Re: [Flightgear-devel] Taildragger takeoff and landing
Jon Berndt wrote: Sent: Tuesday, June 28, 2005 1:20 PM You might want to change the date on your PC. Who should do that ? -Fred ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Jon Berndt wrote: Sent: Tuesday, June 28, 2005 1:20 PM You might want to change the date on your PC. Who should do that ? -Fred -|steve|- HGMINFO See the date at top. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Sent: Tuesday, June 28, 2005 1:20 PM You might want to change the date on your PC. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Arnt Karlsen wrote: On Sat, 31 Jul 2004 22:44:19 +0200, Erik wrote in message [EMAIL PROTECTED]: Arnt Karlsen wrote: Erik (Ever used the bicycle to cycle up a steep hill?) ..is overhang steep enough? ;-) (or did you mean hangover ..?) :-) On a bicycle? ..yup. Classic case of _find_-a-way and stay-_off_-the-brakes to pull G's, but the 2 flat tires, sucked. Gravel pit ridge race. ;-) Wow, I'm not sure I'm even going to try that! Erik -- Now remember kids, blowing sucks too. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Sun, 01 Aug 2004 10:26:48 +0200, Erik wrote in message [EMAIL PROTECTED]: Arnt Karlsen wrote: On Sat, 31 Jul 2004 22:44:19 +0200, Erik wrote in message [EMAIL PROTECTED]: Arnt Karlsen wrote: Erik (Ever used the bicycle to cycle up a steep hill?) ..is overhang steep enough? ;-) (or did you mean hangover ..?) :-) ..well, it did turn out not too terminal. ;-) On a bicycle? ..yup. Classic case of _find_-a-way and stay-_off_-the-brakes to pull G's, but the 2 flat tires, sucked. Gravel pit ridge race. ;-) Wow, I'm not sure I'm even going to try that! ..why not? ;-) -- ..med vennlig hilsen = with Kind Regards from Arnt... ;-) ...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-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Arnt Karlsen wrote: On Wed, 28 Jul 2004 21:42:48 -0400, Ampere wrote in message [EMAIL PROTECTED]: On July 28, 2004 03:06 pm, Jon S Berndt wrote: So, from the point of view of the horizontal stabilizor, that pesky downwash happens because wings really suck. ;-) I guess that's one of the reasons why some planes use canards. =P ..that suck too. ;-) I think all aircraft suck. Only the ones that have a better design suck less. Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Erik Hofman writes: Arnt Karlsen wrote: On Wed, 28 Jul 2004 21:42:48 -0400, Ampere wrote in message On July 28, 2004 03:06 pm, Jon S Berndt wrote: So, from the point of view of the horizontal stabilizor, that pesky downwash happens because wings really suck. ;-) I guess that's one of the reasons why some planes use canards. =P ..that suck too. ;-) I think all aircraft suck. Only the ones that have a better design suck less. No No .. it's the earth that sucks as there is no gravity ! Norman ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Arnt Karlsen wrote: Erik (Ever used the bicycle to cycle up a steep hill?) ..is overhang steep enough? ;-) On a bicycle? Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Sat, 31 Jul 2004 22:44:19 +0200, Erik wrote in message [EMAIL PROTECTED]: Arnt Karlsen wrote: Erik (Ever used the bicycle to cycle up a steep hill?) ..is overhang steep enough? ;-) On a bicycle? ..yup. Classic case of _find_-a-way and stay-_off_-the-brakes to pull G's, but the 2 flat tires, sucked. Gravel pit ridge race. ;-) -- ..med vennlig hilsen = with Kind Regards from Arnt... ;-) ...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-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon S Berndt wrote: On Thu, 29 Jul 2004 10:34:16 -0500 Curtis L. Olson [EMAIL PROTECTED] wrote: Ok, then how do you explain a frisbee that can curve either way, even though it's always thrown with the same direction of spin. And please include the coriolis effect in your explanation (now that it is implimented in JSBSim.) Thank you. :-) Gyroscopic stabilization and tilt. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d Don't forget precession. And, umm, p-factor. Yeah. I think there's some lunar tidal drag in there too. Josh ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 21:42:48 -0400, Ampere wrote in message [EMAIL PROTECTED]: On July 28, 2004 03:06 pm, Jon S Berndt wrote: So, from the point of view of the horizontal stabilizor, that pesky downwash happens because wings really suck. ;-) I guess that's one of the reasons why some planes use canards. =P ..that suck too. ;-) -- ..med vennlig hilsen = with Kind Regards from Arnt... ;-) ...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-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 14:47:43 -0400, David wrote in message [EMAIL PROTECTED]: Jim Wilson wrote: This suggests that both bernoulli and the pushing (gravity) are at play, depending on the airfoil. My (uneducated) guess is the pushing is almost all of it and that the bernoulli effect only augments: http://observe.arc.nasa.gov/nasa/exhibits/planes/planes_1c.html There's a pressure differential either way, but since icing on top of the wing kills lift more than icing on the bottom, I'll guess that the low pressure on top is at least as important as the high pressure beneath. ..generally, say about 3 times as important.. Beyond the stall, ofcourse, the bottom tries to carry all the weight. -- ..med vennlig hilsen = with Kind Regards from Arnt... ;-) ...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-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Lee Elliott wrote Sent: 28 July 2004 21:32 To: FlightGear developers discussions Subject: Re: [Flightgear-devel] Taildragger takeoff and landing On Wednesday 28 July 2004 01:45, Andy Ross wrote: Jim Wilson wrote: Have I had this backwards all along? I knew of the incidence angle on the hstab, but always thought that positive values meant the leading edge was higher than with a negative incidence angle The number is a (conventional, right handed) rotation about the Y axis, which in YASim's coordinate system points out the left wingtip. So a positive incidence points down. Unless there's a sign bug (or three, or five...) in there somewhere. And Lee's surprise was right: you *can't* map a control to INCIDENCE in the control mapper. My head was ahead of the implementation. I've definitely intended to do this (and maybe I've worked on it at some point) but looking at CVS the code just ain't there. Sorry. Andy Heh! - I'm still a bit confused:) I had a look at the dc3 update, where the incidence had been set on the hstab but when I tried using it, it made no difference to the solution, and I couldn't detect any change in the behaviour. I was sure that the hstab incidence was set by the solver (as the 'tail incidence') The incidence +- issue threw me as well - like the others, I've been using +ve incidence to angle the wing up at the leading edge. It does seem to work that way though... My 2p on the 'does lift suck or blow', just to stir it up a bit more, is that the Wrights found that the lift was not perpendicular to the wing/aerofoil axis but was angled