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Rudder Authority?


charlie holdford
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Hi All,

I am practicing for the BMFA B test. I have several aircraft and can fly all the maneuvers badly.

Some models are better than others at certain things.

So my issue is with my Calmato Sport 40. I just can not get it to stall turn or even wing over. Almost as if it has no rudder....

But the rudder works when straight and level albeit with adverse roll

 

Any idea as to why?

Is it the C of G

The Rudder size or servo not up to it

I can perform this on my other models....

 

Cheers

Charlie

 

 

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As Andy suggests airflow over the rudder is likely the issue. You can try a burst of power but you can also try not bringing the throttle all the way back to idle. Work out what level of throttle is needed for a vertical climb and then use a throttle setting just below it. To prevent the climbing section being really long you may need to throttle back to near idle, and then slowly open up to your 'not quite enough to climb' throttle setting just before the model stops moving. Slap the rudder in with a bit of opposite aileron and it should go round. 

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1 hour ago, charlie holdford said:

Hi All,

I am practicing for the BMFA B test. I have several aircraft and can fly all the maneuvers badly.

Some models are better than others at certain things.

So my issue is with my Calmato Sport 40. I just can not get it to stall turn or even wing over. Almost as if it has no rudder....

But the rudder works when straight and level albeit with adverse roll

 

Any idea as to why?

Is it the C of G

The Rudder size or servo not up to it

I can perform this on my other models....

 

Cheers

Charlie

 

 

 

How much movement you got on rudder Charlie, model looks well capable of doing em. Answer is most likely a combination of things. Have you upped the Rudder movement whilst trying ?

 

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Hi Guys, thanks for the replies. I agree prop wash is needed, but even a wing over at full tilt doesn't make the thing go over....

 

John, I have three rate settings 100% (take of and landing) - 65% (normal flight) and 45% (just in case) used all of them to no avail.

 

It is very strange

 

Cheers

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Hi John,

 

It tracks straight up without any rudder, unless its a crosswind.  Elevator is relaxed at the top of the climb I then put in the rudder. either just after I kill the throttle.

It changes end at the top i.e. comes nose down but not when or where I want it ?

 

I have found with my other models it is easier to do a stall turn downwind but with this it makes no difference which way.

 

Its almost laughing at me

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12 minutes ago, john stones 1 Moderator said:

No, I meant is there uptrim in the elevator when sticks in the middle ? You went straight to C.G as the possible problem.

Sorry, a little  I have moved the c of g back a little so I can get it to do the stall spin,

Lets say the marked c of g is 80 -90 cms and I have it at about 95 cms

 

 

Edited by charlie holdford
correction
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While you're trying things, have a go at following the advice to leave some throttle on as given in some previous posts.  I'm sure you'll find it makes a big difference.

 

While you've given us percentages, what are the actual deflections?  100% of not a lot won't be much use...it seems very odd that it won't do a wing over!  What technique are you using?  It would be a very ineffective rudder that wouldn't assist in performing a standard one.

 

 

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16 hours ago, charlie holdford said:

So my issue is with my Calmato Sport 40. I just can not get it to stall turn or even wing over. Almost as if it has no rudder....

But the rudder works when straight and level albeit with adverse roll

 

Charlie, any control surface needs airflow to be able to apply a force. If the throttle is closed and the model is pointing vertically with no airspeed there will not be any airflow over the rudder. It is the same with a boat;- if there is no water flowing over the rudder you will not have any steerage. As others have said, either apply some rudder earlier while you still have a little airspeed or keep some power on to keep the rudder in the slipstream to maintain it's effectiveness. A big rudder also helps!

Incidentally the further effects of roll is yaw and conversely the further effects of yaw is roll (How large these interactions will be vary, according to the design). As Jon says, use some opposite aileron to correct for any roll.

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Well as you've said you can stall turn other models, I'll take your word for it Charlie. Could still be your technique at fault though, best way to decide on that, is pass your box to a clubmate who can fly a bit, then take the advice of said clubmate. Models don't come out the box set to perform aerobatics, they require setting up to perform them well, get that part right then you can hone your technique and improve your skill set, part of which is setting up and trimming a model to help not hinder you.

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One thing that's not been mentioned and it caught me out with my first electric model.

 

With an IC model, there is a small amount of thrust and therefore control authority even at tick-over. With an electric model, there is no thrust with the throttle closed. Could this be a factor here?

 

Regardless of whether flying IC or electric, I think that stall turns look more graceful (slower and more controlled) if the throttle is only reduced to the point where it causes the model's climb rate to reduce and eventually stop, rather than chopping the throttle completely.

 

Some of the best stall turns I've done are at full throttle with an underpowered model that runs out of steam in the climb, rudder applied at this point tips the model into a lovely stall turn.

Edited by Gary Manuel
Final paragraph added.
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Hi Guy, lots of good suggestions that I can try tomorrow. Compared with my other models, all plan built the Calmato is bigger and heavier, so maybe I am waiting too long before adding Rudder and therefore missing the momentum.

