speedracerntrixie

My Feedback: (29)

Not really, during an IMAC sequence there are no turns at all per say. All direction changes are done via turn around maneuver. Point rolls and rolling circles however require lots of rudder work both same direction as roll and opposite.

oliveDrab

My full-size instructor said to lead with the rudder.

Rob2160

No disrespect to your instructor but that is a habit you will have to unlearn if you ever fly for an airline.

Otherwise each time you make a turn leading with rudder everyone in the back of the plane will spill their drinks or become violently ill.

Airliners and corporate jets use a yaw damper and usually have roll spoilers which allow you to bank without inducing adverse yaw so the rudder pedals are basically foot rests in flight unless an engine fails.

AMA 74894

My Feedback: (1)

yup, that may be true, for say a 172..
but (in most cases) you don't want to do that in a gulfstream, a C-5 galaxy or a citation even.


different types of airplanes need to be flown differently, full scale or model.

an F3A airplane is flown with a different technique than an ugly stick (or a cub, or an F-4, sopwith, etc)
different airplanes need different technique and different amounts of finesse.
(with some airplanes you can bang the sticks around without worrying, while other airplanes may head south in a hurry if a pilot 'ham fists' the controls)

AMA 74894

My Feedback: (1)

my point exactly! (well, YOUR point, actually Rob. )

oliveDrab

Not a problem - the Cessna 172 banks w/o rudder inputs anyway.

DrYankum

My Feedback: (11)

That's true....the end box turn around maneuvers are usually combinations of split Ss,, sharks teeth, or 1/2 cubans, but I still maintain that yank and bank turns even for my jets need opposite rudder to keep the nose up.
Also...I'm assuming that Red Bull pylon racers are using opposite rudder as they are almost at knife edge as they turn around the pylons

sensei

Kinda depends on the airplane's attitude, I spend some flights in knife edge flight more then wings level while utilizing rudder to maintain altitude, climb, or dive and elevator to keep the axis of the fuse pointed straight to the path of flight. When I am flying knife edge loops, rudder is all about gaining or losing altitude.

Bob

Top_Gunn

My Feedback: (6)

Sure. But this is the beginners forum, and the OP was talking about how to make ordinary turns with a trainer, having gotten the impression from a ridiculous YouTube video that he was supposed to turn without banking much so as not to lose altitude. How we got from that to aerobatics, I don't know. When you're knife edged, the rudder functions much as the elevator normally does, and vice versa. But that information isn't really of much use to the OP, I suspect.

speedracerntrixie

My Feedback: (29)

If your nose drops in turns it's a good indication you are nose heavy or have a roll couple when elevator is applied.

JPerrone

Great stuff here!!! I've been looking for information on this in other sites and I have not seen this range of input/information elsewhere!.

After seeing the video about slide turns and looking up coordinated turns, I think that coordinated turns is probably the better thing to do. But, as other(s) have pointed out, knowing that you are a coordinated in a model or simulator's not easy or possible, not like on a real plane.

Which brings up another related topic, the fact that a real plane behaves and has different characteristics than a model, a model has different characteristics than a simulator. For example, I have made continuous 90 degree turns in simulator with a trainer.
- I suspect that a real trainer plane does not have enough power to do this, and would suffer a catastrophic structural failure if it came close to a 90 degree turn.
- I suspect that a model HAS enough power; but some, maybe many, of the trainers/ARFS would suffer structural failure in a 90 degree turn.

Yet it can be done in a simulator.

AND; not only is plane different from model different from simulator, but BIG differences between one model an another!!!

I'll add something else to the thread; some of the points/advice carry with them some context. For example, the statements
"If you want to steer with rudder, get a boat!
An aircraft is NOT turned with its rudder "

Well, I think this completely overlooks 3 channel planes with rudder only, doesn't it!!! The unspoken context here is "for 4 channel aircraft"; with an additional implication of "the design of the aircraft is such that the aileron is the preferred means of turning".

I came to this topic because I was wanting to improve my eye/hand coordination, specifically in the use of the rudder, for 2 issues

1) When coming in for a landing, especially at low elevation, I may want to make some adjustments to direction with little to no bank, so that the wing tip does not hit the ground. I believe that this skill will also help in cross wind landing as well, wouldn't it?
2) What if you lose ailerons? Hasn't happened to me; but I HAVE missed something on pre-flight and gone up with ailerons reversed-twice! In both cases, I quickly understood what the problem was. The first time I didn't have enough skill with rudder to keep the plane from augering in. The second time I WAS able to save the plane!!! So I find that skill useful.

After learning "rudder if aileron fails", I'm thinking of "power if elevator fails". That one seems a bit easier, as we practice that on final approach anyway.

Regards

chuckk2

Full size A/C have a lot of variation in how much rudder is used and when. It's interesting to compare an Erocoupe with no rudder pedals and coupled rudders to same vintage A/C that require rudder input to maintain a co-ordinated turn. Many of the later light A/C really use the rudder very little. I've flown A/C that really only use the rudder to correct torque steer on takeoff. Once in flight,
only very minimal rudder might be needed to keep the ball "in the box".

