Now I wanted to bring up an interesting topic that is not talked about much.
What are the pros and cons of ailerons vs dihedral design?
I listed a few I find to be important, have any to add?
Any opinions?
Dihedral
Pros:
-no extra servos
-less structure to wing in sense of not incorporating aileron
-stabilized roll to a certain extent
-less channels needed on rx/tx
Cons:
-limited aerial maneuvers/banked turns
-complexity to wing design and dihedral angle/connection
Aileron
Pros:
-roll control
-more control of aerial maneuvers/coordinated banked turns
Cons:
-added weight from servos/hinges
-structure to hold aileron (hinges/servo connectors)
I bring this up while seeing many more dihedral designs with the new small class of UAVs such as the raven. I can see them being useful for keeping weight down when not needing the extended maneuvers such as barrel rolls, etc. such as an AP application.
Replies
"
Cons:
-limited aerial maneuvers/banked turns
"
I would say the banking is not limited at all for rudder-only design in automatic mode.
In manual mode there is more LAG from manual command but once again this is useful only for light UAV when you are not afraid of stall and you maneuver where in fact you shouldn't. Real UAV's really seem doesnt care about ailerons.
Giving up navigation agility? Cmon.Pteryx is flying 120m diameter turns with 100g/dm2 wing loading in auto mode, can be pushed to 90m diameter manually. 2.4m wingspan, 5kg AUW, 50km/h. All this 25-40deg banks.
Turnrate and radiuses depend on airspeed and bank angle. You can get operationally the same bank angles using aileron machine as with rudder machine, I say in real practice I am using it no problem. The difference is the lag before you get it, say 0.3s vs 1s. Therefore you need to plan more flying rudder only, but the end result is the same. Except with flying wigs.
IMO the only big problem is with rudder only that you must be afraid of sudden crosswind during takeoff. This is however remedied with high wing loading leading to bungee or catapult, or high power and manual takeoff strictly agains the wind, or high positive roll stability.
Concerning the claim tha ailerons produce better nav, I would disagree.
It depends on how you tune it and what PID set do you use. It is true direct roll control is easier and most autopilots support formula translating internally roll to turnrate what easily translates into navigation. So you might need specific autopilot for rudder only (where you can use other PID variable than roll) just because the idea is under-exploited.
Statistically you get more mishaps with aileron servos than crosswid mishaps with rudder-only, in my country.
Ailerons vs dihedral design? Dihedral adds roll stability to the flight characteristics of the wing. This means the wing naturally wants to return to level attitude. This is nice for freeflight aircraft and begginers learing to fly. What are the flight characteristics of an aircraft with dihedral and no alerions? They are nice for soaring around like a lazy hawk, but what I dont like about aircraft with dihedral and no alerions is...
1.) Gusty conditions make it hard to keep it lined up on final approch.
2.) Hard to fly in crosswind or across the wind with out it wanting to just blow down wind. "keep it pointed in to the wind"
3.) It's like flying with your alerions and rudder mixed all the time. UGH!
So I would suggest using both. Just don't use a lot of dihedral just a few degrees 2 to 5 maybe thats off the top of my head, and if you can setup your alerions as flapperions. Cheers!
Stability in level flight is a different topic than dihedral.
You can get the equivalent of dihedral by sweeping back the wings. Or having a high wing design.
Ailerons are really nice for levelling out the wings for squirelly landings. Dihedral in a cross wind
landing will turn the plane down wind, rather then level out the wings.
If you want to lose a servo, make a yank and bank model with no rudder control.
Dihedral is all about the lateral stability of an aircraft but is only one component that affects it the others being wing position relative to CofG, fin area above CofG, wing sweep.
The design will be dependant upon the requirements that are set including lateral stability, numbers of channels of radio to be used, structural and maintenance requirements etc. Dihedral will give greater inherent lateral stability and a tendency to roll back when the wing is rolled.
Peter