forward (they attached spring balances to their kites and measured the force required to hold them, and found that this force was lower that they'd calculated). On more refined aerofoils most of the lift comes from the leading edge region, where the acceleration is highest, although some of the more recent 'super-critical' aerofoils produce lift further back. There again, while I'm reasonably up on physics, I'd only claim to understand about 2/3rds of what I read about aerodynamics. Curiously enough, I was only quite recently discussing bow-waves and drag in relation to sprint racing kayaks with someone:) I rather like this explanation of lift. http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html Regards, Vivian ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon S Berndt wrote: On Wed, 28 Jul 2004 23:55:09 +0200 Erik Hofman [EMAIL PROTECTED] wrote: Jon S Berndt wrote: That's because it's _mostly_ (or entirely) the sucking action above the wing that contributes the most to lift. No, that is the *result* of lift, not the *cause*. No, you're mixing up cause and effect. I have been thinking about this over night and think I agree with you here. I've been biased be a comment a teacher (which I respected much) once told me but which after thinking about it some more is unrelated to this subject. BTW. My comment about the non-existence of pulling forces come from the same issue. Without the existence of pulling forces adhesive and cohesive forces wouldn't even exist. Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon Berndt wrote: One more thing: think of a baseball or better yet a lightweight ball. How do those things curve? I wouldn't know. I haven't thought about that one yet. My first impression would be that of the cohesive and adhesive forces again. Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Tony Peden wrote: I hope you guys realize that this is an ages old debate that still goes on in the relevant academic circles. Yes. There is nothing wrong with fixing this for once and for all isn't there? :-D Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Erik Hofman said: Jon Berndt wrote: One more thing: think of a baseball or better yet a lightweight ball. How do those things curve? I wouldn't know. I haven't thought about that one yet. My first impression would be that of the cohesive and adhesive forces again. Well Jim's make it up as you go along Physics manual says that there is greater pressure against the air molecules in front of the moving ball. Thus there is greater friction against those molecules than the air molecules to the side or behind. If the ball has a sidespin, then the slightly better traction (friction) on the front side will cause the ball to move in the direction opposite that of the forward surface of the spinning ball (as a result of something Newton said). Adding this sideways movement to the ball's trajectory produces a curve. The ball's momentum (speed), air density, size of the ball (amount trailing air turbulance), alignment of the planets, proximity to Fenway park, political persuasion, and the rate of spin will affect outcome. For a demonstration (or proof that I am wrong) see: http://www.grc.nasa.gov/WWW/K-12/airplane/foil2b.html Disclaimer: Use this information at your own risk. I will not be responsible for any broken noses, windows, or egos that result from the application of this theory. Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Thu, 29 Jul 2004 15:01:28 - Jim Wilson [EMAIL PROTECTED] wrote: Jon Berndt wrote: One more thing: think of a baseball or better yet a lightweight ball. How do those things curve? Well Jim's make it up as you go along Physics manual says that there is greater pressure against the air molecules in front of the moving ball. ... etc. Strike 1. Hint: If the curve ball is spinning about a vertical axis, what does this say about the flow of air on the left and right sides of the ball? Here's the windup ... and the pitch ... ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon S Berndt wrote: On Thu, 29 Jul 2004 15:01:28 - Jim Wilson [EMAIL PROTECTED] wrote: Jon Berndt wrote: One more thing: think of a baseball or better yet a lightweight ball. How do those things curve? Well Jim's make it up as you go along Physics manual says that there is greater pressure against the air molecules in front of the moving ball. ... etc. Strike 1. Hint: If the curve ball is spinning about a vertical axis, what does this say about the flow of air on the left and right sides of the ball? Here's the windup ... and the pitch ... Ok, then how do you explain a frisbee that can curve either way, even though it's always thrown with the same direction of spin. And please include the coriolis effect in your explanation (now that it is implimented in JSBSim.) Thank you. :-) Curt. -- Curtis Olsonhttp://www.flightgear.org/~curt HumanFIRST Program http://www.humanfirst.umn.edu/ FlightGear Project http://www.flightgear.org Unique text:2f585eeea02e2c79d7b1d8c4963bae2d ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Thu, 29 Jul 2004 10:34:16 -0500 Curtis L. Olson [EMAIL PROTECTED] wrote: Ok, then how do you explain a frisbee that can curve either way, even though it's always thrown with the same direction of spin. And please include the coriolis effect in your explanation (now that it is implimented in JSBSim.) Thank you. :-) Gyroscopic stabilization and tilt. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon S Berndt wrote: On Thu, 29 Jul 2004 10:34:16 -0500 Curtis L. Olson [EMAIL PROTECTED] wrote: Ok, then how do you explain a frisbee that can curve either way, even though it's always thrown with the same direction of spin. And please include the coriolis effect in your explanation (now that it is implimented in JSBSim.) Thank you. :-) Gyroscopic stabilization and tilt. Which gets us to the one milion dollar question: Can you frisbee on mars? Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Erik Hofman wrote: Jon S Berndt wrote: On Thu, 29 Jul 2004 10:34:16 -0500 Curtis L. Olson [EMAIL PROTECTED] wrote: Ok, then how do you explain a frisbee that can curve either way, even though it's always thrown with the same direction of spin. And please include the coriolis effect in your explanation (now that it is implimented in JSBSim.) Thank you. :-) Gyroscopic stabilization and tilt. Which gets us to the one milion dollar question: Can you frisbee on mars? You can, but south of the equator it will break the opposite direction. Curt. -- Curtis Olsonhttp://www.flightgear.org/~curt HumanFIRST Program http://www.humanfirst.umn.edu/ FlightGear Project http://www.flightgear.org Unique text:2f585eeea02e2c79d7b1d8c4963bae2d ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Curtis L. Olson wrote: Erik Hofman wrote: Jon S Berndt wrote: On Thu, 29 Jul 2004 10:34:16 -0500 Curtis L. Olson [EMAIL PROTECTED] wrote: Ok, then how do you explain a frisbee that can curve either way, even though it's always thrown with the same direction of spin. And please include the