Lateral CG out of limits

[heliflyknow]

Recently when I was reviewing helicopter weight and balance I came across something that I didn't give too much thought the first time I had read it. In the helicopter flying handbook it says that a heli that is out of limits for lateral CG "fore and aft cyclic effectiveness can be limited dramatically". I understand how you would be limited in cyclic movement on the light side, but I'm not so sure about how a lateral imbalance can effect your foreword or aft cyclic. The book doesn't go into any more detail than that, but my hypothesis with my limited knowledge is that it has to do with the pitch of the blades and how the cyclic works. The way the book says effectiveness makes it seem that any amount of fore or aft cyclic movement wouldn't change your ground track/airspeed as much as it normally would and not that movement would be limited. Here are my thoughts, imagine a helicopter heavily weighted on the right side, therefore requiring a lot of left cyclic. The blades are almost at max pitch on the right side(090degrees), any forward flight requires more pitch in the blades when they are at the rear of the helicopter(180degrees)but you still need the pitch on the right side of the helicopter to stay level so really the pitch is highest from about 180-90, therefore requiring more forward cyclic to increase your airspeed since it's not increasing pitch from 270-90 like it normally would. Are my thoughts correct, or is there some other aerodynamic principle that I am overlooking?

[aeroscout]

If you are out of balance laterally you can cause the cyclic to come in contact with your legs. As your legs form a "V" towards the aft travel of the cyclic it limits aft cyclic displacement with the lateral cyclic you need to hold against the lateral out of balance condition.

[Eric Hunt]

If it is out of limits, you should not even be flying, so why ask the question? Limits are there for a reason.

[rotormandan]

Well it's good to understand why the limits are there.

[iChris]

Well it's good to understand why the limits are there.

This something you need not worry about, most light helicopters won’t allow you to get that far out of lateral symmetry. However, if the balance is far enough outside the limit, it will increase drag and limit the required cyclic control needed to trim the aircraft in forward flight. In fact, your forward speed may be limited at the point were you’ll have to give up some lateral cyclic in favor of forward cyclic in order to increase forward speed.

 

It’s also possible that the same is true if external loads are carried in such a position to require large lateral displacement of the cyclic control to maintain level flight, the fore-and-aft cyclic control effectiveness will be limited as seen in the figure below to counter an exaggerated right lateral CG.

 

As far as effectiveness goes, yes, it has decreased due to the increased flapping angles, drag, and inherent sideslip.

 

The few people who have flown the R22 solo from the left seat know a little of the unusual cyclic position required in forward flight to trim that aircraft when flown outside its limits.

 

 

Edited June 3, 2014 by iChris