Hunting

Jim

First and foremost hunting IS NOT a feature of the aircraft design, at least to first approximation.

The fix depends on the cause. The two most likely causes are control binding/slop and misalignment.

I assume since there are ball links, there's no slop. Nonetheless, hold the elevator in place and try moving the leadouts. If the leadouts move to any consequential degree, that's a likely problem.

Then try moving the controls to see if there is drag. Almost any drag will cause a hunt. Try it with both light and heavy tension on the leadouts.

Check the alignments as well. The engine, wing, and tail ought to be at 0 degrees. The engine can have slight downthrust, but no upthrust. The tail can have very slight built-in "down" elevator (positive incidence) but no up at all.

Severe yaw angles can also cause hunting. Make sure you have only the tiniest bit of rudder offset, and the leadouts are about 3/4"-1" behind the CG. The CG should be at 15% of the mean chord, which is about 1.25-1.375 behind the LE. More noseweight will not improve the situation, that's an old wive's tale. Check the yaw angle in flight. First make sure that the wheels are aligned with the wing. Then in flight, see if the wheels are lined up, or at most half a wheel width of the outboard wheel behind the inboard wheel.

There is a remote possibility that there is a flexibility problem. I don't know how to diagnose this without seeing the airplane.

I strongly recommend that you find some experienced stunt flier and let them take a look.

Brett

Nose heavy planes NEVER hunt, no matter how poor the rest of the setup. Tail heavy planes ALWAYS hunt, no matter how well the rest of the variables are set.

Tape a big glob of lead as near the front of the nose as you can. Try flying again, and whittle the lead back on successive flights. When you get close, use Brett's tips.

That is, start real nose-heavy, solve the problems as Brett suggested, then you have a flyer.

Moving the CG forward rarely helps hunting, unless the airplane is grossly unstable to begin with. This is a long held fallacy. Hunting is almost always due to control drag, control slop, or misalignment. If these are present, moving the CG *will not* fix it.

Well, I'm just an old guy with a reconstructive memory. That is, I remember things that didn't really happen. Thanks for all the tips, and I have been wrong more than once before, so we will see how the gentleman's plane works out.

However, check to make sure that the controls are absolutely free and no slop. Sometimes it is a fine line between getting them lose enough so they are free, and "uh oh".

You are quite welcome. Way off leadouts occasionally cause hunting. lots of time because the leadouts rub against hte internal structure. But I'm VERY surprised it's that sensitive to the leadout position. I guess that straight wing with the very high lift and pointy tips doesn't like going edge-on into the air.

Glad it works. The airplane is extremely good and better than most real stunt planes when it's in trim. That's why I suggested to Jon that he might want to build more of them instead of going for something like the Cardinal. A modest airplane, built and trimmed correctly, is much better than a high-zoot model with some mistakes.

Please define "real" stunt plane.

When I say this, I usually use the quotes as well. What I mean is full-house 40-60 models. Most of these models are never trimmed to the max, therefore don't fly as well as the more modest Medic. The Medic (and the Doctor, and a lot of other very simple elevator-only planes), when powered with a very flat-running motor, are like falling off a log to trim, and therefore tend to be trimmed closer to the max. They fly better as a result.

One thing that makes this different from 10-15 years ago is that the speed stability is much better, and tends to get around the bane of the elevator-only plane, namely the tendency to change the response characteristics with speed. Slower, it gets sluggish, faster it gets twitchy. That's why the Skyray is a pretty marginal airplane with a Fox, and capable of 500+ point patterns with a 20FP.

The only real limitation is that the constant-chord wing is much more prone to bouncing around in turbulence.

>I think Brett has given a
>good argument for the less-experienced
>flyer to avoid the 4-2-4
>break type of engine run.
>For the 4-2-4 break to
>be helpful, it has to
>work just right, something the
>less experienced flyer may have
>difficulty achieving.
>

Geez, now I'm going to have to start x-raying my mail again...

I would also point out that a constant 2-stroke run and a constant 4-stroke run are almost indistinguishable. I think that the feel the East coast guys (and that we occasionally get) like about the 4-strokes is very similar to the feel we've been getting with the little FP's and the like - namely, very little engine speed variability during the flight, and resulting very consistent feel in all the parts of the maneuver.

> (...) argument for the less-experienced flyer to
>avoid the 4-2-4 break type of engine run.

Nope, sorry. Disagree.

>For the 4-2-4 break to be helpful,

Helpful how?

>it has to work just right, something the less
>experienced flyer may have difficulty achieving.
>
Since I don't consider it particularly difficult to obtain what I think is a useful breaking run from types of engines that do it well, let's re-define whatever it might be that actually could be difficult. For a sport flier with a 400-450 square inch profile plane and an engine capable of running in the correct 4-2-4 manner, he gets a type of "INSURANCE POLICY" against damaging his engine with a lean run by choosing to have the engine run in a 4-stroke while flying level.

If the engine is too rich to break except when the tank is almost empty, he can still perform most of the stunt pattern. I've had a couple of engines that worked BETTER that way than if they did break for each and every maneuver. I consider getting a "basic" 4-2-4 run pretty easy because I saw and heard young kids of age 9, 10, and 11 setting their engines that way with no trouble at all, while obtaining little in the way of adult coaching.

Now, if I was a budding PA competitor, but with little in the way of motor experience, perhaps still flying a Beginner pattern, or restricting myself to competing in the PAMPA Intermediate ranks, I might end up feeling more need for the steadier engine run that is possible by eliminating the 4-cycle aspect, since when a flier gets into marginal power situations (both a 550 square inch wing, and a muffler, pulled by a baffle piston type 35, almost any brand), it is then that exactitude in getting a 4-2-4 run working at its best might be harder to obtain.

Personally, I only have had a couple of the old Fox 35's, out of over a dozen, that I could set almost instantly to run the way they should for a big stunt plane and never have to reset the (OS) needle (I never had much luck with any Fox needle). I wasn't involved in PA steadily and would occasionally have to re-learn the particular sound to tune to, which differs slightly in different planes - I never even had a Vibra-Tach when those were in use - all tuning by ear alone.

And it had been long enough between last running an OS Max-S 35 (several years, in fact) and last summer, that I didn't quite get a new-to-me Max-S running the way I wanted, even in three tries.

So I can understand that with a possibly overweight, probably oversize (for the engine) model, the perfect needle setting could be elusive, and it was just exactly that (elusive) on a smaller model, even for me, but without any downside except my own preferences. Therefore, *MY* re-definition of Jim's term "less experienced" requires a proviso about "flying an AMA stunt pattern in competition," not just flying stunts, period.

The K.

I think I did.