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  1. Anna Tian

    Propeller thrust line

    Not any airplane has a tailplane at zero-lift AoA during cruise. Some airplanes even don't use symmetrical airfoil at H.T.. From which reference you read that they all have a zero-lift AoA? And from which reference you got that upper bound analysis methodology?
  2. Anna Tian

    Propeller thrust line

    100% momentum gives too huge down force for a slow aircraft. That does give a upper bound. But it's too far from the reality. I don't think a lot of well designed slow aircrafts have been designed to be able to suffer from that huge down force. Thanks for your hint on CFD. I never modeled an...
  3. Anna Tian

    Propeller thrust line

    That's quite clear. Thanks. It seems most of the forward prop design just would like the thrust line almost go through the c.g.
  4. Anna Tian

    Propeller thrust line

    The book 'Mechanics of Flight' frm Wareen F. Phillips tells that the only way to do accurate prop analysis is by powerful wind tunnel test. CFD has a lot of difficulties with this. I guess the main difficulty is the cost. You need model too many things in one model which brings on the grids...
  5. Anna Tian

    Propeller thrust line

    The H.T. is designed not to bring too much down force without prop effect. The momentum equation don't take how far the tail is from the prop into account. And slipstream slows down not slowly. Does momentum equation make a sense?
  6. Anna Tian

    Propeller thrust line

    But when you run the prop at a higher power, the prop slipstream will be stronger. For most of the cases, it will give H.T. a stronger down force which pitches airplane up. How do engineers weight this factor compared with the thrust momentum variation? By the way, it's very difficult to move...
  7. Anna Tian

    Propeller thrust line

    I see the analysis of trim and stability. The explanation of the conventions typically chosen by engineers is what I'm looking for.
  8. Anna Tian

    Propeller thrust line

    If CG move up, it will be closer to the wing a.c. where the drag is typically added in the free body diagram. The moment arm will be shorter. Why you said it will be longer?
  9. Anna Tian

    Propeller thrust line

    Hi, Why propeller thrust line is always a little higher than CG at the vertical direction? The link below gives good discussion. ASK DJ Aerotech Question But i don't understand why he says ' Why can't we just put a post on top of the motor pylon with a large counterweight the top of it...
  10. Anna Tian

    Looking for existing vertical stabilizer and rudder airfoil designs

    Which books introduce more existing designs? The picture I attached is from a book. But it gives no more existing vertical tail pictures and just a few words on vertical airfoil. As from as I know, airplane design books usually give general knowledge. Very few of them give very profound...
  11. Anna Tian

    Looking for existing vertical stabilizer and rudder airfoil designs

    Hi, I’m optimizing my vertical tail geometry by CFD to have the rudder to be able to deflect to a higher angle without causing stall. In order to do this, I was trying to look for existing vertical stabilizer and rudder airfoil designs firstly. The only design I found is shown as the picture...
  12. Anna Tian

    Looking for crop duster flight references

    Hi, I heard about crop dusters typically fly oval flight path. That’s quite interesting to me. I’d like to read more about its flight path planning method and how it adapts to different shapes of farmland. I’m also quite interested in the flight actions the drop dusters typically take including...
  13. Anna Tian

    2D airfoil data conflicts with 3D data

    Here are the grids pictures.
  14. Anna Tian

    2D airfoil data conflicts with 3D data

    Structured grids completely follow CFX's manual’s criteria. Good grids quality (skewness, aspect ratio, expansion ratio, deviation angle.....) with Y+<4. Grids independence studies are done for this comparison. The grids for NACA2415 and Clark Y are almost completely same. I generated grids...
  15. Anna Tian

    2D airfoil data conflicts with 3D data

    I use SST model (not transitional one). I tried transitional model in CFX anf Fluent several times. It is quite costly. So I never used it in the real design afterwards. From the experience I gained from those attempts I made, transitional model's predictions are not very different from SST...
  16. Anna Tian

    2D airfoil data conflicts with 3D data

    CFD generally can give good calculation of pressure field. This is quite well known. I read some papers on CFD calculations for aircraft design and also did by myself some airfoils and 3D wing CFD study and the calculation results are validated by wind tunnel data. Sometimes CFD has problem on...
  17. Anna Tian

    2D airfoil data conflicts with 3D data

    I compare NACA2415 and Clark Y airfoil for horizontal tail application for Re=0.2 million. Both the airfoil data from NACA and my 2D CFD simulation results give that the Clark Y airfoil has a larger Clmax than NACA2415 for Re=0.2 million (CFD data has good match with NACA data as typically in...
  18. Anna Tian

    How high does the manned crop duster fly above the farmland?

    1) Why helicopter is used to for crop dusting as well in US? Because there are also some small farmland in US? Some place is out of run way? 2) Why UAV is still way long for heavy duty work? It does not need to be fully autonomous. RC operator shall be much less paid than high skilled pilot...
  19. Anna Tian

    How high does the manned crop duster fly above the farmland?

    Yes. I'm wondering why none of the fixed wing UAV used for crop dusting? They shall be more efficient, cheaper and easier for maintenance and repair than UAV helicopter once the farmland overpass a certain size. Only for the FAA regulation reason? What about the countries with less strict...
  20. Anna Tian

    How high does the manned crop duster fly above the farmland?

    Why it has to be in flat country? If the autopilot uses a sonar, it can simply fix the flight height with respect to the land.
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