Low tail in turn
 

I thought about asking this in the centerline thread discussion, but it really doesn't belong there.

Here's the question: I went to an auction recently to pick up a plane suitable for engine "break-in" duties. Got hold of a Great Planes sport 60 for 20 bucks, that had been slightly modified in that spacers were used to extend the nose. Previous owner stated it was very tail heavy and extended the nose instead of adding weight.

OK so I get it home slap in a SuperTigre that I want to break in and check CG and all alignments. Wing, stab, and engine all at zero WRT the centerline. CG is a little forward of the 30% point, but better a little nose heavy than the other way round. So I finally get the engine tuned, and have been flying the bird but it has one nasty habit. It will accelerate down the runway, lift the tail and after another 20 yards, rise gently with very little elevator input. At full throttle it will easily hold a 20-30 degree climb. Once at a decent altitude, I cut throttle back to mid range, and it flies level, but here's the rub. a slight left turn started with aileron, followed by some rudder produces a turn, but the tail seem to be very low despite this being a mid wing model. It turns like a heavy J-3 where the tail section doesn't seem to be level through the turn. Same results with a right hand turn.

My first thought was to add a couple of washers under the back mounting lugs so that there's more downthrust, but I'm not sure this would raise the tail in a turn.

I could also shorten the nose spacers thereby moving the CG back, but not sure this would change the way it flies.

Tips or comments welcome.


KKKKFL

RE: Low tail in turn
 

Giving your problem some thought and wondering if a little mre surface area would Help.I think you could just replace rear half of horizontal stabilizer (Elevator) aft of the hinges.Making it larger may help fight centrifigal you get in a turn? Check Out my (Electric Rotowing)charlie111 No other pics

RE: Low tail in turn
 

RE: Low tail in turn
 

With a 0-0-0 setup you're going to drag your tail in turns. If the plane isn't speed sensitive WRT pitch it's not a problem, but if you want it to look right in flight 1/2 degree of positive incidence will make the tail sit higher in all aspects of flight. I would expect you do have some speed sensitivity, as there is nothing in your setup to keep the plane from producing more lift as the speed increases. A bit of positive incidence together with the necessary down trim on your elevator will reduce that tendency since the down trim becomes more effective as speed increases, effectively raising the tail and lowering the lift the faster you go.

RE: Low tail in turn
 

I really cannot change the incidence at this point with the way this plane is constructed.  I can easily add washers under the rear motor mounts.  I can also adjust the flaps/ailerons so that the trailing edges droop slightly.  Any guesses as to what that might do?

KKKKFL

RE: Low tail in turn
 

A tail heavy plane can cause the tail to drag in turns. How does it fly inverted?

RE: Low tail in turn
 

Here is the simplest, easiest, and fastest fix..............

<span style="color: #ff0000">Use more rudder during your turn</span>.

Easy as that.

What it sounds like to me is that the tail volume is not quite right for the size/design of the rest of the airplane, so the tail is dropping when in the turn. You mentioned that it looks the same as a Cub, well, the fix for that problem with a Cub is to use more rudder right??? So, do the same with this airplane.

RE: Low tail in turn
 

I do use rudder in turns, even started cranking in more to see if it would help.  I found little change even with almost full throw on rudder.  That's when i concluded that some other aspect needed to be corrected.

KKKKFL

RE: Low tail in turn
 

Sometimes (high wing) planes exhibit a yaw away from the roll their ailerons are trying to provide. It results from the outside wing having more drag than the inside wing. It's caused by the inside wing having less drag than the outside wing.... chuckle...... yeah.......

One of the visual clues happens because the yaw can make it look to people on the ground like the nose is up and the tail is down.

Differential aileron is often the cure.

RE: Low tail in turn
 

Differential aileron is what you get when you rig your ailerons so their upward deflection of one is greater than the downward deflection of the other. It's most effective when the airfoil is a cambered one.

What happens is that downward deflection of an aileron on a cambered wing simply increases the camber. The movement basically alters the airfoil to have more camber in a somewhat gentle L/D progression. The lift increases gently as does the drag. On the other side of the wing......

The aileron moving up over on the other side of the wing starts to create a significantly different airfoil. As it begins to move, it somewhat radically turns that side of the wing into a reflex airfoil. It starts to lose lift. Less lift often results in less drag. That side of the wing has less drag and is held back less because of it. It moves forward as it moves down. Where would the nose go if that downgoing wing was moving forward? It'd move up. Where would the tail go? down....

