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Originally Posted by JPerrone
(Post 11755208)
It sounds like I missed a really entertaining exchange about airspeed!!! I'm not really much interested in stirring up a hornet's nest, but I am curious about that. And I don't think I have any preconceived notions about what the right answer is.
Lets start with airplane A, flying 30 mph, IN NO WIND. His ground speed (speed relative to the ground) is 30 mph and because there is no wind, I think his airspeed should be 30 mph. Maybe it isn't I'm sure someone knows!!! Now, same airplane, same ground speed, but wind is 10 mph on the nose. This makes the airplanes airspeed 10 mph higher, so it is airspeed is 40 mph, for the same 30 mph groundspeed. Again: maybe this is wrong, etc Now, starship Enterprise (the real one NC 1701 not 1701A, B, etc) swoops in and teleports the plane 180 degrees the opposite direction!!! I think because of conservation of momentum the plane has to be going 30 mph relative to ground; but it's airspeed must now be (30-10) = 20. When you turn a REAL model or REAL plane, it cannot make this instantaneous change in direction, so maybe there is a "conservation of airspeed" but this would imply a change in ground speed. Hmm, wonder if there's any way to confirm/deny that?.... Now COMPLETELY ignoring any theories etc, what I observe when I'm flying my little models (they seem to react more than the bigger ones) is that they go a certain speed into the wind (call it "50 undefined units of speed") and when I turn around, flying in the direction with the wind, they slow down to 20 or 30 UUS. Ground speed reducing. This speed is from my frame of reference, so I think that is ground speed. I think that means that the airplane tries to maintain airspeed, with a resultant change in ground speed. Is that right? Regards |
Tail wind adds to airspeed and ground speed. Headwind reduces airspeed/groundspeed.
Geez. |
Originally Posted by Bob Pastorello
(Post 11755487)
Tail wind adds to airspeed and ground speed. Headwind reduces airspeed/groundspeed.
Geez. |
Hi,
Just have to chime in here - there is a book out there, that describes the art of flying like nothing else : " Stick and Rudder" by Wolfgang Langewiesche ( Macgraw-Hill publishing group ) ! It was published some 60 years ago and is , in my opinion, sill unmatched in introducing beginners as well as established aviators into the basics of flying ! Get that book, spend a few hours of real excitement ! You will NOT be disapointed- promised ! Cheers Hans |
Originally Posted by jwren00
(Post 11755533)
No
Airspeed ain't the same as groundspeed. Which in the case of our RC toys has little relevance, as we are nearly ALL interested in Ground speed, although we may not know it nor admit it. Just like in our case we are ALWAYS interested in relative ground track of our planes through the air, since we're standing still (unless we're running around panicked about what control to give). |
Originally Posted by Bob Pastorello
(Post 11755587)
Thought I'd see if anyone is reading any of these posts.
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Regarding airspeed and groundspeed: as an RC pilot, we are concerned about BOTH. Flying RC is like flying in perpetual ground-reference maneuvers.
The plane neither "knows" nor cares about groundspeed. Groundspeed is only relevant when the plane needs to track in relation to some point or path that is ground-based (like the runway, or the RC pilot's viewpoint), or when we are trying to figure out how long it will take to get somewhere. It has ZERO EFFECT on how the plane flies. This may help: imagine the plane flying on a calm day. Now the earth mysteriously starts spinning faster, but the air does not change. No thinking person could imagine the airplane instantly changing its flight behavior just because the earth below it (which it is not touching) has changed speed. Of course, the plane will APPEAR to be flying at a different speed to a ground observer if there is any wind. Example: flying at 40kts into 40kt headwind will result in the plane appearing to hover in place. I see this often with my powered gliders. If you are at full power (or gliding) and still not gaining ground, the only option is to drop the nose to pick up AIRSPEED, which naturally will increase GROUNDSPEED (assuming steady wind). As RC pilots, it is critical to fully get our heads around this concept if we really want to be proficient pilots. It's not that hard. And the trig stuff and wiz wheels are only required if you are trying to plot ground track or groundspeed. There is also a difference between INDICATED airspeed (or pressure airspeed) and TRUE airspeed (the actual velocity of air molecules passing over the plane), but at the altitudes and conditions we fly RC, this difference is usually not much of a consideration. Matt |
Originally Posted by dabigboy
(Post 11755675)
This may help: imagine the plane flying on a calm day. Now the earth mysteriously starts spinning faster, but the air does not change. No thinking person could imagine the airplane instantly changing its flight behavior just because the earth below it (which it is not touching) has changed speed.
When those two speeds don't match up, their planes start to fall out of the sky when they perform a turn??? |
Originally Posted by bjr_93tz
(Post 11755689)
That's what the downwind turn folks have trouble dealing with. The fact their plane is already flying through a body of air spinning around at nearly 1000mph and it just so happens the surface of the Earth is keeping pace.
When those two speeds don't match up, their planes start to fall out of the sky when they perform a turn??? (jk) I shall now retire to the relative calm of my northern hemispherical, properly-oriented magnetic poles, and correctly rotating propellers....particularly since we started daylight savings time today, and the field is READY !!!! Bye, everyone.... |
Originally Posted by Bob Pastorello
(Post 11755717)
bjr - I think your location, with it's reversed coriolis effect, and pole reversal is probably causing the vortex turbulence created by wrong-way spinning. That's what creates the problems for the rudder>aileron mix and it's impact on perceived airspeed v.s. actual groundspeed.
