Airplane Doesn't Groove Inverted

[Motorman]

So I dialed in some down elevator with the flaps at neutral and it transformed level flight into a very steady thing of beauty.

Then I set neutral on the handle to get a good feel on insides and outsides and a smooth take off. I'm still working on the handle setting but it's close.

When I go to the inverted laps the problems start. The plane wants to float up so I have to feed up into it to keep it down and it's hunting and unsteady. It feels awkward to me to ride up when inverted so maybe that's it or, is this just the payoff to get great upright laps?

Thanks,
MM

 

[Brent Williams]

What handle?  

Are you dialing in handle neutral bias that is now manifesting itself in your inverted laps?

[Dan McEntee]

    If it's "a very steady thing of beauty" in upright level flight, it should be the same inverted. It ain't the airplane, it's you.  
     Type at you later,
      Dan McEntee

[Russell Shaffer]

I was also thinking that it's the pilot.  My planes all fly just fine in normal flight and hunt pretty bad in inverted.  Something about being upside down makes for uneven flying for me.  Anyone have suggestions, or should I just try flying a lot of inverted?

[Tim Wescott]

I was also thinking that it's the pilot.  My planes all fly just fine in normal flight and hunt pretty bad in inverted.  Something about being upside down makes for uneven flying for me.  Anyone have suggestions, or should I just try flying a lot of inverted?

Could be.  But...

Are you dialing in handle bias that is now manifesting itself in your inverted laps?

This is a real thing.  It's exactly what I was going to suggest.  If the airplane wants to fly at 12 feet and you're holding it at 5 (or if it wants to fly at -2 and you're holding it up), then it'll hunt.  You have to get it happy both upright and inverted, indepndently.  There's a happy place between the handle bias and the elevator bias, and possibly the CG, that leads to sweetness and light.

[Tim Wescott]

Nobody's said it but it bears mention: make sure that there's not a sticky spot in the control motion -- if that sticky spot happens to be at the perfect inverted flight setting then it'll hunt no matter what you do.  The DuBro pinned hinges tend to have flash on them that makes this happen; I work them over with a knife before I put the surfaces on.  It can also crop up in covering and painting, or be built into the rods & cranks & whatnot.

[Mark Scarborough]

see now I found the cure for inverted tracking in Salem, mine tracked the bottom of hte square perfectly,, well for half a lap

[Russell Shaffer]

Yeah, and mine tracked the bottom of the outside square the same way.  Good thing we didn't go to Madera.  I'm pretty sure my inverted hunting is due to my flying since ALL of my planes do it. 

[Motorman]

There's nothing wrong with the control system or my flying. It's some kind of trim problem.

The handle is a straight hard point handle, the only adjustment is to use different length line clips. I only took 4 flights and realized the problem on the last flight so tomorrow's another day.

I think I need to adjust it so I have to feed some down into it on take off. Take off seems to be a good indicator of the up/down bias for some reason. I think it's because I hold the handle where it feels neutral and then the plane either jumps off the ground or hugs the ground too close so it tells me where I'm naturally holding neutral.

I put on a clip to relax the down line a bit for the next flight.

MM

 

[Tim Wescott]

see now I found the cure for inverted tracking in Salem, mine tracked the bottom of hte square perfectly,, well for half a lap

Paul Walker hisself could not have flown that half lap more level.

[Steve Helmick]

Keep looking for a better neutral than what you have.  Steve

[Dan McEntee]