Look that trainer over. Does it look like it'd do all that stuff? If its got a servo for each aileron, it's dead simple and easy to re-rig the servo arms and get differential.

RE: Low tail in turn
 

Thanks guys,
I have a little experience and there is differential plugged in..  almost 3 to 1 more up than down is programmed in.  I have seen the High wing types back in olden days especially seen with Clark "Y" airfoils.

Here we have a Trainer type, mid-wing, well powered, light wing loading and very nearly a symmetrical airfoil.  Rudder is used in turns, and more and more was cranked in as the day went on.  I'm just wondering if more down thrust or moving the CG back would make a change in the turning attitudes.


KKKKFL

RE: Low tail in turn
 

Interesting there is 3:1 differential in the ailerons. Great Planes Sport 60 is a low wing and definitely doesn't have a Clark Y.

I think the first thing I'd try would be to take that differential out. Years of experience with Tigers, Calmatos, and other very similar models would puzzle me greatly why anyone wanted differential in that type model. You most certainly have a mystery there.

RE: Low tail in turn
 

Musta confused some... will try again.   The plane is a mid wing WITH a semi symmetrical airfoil.  I started with some differential but(a little less than 2:1) increased it trying to make the roll rate better, which it now does....  roll rate is much better, but the plane has ALWAYS exhibited poor yaw performance hence I have to crank in lots more rudder than most.  Even when I get a decent bank and turn the back end is low....

I believe this is due to the motor being extended for better balance departing from the original design.  The spacers added by the PO push the engine out about 2 inches in front of where it should be located according to the plans.   When asked why, he said it was because the original location made the plane tail heavy and this minimized the lead needed to balance it correctly.  I think the long nose moment is responsible for poor rudder response, but doesn't explain the low tail position in turns.

KKKKFL

RE: Low tail in turn
 

The Great Planes Easy Sport is a shoulder wind second plane type.

Some aileron differential should do no harm, IMHO.

The AOA increases during turns, so the fuse should pitch up some.

If the incidence angle is incorrect (too positive), the tail-down effect will be more evident.

If what you see is yaw deviation, then rudder is the only way to coordinated the turn.

CG location has nothing to do with this problem: planes that fly and land in one piece are more or less nose heavy, but are never tail heavy. :)

You are correct, with the extended nose, there is more side surface aft the CG that is fighting the rudder in a coordinated the turn.

RE: Low tail in turn
 

By extending the nose you have added more lateral area ahead of the CG. What this has done is make the fin area inadequate to handle the aerodynamic balance in turns. My Seamaster 120 did exactly the same thing and it was almost impossible to steer through the corners. Mixing in a lot of rudder helped (80%) but it was still imprecise. The solution came from the addition of a pair of subfins beneath the stabilizer. Now it flies great. The total area was about 30 sq. " for the two fins.

RE: Low tail in turn
 

We're talking about the Great Planes EASY Sport?
http://www.greatplanes.com/airplanes/gpma1036a.jpg


Ultra Sport
http://www.greatplanes.com/airplanes/gpma0410.jpg


Super Sportster
http://www.greatplanes.com/airplanes/gpma0205-1a.jpg


or something else?
I'm not familiar with the great planes 'Sport 60' and just trying to make sure we're all on the same page :^)

RE: Low tail in turn
 

The original owner provided the plans this weekend.  The plans are for a Sport 40.  He changed the landing gear to Conventional, put a tail wheel on it and 3 half inch pine blocks that moved the engine forward of the designs original location.  I bolted in a SuperTigre .61 ABC in the
motor mount holes that were previously drilled for a ,40 something.

I removed the coat hanger wire that was used for control rods, Tossed away the plumbers nightmare Aileron hinge rod, added 4 servos to the wings for independant Flaps and ailerons.  Also tossed the 6 ounce tank in favor of a 10 ounce slanted tank.  Once the modifications were made, I checked the balance.  It's between 25 and 30% with a full tank.

This past weekend, I added full telemetry to it, and also added two washers beneath the rear mounting lugs to give it more downthrust.

The added downthrust seemed to help immensely.  I also bumped the rudder clevis in a hole on the control horn to get more throw.  These changes seemed to really work well.  There's still a little of "Low Tail" in a turn, but it is marginal compared to what it used to be.


Thanks guys... 

Will post a flight picture as soon as I get one.


KKKKFL