control system layout and dimension

[John Carrodus]

I would appreciate guidance here please.

Using say a 40 power typical stunt model. profile or built up......
What would be your recommended layout with dimensions from the wingtip to the elevator horn, include of course any other additional helpful information. A diagram or sketch would greatly appreciated.
Thanks in advance
John Carrodus

[Jim Svitko]

I do not fully understand why you would want the wingtip to elevator horn distance.  Are you trying to establish the length of the aft fuselage?   

[John Carrodus]

Jim, apologies, I was not very clear.
I'm talking a walk through each component from wingtip to finish at the elevator control horn.

[Mark wood]

John

Me being the supernerd that I am whom goes into extra deep analysis, I would advise that the best way to accomplish what you are asking is to acquire some plans of a well known good flying model in the size you are interested in. Then copy the basic layout and make the changes you like. Cosmetic and style changes to fit your personality are essential. Besides, this is how 95% of the models have been designed. It's always best to plagiarize the best parts of others and go from there. Something like a Vector 40 would be a great starting point and could be made either full fuse or profile.

that's my $0.02

[Ken Culbertson]

Mark's idea is a great place to start, however most of the "40" sized ships were designed in the 60's to 80's were built with a grade of balsa that simply does not exist any more.  Weights were in the 35-40oz category.  With today's materials you are lucky to get out at 50oz and a .40 is not enough power for a 50oz plane.  A 46 maybe.

What all of this leads up to is what is the goal for this plane?  Competition "Pattern", learning the pattern, fun flying?  All of that makes a difference in what you choose. 

Ken

[Steve Helmick]

Biggest bellcrank you can fit into the wing structure, 4" minimum. Flap horn 1.25" from flap to top hole, minimum. Elevator horn 1" minimum. Don't be shy about making the controls SLOW. You can easily "speed up" the control response at the handle end. NEVER use solid leadouts. ALWAYS build the controls expecting the model to last for 5,000 flights or more. Yep to CF pushrods. Nope to flexable pushrods.  Steve

[Howard Rush]

Biggest bellcrank you can fit into the wing structure, 4" minimum. Flap horn 1.25" from flap to top hole, minimum. Elevator horn 1" minimum. Don't be shy about making the controls SLOW. You can easily "speed up" the control response at the handle end. NEVER use solid leadouts. ALWAYS build the controls expecting the model to last for 5,000 flights or more. Yep to CF pushrods. Nope to flexable pushrods.  Steve

Yup.  Details upon request.

[John Carrodus]

Many thanks for the answers so far. I ask this question because when I study various plans the details are often different from one plane to the other and I'm not sure why. For eg - some plans have one pushrod hole in the bellcrank, some up to three. Some flap horns are short , some long. Some have the pushrod from the bellcrank to the top, some to the bottom hole in the flap horn. Some elevator horns are extremely short and some appear extremely long. I would think that with all the individual variables and combinations available to tune a model, there would be some numerical general solution that worked well on any stunt model where the primary aim is to achieve tight turns and stable, predictable handling. I guess in a way I have answered my own question. .Make allowance for changing setups from a variable lines out setup through longish horns and try various combinations till the plane flies right/best. The hard one would be bellcrank adjustment in an inclosed setup in the wing, which I guess is 90% of the time.

[Mark Gerber]

Howard's Excel program is extremely helpful.  With it you can experiment with different bellcrank and horn geometries to predict control sensitivity and linearity before you build.  I used it for the first time on my Bearcat and the plane handles very well.

Mark Gerber

[jerry v]

Many thanks for the answers so far. I ask this question because when I study various plans the details are often different from one plane to the other and I'm not sure why. For eg - some plans have one pushrod hole in the bellcrank, some up to three. Some flap horns are short , some long. Some have the pushrod from the bellcrank to the top, some to the bottom hole in the flap horn. Some elevator horns are extremely short and some appear extremely long. I would think that with all the individual variables and combinations available to tune a model, there would be some numerical general solution that worked well on any stunt model where the primary aim is to achieve tight turns and stable, predictable handling. I guess in a way I have answered my own question. .Make allowance for changing setups from a variable lines out setup through longish horns and try various combinations till the plane flies right/best. The hard one would be bellcrank adjustment in an inclosed setup in the wing, which I guess is 90% of the time.


John,
You can make mechanical jig with all control parts and test it before installation into the airframe.
Vector 40 , Nobler ARF have non-adjustable control horns. Control horns for flaps and elevator  have three holes. For mass production horns are identical . The bellcrank closer to pivoting hole connected to the furthermost hole in the flap horn. Middle hole in the flap horn is connected to middle hole in the elevator horn. This will make flap to elevator movement ratio 1:1. In the real flight you need the minimal amount of flap deflection to make sharp corners and in the same time not to stall the model in the turn. And to make better control during flight you need more elevator deflection than flaps. Most of models use preset (buried) in the fuselage flap/belcrank connections and have adjustable elevator horn. It’s easier to access the control horn in the tail than flap controls trough the canopy. Personally I like the biggest possible control horns - at least 1 inch shoulders to maintain less sensitive controls and have minimal effect from the backlash  in the control system.

