kuobin

I have a tiger trainer for long .it flies well.But I feel it is some kind of sluggish.I was wondering If I remove dihedral from the wing(straighten it).will it become more agile?

flyinwalenda

My Feedback: (5)

Typically that will make the plane more aerobatic lowering the keep wings level factor.

rgburrill

I did that with an EasyFly 40 and it certainly does make it more aerobatic.

JohnBuckner

My Feedback: (1)

Yes! but don,t stop there and go to a full anhedral drop the wings about the same amount as it formeraly used in dihedral. That will result in a very neutral roll stability and that fabled "stays where you put it" feel that is sought after by so many.


This is only for high wing cabin types and it fungreat fun. Yes I have done this on four generic trainers over the years. The problem with it is people keep talking me out of them.

John



The reason for the curious gear in the second photo is I also used the same airplane at times in in our wingless trainer races.

foodstick

John, do you keep the typical washout in the wingtips with your anhedral wing?

Rodney

You do not want washout if you are interested in airobatics as it becomes washin while you are inverted.

buzzard bait

Just to add to John Buckner, above, a high wing plane without dihedral will fly like it has some, i.e., give it rudder and it will bank as well as yaw. That's because in a skid, pressure increases under the wing at the fuse junction and tends to lift. In a slip, it is the opposite...pressure increases next to the fuse under the inboard wing.

Most high wing planes also have some dihedral, which makes them pretty stable, meaning they resist rolling a little and if rolled, they tend to self-correct. So if you take away the self-correcting tendency, they will roll faster.

So John's unusual airplanes above counter this tendency with anhedral. Good idea! Looks kind of weird, but I can see the sound thinking behind it.

With low wing planes it is the opposite. Some people take all the dihedral out low wing planes, but if you do that you have an airplane that prefers to be upside down! That's why designers always use some dihedral on low wing airplanes. The purpose is to achieve something like neutral stability. Neutral stability in this case meaning that a rudder input does not cause roll either way.

Note that a high wing with anhedral and a low wing with dihedral are sort of mirror images of each other. Both of them, if the angles are right, can be neutrally stable.

Jim

JohnBuckner

My Feedback: (1)

Foodstick on the four I have done over the years, the first back in the sixties I just used generic trainer wings and what ever degree of washout that may have existed. They all became very aerobatically inclined trainers however that were a joy to fly. Never have understood the resistance to this simple kit bash. There is however one draw back and that is it is more difficult to maintain orientation at first until one becomes more used to the unusual visual configuration so suggest keeping close on first flight even though it is a trainer.

And indeed what is pointed out above by buzzard bait, this is not for a mid or a low wing airplane. If this is done to a low wing the stability will diverge away from that neutral ideal.

A low wing always needs a small amount of dihedral or dihedral effect from airfoil taper and wing tip design. A mid wing needs no anhedral or dihedral, a midwing airplane is the only configuration that is already near that totally neutral ideal. Perhaps maybe that's that's why all the many great flying sport aerobats are midwings

Here are some random photos during the bash of this last one with the hacksaw (the trainer is a Midwest Aerostar trainer mostly stock except the wing.

John

tony0707

Anheadral was the best thing i did to my Midwest 40 size stick and 60 size to improve its flying quality
Just turn the wing upside down with the servo on top
a wing with diaheadral will then become an anheadral wing
Plane rolls so much better and smoother in a tighter circle
That works only for high wing airframes

I very much like the looks of your sweet trainner with the anheadral a very clean looking aircraft

I scratch built a low wing tail dragger and built no diaheadral into the low wing
When i apply right rudder the nose goes rleft which is called adverse yaw and a bad quality
The Gruman Enginners ( full scale aircraft ) at my field in NY explained to me thst i should have built diaheadral into a low wing tail drager
Keeping the wing tips a bit higher off the runway is a good thing as well

You can view my 20 year collection of some of the very best two cycle 40 to 1.80 glo engine aircraft in my Galley to the left of this post if you like

Enjoy

BMatthews

Removing the dihedral will greatly reduce the ability to self correct back to level flying. But it won't make it respond more strongly to the aileron controls. So while it may not try to fight you to return to upright and level it will only be more responsive if you also increase the amount of aileron throw.

You might try another option that does not require you to modify the model. What you can do is move the CG back a little to make it handle with less tendency to recover in pitch. That will sharpen up the elevator response even without altering the amount of elevator throw.

For rolling maneuvers you can use aileron with rudder at the same time to really speed up and sharpen up the roll response. In this case the rudder and dihedral work with the ailerons and the results can be quite amazing and startling. Using the two controls together makes the rolls look more like snap rolls. Yet when you use one or the other by themselves you still have the softer almost training like response.

To aid in making a flat bottom wing fly better inverted you can reflex the ailerons upwards about 5°. It will make the model fly a little faster upright and not slow down as well for landing. But it makes it so with a rearward CG trim you can fly a flat bottom wing upside down quite well.

Try it. The results will almost certainly surprise you. And all without the need to do any big wing modifications.

The bench time you save can then be put into buying and setting up a more seriously aerobatic sport model.

kuobin

I made it.Now it is a real tiger.

JohnBuckner

My Feedback: (1)

Excellent Kuobin and congratulations on your courage to take to the hacksaw Perhaps next time even anhedral or anything else you can dream up. Not all will be successful but those that do makes it all worth while.
Glad to see the time honored craft of Kit Bashing is alive and well, certainly never a waste of time in saving up for just another serious cookie cutter airplane.

John

skyflier

That looks really good

buzzard bait

Good move, but if you really want a tiger don't overlook what BMatthews wrote about moving the CG back a little, reflexing the ailerons, and combining rudder and aileron for rolls (with the straight wing you still have some dihedral effect, so rudder will help the rolls).

speedamigo

why don't you just build a midwing airplane - looks better and flys better - ��

JohnBuckner

My Feedback: (1)

speedamigo perhaps its simply because not every one is interested in just another pretty cookie cutter aerobat. I am not sure about where you are from but in this country the time honored practice called Kit Bashing is alive and well. This practice being well respected and its not about having the perfect airplane but more about the spirit of experimentation as well as ones own education.

To anyone contemplating a simple kit bash to a basic trainer type will find this one most rewarding if you go full anhedral and not just a flat wing. As I outlined in previous posts above.

John

buzzard bait

Yeah, it's a hobby, we do as we pleases.

I think tip plates that extended below the wing but not above it would have the same effect. That's a bash I''l have to try!

Jim

Hydro Junkie

If you want to see the effect of a high wing with anhedral, just look at the A-7 Corsair and it's big brother, the F-8 Crusader.

buzzard bait

The Mig 15 had anhedral too...

r ward

even in a high wing plane, the lack of dihedral will slow it's tendency to self right because it will use only the pendulum effect of the CG being lower than the center of lift. dihedral accentuates this pendulum by allow air to slip off the wing tips until the lift on the high side equals the lift on the low side. that, is the whole purpose wings have dihedral. with a straight wing it is generally accepted that you have to use some opposite aileron input, to return the plane to level flight after a bank.

r ward

andihedral is an attempt to lessen tip stall at lower airspeed by causing the airflow to drift towards the wing's root chord and compress rather than away from it as it slips off the wing tip lessening it's density, which causes stall.