• Jon

How to Build an Aeroplane - Day 6 - Aileron and elevator hinges

There are so many different ways to create hinges for the control surfaces. Some of them are obviously better than others. I guess the considerations that need to be taken in to account are, weight, reliability and difficulty level.



I always find this part of the build a little bit tedious. When modelling the overall shape of the aircraft it is quite satisfying seeing it come together, but these small parts take a lot of fiddling for a small (visual) reward.


The different methods I have seen lately are; flexible TPU printed hinges, snap-in hinges using a small piece of filament or cocktail stick, or piano wire full length hinges.


There are benefits to all of these. For this model I am going to use the piano wire hinges as they are probably the easiest to model, for anyone following along. These type of hinges also do not require any exotic filament like TPU.


The ailerons on the Cessna 337, like most Cessna's are frise ailerons. This type of aileron has an offset hinge which pushes the bottom of the up-going aileron into the airstream, causing drag.



The purpose of this is to oppose 'adverse aileron yaw', the yawing affect of rolling the aircraft, where the up-going wing produces more lift than the opposite, lower lift, down-going wing. This all causes a yaw toward the up-going wing, away from the direction of the turn, hence, adverse - aileron - yaw. Clear? Um, here is a video from YouTube

to better explain...




To stop this undesirable tendency you can design in some features, such as frise ailerons, or pilots can coordinate their turns, however you need a rudder for coordinated turns. And we are not going to have a rudder...


All aircraft designs are a series of trade-offs, from the smallest Gri-Gri all the way up to the A380. This model plane is no different. To put rudders into this twin boom design would increase the weight and complexity, and decrease the strength of the tail section. I'm not saying its not possible, just not worth it.


So to alleviate the adverse aileron roll we need a design feature. Frise ailerons (a la Cessna) are fairly easy to design however the right amount of protrusion would require trial and error testing, print and re-print. As an alternative we can take a leaf from the Piper book of aircraft design and use differential ailerons. This method works by having the down-going aileron deflect less than the up-going aileron, i.e. the up-going aileron (on the down-going wing) does most of the work. Airliners go one step further and use spoilers on the down-going wing to assist the roll as well. This can be done by programming your transmitter later and adjusted as needed with re-designing the aircraft.





 
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