Lnewqban

Nice model, Propbuster!
Good comments, Da Rock and BMatthews!!

Propbuster, you have solved the situation eliminating the longitudinal dihedral or decalage of your model.
The 1/4 in 7 inches is equivalent to 2 degrees of decalage, which is normal.
Decalage is needed to compensate for increments of the pitching moment produced by any non-symetrical wing with increments of air speed.
Hence, your model will not self-adjust to horizontal flight, requiring constant adjustment from you during flight.

I believe your problems can be only caused by insufficient downthrust (easily verifiable observing reactions for power and powerless descending flight), and CG too far back (regardless of manufacturer specs).

Excellent reference: http://www.masportaviator.com/ah.asp?CatID=8&ID=141
http://www.masportaviator.com/ah.asp?CatID=8&ID=142
http://www.masportaviator.com/ah.asp?CatID=8&ID=144

Good luck!!

tucker1865

My Feedback: (6)

OK, now I am confused or stupid. I have 2 trainers, PT-60 and PT-40 both later versions (MK II) and both climb (elevator trim tabs all the way forward). I think that there are now designed this way. I had a PT-40, older version that did not display this problem, but was slightly tail heavy (added a little weight). I had a OS FP60 on the sixty size (tailheavy) and changed to OS61FX (heavier) . This helped balance with the recommended CG. Still climbs. da Rock says washers under the bottom mounting holes and meaden says under the top holes in the firewall. I couldn't add washers to the firewall (needlevalve and muffler clearence) so I added washer (1) under the engine in the rear. This helped a little. To balance the planes both engines are moved forward of the recommended mounting locations. They balance at the recomended CG. I would rather not add weight so, should I add more downthrust (nose down). I could use the firewall method and cut more clearence. Confused

Bax

My Feedback: (11)

As has been discussed many times, in several threads, when an airplane tends to climb, what is the throttle setting? A good trainer should be able to hold level flight at a moderate throttle setting, climb when you increase the throttle, and descend when you decrease the throttle. If the wing has a flat-bottom or semi-symmetrical airfoil, then it will need less positive incidence in relation to the stabilizer than a fully-symmetrical wing. The airplane with non-symmetrical wing will also need to have more downthrust than the airplane with a symmetrical airfoil.

Downthrust is used to reduce or minimize the trim change with power setting. If you add power and the nose climbs very abruptly and a lot, then add some downthrust. If the nose drops abruptly and a lot with power reduction, you need downthrust. When you change power settings, you want the model to continue on its path a bit before you get a pitch change. Some nose-up with power-up, and some nose-down with power-down. If the model's properly set up, then you can set a moderate throttle setting and the model will hold its altitude. Add power and the model should climb, reduce power and the model should come down. As stated above, this is highly-desirable performance for a trainer.

The Great Planes PT-series of airplanes should display this behavior when they are built straight and properly set up. To get the best performance out of them, or any trainer...or even ANY airplane, you do have to spend some time "tuning" the model.

If a model tends to float too much when you are trying to land, the model simply has too much speed. If you cannot reduce the power enough, then the model is over-powered, or your engine isn't running slowly enough. Many times, you need to add more drag in order to help the model land. Use of a larger-diameter but flatter-pitched propeller can help. So can flaps or spoilers (depends upon the model).

A lot of practice will help if you're trying to fly too fast, which is the very most common difficulty. Take the model up high and see how slowly you can fly it in level flight and retain control. Then fly at that speed and gradually reduce the throttle. If you have the model set up correctly, it will descend at that speed under full control. Now you just need to learn how to set up the landing pattern so that the model will descend to the runway and touch down at the spot you chose. As said above, it takes practice...lots of practice to really nail the landings.

tucker1865

My Feedback: (6)

Both planes would climb at a little below 1/2 throttle. They were both maidened by experienced pilots. When trimmed they both had trim tabs all the way forward (1/2 throttle, level flight), not so with the older PT-40. It flew level with no trim adjustment. They are built carefully and are straight and true and balanced at the recommended CG. Should I add downthrust to bring the trim tab to neutral? Don't I want 1//2 throttle, hands off, level flight?

Lnewqban

Tucker1865:

If you fly model airplanes, you cannot be stupid; I believe we could help with the confussion.

Your newer trainers should not climb at a little below half throttle with elevator trim forward; they should not need any trim; the same applied for the trainers of the last century.

Do the tests recommended in the Pitch Flight Testing section of this article written by Dean Pappas:
http://www.masportaviator.com/ah.asp?CatID=8&ID=141

I had the opposite problem, and I could solved it with the help of those tests; now my trainer flies as you have described it: "1//2 throttle, hands off, level flight".

The elevator of a trainer is to be in line with the stabilizer.
A trainer should climb and descend using only the throttle, not the elevator; otherwise, the flight of a trainer is not as enjoyable as it can be.
Remember that free flight models were flying long before radio control.

I believe your trainers have one of the following problems, or a combination of all:
-Excesive incidence angle of the wing (it should be around 2 degrees).
-CG located at more than 33% from the leading edge.
-Insufficient downthrust of the engine (between 2 and 5 degress).

Regards.

tucker1865

My Feedback: (6)

Thanks for the heads up on the article. It is a big help. Thanks again

rustypep

My Feedback: (6)

I had the plane that came before this one called just the Easy Fly 40. It had the flimsy wire main landing gear and an excessive amount of dihedral (more so than trainers you see today). I had similar issues and bandaged the problem by increasing downthrust first and later raised the trailing edge of the primary wing. There was too much incidence in the horizon stab that caused the plane to climb excessively at moderate and higher speeds It made landings difficult and initially inverted flight was impossible because of the amount of down trim that was required to fly it until I made a few changes. I still have the plane (12 years old now) and plan to bring it back into service with floats, a bigger engine, and a corrected stab. It still looks good and flew great on a OS 40 FP. When I progressed to an Ultra Stick landings became a lot more enjoyable. Glad to see your mods worked out.

propbuster

My Feedback: (1)

Yup, the decalage change was definatley the answer to the excessive climbing problem at only 1/2 throttle. It still will float forever on final, and I have to fly it down to the deck which of course makes for a hot landing. I have the semi-symetrical wing almost done (with a lot less dihedral also), and that should be another big improvement too. There are a few nice size ponds around me and after reading this months MA, floats are another possible addition.[8D]

airraptor

My Feedback: (66)

this is a trainer plane and is supposed to fly that way nice and slow. why spend the time to hack it up and make it fly the way you want now. It seems your flying skillzs have improved to where you are flying it with more throttle for the extra speed. there are many second plane models out there that would be better suited for your flying.

propbuster

My Feedback: (1)

Just something to do? I really enjoy the design/build aspect of the hobby and love tinkering around with planes. I've got more planes in the hanger than radio gear to fly them all!.

rustypep

My Feedback: (6)

The other minor change I made that improved that trainer once I got comfortable was adding differential to the ailerons. That wing didn't roll very well unless you used a lot of rudder which forced me to learn how to use it. That trainer had the one servo setup in the middle of the wing so I did it mechanically but it did make a difference.