JPerrone

I confess to being the OP and therefore the instigator of this thread (!). It's been very interesting and I think I've learned a lot. Some of it I will probably think about and I'll probably come back to re-read some of the entries.

After all that's been said, I believe that I WON'T attempt cross controlling at this time, I'll use some other method to learn how to use rudder but not cross controlling.

The frise hinge was interesting, and the example looked like a work of art. It looked like at one extreme, the front of the aileron was exposed to the airflow and would have partially balanced the force on the control surface. Was that the intention? It only does that in one direction so I am assuming that was the desired effect.

Some people have made the point that the models fly just like their full scale brethren; however, there IS one big difference. That is the POV of the pilot. A full scale pilot perspective is always the same; he/she is looking out the windshield of the plane. The RC pilot is sometimes looking towards the plane coming at him/her, other times at the plane flying away, and also from the side. I'd say that is different... A full scale pilot also has instruments, the string thing, and lets not forget the seat of the pants thing.

Regards

speedracerntrixie

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Al, we would seem to have different definitions, The way I see it, holding a very slight amount of rudder to hold ground track is not a turn. I fail to see that if the airplane's ground track is strait regardless of the control input how it can be considered a turn. I suppose you would consider a knife edge pass a turn, after all the wings are banked and rudder is applied right?

Rob2160

In knife edge you are opposing the very real force of gravity being applied to the side of your aircraft. Holding rudder in this case effectively gives your fuselage an "angle of attack" to the airflow and this, plus a component of engine thrust balances the force of gravity.

In wings level flight, there is no such force acting sideways on the aircraft as it is flying within the moving air. Its a different scenario, there is no such thing as horizontal gravity. Let me ask a hypothetical question, how would you fly knife edge in a zero g environment? (Ie flying an RC aircraft inside a space craft) Would you need to hold rudder? and what would happen if you did?

speedracerntrixie

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Thanks for the laugh Rob but I do know the dynamics of knife edge flight, I was being sarcastic with Al. So now we are flying our models in space to prove out your point? This is getting a little on the silly side. All I'm saying is that you guys seem to have the pre disposition that if you can't do it with your full scale aircraft then you can't do it with the models either. All I'm saying.

Al seems to think that every time rudder is applied it's going to result in a turn.

Now that we are flying in the space station as it orbits the earth. Once air born does the model slam into the wall because it is no longer moving with the station? Or does it move with the air in which it is flying?

AMA 74894

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if you have a cargo airplane full of caged birds....

(don't get me started on Flight Engineer stuff... now you're bringing back some memories! )

cfircav8r

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I have a question, if your plane is trimmed for straight and level and you hold rudder, even a little, won't it just continue to yaw? In my world when you apply a control force it will continue until it is released or an outside force acts upon it.

AMA 74894

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I'm pretty sure that was beaten to death errr I mean 'discussed' about 140 posts ago...
yes, if you hold rudder the airplane will continue to yaw. (on the planet earth, with the airplane (as defined by Miriam Webster) upright / essentially straight and level / in 99.9% of the cases)

speedracerntrixie

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cfircav8r, I think this is where the split in opinion is happening. I am of the opinion that the cross wind is the outside force and the applied rudder is to null the effects of flying in a drifting section of air. Remember the goal is maintain ground track. So essentially the guys are correct in that the airplane is constantly turning but at the same rate as the air is moving. kinda like walking the wrong direction on an escalator at the same speed the escalator is running. Sorry best example I could think of at the moment.

Top_Gunn

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This is simply wrong. A steady crosswind carries the plane in the direction in which the wind is blowing, but it does not change the plane's heading. Applying rudder changes the plane's heading, and until the rudder is neutralized the heading will continue to change. It is therefore impossible for applying and holding rudder to "null" the effect of a crosswind, unless you do something else like using opposite aileron. Or neutralizing the rudder once you've reached a good crab angle.

I thought we had agreed on this quite a few posts back.

speedracerntrixie

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OK Al there is no way we are going to settle this at a keyboard. Next time you are out flying in a cross wind try flying passes back and forth 200 ft out using a 1/2 cuban at each end to turn around making rudder corrections only at the end and see how that works for you. I have coached enough beginning IMAC pilots to know the outcome but I realize you will need to see for yourself.

zacharyR

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this thread needs to be longer and needs more input from " experts " on some of the most basic and easy flying functions ,

Top_Gunn

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Speed,

I don't deny that you can keep your plane on a straight ground track in a crosswind with rudder corrections. I just deny that you can do it by applying rudder and keeping it applied, which is what I understand you to mean by "holding rudder.". What is your reasoning here? Is it that the crosswind changes the plane's heading? Or that applying rudder doesn't change the plane's heading? Unless one of those things is true, and neither of them is, applying rudder and keeping it there will not offset a crosswind.

