wlbragg
commented
4 years ago @HHS81 Thank you for the detailed explanation.
I was fortunate enough to get a contact with a "real" Erickson AirCrane pilot courtesy of @wkitty42.
The pilot was able to answered some questions regarding rotor and turbine RPM values and also provided me with. S-64E Model Training Manual S-64F Model Training Manual S-64 Drive Train values xlsx S-64E Flight Manual S-64F Flight Manual
So I have a whole bunch of new and excellent references material. I can also get details when needed from the pilot as I go. Unfortunately I know very little about FDM neither YASim or JSBSim. It really is over my head as of right now. I could use help with all of this.
I don't really even know where to start, so your suggestion is really helpful. Do you know were to find the original YASim-fdm by Maik? Sounds like a good starting point regardless of which FDM is finally adopted. I am pretty well decided this needs to be JSBSim. I really want the flexibility not just for the FDM but for all the other systems than need to be modeled.
Some light regarding fdm and for dicussion regarding a further developement: the original fdm of the AirCrane is based on the flight test data of the CH-53D collected by NASA many years ago (search NASA-CR-3144; TR-1087-1. ) and mady by Maik Justus. Maik Justus is the code developer behind the YASim helicopter solver. Then helijah changed it without any knowledge, and....
The YASim for fixed-wings is just geometry-based, and has nothing to do with blade-element-theory. The YASim for helicopters instead works with real blade-element-theory according to mails and personal talks with Maik. (I used to live in the same small county like Maik some years ago)
It is even easy to see for users: you have to set all airfoil coefficients (not possible with YASim-fixed-wings!); it ignores the YASim-fixed-wing solver (you have to set yasimdragfactor/ yasimliftfactor by yourself based on known helicopter perfomance), and you can set the number of elements and parts of the rotor, in which should the rotor to be broken for simulating the forces. So the YASim-helicopter differs a lot of the YASim-fixed-wings.
Problem with YASim: no real engine-simulation, and missing vortex ring state, not clear to me the effect of downwash on the fuselage. It is true, that with JSBSim we already get (engines!) or could get by creating own tables and function those things without digging in the core code. Very flexible indeed! But even the Alouette III by Thorsten doesn`t show vortex ring state...
About the documentation: the yasim-doc says a lot - but you need some knowledge behind real helicopter-flight dynamics to understand what each of those parameters do - I can help you there.
But problem will always be: without known datas we never get a realistic simulation- either YASim or JSBSim. And I don`t mean flight perfomances like climb rates etc. - I mean the reaction of the rotor to any pilot inputs, and the following reaction of the helicopter itself to this inputs.
Only the bo105 in FGAddon, the original UH-1 in FGAddon, and the EC135 P2 in FGAddon are showing realistic and proved behavior based on NASA-reports and other published technical reports, but might not be realistic regarding climb rates etc.... Those datas reagarding rotor reaction to pilot inputs are very hard to get, and only known for very few helicopters.
So: Don`t underrate YASim for helicopters- it differs form fixed-wings But JSBsim is more flexible, and allows realistic and easy simulation of engines and effects missing in YASim. The original YASim-fdm by Maik could be a good reference to start a JSBSim-fdm.