First, we should all start naming our planes "The Compromise", because that's what a stunt plane is -- it's a giant compromise between competing requirements, and any time you completely solve one of them then (unless you're hard up against some limit imposed by the rules) you create another.  That would make our naming perfectly honest -- except then you wouldn't be able to tell the planes apart.  Ahh, compromises...

As an example that's pertinent to your question, if you go with a 1:1:1 crank, flap and elevator ratio then you get a nice mostly-linear ratio (but not quite, alas, because the bellcrank is working in a different plane than the flaps are).  However, that means that you give up a whole lot of leverage on the bellcrank.  That means that the lines don't have to move as much for a given control surface motion (nice!), which in turn means that the force on the lines for that given control surface motion is increased.  Because your lines are curved in flight, not straight, they act like springs -- and by reducing the leverage that they have on the control surface, you increase the effect that their springiness has on the control system.  This is an effect that I've experienced myself, on a Ringmaster which I built with the pushrod too far out on the bellcrank; when I made a super-long elevator horn for the thing, that dragged in the mud every time I landed on grass, the airplane performance perceptively improved.

I think that as pertains to your question, the things you want to achive are -- sort of in order of importance -- the following:

• Good workmanship -- make it so it doesn't wear out until over 1000 flights, passes pull test, etc.
• Make the controls free-moving and free of slop (already, two competing requirements)
• Use the biggest bellcrank that'll reasonably fit.  For a Vector 40, that's probably a 4" bellcrank.  "Reasonably" is a judgement call because the bigger the bellcrank, the more room you need for it and the more the leadouts will bend at the wingtip, which is bad, but a bigger bellcrank means that the lines have more leverage, which is good. 
  
  • You can go overboard on this -- at one point people were experimenting with pulleys instead of bellcranks (Ted Fancher either originated this or was the most famous guy doing it) it turned out to be more trouble than it was worth
• Get the elevator travel correct with respect to the bellcrank.  +/- 20 degrees at full bellcrank travel is probably as much as you'll ever need, but I usually make plenty of room for the bellcrank to move and set the travel at +/- 30 degrees on the bench, before the fuselage is buttoned up.  I'm probably giving up line leverage -- but my planes always have plenty of turn.
• A 1:1 flap:elevator ratio isn't always best -- and "best" depends on a number of factors, including pilot preference and how heavy the plane comes out.  You won't find out until you start trimming.  So, if you're serious, make the ratio adjustable.  Most people do this with a slotted elevator horn and a carrier for the pivot pin that can be loosened, adjusted, and tightened.
• You won't know the best flap:elevator bias until you trim.  So while you're making the elevator horn slotted, use a ball link on the end of the pushrod that can be screwed in and out (and note that this presupposes an access door unless you're using a take-apart plane)
• Other stuff I'm forgetting at the moment
• Oh, yes -- a perfect relationship between handle and elevator/flap motion.  Note that I don't say "perfectly linear" because -- especially for heavier planes -- folks are going to logarithmic flap control, where the flaps tend to move a lot around center, but slow down after a while with respect to the elevator.  The idea is that in level flight and in round maneuvers you want to vary the lift for smooth groovy level and round which is aided by lots of flap, but in square corners you want to turn the airplane -- having more elevator than flap at that point helps

Howard Rush has gone to the trouble of making an Excel spreadsheet that lets you enter in all sorts of parameters of your control system, then calculates the actual flap and elevator motion.  This won't let you make that perfect control system, but it lets you figure out your own personal best compromise -- especially if you're fabricating your own bellcranks so that you can do things like offset the pivot point or the flap rod pick-off point.  It's available for the asking.[/list]

There are a bazillion solutions to this. On my Brodak Ventor 40 I went middle hole bellcrank to outer hole flap and middle hole flap to middle hole elevator. That's about (eyeball measurements) 1/2" to 7/8" and 1/2" to 1/2". The total unrestricted travel of the flaps reaches a bit over 30 degrees which in turn means the elevator reaches a bit over 30 degrees. My protractor wasn't anyplace easy to find although it was most likely within arms reach and I'm guessing a bit over 30 degrees could be close to 40. It doesn't matter a whole lot as I don't go to lock during flight. The same result or could be reached by going inside hole on the bellcrank to the middle hole on the flap lever and outside to outside flap and elevator lever but then there wouldn't be any option to reduce the elevator travel which I don't think would be necessary.

Uh, post #2 outlines the whole Tom Morris system for that size plane.