HarryC

My Feedback: (1)

There is no fundamental difference between the characteristics of a model and a full size. There is only one set of laws of physics! The laws of physics do not recognise "model" or "full-size". There are differences due to size but the difference between a large model and a full size Cessna 150 is a lot smaller than the difference between a full size C150 and a full size Boeing 747, so the phrase that models are different to full-size which is often trotted out, is just plain wrong.

I did not overlook 3 channel planes, if you like to read my whole post i talked about the secondary effect of rudder being roll on a plane with dihedral but that it is untidy since the first thing you get is yaw out of balanced flight. 3 channel models are a hangover from long ago when channels and servos were very expensive, model radios started with just one channel bolted onto a stable free flight models with lots of dihedral. But if you have ailerons, the correct way to control bank is with aileron. Ailerons cause adverse yaw yet you don't hear anyone saying to control yaw with aileron do you? Equally wrong is trying to control bank with rudder! Yes I know you can and in certain circumstances when you have ailerons it is ok or even necessary to use rudder, I have plenty full size experience using rudder in the right circumstances, but usually those are in special and experienced circumstances, beginners should stick to - aileron for roll, rudder for yaw.

You also mention not using aileron at very low level when landing so that the wing tip does not hit the ground. If you use rudder when slow the wing tip will hit the ground very hard as the model starts to flick/spin! The control inputs to generate a flick/spin are up elevator and rudder. If you are slow, then you have a lot of up elevator, so adding rudder is asking for trouble. It's why its so dangerous for untrained people to say use rudder to steer when on landing approach, it's always aileron.

Some say "lead with rudder" which is misunderstanding what some instructors phrase very poorly. You never use rudder before aileron, what they mean but express very badly is be using rudder as you use the aileron to counter a plane that has strong adverse yaw, don't wait for the yaw and then use rudder. Also what they mean is use the rudder to stop the adverse yaw, use the rudder to keep the plane straight, they don't mean use the rudder to turn the plane.

HarryC

My Feedback: (1)

The sims are really games at heart and don't want to make it as difficult as it really is. The model flight sims do have good uses but they also have their limits, I recall one chap in my club telling me he could do rolling circles, turned out he meant on his sim, and he could, I saw him do it, yet in the real world he couldn't fly a level turn never mind a rolling circle!

No plane can do a "proper" turn at 90 degrees of bank, it is physically impossible. By "proper" turn I mean a balanced level turn, not an aerobatic knife edge manouevre. Any plane can do a balanced turn at 90 degrees of bank but it won't be a level turn - a level turn means maintaining height. It must lose height. The wing is what holds a plane up. When banked the lift force is angled away from vertical, that's what makes the plane turn, but there is not enough vertical component so the total lift must be increased. That's why you pull back on elevator, to increase the angle of attack and get more lift, it's also why the stall speed rises when you turn. But at 90 degrees of bank, all the lift force is pointing sideways, there is no vertical component, so no wing lift to hold the plane up. It must either lose height, or the pilot goes knife edge to get lift from the fuz, but for those of you who have no experience of full-size aerobatics, believe me it is most uncomfortable for those not used to it, and the drag rise is a heavy penalty. It is potentially dangerous since it is up elevator and lots of rudder, again the controls for a spin/flick, so should only be done by experienced pilots with a suitable model and safe height.

JPerrone

For HarryC and others more technically inclined:
I usually try to avoid getting to technical as there's a very wide range of knowledge in these forums, easy to get lose in it. Yes, there is only one set of laws of physics. But when we compare models of objects, even if they are "exact scale" models, they don' behave the same.
Dynamic similitude requires that kinematic, dynamic, and geometric similarity all exist simultaneously. When you take a model into a wind tunnel, or a tank, you can get one set of dimensionless parameters to match (eg, Reynolds number), but then another one (mach number) is not representative. The smaller the scale, the worse it gets. That is one of the challenges in wind tunnels, getting a model big enough to be close to similitude, without being prohibitively expensive.
My memory is fuzzy on this as it's been a number of year, but I recall reading about the difficulties in doing hypersonic testing (mach 20); eventually they went to full scale testing rather than rely on scale models. Results on that weren't encouraging.

HarryC

My Feedback: (1)

But what I said was, and I quote
"The laws of physics do not recognise "model" or "full-size". There are differences due to size but the difference between a large model and a full size Cessna 150 is a lot smaller than the difference between a full size C150 and a full size Boeing 747, so the phrase that models are different to full-size which is often trotted out, is just plain wrong."

I said there are differences due to size but that is all, the laws of physics do not recognise "model" or "full-size", show me where such a parameter exists in any equation. A large model is very similar in character to a full-size C150, much closer than the full-size C150 is to a full-size B747, hence the phrase that "models are different to full size" is nonsense. The fundamentals of piloting a model are the same as full-size.

To do a turn you bank with aileron and hold the height with elevator. If the plane is travelling a bit side on to the direction of travel you use rudder to keep it straight on to the direction of travel, you don't use the rudder to turn it like a boat which is a popular misconception amongst model fliers.

sensei

Don't get your panties in a bunch there Top_Gunn, I was just having a little fun with SrTelemaster150. Anyways... Carry on...