        If it is truly a "very steady thing of beauty" upright, it should be the same inverted. The airplane and it's aerodynamics don't know what the orientation is in level flight. If it locks in and flies level without you moving your hand, then it should do the same inverted. If it does move, you are moving your hand trying to find a comfortable position and your mind is racing "up is down and down is up" at the same time. Some mild panic sets in and you over control. I don't call it a "hunt." Hunting is really caused by the before mentioned sticky controls, or some other type of misalignment, and some times pointy leading edges. If it's you causing it it's called "pilot induced oscillation." People are always more nervous when flying inverted, especially in their early stages of leaning the pattern. You are in your early stages of learning  the pattern and trimming models, and if you ask the question here on the list, then you will have trouble determining the problem in real time. Your best bet is to have a genuine expert class flier fly the airplane and have him feel out the model in inverted flight while you watch. You have to come up with your own style of doing the maneuver that makes you feel comfortable so you can relax while flying that six laps. Some guys hold their hand like normal, some lay their hand over on it's side and everything in between. Laying your hand over on it's side can cause issues like you describe, especially if you can't "lead" the airplane properly to keep the up and down line tension the same. Easy to do when the handle is upright. You are probably flying like this when you fly inverted. And you are best to keep the control direction as "top control" and "bottom control." No matter what the orientation of the airplane, the top is always the top and bottom is always the bottom. You give the control movement in the direction you want the plane to go. I guaren-damn-tee you that is you were flying Dave Fitz's own Thundergazer in this manner, you would probably still get some "hunt" while flying inverted.  If you can not fly inverted correctly yet, then you will never trim a model into it. if it was that rock steady and solid, it would NEVER turn a corner!
     I'm Just Sayin',
   Dan McEntee

[Brett Buck]

There's nothing wrong with the control system or my flying. It's some kind of trim problem.

The handle is a straight hard point handle, the only adjustment is to use different length line clips. I only took 4 flights and realized the problem on the last flight so tomorrow's another day.

I think I need to adjust it so I have to feed some down into it on take off. Take off seems to be a good indicator of the up/down bias for some reason. I think it's because I hold the handle where it feels neutral and then the plane either jumps off the ground or hugs the ground too close so it tells me where I'm naturally holding neutral.

I put on a clip to relax the down line a bit for the next flight.

 

   If you put in down elevator and it smoothed out upright but made inverted less stable, perhaps you need to reduce the amount of down elevator. Note that the act of putting in down also changes neutral.

    Brett

[Paul Smith]

CL airplanes, when set up normally, are naturally self-correcting level and naturally unstable inverted.

The only way to reverse this is to fly in the down-is-up mode, as a few people do.

[Brett Buck]

CL airplanes, when set up normally, are naturally self-correcting level and naturally unstable inverted.

The only way to reverse this is to fly in the down-is-up mode, as a few people do.

    Brett

[Motorman]

I thought it might have to do with the stab being lower than the wing when upside down. If it's trimmed for down elevator at neutral flap then you have to give it up to keep it level which puts the flap down and gives it the lift to fly flat right?.

When inverted the down elevator lifts the nose to give it positive AOA with the flaps at neutral. If there's too much down built into the stab then you have to give it up elevator to keep it level and this gives you up flap. So, between the stab being lower, up flap and the AOA you need inverted the tail must get blanked out. lol my theory anyway.

MM

[Tim Wescott]

    Brett

See, Brett -- it's because you don't understand how CL airplanes work that you never, ever, make it into the top 5 at the Nats.

[Tim Wescott]

I thought it might have to do with the stab being lower than the wing when upside down. If it's trimmed for down elevator at neutral flap then you have to give it up to keep it level which puts the flap down and gives it the lift to fly flat right?.

When inverted the down elevator lifts the nose to give it positive AOA with the flaps at neutral. If there's too much down built into the stab then you have to give it up elevator to keep it level and this gives you up flap. So, between the stab being lower, up flap and the AOA you need inverted the tail must get blanked out. lol my theory anyway.

You should -- at least initially -- trim the airplane so that the fuselage is dead level in level flight both upright and inverted.  For each mode, this means that the flaps will be deflected toward the ground, and the elevator will be deflected in whatever direction it needs to be to keep the thing from rotating.  To achieve this you need to start by diddling the flap-elevator bias so that the fuselage is at the same angle with respect to the ground both upright and inverted.  When you get there, diddle the flap-elevator ratio until you achieve dead level.  Nose up in both attitudes means that you don't have enough flap.  Nose down means that you have too much flap.

