"Differential spoilerons" for high alpha handling

Hi everyone -

I was out dialing in a plane today trying to optimize it's balance and handling for best high alpha performance.

Since Stephan wrote this great article http://migsrus.blogspot.ca/2014/12/trimming-rc-airplane-determining-cg.html , I have been trimming all my planes using this method and have noticed a much more responsive and balanced plane as a result as well as my CG and components being moved back significantly.  I had obviously just grown used to flying my planes far too nose heavy and didn't really notice until Stephan educated me on these new methods of properly finding CG and trimming the plane for a more balanced and maneuverable setup.  Big thank you to Stephan once again... :)

The planes all rotate much better in all axes which makes general handling and aerobatics much more fun and responsive.

However, as the weight has been moved back and the rotation made easier, I have also noticed the affect of prop wash in high alpha has become more pronounced, especially on the Mig I was flying today.

Stephan and I have both written articles that might help understand better what we mean about the affects of prop wash in high alpha

http://migsrus.blogspot.ca/2014/08/mig29-v4m3e3-hi-alpha-testing.html

http://migsrus.blogspot.ca/2014/08/the-high-alpha-right-turn.html

So today as I was dialing in this plane, I found that right turns in high alpha were a real challenge and that if I took my thumb off the rudder stick, it would do a left turn on it's own, completing a full circle in about 25 ft.  So I suppose I could just turn left all day, but that gets pretty boring after awhile and doesn't challenge my skills much.  So I fought with it, had the tail slide around pretty aggressively a few times as the rudder bit too aggressively in right turns and at one point over controlled/dumb thumbed my way into the ground.  So a bit of a nose "gonk", my pride hurt more than my plane, it will be easily fixable.

But as I did my short, solitary "walk of shame", I started wondering if there was some way I could put a setting in my radio to help offset the effects of prop wash to make high alpha a bit more manageable and right turns not so difficult.

I use a Turnigy 9x radio with er9x firmware, so it is far more capable than I will probably ever utilize, but it is pretty versatile for the price.

So at first I thought about having a switch where when I started high alpha I could select preset rudder trim to the right.  This would help, but would then reduce my rudder travel to the right if I needed it (which I knew I would).  It is also another switch to select in addition to spoilerons which I like to use for high alpha to help keep the plane more stable and the nose up a little higher without too much elevator/elevon deflection.  Not a good option as too many switches spells trouble for my limited skills.

Then I thought, why not have the spoilerons deflect differently?  In other words, have the right spoileron deflect a bit more, helping to keep the plane from pulling left all the time.  I'm sure others have thought of this and use it, but honestly I never have heard or read about anyone using it.  I have always been locked into the paradigm that both spoilerons have to be deflected the same amount in high alpha, drilled into me by whoever had my attention at the time when I was still learning high alpha.

So as I looked at the blemished nose on my plane I thought, what the heck, I've had one crash already, what is the worst that could happen?

So since I can adjust the "weight" or percentage of the spoileron deflection individually in each of the "aileron/spoileron" servos without affecting how the aileron works when spoilerons are not employed, I started off with 10% more weight on the right spoileron than the left.  I should add that this plane requires very little spoileron deflection for good high alpha angle of attack (AOA) and stability, actually only about 1/4" deflection.  So this 10% difference did help, but I felt more could be done.  So through several flights, I increased it by 5% at a time until I had 30% more "weight" on the right spoileron than the left.

Although not eliminating the effects of prop wash completely, it makes high alpha handling much smoother and more relaxing even.  The plane still drifts slightly to the left, but would take about 100 ft to do a full circle on it's own if I let it go and for about 80% of the time flies pretty straight with no right rudder input, requiring just the odd minor correction now and then instead of constant right rudder input like I needed without "differential spoilerons".

This setup made right turns much easier, it still occasionally got hung up/delayed, but about 80% of the time, it only needed gentle right rudder input to come around to the right and it responded almost right away instead of having considerable delay like often happened without the "differential spoilerons".

However, as my sage friend from Alabama (Stephan) has often said, aerodynamics is all about compromise, change one thing, it can often affect another.  So there is a caution I will pass along if you try this that I learned today (didn't result in a crash, just a little more excitement than I wanted at the time... :/).  If I got too slow or didn't have the power setting up high enough when I deployed these differential spoilerons, it would pull to the right and drop the right wing.

I have been able to alleviate some of this again with my radio.  In the er9x firmware I can set the speed with which the function deploys, so I slowed the right spoileron down about 30%, meaning it would take a couple seconds longer to fully deploy than the left one, making for a more balanced transition into high alpha.  This didn't mean once established I could get lazy, as it would still drop a wing or pull right if I got too slow with too little power, but once established, the improvement in handling is well worth the risk in my experience.

So now basically I have 1/4" deflection on my left spoileron and about 3/8" deflection on my right spoileron, doesn't seem like much, but it is a 50% increase in deflection to help with high alpha prop wash.

So if you have a radio that allows for this type of adjustment and have noticed this constant "drift to the left/difficulty turning right" with your planes in high alpha, I encourage you to try it or think about it.  Start off high obviously to allow for recovery if it goes wonky on you and I would suggest starting off with a small difference working up in very small increments until you find what you like.  Just because 30% worked for me on this plane, doesn't mean it will work on all planes or that it will work for you, but even with the slight risk, I mention above, it was well worth the reward with much smoother overall handling and performance in high alpha.

Cheers,

Scott