Bob

SrTelemaster150

Where did i mention knife edge turns which requires opposite rudder?
I posted to use coordinated rudder to keep the tail from DROPPING. That's just the opposite of what is done during knife edge turns.

I see it all the time, both when I fly & on YouTube. People try to turn W/moderate bank & the tail drops. The nose is pointed skyward & the turn is not "level" as far as the fuselage & the line of flight.

The fuselage is not an airfold that provides significant lift. You need the rudder to lift the tail a bit, especially if there's no aileron differential & the aileron on the high wing is inducing drag..

It's so easy to set up the aileron linkage for aileron differential if you can't do it W/the Tx program. I don't know why it's not standard practice on non-aerobatic airframes.

sensei

Happy flying old buddy...

Bob

oliveDrab

All of this discussion concerning use of the rudder is well and good but I just gotta say..............absolutely all of my model aircraft bank/turn just fine with no rudder input whatsoever. 4*60, SIG King Kobras, ESM Bearcat, Hobbistar 60. And the Great Planes Siren Hotliner doesn't even have a rudder and banks/turns fantastically well. If I were to use rudder along with aileron to bank my 4*60, the plane would land, roll over to me, grab me by the throat and say: "RUDDER with aileron to bank?!? What the heck do you think you're doing?!?".

Sgt. Meyer

Removed comment.

oliveDrab

For ground handling, taxiing, takeoff, landing, knife edges, aerobatics. I'm on the rudder every flight....but not to bank/turn.

Sgt. Meyer

You responded before I could remove my post. Obviously there are other things to use it for.


Duh!

Rob2160

I totally agree with this post and your previous one.

I will preface this explanation by saying that we are NOT considering use of rudder for any degree of knife edge input, I'll get to that later,

No plane can do a proper 90 degree 'LEVEL' turn by increasing elevator alone.

The math is actually pretty easy to prove this.

To maintain level flight lift must equal weight. IE 1 G of vertical lift must be produced (opposite to gravity)

Wings develop lift perpendicular to their span. IE looking at a plane from behind, the lift is directly up if the wings are level.

As you bank the wings, that lift tilts over to remain perpendicular to the wing.



You gain a turning force but lose vertical component. If you just bank and do nothing else with the controls the plane will descend.

If you increase elevator your lift force increases. At 60 degrees bank you need 2 times the lift (2G) as this will give you 1G of vertical component,

Simple trigonometry. Cosine of 60 is 0.5. 2 x 0.5 = 1

To calculate how much extra lift you need to sustain a level turn at any bank angle use this forumula.

1/(cosine of bank angle)

eg 30 degrees bank = 1.15G
45 degrees bank = 1,41G
60 degrees bank = 2G
75 degrees bank = 3.8G
85 degrees bank = 11.5G
89 degrees bank = 57 G
90 degrees bank = infinity G

I'm pretty sure no plane can pull 57 G let alone infinity G.

a sustained altitude 90 degree bank level turn is impossible using the lift from the wing alone.

Enter rudder and knife-edge flight.. At 90 degrees bank your wings are doing nothing to support the weight of the aircraft.

You can apply rudder which then gives the fuselage an angle of attack to the airflow and there is a lifting force generated by the body.

Depending on power and aircraft design you may be able to sustain level knife edge flight indefinitely.

Getting back to normal bank (no knife edge input) we can calculate stall speed increase quite easily too.

New stall speed at any bank is 1G stall speed x (square root of G)

so for a 60 degree bank the new stall speed will be (square root of 2) = 1.4.

IE 40% more than in level flight.

Increasing lift to produce extra G has the penalty of producing extra drag.

This is usually the limiting factor in light aircraft. Most cessna's and small piston aircraft run out of puff around 2.5G sustained turn.

They can pull more G momentarily but not sustain it due to insufficient power.

now the final part. Structural limit.

Example - (real numbers for a Robin 2160)

A typical light aerobatic plane such as a Robin 2160 has a flight g limit of + 6 and - 3 G.

this means it can pull 6 G every day without damage.

if we know the stall speed we can calculate the maximum manoeuvre speed very easily.

assume stall speed is 55kts.

Stall speed at max G (6 in this example) is:

55kts x (square root of 6) = 135 kts.

this is the maximum manoeuvre speed for this aircraft.

what does it actually mean?

Flying less than 135 kts you cannot pull 6G as the plane will stall before achieving 6G.

IE flying less than 135 kts it is impossible to break the aircraft in flight.

Flying above 135 kts it is possible to exceed 6G if you apply full control deflection. IE you can break the aircraft

in a light aircraft this number is where the green arc on your airspeed indicator become orange (amber)

Flying in the green speed range you can use full control input.

If your speed is in the amber range you must use caution and limit control inputs accordingly.

I doubt most of us know the structural limit of our models.

Also no way to know exact airspeed either unless you use telemetry.

Personally I have dived all my RC planes at full power and then used full elevator to pull out and not one has ever broken.

The principles still apply.

oliveDrab

Some great information - thanks for sharing. Are you an airline pilot by any chance?