But I don't think that this really touches on your problem.  I have several flapless stunters, and I've had others in the past, that fly like they're on rails both upright and inverted.  Being flapless, they fly nose-up ("up" meaning away from the ground, not in the direction of the canopy).  But they fly steadily without hunting.

The lesson from the flapless-flies-smoothly factoid is that you should be able to achieve smooth level flight both upright and inverted, even if your flap/elevator relationship is totally screwed up.  You either have some mysterious aerodynamic issue in play, you have some stickiness in your control system, you just haven't learned how to fly inverted (I've never flown with you, so I can't tell), or there is some other trim issue in play (probably having to do with some interplay between CG and handle neutral).

[Brett Buck]

See, Brett -- it's because you don't understand how CL airplanes work that you never, ever, make it into the top 5 at the Nats.

    I wasn't being a wise guy, I just don't understand what he was talking about.

     Brett

[Russell Shaffer]

Quick question for Brett - is your handle vertical when flying inverted?   

[Randy Cuberly]

If you fly with your hand turned sideways (like I do) it is problematic if you do not keep your hand aligned with the airplane when inverted.  With your hand sideways, if the airplane leads or falls behind your hand position it is automatically receiving control input by the shortening of one line compared to the other.  Not hard to figure out but often overlooked by many as it was for me until pointed out by a friend from Switzerland long ago.

I still fly with my hand sideways and have tried to change but to no avail...muscle memory is very strong for me.  By simply keeping my hand carefully aligned with the airplane during inverted flight the problem went away.

Randy Cuberly

[Brett Buck]

Quick question for Brett - is your handle vertical when flying inverted?  

   Of course!   But while holding it sideways causes some other interesting and bad side effects, I can't see how it makes it intrinsically unstable inverted.

     Brett

[Tim Wescott]

    I wasn't being a wise guy, I just don't understand what he was talking about.

I was the wise guy, poking fun at the whole thread.

[Joe Yau]

I think I need to adjust it so I have to feed some down into it on take off. Take off seems to be a good indicator of the up/down bias for some reason. I think it's because I hold the handle where it feels neutral and then the plane either jumps off the ground or hugs the ground too close so it tells me where I'm naturally holding neutral.

I put on a clip to relax the down line a bit for the next flight.

MM

This some times do works.    Even if the plane has absolutely no problem tracking inverted.. having the line length setting with slightly more down = shorter (1/16" or so) vs up at your handle neutral could effect it from locking on track.

 

[Larry Fernandez]

    I wasn't being a wise guy

     Brett
[/quote


That would be a first 😆

Larry, Buttafucco Stunt Team

[john e. holliday]

Really it is in the person on the handle end of the lines.  I have flown up right and inverted level laps with the neutral off one way or the other.

[Randy Cuberly]

   Of course!   But while holding it sideways causes some other interesting and bad side effects, I can't see how it makes it intrinsically unstable inverted.

     Brett

Brett,

I don't think it makes the airplane unstable, but it can make the input from the handle intrinsically unstable.  The airplane gets a little ahead of the handle and control input is automatically given (small amount yesbut enough to notice and make it necessary to correct for,,, this continues and becomes a cycle of input and correction!  Seems like an unstable condition even though it is not the airplane that is unstable it's a combination of unknown input to the controls and correction and then another cycle etc.  Turn your hand sideways and you can see it unless you carefully keep you hand aligned with the airplane.  Basically the same thing happens in most maneuvers if you don't carefully follow the airplane with the handle!

Randy Cuberly

[Steve Helmick]

A few years ago, I decided I needed to use a new set of lines on the same old airplane. Some fiddling with line clips later, I thought it was working out ok...except that I noticed that I tended to fly inverted with my hand/handle down around my waist. And I thought that odd and new.

My conclusion was that this was my subconscious attempt to get my inverted laps to a lower altitude. More clip fiddling later, it was fixed. The story doesn't answer the inverted groove question, but does show a bit about the effects of a maladjusted neutral, and I still think that might be the problem. I've also seen others flying with a bad neutral setting, and it was obvious to me that was the problem. Can you get somebody to watch your flying and look for that?

