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Ben_Chiu Certificates/Ratings/Crew Stations: 22. "RE: Adverse yaw and roll coupling" 11-25-02, 22:37z  Greetings Dave: Thanks for the links. It seems I have a lot of reading to do! > The most relevant to your question is, however, > NASA TN D-6946 > Lateral-Directional Aerodynamic Characteristics of Light, Twin-Engine, > Propeller-Driven Airplanes. > Its a cookbook of how to estimate the stability and control derivatives. > I wasn't able to find it quickly online - it may be there at > http://techreports.larc.nasa.gov/cgi-bin/NTRS > or > http://www.sti.nasa.gov/RECONselect.html > > I have these on a CD - the NASA Legacy collection, from the Langley > Research Centre. I'll have a look for it. If I can't find it, and if it's not too large, perhaps you could email the report to me. > The next step is the effect of rudder, sideslip and roll/yaw rate on > pitching - most reports and textbooks ignore the cross-derivatives. ie > they separate life into either lateral-directional or longitudinal > characteristics. That's what I've found as well (although I've only searched as far as the aviation books and aerodynamics texts found in pilot shops and local libraries). There are many factors involved and I suspect that due to these complexities (and relative low interest level from most pilots) have contributed to the lack of available text on the topic specifically. > This was the cause of an in-flight tail failure on a Tucano - during > flight testing of rudder deflection and sideslips at high speed the > downward pitch resulted in overloading the horizontal stabilizer. I never heard of this. It looks like a standard tail configuration and aileron setup. Interesting that there's a downward pitch in this case... I suspect that effects seen would vary based on the bank angle and angle of attack at the time of rudder input. > You > often see tailplane inboard leading edge strakes on single engine > turboprops to reduce the asymmetric effects on tailplane lift. > Then there's the gyroscopic effects of the propeller. eg applying left > rudder briskly results in a pitch up. Rgr. I think this can be eliminated (effects reduced) from our discussion if we apply rudder slowly. My thoughts are that reasons why we see roll-coupling rather than pitch changes is due to four factors. Although please note that without some input from real world or model experience, this is all purely theoretical. 1. The proximity of the horizontal stabilizer causing a build up of pressure on the side that the rudder is applied. This increasing downward pressure on the half of the horizontal stabilizer causes the aircraft to roll. So, it's my belief that the placement of the horizontal stabilizer will change roll coupling tendencies (reduce or increase, but not eliminate). 2. The airfoil shape and AOA. Both are interrelated in level flight (e.g. a symmetrical airfoil requires a positive AOA to to to to fly level). The higher the AOA at the application of rudder, the more likely there'll be a pitch change. 3. The roll stability of the aircraft. I believe as Dave H pointed out that dihedral and other roll stabilization designs will affect the tendency to roll with the application of rudder. 4. Related to #2, the relative direction of gravity. Which goes back to my diving towards the ground scenario. I think that if lift is not being generate, we would see a adverse yaw type situation with the application of rudder, but that's just a guess. Anyone willing to test out my theory? I think it would be possible to test this in knife edge flight as well (the application of top and bottom rudder should produce pitch changes and less roll-coupling as compared to level flight). Again, there are all just guesses. If anyone has thoughts contrary to mine, please speak up. > From here - next time you're in Australia this is a good topic for > discussion over a bottle of Long Flat Red. > Or, online real time discusison sometime. I haven't made over to Australia yet, but it's one of few places that I've have on my "someday" list. I would greatly enjoy such a discussion in person. However, it may be quite a long time before that might happen, so an online discussion (we do have regularly scheduled chats here at the VPC) or continuation of this thread is most welcome. Best! Ben -= VPC OffLine Reader 2.1 =- Registered to: Ben Chiu -OLR.PL v1.80- Remove | Alert Edit | Reply | Reply With Quote | Top

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Subject      Author      Message Date     ID      Adverse yaw and roll coupling    Ben_Chiu       11-16-02              RE: Adverse yaw and roll coupling    Tarmack       11-18-02       1            RE: Adverse yaw and roll coupling    Ben_Chiu       11-18-02       4                 RE: Adverse yaw and roll coupling    djpacro       11-19-02       9                      RE: Adverse yaw and roll coupling    Ben_Chiu       11-19-02       14                 RE: Adverse yaw and roll coupling    Mike_Greenwood       11-19-02       10                      RE: Adverse yaw and roll coupling    DHamblin       11-19-02       12                      RE: Adverse yaw and roll coupling    DHamblin       11-19-02       13                           RE: Adverse yaw and roll coupling    Ben_Chiu       11-19-02       16                      RE: Adverse yaw and roll coupling    Ben_Chiu       11-19-02       15                           RE: Adverse yaw and roll coupling    djpacro       11-25-02       21                                RE: Adverse yaw and roll coupling    Ben_Chiu       11-25-02       22         RE: Adverse yaw and roll coupling    DHamblin       11-18-02       2            RE: Adverse yaw and roll coupling    Ben_Chiu       11-18-02       5                 RE: Adverse yaw and roll coupling    DHamblin       11-18-02       7                      RE: Adverse yaw and roll coupling    Mike_Greenwood       11-19-02       11                           RE: Adverse yaw and roll coupling    AlanParkinson       11-22-02       19                                RE: Adverse yaw and roll coupling    Mike_Greenwood       11-23-02       20                      RE: Adverse yaw and roll coupling    Ben_Chiu       11-19-02       17         RE: Adverse yaw and roll coupling    IFLYExtra300S       11-18-02       3            RE: Adverse yaw and roll coupling    Ben_Chiu       11-18-02       6                 RE: Adverse yaw and roll coupling    Tarmack       11-18-02       8                      RE: Adverse yaw and roll coupling    Ben_Chiu       11-19-02       18                 RE: Adverse yaw and roll coupling    ghmorris       12-01-02       23                      RE: Adverse yaw and roll coupling    ghmorris       12-01-02       24                      RE: Adverse yaw and roll coupling    Ben_Chiu       12-01-02       25                           RE: Adverse yaw and roll coupling    ghmorris       12-02-02       26                                RE: Adverse yaw and roll coupling    Ben_Chiu       12-02-02       27                                     RE: Adverse yaw and roll coupling    ghmorris       12-02-02       28

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