Hi guys,
was hopping for some feed back from you guys.Idesigned a lowwing plane.It has a constant cord wing, split elevator ,and large rudder.the problem is that the rudder has very little yaw effect. At hi speed when you kick the rudder it kind of stalls with the nose dropping and the plane just hagging there.I have another plane a contender 60 and has same caracteristics.Was wondering if anyone had any idea why they are doing thisboth planes have no dehedral in them. thanks for listening. appreciate any feed back.heres a picture of the plane.
joel

Hmmm..... hard to tell. What about a side shot. Preferably right down on the floor so it's sort of like a plan's side view. And perhaps a top shot as well.

And how much throw are you using?

qfrc flier,

I think the side view would be useful. A couple questions pop into my head. Is the rudder hinge line vertical? Is the rudder reasonably well balanced above and below the thrust line? Is the canopy really a sharp step, as it appears to be in the picture, with no rounded leading edge? A canopy shaped like that could conceivably blanket your rudder, reducing its effectiveness. Post a side view picture if it's handy, and maybe something will be more visible.

Good luck,

banktoturn

And perhaps you could elaborate on the response you're getting from the model. You said....

"At hi speed when you kick the rudder it kind of stalls with the nose dropping and the plane just hagging there."

So you're saying the model goes from flying fast to dead slow and then the nose drops? Is this the same with the Contender as well?

I had that happen on an own design plane only worse. I would give right rudder and it would turn left. I put about 1in. more dihedral under each wing and it was fine. When you give right rudder, with dihedral, the left wing goes forward giving it more affective incidence, causing the plane to turn right. The opposite with anhedral.

Here's the best shot i have of side view. Yes the contender does the same thing but a little more violent.If you hold it there with the contender it will slowly start to roll in a almost stalled condition.One of the guys i fly with said he heard of that condition but never saw it.the contender has a conopy too. when you look at contender from the top the fuse is shaped like an air foil with the nose cone on.I'm wondering if i should have put some dihedral in the wing when i built it.I like no dehedral though they fly real nice.They tend too track very nice. Ill be waiting to see you're replies.Thanks
Joel

the top view

How much incidence do you have on the wing?

I ask that because it's possible that you have some incidence that is being canceled out by the angle of the horizontal stabilizer, and that, in turn, is creating so much turbulence around the rudder that it's making it ineffective.

It's amazing how much the effectiveness of the tail can be affected by the wing. - Hence the fact that full size airliners have the stabilizer positioned as far out of the stream created by the wing as possible.

Just a thought!

David C.

I'm with banktoturn on this one. It looks like you need to put a canopy or some sort of smooth fairing over that sharp step at the front of the turtle deck. I'm sure it's messing up the airflow over the vertical fin.

I had a friend with a Kaos, similar plane. He thought it would look cool with the cockpit canopy way back towards the tail like a Geebee. It was cool, except it wouldn't knife edge. I'm betting this step on top of the fuselage would have the same effect, only worse.

With the nice (he says with tongue in cheek) square nose you have a great drag producer. A little yaw and you get much more drag than a nicely streamlined nose would produce and you slow down. Stick the square nose in the airflow and the dynamic pressure aft of it drops. Lower dynamic pressure from any of the causes means that at the tail the initial high speed trim is no longer working.

You end up with the airplane slowing down and pitching nose down. Make a nice streamlined nose and try the maneuver. It might make the rudder more effective.

------------------- I ask that because it's possible that you have some incidence that is being canceled out by the angle of the horizontal stabilizer, and that, in turn, is creating so much turbulence around the rudder that it's making it ineffective.

It's amazing how much the effectiveness of the tail can be affected by the wing. - Hence the fact that full size airliners have the stabilizer positioned as far out of the stream created by the wing as possible. ---------------

David, wrong concept. If you ignore the boxy front end (a really bad one I might add) and the bump of the headrest the lines are those of any classic pattern design as far as incidence goes. If I were making an airliner or competition glider I would get the tail high, it is a drag thing they are trying to minimize. The effectiveness of the tail to determine pitch is not really a position thing. Keep the speed up and it will work fine regardless of where it is.

As I have mentioned in other discussions I would offer in evidence the years of competition pattern airplanes most of which have the horizontal tail within inches of the wing horizontal line and all of which have great stabilizer/elevator effectiveness.

Hmmmm again....

This is all very hard to diagnose over the internet let alone without seeing the model flying but I wonder if you aren't just getting the rudder so far over that the drag of the slideslip (yaw) and the deflected rudder aren't just too much for the engine to handle and the model is acting like you put on a speed brake.

To help answer this how well does it do a wingover. You know, vertical climb, throttle back, cut in full rudder, add blip of throttle to blow air over rudder to kick model over to one side. If a stall turn like this is pretty much a pivot and down the same up path then the rudder may just be yawing the model so hard that the drag is too much and the model settles due to lack of speed.

What size engine is on there and what's the wing area and weight?

Oh, and I know this is a personal taste issue but I go along with Ben about the need for a cowl. Or at least the lower part of the nose could have been angled up more to help the aerodynamics.

Is this an original? If so it's pretty darn good other than these few niggling details.

