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HI:
I wrote this over the day whenever I had a little time. In the meantime
there was really much activity on the list from people who already
created some helo-stuff or have the intention to do so - I did not know
that we have already more 3D helo modells then the BO105. But I don't
want to write this mail again or correct it. So please all of you, you
are meant too, feel free and invited to discuss what we could do and how
we should do it:
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Hi all helo-addicts and helicopter-flight interested people!
*** Excuse my very long mail ***
We have now got to a point where it seems that a new helicopter-project
could be started.
So please excuse me for writing this very long mail, but if you compress
some content it might be misunderstood:
*** Won't read all that? - get a wonderful free FAA helicopter manual
though!***
(For those not willing to read this all, have a look at the link at the
bottom of the page, that might be of interest also for you :-) )
*** What do we need - 3D-modells or a better FM? ***
So, if we are really interested in doing some work, let us speak of
coding first not make 3-D modells. The reasons are
1. that we have a very nice BO105 which can be the base for further
improvements
2. that all further 3D-stuff is useless without a basic helicopter
flightmodell which gives us at least the most relevant basic functions.
*** Why not use the existing flightmodell? What is wrong? ***
I would not say it is wrong, it just covers only some aspects of blade
and rotary wing aerodynamics.
But let me first I thank *Maik Justus* for his work and that we are able
to simulate helicopter flight in FlightGear. It was a first step and
therefore very important but let me explain why I think we cannot simply
refine his flightmodell to get what we wish:
If I understand the right way what he tries to do is calculating the
forces and effects of the rotor by calculating it for every blade in
discrete time-steps and from this calculation the resulting forces on
the helicopter. This is far too complex to handle after my opinion as we
do not have the necessary hardware for the resulting flightmodell and
the man-power for all that coding.
The actual flightmodel only looks at a small part of all possible
effects and the result is that we can do a pretty normal hover and some
simple flight-maneuvers but many important things are simply wrong (ie.
yaw and tail-rotor aspects, influence of wind when turning on the spot
too heavy modelled, reducing collective/torque to minimum on straight
and level flight with no adequate reaction/helo flying like a fixed
wing) or lacking (no ground-effect, no realistic translational lift, no
vortex state ((settling with power)), no airflow driven rotorblades/no
autorotation possible, etc). This is only what I am just thinking of,
there are many other arguments.
*** Rotorblade aerodynamic is really complicated ***
But we can understand this when we just have a look what we had to
modell/calculate only for the blades:
IF YOU KNOW that the blades are not only moving against the moving air
(if not in a hover)which results in an asymmetric lift but can
flap/drag (up/down, forw./back) and/or bend/twist (what results in
different blade-angles (AoA) against the airflow over the whole blade)
*AND* that you don't have a laminar airflow over the whole blade *AND*
that the blades not only are driven by the engine but also by the
airflow through the blades (ie if you have low collective pitch and a
fast descend the airflow can! increase rotor-rpm) *AND* there are
flight-envelopes where you have increasing vortex with blade-stall in
the center of the bladepart (vortex state, settling with power) *AND*
you have the situation where a*part* of the blade is stalling (center)
and a *part* of the rotor-blade is driven by the airflow (middle) and
the *other part* of the rotorblade is giving lift (outside) and that
these zones differ from the position of the blades (movement against air
or retreating blade) *AND* you may have blade-stall of the retreating
blade if relative airflow is to low (forward-speed or heavy gust) *AND*
... much more :-) THEN YOU WILL EASILY SEE that it is very difficult to
calculate the resulting forces an the rotorhead (and the appending
helicopter, of course).
For the EC135 flightsim they have one medium workstation only to
calculate the blade aerodynamics - and this from predefined tabels!!! :-)
*** We won't speak of rotorblade aerodynamic alone when it comes to
helicopter aerodynamics ***
And, mainrotor is only *one* part of many aspects. The other parts of
the helo (body, tail, finns etc) are influenced as well of the rotor
downwash and the airflow when moving in any direction.
Not enough, it makes a big difference whether your downwash gets into
free air or onto a surface, this results in effects as ground effect
(which is quite different depending onto the surface, ie. grass or
asphalt) or difficulties to control the craft if only a part of the
rotordisk has groundeffect (ie. wrong landing procedures on
platforms/roofs/etc but also special terrain).
And you have translational lift, influence of wind, gust, temperature,
air desity and ..
*** Now what, give up and wait for a genious-coder? ***
If we want to improve the flightmodell we have to think about the right
way to get at least the most important aspects covered in real-time,
this is very pretentious! After my opinion this is not possible if we
just "tune" the actual FM.
But it could make sense to improve it ("fake it") so that we get some
better results until we are able to create a new one.
*** A quick step forward - what can we do to get some result pretty
soon? ***
To make helos more realistic in FlightGear will result in a heavy
work-load, only to manage if we *part* it:
1. If *Melchior Franz* would like to create the very essential
instruments like torque, N1/N2, TOT (turbine outlet temperature),
fuel-pump switches (very essential for the BO105!) and (if possible)
throttle levers (with starter buttons?) ... etc
2. I sent a lot of stuff to *Andy Ross* who intended to write an
improved turbine modell - if the work is not cancelled (I got absolute
no feedback) then there might be another big improvement
3. We need a statement from *Bill Galbraight* whether the
helo-flightmodell he is working on is a full *GNU* licence complaint
release. If *yes* we should wait and see what is up with his work, if
*not* then forget about it and we have some other options
4. I assume there are people who know a lot about C++ structures but not
a lot about the aerodynamics and vice versa (people like me). It could
be a first step to analyze the code-structure and comment it out so that
we really know how it works.
After discussing the possible wrong simulation-parts and/or the lacking
effects we could try to improve it.
The result could be
a) an improved flight-modell, though not the wished one
b) increasing knowledge about rotary wing aerodynamics
b) ideas how a better flight-modell could be structured (and realized)
*** Ok, ok this is the end of the text ***
but hopefully not the end of a project that has not started until now.
Let me know what you think about my proposals.
But, please, give me some time to answer. To earn my money I have to
work more than 50h the week on average, day and night.I will always
answer as soon as possible, but sometimes there might be a longer delay.
Sorry! :-(
*** Go get this wonderful and free! FAA brochure about all heli aspects ***
5. I spend a lot of money in the past for helicopter books before I
discovered this excellent *.pdf file from the FAA.
It is *free* and the very best I ever saw until now: many pages about
helicopter technic, aerodynamic, flight procedures, errors and even
gyrocopter as an appendix. And you get a lot of pictures and graphs wich
explain very clearly what is very difficult to read. If the choice would
be either to hold this file or some of my books I would give the books
away (although some aspects are simplified in the FAA brochure) :-)
So, if you want to sim heloflight in a serious way, do not read this
file, *study* it page for page! It is the time worth you need, if you
understand it you become a serious sim-helopilot: (10 MB download, don't
try to open that pdf in your brownser *online*):
http://www.faa.gov/library/manuals/aircraft/media/faa-h-8083-21.pdf
Best regards
Georg EDDW
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