Hi guys.............I´ve been flying my Funtana 90/OS 120 combo for about 7 month now and after a very long and careful trimming period the tendency to right roll when pulling hard is still there. Have anybody experience the same??.If so, what did you do to solve/reduce this tendency??
Thanks

Marcos

Did you balance the plane laterally? (ie add weight to the left wingtip as needed)

I held the plane using string from the rudder post and another string around the bulkhead at the front with the canopy off. The front string was carfully attached to the frame at the center. Then I put about 1/2 oz of lead in the left wingtip (remove covering, glue in place with CA, light glass cloth).

Hi Marcos:
Yes, the Funtana 90 pulls hard to the right when you pull hard up.
Personally, I feel it is because of the P factor and if you sit the airplane on a bench and run the engine up, you will notice that the prop blast will press on the right side of the rudder and vertical fin. Now put your hand on the left side and you will notice almost no airflow compared to the right side. This is the twisting action from the propellor and the air comes off the left side of the prop, down and under and around to the right side.
Apparently the designer had this problem as well and that is why they intalled those wedge shaped sections to the back of the wing at the root. We've tried everything and so far, have found no cure. I've tested three Funtana 90's and they all do the same thing.
We even tried a balsa ventral fin in front of the vertical stab and it just made it worse.
Let us know if you come up with a solution.

3dbob

Hi everyone.......I don´t think is a matter of lateral balance as the plane have the same tendency when you pull hard up from a level flight and when you pull up hard from a dive. In the first case the plane is pulling up into an inverted posture when it start rolling right; in that case the left wing appears to be heavier than the right one. But when pulling from a dive into a level flight the same right rolling tendency implies that the right wing is heavier. In any case I´ll double check the lateral balance as I have made some changes since I first laterally balanced the plane.
The puzzling thing is that I have exactly the same tendency in a old Uproar 60/OS 91 2T that I´ve been using to practice the more challenging maneuvers before attempting them in the Funtana
Thanks

Marcos

Marcos I don't think lateral balance has anything to do with it at all. As I mentioned, it happens to ALL Funtana 90's. They can't all have heavy right wings.
Do that test I mentioned and see what you find out.
Sometimes aircraft designs end up with a peculiarity such as this, the right combination of thrust line, moments, wing area, P factor and other factors combine to form a built-in problem that cannot be overcome. In full scale aircraft and before computerized design assistance, many of our civil aircraft had peculiarities that were built in and pilots had to be aware of them.
Although a lot of fun to fly, the Funtana 90 does have it's faults.

3dbob

I would wager that MOST Funtanas DO have "heavy right sides" (not necessarily the wings) if they have side mounted motors. In a side mounted motor with the cylinder head sticking out the right side of the fuse, the right side will be heavier unless steps are taken to balance the weight of the offset motor. A pattern flyer will always laterally balance his plane after the installation is complete to avoid problems like these.

But it is interesting that Marcos said it rolls right even from inverted pullouts, which negates my suggestion anyway (because if the right side were heavy, it should roll left when the pullout is made (this should be a "push" or down elevator to climb out from inverted).

Note, "pulls" on the elevator (up elevator) will cause right roll with a right heavy plane always, regardless of attitude. I assume that's what Marcos means when he said sometimes the left side is heavy, is because in the first case he pulls "up elevator" and the second case (left heavy) he's actually pushing "down elevator." The attitude of the plane has nothing to do with this phenomena -- only the G forces induced by the elevator.

I do agree that they are fun to fly though. Once I spent the time to mix out (nearly all) of the bad habits, it flys as well as it looks.

One thing not caught on this is possibly a differential in elevator halves. You will want to rotate the two elevator servos so the rotational axis is as close to each other as possible. This will make the control arm lengths as close as possible. Then pull full up and full down elevator and make sure the elevators are moving exactly the same distance throughout the travel. If you are using a Y-harness it will be incredible difficult to mix this out so I suggest using ch- 6/7 and mix them in the radio. But the difference in servo position and control linkage length will naturally add differential in the two surfaces.

