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Do flaperons warrant a caution when landing crosswind?


Ed Cesnalis

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...The control system in the CT is designed so ailerons also operate with the flaps (flaperons). Because of this feature it allows the airplane to have a very slow stall speed and it will operate from very short runways. When flaps are applied adverse yaw becomes more pronounced, because with aileron application you are creating much more drag on the side opposite to the direction you are pushing the stick. When you get the airplane put on full flaps and have someone hold the stick to the side and you will see what I mean.

Because of this use caution making crosswind landings with more than 15° flaps. There has been more than one case of CT's having the downwind wing stall and drop un-expectantly causing damage to the airplane.

 

 

 

 

Tom,  you really made me think and I thank you.
 
I have heard the above a number of times and it never rang true for me. Here's why, the fix isn't avoiding the configuration the fix is the rudder.  Most of the time I side slip without even noticing, its burned in and takes no thought.  Then there are those days.  Its not a limit that you can hear on the AWOS wind report but it is a limit you can feel. On these days it doesn't feel right to have your nose off the wind and aligned with the runway.  My inner voice won't let me go there, better to crab today and keep the wind on both wings.  Its a feel and I understand it comes with time you can't teach it unless its one of those days.
 
The nose belongs where you decide to put it. If 30* effects the nose more than 15 then you need more correction, that is automatic you don't think about it. Avoiding 30 due to adverse yaw concerns might make sense if you were running out of rudder but if you can keep the nose where you want it then the caution isn't warranted in my opinion.  The better question is do you really want your nose aligned today?
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At higher flap settings there is also less roll authority to counter crosswind gusts.  I've never been put in trouble by it, but it's just a fact of the design.   

 

That is a 'fact of all designs' not in any way unique to a CT.

 

Gusts or as I like to say shear is another issue one that very often calls for more speed. 

 

Positive wind shear robs airspeed so a margin is called for.  Its not productive to argue both crosswinds and shear together.  The vast majority of our landings do have crosswind but lack enough shear to warrant additional speed. 

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As LSA pilots we are very much in touch with shear in all phases of flight.  By the time we are ready for landing we likely know a lot about local wind shear.

 

When landing in shear we need to be concerned about both wings and our tails not just the downwind wing. This is another reason to separate cross-wind concerns and shear concerns.  Shear does not come without wind but most of the time your plane is drifting with the airmass (wind) and you only feel the sheer.

 

If shear is not present does it make sense to limit our landing configuration based on crosswind alone?  I guess the answer is yes but the limit is higher.  My wind limit for 30* is approaching 20kts and my shear limit is when I loose fine control over my vertical speed or when keeping wings level or coordinated is a constant chore.

 

Put simply bumps and air pockets cause me to limit my landing flaps more than crosswinds.

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At higher flap settings there is also less roll authority to counter crosswind gusts.  I've never been put in trouble by it, but it's just a fact of the design.   

 

You guys argue both roll authority and adverse yaw as reasons to limit flaps.  Traditional designs have both reduced roll authority and increased adverse yaw with flaps yet they benefit from their flaps.

 

The fact that diminishing roll authority and adverse yaw exist isn't persuasive both are instinctively countered with correction. One takes more rudder and the other takes more stick.  We don't have predefined amounts of correction we apply it until our nose is on the wind or until or attitude is correct so a need for more isn't argument to not use a normal landing configuration.

 

Needed too much is another story.  If you don't have enough rudder you don't want to land, that is persuasive.  That's different then you have to use more rudder, more rudder is a so what.  Same for stick, as long as you can still roll who cares how far you push?

 

I think its like landing with the stick full aft, some like to freeze and watch things happen.  If a little stick doesn't get it use a lot.

 

I have yet to hear a CT pilot say he landed with 15 because at 30 he ran out of rudder.  I have yet to hear one say he landed at 15 because at 30 he ran out of stick.

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A very interesting discussion. In conventional teaching we are told to use less flap in strong wind (headwind or crosswind) conditions. This is for better penetration, whatever that means. It works ok in a Cessna or piper because there is a fair bit of drag and you can carry a bit of power to the ground with no flap. Slippery aircraft cannot be treated this way, use power with no flap and it will not slow down.

I use full flap all the time to land because the ground speed is less, but use power in strong wind because the prop wash increases the control authority. I once discussed this with a FD test pilot and he said that as a responsible manufacturer they have to advise the most idiot proof way of doing things, and as such have a lower crosswind tolerance than the CT is capable of. In other words a bit more skill and thought will allow more difficult conditions to still be perfectly safe. ps I like to keep the nosewheel off the ground as long as possible in most landings but let it down earlier in difficult stuff to reduce the angle of attack for protection against gusts.

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I never argued limiting flaps. I simply said that the flaperon design lessens roll authority with higher settings. Each pilot can judge how to deal with that fact. You can say that's true of all designs, but limiting aileron travel proportionally to flap deflection exacerbates any other designed in loss of roll.

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I never argued limiting flaps. I simply said that the flaperon design lessens roll authority with higher settings. Each pilot can judge how to deal with that fact. You can say that's true of all designs, but limiting aileron travel proportionally to flap deflection exacerbates any other designed in loss of roll.