PTG is said to have spent many months changing clips before getting it right. Maybe years for me. I'm a slow learner. Steve

[Rick Bollinger]

What I am reading from Motormans orig post is that he added down elevator at flaps neutral. How did it fly before that change? Maybe too much down elevator.

[Brett Buck]

Brett,

I don't think it makes the airplane unstable, but it can make the input from the handle intrinsically unstable.  The airplane gets a little ahead of the handle and control input is automatically given (small amount yesbut enough to notice and make it necessary to correct for,,, this continues and becomes a cycle of input and correction!  Seems like an unstable condition even though it is not the airplane that is unstable it's a combination of unknown input to the controls and correction and then another cycle etc.  Turn your hand sideways and you can see it unless you carefully keep you hand aligned with the airplane.  Basically the same thing happens in most maneuvers if you don't carefully follow the airplane with the handle!

Randy Cuberly

  Yes, those are what I was referring to as interesting and bad side effects, but I don't think I would describe that as instability.

   Brett

[Dan McEntee]

  Yes, those are what I was referring to as interesting and bad side effects, but I don't think I would describe that as instability.

   Brett

   That is why I called it "pilot induced oscillation," because that's what it is. If a plane is flying true upright, it should fly true inverted. The aerodynamic forces in effect for the air frame while in upright flight are in effect while inverted also. I have never heard of anyone trimming a model to fly upright and then changing trims so it will fly inverted. Once you have a model to a certain level of trim, ANY CHANGE you make for it flying inverted will effect it's upright flight. Any control input that you think you put in to hold level flight, must also be put in to hold inverted level flight. Think about it! The model and the air it is flying through don't care if it's upright or inverted, nor do they know it!!! You just have to learn how to fly inverted, period.
    Type at you later,
     Dan McEntee
     

[Brett Buck]

   That is why I called it "pilot induced oscillation," because that's what it is. If a plane is flying true upright, it should fly true inverted. The aerodynamic forces in effect for the air frame while in upright flight are in effect while inverted also.
     

    I can see the possibility of PIO.

    But the aerodynamic and other forces are not the same upright and inverted. The usual aerodynamic layout is not symmetrical. And there is the pitch gyroscopic torque from the continuous yaw rate which is the same direction as the lift vector upright, and opposite the lift vector inverted. And in this case, the down-rigged elevator causes the flaps to be aligned differently and the camber (and thus the angle of attack) is different upright and inverted. This also causes the P-factor to be different upright and inverted.

     None of those are necessarily destabilizing, but it certainly isn't the same.

      Brett

[Bill Johnson]

   That is why I called it "pilot induced oscillation," because that's what it is. If a plane is flying true upright, it should fly true inverted. The aerodynamic forces in effect for the air frame while in upright flight are in effect while inverted also. I have never heard of anyone trimming a model to fly upright and then changing trims so it will fly inverted. Once you have a model to a certain level of trim, ANY CHANGE you make for it flying inverted will effect it's upright flight. Any control input that you think you put in to hold level flight, must also be put in to hold inverted level flight. Think about it! The model and the air it is flying through don't care if it's upright or inverted, nor do they know it!!! You just have to learn how to fly inverted, period.
    Type at you later,
     Dan McEntee
     

While not as knowledgeable as Brett, I would say your statement is true only if:
1) the wing and horizontal stab airfoils are truly symmetrical, and
2) the angle of incidence of the wing and horizontal stab are the same.

[Brett Buck]

While not as knowledgeable as Brett, I would say your statement is true only if:
1) the wing and horizontal stab airfoils are truly symmetrical, and
2) the angle of incidence of the wing and horizontal stab are the same.

  No, that is not required (although that is probably true to some extent). The fact that the airplane itself is also asymmetrical in terms of layout is fundamental to why upright and inverted are not the same.

     Brett