BlueMax3

My Feedback: (1)

Hello,

I am flying a GSP Spitfire with a Saito 100 and it requires down elevator trim to maintain level flight. By down elevator trim, I mean that the elevator is trimmed down from being level with the stabilizer. With the elevator level with the stabilizer, the plane wants to climb and I believe that it gets worse at higher speeds, although I need to check this to be sure. Should I expect to be able to get it to fly level without any elevator trim? If so, what are the suggested remedies? I am wondering whether adding a little down thrust would help? This is an inconvenience because if I forget to take out the down trim after landing, then on the next take off, it has a tendency to nose over.

Thanks,

Travis

MinnFlyer

My Feedback: (4)

How does it fly inverted? Does it need any down stick to maintain level flight?

BlueMax3

My Feedback: (1)

I believe that it flys level or climbs when inverted, without down elevator. It definately does not dive when inverted. How does this affect things? Should I test this specifically the next time I fly?

Travis

JoeAirPort

My Feedback: (41)

Could be tail heavy. If it still climbs inverted it would be tail heavy.

Maybe the incidense is off on the stab?

BlueMax3

My Feedback: (1)

The thought about the plane possibly being tail heavy is very Interesting because this particular model has a history of that. The recommended cg range is 125-135 mm back from the leading edge and I had originally set the dg at the middle--130mm. The plane flew reasonably well, but I had a difficult time landing, particularly with an empty tank and the flaps and gear down. The elevator became very sensitive. Several people who had this plane characterized it as "flying tail heavy" and recomended a more forward cg. I have since moved the cg to 122mm, just infront of the recommend range, and this fixed the sensitivity problem. The plane is very stable and a joy to fly. Not the easiest to land, but much, much better than before.

At the next flight, I will observe the inverted flight charactertics a little more.

Question: Is there anything else to be learned from the behavior tied to speed? For example, if it's tail heavy, how will the condition be exhibited at different speeds?

Thanks,


Travis

ksechler

It's probably the stab incidence. Does the trim chang alot with different throttle settings or when you dive?

Rodney

Check the thrustline; sounds like you need more downthrust. If you have double checked the relative incidence of the wing vs stab and the CG is correct, thrustline is the only factor left.

BlueMax3

My Feedback: (1)

How do I check the thrust line and wing to stab incidence? The next time I fly it, I will gather more information.

Travis

Bax

My Feedback: (11)

There a good way to check a model's balance when you're flying. This method is popular with glider flyers, but works well for powered airplanes, too. Trim the model for hand-off level flight. Start a steep dive and let go of the elevator. If the model pulls up, then you have it nose-heavy. If it steepens, then it's tail-heavy. The preferred balance would be if the dive results in a slight pull-up. If the model is too sensitive in pitch when it's balanced this way, then you have to adjust the wing/stabilizer relationship. Raise the leading edge of the wing a degree and try again. You'll find the balance point will move forward, and the model will be less sesitive in pitch.

The thrustline is adjusted to eliminate/reduce the amount of pitch change when you change the throttle. To check thrustline, trim the model for full-throttle level flight. When the model will fly hands-off level at full-throttle, abruptly chop the throttle. If the model pitches down very strongly, you need downthrust. If the model pitches up strongly, you need to take out downthrust/add up thrust. You want the model to basically coast straight ahead and then ease down into a dive when you cut the throttle. Add power and the model should accelerate forward and ease into a climb.

BlueMax3

My Feedback: (1)

Bill,

Those are great suggestions. I will test those as well as inverted flight and report back with more information.

Travis