I don't know why......

When I turn my new model (Excaliber) inverted the thing wants to hunt !! Upright it is like it's on rails.
Has anybody got suggestions on what to do ??
Thanks for the help......

>
> When I turn my new model (Excaliber) inverted the thing
>wants to hunt !! Upright it is like it's on rails.
> Has anybody got suggestions on what to do ??
> Thanks for the help......

Check the alignment of flaps to elevators. Is the engine thrust line square with the wing? Is the stabilizer absolutely square with the thrust line? Are the elevators at neutral when the flaps are at neutral?

That would be the first thing I would check. If everything is at neutral and properly aligned, then maybe try drooping the elevators just slightly when the flpas are at neutral and see what happens. If that helps, you are in business. If it hurts, go the other way. Just remember that if the elevators are slightly up when the flaps are at neutral it will kill your glide.

Gil, This is one of the most common trim problems with any plane. How to fix it?
Always put some downthrust and side thrust in the engine. The only time this is not needed is with counter-rotating twins.
Set the flaps at neutral, then bias the elevator down a minimum amount (1/32") for starters.
Set your handle as neutral as possible meaning dead vertical holding it and the line spacing equal up and down.
Check for wings level and in line with the lines.
You are going to hear from some that engine offset is not necessarily needed and/or no down elevator trim is needed. Nearly always not true.
Try these items, you will be shocked and amazed at how much better the plane will fly. RJ

>Gil, This is one of the most common trim problems with any
>plane. How to fix it?
>Always put some downthrust and side thrust in the engine.
>The only time this is not needed is with counter-rotating
>twins.
>Set the flaps at neutral, then bias the elevator down a
>minimum amount (1/32") for starters.
> Set your handle as neutral as possible meaning dead
>vertical holding it and the line spacing equal up and down.
>Check for wings level and in line with the lines.
>You are going to hear from some that engine offset is not
>necessarily needed and/or no down elevator trim is needed.
>Nearly always not true.
>Try these items, you will be shocked and amazed at how much
>better the plane will fly. RJ

Bob, could you explain the reason you recommend down thrust and side thrust? Most people will take this far too literally. I have seen some planes with half an inch or more side thrust built in. Way too much. I am one who doesn't recommend any side thrust simply because we already have it built in by the fact that we are always turning left. I suggest 0 - 0, but if you have to err, err by giving it half a degree out. You don't want to go overboard because you just add other trim problems.

As to downthrust, most designs have the thrust line about an inch above the wing center line. Not significant enough to bother with--especially with the tail another inch above that. I always suggest starting everything at 0 - 0. The drooping of the elevators might help in some cases, but that needs to be tried on a case to case basis and only if a problem exists. Al mentions dong that, but his planes generally have the thrust line and stabilizer line farther above the wing center. And David mentioned that with a couple of his planes tilting the front of the stabilizer up just slightly helped. But his was hunting upright where the case here is inverted.

Matt has only had one plane that exhibited any hunting characteristics and that was cured on the next version by changing the airfoil. Everything else remained at 0-0-0.

Alfa & Leonard,
I have everything EXCEPT the 1/32" down elevator.. That sure is next...
Bob I remember you & I talking at the 1999 Nats about this very thing with down thrust and side thrust. I came home and tried it and the models flew better, so I'm gonna try the down elev.....

Thanks to both of you fellows......

I don't understand how a CL model can hunt inverted but not upright. Seems to me if it's hard to fly level inverted it's going to have the same problem upright and visa versa. Are you sure you don't have a simple handle adjustment issue..

Of course most of us are much better at flying upright so might just be able to compensate better for some tendency to climb or dive. I don't think I would just blindly crank in down elevator until I was sure the airplane needed it. Does it have a tendency to climb upright if you relax your wrist.. or maybe even dive.. If it tends to climb then cranking in down elevator might help but if it's actually trying to dive your just going to make it worse.

Hi Gil and Leonard and Bob,
I know all of you have seen some of my last posts so let me apologize up front if I seemed a little ornery or cranky. Just my short attention span nature.