coriolis effect in your explanation (now that it is implimented in JSBSim.) Thank you. :-) Gyroscopic stabilization and tilt. Which gets us to the one milion dollar question: Can you frisbee on mars? You can, but south of the equator it will break the opposite direction. I like it when people share their valuable experiences ... :-) So, the next time I'm there I'll be careful ! Boris ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Curtis L. Olson wrote: Erik Hofman wrote: Jon S Berndt wrote: On Thu, 29 Jul 2004 10:34:16 -0500 Curtis L. Olson [EMAIL PROTECTED] wrote: Ok, then how do you explain a frisbee that can curve either way, even though it's always thrown with the same direction of spin. And please include the coriolis effect in your explanation (now that it is implimented in JSBSim.) Thank you. :-) Gyroscopic stabilization and tilt. Which gets us to the one milion dollar question: Can you frisbee on mars? You can, but south of the equator it will break the opposite direction. It must be a great sight, the first man on Mars playing frisbee with a colleague. Erik (Now I start to wonder why we always smash our probes on the surface of Mars). ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Thu, 29 Jul 2004 19:37:08 +0200 Boris Koenig [EMAIL PROTECTED] wrote: I like it when people share their valuable experiences ... :-) So, the next time I'm there I'll be careful ! Why? You won't hit anything! :-) Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Thu, 29 Jul 2004 19:38:44 +0200 Erik Hofman [EMAIL PROTECTED] wrote: (Now I start to wonder why we always smash our probes on the surface of Mars). NASA does it by design. (Well ... except for the Mars Polar Lander.) :-) Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
David Megginson wrote: I've been frustrated with the tendency of the DC-3 (--aircraft=dc3) to noseover during the takeoff and landing rolls, and of the J3 Cub (--aircraft=j3cub) to nose over during wheel landings. I've fiddled with the YASim files a lot in the past but have never found a good solution. Finally, today, I had a DUH! moment. On non-aerobatic planes, the horizontal stabilizer is set at a negative angle of incidence so that it will not stall before the wings (tail stalls are rarely recoverable). I set the hstab on the J3 Cub and DC-3 to -3 degrees of incidence, and the tendency to nose-over has virtually disappeared. The takeoff roll of the DC-3 is a joy, and for both planes, I can now use the technique described in STICK AND RUDDER for taildragger wheel landings -- just as the wheels touch the pavement, push the stick or yoke full forward. Sounds exciting, I'll have to try both of them now! Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jim Wilson wrote: You are right, that doesn't sound right. At least if a positive value did point down, it would be in conflict with the AOA parameter. That said, are you sure the DC-3 is supposed to have a negative incidence? I just looked up the p51 and the diagram clearly shows a positive incidence. The tail is +2.0 degrees (so that at level AoA=0 on main wing, the tail would have a AoA of 2.0 degrees). The role of the horizontal stabilizer is to produce negative lift to keep the nose from dropping -- you balance the plane so that it is slightly nose-heavy, then use the hstab (which is on a long lever arm) to apply just enough down force to keep the nose balanced. Flying with an aft CG is more efficient, since you're not making as much (if any) downforce with the hstab, but it can also result in pitch control problems and violent stalls. On typical non-aerobatic aircraft, the horizontal stabilizer has a lower angle of attack than the main wings in any given flight regime, but there are two ways to accomplish that: 1. give the hstab a lower physical incidence angle than the wings; and/or 2. take advantage of the downwash from the wings, which comes from above rather than straight on (will not work for a t-tail, obviously). Since YASim does not model downwash, we have to adjust the incidence angle to simulate it where the hstab should be according to its relative airflow as well as its physical incidence angle. This isn't an issue for nose-wheel aircraft, since the front wheel keeps them from nosing over most of the time, but it makes a significant difference for controlling taildraggers on the ground. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
David Megginson said: Jim Wilson wrote: You are right, that doesn't sound right. At least if a positive value did point down, it would be in conflict with the AOA parameter. That said, are you sure the DC-3 is supposed to have a negative incidence? I just looked up the p51 and the diagram clearly shows a positive incidence. The tail is +2.0 degrees (so that at level AoA=0 on main wing, the tail would have a AoA of 2.0 degrees). The role of the horizontal stabilizer is to produce negative lift to keep the nose from dropping -- you balance the plane so that it is slightly nose-heavy, then use the hstab (which is on a long lever arm) to apply just enough down force to keep the nose balanced. Flying with an aft CG is more efficient, since you're not making as much (if any) downforce with the hstab, but it can also result in pitch control problems and violent stalls. On typical non-aerobatic aircraft, the horizontal stabilizer has a lower angle of attack than the main wings in any given flight regime, but there are two ways to accomplish that: 1. give the hstab a lower physical incidence angle than the wings; and/or 2. take advantage of the downwash from the wings, which comes from above rather than straight on (will not work for a t-tail, obviously). Since YASim does not model downwash, we have to adjust the incidence angle to simulate it where the hstab should be according to its relative airflow as well as its physical incidence angle. This isn't an issue for nose-wheel aircraft, since the front wheel keeps them from nosing over most of the time, but it makes a significant difference for controlling taildraggers on the ground. Excellent, thanks for the clarification. Just looking at the cub you can see down-wash is a major design feature. The DC-3 has a high tail, but I can see the incidence in the main wing is pretty high. I wonder what happens when you increase the wing incidence and set the horizontal stabilizer to 0 or whatever it is supposed to be. As for the P51-D, here is a page out of the reference: http://www.spiderbark.com/fgfs/sec1_0001.JPG http://www.spiderbark.com/fgfs/sec1_0001a.JPG For some reason the designers seem to be going the opposite direction (positive tail incidence). I'd like to understand the reason in order to make a decision on the p51d fdm config. It did seem to handle better with the negative incidence number. But down-wash certainly isn't present on the hstab and the diagram appears to show positive incidence. The other related problem I'm not sure of is that with or without reducing the incidence value, I can't seem to take off in a moderate cross-wind ( 12kts). The tail always blows around and the rudder/brakes can't stop it. Does anyone know if this is normal behavior? Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jim Wilson wrote: Excellent, thanks for the clarification. Just looking at the cub you can see down-wash is a major design feature. The DC-3 has a high tail, but I can see the incidence in the main wing is pretty high. I wonder what happens when you increase the wing incidence and set the horizontal stabilizer to 0 or whatever it is supposed to be. I'm getting seriously out of my depth here, since I didn't even take high school physics, but as far as I understand the most important part of lift is the suction created by the partial vacuum *above* the wings -- that means that wings are pulling air down more than pushing it down, effectively, and the hstab will be in downwash even if it is level with or slightly above the wings. Only a very high hstab, like the one on a t-tail, will be clear of it. Now Jon, Tony, or Andy can step in and explain how I've totally misunderstood the aerodynamics. For some reason the designers seem to be going the opposite direction (positive tail incidence). I'd like to understand the reason in order to make a decision on the p51d fdm config. It did seem to handle better with the negative incidence number. But down-wash certainly isn't present on the hstab and the diagram appears to show positive incidence. It's very hard to see this with the naked eye because you cannot tell the angle of the downwash. I imagine that downwash would be more dramatic in a plane with higher wing loading, so the hstab could have a less negative (or more positive) incidence angle and still have effectively a lower angle of attack. The other related problem I'm not sure of is that with or without reducing the incidence value, I can't seem to take off in a moderate cross-wind ( 12kts). The tail always blows around and the rudder/brakes can't stop it. Does anyone know if this is normal behavior? The vstab is probably too effective at low speeds, and I have no real-life taildragger experience, but a 12 knot crosswind component is not small -- the Cessna 172, for example, has a maximum demonstrated crosswind component for landing of only about 15 kt, if I recall correctly. Can you lock the tailwheel so that it doesn't castor? If so, try to keep backpressure on it to hold the plane straight. You might also want to shift the CG back a bit so that the tailwheel doesn't go too light. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Matthew Law wrote: It seems much, much better to me. However, I can sit at minimum power with the brakes on in nil wind and rock from one main wheel to the other using the ailerons. I can also lift the tail off the ground at minimum power. I'm not sure if that is a side effect of what you've done, but I'm sure that shouldn't be the case :-) That shouldn't be from my change -- can you do it with other YASim planes? All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
David M. wrote: I'm getting seriously out of my depth here, since I didn't even take high school physics, but as far as I understand the most important part of lift is the suction created by the partial vacuum *above* the wings -- that means that wings are pulling air down more than pushing it down, effectively, and the hstab will be in downwash even if it is level with or slightly above the wings. Only a very high hstab, like the one on a t-tail, will be clear of it. Now Jon, Tony, or Andy can step in and explain how I've totally misunderstood the aerodynamics. I've heard it described several ways (lift); I think you're pretty close. I don't know if I'd say partial vacuum, though, which might give an exaggerated impression. Thinking of Bernoulli's nozzle example from elementary physics, the flow over the top, curved surface of a wing sees faster airflow, and lower pressure. Integrating the pressure over the lower and upper surfaces of the wing results in a net upward force (assuming steady-state flight). Probably there is a bit of both pushing _and_ pulling going on. If the lower surface of the wing is at a positive alpha, it's not too difficult to think that there is some pushing going on. Well, it would be interesting to get Tony's impression, and of course a physicist will describe this in his own way, too. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
-Original Message- From: Jon Berndt Sent: 28 July 2004 3:47 pm To: FlightGear developers discussions Subject: RE: [Flightgear-devel] Taildragger takeoff and landing snip I've heard it described several ways (lift); I think you're pretty close. I don't know if I'd say partial vacuum, though, which might give an exaggerated impression. Thinking of Bernoulli's nozzle example from elementary physics, the flow over the top, curved surface of a wing sees faster airflow, and lower pressure. Integrating the pressure over the lower and upper surfaces of the wing results in a net upward force (assuming steady-state flight). Probably there is a bit of both pushing _and_ pulling going on. If the lower surface of the wing is at a positive alpha, it's not too difficult to think that there is some pushing going on. Well, it would be interesting to get Tony's impression, and of course a physicist will describe this in his own way, too. Jon Well as a physicist (but with no formal aeronautical education), I always think of it as the wing is pushing air down, which causes an equal and opposite force (to quote Newton) of the air pushing the wing up. Hence acrobatic aircraft with symmettrical wings can still fly. The key to wing shape design is to keep the air flow attached to both the upper and lower surface so that you can change the direction of airflow. Once the flow detaches (a stall), you are not pushing the air down any more, so it isn't pushing you up. Richard This e-mail has been scanned for Bede Scientific Instruments for all viruses by Star Internet. The service is powered by MessageLabs. For more information on a proactive anti-virus service working around the clock, around the globe, visit: http://www.star.net.uk ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Richard Bytheway said: -Original Message- From: Jon Berndt Sent: 28 July 2004 3:47 pm To: FlightGear developers discussions Subject: RE: [Flightgear-devel] Taildragger takeoff and landing snip I've heard it described several ways (lift); I think you're pretty close. I don't know if I'd say partial vacuum, though, which might give an exaggerated impression. Thinking of Bernoulli's nozzle example from elementary physics, the flow over the top, curved surface of a wing sees faster airflow, and lower pressure. Integrating the pressure over the lower and upper surfaces of the wing results in a net upward force (assuming steady-state flight). Probably there is a bit of both pushing _and_ pulling going on. If the lower surface of the wing is at a positive alpha, it's not too difficult to think that there is some pushing going on. Well, it would be interesting to get Tony's impression, and of course a physicist will describe this in his own way, too. Jon Well as a physicist (but with no formal aeronautical education), I always think of it as the wing is pushing air down, which causes an equal and opposite force (to quote Newton) of the air pushing the wing up. Hence acrobatic aircraft with symmettrical wings can still fly. The key to wing shape design is to keep the air flow attached to both the upper and lower surface so that you can change the direction of airflow. Once the flow detaches (a stall), you are not pushing the air down any more, so it isn't pushing you up. This suggests that both bernoulli and the pushing (gravity) are at play, depending on the airfoil. My (uneducated) guess is the pushing is almost all of it and that the bernoulli effect only augments: http://observe.arc.nasa.gov/nasa/exhibits/planes/planes_1c.html Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