I think he has the Brodak model that doesn't have slotted flap and elevator. The setup I used on mine is not far from the TM. Bellcrank middle hole to outside flap hole. From middle flap hole to middle elevator hole. As I recall both flap and elevator horns are the same.

While we are on the subject of setting up the control system of a Brodak Vector 40 ARF, I have a question about "slop" in the elevator horn.    Back in the days of old my friends were flying the pattern and I was still trying to not crash... they intentionally built some "slop" into the elevator supposedly to stop "hunting" in level flight. Is this still common practice and does it really reduce or prevent hunting? If so, How much slop is desirable?

Let me follow up on Mark since the V40 has been virtually all I have flown in the nearly 2 years since our fire.  It does not hunt on it's own, period and it turns fairly well nose heavy (electric) if you are so inclined (I am not).  The one I flew had 1:1 with 30 degrees movement and no slop at all in the controls.  It also recovers nicely from the drifting kind of hunting caused by wind with minimal effort on your part.  I never once got the porpoise kind that slop in the elevator would "help".  It had 1/4" slab flaps (which I hate - I build mine from 3/8" tapered to a 1/8" CF TE cap).  IMHO if you are going to have slop it makes sense to have it between the BC and flap horn, not the elevator.  Having the flaps move slightly w/o any elevator movement is going go create a movement opposite of the direction you thought you needed to go. 

You mentioned that you will be electric.  Very important to keep the controls free, especially around center.  "Stickshion" (sp?) is real! 

Ken

While we are on the subject of setting up the control system of a Brodak Vector 40 ARF, I have a question about "slop" in the elevator horn.    Back in the days of old my friends were flying the pattern and I was still trying to not crash... they intentionally built some "slop" into the elevator supposedly to stop "hunting" in level flight. Is this still common practice and does it really reduce or prevent hunting? If so, How much slop is desirable?

   I think that probably got started when people rebuilt their controls from "loose"/worn out to "tight" and in the process created some binding - which is what causes hunting. I think as long as it is free to move, it has enough slop, you don't need more.

     Brett

Problems I see from poorly analyzed control systems are: 1) inadequate leverage over flap hinge moment and 2) asymmetry between up and down. Neither can be fixed with handle geometry.

I spent some effort on a 737 issue where hysteresis caused a limit cycle. You controls guys can explain to me how it fixes one. 

     While I was not the one advocating slop, you can turn a big one (caused by control binding) into a little one (caused by .005 worth of free play). Mark's rather strange description is right in at least one regard, your second-order pilot response causes the big one in the binding controls case, and free play removes that but causes an "automatic" little one.

   My predecessors and mentors were the ultimate wizards of using intentional non-linearities to work around other, unavoidable, discontinuities and non-linearities.

    Brett

     

My understanding of the action of elevator slop and a no-slop flap mechanism is that it provides the ultimate in logarithmic control, in that right around zero handle motion the elevator isn't engaged at all, only the flaps.  So -- according to the theory -- gentle up or down corrections result in the airplane rising or falling without changing its direction of flight.

I'm not sure how true that is, or how much the actual behavior diverges from theory when you add in aerodynamic forces and a giant methanol-powered vibrator to the front of the plane.

Does anyone here know if the Igor Burger logarithmic flap thing could be made to affect this outcome?  I'm pretty sure that it drives the flaps and not the elevator, so you really only get the option of desensitizing the flaps at the extremes, not desensitizing the elevator around neutral.

We could do this all with electronics and servos, if only some over-enthusiastic fellow hadn't allowed himself to be talked into filing a freaking rules proposal that rules that out.

I have in Howard's words, a RCH of slop in my logarythmic flaps and zero in the elevator.  In the logarythmic the transition horn drives both the flaps and the elevator.  The link to the elevator is basically ball links so zero slop.  The flaps are driven by the bearing arm and that is where you have a tiny bit of slop. In my plane I have just under 1/8" total with the elevators locked down.  So basically I have a zero slop setup from the handle since the elevator will start moving before the flaps.

It is different.  When you have zero slop in the flaps and some in the elevator you get a negative response near center.  For most of my competative years I flew with 1/8" or so slop in the elevator.  My muscle memory knew that I should "turn into the drift" so to speak to keep the plane level.  On my first flights with the logarythmic I nearly pancaked on my first inverted because the plane went in the direction I told it to. What I mean by that is that with normal controls, the plane will move slightly in the opposite direction from the control at the handle until the elevator engages.  With logarythmic the elevator always moves first.  That is why planes with too much slop tend to drift up and down.  You are giving it a hint of control one way but the plane is getting the opposite from the flaps.

Ken