If you look at the Showtime 4-D Mike McConville addressed this by having the two elevator servos sit exactly opposite from each other so the linkage lengths would be exactly the same. By design you cannot get the elevator servos exactly the same distance in the Funtana but you should be able to dial it out pretty closely.

Good luck

JP

I have had two funtana 90's and never noticed this. I never had any problems and have done full power parachutes, I'm sure I would have noticed then. I would check your linkage and make sure both elevator halfs are moving equally.

Lee

Oh, good point! I forgot it took me a while to address that with a mixing curve that was good for 3D throws.

Also, nobody mentioned this, but not sealing the aileron hinge gaps might also be an issue. The manual does cover that.

Two of our Funtanas have gizmo's (whatchamacallits) that equalize elevator throw and direction and so far, have not noticed any unequal elevator movements.

Ordinarily, torgue would cause the aircraft to roll to the left, not the right.
The roll to the right is rather extreme and not likely the result of a side mounted engine because it is so extreme.
Hey guys, just run the engine up on the ground and feel the air flow over the right side of the vertical fin/rudder and compare it to the left side. It is very easy to feel with a bare hand.
Try it and then let everyone know what you found out.
The problem only seems to occur when you pull really quick likie for a wall.

3dbob

3dbob

Hi guys..............I agree with 3dbob, it is not a matter of uneven elevator movement. First thing I did when first notice this tendency was to check differential elev. movement. And yes there was a very small difference that was corrected with no results.
I think that for such a dramatic rolling tendency there should be a measurable differential movement which is not the case....I also checked for deformation in elev/push rod/servo set using a 5 oz weight at max elev deflection. Both halves moved down exactly the same small amount under this load and no deformation, twisting or bending in elev/push rod/servo set was observed.
I think that the problem is elsewhere, and with your opinions and some testing we´ll get the solution.

Thanks

Marcos

No offense but I think you just have a bad plane or are missing something. Like I said I have had two and also flown others at the field and never noticed this. The only Funtana I ever noticed a problem with was the Funtana 40 which everyone has heard about the tip stalls with that plane. Even with the right setup with the 40 you could almost completely eliminate the problem. I didn't check before writing this but if you havn't posted to mike about this in the pilot forum you should, maybe he can answer this better. Again I have never noticed any roll tendancy with this plane. Have you seen Kyle's video's of this plane, I wish he would chime in here I'm interested if he ever had any problems like this.
Lee

This is a very interesting question of aerodynamics. If you include my Funtana 90, there are four of them flying in our area, three in our club, and I can tell you that they all roll to the right when you pull hard as in a wall. None of them are free it.

If you will give it that test I mentioned earlier, I think you will find the source of the problem.
Plus, note that the designers had to add that wedge to the trailing edge of the fuse at the root.
Why else would anyone install a wedge like that?????
The prop blast is curling under the wing and fuselage and hitting the vertical fin and when you suddenly pull hard, it becomes noticable.
We need a wind tunnel or a computer simulation.

3dbob

The F40 and the F90 both do it. Not to mention dozens of other models. A lot of it is in the setup; however, the thumbs (or thumb and forefinger..) are what ultimately control it. It's all about finesse, really. Provided your CG, throws, lateral balance, wing loading, etc.. are all correct, if it still snaps/rolls out, you've used too much elevator throw the wrong time. Rarely do I need all 50+ degrees of elevator throw I've got in my Funtana. If I use it at the wrong time, it will drop a wing. You don't need full slamming 3D rates to do a nice crisp wall depending on airspeed, attitude, etc.. Jamming the elevator at full deflection for every "3D" move is not needed and will lead to exactly what you're experiencing.

mxcop114 brings up a good point and good example. If you haven't seen Kyle's F40 and/or F90 videos - watch them. That's the epitome of control. There's nothing magical at all about his setups and you don't see him fighting tip stalls.