David Megginson wrote: I'm getting seriously out of my depth here, since I didn't even take high school physics... Just a lurker at present until I can find a way to contribute more usefully but try this... http://www.av8n.com/how/ HTH -|steve|- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 17:25:31 - Jim Wilson [EMAIL PROTECTED] wrote: Richard Bytheway said: Well as a physicist (but with no formal aeronautical education), I always think of it as the wing is pushing air down, which causes an equal and opposite force (to quote Newton) of the air pushing the wing up. Hence acrobatic aircraft with symmettrical wings can still fly. The key to wing shape design is to keep the air flow attached to both the upper and lower surface so that you can change the direction of airflow. Once the flow detaches (a stall), you are not pushing the air down any more, so it isn't pushing you up. This suggests that both bernoulli and the pushing (gravity) are at play, depending on the airfoil. My (uneducated) guess is the pushing is almost all of it and that the bernoulli effect only augments: http://observe.arc.nasa.gov/nasa/exhibits/planes/planes_1c.html The pushing comes into play in Newtonian flow, such as at hypersonic speeds. In that case, the momentum transfer of many impacts with air molecules and the resulting exhange of momentum might be seen as pushing the wing upward. Also, past stall a wing will see a decrease in lift, but then an increase again - perhaps to an even higher degree than it had prior to stall - at about 45 degrees, like a flat plate. In that case, the airflow on the back side of the wing is obviously going to be detached, but there is lift, nonetheless. It seems to me that this could be seens as the airflow pushing the wing up, and the airflow being deflected downward. Not sure how that fits in with Bernoulli, if at all. However, at normal angles of attack below stall, the Bernoulli principle is, I believe, the explanation for lift. The _resulting_effect_ of the lower pressure on the top surface of the wing than on the bottom, gives a net lift - which *results*in* airflow being deflected (i.e. pushed downward). It could be a matter of point-of-view: the direct cause of the lift is the pressure differential, the effect is that airflow is deflected downwards. It's not the other way around - that is, the air that is pushed downward does not cause the pressure differential over the wing surfaces. That's my further explanation, in any case. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Tue, 28 Jun 2005 19:20:17 +0100 SGMINFO [EMAIL PROTECTED] wrote: David Megginson wrote: I'm getting seriously out of my depth here, since I didn't even take high school physics... Just a lurker at present until I can find a way to contribute more usefully but try this... http://www.av8n.com/how/ Yes, this seems liek an excellent piece. See section 3.14 and 3.15 for pertinent discussion. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Jim Wilson writes: Well as a physicist (but with no formal aeronautical education), I always think of it as the wing is pushing air down, which causes an equal and opposite force (to quote Newton) of the air pushing the wing up. Hence acrobatic aircraft with symmettrical wings can still fly. The key to wing shape design is to keep the air flow attached to both the upper and lower surface so that you can change the direction of airflow. Once the flow detaches (a stall), you are not pushing the air down any more, so it isn't pushing you up. This suggests that both bernoulli and the pushing (gravity) are at play, depending on the airfoil. My (uneducated) guess is the pushing is almost all of it and that the bernoulli effect only augments: http://observe.arc.nasa.gov/nasa/exhibits/planes/planes_1c.html This is a 100 year old argument :-) http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html If you really want to know read everything you can wriiten by Koukowskii and Prandtl Cheers Norman ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 14:15:04 -0400 Norman Vine [EMAIL PROTECTED] wrote: This is a 100 year old argument :-) http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html If you really want to know read everything you can wriiten by Koukowskii and Prandtl Is light a wave or a particle? :-) ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jim Wilson wrote: This suggests that both bernoulli and the pushing (gravity) are at play, depending on the airfoil. My (uneducated) guess is the pushing is almost all of it and that the bernoulli effect only augments: http://observe.arc.nasa.gov/nasa/exhibits/planes/planes_1c.html There's a pressure differential either way, but since icing on top of the wing kills lift more than icing on the bottom, I'll guess that the low pressure on top is at least as important as the high pressure beneath. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon S Berndt wrote: On Tue, 28 Jun 2005 19:20:17 +0100 SGMINFO [EMAIL PROTECTED] wrote: David Megginson wrote: I'm getting seriously out of my depth here, since I didn't even take high school physics... Just a lurker at present until I can find a way to contribute more usefully but try this... http://www.av8n.com/how/ Yes, this seems liek an excellent piece. See section 3.14 and 3.15 for pertinent discussion. Actually, this one might be most pertinent to the original discussion: http://www.av8n.com/how/htm/airfoils.html#fig-3pv The important thing to note is that the airflow *above* the wing also curves down, not just the airflow below it. That is why, even with the same incidence angle, the hstab sees a different angle of attack in the wings' downwash even if it is level with or slightly above the wings themselves. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 14:52:24 -0400 David Megginson [EMAIL PROTECTED] wrote: The important thing to note is that the airflow *above* the wing also curves down, not just the airflow below it. That is why, even with the same incidence angle, the hstab sees a different angle of attack in the wings' downwash even if it is level with or slightly above the wings themselves. David So, from the point of view of the horizontal stabilizor, that pesky downwash happens because wings really suck. ;-) Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wednesday 28 July 2004 19:35, Jon S Berndt wrote: On Wed, 28 Jul 2004 14:15:04 -0400 Norman Vine [EMAIL PROTECTED] wrote: This is a 100 year old argument :-) http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html If you really want to know read everything you can wriiten by Koukowskii and Prandtl Is light a wave or a particle? :-) Does it even occupy a volume? :) LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon S Berndt wrote: On Wed, 28 Jul 2004 14:15:04 -0400 Norman Vine [EMAIL PROTECTED] wrote: This is a 100 year old argument :-) http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html If you really want to know read everything you can wriiten by Koukowskii and Prandtl Is light a wave or a particle? Yes. Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