Rob2160

LOL.. It should actually be true on any planet with an atmosphere.. Try Austin Meyer's X-Plane - you can design aircraft and test them in an accurate Martian Atmosphere.

http://www.youtube.com/watch?v=-mKDbDO174I

Rob2160

Well I agree with you and so does my crutch. NASA.

https://www.grc.nasa.gov/www/k-12/airplane/move3.html

thatairplaneguy

My Feedback: (50)

I'm probably late on the discussion but way too many modelers just fly bank and yank and never learn different then teach new people how to fly and the newbies learn the same and no one ever learn how to use rudder or even fly in a right hand turn because it was hard enough to learn to keep a plane in the air by bank and yank so once they learned that and were successful they never cared to learn anything else as far as pilotage and full controlling the plane.

This is is honestly dangerous and I don't let my students solo until they can taxi, take off in a strait line and land with a slip on the runway. If they don't learn to use the rudder takeoffs can go hard left and into the grass or people or crash the plane. Landings can be way off the runway. Crosswind operations are impossible and scary. Slow speed flight can turn ugly and aerobatics are always ugly without rudder not to mention your very limited in what you can do in the aerobatic box by ignoring the rudder.

I always suggest the first airplane should be a 3ch rudder/elev/throttle plane like a powered glider or slow stick or a simple cub like the PZ cub. This will teach the left thumb to work right off the bat and honestly you use the rudder and elevator in coordinated turns way more than the ailerons. Ailerons start and hold and end the bank. The rudder pulls the plane around the turn and the elevator controls altitude.

For those pilots who do not use rudder its never too late to learn and its nothing to be ashamed about not knowing yet.

Take ke a step back and get a trainer out and learn it. Practice using only rudder to turn.
The best trainer for this is a telemaster because they will not turn without rudder!

After er you can do a pattern in a coordinated faction practice figure 8s and then move on to forward slips to landing and knife edge slips that hold the slip but using throttle to hold altitude across the field.

bjr_93tz

Seriously, If you're holding in rudder you're doing it wrong. Now you may be doing it wrong better than those who are doing it right, but it's still wrong.

There's no way your plane won't change heading if your wings are level and you're holding in rudder, and if you're changing heading in a constant crosswind then your ground track isn't straight. You WILL have to lean on the rudder during each pass IF you start the pass slightly nose in and you need to hold it out by arcing the baseline.

The only way your plane won't change heading if you hold in rudder is if your opposite wing is low as it would be in a side slip case. Back in the day with skinny fuses you could get wonderfull (flatish) sideslips but now with modern F3A ships you need a 45deg opposite bank angle otherwise when you poke in the rudder your plane will just do a 180 and head back the way it came..

Bozarth

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Are you saying that you set the transmitter up so that the typical aileron input (right stick in mode2) results in nothing?

Kurt

thatairplaneguy

My Feedback: (50)

If you have a 4ch plane and really want to learn rudder control then you could setup a switch to turn the ailerons off, sure. Then flip it on if you get in trouble or an attitude where the rudder isn't enough to correct it and flip the aileron back "on".

But it for sure always use rudder on the rudder stick. I have to clarify that because a couple new pilots I've taught, after suggesting only useing rudder for a time, just unplugged the ailerons and plugged in the rudder on the aileron channel. This really doesn't teach anything other than the plane can be manipulated by rudder. It didn't teach them to use their left thumb.

bjr_93tz

Tough call on that one. Traditionally the rudder is operated from the aileron stick on a 3-channel plane but this has caused minor problems down the track when switching over to 4-channel planes and the "aileron" stick now won't keep the plane straight on takeoff or on a bungie/winch requiring the previously unused rudder stick to get some action. I can see the reason for having it "correct" from the start but it might be a mode I vs mode II human factor thing?

Now I'm experienced (?) I set up my 3 channel planes with the rudder on the correct stick BUT mix it over to the Aileron stick as well so I've got rudder on both sticks. Sometimes I find myself holding in a bit too much rudder and a bit of opposite "aileron" during a thermal turn like I do with the DLG ????

JPerrone

I thought that rudder on right stick for a 3ch was right; because you are mostly using aileron for turning, and the right stick becomes the "turn" stick, whether it is using the rudder (3ch) or aileron (4ch).
However, "thatplaneguy" (TPG) makes a good point. How will you learn rudder if you keep moving it around?

