Matt Merciez

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I recently had a mishap witch resulted in some minor damage to my plane but more importantly, taught me a valuable lesson in setting up a plane for 3D flight. I am making this post to hopefully prevent someone else from repeating my errors .

The picture below is of the stab and elevators from my prized plane The stab failure was a result of a violent elevator flutter.



I assembled the ARF and setup the control horns based on the simple theory of shortening the horns will allow for increased throws, which at the time seemed like a no brainer for a 3D plane. The gaps were sealed and the servos used were the recommended servos for torque ratings but were not metal gear servos as recommended by the manufacturer. The servos that I was using I had purchased off EBAY and never opened the cases to inspect the gear trains. I basically set myself up for failure and did not realize it. I setup the plane with a very poor mechanical linkage setup and added to the problem by using servos that may have been questionable.

On the maiden flight, flying at half throttle, the left elevator started to flutter very violently, it took only a few seconds for the entire stab to blow apart and separate from the fuse. The pilot that was maidening the plane was able to land the plane inverted with minimal damage. The flutter and subsequent failure happened so fast the pilot did not have a chance to cut throttle. When we recovered the plane, many of the pilots at the field (myself included) felt the failure was attributed to a poor design (weak) stab.

I sent the above picture to the manufacturer for help in determining the problem. He took only a few seconds to tell me the setup of the control horns most likely contributed to the flutter and subsequent failure of the stab. Basically, in a very nice way, he told me I had screwed up and this was not a faulty plane He was nice enough to send replacement parts (stab, elevators and canopy).

With the replacement parts in hand, I reassembled the new stab and elevators with a the control horns as far as possible from the surface for maximum mechanical advantage (based on the manufacturers recommendation). The servos that were in the plane were removed and repaired (converted to metal geared) and reinstalled.

The subsequent flights were flown without any flutter which confirmed the manufacturers position that I was a dummy in setting up the plane.

In learning about mechanical linkage setups I found a great article on the Horizon Website which goes through and explains what I failed to do. The link for the article is here: [link]http://horizon.hobbyshopnow.com/ProdInfo/PagesAUX/1192-ART.asp[/link]

Hopefully, the above information might help someone from repeating my mistakes

Kyle300S

what plane was this on? i have learned a little about set up. Thanks!!!

Matt Merciez

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Extreme Flight Yak-54. The plane is awesome (when setup correctly)!

rc-sport

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Matt, it's refreshing to see someone admitting the demise of their plane was their own fault unlike someone else's "defective" claim. Thanks for the link it was very informative.

Kyle300S

my thoughts too. and he gave us a ton of info that can help us out. thanks again!!

wgeffon

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Great thread Matt!

TT2

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I echo Wayne's reply! You can't have too much mechanical advantage. I try to keep mine at least 1:1 which (I though) was fine since I always use 'overkill' servos. However...I lost a GSP Katana earlier in the year due to what could have been flutter...impossible to tell. The servo was a HS 5925, 1 1/8" arm (center to last hole), CF rod, Nelson ball links, Robart 1" horn...with the thickness of the surface at the hingeline, the connection point of the horn was about 1 1/4" - 1 1/2" below the hingeline. I 'thought' that I had plenty of mechanical advantage, but I KNOW I didn't have as much as I could have. Really, I think in a panic I oversped the plane...but it's all water under the bridge...somewhere in that water is my OS 160 / VP30 pump / BCM Pitts muffler / Mejzlik prop / TruTurn spinner. Lesson learned. The radio gear survived and the aileron servos were not stripped.

Seems the current trend (at least on the last 3 ARFs and 3 kits I have built) is to have enormous ailerons. Typically I set up my radio and linkage to provide the maximum amount of travel allowable for rudder and elevators...but if I apply the same practice to the ailerons I ALWAYS have more aileron than I can use. Typically my third aileron rate is reserved for the guys that ask 'How fast will it roll?' (I'll click up to the third rate, show them, their response is usually 'Holy $h!t')...other than that I never use it. I could gain some serious mechanical advantage by having the throws in my second rate be the mechanical max.

Another consideration is servo resolution. It's wise to always adjust your endpoint adjustments to the max (providing maximum servo rotation) and go back from there to even out throws if needed. Also it would be wise to adjust your rates to be as high as possible on high rates...don't knock the highest rate down below 100%...if you do, you're cheating yourself out of servo travel. This allows you to use LONG horns on the surface but short arms on the servo, and provides the maximum amount of mechanical advantage.