Wing loading has A LOT to do with it. Case in point, my buddy's F40 is about a lb ligher than mine and you have to force it drop a wing. It will still do it, but you have to be pretty deliberate about it. Mine is a bit more 'snappy', but that's the way I like it.

My .02

Abram

I always thought it was mostly for looks. That's what makes a Funtana "A Funtana".

It also stops you from being able to get a set of wing bags that fit, and needing to take extra care in storage and transport.

I don't buy any magic aerodynamic hocus pocus going on here. Besides, nobody said anything about what engines and motors everyone's running. That's got to affect the air turbulence patterns your'e talking about.

If mine does roll to the right in walls and hard pull ups, it's so minor that I just roll it opposite without thinking about it.

I'll throw my hat in the ring. Here's a scenario:

In a 3D "wall" with the strong pitch up from level to vertical (90 deg
pitch up in ~.1 sec), there's a very large pitch rate. On the
Funtana90 with a big prop, this large pitch up causes the prop to
produce a gyroscopic force that yaws the airplane to the right. Since
the airplane at this instant is seeing a very high angle of attack,
it's in the "post-stall" regime. But with the strong yaw, the left
wing is not as far into post stall as the right wing. In other words,
the right wing is seeing a higher post-stall angle of attack. This
setup in right/left wing aero is somewhat similar to the entry into a
snap roll, and that's what I think is happening -- a slight snap roll
(~1/8 roll) to the right.

I'll emphasize that I think this sequence only occurs in a very rapid
pitch-up with, say, a 50-deg of elevator deflection on a 50%+ elevator
control surface like the Funtana90 has. This is the kind of move that
can nearly blow off wings. Also, none of this works unless the
gyroscopic force is high, which requires a big prop, high RPM and also
a high-speed entry to get the high pitch rate. So all of this is a
pretty extreme maneuver and airplane setup.

Michael

Are you the airfoil designer Selig????

OK, now plug in the fact that the left side of the vertical fin is getting more airflow than the left side when you run the engine up on a bench. What effect, if any, do you see here?
The airflow is obviously twisting around and landing on the vertical fin. I would assume the same airflow would exist during flight but is swept away except when you come to a wall.
Is the gryoscopic effect the same as torque? If so, then the model should turn left instead of right.
And, I would have to state that the twist occurs at small elevator deflections and not just at high deflections. It does, however, have to be sudden as used in a wall.
I have found that the problem can be eliminated with a cleaner entry into the wall but it is still a bewildering aerodynamic effect and unless you come to a complete stop, you are not in a wall, just a steep climb. That's where the wall name comes from. Slam!
Your thoughts on the matter are most welcome.

3dbob

Hey, wait a second, why are you guys talking about prop blast and high RPM when you do WALLS [sm=confused.gif]

When I do a wall, I go from high throttle inlevel flight, then cut the throttle and just yank the plane up and then finish with a TR, harrier or something else. The best walls IMO don't rise that much. The nose just pitches up (in heart attack fashion) and all the momentum just goes noplace.

Maybe I'm doing them wrong, but how do you do them? I thought we were just talking about the F90 wing and trim affects when pulling up hard?

Good points guys,

but don't confuse torque, spiral slipstream & right thrust, p-factor and gyroscopic precession! This are all different effects that a rotating propeller produce, and they are a bad thing if we want do to straight manouvers... vice-versa, they helps during snaps and lomcevacks!

First of all, we must watch carefully if the induced behaviour is a roll or a YAW. Also, Marcos it is not clear to me if you do the pulling hard. To understand where is the problem you HAVE TO pull with throttle idle: this is a way of throwing away all the undesired behaviours listed above. The worst situation is at low speed - full throttle: here you can't almost have a straight pull! Deviatios will certainly occur, even if of minor entity. Sooooooooooo.... the better situation is no throttle and full speed. Perform the pull from a vertical dive. If you still have this behaviour with the plane trimmed for straight flyght, you may have some twisted surface .

