Just wondering what dihedral in a wing does? What happens if you take it out?

For the plane's wing to be most efficient, it needs to be horizontal (lift force is directly up...). By building in di-hedral, neither wing is optimal when the plane is level, but the moment the plane banks slightly, the lower wing is more efficient than the higher wing, and thus produces more lift. This tends to make the plane more stable, because the plane is "self leveling".

It also makes inverted flight less stable.

Very good idea for trainers, and almost all full scale planes.

gus

Thanks Gus. Very informative. I have seen articles about taking out the dihedral. Will give a trainer more performance or fly faster?

Taking the dyhedral out of a trainer will make it more agile in the sense that there will not be any forces working against your commands other than the fuse working as a pendulum. So, you will have more control. In terms of flying upside down, taking out the dyhedral will help tremendously but with flat bottom/asymmetrical wings, it is unlikely that you will be too satisfied with the upside-down performance.

In terms of flying faster, it won't. In fact, you can argue that by straightening the wings, you actually increase their efficiency... hence you fly slower. However, I know that many people clip their wings (make it shorter) when they eliminate the dyhedral, which will make the plane fly faster.

Didn't put much effort in refining this post. Hope it is still comprehensible.

Dihedral provides lateral stability - which means that if the airplane is bumped off level flight to the right, the increase in right wing lift returns the airplane to level flight. Removing dihedral makes the airplane more responsive in roll, at the expense of stability....

FWIW, stability is the enemy of controllability and vice versa....

Cheers!

Jim

For high & mid-wing a/c, dihedral is a performance limiter (in the sense of aerobatic capability) & once a beginner has mastered basic flying skills, dihedral in those a/c types is of no benefit -- removal is desirable.

In low wing a/c, a small amount of dihedral is actually necessary, & removal of dihedral (unless it is excessive) reduces aerobatic capability.

Control authority in models is so powerfull that stability is not usually a real issue for rc pilots once they are past the beginner stages.

Would I be right in saying that a symmetrical dihedral isn't self leveling, assuming no angle of attack? I am asking beause my dihedral symmetrical winged Prangster flies inverted well and isn't at all unstable, yet it has a lot of dihedral in the wing.

Try the following:

Get your plane flying up-right, straight and level using your trim settings to get it flying "hands-off".

Now do the same thing with the plane inverted. In theory you should only have to adjust the elevator trim.

The dihedral "self-leveling" stability is nothing like the forces applied by ailerons, etc. You will find that the plane "falls out" to one side of inverted, but will remoan very stable upright.

gus

Did you ever fly a Kite?

Remember how you would tie a string across the back to "Bow" the surface?

That's dihedral.

Without that bow, the kite would wobble for a bit, then turn sideways into the wind and fall. But because of the bow, if one side turns into the wind more than the other, it gets a more direct hit from the wind.

In the illustration below, you can see how the wind affects the surface of a Kite. Next you can see how this same priciple is applied to a wing.

And finally, you can see how dihedral will help an inverted wing right itself.

I'd like to expand on Gus's & others explanation. Wings aren't exactly more efficient in lift when they are level. A wing will produce the same lift reguardles of orientation, assuming all else is equal. The diff, which is what I believ Gus was getting at, is the vertical portion of the lift can change. It is only the vertical portion of lift that fights gravity. With dihedral, as the low wing goes level, it produces more lift in the veritcal vector; this outweights the vertical lift vector on the high wing, hence the low wing lifts more than the high wing and the plane levels, note that gravity is a key part of the equation. Likewise, the high wing reduces it's lift in the vertical and increases its lift in a sidways vector, the sideways vector outweights any sideways lift from the low wing, hence the plane turns toward the low wing. Maybe MinnFlyer can produce a wizbang photo that explains this better than my ramblings.

less diehedral also means less roll when the wing yaw or when rudder is applied

Enya engine - an assymetrical wing doesn't hurt the axial stability as much as the performance of inverted flight. An assymetrical wing will create lift without any angle of attack, which is to say it is parallel to the line of flight. Thus, to hold level flight inverted, where you must fight the effects of the wings normal lift (which is now pulling the plane down) you would need a more reverse elevator to keep it level. On a symmetrical airfoil, lift is created by keeping the wings at a shallow but positive angle of attack. Thus level flight can be achieved either through trimming the elevator or balancing the plane so that it naturally flies level without trim. The latter method allows you to fly level inverted without additional elevator input.