All the recent flutter problems have made me take a serious second look at my setup methods. I'm glad you posted this Matt!

-Tom

Note: I edited the post...for some reason I was thinking the rates on my 10x could be adjusted higher than 100%...they can't. Kicking up the ATV values is good enough.

TT2

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One more thing...increasing the mechanical advantage will reduce the free surface movement (slop) due to servo backlash.

-Tom

Doug Cronkhite

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Exactly Tom,

On all my airplanes (precision, 3D, etc) I setup the controls so that the maximum travel needed (not possible.. just needed) is acheived with my ATV's maxed out using the shortest servo arm, coupled to the longest control horn I can get. This gives the maximum leverage at the surface, and you're absolutely correct in the effect this has upon slop.

One other thing.. I know some people are hesitant to use digital servos on this airplane and others like it. The biggest benefit from digital servos is not the torque, or speed, but the fact that they develop their maximum torque at only 2 degrees off center from neutral, whereas a non-digital doesn't reach maximum torque output until around 18 degrees.

Len's article is a good one and worth reading by everyone.

Matt Merciez

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Tom, what you mentioned in the above paragraph is what I am now experimenting with. I am now starting to reduce my servo arms length to increase my servo travel for the desired surface travel. Instead of setting up the plane with max surface travel initially, it seems like the smart thing to do is setup for moderate travel and slowly increase the travel until you have enough travel for your desired mode of flight. I am starting to think that I have too much travel in the surfaces for what I need, and I am wasting mechanical advantage, as well as servo resolution at the expense of high throw rates that I can't use.

Doug Cronkhite

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So long as you're not reducing the throw via ATV's you doing it right. If you're running your ATV's reduced you're giving up servo resolution. Set your ATV's to maximum (I actually set it just short of maximum to account for centering adjustments.. about 140%), and then adjust throw mechanically to get what you want. THAT'S maximum resolution and mechanical advantage.

There's a nice linkage design/analysis thing for Microsoft Excel that will tell you how much force will be exerted on your servo. It's located at:

http://members.cox.net/evdesign/page...ge_design.html

It's worth the money for sure and I find it to be invaluable in determining if I'm using correct servos for an airplane.

EDIT: updated link

TT2

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Good to know! I've pretty much convinced myself to use nothing but coreless digitals in anything 65" and up. Expensive servos, yes, but cheap insurance if you ask me.

If you don't need the travel, well, you know. Seems like on my last few planes I wanted ALL the elevator throw and rudder throw I could get for 3D flying. However that may change with the maiden of my 31% CA Extra / ZDZ 80 this weekend (hopefully)...the rudder is ENORMOUS.

Good idea on the 140%. For sake of argument, say I'm using 140% ATV on the ailerons...now I'm adding snap spoilerons...now for some weird reason I'm using full spoilerons and full ailerons...what will happen to the servo?

-Tom

Doug Cronkhite

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Nothing at all will happen. Well nothing bad at least. Your radio still won't tell them to drive further than 140%. What will happen is you'll get both deflected up for the spoileron, and then the down travelling aileron will come back down, while the up travelling aileron will stay put.

Matt Merciez

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Great information and link Doug. Would you please explain a little more about why the 140% to allow for centering adjustments. I guess I don't understand the centering adjustments enough to make sence of what you are saying. How does subtrim affect ATV? I have been setting up the ATV's to 150% and then reducing the ATV on the surface that is traveling more than its conterpart to have equal travel for both surfaces.

Doug Cronkhite

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Sure. The servo can only travel so far before it runs into it's internal mechanical stops. If you run the ATV to 150%, that's basically the max it will travel. The servo itself can actually handle what would be the equivalent of 160% or so of travel to keep the radio from overdriving and burning them out. BUT.. if you run the centering (like in Code 15) too much either way, you can affect the total travel available.

Try this sometime.. you won't hurt the servo. Take your radio on a clean model memory. Go to Code 12 and run the ATV's to 150% in both directions. Now go to Code 15, and set some centering value of like 45%. Now center up the servo arm and move the control full deflection both ways. You'll see the servo stop short of the full stick travel in one direction. Now mind you, this is a very exagerated centering value (or should be.. you should never see anything higher than about 20% max), but it illustrates what I mean.

