Wing servo and flaps

[Gaz Elliott]

Okay i have already got a load of hitec standard size servos to fit out the tri pacer 1/4 scale 8ft wing span.

Now The previous builder left the model unfinished about 25 years ago however fitted the bell cranks and rods. Do you advise I use these or fit a servo midway on the airleron and flap drirectly with a rod to each?

If so what wood do you suggest to do the attachments or I have heard of servo boxes are these any good??

 

 

Gaz

[andy watson]

Lots of different ways to do it.

 

Virtually no one uses bell cranks in this way anymore, but I suppose if they are well built they served people well for plenty of time.

 

To make a box for the servos in the wings there are a number of options.  Basically I make mine out of ply and/or pine strip wood.  Might be some details on my stuka blog. 

[Biggles' Elder Brother - Moderator]

It may seem strange - me bing a mechanical engineer and all that - but the less mechanical linkage you have the better it all works is the conventional wisdom. So go for in in-wing servos and simple rod linkages is my advice.

 

Simple bit of quality 3mm ply for the servo hatch plate then two pieces of hardwood bearer (spruce or beech) to screw the servos to should do the job just nicely.

 

BEB

[Boots]

only 6 months ago I fitted ailerons 1 servo and  2 bell cranks but instead of push rods I used a double cotton arrangement , pull pull system I guess, so far so good

[Mudflap]

I have found, with those white plastic bellcranks readily available, that in time, they go an off white colour and very brittle. I lost a 80  ish inch Harvard to this. Servo in the wing where I can now

[Bob Cotsford]

I'm still flying a Flair Baronette with belcranks, including one that takes the drive from the mid wing servo location to the top wings turning the motion through 90 degrees, then one in each wing to drive the ailerons, 3 belcranks and 5 pushrods in all.

It's horses for courses, slow impecise models work fine with belcrank linkages, faster aerobatic models need the precision of direct links.