David Megginson wrote: The important thing to note is that the airflow *above* the wing also curves down, not just the airflow below it. That is why, even with the same incidence angle, the hstab sees a different angle of attack in the wings' downwash even if it is level with or slightly above the wings themselves. This is exactly the reason why pressure is build up underneath the wing (pushing the airfoil up on air molecules == force). Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 22:56:59 +0200 Erik Hofman [EMAIL PROTECTED] wrote: This is exactly the reason why pressure is build up underneath the wing (pushing the airfoil up on air molecules == force). No, not really. See: http://www.av8n.com/how/htm/airfoils.html#sec-consistent Excerpt: Of course, if there were no atmospheric pressure below the wing, there would be no way to have reduced pressure above the wing. Fundamentally, atmospheric pressure below the wing is responsible for supporting the weight of the airplane. The point is that pressure changes above the wing are more pronounced than the pressure changes below the wing. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon S Berndt wrote: On Wed, 28 Jul 2004 22:56:59 +0200 Erik Hofman [EMAIL PROTECTED] wrote: This is exactly the reason why pressure is build up underneath the wing (pushing the airfoil up on air molecules == force). No, not really. See: http://www.av8n.com/how/htm/airfoils.html#sec-consistent Try this for a start: An airflow over the wing is causing the downwash at the end of the airfoil. The airflow below the wing is now kind of captured between the airfoil and the layer(s) of air underneath itself. In this situation it can go in just two directions, up or down, The majority of the flow will go down, bu a tiny fraction of the molecules has to go up. If the number of molecules that go up is high enough it will lift the airfoil up with it. This is really what DaVinci already had discovered back in 1530-something. Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 23:28:55 +0200 Erik Hofman [EMAIL PROTECTED] wrote: Jon S Berndt wrote: No, not really. See: http://www.av8n.com/how/htm/airfoils.html#sec-consistent Try this for a start: An airflow over the wing is causing the downwash at the end of the airfoil. The airflow below the wing is now kind of captured between the airfoil and the layer(s) of air underneath itself. In this situation it can go in just two directions, up or down, The majority of the flow will go down, bu a tiny fraction of the molecules has to go up. If the number of molecules that go up is high enough it will lift the airfoil up with it. This is really what DaVinci already had discovered back in 1530-something. Which is why he never flew. See the argument about bullets in the link provided, above. In the case of the airflow below the wing, it's not really trapped. It gets out of the way, below. Also, consider the wing of a B-52. I believe it is entirely possible that a wing such as that on the B-52 can have a lower surface that is parallel to the airflow, but still provides lift. That's because it's _mostly_ (or entirely) the sucking action above the wing that contributes the most to lift. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Lee Elliott writes: My 2p on the 'does lift suck or blow', On more refined aerofoils most of the lift comes from the leading edge region, where the acceleration is highest, although some of the more recent 'super-critical' aerofoils produce lift further back. There again, while I'm reasonably up on physics, I'd only claim to understand about 2/3rds of what I read about aerodynamics. When building sails and fins it is useful to think of Lift operating perpendiculary to the point of maximum 'curvature' of the foil. this just usually happens to be very close to the point of maximum velocity of the stream Cheers Norman ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jon S Berndt wrote: Which is why he never flew. See the argument about bullets in the link provided, above. http://dsc.discovery.com/news/briefs/20031201/leonardo.html In the case of the airflow below the wing, it's not really trapped. It gets out of the way, below. But it will encounter a force of the airflow below. Remember, an airflow is not without mass, there is really something there that acts, and reacts to it's surrounding. Also, consider the wing of a B-52. I believe it is entirely possible that a wing such as that on the B-52 can have a lower surface that is parallel to the airflow, but still provides lift. That's because it's _mostly_ (or entirely) the sucking action above the wing that contributes the most to lift. No, that is the *result* of lift, not the *cause*. Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wednesday 28 July 2004 22:47, Jon S Berndt wrote: On Wed, 28 Jul 2004 23:28:55 +0200 Erik Hofman [EMAIL PROTECTED] wrote: Jon S Berndt wrote: No, not really. See: http://www.av8n.com/how/htm/airfoils.html#sec-consistent Try this for a start: An airflow over the wing is causing the downwash at the end of the airfoil. The airflow below the wing is now kind of captured between the airfoil and the layer(s) of air underneath itself. In this situation it can go in just two directions, up or down, The majority of the flow will go down, bu a tiny fraction of the molecules has to go up. If the number of molecules that go up is high enough it will lift the airfoil up with it. This is really what DaVinci already had discovered back in 1530-something. Which is why he never flew. See the argument about bullets in the link provided, above. In the case of the airflow below the wing, it's not really trapped. It gets out of the way, below. Also, consider the wing of a B-52. I believe it is entirely possible that a wing such as that on the B-52 can have a lower surface that is parallel to the airflow, but still provides lift. That's because it's _mostly_ (or entirely) the sucking action above the wing that contributes the most to lift. Jon Although it