Yes the plane is an original.I made one similar but only 2 channel ailerons and elevator. with an .049 engine.this one is full 4 channel with a throttle .061 norvell. The wing span is 30" and chord is 6.75 for a total of 202 sq. inches, wieght is 18 oz.It flies real nice comes right off the ground in maybe 15to 20 feet.Also has fully symetrical wing.slices threw the air nicley even in ten mile an hour winds.All my other planes are 46 size engines and one that is a 60 size.I've only flown it twice so far going to see this weekend and see what it can really do with the nevers settled down.This is my first 1/2 a plane made for the field close to my house.For when i dont have enough time to go to my club field. Will be waiting for youre reply
Joel

What percentage of the wing area is the horizontal tail area? Is it the angle of the picture, my perception or is it really as small as it looks??

My smallest full house airplane was a shoulder wing original with an .09. It was modeled after the old 1960s design called the Stormer. The little planes are nice and fun to play with but do have some interesting characteristics.

the tail is arond 12% of the wing flies real good the tial is very sensitive even at that percentage.It looks smaller in the photo because of the angle.
joel

I would suggest at least 20% and possibly 25% would be a better size and will help in stopping the nose down pitch you are describing. It will put more horizontal tail outside of the really messy goings on next to the fuselage (whatever they are and wherever they are coming from ). Then see what happens.

Good luck!

Did someone say dihedral?

How bout inverting the motor?

How bout keeping the weight down with a rossi 40.

Didn't double up the wing tips either. I love this plane, learned to fly with one 20 yrs ago.

Square nose...hummm, dont ugly sticks have the same nose, and do not have the same problem?

I would lay my money on the excess rudder deflection theory.

Plane looks like fun

BTW, did you miss the intended forum Hoverit? *chuckles*

Ugly Sticks have a 20% horizontal tail area. Just excess rudder won't cause nose down unless there is a loss in horizontal tail effectiveness. You lose porportionally more tail tail effectiveness due to loss of dynamic pressure recovery when the tail is as small as the airplane in question. If it is just drag from rudder deflection slowing the airplane down both wing and tail see the same reduction in dynamic pressure and similar lift losses which would lead to some nose down but not as much as when the horizontal tail is wiped out.

My nose comment was about the square nose causing so much drag. I dont think it is that fatal to have a square nose 'cowled' only by the motor.

There was no mention of elevator deflection in his post, just ineffective yaw. If the elevator is suddenly stalling when rudder is used, it must be losing airspeed, or the elevator would have been stalling before rudder was applied. Doesnt sound like it was already nosing down before the rudder was applied, so it sounds like the rudder is bleeding airspeed much the way a good air brake would do.

He can try less deflection to check, very easy diagnostic. If it turns out that deflection is stalling the plane, then he can remedy that with a hog of a motor, al la 3D, or reduce the throw and let the wings do some of the flying!

He should also remove the turbulance caused by the lack of a smooth canopy, that will indeed make the rudder less effective. A simple wedge in front of the step-up might suffice.

Dihedral & Wing Vertical Location.

Wing location on the fuselage can affect the roll coupling of an airplane. Picture a plane with a low wing. Let's say you put in right rudder. Now the air flow is hitting the left side of the plane. The air flow tends to split at the center of the fuselage with part flowing over the top and part over the bottom. On a low wing plane, the flow going over the top of the fuselage goes over unrestricted and joins back up with the airflow. But, the part flowing under the fuselage hits the top of the left wing, pushing it down, causing a left roll, opposite to the rudder.

Visualize a wing with dihedral in a right yaw. With the wing cocked to one side, the air flow is now hitting the bottom of the left wing and the top of the right wing, causing a right roll. Conversely, anhedral causes roll opposite to the rudder.

This is the reason that most low wing planes need dihedral. The dihedral causing roll with the rudder should cancel the low wing location causing roll opposite to the rudder.

Conversely, high wing planes steer in the direction of the rudder. This is why Sticks with flat wings, like the Ultra Stick, will still roll in the direction of the rudder. High wing planes need anhedral to cancel the wing location and be neutral with regard to roll coupling with rudder.

Wing sweep does the same thing. Visualize a plane with swept back wings with right rudder. The right wing is now more in line with the air flow and produces slightly less lift. The left wing with right yaw is now more square to the airflow and will produce slightly more lift causing a right roll. Sweep back produces roll in the same direction as rudder. With a swept wing, you need less, or no, dihedral in a low wing plane. Sweep forward produces roll opposite to the rudder.

In summary,
High wing, sweept back and dihedral produce roll with the rudder.
Low wing, sweep forward & anhedral cause roll opposite to the rudder.

A designer can make estimates as to what he needs, but it is really a "cut & try" type thing to get all the roll coupling cancelled out.

With regard to your nose dropping, you may have some pitch coupling or you may be unconsciously corecting for the roll coupling, causing a slight loss os speed and the nose to drop.

Pitch coupling is another mess that is hard to correct. Computer radios and mixing will work, as will canopy location, side area, gear type, tuned pipe location and CG.

Basically you need dihedral for rudder to work at anything faster than a stall.

Here is a good site with lots of moving animated examples of dihedral effect etc. It is written in a non technical way and should be of use. The location below is only one of many good examples shown of stability and control effects of airplanes.

http://142.26.194.131/aerodynamics1/...ity/Page5.html