A word about lateral balance. It has little effect to static balance the plane; it must be checked in flight. This is a suggestion by a top pilot (not me, obvoiusly !

How heavy is the os 120 compared to say a Saito 100 or ys 1.10. I wonder if your a little too heavy with that engine, I have flown them with the above two mentioned engines and not noticed a wing drop. Just a thought because I flew a Funtana 40 with a 100 and it dropped a wing like crazy, but with the saito 72 or 82 it didn't drop as bad. The perfect match for this plane is a ys 1.10 in my opnion. All I can say is with my plane I can fly level a full power, cut the trhottle right in frnot of me a cuople feet off the ground and pull full up into a wall that should rip the wings off and I havn't noticed any rolling out problems.

I forgot one important thing, as mxcop suggest: CG.

Perhaps the roll that you speak about is just a wing stall. To see if this is the case, you might move the CG a bit aft.

We've been flying them with all sorts of engines on up to a Saito 150. I don't think the engine would make much difference. They all seem to do that flop regardless of engine.

mxcop, I don't really remember trying it by cutting the throttle with lots of speed on the aircraft and don't know if anyone else did either.
This is something we will have to try. But, it's very cold here in the mountains and we may not fly until the weather calms down.

3dbob

I have two Funtana 90's and they both have the problem. I believe the source of the problem is precession. The propellor is acting as a large gyroscope rotating clockwise ,when viewed from the rear. When the aircraft is violently pulled up, as in a wall, precession acts by producing a force 90 degrees to the applied force, ie: the applied force is at the bottom of the arc so moves through 90 degrees to apply a force to the 9 o'clock position, when viewed from the rear, yawing the aircraft to the right. With the left wing now moving further, and therefore faster, than the right wing the aircraft also now rolls to the right.
Other than anticipating it with opposite rudder, there is not much you can do.

John

Ok guys I give up. I'm over this topic and all I can say is I hope you can figure out the problem. Hopefully it isn't bad enough to ruin your enjoyment of flying the plane. There is no perfect plane out there, they all require some kind of extra imput at certain times. Maybe I'm just use to flying the plane soo much that I don't even realize it. Never the less I love my Funtana 90's and don't think you can get much of a better plane for the price that flies soo well.
Lee

Reading along and taking all of this together: This problem is not
specific to the Funtana, and frankly it's not really a problem. It
happens on a lot of airplanes when pulling hard and pitching up
vertically into a "wall". If the entry into a wall is smooth (not
pulling so quickly with up elevator) it does not happen at all.

So I'm pretty sure about what I wrote before that the gyroscopic force
(precession as mentioned above) causes a right yaw. If the airplane is
pushed into the stall region for just a moment, then a slight right
snap roll (1/8th roll or a bit more) will happen. It makes the wall
look a bit sloppy. If, however, the elevator pull is less aggressive,
then the airplane does not get into the stall region and the snap
thing does not happen. Instead the airplane points straight up
without the wobble.

I think most people do walls at near full speed and drop back on RPM
just before going into the wall. Whether it's full throttle or not,
the prop is still spinning so the gyroscopic force is still there.
Also, if the airplane gets into the post-stall area, this stuff shows
up (independent of the entry speed).

A couple of more things: Yes, there's prop swirl that hits the left
side of the rudder. This produces a left yaw. There's also P-factor
which causes a left yaw in a pull up. But I'm thinking the gyroscopic
force is winning the war, and then some interesting post-stall aero
happens per above.

Some ideas for experimentation:

- Do a wall more smoothly, less elevator. Problem goes away because
the plane does not go into post stall.

- Do a wall coming down the vertical line with the engine killed.
(what's this an "elevator" or "parachute" in 3D jargon?). Problem
goes away because there's no gyroscopic force from the stopped prop.

I've seen this in real life, thought about it before, and this is my
thinking on it so far. Caveat: My thinking is subject to change.

Michael