Jerry

[Dennis Toth]

One way is of course to copy an existing setup, but if you are building a scratch build or Classic/Old Time some of the setups they used back in the day are not as good as what a current day setup would be or you may need a different ratio then 1:1 for older ships so you would need to guess at the throws.

What would be really useful is if we could input the degree of control throw (like 30 deg) we want for the flaps and the elevator. Then input the length of the of the bellcrank that would fit the particular wing (like 3 or 4 or 5), input the stab thickness at its trailing edge so you know what the horn has to clear, same for wing) and have the program calculate the hole distance from the bellcrank center pivot hole to the pushrod hole, the length of the flap horn and distance from flap horn CL to its pushrod hole and the same for the elevator.

This would allow buying the correct size hardware and once a flier found a particular setup they liked could use it for other ships as a starting point even if they had to change bellcrank sizes to fit smaller ships. Maybe Howard can work this into his spreadsheet program.

Best,    DennisT

[Ken Culbertson]

Most of today's successful designs are an evolution that started with the introduction of the piped engines.   Much of the knowledge accumulated was shared which led to a very similar set of dimensions among the top designs.   From there they developed to match flying styles, etc.   I don't know of too many designs that have been published in the last 20 years or so.
It may be that the plans you are looking at are from an era where basically everything was different.  Don't make the mistake I did in starting back thinking that things were the same.  They aren't.  Focus on the designs from the 2000 era and you will find some things more common.  Thick rounded LE airfoils, 4" bellcranks, Tall horns, CF Pushrods and power that was only dreamed of in the 70's and 80's and adjustable wherever you can.

The current plane I am flying which is well documented in my build & trim threads is a test bed I am using to test several theories and hardware setup's.  You might try something similar.  The bottom of the fuselage is a full length hatch running from the back of the motor to 2" behind the flap horn.  All of my controls exit the bottom of the wing (it doesn't matter where it exits or whether horns are on top or bottom).  If done right you do not lose any fuselage strength. You have access to all the toys, but it does add some weight.

Ken

[John Carrodus]

I thanks each and every one of you. You have thought long and hard and made the effort to help me find a solution You guys have encouraged me to go a little further with this one and develop on the back of what you guys are doing already to make an analog test control computer out of plywood, wire and foam. ( I will show pictures later when complete - next day or so, God willing.)

Attached is a roughed out drawing of the thing. Nothing is accurate on the drawing eg degrees etc. It is just a conceptual layout. But it should provide lot's of flap / elevator combination solutions when variables are changed. Get what I want - then build it to make it so.

Any ideas / improvements and suggestions very welcome.
Cheers
John

[Howard Rush]

Maybe Howard can work this into his spreadsheet program.

Maybe it’s there.

You need a 3D analysis like John’s, but a problem with a mechanical model is that it’s hard to include all the variables. Odd little things seem to have big effects on control linearity: stuff like bellcrank axle sideways position and bellcrank output hole angular position.

I think that leverage over control surface hinge moment (ratio of leadout travel to control surface deflection) is a big deal. I  would use as big a bellcrank as possible moving through as big an angle as possible. One problem with that is that the leadout swath hollows out your wing. You can get the same leverage with a big bellcrank moving through a small angle or a small bellcrank moving through a big angle. That’s an interesting trade.

I’ll have more time to harangue in a couple weeks.

[John Carrodus]

I have made a working control computer. Dial in the flap and elevator setting you need and pin the pushrods in place and have a play around till you get what you need eg 25 degrees of flap 35 degrees of elevator. I started by doubling the dimensions I would normally use in a medium large stunter. This gives ample room to increase choices in adjustment and increases accuracy.

I used a 20mm thick foam sheet for the mounting board. I used black 4 mm thin foam for the pushrods, bellcrank and horns. Make sure all your cuts are precisely straight and square. Draw degrees onto A4 sheet and position / glue to foam mounting board.

The triangles represent the horns and flap or elevator on the right angled long side. I used pins to locate all the parts and for easy adjustment. After fiddling around you will soon get the desired results you are looking for. There are other variables which I'm sure you will think through or find out yourself and allow for these in your final solution.

If you make and operate this device carefully, you will get a more accurate setup for your next stunter.

When you are happy with your final setup on the board, measure everything as accurately as possible ( I use mm ) Record them , then simply multiply those values by say 0.45, 0.6, o.55 or whatever you feel will be the best size for your model.

If you make your own components leave room for adjustment later if needed in flight trimming. Some folks wisely leave access panel to their horns for easy adjustment. A good idea.

I hope this may be of use
Good luck
John

[Dave_Trible]

This is neat!  I will make one similar to play with.  Thanks !

Dave

[Ken Culbertson]

Me too.  Better than the one I use.

Ken