By setting your ATV's down a few percent in each direction, you give yourself a little headroom to work with in the electronic centering. If you can't seem to center your servo arm, try swapping the arm 180 degrees or try a different arm. JR servos have an odd number of splines, so flipping the arm 180 will give you a different arm position.

3D ONdaEDGE

So basically you can run your servos up to 140% with no problem in the servo. The most I ever run them up is 115%. I thought that it might be bad for the servo if you run it up too far. I guess not if what you say is true. If it is safe then I may go ahead and turn all mine up to 140% and adjust my throws mechancally from there if that is what you are recommending.

TT2

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As always, thanks for the great info. I think I tested this during my HLG years with an X-388S (my first computer radio)...but that's been ten years ago. Used to use full spoilerons and 'elevator' the planes down on landing using the throttle stick.

Thanks,
-Tom

Mike Parsons

Great thread guys. I have learned something today.

-Mike

rc-sport

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I was working on the linkages on my 2nd Funtana and all I kept thinking was "Mechanical Advantages". Excellent info.

MHester

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Yep I'm about to rig a Funtana Pro, and this is GOOD STUFF!

-Mike

Stanoo

Sombody eloborate onthe ATV or JR travel adjustments I have always maxed mine out [] ignorance is bliss I suppose heh and used the dual rates to set my throws mostly on small planes but im fixing to purchase the Big Extreme flight YAK

bentgear

Great thread guys and thanks for starting it Matt. Good info, good discussion....RCU at its best.

Ed M.

TT2

My Feedback: (13)

The 'stock' settings for servo ATVs (or endpoint adjustments) are 100. The maximum value is 150. By increasing the value to 140 (Like Doug mentioned earlier, 140 is a good place to start because it leaves 'padding' for any subsequent sub-trimming you may need to do) you gain a few degrees of servo travel. This allows you to use a longer surface control horn or shorter servo horn...either or both of these scenarios increase mechanical advantage.

If you are decreasing your throws by adjusting the dual rates BELOW 100% then you're effectively decreasing the amount of servo travel. You always want as much servo travel as you can get. Instead of decreasing the rates, move the linkage inward on the servo arm or outward on the control surface horn. Your highest rate should always be 100%.

For people that are having a tough time grasping the 'mechanical advantage' concept this analogy is a good one, and has been used in the past. Think of it like gears on your mountain bike. The front chainring acts as the servo arm, the rear sprocket acts as the control surface horn. For climbing you want to use first gear (smallest chainring in front, largest sprocket in back). This is maximum mechanical advantage and increases the amount of torque to the rear wheel for a given amount of effort applied to the pedals. For speed, you want the highest gears (largest chainring in front, smallest sprocket in back). This is maximum mechanical DISadvantage and makes the bike harder than hell to pedal...less torque to the rear wheel. Obviously there is a trade off for control surface speed when maximizing mechanical advantage, but this is a trade-off you should be willing to make.

I think that the practices listed in this thread should be applied to every plane...from trainers up.

OK, now this is just my opinion...you can NEVER have too good of a servo. Granted putting 8611s all the way around on a trainer doesn't make much sense, but spending $200 more in servos than you had planned for may save you a $200 plane, a $300 engine, and LOADS of bench time. Cheap insurance. Coreless digital metal geared servos on a Funtana 90? YOU BET!

-Tom

ben flyn

GREAT THREAD!!!!!!
So I set my servo horn and contol horn to 1:1, then adjust my radio ATV to 140%, then how do I get low rates?

Doug Cronkhite

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With your radio set to 140%, and your mechanical linkage giving you the high rate you want, you can then use the dual rates to lower your throws down to a normal flying rate. Dual rates won't change your resolution like ATV's will.

Don't get fixated on the 1 to 1 relationship. If you can get the throw you need with a 3/4 to 1 (servo arm to control horn) relationship then do it. Any time you can move closer to the center of the servo you're increasing the leverage at the surface. My precision setups wind up at a ratio of about 1/3 to 1 or less on the elevator giving me only about 15 degrees of throw on high rate with ATV's maxed out. You really can feel the lack of slop and increased servo precision on something like this.