I bought a Modeltech Great Planes at a recent swap meet. This plane has a reputation for being VERY tail heavy. When I opened it up, I found the previous owner put the receiver battery in front of the firewall and 1lb-4oz of lead weight also in front of the firewall. That's an aweful lot of weight for a 40-size airplane. I haven't flown it, but it must fly like a brick with all that weight n it. I decided I didn't want all that weight in the plane, so I extended the firewall forward 1-3/8" to get it balanced with just the battery and the Magnum .52 engine. Purists won't like that because the plane is not as snub-nosed as the original Great Planes, but for me it's a good trade-off and the plane still looks good.

The next problem was this plane also has a reputation for being quite squirrelly on the ground (pronounced tendancy for ground loops). I installed a cheap gyro on the rudder to help hold it straight when taking off/landing.

The last problem is wing incidence. Relative to the hor. stabilizer, the bottom wing is 0 degrees and the top wing is minus 1 degree. The manual makes no reference what-so-ever to what this should be, and I have found some calculations on the web that are well beyond what I understand. Does anyone know what the wing incedence for this plane is supposed to be or better yet, what works best on this biplane?

I generally respect a posters request and acknowledge that your request was to owners of that particular plane. With no answers coming, I'll offer that on a bipe, 0 on the bottom and -1 on the top is not unusual. The stab often suffers a down force couple from air off the top wing that will make the plane climb excessively with an artificial positive incidence forced by the couple. A little negative in one or the other wing counters that couple.

With it often harder to add negative to the bottom wing, it is often done on the upper because it is easy to shim the incidence adjustment by trial and error. On the bottom wing where the forward dowels would need their holes adjusted or the wing saddle shaved, trial and error is more difficult hence the bottom wing is often fixed at zero and the adjustments done to the upper.

I'd go with it as it sits now.  A few clicks of elevator trim will get things right soon enough.

And that was an excellent move on your part to extend the fuselage.  Looks and moment arms be damned, the advantages of removing that lead will easily make up for any other issues many times over.

By lengthening the nose you may already have corrected some of the ground twitchiness issues just by creating a longer swing length on the nose.  Also if the landing gear is located quite forward from the CG location this can lead to a lot of twitchiness in ground handling.  If you can see that the LG is quite forward and if it's possible to unbolt the gear and swing it around to move the axles back even a hair that'll aid in taming the issue.  A wedged plate that angles the whole gear back even further would not be amiss either if the wheel axles are well forward of the CG lcoation.

When the model is lifted to level at the tail you want the angle from the true 3D location of the CG to the axles to be about 30 degrees.  To find roughly the true CG location you can balance the model from the upper wing tips and find the vertical line and then hang the model from the wheels and where the two plumb lines cross is the true 3D location of your CG.  If this second hanging from the wheels line is a lot more angled forward then 30 degrees then figuring out a way to angle the gear back to reduce this angle would aid in reducing the ground squirreliness.

Well, I left the incidences the way they were and flew the thing. Either the longer nose or the gyro or both fixed the ground loop problem. Once in the air the plane seems to fly like it weighes a ton. Anythng less than 3/4 throttle in a turn and she heads straight for the ground. It's also quite twitchy about it's ailerons even at the low throw settings. Somewhere just under 3/4 throttle it gets hard to control even in straight-line flight. Landings need to be performed like a jet coming in hot. I crashed it twice already. It is now pretty obvious why this biplane was for sale in the first place. All the negative comments on the web about this biplane seem to be fairly accurate. The best luck people have had is with larger engines that overcome some of the tail heaviness and then give it enough power to actually fly decently. I'm just not willing to risk a new Saito 82 4-stroke in it. I'll fix it one more time and put a dummy engine in it. It will look nice hanging from the ceiling.

Meanwhile, the best thing about that bird was the Magnum .52 4-stoke engine. It sounds like it's twice as big an engine and runs and transitions very smoothly. I'll put that in a World Models 40-size Ultimate Biplane and my bet is it will fly a whole lot better.

Thanks for all the help from forum members. Unfortunately, sometimes a turd is just a turd and there just ain't a clean end to pick it up by.