OK, here is the whys' and wherefores. First, I do understand that we fly in a circle. Nearly all of our problems are caused by this.
The very first trim item to be addressed is level flite. Let's talk real planes first. Almost always all prop planes are trimmed for level flite at cruise speed and max weight. This means hands off flite for a reasonable amount of time before being re-trimmed due to less fuel and crew pit stops. Look at any single engine prop driven plane with a clockwise prop rotation as seen from the pilots view. Three things become casual to the most obvious observer, down and right thrust in the engine and vertical stab offset for right trim. Naturally these are all variable on different aircraft. Anyone with power free flite experience knows exactly how this works.
Our models are no different, just smaller. A model with 0-0-0 setup will always turn left and climb. Period. Since this is an actual fact just putting lines on a model doesn't fix this problem. We need to set it up for cruise speed so as to have a neutral starting point which goes back to down and right thrust and down trim on the elevator. You allude to Als' models and you are correct. The farther away the engine centerline is from the chordline the worse the effect. Look at any scale 3 view of a P51 and you can easily see the down and right thrust built in and also the vertical fin offset. I have used positive offset on my stabs for years instead of using down elevator. Either way will work but the fillets won't line up with the elevator in the latter state.
As for handle bias, without some help most people hold their handle incorrectly, meaning it is not in the vertical position with controls in neutral. Also the line spacing at the handle should start out equal. This is no different than learning the correct golf swing or how to hold and use a tennis racquet.
Let's assume you have done all the above. The model will now be very close to a zero trim condition such that all the rest of the fine tuning will actually accomplish something. This is the zero starting point for final trim. Anyone remember that R/C plane called the Eyeball? Didn't fly worth a darn. Set up correctly was an OK plane.
Now as to the hunting issue, either up or down or both. First we need to define what we mean by "hunting." Is the model sensitive or does it want to wander up and down slowly? The answer to the first is it is tailheavy, the second is nose heavy. Once these are taken care of we can then work on making the model "track" both inverted and upright. Almost always this is due to an alignment problem, hopefully flaps and elevator, not wing and stab. Using the wing chord as our zero or ref point, about 1/32" positive stab incidence and one degree down and right in the engine should appear. If not, make it so. Next, set the flaps neutral and the elevator neutral. This is your starting point. If you need down pressure or input at the handle when inverted, dial in some down elevator AT THE MODEL, not the handle. Just a little at a time. Usually takes care of it. The reverse is also true.
Some of you may say you have been flying for years holding the handle a certain way. I couldn't agree more. You want to get better and win more? Practice with a coach and use the right trimming methods. Trust me, all the above will work without exception. There are many more trimming hints so maybe later I'll list them but the above are certainly the very minimum to make a model fly well. Regards, RJ

>I don't understand how a CL model can hunt inverted but not
>upright. Seems to me if it's hard to fly level inverted it's
>going to have the same problem upright and visa versa. Are
>you sure you don't have a simple handle adjustment issue..
>

It's a common knowledge around here that CL planes are naturally more stable when the "UP" line is on the top of the handle. In this config, when the plane gets a little high, it self-corrects. In the inverted mode, occilation makes itself worse.

Two good flyers that I know fly with the down line on top and are therefore able to fly inverted better than upright.

If you set up a CL model to fly off a stationary pylon, you need to put the UP line on top. It will then seek an altitude and fly perfectly level.

If you do the opposite, it will crash within a lap. Like wise, you can relax and fly a plane level. It takes effort to fly inverted.

>Matt has only had one plane that exhibited any hunting
>characteristics and that was cured on the next version by
>changing the airfoil. Everything else remained at 0-0-0. Leonard.

Leonard (or Matt),
That's interesting! Would you like to tell us what change you made to the airfoil?

Thanks,
Kim Mortimore

>
>>Matt has only had one plane that exhibited any hunting
>>characteristics and that was cured on the next version by
>>changing the airfoil. Everything else remained at 0-0-0. Leonard.
>
>Leonard (or Matt),
>That's interesting! Would you like to tell us what change
>you made to the airfoil?
>
>Thanks,
>Kim Mortimore

Just went back to an earlier airfoil we were using that was a little thicker and a little blunter at the front. The planes using that airfoil seemed to track better.