Hey all, I rescently maidened my new avistar elite (nitro). As my instructor took it up, the plane wanted to go up, up, up, the nose wanted to point up. It took a bit of trim, and it flew normally. The plane rolled fast, altough it does have a high roll rate. The landing was fast, and a bounce. I put in 100 grams of lead in the tail and it seemed well balanced at the recommended spot, maybe a tiny tiny bit tail heavy. Should I take away some weight?

I don't know about you but your airplane sounds fairly well-balanced. Adding 100 gms to the tail is extremely unusual, but what matters most is whether your balance point is correct. When a plane is tail heavy it is very hard to control in pitch because it exaggerates every input. It's climbing so you give it some down and it dives so you give it some up and it swoops up again, without being able to get a happy medium. That's tail heavy. It will make your knees shake at the least. Simply climbing by itself does not mean the plane is tail heavy. If you can trim out the climb, then the balance point is not bad.

However, when a plane feels a little uncomfortable, even after trimming it out, it is often because the balance point is close to the point where it goes unstable. Moving the balance point forward, often even just a little, can smooth out the flying. You said it might have been a little tail heavy when you balanced it, so a good first step it to move the balance point forward so that you are sure it is not behind the point given on the plans.

If you had to add 100 gms to the tail to get to the balance point on the plans, first double check to be sure you really have it right. Then, if so, see if you can move the battery pack to improve the balance, instead of adding dead weight.

Make sure the airplane is level or slightly nose down when perched at the balance point with an empty tank.

Do not put weight in the tail.

Do the following: Ailerons_ move the control rods on the servos in one hole....move the control rod at the aileron out one hole unless it is already there. That will slow down your control rates.

Most important: Put a couple of washers on the motor mount to tilt the engine downward...that stops the tendency to climb.

On a new airplane do the following:

Trim hands off at half throttle.

Fly by in front of you at 20 to 50 ft altitude.

Apply full power and see what happens.

If the aircraft climbs tilt the engine downward.
If the airplane turns right or left, adjust the engine mount to pull in the opposite direction.

There are more things you can do but this will get you safe to fly and have some fun with no surprises.

Hope this helped.

Why is it assumed that when a model wants to climb,, that it is tail heavy ?

Alright thanks guys, I think I will check the CG again and probably take away some weight.

I didn't think that it was tail heavy because it went up, but because it also rolled very fast, aswell as went up.

My instructor made it roll slower with expo (I think that's what it is called). Now its like my old LT 40, other than the fact that it lands fast. (I wish I bought a 5 or 6 channel rx for flaps)

because it will make it climb. You can trim it out, however, it will try to pitch up and down only if is actually tail heavy.

The main reason is there is no offset on the engine 3 !/2 deg down for thrust and 3 1/2 deg right for "p-factor" p-factor is the paddle wheel a
effect the prop has due to the relative wind caused by a high angle of attack.It makes the aircrasft roll left when power is added.

does that help?

hold on....if it lands fast it means it is nose heavy...tilt the engine like i said and add a small amount of lead to balance.

HOW TO FIND THE CG ON A STRAIGHT WING TRAINER. MEASURE THE WING CORS INCLUDING AILERONS. EXAMPLE 10 INCHES.
MULTIPLY BY 28% AND THAT IS THE CG YOU WILL WANT. 2.800 IN FROM THE LE OF THE WING. PRETTY SIMPLE. FORGET WHAT THE BOOK TELLS YOU.

Alright, so the engine is offset to the right for sure, and it might be down to, thats the way it came from the factory. (It was an ARF but the fire wall was offset). I will check to see if it is tilted down, if its not I will put a few washers, but I gues it really is not tail heavy since it does not pitch up and down.

I'm surprised nobody mentioned wing and stab incidences at all. All elements, engine down thrust to the left, balance (a touch nose heavy is always safer than not), and wing/stab incidence all play a role in how an airplane comes off the bench to fly. Any of which can effect what happens to a plane. If it jumps off the ground with high/full throttle with trims set level then I'd wonder about incidence and engine first. Being tail heavy would be a secondary reaction once the plane got up in the air. But in all cases for me, I would check each and everything separately to be sure each element was correct and we weren't missing something important. Everything has to work together in harmony, and when it does you have a smooth flying plane.

The Avistar is a ARF and everything is set from the factory. I own one and did a electric conversion. It does none of the stuff the OP has said his does. His CG has to be off. 100 grms of weight in the tail ?
I also know of 2 others that are glow and none of those required tail weigh either. Something ain't right there.

Mike

My Kadet Senior Sport is an ARF, with everything set at the factory. It wanted to climb like crazy.

The problem was that it needed down thrust, even though it wasn't mentioned in the assembly manual.

The OP's model may indeed be tail heavy, but I wouldn't assume so without knowing if it glides well, without power. If so, I'd look at thrust issues. If not, it could be decalage issues, as radiisteve suggests.

I may be a bit tail heavy, but the weight in the back was necissary, unless if I somehow put the batt all the way in the back, or moved the servo tray etc. If i put 100 grams of unnecissary weight in the tail, don't you think it would rather be unflyable?! Or atleast very pitchy?

I can appreciate your thoughts on a plane being set from the factory, but my general rule is in God I trust, everything else I verify. Mistakes can always be made, QA can always miss something and for every pilot we should always check all of the basics of a new aircraft before flying. It would seem to be a good general rule of thumb, (not that you were at all) but everyone should always learn how to set up their own plane properly and never assume everything is right because someone else says it is. Unless it's a high quality builder you have great trust in. Check it, know it from top to bottom, if for nothing else always for safety. How many times do we do a check when everything is fine only to find something, some damage or weakness or anything that makes us stop and think, wow I didn't even know that was happening? I've been very lucky to have most every plane fly straight and true off of the bench, but I attribute it to triple checking everything with great care and it's always paid off.

It's got down and right built in.

Mike

Wow! This thread got complicated in a hurry. We habdy a guy diagnosing thrust line issues even though no thrust line test has been done, and another who wants to redesign the wing mount to keep from having to adjust the elevator trim. Both might make sense in other scenarios, but are not called for here.

The truth is that the way the elevator needs to be trimmed on a maiden has very little to do with whether the plane is set up right. CG is 100% about pitch stability. If the plane glides smoothly and drops its nose gently on a landing approach but you still have enough elevator to flare then you aren't too nose heavy. I start at 25% and move it back until I get that kind of response. On a trainer, that's usually around 26-27% MAC. You check for a thrust issue by letting off the throttle and watch the nose. But your climbing issue was nothing more than the elevator trim being a bit off from where it needed to be for that plane.