Also: during takeoff whilst still on ground, I want to control heading with the rudder. Right now I have both 4 and 3 ch airplanes; and on my 3ch, "heading" is on the right, and on my 4ch, it's on the left!!! Wouldn't it be better in the long run FOR BEGINNERS to just keep the rudder on the left? The worst thing they would to then would be to try to turn with the rudder rather than the aileron. That's not always a fatal error; not like using down elevator to make a turn!!

I'll admit to knowing very little about how an airplane REALLY works, but I was going to weigh in on the holding rudder, on the basis of the resultant forces. Rob2160 found the perfect link to explain this. But here it is in my words

When you have cross wind, some of the wind is trying to push you to one side, some of it is along the path of the craft (this is breaking the wind into its vectors). In the absence of this force, the aircraft would have a vector parallel to the strip. However, the sum of these forces results in the airplane moving in the direction of the strip, plus a little bit to the side. The nature of this can be deceptive, as the aircraft HEADING is straight down the strip; but it's moving sideways!!

Now if you want the aircraft to follow a vector parallel to the strip, you need to introduce a force offsetting the sideways force. Some people think this is caused by the shape of the craft, some by the engine thrust vector. I think it's the thrust vector. You use the rudder to change the heading of the plane. It is just enough so that the thrust vector in the direction opposite of the wind is equalized. The aircraft will have a slight heading into the wind; but it's vector is parallel to the ground. This looks like all the crabbing videos although maybe crabbing is not the correct term.

Now if that is correct (I'm no expert right so maybe this is wrong. But the dynamics and vectors sound right, and agrees with NASA and they put people on the moon....) then if you release rudder; you take away the small component of force maintaining your heading and vector.

Did I miss something?

Regards

bjr_93tz

Yep you missed something.

Your plane is pretty much always flying aligned with the airflow until you poke the rudder in. Wind or no wind when you poke the rudder in you yaw the plane to one side, the fuse generates a sideways force which changes the flightpath and when you let go of the rudder the plane points back into the airflow again and your plane continues along the new flightpath. If the airmass is traveling across the ground at an angle to your flightpath (ground track), you won't be going to where your nose is pointing.

If in a "crosswind" you start out flying towards something with your nose pointing at it, you will drift to one side and need to apply rudder to keep the nose pointing where you want to go, but you're flying in an arcing groundtrack (your compass will be moving), NOT straight (compass not moving) which is why you need to hold the rudder in. Guys that fly long distances please ignore the compass moving/not moving references ;-)

JPerrone

Yes, NOW I understand. And this explains an observation I made, which is that my airplane only wants to go in one of 2 directions!

Let's say the wind is coming from North (call it 0 degrees). Let's say the airplane is heading towards the north. So, I am now aligned with the airflow. That direction, and the opposite one (south, 180 degrees, flying aligned with the airflow in the same direction as the wind) is the only OTHER direction my plane can wants to/can fly.

Oh, but that's not always true, I don't think. In fact there are times that I've been able to fly my plane at 30 degrees; 90 degrees; 270, and a lot in between. And most of the time, I got to that direction by turning (rudder, aileron, or combination) and once vector is established, I return surfaces to neutral. The plane seems like it is staying on that new heading, which is NOT the same direction as the wind. Unless there is a different definition of the term "aligned" then the airplane is actually flying in a different direction of the wind.

Just as in sailing, there is the "apparent wind" which is the wind direction that the aircraft experiences. This would be the resultant vector that is the summation of the wind vector, and the aircraft vector. This tends to make the apparent wind somewhere between the true wind and the aircraft vector. The nature of vector summation is that it is difficult for apparent wind to equal true wind.

Or is there something I'm missing?

Regards

bjr_93tz

It's that vector thing you spoke of. If a wind of 20 kn is coming from the north (say 0deg) while you want to fly east (say 90deg) with a groundspeed of 100kn then you'd need an airspeed of 101.98kn and your nose would be pointing 11.3 deg north of east (say 78.7deg).

Your plane would be flying straight and level and happy to stay that way and you'd still be pointing north by 11.3 degrees as you fly directly over the target tracking due east over the ground.

IF you started out pointing due east with 100kn airspeed, your ground track would be 101.98kn @11.3 deg south of east so you be leaning on the rudder all the way to not only fix the initital 11.3 deg error from the start but also to make up the lost ground from flying slightly south for a while..

JPerrone

What you described is exactly what I was thinking. Force diagrams are easier to explain this stuff; but I'm not good with computer stuff and applications.

Thanks!!!

bjr_93tz

Force/vector diagrams would explain things easier it but you're right about the computer graphics.

With a sailing boat you've got a moving airmass and moving water mass to worry about to get from point A to point B :-)