what's keepin' me busy

Nice work! Where is the other servo going to be?

In the middle of the wing. It's going to be 3ch - ailerons, elevator, throttle.

Looking good Dirk
Careful of the engine though it's likey to have the C.E.F. Villagers
reaching for their pitch forks......

John Goddard wrote:Looking good Dirk
Careful of the engine though it's likey to have the C.E.F. Villagers
reaching for their pitch forks......

They'd be after me first, all my planes and helicopters are electric too

John,

That's not the engine. It's obviously a cooling fan that mounts behind the engine. The engine will go in front of the fan. What else could it possibly be. Besides, my pitchfork is at the shop being sharpened and polished so it can't possibly be anything else.

Bob

OOPS, I forgot I fly electrics too. That's why I don't keep a pitchfork around.

You guys are killing me

It turned out that the non-foam flyer became a non-flyer after having been rebuilt.
I gave it a foam wing that is 100% identical to the original foam-flyer. All the sizes are the same as well, within a small margin of error.

All the difference is I lenghtened the model's nose slightly (about one inch) to make balancing easier, and I added the pilot's cabin, so now the wing is about 1.5 inches higher than it was in the foam-flyer.

Apparently, due to these changes the model became totally unstable and is falling into a tightening left spiral as soon as I give any up elevator. I tried to experiment with the size of the rudder, aileron trim, right hand thrust, CG to no avail. I made sure no part of the plane is warped. I even rebuilt the whole wing from scratch taking good care that it is symmetrical. After all that failed, I am desperate and can only hope for Your help.

dirk gently wrote:It turned out that the non-foam flyer became a non-flyer after having been rebuilt.
I gave it a foam wing that is 100% identical to the original foam-flyer. All the sizes are the same as well, within a small margin of error.

All the difference is I lenghtened the model's nose slightly (about one inch) to make balancing easier, and I added the pilot's cabin, so now the wing is about 1.5 inches higher than it was in the foam-flyer.

Apparently, due to these changes the model became totally unstable and is falling into a tightening left spiral as soon as I give any up elevator. I tried to experiment with the size of the rudder, aileron trim, right hand thrust, CG to no avail. I made sure no part of the plane is warped. I even rebuilt the whole wing from scratch taking good care that it is symmetrical. After all that failed, I am desperate and can only hope for Your help.

I am sure it was frustrating for you but, that was a funny video!!!!!


Is the rudder true? When sighting down the leading or trailing edge of the wing is it straight? How about the elevator?

Good thing is it pulls left and down every time. It honestly looks like a trim issue. That and there is no Cox engine. Best fix the latter first.

Ron

What if you reversed the prop direction, would the torque help straighten it out?

Have you tried throwing it out there and letting it glide? If it glides straight and true then your motor/prop is producing more torque than your plane is set up to counter act.

RknRusty wrote:What if you reversed the prop direction, would the torque help straighten it out?

I don't have a left hand prop, do you think just reversing a regular prop would do?

fit90 -> I guess the motor is not producing too much torque, as I am using the same equipment as in the previous version, which was flying just fine. I did try throwing it into the air with the engine dead, but I guess it's just a bit to heavy for that, sank too fast, couldn't tell if it's gliding corectly or not.

dirk gently wrote:

RknRusty wrote:What if you reversed the prop direction, would the torque help straighten it out?

I don't have a left hand prop, do you think just reversing a regular prop would do?

fit90 -> I guess the motor is not producing too much torque, as I am using the same equipment as in the previous version, which was flying just fine. I did try throwing it into the air with the engine dead, but I guess it's just a bit to heavy for that, sank too fast, couldn't tell if it's gliding corectly or not.

also did you check for wing balance. are the wings of equal weight when on the plane. the best way to check is to hold the plane fore and aft, nose and tail and see if the plane is heavy on one wing. try to balance the plane upside down as usually the wings have dihedral and are heavier towards the wingtips. if one wing is heavier try tapeing a penny or small weight to the opposite wingtip to counterbalance. with all our modern glues and lightweight woods any tiny bit of extra weight on one side can throw the plane into a turn toward the heavy side. been there done that.
p.s. reversing a RH, or LH, prop does not reverse the pitch, just the leading edge of the prop. happydad

Same size vertical stab as foamie? Did foamie have a rudder, in addition? Wonder if combination longer nose and what looks like clear plastic on front of the cabin is making it unstable in yaw, with motor torque consistently spinning it left. Maybe a larger fin, existing one looks small (by my calibrated eyeball) in relation to rest of plane...

Try a smaller prop to lessen the torque roll. Be sure the wing is not skewed with the right wing ahead of the left. Be sure you don't have left thrust on the motor.

What I think it looks like is the plane being launched at a very low flying speed, slowing then stall/spinning. You might want to go with a shorter prop with more pitch, another cell on the battery or some combination of these. A little more right thrust for the motor might also lessen the effects of torque.

Good luck with it. It is a good looking plane.

