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Old 05-18-2013, 07:09 PM   #31
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Re: Yelled at TV

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I am also an AME (40 years) you may recall some of the AC you worked on had an interconnected aileron and rudder. A few come to mind--PA-22 Tri Pacer, PA-31, Later models Cessna 180/185. The Cessna 208 also had spoilers to augment the differential aileron. A few AC that com to mind that flew badly with just aileron were 11AC, DHC-2 and Seabee.

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Old 05-21-2013, 10:50 AM   #32
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Re: Yelled at TV

Looks like you need to have some credentials on this thread to have some credibility so here it is: I'm a comercial pilot, flight instructor, aerobatic flight instructor with a total of more than 7500 hours, been flying for 25 years and been working for the past 10 years as a flight instructor for the Royal Canadian Air Force. Hope it's enough...

Having said that, sorry Kip but you got it wrong on several points. First, not all aircraft have differential ailerons. For example, the very modern and all composite Grob G120A has no differential ailerons. Actualy the ailerons deflect one more degree down than up. I'm not sure why but I'm sure it's not because the German engineers who designed it never heard of that great invention of Glenn Curtiss

The reason why some aircraft need some rudder not only while rolling in the turn but also once established in the turn as to do with the inherent stability of the airframe. An aircraft with Positive stability (High wing, lots of dihedral, etc...) will always have a tendency to return to level flight and will therefore require aileron and rudder input to stay in the turn. Aircraft with Neutral stability ( Aerobatic airplane with straight wing for example ) will need rudder mostly for the roll to initiate the turn.

As for the differential ailerons, it's purpose is not really to slow down the down wing. It's to counteract the increased induced drag (drag created by lift) of the down going aileron of the up going wing. Simply said, if you turn left, you have to raise the right wing by increasing lift on that side and you do so by lowering the aileron. Inceased lift=Increased drag. This increased drag of the up going wing produce ADVERSE YAW (Not Negative Yaw) wich is reduce by having the aileron going up more (in degrees) on the down wing than the aileron going down on the up wing. By going up more, it deflects more air upward and increases profile drag which than counteract the induced drag of the up going wing.

On conclusion, there is a lot more to it than those simplified concepts and I don't have the pretention to know it all. But one thing I know for sure is that all aircraft are different, they all have their own caracteristics and differential ailerons is not a magical device or caracteristic that prevent the use of rudder.

Disclaimer: Having said that, this is just my personal opinion, I might be wrong, please don't quote me, have a nice day.
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Old 05-21-2013, 11:02 AM   #33
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Re: Yelled at TV

Thanks Alain!

Very well explained!
Hope this will close this issue...

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Old 05-21-2013, 11:11 AM   #34
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Re: Yelled at TV

Thanks Alain, you saved me a lot of writing. 26 yrs military, son of parents who owned and flew various aircraft, lifelong pilot of anything I can get my hands on, yada yada. To make a long story short:

Rudder=good. I get comments all the time about how wonderfully scale all my flying is. 2 reasons. 1, I fly or have flown a lot of the real aircraft, 2, I use rudder when it's called for.
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Old 05-21-2013, 12:23 PM   #35
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Re: Yelled at TV

The Wrights used wing warping. Glenn Curtis invented the aileron. Not all aileron installations have differential motion. The most common methods for achieving differential motion are through clever use of the geometry of the hinge and actuator, as in 'Frise' type ailerons, and through mechanical linkage design such as in 'differential ailerons'. I do not believe either form of achieving differential movement was invented by Glenn Curtis nor is he listed on the patents. As has been said already, another method of assisting the pilot in performing coordinated turns was the use of aileron-rudder interconnects which function mechanically (think bungee connection!) in a very similar fashion as aileron/rudder channel mixing does for RC.

The additional fins on many float/amphib equipped aircraft are there due to the yaw destabilizing nature of the floats: they present a large surface area in front of the c of g which reduces the yaw stability of the aircraft. The additional fins are there to counteract this. They are not rudders.

Spoilers are used in many aircraft to effect roll control through the disruption of airflow over the top of the wing and subsequent reduction in life and generation of a roll moment. They also create drag which can produce yaw into the roll however it's usually not a perfect balance. While a few aircraft have no ailerons for roll control and use spoilers only (the aforementioned MU-2 is a great example), they tend to lack the control 'feel' that you get with ailerons. They tend to be used only when you have a small wing and you want to install flaps across the entire trailing edge.

Modern airliners often use spoilers to assist with roll control. It allows smaller surfaces to be used and avoids issues associated with wing twist and control reversal that would occur at higher airspeeds unless an unrealistically sturdy/heavy wing was used. Most Boeing wing designs use inboard and outboard ailerons supplemented by spoilers. The outboard ailerons are only active when the flaps are selected.. which only occurs at low speeds... in order to avoid excessive control authority and especially to avoid wing twist/control reversal. Use of spoilers also adds more control authority at slower speeds and allows designers more flexibility in sizing ailerons for an aircraft that operates over such large speed extremes.

A discussion on differential ailerons is somewhat of a moot point for airliners however (or any swept wing jet for that matter), as they all must be flown with Yaw Dampers, except during take-off and landing due to issues with Dutch Roll (a yaw-roll coupling effect that is part and parcel of high-speed, swept wing flight). The yaw damper functions similar to a yaw gyro on an RC helo and the system ensures the aircraft does not yaw during rolls or other maneuvers unless commanded by the pilot.

Were they perhaps thinking about water rudders? What they said makes perfect sense if they are talking about water rudders.

Either way, I'm all for live and let live and have fun!
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Old 05-21-2013, 12:24 PM   #36
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Re: Yelled at TV

Alain: Rats.. sorry.. Didn't mean to jump on you. I was writing this off and on through lunch prior to your posting and just posted it late. A great summary.

Last edited by davf; 05-21-2013 at 06:21 PM.
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Old 05-21-2013, 12:46 PM   #37
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Re: Yelled at TV

I was at the field yesterday and a nice scale biplane was flying. Every time he used the ailerons the nose would pitch in the opposite direction about 20 deg. You do not see any full size aircraft doing that.

"If my being here has made your day a little more pleasant then I have done my job" Red Skelton 1913 - 1997 (famous Comedian)
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