might not be accurate in my model, the B-52 wing is set at six deg incidence, and while it does fly a little nose-down in some circumstances, six deg worth would be worrying;) Heh - not that I haven't seen some of my FDMs for it do exactly that:) I guess that the lower trailing edge (flaps up) could approach it though... Re the comment made about flying inverted, here's an interesting pic of Geoffrey Tyson flying the SR-A1 inverted. Check out the apparent AoA, the wing incidence and the elevator deflection:) http://www.overthetop.freeserve.co.uk/SR-SR-A1-Another_Eyebrow_Raiser.jpg LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 23:55:09 +0200 Erik Hofman [EMAIL PROTECTED] wrote: Jon S Berndt wrote: That's because it's _mostly_ (or entirely) the sucking action above the wing that contributes the most to lift. No, that is the *result* of lift, not the *cause*. Erik No, you're mixing up cause and effect. From Fundamentals of Aerodynamics (John Anderson) is this succinctly put explanation: No matter how complex the body shape may be, the aerodynamic forces and moents on the body are due entirely to the above two basic sources. The two sources were listed as, Pressure distribution over the body surface, and shear stress distribution over the body surface. If you integrate the pressure distribution over the body (a wing, for instance), you get lift (and drag, if you componentize them in a coordinate system aligned with the velocity vector). Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 28 Jul 2004 23:16:05 +0100 Lee Elliott [EMAIL PROTECTED] wrote: Although it might not be accurate in my model, the B-52 wing is set at six deg incidence, and while it does fly a little nose-down in some circumstances, six deg worth would be worrying;) Heh - not that I haven't seen some of my FDMs for it do exactly that:) Take a look at the NACA wing section lift curves. The ones with a camber have a positive lift coefficient at zero degrees alpha. The lift is due to the net pressure difference across the wing surfaces. The same action (pressure difference) that causes the lift, also causes the downwash. You can't have one without the other. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Downwash (was Re: [Flightgear-devel] Taildragger takeoff and landing)
Getting back on topic, I think everyone agrees that the horizontal stabilizer on a typical plane (excluding t-tails) should be seeing downwash -- in other words, its relative wind will not be the same as the relative wind seen by the wings. For JSBSim, we don't have to worry about this, because the coefficients already take it into account. For YASim, we *do* have to worry about downwash, since it will change the effective angle of attack for the tail. I'd be interested in which approach Andy and others prefer: 1. set the tail incidence down a few degrees to compensate for the lack of downwash (as I have done on the DC-3 and J3 Cub); or 2. add a downwash parameter giving an offset for the relative wind over each lifting surface. This will normally be 0 for the wings, of course (I doubt the downwash from canards is enough the change the effective alpha of the main wings, but who knows?). This problem has little effect on normal flight, but it matters a lot for the landing and takeoff rolls of taildraggers -- without it, they have an unrealistic tendency to nose over. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: Downwash (was Re: [Flightgear-devel] Taildragger takeoff and landing)
Getting back on topic, I think everyone agrees that the horizontal stabilizer on a typical plane (excluding t-tails) should be seeing downwash Yes. _When_ there is positive lift being generated by the wing. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Erik Hofman [EMAIL PROTECTED] wrote: Jon S Berndt wrote: That's because it's _mostly_ (or entirely) the sucking action above the wing that contributes the most to lift. No, that is the *result* of lift, not the *cause*. Erik No, you're mixing up cause and effect. One more thing: think of a baseball or better yet a lightweight ball. How do those things curve? Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
I guess that's one of the reasons why some planes use canards. =P Regards, Ampere On July 28, 2004 03:06 pm, Jon S Berndt wrote: So, from the point of view of the horizontal stabilizor, that pesky downwash happens because wings really suck. ;-) ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Wed, 2004-07-28 at 14:28, Erik Hofman wrote: Jon S Berndt wrote: On Wed, 28 Jul 2004 22:56:59 +0200 Erik Hofman [EMAIL PROTECTED] wrote: This is exactly the reason why pressure is build up underneath the wing (pushing the airfoil up on air molecules == force). No, not really. See: http://www.av8n.com/how/htm/airfoils.html#sec-consistent Try this for a start: An airflow over the wing is causing the downwash at the end of the airfoil. The airflow below the wing is now kind of captured between the airfoil and the layer(s) of air underneath itself. In this situation it can go in just two directions, up or down, The majority of the flow will go down, bu a tiny fraction of the molecules has to go up. If the number of molecules that go up is high enough it will lift the airfoil up with it. This is really what DaVinci already had discovered back in 1530-something. I hope you guys realize that this is an ages old debate that still goes on in the relevant academic circles. Erik ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d -- Tony Peden [EMAIL PROTECTED] ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
RE: [Flightgear-devel] Taildragger takeoff and landing
Tony wrote: I hope you guys realize that this is an ages old debate that still goes on in the relevant academic circles. I've heard about the debate on whether it is circulation or the pressure difference that causes lift. I've never heard it argued that mechanical deflection is the cause for lift in subsonic flight. In my mind (and I've read this, too), circulation causes the pressure difference which in turn causes lift. Think of a baseball thrown with a spin. In that case, the lift generated is purely by circulation. Same thing with a cambered airfoil. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
On Tuesday 27 July 2004 22:46, David Megginson wrote: I've been frustrated with the tendency of the DC-3 (--aircraft=dc3) to noseover during the takeoff and landing rolls, and of the J3 Cub (--aircraft=j3cub) to nose over during wheel landings. I've fiddled with the YASim files a lot in the past but have never found a good solution. Finally, today, I had a DUH! moment. On non-aerobatic planes, the horizontal stabilizer is set at a negative angle of incidence so that it will not stall before the wings (tail stalls are rarely recoverable). I set the hstab on the J3 Cub and DC-3 to -3 degrees of incidence, and the tendency to nose-over has virtually disappeared. The takeoff roll of the DC-3 is a joy, and for both planes, I can now use the technique described in STICK AND RUDDER for taildragger wheel landings -- just as the wheels touch the pavement, push the stick or yoke full forward. All the best, David I just saw the cvs entries go in - the ability to set the hstab incidence was a bit of a revelation to me:) One of those !??? moments:) LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