Bob

When you lengthened the nose you increased the torquing effect of the motor (force X lever arm). You might also want to try shortening the nose back to its original dimensions.

Bob

Also, when you added the cabin you took the wign out of the slip stream. This means that the empannage gets the full effect of the slip stream. If you lower the wing back into the prop wash it might help to minimize the slipstream effect on the tail feathers.

You've got your work cut out for you.
You're flying a tail heavy airplane with extreme dihedral and not enough rudder to control the yaw. That's three strikes.

That was the easy part...

Look at your video and stop it at .17 - Look at that left aileron. See how it's deflected downward? That is creating an enormous amount of drag because you have a flat bottomed airfoil. The more you push that left aileron down, the more drag it creates. As you input more deflection to bring that wing back up, the assymetrical drag actually makes it worse. This is why planes with flat bottom wings and lots of dihedral are usually steered with rudder input. (The typical 3 channel plane)

Anyways...
So now you are tail heavy, stalling, and as the left side of the wing has more drag, the plane starts to turn to the left. The torque of the motor also tries to roll the plane to the left. The plane stops flying and spins into the ground like a leaf falling from a tree.

The fix requires first that the plane be balanced and the rudder enlarged. Those two things will make it fly. As long as the wing has dihedral however, it will not "steer" properly unless the rudder has a servo on it. If you remove the dihedral from the wing (make it flat), you will be able to "bank and yank" the plane through a turn using ailerons and elevator.

Balancing the plane is simple:
With the motor off and the controls set at neutral, you can toss the plane straight ahead at shoulder height and it should fly level and flat until it reaches the ground. If it pitches up, it is tail heavy. Add weight to the nose and try it again.
Definitely double the rudder area.
After the plane is balanced, if you are dead set on trying it with the ailerons setup that you have now you should reduce the total throws to about 1/4" up and 1/4" down. When neutral, the bottom of your aileron should be flat with the bottom of the wing.

Ditto, what L. Flyer just posted, test glide first. Make sure engine is trimmed down and right a couple degrees. It does look a little under powered and the turn is making it stall? it's kind of hard to trouble shoot it by video, but what L. Flyer and fit90 posted should get you going in the right direction, you might try rudder only.

Thank you all for input.
I just wanted to say first that the plane is not tail heavy at all. I tried balancing it to get move the CG forward or back and it made no difference.
I also doubt the rudder is too small, it's even a tad bigger than it was on the foamie. I tried to make it smaller, as I was suspecting spiral instability, but it made no difference.

Underpowered, yes, that might be the case. Theoretically, the engine has over 400g of thrust, which should be more than enough for a 290g plane. But I don't think it's actually giving that much thrust, I'll have to check it out.

Slipstream of the wing disturbing the flow over the stab? I was afraid someone will say that. Now I will have to cut out the cabin to check if it helps, and that'll make the plane not look as good anymore. But if it will make it fly, that's fine.

BTW, the reason I'm having the left aileron down, is because i was trying to counteract the left turn. It wasn't like that from the start. But you guys are probably right, it only makes things worse. Come to think of it, I guess it effectivelu increases the angle of attack of the left wing, making it stall sooner.

All in all, you gave me a lot to think about, thanks a lot. I will try the gliding as well to see if the problem is caused by engine torque.

For everyone's reference, this is how the old one used to fly:

The new one has the same weight, hardware, all the sizes, angles and airfoils are the same. I just changed the shape of the fin and elevator slightly.

Please let us know how it turns out for you. Small planes like these are a lot of fun.

Up until recently, I thought I have a basic understanding of aerodynamics. I don't anymore.

Following your advice, I cut off the pilot's cabin, lowering the wing (still, the wing was a bit higher than in the old foamie, where the top of the wing was flush with the top of the fuselage). And there was improvement! The plane flew again, although uncontrollably. I mean, the elevator worked as expected, but the ailerons did not have any effect at all, even though I could clearly see them moving while the model was airborne. It was just doing wide circles, this time, strangley, it was in a RIGHT turn (perhaps I overdid the right-hand-thrust of the engine).

It actually managed to drift quite a distance away with the breeze, before I relized, i won't be able to fly it back! I promptly shut down the engine, and commenced a search in chest-high grass. I wouldn't be abe to find it if, but I had the idea to remotely reset the rpm controller on the model. The controller beeps when it's reset, and using that beep I was eventually abpe to find the plane.

I also tried flying with the engine dead. The model glides gracefully, yet uncontrollably, I actually think giving down aileron makes the wing stall, so there is no lift gain on that wing.

I slept on it, and I no longer think the wing is stalling. What I now believe is happening, is the drag from the aileron-down wing counteracts the lift increase. I noticed that both ailerons face a bit down when the controls are in neutral position, so that might be it.
Also, I don't think the right turns are caused by the engine tilt anymore, as I realized theat the plane also turns where gliding. There must be a bit of assymetry somwhere, perhaps I glued the fin a tiny bit off when I repaired it after the crashes.