Of course, all this is based on my knowledge of engineering and I'm sure there are far more qualified people than I to speak on this matters. But since your post went unanswered, this is my two cents.

I just re-read this thread & I noticed something that I had missed previously. The question was asked if removing the dihedral will make the plane faster, & fourstroke replied -- "In terms of flying faster, it won't. In fact, you can argue that by straightening the wings, you actually increase their efficiency... hence you fly slower" -- this is not correct. As already noted, the lift vector with dihedral wings is not vertical, so only a portion of the total lift actually supports the plane. This results in a necessary increase in the AOA, relative to a flat wing, to provide the equivalent lift. The higher AOA results in higher induced drag, so the identical flat wing with the same available power will be faster. The greater the dihedral angle, the greater the flat wing speed differential will be. However, in reality it will probably not be noticeable.

britbrat - i stand corrected. your logic is impeccable for symmetrical planes where wings do not have any inherent lift built in them. But for asymetrical or the extreme flat bottom wings, i believe that the dihedral helps to decrease their efficiency without increasing drag. for example, on a trainer, you would have to apply down elevator to keep it level otherwise it will continue to rise. taking out the dihedral would create even more lift but lift does not equal forward speed. but of course, this is only applicable for planes that have asymmetrical more power than it needs to maintain a level cruise. the optimum would then be to dial in as much dihedral as it takes so that the wings create enough lift for level flight at full throttle while maintaining the smallest AOA. britbrat... i know what you're thinking ("i'll have some of whatever HE's smoking..."

Actually, unloading the elevator makes a plane go faster. In normal flight, the tail surfaces must provide a down load (negative lift) to hold the planes nose up & that down load comes from elevator or wing-tail incidence --- it creates drag. Unloading the tail, as in the example that you just gave, reduces tail negative lift (it is still lift) & reduces drag. That is why "tail heavy" planes go faster than "nose heavy" planes.

Flat bottomed airfoils are often faster than symetrical, or semi-symetrical foils, for all of the noted AOA reasons.

Taking out the dihedral will neither increase lift, nor make for a more efficient wing.

Ok, MAYBE - In some EXTREMELY insignificant amount it might, but you'd need some pretty sensitive equipment to measure it. And you certainly wouldn't be able to notice that difference in flight.

The main porpose of dihedral is to keep the plane stable in its Roll Axis. Remove the dihedral, and the plane will roll better, and fly inverted with less effort, but it won't run faster, or jump higher, or leap through hoops.

I already stated that you probably won't be able to see it --- but taking out dihedral does indeed increase lift & it reduces induced drag -- period. Whether or not you can tell the difference is of no consequence --- unless you are trying to go fast -- which is why you don't see a lot of extreme speed planes with dihedral.

okay... britbrat, as you mentioned before and minnflyer reiterated, regardless who's right, it won't make a noticeable difference in terms of speed.

as for extreme planes, you don't see them with dihedral or symmetrical wings because they are designed for speed alone. thus, it is down to less drag and more horsepower. therefore they have SHORTER, MORE AERODYNAMIC WINGS (to reduce drag) that are asymetric with no dihedral (so they are as efficient as possible give their span and thickness) so they create just enough lift to maintain level flight at their intended racing speed.

anyway, if you want speed, clip the wings and you'll get it. all this dihedral/no dihedral, nothing you are saying is wrong. now THAT is a statement you cannot argue :-)

Agreed There is, however one aspect of flight where lack of diherdral makes a noticeable difference in speed & that is the case of inverted flight with flat-bottomed wings.

If you take a typical trainer -- like a Hobbico Superstar, with an OS .40 LA, & fly inverted, it can maintain level flight but will barely be able to climb. The reason is that the flat bottomed wing, plus the dihedral, requires a large AOA to develop sufficient lift for flight, which creates so much induced drag that there is virtually no reserve power for inverted climb. If you take the dihedral out of the wing & fly inverted again, the aircraft flies noticeably more quickly & can actually develop a modest rate of climb -- because the lift vector is now vertical, making all of the lift available for flight, thus reducing the AOA & some of the linduced drag. This is enough to increase speed sufficiently for inverted climb.

This isn't theory -- I've done this with several trainers & the effects are quite evident.

My Afla trainer will climb out of inverted flight fairly easy and i haven't made any changes to it yet. I'm goona put a MDS .68 engine, take out the dihedral, and turn it into a tail dragger.

Sounds like a good plan -- the .68 will be more than a bit exciting in it.