David Megginson wrote: I've been frustrated with the tendency of the DC-3 (--aircraft=dc3) to noseover during the takeoff and landing rolls, and of the J3 Cub (--aircraft=j3cub) to nose over during wheel landings. I've fiddled with the YASim files a lot in the past but have never found a good solution. Finally, today, I had a DUH! moment. On non-aerobatic planes, the horizontal stabilizer is set at a negative angle of incidence so that it will not stall before the wings (tail stalls are rarely recoverable). I set the hstab on the J3 Cub and DC-3 to -3 degrees of incidence, and the tendency to nose-over has virtually disappeared. The takeoff roll of the DC-3 is a joy, and for both planes, I can now use the technique described in STICK AND RUDDER for taildragger wheel landings -- just as the wheels touch the pavement, push the stick or yoke full forward. It seems much, much better to me. However, I can sit at minimum power with the brakes on in nil wind and rock from one main wheel to the other using the ailerons. I can also lift the tail off the ground at minimum power. I'm not sure if that is a side effect of what you've done, but I'm sure that shouldn't be the case :-) All the best, Matthew. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
David Megginson said: I've been frustrated with the tendency of the DC-3 (--aircraft=dc3) to noseover during the takeoff and landing rolls, and of the J3 Cub (--aircraft=j3cub) to nose over during wheel landings. I've fiddled with the YASim files a lot in the past but have never found a good solution. Finally, today, I had a DUH! moment. On non-aerobatic planes, the horizontal stabilizer is set at a negative angle of incidence so that it will not stall before the wings (tail stalls are rarely recoverable). I set the hstab on the J3 Cub and DC-3 to -3 degrees of incidence, and the tendency to nose-over has virtually disappeared. The takeoff roll of the DC-3 is a joy, and for both planes, I can now use the technique described in STICK AND RUDDER for taildragger wheel landings -- just as the wheels touch the pavement, push the stick or yoke full forward. Have I had this backwards all along? I knew of the incidence angle on the hstab, but always thought that positive values meant the leading edge was higher than with a negative incidence angle (assuming the trailing edge stays the same). IIRC P51 specs I have show a positive number for this. On the P51-D I generally hold the stick back a bit to keep things under control which is actually compensating for the extra tail-incidence (combined with the attitude of the a/c on ground). I believe this is normal procedure. In general though, I do not think that the ground modeling is very accurate in any of the flight models (a bold statement for a non-pilot :-)). What you are saying regarding stall angle makes sense, but this web page describes an opposite technique than the one you've quoted from Stick and Rudder: Once on the ground the elevator control should be 'sucked into your gut,' that is, it is held back firmly as far as it will go. This places weight on the tail wheel and provides more steering authority. If the airplane touched down in the three-point attitude, moving the elevator control full aft will prevent bouncing or skipping. see http://www.mountainflying.com/taildrag2.htm Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Jim Wilson wrote: Have I had this backwards all along? I knew of the incidence angle on the hstab, but always thought that positive values meant the leading edge was higher than with a negative incidence angle The number is a (conventional, right handed) rotation about the Y axis, which in YASim's coordinate system points out the left wingtip. So a positive incidence points down. Unless there's a sign bug (or three, or five...) in there somewhere. And Lee's surprise was right: you *can't* map a control to INCIDENCE in the control mapper. My head was ahead of the implementation. I've definitely intended to do this (and maybe I've worked on it at some point) but looking at CVS the code just ain't there. Sorry. Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Andy Ross wrote: The number is a (conventional, right handed) rotation about the Y axis, which in YASim's coordinate system points out the left wingtip. So a positive incidence points down. Unless there's a sign bug (or three, or five...) in there somewhere. A positive incidence points down?? So if I set the incidence angle of the wings to 3 degrees, the angle of attack of the wings when the fuselage is level will be -3 degrees? That doesn't seem to be happening with the models. I'd also like to take this opportunity to ask (well, beg) that YASim could start using the same coordinate system as JSBSim, most textbooks I've seen, and every POH I've read, where X is positive moving back from the nose. I'm willing to fix all of the config files currently in CVS if will agree to the change. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
Andy Ross said: Jim Wilson wrote: Have I had this backwards all along? I knew of the incidence angle on the hstab, but always thought that positive values meant the leading edge was higher than with a negative incidence angle The number is a (conventional, right handed) rotation about the Y axis, which in YASim's coordinate system points out the left wingtip. So a positive incidence points down. Unless there's a sign bug (or three, or five...) in there somewhere. Well maybe two or four, because it seems to be working as expected. I'm going to commit a change to the p51 as well. It still works fine going with full stick/yoke back on landings (assuming you've landed in a stall). Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Taildragger takeoff and landing
David Megginson said: Andy Ross wrote: The number is a (conventional, right handed) rotation about the Y axis, which in YASim's coordinate system points out the left wingtip. So a positive incidence points down. Unless there's a sign bug (or three, or five...) in there somewhere. A positive incidence points down?? So if I set the incidence angle of the wings to 3 degrees, the angle of attack of the wings when the fuselage is level will be -3 degrees? That doesn't seem to be happening with the models. You are right, that doesn't sound right. At least if a positive value did point down, it would be in conflict with the AOA parameter. That said, are you sure the DC-3 is supposed to have a negative incidence? I just looked up the p51 and the diagram clearly shows a positive incidence. The tail is +2.0 degrees (so that at level AoA=0 on main wing, the tail would have a AoA of 2.0 degrees). Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