Still good discussion.

Cheers

 

 

PS Martin, The Rudder throws are 35mm each direction at full rate. Some time ago I also increased the rudder size by an additional 20mm (aft)

Edited by charlie holdford
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44 minutes ago, charlie holdford said:

Hi Guy, lots of good suggestions that I can try tomorrow. Compared with my other models, all plan built the Calmato is bigger and heavier, so maybe I am waiting too long before adding Rudder and therefore missing the momentum.

Still good discussion.

Cheers

 

 

PS Martin, The Rudder throws are 35mm each direction at full rate. Some time ago I also increased the rudder size by an additional 20mm (aft)

Charlie, If you apply the rudder earlier in order to use momentum, then it is not a proper stall turn. Ideally a stall turn should be at virtually zero speed and the rotation should be around the CofG. If done with any degree of forward speed, the result will be a wing-over (Chandelle turn). 

 

If done too late, the result will be a tail-slide (possibly followed by a flop to the opposite side than you were expecting).

 

A stall turn is somewhere between the Wing-Over and the Tail-Slide.

Edited by Gary Manuel
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I do not claim to be any sort of aerobatic expert but if you let a model come to a complete stop in a vertical position and then close the throttle (electric) where is the airflow over the rudder coming from?

Reduce the throttle to bring it stationary but as soon as it is increase the throttle back towards a 1:1 thrust to weight level as the rudder is applied.

 

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5 hours ago, Simon Chaddock said:

I do not claim to be any sort of aerobatic expert but if you let a model come to a complete stop in a vertical position and then close the throttle (electric) where is the airflow over the rudder coming from?

Reduce the throttle to bring it stationary but as soon as it is increase the throttle back towards a 1:1 thrust to weight level as the rudder is applied.

 

Spot on Simon

I fly both electric and I/C regularly

And timing is different due to as you say " where is the airflow over the rudder coming from? "

In the vertical position, with the throttle stick at " idle " my I/C motor is ticking over at 2000rpm giving off some air movement, where

my electric motor at " idle " is at zero thrust.

Stall turnTiming, and a mental note of leaving in some throttle is practiced.

 

It is pretty much the same stick timing issue with an electric/ IC " touch and go"

Where, On nearing the ground, throttle is progressively applied as to be ready to touch and go under power, before the wheels actually touch the ground.

The I/C motor is already at 2000rpm moving air over the surfaces to maintain authority

Where the electric motor goes through zero thrust if you move the throttle stick too low and stick timing needs to be practiced

 

Both types of motor go to idle with the throttle stick fully down

But the I/C motor still has some airflow over the surfaces, which is good for soul, flying and learning both types.

Edited by Denis Watkins
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But then if you setup your leccy plane so that at idle it too is spinning at 2000rpm then it would behave the same as the IC. Added advantage is the breaking effect of the spinning prop. Obviously all on a switch if you want more control.

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3 hours ago, Ron Gray said:

But then if you setup your leccy plane so that at idle it too is spinning at 2000rpm then it would behave the same as the IC. Added advantage is the breaking effect of the spinning prop. Obviously all on a switch if you want more control.

That is how I have my Pitts set up - throttle right back leaves the motor spinning at about 750 rpm.

As well as providing prop braking it also improves throttle pickup from full back as the motor is already running and so it eliminates that slight delay as the ESC and motor synchronise.

A side benefit of this is a continuous airflow even with the model stationary. That and the quicker throttle pickup for a quick blip probably help with the stall turns.

 

I also have a locking switch as a "throttle OFF" switch to shut the motor down when required (or prevent it staring when not required!).

 

Dick

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I'm wondering whether the slowly spinning prop on electric models also has a safety advantage.

i.e. If it's spinning it's armed ? . If it's not spinning, it's disarmed ? . Just like an IC engine.

 

It also forces you to disarm from the transmitter before the ESC livens up as most ESCs require throttle at zero before initiating. Easy to implement too on most systems i.e. throttle cut = -100 (ESC will initiate but not spin) but throttle travel limit = -85 (or whatever suits - throttle won't initiate but once initiated via throttle cut, will spin slowly at this setting).

 

I might have a play and see whether I get on with this or not.

 

Edit - It should also make failsafe easier to test as switching tranny off / on with motor armed but throttle at minimum will (should) result in motor stopping and starting. At the moment, I need to have throttle partly up so that I can see the motor stop when tranny switched off, but the motor won't restart when I switch back on because my tranny checks for throttle at minimum.

Edited by Gary Manuel
Failsafe note added.
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PS - apologies for thread drift.

Nothing to do with Rudder Authority / Stall Turns, but hopefully useful to someone.

 

Edit - regarding my previous edit, (which I can no longer edit due to 20 mins timeout) It won't be easier to test the failsafe because my tranny defaults my engine cut to OFF when it boots up. I would still need to press my switch for 3 seconds to rearm the motor. At least I wouldn't need to touch the throttle.

Edited by Gary Manuel
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