On Sun, 29 Oct 2006 01:31:03 +0200, Georg wrote in message <[EMAIL PROTECTED]>:
> _____________________________________________________________________ > _________________________ 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: > _____________________________________________________________________ > _________________________ > > 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 ..define "through the blades". ;o) http://home.att.net/~dannysoar2/Whirlygig.htm > 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 > > > > _______________________________________________ > Flightgear-users mailing list > Flightgear-users@flightgear.org > http://mail.flightgear.org/mailman/listinfo/flightgear-users > 2f585eeea02e2c79d7b1d8c4963bae2d > -- ..med vennlig hilsen = with Kind Regards from Arnt... ;o) ...with a number of polar bear hunters in his ancestry... Scenarios always come in sets of three: best case, worst case, and just in case. _______________________________________________ Flightgear-users mailing list Flightgear-users@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-users 2f585eeea02e2c79d7b1d8c4963bae2d