Cheers |
It's easy. When you move your right thumb move the left thumb the same direction. Mix as needed to maintain a co-ordinated turn.
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OK, spent most of the weekend moving, good news is the new 40% Extra can come out of storage and I can get her finished up. So I figure when I do get her flying I will give you guy's method a try. With that said lets see if I have this correct.
If I'm flying in a cross wind I first have to determine the angle the wind is coming relative to the runway. Then based on the airspeed I think I'm going to be flying I will need to determine the amount of crab angle into the wind. Then without any instruments at all I am supposed to duplicate from one pass to the next the same exact airspeed and crab angle on an airplane flying anywhere from 300 ft to 1200 ft away from where I am standing? If I do all this correctly I will be able to do strait passes parallel to the runway? Will the 1/2 gallon of fuel I will be burning be a variable? It is approx 15% of total aircraft weight at take off. I suppose I can have my caller standing there with a wiz wheel. I hope this sounds as silly to you guys as it does to me. |
Has anybody watched those rc crash vids on YouTube as the plane lands? Ever noticed that a lot of the pilots NEVER use rudder. Land on the grass next to the strip, taxi into the pits....anywhere but the runway. No one corrects the path of the approaching plane with the rudder, a lot just use aileron....this is just wrong. If the plane is on finals and the wings are level keep them level and change the direction by using the rudder. With the power bleeding off as well as air speed, wings level the plane has to land, end of story.
Also these vids also reveal that these plane are slightly tail heavy or have far too much elevator throw. A lot of those pilots need to go back to flying a trainer and learn how to use a rudder properly, that and a throttle. The two most under rated, under used and mis understood of all the controls. End of rant:mad: Useful reading. HERE |
Originally Posted by cymaz
(Post 11756098)
If the plane is on finals and the wings are level keep them level and change the direction by using the rudder
Originally Posted by cymaz
(Post 11756098)
learn how to use a rudder properly, ....................mis understood of all the controls.
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A lot of pilots , not every pilot , I admit. Still it is a well under used control and mis used. Some of the clips show get skilful landings and you can see rudder used. And on take off too.
Useful |
Originally Posted by HarryC
(Post 11756118)
Completely wrong!
And thanks for demonstrating your own point!!!!!!!!!!!!!!!!!!!!!!!!!!! So please explain exactly why this would not work on a model airplane, the over use of exclamation points leaves a bit to be desired. |
Originally Posted by Bob Pastorello
(Post 11755487)
Tail wind adds to airspeed and ground speed. Headwind reduces airspeed/groundspeed.
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Now that we have radios with real time telemetry capabilities, I can't wait for the manufacturers to give us a slip/skid sensor. Then RC pilots can learn to step on the ball!
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I found an interesting picture. It's one of my pylon airplanes from last season of a landing that went horribly wrong. We were landing left to right and there was a slight crosswind blowing out at approx 60 degrees. At the end of the heat I was the last airplane to land. There was some confusion and a couple guys getting ready for the next heat thought the runway was clear. As a result they had walked onto the runway just as I was starting to flare blocking my view of the airplane for a couple seconds. When the airplane came back into view, I found myself over the grass. Now although the ailerons did get away from me and I am clearly in an opposite bank, it is also obvious that I used rudder to get back to the runway. As a side note, the airplane is clearly cross controlled, slow and at a high angle of attack. It did not throw it's self to the ground in a tantrum. A few moments after this picture was taken I touched down on the left wheel and wingtip then rolled strait until stopped and shut the engine down so my caller could retrieve the airplane. My apologies for a link to the picture rather then dropping it in the thread, it is a copy written picture.
http://shanksphoto.smugmug.com/Airpl...ce/i-8KJ9Zgx/A Found another picture taken on the second day of the event. This time the wind is going the prevailing direction with the same cross wind only blowing in. Much better landing, although quite difficult to see, I am holding in a very slight amount of right rudder. http://shanksphoto.smugmug.com/Airpl...ce/i-JMbnkK7/A |
How much right rudder were you giving it! Lots by the look of it. Windsock doesn't look very busy :eek:
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Not a wind sock, it's one of the pylons.
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OK.........this video is of my Meteor on take off. Really blustery cross wind. Rather than bank using aileron just after take off (low airspeed - aileron turn - risk of stall), I used a shed full of rudder at about 3-4 secs into the video. I was flying past trees causing turbulence.
http://youtu.be/XOuqBcWkmkU Apologise for the mistaken pylon |
No worries about the pylon, at least I don't have anyone trying to say it isn't my airplane LOL
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Originally Posted by speedracerntrixie
(Post 11756084)
If I'm flying in a cross wind I first have to determine the angle the wind is coming relative to the runway. Then based on the airspeed I think I'm going to be flying I will need to determine the amount of crab angle into the wind. Then without any instruments at all I am supposed to duplicate from one pass to the next the same exact airspeed and crab angle on an airplane flying anywhere from 300 ft to 1200 ft away from where I am standing? If I do all this correctly I will be able to do strait passes parallel to the runway? Will the 1/2 gallon of fuel I will be burning be a variable? It is approx 15% of total aircraft weight at take off. I suppose I can have my caller standing there with a wiz wheel..
And no, you don't have to have your upwind wing low either. You just don't turn the airframe through 180 deg at each end, just like you don't rotate the airframe through 90 deg into a vertical upline if you're flying into a headwind. Serious question, do you rotate through 90deg until your nose is pointing straight up, then start leaning on down elevator to stop it getting "blown" backward when pulling to a vertical upline in a headwind?. |
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