skid, the angle of attack of the wing is so high that it is
mostly stalled and the flow off the aft fuselage is also not well
behaved. The result is that there is not much dynamic pressure
(flow speed) on the vertical stabilizer, so there is little rudder
authority in this condition. As a point of interest, why would the
designers settle for this result? It's because of the rotary
engine. The max speed is limited to 1200 rpm because of the
otherwise higher stresses on the rotary engine parts. To obtain the
necessary thrust at such a low rpm, a large diameter ~8.5 ft
propeller was required. With such a large diameter propeller and
short stubby fuselage, the aircraft sat nose high.
* Interesting flight characteristics to note:
- Just as with the Sopwith Camel and other WWI vintage aircraft, the
gyroscopic forces of the engine tend to couple the aerodynamic
controls. For example, pulling up will cause the aircraft to not
only nose up but also yaw to the right, requiring left rudder to
coordinate. A more general discussion of this effect can be found
in the file: ~/Aircraft/UIUC/sopwithCamel/README.sopwithCamel.html
It should be added, however, that the engine polar moment of
inertia of the Dr.1 is approximately half that of the Camel. The
effect of the gyroscopic forces is not exactly "half" because the
aerodynamics that resist these motions are somewhat different
between the two aircraft. Nevertheless, when flying, the effects
of the gyroscopic forces are appreciably less than those on the
Sopwith Camel.
- I have a sense that there needs to be more yaw damping, but I
cannot justify it just yet. So I am sticking w/ the computed
figures. Also, the pilot report (URL below) makes mention of the
fact that one needs to be on the rudder all of the time, which
suggests poor yaw damping.
- On takeoff, there is a tendency for the wing to dip and drag on
the ground. The same thing happens on landing. This is not an
artifact of some modeling approximations, but in fact the Fokker
Triplane was known to "dip" a wing on takeoff and landing. The
solution was to add the "axe handles" or wooden pool skids at the
tips of the lower wing. The pilot's solution to avoid it in the
first place is to use cross controls: right aileron and left
rudder and vice versa until level again.
- The ailerons on the Fokker triplane were "heavy", meaning that
considerable stick force was required to maneuver. For this
reason, "elephant ears" were used on the tips of the ailerons for
mass balance. The trouble with putting the mass balance at the
wings tips is that on the side with the aileron down, the upwash
around the wing impinges on the balance horn and this produces
high drag. On the other aileron in the up position, it is more
aligned with the upwash coming around the wing tip, so there is
little added drag. As a result of this rather large difference in
drag, strong adverse yaw is the outcome. For instance, a left
roll with the right wing aileron going down produces high drag at
the tip of the right wing. As a consequence, this yaws the
airplane to the right, opposite the intended direction of the
turn. There were three variations on the design of the "elephant
ears" and I speculate that it was driven by this substantial
adverse yaw problem. Smaller "elephant ears" produced less
adverse yaw, which is good, but they also provided less balance
and therefore higher stick force, which is bad. My guess is that
it was a case of "pick your poison". Generally, with the adverse
yaw problem generous use of the rudder is required when banking to
turn.
* Some pilot reports based on full scale replicas:
http://rwebs.net/avhistory/flight.htm
http://www.airandspacemagazine.com/asm/web/special/ethell/pirep1.html
* To those having specific knowledge of the Fokker Dr.1, I am
interested in obtaining the following data:
[] RPM when the throttle is blipped. I am currently using 300 RPM.
The current aircraft uses a 110-hp Uberursel UR-2, which I
believe is what is Baron von Richthofen (The Red Baron) was
flying on the day when he was shot down.
[] Engine mass characteristics on a component-by-component basis.
This information will help me refine the polar moment of inertia
that drives the gyroscopic forces.
[] On a related note, the mass of the propeller which also figures
into the gyroscopic forces.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
**************************************************
Prof. Michael S. Selig
Dept. of Aero/Astro Engineering
University of Illinois at Urbana-Champaign
306 Talbot Laboratory
104 South Wright Street
Urbana, IL 61801-2935
(217) 244-5757 (o), (509) 691-1373 (fax)
mailto:m-selig@;uiuc.edu
http://www.uiuc.edu/ph/www/m-selig
http://www.uiuc.edu/ph/www/m-selig/faq.html (FAQ)
**************************************************
_______________________________________________
Flightgear-devel mailing list
[EMAIL PROTECTED]
http://mail.flightgear.org/mailman/listinfo/flightgear-devel
-- "C makes it easy to shoot yourself in the foot; C++ makes it harder, but when you do, it blows away your whole leg." - Bjarne Stroustrup
_______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