 

Do you think your CTs 'loss of roll' gives any reason to limit flaps in a steady state crosswind?  Personally I can't see it.

 

I see roll authority and adverse yaw as having little relevance in steady state cross wind landings.  I'm talking about the phase where we use anecdotal evidence of more than 1 guy bending his gear.  I can see adverse yaw being a concern when turning base and final especially in right traffic but in the final landing phase where the bending the gear happens there aren't any turns so yaw and roll play a limited roll.  Once you have yaw and roll corrections in you can just hold it there.

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Do you think your CTs 'loss of roll' gives any reason to limit flaps in a steady state crosswind?  Personally I can't see it.

 

I see roll authority and adverse yaw as having little relevance in steady state cross wind landings.  I'm talking about the phase where we use anecdotal evidence of more than 1 guy bending his gear.  I can see adverse yaw being a concern when turning base and final especially in right traffic but in the final landing phase where the bending the gear happens there aren't any turns so yaw and roll play a limited roll.  Once you have yaw and roll corrections in you can just hold it there.

 

I mentioned crosswind gusts, I think that is the danger.  In steady state wind there is not a problem unless you lack aileron/flaperon authority to maintain the runway center line.  The CT has PLENTY of rudder, so I can see you running out of roll authority before running out of rudder to maintain a landing slip in a strong enough steady crosswind, at higher flap settings.  But in that case you will know it well before reaching the ground.  

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I mentioned crosswind gusts, I think that is the danger.  In steady state wind there is not a problem unless you lack aileron/flaperon authority to maintain the runway center line.  The CT has PLENTY of rudder, so I can see you running out of roll authority before running out of rudder to maintain a landing slip in a strong enough steady crosswind, at higher flap settings.  But in that case you will know it well before reaching the ground.  

 

I agree there is no reason for this caution without the gusts.  My experience is the great majority of my landings are steady state crosswind so this applies for me most of the time.

 

Look at gusts / shear and ask yourself is avoiding the 30* configuration the right adjustment?

 

We talk about 15 vs 30 as though there is only one variable.

 

Here's my thinking that leads me to using 30* even when gusty.  I'm willing to give up some control responsiveness to get my speed down into a safer landing range.  When I get slow with 15* I loose any sense of buoyancy.  Its not really the airspeed loss that sucks its the rapid sink part.  At 62kts with 30* I'm incredibly buoyant, I've now supplemented my kinetic energy with even more engine power.  The kinetic energy can be robbed by gusts but the engine supplied energy remains at my disposal to either chop it and get on the ground when the getting is good or to use it to counter unwanted rapid sink.

 

With 30* in gusts I have an additional source of energy at my disposal thereby enhancing my safety.

 

With 15* in gusts I have more lag time if I need to counter sink with power, even a Rotax takes time to spool up. 

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CT, I will offer a reply at some time, but it will be quite lengthy. It is something that is much easier to explain in person with a few airplanes around to show the differences.

 

Thanks Tom,

 

My experience says the conclusion of the argument supporting the warning is unwarranted.

 

I have had a wing drop in a dramatic fashion in the final moments before touchdown a number of times.  Opposite rudder allows me to make the contact soft and it is always followed by a pivot that gets me strait and the other wheel settling.  My guess is that the experienced pilots transitioning into CTs 10 years ago that  got this specialized training (15 before 30) started in the first place, weren't failing to use the opposite rudder but more than that they were trying to hold off the CT from 4' too high in the air.  If you try and land a CT like a skyhawk using a skyhawk sight picture for height above the runway you could surely bend the gear due to a high sink rate and it could very well be downwind wing first.

 

I think the problem with the argument is its based on our drooping ailerons increasing drag and adverse yaw.  You can show this relative to designs without flaperons.  The problem is your reaching the wrong conclusion.  The right conclusion is that the CT likely experiences more downwind wing drag and more adverse yaw than it would with typical ailerons.  That doesn't get you all the way to its problematic and a warning is warranted. The truth is that my CTSW has far better manners when landing with 30* flaperons than many other aircraft.

 

This is something that can be simulated at altitude.  30* crosswind landing approach at altitude until stall.  Can you make it drop the downwind wing in a landing attitude at all?  If so can you counter it with opposite rudder?  If so is that natural or is training needed in case such an event happens in an actual landing?

 

This is far more productive than a warning to avoid.  Why?  The skill needed when a wing drops could be needed with 15* or any setting.

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Another thought:

 

Steady state crosswind presents no significant risk.  Sure the downwind wingtip will stall 1st but it presents no problem.  Remember you have an inboard stall strip and a wing designed to remain flying inboard when that happens plus the CT always settles level in a steady state crosswind by experience.

 

Lets look at gusts instead and the first thing you realize is the vast majority of them add lift because gusts from the opposite direction are far more rare.  The worst case for dropping the opposite wing would be a quartering tail wind gust from the downwind side.  Not only is this rare but I would  already have pressure on the opposite rudder which I would increase in response to the wing dropping.  The wind direction would have to be variable by 250* or so with good velocity and I'm betting few CTs are even attempting landings in such conditions.

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